# poor performance with new heads



## mbspeed (Sep 25, 2012)

Hi guys I have a 67 gto it' s running 455 9.5 compression with # 62 heads I wanted more power so I got custom made KRE aluminum heads 310 cfm ported heads car now feels little slower ...what am I doing wrong it has an 850 demon carb roller comp cam 500/510 msd running total 38/40 timing at full rpm I spent so much money on car make quick do I need to go crazy with carb jetting its a 4 speed with 3.55 gears any info would help car runs good just no power any help would be great I f I could go back in time I would have done LS3 but I am stuck now  please help


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## ALKYGTO (Mar 29, 2010)

What is your timing set at? Have you talked with Kaufman Racing about this? Do you have a local chassis dyno to do some tuning on? That would be my recommendation is to get your car on the rollers and do some tuning, much safer than doing it on the street and gauging it with the butt dyno.


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## BearGFR (Aug 25, 2008)

You're not going to like this --- but 9.5:1 is not enough compression for aluminum heads. They really need to be up around 10.2:1 or so. Aluminum is a better conductor of heat than cast iron is so they tend to "pull" more heat out of the combustion chambers and this has a negative effect on combustion efficiency. It also makes the chambers run cooler so there is less tendency to form hot spots - and that means that higher compression (up to a point) won't cause detonation like it would with cast iron. Before I dive off into this any deeper though, are you _positive_ this engine is only 9.5:1? How did you get it "down there" running #62 heads (which have 'nominal' 72cc chambers?)

You may have options. Has the engine been zero-decked? If not (hopefully not) you can get a bump in compression by running thinner head gaskets. (You may have already been running "fat" gaskets to help get those #62's down to 9.5:1 - were you?). Another benefit of that will be improved quench characteristics. Having the piston tops get "closer to" the head surface leads to more turbulence in the chamber, and that helps with both keeping the fuel/air mixture "mixed" and with flame propagation. Both helping combustion efficiency. You need some safety margin - you don't want them getting any closer than about .030-.035. otherwise as things heat up and you get a little 'stretch' at rpm, you run the risk of contact - and that's no bueno. If you want to give this a try, MAKE SURE YOU MEASURE EVERY CYLINDER for deck clearance using a good depth mic or accurate dial indicator. "Most" Pontiac engines have the pistons about .020 down from the block deck at TDC (unless they've been zero-decked) so if that's the case on your engine, you could run thinner than factory .035 or .032 head gaskets and "get some back". Or, since you have to pull the heads to change gaskets anyway, you could mill some off the heads to make the chambers smaller

I did some playing around with my compression ratio tool, and I assumed your 455 was 0.030 over. Getting it to 9.5:1 with 72cc #62's would have required a lot of additional chamber volume from "somewhere" - 25 cc's of piston dish (everything else "standard"), 19 cc's of pistion dish _AND_ 0.075" head gaskets - some combination that would have increased the volume in every chamber by about 20 cc's over what it would have been with everything "stock". So.... if you can tell us how you got it to 9.5:1 to begin with, perhaps we can suggest some ways to get it to where you can take advantage of those shiny new heads.

Bear


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## geeteeohguy (Feb 2, 2008)

Also, an engine is an air pump. All the parts must work together in harmony. When you install high CFM heads on a 455, you lose the low end torque and trade off for high RPM power...IF you have the right cam, jetting, timing, and exhaust. 455's are happier in the lower RPM range with less flow on the street. For 315 CFM heads to work on a 455, you need a very aggressive cam, spot-on timing curve and a lot of fuel. The guy to talk to IMO would be Cliff Ruggles on the PY forums. He does a lot of 455's, and his cars generally run very, very strong. X2 on not enough compression: you should be running at LEAST 10.25:1, and probably more with 315 CFM heads.


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## PontiacJim (Dec 29, 2012)

You have to understand that heads that flow bigger CFM's (ported or aftermarket) lose port velocity at lower RPM's. Heads that flow less (stock), develop higher port velocity. Each has its advantages and disadvantages.

Air flow is just like liquid ( let's use gasoline) flow. If you use a smaller pipe, the gas travels faster (velocity). If you use a larger pipe, the gas travels slower. BUT, the smaller pipe delivers less volume of gas for the same given amount of measured time that the bigger pipe delivers gas. If you set up a gallon of gas and attached a straw to it, and did the same thing with a garden hose -which would empty faster? The garden hose, right? It flows more gas. The larger flow of gasoline does NOT mean that it has more velocity, just more flow. Now if we equally pressurized both gallons of gas, the straw end would would shoot gas much farther than the garden hose because the pressure builds more velocity in the smaller diameter straw versus the larger diameter garden hose.

