# Engine Help ...455



## vera_jr (Aug 17, 2012)

I am trying to determine the compression ratio on my '69 GTO. It has a '74 trans am 455 engine. I saw 6X casted on the side of the heads. 
Are 6X heads standard on the '74 455 or are they after market? 
How do you measure the stroke?


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## cuz68 (Feb 19, 2013)

You need to look for a two leter code below the pass side head and let us know what it is like YC or what yours is then we will let you know what you have.


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## 68greengoat (Sep 15, 2005)

6x heads are Pontiac and were found on 350/400 blocks. 4x heads were common on '73/'74 455's....


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## Instg8ter (Sep 28, 2010)

there are several variations of the 6-x head all having slightly different CC's also.


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## vera_jr (Aug 17, 2012)

Ok, I looked at the head, here is what is says.....

6X......GM8......DN.........D185

does that help???


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## vera_jr (Aug 17, 2012)

Ok, checked again...the passenger side is 6X GM8, the drivers side head has 6X GM6 on it.


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## leeklm (Mar 11, 2012)

I like the wallaceracing.com website, lots of good pontiac info on coding heads and engine blocks. Can give you an idea of the various chamber volumes, etc. Without knowing "exaclty" what you have for crank, pistons, and chamber volumes, you can only guess on Compression ratio, unless you used a "Whistler" test or something similar. You would likely need to find a performance shop that would have the right equipment or a Whistler. We always had one at the local circle track tech barn for checking CR.

There may be other ways to find CR that I am missing...


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## BearGFR (Aug 25, 2008)

You do have to have some very accurate measurements to get an accurate CR (or access to some very high dollar test equipment).

Let me ask you, why are you looking for the information --- I mean, how does that figure into your plans?

It'd be good for you to visit some of the various sites that have information on how to decode all the various markings on Pontiac engines (Google "pontiac engine codes" for starters).
I recommend you start by positively identifying exactly what you've got there, then working from that point. By that I mean making _sure_ it's a 455, what model year it is, what haeds are on it, etc.

We can help if you get stumped but it's more fun to figure it out on your own.

Bear


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## vera_jr (Aug 17, 2012)

im trying to just find out some information about my car. when i bought the car 7 months ago, i found th code on the engine. it matches a 74 trans am 455. The heads dont seem to be stock to the engine based on the numbers (D185 is not off a 74). So what could have gone into this thing? with thos heads, what kind of horsepower should I be getting? better than the 250 it advertises??? I love a mean sounding muscle car and would like to put a street/strip cam in it, but i need to know the CR. 
I am slowly upgrading parts on it. Getting a HEI distributor and coil next month, getting rid of the points. Adding A/C..too damn hot in south texas...need some body work for rust issues. minor cosmetics interior (mainly just dash, rear tray, and headliner. 
Its a great car. I just wanna be able to answer questions from peopl and myself about what kind of power it really has.


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## BearGFR (Aug 25, 2008)

D185 indicates model year 1975, so you're right about that.
What's the block date code? Casting number? Block code?

Bear


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## vera_jr (Aug 17, 2012)

I dont have it off hand, but when I found the block code/vin, i was able to find engine codes for pontiacs and it matched a '74 Trans Am 455. I was hoping for a SD, but it didnt say that. I will post the code on here when I find it again, I have it written down somewhere.


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## BearGFR (Aug 25, 2008)

For a positive id you really have to use all 3 pieces of information off the block, not just the 2 character code on the front. This is because Pontiac in some cases used the same front code in different years to mean different things.

Bear


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## vera_jr (Aug 17, 2012)

having trouble finding the block code and date code.
Vin #22P391329
Cast Code 85428
DN is written on the block as well.


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## 68greengoat (Sep 15, 2005)

The second digit of the vin is the year. In this case, '72........

I believe the cast(block) code is "4"85428? 455 block.

Engine displacement was also cast in the side of the block.

Date code/block casting number.








2 character engine id next to the head.


