# Advice requested regarding 400 and 670 heads



## goat671 (Apr 13, 2019)

Looking for some options on what I can do with my engine.

Background: I needed to pull the heads to determine the condition of the internals due to the engine not being turned over for a very long time.
Future: I will at some point be replace/rebuild engine more than likely looking to get to a 461 stroker.
Immediate need. Want to have a running engine having body work and paint started now want to put the engine in before body work is started.

So good news is all is fine in the engine no rust or any reason to disassemble any further. 
I purchased the required gaskets to reassemble but I got to thinking what can I do to make sure I can drive the car with todays gas? 

So wondering if I should put another set of heads on? I seen in another post I can get a set for 1600.00 - 2000.00 complete from Nitemare Performance.
Maybe I could use these in the future when I go to the 461?

Parts that I have that if would work could use.
1971 455 66 heads these are 114 cc I do not think I can use these as the CR would be way to low.
Crane 969681 cam which is a 041 replacement do not think this will be of any use either.

So if I can get some of your thoughts that would be great.


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## LATECH (Jul 18, 2018)

the 670 heads are 72 CC too tight for pump gas with a 400 or a stroker crank.
Some body will likely want them so hang on to them.
Get some aluminum heads with chambers around 80-82 CC . That will put the CR around 10 .5 ish on a 462 CI.
85 CC would be at 10.0 to 1 so that would give some wiggle room for octane /hot days/etc
safe enough for aluminum heads as long as your cooling system is top notch and you have the right curve on the dizzy/timing (93 octane of course)


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## Jared (Apr 19, 2013)

goat671 said:


> Looking for some options on what I can do with my engine.
> 
> Background: I needed to pull the heads to determine the condition of the internals due to the engine not being turned over for a very long time.
> Future: I will at some point be replace/rebuild engine more than likely looking to get to a 461 stroker.
> ...


I'm running a pair of Nitemare stage II heads on mine. They are fantastic! I opted for the larger exhaust valves and had the header surface cleaned up. Engine is a 461 with flat top pistons (just the very small valve relief area). Heads are 6X with 96cc combustion chambers so it runs fine on premium pump gas. If you're thinking of going that route, I'd reach out to them to get the ball rolling. They are machined to order and there was a wait when I had mine built. The shop owner's name is Darrin. He is quick to respond and extremely helpful. I had trouble getting mine to fire up the first time and he took a call from me after dinner on a Thursday. I can't say enough good things about Nitemare.

BTW. If you are planning to build a 461, the larger cc heads may not be as bad as you think. Keep in mind, the CR goes up as the CI of the engine increases. That's why many run dished pistons with the smaller cc heads.

I've posted this on here before but this may help you out.



https://butlerperformance.com/n-12872-compression-calculator.html


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## BearGFR (Aug 25, 2008)

You're in a really good spot with it right now because you (presumably) haven't bought your stroker kit and pistons yet. 670 heads are closed chamber designs and generally need a little more than the usual 34-36 degrees of total advance at WOT to get the maximum performance out of them. They have relatively small chambers. Some reference pages on the 'net list them as nominal 72 cc's, others at 70 cc's, and that will apply only if you're positive they've never been surfaced/cut/milled. Even then, untouched from the factory, chamber volumes on heads have been known to vary some so it's always best if you cc them yourself to find out what your chamber volumes actually are - and that means all 8 of them.

670's have been very popular for performance builds for years because even though they need more timing, they flow as good if not better than any other Pontiac D-port head.

670 heads on a 461 with "flat top" pistons is going to put you well over 11:1 static compression, which in my opinion is WAY too much for pump gas with iron heads and very likely to knock harder than a hoard of JW missionaries.

An aside on that topic, you will find various opinions on how much compression you can run all over the net. Some people can and do successfully run a lot of compression on the street with iron heads. They generally will be running "a lot" of cam with very late intake closing events to try to manage low RPM cylinder pressure (via "dynamic" compression) so as to avoid detonation, and they also have to stay really on top of other items such as engine cooling system, fuel mixture, etc. to keep their engines alive. 

Know this though: running a cam like that, or even running with a 'normal' cam but installed significantly retarded (to accomplish a similar effect) is going to shift the engine's peak VE to a higher RPM which means low RPM torque (where you'll spend 90% of your time driving on the street) is going to take a significant hit.
Also, on a stout 461 that's already close to or even north of 500 HP, the difference between 9.5:1 compression and 10.5:1 compression is only going to buy you about 8 HP, all else being equal. Is that much gain "worth" the difference between having an engine you don't have to worry about, and one that you do? That's your decision to make, but it's not worth it to me.
(Aluminum heads can tolerate a little more compression due to their improved heat transfer properties).