Now reverse this. Rather than putting pressure at the gas side, we apply suction to the end of the straw and the garden hose. This would be your *engine* as it draws in (like a suction) to fill the cylinders. On the straw side, the engine would "suck" extremely hard to pull the gas through the straw which would develop a heck of a lot of velocity (and your engine would be real responsive), but would at some point in the RPM's, not get enough volume of gas and the engine would "starve" at which point your engine would not increase any further in RPM's -the size of the straw just limited your RPM's (just like smaller CFM heads). On the garden hose side, the engine would get plenty of gas (volume), but because the hose is larger, the velocity of the gas would not travel fast enough to get a full charge of gas (and your engine would be sluggish) UNTIL the higher RPM's developed enough suction to increase the velocity of gas which in turn would now give your engine a good volume of gas. The garden hose no longer limits your RPM's like the straw did, so you can really wind that engine way up into the higher RPM range (why we want bigger CFM heads).

Moral of the story. Bigger CFM heads means higher RPM's to make them work. At lower RPM,s the air/fuel mixture is slower and the engine may be "softer" on the lower RPM's. Smaller CFM's limit RPM's, but the air/fuel mixture travels faster and the engine is more responsive. As with any engine build, some bigger CFM's can be too much and some smaller CFM's not enough.

So how do you remedy this? A smaller carb MAY work better to actually develop more velocity by using the smaller throttle bores to regulate the amount of air (much like the straw) to get velocity back up in the air/fuel mixture. My guess would be to use a vacuum operated secondary opening carb that is tailored to open higher up on the RPM scale thus using the smaller primary side longer to get the velocity built up in the intake/heads (what a Q-jet does so well).

The next option is gearing. 3.90's, 4.10's, 4.56's and high stall converter for automatics so as to transition faster into the useable RPM range of the bigger CFM heads -just like is required with a big cam. This is why the Ram Air GTO's had factory 3.90 and 4.33 gearing. Great for racing, not so great on the street.

I agree with the need for higher compression on aluminum heads. However, there is static compression, which is fixed and you figured to be around 9.5. Then there is dynamic compression, which can be changed by the opening or closing of your valve timing. Did you select your cam yourself or did Competition Cams work with you on the cam you have? 

It is possible that changing your cam timing at the crank a few degrees may help - I would think that you want your valves to open sooner. I would call Competition Cams and tell them what you are experiencing. They may suggest a cam timing change or recommend a different grind that will raise your dynamic compression by altering your valve opening timing/ lobe separation angle, or both. A different cam may change the entire engine and all will be well. 

So you may have to play around with a few things, cam timing, different/smaller carb, gearing, converter, or another cam to sort stuff out. I would not be discouraged, just try a few things first. Again, my opinion and no real experience here with aluminum heads or roller cams.


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## mbspeed (Sep 25, 2012)

Hi Bear motor was 9 .5 with steel 64 heads the heads that were made by Kauffman are 72cc cnc d port took 55. off face of heads to bring compression back up block also 0 deck Kauffman ported to 310 also used 1.6 rocker arms on my 500/510 hydro roller cam make little more power just does not feel fast ....funny it gets 17 hg of vac could that be hurting my power level don't have dyno tune shop around me its so depression $3000 for head and car feels slower 



BearGFR said:


> You're not going to like this --- but 9.5:1 is not enough compression for aluminum heads. They really need to be up around 10.2:1 or so. Aluminum is a better conductor of heat than cast iron is so they tend to "pull" more heat out of the combustion chambers and this has a negative effect on combustion efficiency. It also makes the chambers run cooler so there is less tendency to form hot spots - and that means that higher compression (up to a point) won't cause detonation like it would with cast iron. Before I dive off into this any deeper though, are you _positive_ this engine is only 9.5:1? How did you get it "down there" running #62 heads (which have 'nominal' 72cc chambers?)
> 
> You may have options. Has the engine been zero-decked? If not (hopefully not) you can get a bump in compression by running thinner head gaskets. (You may have already been running "fat" gaskets to help get those #62's down to 9.5:1 - were you?). Another benefit of that will be improved quench characteristics. Having the piston tops get "closer to" the head surface leads to more turbulence in the chamber, and that helps with both keeping the fuel/air mixture "mixed" and with flame propagation. Both helping combustion efficiency. You need some safety margin - you don't want them getting any closer than about .030-.035. otherwise as things heat up and you get a little 'stretch' at rpm, you run the risk of contact - and that's no bueno. If you want to give this a try, MAKE SURE YOU MEASURE EVERY CYLINDER for deck clearance using a good depth mic or accurate dial indicator. "Most" Pontiac engines have the pistons about .020 down from the block deck at TDC (unless they've been zero-decked) so if that's the case on your engine, you could run thinner than factory .035 or .032 head gaskets and "get some back". Or, since you have to pull the heads to change gaskets anyway, you could mill some off the heads to make the chambers smaller
> 
> ...