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## vera_jr (Aug 17, 2012)

C012 is the date code
the cast code does have a 4 in front. I missed it, some old oil/grime was covering it.


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## vera_jr (Aug 17, 2012)

Block Code on front (by timing cover, pass side front)

C435411
YH

Is that everything??


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## BearGFR (Aug 25, 2008)

Ok... now we've got something.
C012 says the block was cast March 01, 1972 -- making it year model 1972.
485428 pegs it as a 455
YH for 1972 marks it as having originally been installed in a B-body (big car) with a TH-400 transmission, 2 barrel carburetor. (RPO code L-75) rated at 200 HP. It would have originally had either 7D4 (early production, no divider on center exhaust ports) heads or 7L4 heads. Both had smaller valves (1.96 intake, 1.77 exhaust) and pressed in rocker studs.

Don't despair though. It's still a 455, and with the different heads and (I assume) different carburetor that's on it now, it's making more power than that. Plus it most definitely has got some serious potential.

Next step is to get a positive ID on the heads. You've already said 6X, but there are two varieties of 6X: 6X-4 and 6X-8. Here's a photo of some 6X-4's









See that "4" down on the far right hand exhaust port? That's one of the ways you tell. Some of them had either a 4 and an 8 in smaller size on the "side" of the head sort of above the spark plugs. Knowing if they're -4's or -8's matters because the chamber sizes were different, making compression ratio different.

Bear


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## vera_jr (Aug 17, 2012)

6X: Pass Side says M 8, Driver side says M 6


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## BearGFR (Aug 25, 2008)

Hmm.. never heard of a 6X-6.. check for smaller numbers on the side of the head, like on that small square flat face on that raised part between the spark plug hole and the head bolt hole on the left side of that photo I posted.

Here's another photo showing the location.









..and another link
http://www.pontiacstreetperformance.com/psp/6XheadID.html

Bear


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## vera_jr (Aug 17, 2012)

Carb. Edelbrock 4BB 600CFM


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## vera_jr (Aug 17, 2012)

It has a 4 on both sides. Just found it. needed a mirror to read it, its facing down. couldnt see it from above view 
So they are 6X-4


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## BearGFR (Aug 25, 2008)

Awesome. Those are some of the better D-port heads. They have screw-in rocker studs and the larger valves (2.11 intake, 1.77 exhaust).
Factory nominal chamber size is 94 cc's, but don't take that to the bank. We don't know if they've ever been millled/machined, and also Pontiac heads are known to sometimes vary quite a bit from the factory spec. There are other details about the engine we'd have to know in order to calculate the true compression ratio and the only way to get those measurements would be to tear it down and start measuring things.
However, if we make some ASSUMPTIONS about the engine, we can probably get reasonably close.
If we assume:
* It's a standard bore 455 (never been bored) - bore size:4.150
* It's not running a stroker crank. stroke length: 4.210
* It has 'nominal' deck clearance (pistons are .020 "down the hole")
* It's running standard head gaskets (4.160 bore, .042 compressed thickness)
* It has flat top pistons with 6 cc's of clearance in the valve reliefs
* The heads are 'factory nominal' with 94 cc chambers

If we make those assumptions, then the engine has 9.20:1 static compression ratio. 
That's just about perfect for an iron-headed street engine that can run and stay healthy on 93 octane pump gas.

Wish we knew the specs on the cam...

That 600 cfm Edebrock carb is a little small though, especially if the motor has any "cam" in it at all. It'd be a lot happier with 750+.

Sounds to me like you've got a very good start there on a good street engine, and whoever built it at least knew a little bit about what they were doing.

Just so you can see how small changes can affect things. If we change just two assumptions, namely if
1) The block has been zero-decked (pistons are .000 "down the hole)
2) The block has been bored .030 oversize so that bore=4.180

That bumps the compression ratio up to almost 9.7:1 (9.660) which (again in my opinion) is starting to get into the danger zone for detonation on pump gas with iron heads.