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## mbspeed (Sep 25, 2012)

mbspeed said:


> Hi Bear motor was 9 .5 with steel 64 heads the heads that were made by Kauffman are 72cc cnc d port took 55. off face of heads to bring compression back up block also 0 deck Kauffman ported to 310 also used 1.6 rocker arms on my 500/510 hydro roller cam make little more power just does not feel fast ....funny it gets 17 hg of vac could that be hurting my power level don't have dyno tune shop around me its so depression $3000 for head and car feels slower



Hi bear you helped me before with this stupid motor problems I am the guy that had the buttler boys make a custom set of ross/buttler pistons to work on 670 heads the dish on the pistons are 30.00 after the 670 heads did not work out I went with 061 heads then 62 ...and now custom kre aluminum 72cnc shaved down 55.00 block id 0 deck think I am doomed :rant::banghead::banghead::banghead::banghead:


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## mbspeed (Sep 25, 2012)

PontiacJim said:


> You have to understand that heads that flow bigger CFM's (ported or aftermarket) lose port velocity at lower RPM's. Heads that flow less (stock), develop higher port velocity. Each has its advantages and disadvantages.
> 
> Air flow is just like liquid ( let's use gasoline) flow. If you use a smaller pipe, the gas travels faster (velocity). If you use a larger pipe, the gas travels slower. BUT, the smaller pipe delivers less volume of gas for the same given amount of measured time that the bigger pipe delivers gas. If you set up a gallon of gas and attached a straw to it, and did the same thing with a garden hose -which would empty faster? The garden hose, right? It flows more gas. The larger flow of gasoline does NOT mean that it has more velocity, just more flow. Now if we equally pressurized both gallons of gas, the straw end would would shoot gas much farther than the garden hose because the pressure builds more velocity in the smaller diameter straw versus the larger diameter garden hose.
> 
> ...


Hi jim I run vac 2nds on my two carbs I have a demon 850 and a holly street advenger 870 cfm I am running a single plane manifold could go back to duel plane if it would help think still have my edekbrock 800 cfm carb someplace 3.55 rear diff 4 speed manual m20 running ramair exhaust manifolds


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## BearGFR (Aug 25, 2008)

A dual plane manifold might help a little. I'd forgotten about the custom pistons you had made with those huge dishes... In all honesty, with the way the rest of the engine is set up you're probably going to be better off running the iron heads. If you want to get the potential out of the new heads, you're going to need to get that compression up. You might be able to "fool" the engine a little by advancing the cam some (doing this requires pulling the front of the motor down and replacing the timing set with one that has multiple keyways for adjustment, if you don't already have one of those.) Closing the intake valve earlier will let you build a little more cylinder pressure, but doing that also tends to shift peak VE to a lower rpm - just the opposite of what you need in order to be able to take advantage of the flow potential you have in those heads. I hate to be the bearer of bad news but you've sorta gotten yourself into a pickle with this combination.

I also don't remember - which connecting rods are you running? If they're stock cast iron, you want to be very careful about spinning that engine much above 5000 rpm in that 455.

Depending on your personal money situation, ifn' it were me I'd do one of two things: 1) Bite the bullet and buy another set of pistons that'll put compression where it needs to be for those heads (and some good forged rods if you don't already have them) or 2) Cut my losses and sell the heads and try to recoup as much of the cost as I could.

Bear


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## GTO70455 (Feb 10, 2009)

If I can suggest, and this is just a suggestion. There are very knowable people on this site and a great resource. But if you are a Pontiac enthusiast as we all. Go to Barns and Noble, or Amazon and buy Rocky Rotella's book on High Performance Pontiac Engines. I hate to see people spend hard earned money and not understand how this motor works. This is a great resource and after you finish the book you will understand that big lump under the hood...It's well worth the $19.00.....