Bear


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## vera_jr (Aug 17, 2012)

Awesome. I hope that is all correct. I feel better about the engine now. I do want to change to a more aggressive cam, which a 9.2:1 CR will allow. 
one of my plans involves taking the engine out, and apart, cleaning it all up, repainting, and reinstalling. We can take more measurements or do upgrades at that time.

Thanks Bear for helping...I may have more questions for you later.


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## vera_jr (Aug 17, 2012)

what kind of HP should I be getting out of that engine??
What Cam would you recommend?


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## BearGFR (Aug 25, 2008)

There's a whole lot that goes into a cam choice. You've got to think about how you plan to drive the car, what RPM range it's going to "live in" most of the time. What transmission and rear gear are you running, do you have vacuum operated accessories like power brakes and/or factory a/c, etc. 

For a "mild" to moderate street engine build using mostly what you already have, I'd say power in the 400-450 range (at the flywheel) is easily attainable at reasonable cost while retaining good manners. If your pockets are deeper and your tolerance for maintenance needs and more "attitude" is higher, and you're willing to sacrifice some street manners, then you can get a lot more. Like A.J. Foyt once said, "Speed is just a question of money. How fast do you want to go?" 

Bear


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## vera_jr (Aug 17, 2012)

im not a racer, but i love to go fast on occasion. it may sound silly but i just want a good sounding lope. I love having a car that is a true muscle / street machine. I need low end performance since I will do almost always street driving. I do want to dyno the car one day and would love to be in the 400-450 range. 
Power Brakes: Yes
A/C : Yes, after market.
Power Steering: Yes
Am i going to have to change all the lifters with the cam??


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## leeklm (Mar 11, 2012)

Yes, ALWAYS keep lifters with the cam, and keep them in the proper order if removing or switching cams.

I just finished a build on my iron head 455, which would be similar to yours. I did install H Beam rods just to be on the safe side. The Cam I installed is:

Advertised Duration (Int/Exh): 262/268
Duration @ .050 (Int/Exh): 219/227
Gross Valve Lift (Int/Exh): .468/.489
LSA/ICL: 112/108
Valve Lash (Int/Exh): Hyd/Hyd
RPM Range: 1300-5500
Part Number: 10510702LK

On the dyno, we ended up with 410hp and a little over 500 Tq. I have the engine installed and have been tuning my qjet in the garage, waiting for "spring" to get the car outside. To be honest, I was hoping for a little more lope for that muscle car sound, but this one does idle plenty smooth with about 17" of vacuum at 600-700rpm. Since I have power brakes, guess I would rather error on the side of too smooth rather than too lopey. 

I have another Lunati that the engine came with 

http://www.lunatipower.com/CamSpecCard.aspx?partNumber=07703

but that one is on the other extreme with a very rough idle and likely low vacuum numbers. The previous owner could hardly keep it running, but he had no idea what he was doing, and trying to run a qjet that had an idle circuit for a 301 Pontiac.

My plan is to run with the one in my motor for a while to see how I like it. Looks like it will have plenty of TQ to smoke the "tire" at will, so a cam change is likely not worth the expense or effort for me.

For more reading, you can check out a few comments on this thread...

http://www.gtoforum.com/f50/solid-hydraulic-39464/


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## vera_jr (Aug 17, 2012)

Looking at putting this cam in it
COMP Cams: Xtreme Energy™, XE284H: Cam & Lifters

how would the rest of the components be? Should I change everything? Pushrods, rocker arms, valve springs?

Would this be too much cam for the power assisted devices??


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## leeklm (Mar 11, 2012)

Just reading the notes on the cam spec page, you will need everything, including machine work on the heads for the springs.

[1] Requires screw-in studs & guide plates.
[2] Requires machining on cylinder heads.
[3] Standard weight and lightweight retainers
[7] Stock springs cannot be used.
[37] Adjustable valve train required.