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## mbspeed (Sep 25, 2012)

BearGFR said:


> A dual plane manifold might help a little. I'd forgotten about the custom pistons you had made with those huge dishes... In all honesty, with the way the rest of the engine is set up you're probably going to be better off running the iron heads. If you want to get the potential out of the new heads, you're going to need to get that compression up. You might be able to "fool" the engine a little by advancing the cam some (doing this requires pulling the front of the motor down and replacing the timing set with one that has multiple keyways for adjustment, if you don't already have one of those.) Closing the intake valve earlier will let you build a little more cylinder pressure, but doing that also tends to shift peak VE to a lower rpm - just the opposite of what you need in order to be able to take advantage of the flow potential you have in those heads. I hate to be the bearer of bad news but you've sorta gotten yourself into a pickle with this combination.
> 
> I also don't remember - which connecting rods are you running? If they're stock cast iron, you want to be very careful about spinning that engine much above 5000 rpm in that 455.
> 
> ...


your correct I am screwed with this set up it has the stroker kit from buttler has forged rods but now ....heads cost 2800 kuffman said could pick up 80hp with new heads now I cant run flat top pistons or compression will be too high anybody want buy a slow 67 GTO :banghead::banghead:


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## mbspeed (Sep 25, 2012)

GTO70455 said:


> If I can suggest, and this is just a suggestion. There are very knowable people on this site and a great resource. But if you are a Pontiac enthusiast as we all. Go to Barns and Noble, or Amazon and buy Rocky Rotella's book on High Performance Pontiac Engines. I hate to see people spend hard earned money and not understand how this motor works. This is a great resource and after you finish the book you will understand that big lump under the hood...It's well worth the $19.00.....


I do have all the books by rocky and jim hand even got 2nd printing of how build max Pontiacs came out few years after first so I did not miss anything 

I called buttler performance today talked with them he punched all the numbers he thinks my cam is too small for my set up also I need re jet carb but compression in where it should be 10.2 1 pulling 17hg of vac now anyway thanks for all the good info you guys allays give me hope I can get this GTO into the low 12 be happy for now :reddevil:


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## mbspeed (Sep 25, 2012)

BearGFR said:


> You're not going to like this --- but 9.5:1 is not enough compression for aluminum heads. They really need to be up around 10.2:1 or so. Aluminum is a better conductor of heat than cast iron is so they tend to "pull" more heat out of the combustion chambers and this has a negative effect on combustion efficiency. It also makes the chambers run cooler so there is less tendency to form hot spots - and that means that higher compression (up to a point) won't cause detonation like it would with cast iron. Before I dive off into this any deeper though, are you _positive_ this engine is only 9.5:1? How did you get it "down there" running #62 heads (which have 'nominal' 72cc chambers?)
> 
> You may have options. Has the engine been zero-decked? If not (hopefully not) you can get a bump in compression by running thinner head gaskets. (You may have already been running "fat" gaskets to help get those #62's down to 9.5:1 - were you?). Another benefit of that will be improved quench characteristics. Having the piston tops get "closer to" the head surface leads to more turbulence in the chamber, and that helps with both keeping the fuel/air mixture "mixed" and with flame propagation. Both helping combustion efficiency. You need some safety margin - you don't want them getting any closer than about .030-.035. otherwise as things heat up and you get a little 'stretch' at rpm, you run the risk of contact - and that's no bueno. If you want to give this a try, MAKE SURE YOU MEASURE EVERY CYLINDER for deck clearance using a good depth mic or accurate dial indicator. "Most" Pontiac engines have the pistons about .020 down from the block deck at TDC (unless they've been zero-decked) so if that's the case on your engine, you could run thinner than factory .035 or .032 head gaskets and "get some back". Or, since you have to pull the heads to change gaskets anyway, you could mill some off the heads to make the chambers smaller
> 
> ...


Sorry MR.B gave you miss info compression was 9.5 with old steel heads with new kre heads it is 10.2 1 I called buttler today I was all set to buy new set of flat top pistons but he talked me out of that... he ran all the numbers talked to them for a good 45mins he thinks my cam is way to small for new heads and I need too feed the motor with way more fuel he said a 870 holly well set up re jetted is the way to go .. cliff is a year out on a good q jet :nonod: he also wanted me to go with headers but that will be last option if all fails its to much of a PITA headers I will have cut my z bar may not fit back unless I can get 100 HP out of a good set ....also the block was decked 0 think that matters as well :cheers:cheers thanks again


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## PontiacJim (Dec 29, 2012)

mbspeed said:


> Hi jim I run vac 2nds on my two carbs I have a demon 850 and a holly street advenger 870 cfm I am running a single plane manifold could go back to duel plane if it would help think still have my edekbrock 800 cfm carb someplace 3.55 rear diff 4 speed manual m20 running ramair exhaust manifolds



The 3.55's and 4-speed should be workable, so keep these as is.

The single plane can hurt low end performance. It is better for mid/upper RPM's. The dual plane would definitely be better for bottom end response. I would try the dual plane manifold and the Q-jet first before doing anything else. See if this changes throttle response and engine performance any, but read below.


You have the Ram Air exhaust manifolds. It is very possible that these are too restrictive with the big flowing heads. Are your Ram Air manifold outlets 2 1/2"? Here is my personal experience I had with the 409CI Chevy I once built up -factory large port rectangular heads, 2.19" intakes, .530" lift solid cam, dual 750CFM 4-bbl. The factory exhaust manifolds I used were a one year version made for the 1965 Impala and were basically cast iron manifolds like what the Ram Air are to Pontiacs. They had 2 1/2" outlets. I installed 2 1/2" head pipes to match the manifolds. Like you, the engine did not perform like I thought it would, or should. It was kind of flat. I was disappointed in it as the 409 had its reputation. I had my GTO, and it seemed faster to me. I decided to use a 3" dia exhaust pipe. I simply used an exhaust pipe adapter (about 4/5" in length and you can get them usually at auto parts stores -the shorter the better as you want to transition quickly) that went from 2 1/2" dia to 3" diameter. I cut the 2 1/2" exhaust pipe flange I was using to attach to the exhaust manifold about 1" back from the flange, keeping the metal collar/clamp in place, and welded the 2 1/2" pipe adapter to the cut flange. Had to do this because the metal collar/clamp that bolted to the exhaust manifold was 2 1/2" and you would not be able to slip it over the 3" dia pipe on the other end of the adapter. Once done, I was able to run 3" diameter pipe and elbows which I welded up myself to make my exhaust system (you can get these already bent for the GTO, so makes it easier). Got in the car, fired it up, and..........it was like day and night. That engine came alive and nothing could touch it. The 2 1/2" pipe was too small and choking the engine.:yesnod: 

Many of the early 1960's drag cars came with 3" pipes -some even had factory cut outs once you got to the track. This might be something to look into as well. You have all that flow going into the engine, but might be choking it off because it cannot flow out the engine exhaust system (headers would be better, but the Ram Air manifolds are easier and can probably be retained as I did on my 409). You might just invest in 2 head pipes made of 3" dia, and have a local muffler shop fabricate the 2 1/2" exhaust manifold flare/flange, get another collar so you can bolt it back up to your manifolds, slip it on, then weld your 2 1/2" to 3" pipe adapter, then fit your 3" head pipe to this. Don't know where you live or what neighborhood, but I would leave the pipes open and take a quick blast down the road. If you can feel the difference, then I would make the rest of my exhaust system 3". If no difference noticed, then get another adapter and simply reverse it and go from your new 3" pipe down to your existing 2 1/2" system and you don't have to invest in a new complete system.

Also, check this out. FORDMUSCLE webmagazine: Timing is Everything - Distributor Curving for Maximum Power

It is a Ford site, but goes into detail about distributor timing which can apply to your engine as well. Something to think about as timing and timing curves are very important on high performance engines.


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## mbspeed (Sep 25, 2012)

PontiacJim said:


> The 3.55's and 4-speed should be workable, so keep these as is.
> 
> The single plane can hurt low end performance. It is better for mid/upper RPM's. The dual plane would definitely be better for bottom end response. I would try the dual plane manifold and the Q-jet first before doing anything else. See if this changes throttle response and engine performance any, but read below.
> 
> ...


wow thanks jim my ramair exhaust manifolds is only 2.25 I could upgrade tp the 2.5 and do the 3 " head pipes :cheers


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## BearGFR (Aug 25, 2008)

Ah, ok - good. Yes, 10.2 is right where you want to be for the street on pump gas. Ok, you've got forged rods --- also good. I'm going to agree that you need more air flow to take advantage of those heads. One thing you might try: connect up a GOOD vacuum gage with fine graduations to manifold vacuum and position it where you can see it while driving. "Make a pass" or something where you can hang your foot in it for a bit. You should see manifold vacuum readings very close to zero while you're under load at WOT. If not then that confirms that the engine "wants" more air than it's getting. Work on the possible sources of restriction. Intake and exhaust systems. However, resist the type of thinking that tempts you towards "too big". A few posts back PontiacJim talked about flow velocity and he was dead on. Especially on the exhaust side, if you go "too big" it'll kill flow velocity and make the engine have to work to pump the exhaust out instead of having the inertia from flowing gas help "pull" it out. That'll cost you torque - big time. General "rule of thumb": 2.5" exhaust pipes are good up to around 500, maybe 550 HP flywheel. Above that you should go 3". The bigger carb is probably a good idea. Be wary of some folks who "do the math" and want to impress you with all the calculations about how to size a carburetor based on engine displacement, rpm, and rated carb capacity. The approach looks good on paper but there are some key points they may not realize, one of them being that carb 'CFM ratings' aren't performed under any kind of standardized controlled process. They're supplied by the manufacturers themselves by flowing air through them, usually at a larger vacuum depression than you'd ever want to see in an engine running at WOT (if you suck on it 'harder', it'll flow more air - up to a point). But like I said earlier, if your engine is still making a lot of vacuum at WOT it's telling you it wants more air than it can get. So, manufacturer CFM ratings are at least partially there to help sell product.
Like exhaust though, it is very possible to get a carb that's too big. A carb needs a certain amount of air flow velocity and 'vacuum' in order for all its systems to work. Go too big and it's going to be impossible to tune and also run like a dog. 