Also, this is a high rpm cam that will require a good motor (new rods, pistons, etc) in order to hold up. Do a search under "cam" on this site, and you will find lots of good info. Also, place a call to the cam mfg, and they will give you recommendations based on your needs.


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## BearGFR (Aug 25, 2008)

vera_jr said:


> im not a racer, but i love to go fast on occasion. it may sound silly but i just want a good sounding lope. I love having a car that is a true muscle / street machine. I need low end performance since I will do almost always street driving. I do want to dyno the car one day and would love to be in the 400-450 range.
> Power Brakes: Yes
> A/C : Yes, after market.
> Power Steering: Yes
> Am i going to have to change all the lifters with the cam??


What kind of transmission, and what's your rear axle ratio?

Keeping your power brakes working means you need at least 15" of vacuum at idle, and that's a minimum. Or - you'll have to either add an auxiliary vacuum pump (noisy) or convert to a hydroboost brake system (expensive).

Keep in mind a 455 is NOT a high rpm engine. 5500 is going to be your upper limit - in fact with factory rods I'd recommend keeping it at 5000 or below. Going to a cam that makes peak power above that would be dangerous and a waste of money, unless you also install a GOOD set of forged H-beam rods but even then, if you're realistic how often is the engine going to see that kind of rpm with the driving you'll be doing? Probably not often - so you'd be sacrificing torque down low, where you'll be spending most of your time, to gain torque up high, where you rarely go.... doesn't sound like a wise move to me. 

All a cam change really does is move the point where the engine's peak volumetric efficiency occurs to a different rpm range - higher or lower depending on the cam. Remember HP = (torque * rpm) / 5252, so if you move the torque peak to a higher rpm, you get more power --- but you don't get any more torque. But since there's no such thing as a free lunch, if you make the motor more efficient at a higher rpm, it's going to be LESS efficient at a lower rpm (less torque). That lopey, rumpity rump idle everyone associates with a hot motor? What's really going on there is the darn thing is so inefficient at low rpm it can barely _stay running_, much less make any power down there.

Here's a great video that illustrates what I'm talking about. It's a little contest between a sport bike that makes 180 or so HP way up at 9000 rpm and an old Harley that barely makes half that much horsepower, but has some torque way down low.

http://www.liveleak.com/ll_embed?f=4a88a935f5f0


Bear


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## Instg8ter (Sep 28, 2010)

Yamazuki....LMAO. Horsepower sells motors, torque wins races.


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## vera_jr (Aug 17, 2012)

Transmission is a Tremec T56 Magnum 6-Speed.
I dont know the rear axle ratio. . . how do I find this out??


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## Rukee (Feb 8, 2007)

vera_jr said:


> Transmission is a Tremec T56 Magnum 6-Speed.
> I dont know the rear axle ratio. . . how do I find this out??


If it's a POSI unit jack up both tires off the ground. Turn the tires 1 revolution while counting how many times the driveshaft turns. The # of turns the driveshaft turns is your gear ratio. If it's a 1 wheel wonder jack just one tire off the ground and then turn that one tire 2 full revolutions counting the driveshaft turns. You should end up with anything from 2.75 to 4.11.


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## vera_jr (Aug 17, 2012)

Gear Ratio: about 3.65:1 (its a POSI unit)
Transmission: Tremec T56 Magnum 6-Speed.


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## vera_jr (Aug 17, 2012)

never realized axle ratio played that big a part in a cam. Choosing a cam is actually a pain in the tush. Lunati has this one that I am looking it. 

Lunati 265 455 Pontiac 262 268 468" 489" 112° Voodoo Hyd Cam Camshaft SK Kit | eBay 

Seems like it would work, but I like your guy's opinions. Im learning a lot here. Can someone send me a model number or link to something you think would better suit my car???


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## BearGFR (Aug 25, 2008)

5 speed manual, "approximately" 3.50-ish gears. Ok good for two reasons: 1) with a manual you don't have to worry about selecting the proper torque converter for launch rpm like you do with an auto, and with the overdrive tranny you can still tame those rear gears down some for highway cruising.
So your limiting factor on "going nuts" with the cam just became those power brakes. They will be affected before anything else is. To keep from killing vacuum, you've got to watch the overlap period (period when both intake and exhaust valves are open). The variables that affect overlap are LSA (lobe separation angle), lobe duration, and also lobe shape.
Take them in reverse order. Lobe shape is limited by the type lifters you use. If you select a flat tappet cam, then those lobes can only be so steep before the edge of the lifter starts digging into the cam lobe. You can get around that by running roller lifters, but that solution is a lot more expensive than a flat tappet cam. Your choice there.
lobe duration - how long they hold the valve off its seat - is the primary factor in determining which rpm range the cam is optmized for. More duration = higher rpm efficiency, but at the expense of lower rpm efficiency as previously mentioned. Lastly, LSA - lobe separation angle - how far apart in degrees are the peak lift centerlines of the two lobes (intake and exhaust). The farther apart they are, the less overlap.

Looking at that Lunati that caught your eye:
it has an LSA of 112 degrees (a little on the wide-ish side, so good for vacuum)
lobe duration at .050 of 219 (intake) 227 (exhaust) --- seems way low to me
it's a hydraulic flat tappet cam (relatively economical, gentle opening/closing ramps)
it's got .468/.489 valve lift with 1.5:1 rockers (also relatively mild)

This cam in a 455 is going to make plenty of vacuum for brakes (good), it's going to have a dead smooth idle like a stock engine, and the short duration and wide LSA is going to tend to make lots of cylinder pressure (bad for detonation). Lift is... eh.. doesn't matter because there's not enough duration there to do much with the lift.

(Don't pay any attention at all to all the verbiage that says things like "Torque Monster for 400-455 c.i. daily driven street performance vehicle. Excellent torque and horsepower production with heavier emphasis on the low to mid range." It's all just advertising hype, usually written by someone who might know a little about small block chevys, but not much else. Besides, would YOU buy a cam if the description said instead, "Idle that sounds just like a bone stock cam. Torque range good for RV's and tractors."? --- which is about how this cam would act in a 455 Pontiac. Pontiacs are NOT chevys. Pontiac engine never have to "worry" about losing low end torque like the bowtie boys do because they make great heaping buckets of it. Sometimes, it's good to do things to take some of that torque OUT of them in order to try to find some traction. When starting with a stock engine, you never have to make a cam change to try to "help" the bottom end of the torque curve on a Pontiac, especially a 455.

Always always always -- evaluate a cam by the spec numbers and ignore the hype.

To get you where you probably want to be with this car, I'd like to see duration numbers in the low 230's at .050. Maybe 235 or so tops on the intake side IF it also has a 112 degree LSA. -and- is a roller profile A little less if it's 110 degrees. If you can afford a roller (solid or hydraulic - I prefer solid myself) then you can push duration a little higher, maybe. I'm running a solid roller in my 461 that has 236/242 duration at .050 on a 110 degree LSA, and it makes about 14 in vacuum at idle. That's borderline too low for power brakes (in my opinion) which is why I'm running a hydroboost brake system. A cam identical to mine in all respects except with a wider LSA of 112 instead of 110, ought to raise idle vacuum just enough to make power brakes workable while only giving up a "tiny" bit of torque and power. Again though, that's for a solid roller profile that may be more than you're willing to spend - I don't know. Just for reference, my engine (which is a 461 - a stroked 400) is making right now somewhere around 520-530 "or so" horsepower. It also has some very good heads on it (professionally ported Edelbrocks).

Choosing a cam is fun. But then I've got some simulation software here that lets me put in various profiles and "run" them in an engine to do comparisons.