It's all a dance. The key is to hit the sweet spot so that all the components in your engine's air flow path are "big enough" to supply it all the air it wants, but not "so big" that you get into the zone where decreased flow velocity starts to hurt you.

Bear


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## ALKYGTO (Mar 29, 2010)

"Bigger" carb?? OP is already running an 850 cfm carb. I still stand by my timing recommendations and a visit to a chassis dyno. All this "tuning" on the street is asking for trouble and leads to inconclusive results. A chassis dyno will be able to tell you lean/rich condition at all rpm and load levels (full and part throttle), whether or not any timing changes make a difference and allow you to "creep" up on an optimal tune. All without getting a ticket or endangering yourself or others. I've seen cars gain 50 rwhp by tuning on the dyno versus what they "thought" was an optimal tune. 

OP, if you do visit a dyno the best advise I can give you is to be fully prepared for everything you want to try. A fresh set of plugs, some jets for the carb and a small selection of hand tools if they will let you do your own work. Drop the pipes there and see if it makes a huge difference before you spend the money on new downpipes. A lot of shops now specialize in late model EFI computer controlled cars so I would ask if they have anyone there than knows carbs and distributors. Tell the issues you are having and what you want to try to alleviate it. The dyno will also tell you where your distributor is curved and you can tune your advance and total timing.


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## BearGFR (Aug 25, 2008)

ALKYGTO said:


> "Bigger" carb?? OP is already running an 850 cfm carb. I still stand by my timing recommendations and a visit to a chassis dyno.


I missed that 850 -- that's what I get for trying to follow multiple threads - sometimes I get them confused. Anyway, what I was trying to say was on all the air flow components, it's important to get them "big enough" but not "too big". Careful planning and testing is the key, which leads to...



> All this "tuning" on the street is asking for trouble and leads to inconclusive results.


'Zactly. Objective, repeatable measurements are the best way to go.


Bear


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## mbspeed (Sep 25, 2012)

BearGFR said:


> Ah, ok - good. Yes, 10.2 is right where you want to be for the street on pump gas. Ok, you've got forged rods --- also good. I'm going to agree that you need more air flow to take advantage of those heads. One thing you might try: connect up a GOOD vacuum gage with fine graduations to manifold vacuum and position it where you can see it while driving. "Make a pass" or something where you can hang your foot in it for a bit. You should see manifold vacuum readings very close to zero while you're under load at WOT. If not then that confirms that the engine "wants" more air than it's getting. Work on the possible sources of restriction. Intake and exhaust systems. However, resist the type of thinking that tempts you towards "too big". A few posts back PontiacJim talked about flow velocity and he was dead on. Especially on the exhaust side, if you go "too big" it'll kill flow velocity and make the engine have to work to pump the exhaust out instead of having the inertia from flowing gas help "pull" it out. That'll cost you torque - big time. General "rule of thumb": 2.5" exhaust pipes are good up to around 500, maybe 550 HP flywheel. Above that you should go 3". The bigger carb is probably a good idea. Be wary of some folks who "do the math" and want to impress you with all the calculations about how to size a carburetor based on engine displacement, rpm, and rated carb capacity. The approach looks good on paper but there are some key points they may not realize, one of them being that carb 'CFM ratings' aren't performed under any kind of standardized controlled process. They're supplied by the manufacturers themselves by flowing air through them, usually at a larger vacuum depression than you'd ever want to see in an engine running at WOT (if you suck on it 'harder', it'll flow more air - up to a point). But like I said earlier, if your engine is still making a lot of vacuum at WOT it's telling you it wants more air than it can get. So, manufacturer CFM ratings are at least partially there to help sell product.
> Like exhaust though, it is very possible to get a carb that's too big. A carb needs a certain amount of air flow velocity and 'vacuum' in order for all its systems to work. Go too big and it's going to be impossible to tune and also run like a dog.
> 
> It's all a dance. The key is to hit the sweet spot so that all the components in your engine's air flow path are "big enough" to supply it all the air it wants, but not "so big" that you get into the zone where decreased flow velocity starts to hurt you.
> ...