Bear


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## vera_jr (Aug 17, 2012)

I seem to be looking for the impossible combination in a cam. This one is close, but I dont believe I have the compression for it. the axle ratio is close, 3.65-3.75 (by my measurement). Street Strip Solid Roller Cam - Pontiac V8 290/290 - Lunati Power


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## vera_jr (Aug 17, 2012)

Comp Cams has the XE274H that would fit it, but would require some grinding to get it to 112 lobe seperation. Is this something that will work?
51-224-4 - Xtreme Energy? Hydraulic Flat Tappet Camshafts

Problem is all the machining and valve adjustments that is says are required.


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## vera_jr (Aug 17, 2012)

This is one Lunati recommended to me. will need grinding as well to get to 112 Lobe Seperation.
Voodoo Hyd Cam - Pontiac V8 276/284 - Lunati Power


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## Rukee (Feb 8, 2007)

3.55 Gear ratio is a factory option. That's what my car and most factory non A/C stick cars are running.


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## BearGFR (Aug 25, 2008)

The Lunati 290/290 isn't going to make enough vacuum
The Comp XE274H is going to also be low on vacuum. Regrinding it to 112 LSA helps, but not enough probably.
Ditto for the VooDoo 276/284.

The Comp Cams 268H is going to be close
So would the Lunati Streetmaster 280/288

Bear


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## vera_jr (Aug 17, 2012)

both of those, even at 110 LSA?


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## leeklm (Mar 11, 2012)

Hey Bear, was interesting on your comments regarding the Lunati, which is what I ended up with...

"Looking at that Lunati that caught your eye:
it has an LSA of 112 degrees (a little on the wide-ish side, so good for vacuum)
lobe duration at .050 of 219 (intake) 227 (exhaust) --- seems way low to me
it's a hydraulic flat tappet cam (relatively economical, gentle opening/closing ramps)
it's got .468/.489 valve lift with 1.5:1 rockers (also relatively mild)"

You hit the nail on the head from what I have seen so far, but have not been on the street yet...

I am curious, with all else being equal on a cam like this, what kind of impact would an increase in lift via 1:65 rockers have? It is not much work and I have the rockers, so may have to try it. I had hoped to run this test at the dyno, but ran out of time.


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## BearGFR (Aug 25, 2008)

leeklm said:


> I am curious, with all else being equal on a cam like this, what kind of impact would an increase in lift via 1:65 rockers have? It is not much work and I have the rockers, so may have to try it. I had hoped to run this test at the dyno, but ran out of time.


I fired up my copy of Engine Analyzer and built a model of your 455. I was able to dial it in pretty close to what your engine actually made on the dyno with headers. Then I changed to 1.65 rockers, and ran it again. I think you'll like the results.

You should pick up another 15-18 HP without hurting your idle vacuum or losing any bottom end. Under ideal conditions, that'll cut your quarter mile e.t. by about a tenth. The improvement comes mostly from the 1.65's making the cam "act like" it has slightly more duration.

One thing - if you're running factory iron heads (you are, aren't you?) the pushrod passages in them will need to be elongated (if they haven't already) - otherwise the pushrods will probably rub on the heads there.

Bear


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## leeklm (Mar 11, 2012)

Thanks Bear, as usual, great info! I have a set of full rollers, so will try it after i put some miles on the current setup. I did have the holes elongated in the heads. 

What is the max total cam lift you guys like to run with stock height springs?

Sent from AutoGuide.com Free App


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## leeklm (Mar 11, 2012)

Pulling up this old thread with a quick update... I installed the 1:6 rockers, and the engine does feel a little more alive in the upper RPM band. I can now easily run to 5,500, where it really did not want to get there all that easily with the 1:5 rockers. 

I pulled both an intake and exhaust valve spring to be sure the retainers were not bottoming out on the head, which they are not. Plenty of lift with this combo, and stock spring height so had to be a little cautious.

Maybe it is my imagination, but I like the feel of this ratio and my mild cam. More torque than I can put to the ground, and a strong pull up past 5K. In addition, good street manners, and sounds awesome at 2,500 rpm cruise speed.

Takes a lot to make me happy, and I like it


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## BearGFR (Aug 25, 2008)

I love it when a plan comes together 

Bear


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