Thanks for the info mr. B ...I have the factory Pontiac vac gauge that mounts on the center console got it used from e bay looks cool don't know how accurate it is but when I am cruzin say 30 mph foot off the gas its pegged at say 23 Hg vac then when I hammer the gas in say 2nd vac will drop like a stone too zero at idle got 17 Hg this is with demon carb 850 cfm new out box no mods to carb yet atriot:


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## mbspeed (Sep 25, 2012)

I also ordered an air fuel ratio gauge so I don't blow up my new motor again don't have a dyno shop close to me live in mass about 15 miles outside boston so if anybody knows a dyno shop that still will work on carb cars :nonod:


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## mbspeed (Sep 25, 2012)

*air/fuel*



BearGFR said:


> I missed that 850 -- that's what I get for trying to follow multiple threads - sometimes I get them confused. Anyway, what I was trying to say was on all the air flow components, it's important to get them "big enough" but not "too big". Careful planning and testing is the key, which leads to...
> 
> 
> 
> ...


I have install my new w/b air fuel meter looks like go full lean when I hammer gas also my Hg goes to 0 I guess I need some carb work done fatting up mixture some :nonod:


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## PontiacJim (Dec 29, 2012)

mbspeed said:


> I have install my new w/b air fuel meter looks like go full lean when I hammer gas also my Hg goes to 0 I guess I need some carb work done fatting up mixture some :nonod:


I want to get an air/fuel meter for my project. Was yours easy to install? Did you have to install an O2 sensor on the exhaust pipe?

I can't help much on the Holley. Never really played with any, always went with AFB's and Q-jets. I know its not to difficult to work with changing jets, but other things to consider is the power valve, accelerator pump as I think they come in a 30cc and 50cc size, and you may be able to swap out the squirters that shoot the gas in when you hit the throttle if your carb is so equipped, and a few other tweaks.

Should be a lot of info online or buy a book on Holley carbs off of Amazon.


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## mbspeed (Sep 25, 2012)

PontiacJim said:


> I want to get an air/fuel meter for my project. Was yours easy to install? Did you have to install an O2 sensor on the exhaust pipe?
> 
> I can't help much on the Holley. Never really played with any, always went with AFB's and Q-jets. I know its not to difficult to work with changing jets, but other things to consider is the power valve, accelerator pump as I think they come in a 30cc and 50cc size, and you may be able to swap out the squirters that shoot the gas in when you hit the throttle if your carb is so equipped, and a few other tweaks.
> 
> Should be a lot of info online or buy a book on Holley carbs off of Amazon.


It was very easy I got a special SS exhaust clamp made by AEM with o2 sensor threaded into the clamp so no welding drill the 1/2 hole and use this tayco style clamp nice heated o2 sensor goes right in clamp is $40 its a pita to weld SS pipe so I went easy way out but you don't need clamp gauge comes with the bong that welds too pipe put mine on head pipe before it 90 s and bolts too mainfold:thumbsup: pic of clamp


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## BearGFR (Aug 25, 2008)

Good move, getting the meter. Sounds like you've got a plan now. 

Bear


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## mbspeed (Sep 25, 2012)

BearGFR said:


> Good move, getting the meter. Sounds like you've got a plan now.
> 
> Bear


Yes sir master plan is not let that meter peg out at 20:1 need keep in sweet spot or run little richer 12:1 or lower we will see :cheers


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## 646904GTO (Feb 10, 2008)

AFR of 14.7 is perfect...for todays engines..your target should be 13.5. On dyno I have seen the most WOT HP on the Pontiac there. BTW after I was tuned to my liking I ended up removing the AFR meter and wide band. Constant need for calibrating was my demon and after you are all set it isn't really something that needs to be monitored.


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## PontiacJim (Dec 29, 2012)

646904GTO said:


> AFR of 14.7 is perfect...for todays engines..your target should be 13.5. On dyno I have seen the most WOT HP on the Pontiac there. BTW after I was tuned to my liking I ended up removing the AFR meter and wide band. Constant need for calibrating was my demon and after you are all set it isn't really something that needs to be monitored.


You make a good point here. I have read that ethanol in the gas causes the engine to run leaner. Does this affect the A/F ratio reading at all? Is 12.5 on what used to be straight gas the same as 12.5 using gas with 10 per cent ethanol?

However, I agree with running a little richer than what is said to be "optimal." Good tip from your hands on experience.


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## geeteeohguy (Feb 2, 2008)

I'm pretty familiar with emissions gasses/fule mixtures, etc. 14.7:1 is the most efficient, sweetest spot for the _lowest tailpipe emissions_. Period. If you look at a 4 or 5 gas chart, it's the low point for HC, CO, NOx, and CO2. Leaner mixtures are more economical, but will produce high HC and NOx due to heat. (Chrysler's Lean Burn in the '70's ran
16:1 and was terrible for drivability due to being too lean) Richer mixtures produce more power, but excessive amounts of CO are produced. The sweet spot, for emissions, is 14.7:1. The fuel economy at this ratio is pretty close to as good as it gets, though. That said, when you boot your old school car and get on it, you want rich mixtures....like 12:1 or less. Alcohol has about 1/2 the energy of gasoline, and needs bigger jets and more of it to run the same engine. So yeah, running our present crap 10% alcohol fuel would require fattening up the mixture a bit, I would think. I probably should do it to both of my rides, too.


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## PontiacJim (Dec 29, 2012)

geeteeohguy said:


> I'm pretty familiar with emissions gasses/fule mixtures, etc. 14.7:1 is the most efficient, sweetest spot for the _lowest tailpipe emissions_. Period. If you look at a 4 or 5 gas chart, it's the low point for HC, CO, NOx, and CO2. Leaner mixtures are more economical, but will produce high HC and NOx due to heat. (Chrysler's Lean Burn in the '70's ran
> 16:1 and was terrible for drivability due to being too lean) Richer mixtures produce more power, but excessive amounts of CO are produced. The sweet spot, for emissions, is 14.7:1. The fuel economy at this ratio is pretty close to as good as it gets, though. That said, when you boot your old school car and get on it, you want rich mixtures....like 12:1 or less. Alcohol has about 1/2 the energy of gasoline, and needs bigger jets and more of it to run the same engine. So yeah, running our present crap 10% alcohol fuel would require fattening up the mixture a bit, I would think. I probably should do it to both of my rides, too.


Good points geeteeohguy. There are many articles online about the 10% alcohol in our gas. Doesn't seem to be a good thing with regards to older engines that are not designed for it. The stuff deteriorates rubber lines, so you have to make sure you have the proper type rubber lines. Had my older weed-wacker die on me because the gas literally disintegrated the little gas line pickup tube -tiny bits flaked off which plugged up the carb. Had to buy a new carb, then purchased the correct line designed for alcohol, and added a small filter at the pickup end.

Read that the old rubber lines deteriorate, that the gas draws moisture/water, can be very corrosive on the guts of your carb and other softer metals, and can rust out your gas tank due to moisture accumulating inside if you don't drive the car much or let it set for long periods. We had a local news story about a woman who had to have big repairs done to her car because of what they call "phase separation".

When this Phase Separation occurs you will have an upper layer of gasoline with a milky layer of Ethanol and Water below it, and then in many cases a third layer of just water at the bottom. If this happens and you try to start the engine you can have one or more of the following problems. If your fuel tank pick-up tube is in the water layer, most likely the engine will fail to start. If the engine is running and suddenly draws water you can have damage from thermal shock or hydro-lock. If the pick-up tube draws the Ethanol-Water mixture or just Ethanol you can have problems where the engine will operate in an extreme lean condition, which can cause significant damage or even catastrophic failure. If the pick-up tube draws the gasoline, it will operate very poorly due to lower octane that is the result of no longer having the Ethanol in the fuel. Phase Separation is also temperature dependent. For example, E-10 can hold approximately .05% water at 60°F. To better understand the amount of water that we are talking about, picture 1 gallon of E-10 at 60°F. This gallon will hold approximately 3.8 teaspoons of water. However if the temperature drops to 20°F it can only hold about 2.8 teaspoons of water. At the lower temperatures where it reaches a lower saturation point, the Ethanol and water will Phase Separate, actually coming out of solution and forming two or three distinct layers in the tank.

Sta-Bil makes a fuel additive I get at Wal-Mart that I now use in my '97 Toyota which seems to make it run better as opposed to some days it would run balky and then clear up, then run rough, and clear up, etc.. Now I don't seem to have that problem, it runs consistently smooth.


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## BearGFR (Aug 25, 2008)

+1 on the ethanol fuel stabilizer. Just a little prevention can save you many expensive headaches down the road.

Bear


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