Once you know that, you can use any of several available tools (there's even a spreadsheet that I wrote out on this site - somewhere) to 'back into' how much dish volume you'll need in your pistons in order to result in a safe compression ratio for street pump gas. Then order your stroker kit accordingly. For a street engine on pump gas with iron heads, personally I prefer to keep static C.R a 9.5:1 or slightly below. On a 461 that actually does actually have 72 cc chambers, and all other measurements, head gaskets, etc. being "factory usual", that will require running pistons with at least 25 cc's of dish volume in the crowns.

One more thing. Resist taking the 'easy path' of just running super thicker/fatter head gaskets than the factory 0.045/0.042 compressed thickness to get the additional clearance volume. That will work to get compression down, you bet, but it will also murder the quench properties in the cylinders. 'Quench/squish' results when the piston top gets close to the head surface. This promotes turbulence in the cylinder that helps keep the fuel mixture "mixed", promotes an even burn, and helps prevent detonation inducing hot spots in the chamber. With good steel rods (that don't stretch a lot at high RPM) you can run as little as 0.032, but it's safer to keep that distance between 0.040 and 0.060. Aluminum rods (which are a bad idea on the street anyway) need more clearance than that because they stretch more at RPM. That's also why they aren't great on the street. All that stretching causes them to work harden and get brittle, then they break. 

Maybe more than you asked for, but I've spent a lot of effort looking into this topic.

Bear


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## goat671 (Apr 13, 2019)

Great info 

My question now is can I get a set of heads now that I can use with the stock 400 that I could then reuse in the 461 stroker later.

Also I bought that crane cam for 49.99 many years ago I am not married to using this cam.

I want to have something to drive but all of my funds are going to the body work and paint right now.
I do not have the ability or the resources to do the body work and paint so I am having the work done at the Hotrod Factory it is going to be a fair bit of money
but when I watch a commercial telling me I can get a new Grand Cherokee for $89999.99 I guess it is not so bad.


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## geeteeohguy (Feb 2, 2008)

goat671 said:


> Looking for some options on what I can do with my engine.
> 
> Background: I needed to pull the heads to determine the condition of the internals due to the engine not being turned over for a very long time.
> Future: I will at some point be replace/rebuild engine more than likely looking to get to a 461 stroker.
> ...


I blazed your exact trail for the past few decades with my '67 GTO with the original 400 and 670 heads. Even in the 80's, the 94 octane pure gas didn't do the trick.
670's are closed chamber and prone to detonation. I'm running flat top pistons, installed in the '80's when I overhauled it. Dished pistons were not available then. 
I next tried the #66 455 heads with 114 cc. This let me run on regular fuel no problem. The performance difference from the stock 10.75 to the now 7.25 was huge.
The car ran ok, but guzzled gas and was a slug. I next installed a set of 1970 #15 heads from a 455. These were small valve 87 cc iron heads. I converted them to screw in studs and have ran them the last 12-15 years with an 068 cam. My car now will run on 91 pump gas and only detonate on days like today (105 degrees) pulling a grade. 
My CR is now about 9.3 to 1 and my fuel economy is excellent. 
The 1970 #64 455 head is also 87 cc and has the big valves, but these are expensive and rare. There are several sets of #15 heads on line right now. 
My heads were so hammered it cost about $1400 to re-do them. IN retrospect, I should have spent another grand and gotten aluminum aftermarket KRE's or Edelbrocks. 
The only way to run one of these engines with stock profile flat top pistons on todays pump gas is to lower the CR by using a head with a bigger combustion chamber. You want anywhere from 85cc to 95cc and you'll be fine. The 114 cc heads are too big for a 400 unless you are going to supercharge it, etc.


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## Jared (Apr 19, 2013)

Quick answer to your question is yes. Choose a combustion chamber size that'll be pump gas friendly for the 461 and run them on the 400. Your CR will be lower on the 400, but as long as it isn't too low, it should work OK. Only other thing that may change would be valve spring choice for whatever cam you are going to run. Keep in mind that a cam that would be considered as pretty aggressive in a 400 will be milder in a 461.

One thing to consider here is it will be way cheaper in the long run to build the engine you want than to build up a 400 and then a 461. Many of the components won't/may not be transferable. The added costs will add up.


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## BearGFR (Aug 25, 2008)

goat671 said:


> Great info
> 
> My question now is can I get a set of heads now that I can use with the stock 400 that I could then reuse in the 461 stroker later.


I don't know why I hadn't already done this, but I just finished putting up a link in the FAQ section here on this topic, that also contains my own compression ratio tool (plus a tool that can be helpful if you want to order full custom pistons)

FAQ => Engine Building: Determining Compression Ratio (includes measuring tool)

Cheers,
Bear


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## goat671 (Apr 13, 2019)

Jared said:


> Quick answer to your question is yes. Choose a combustion chamber size that'll be pump gas friendly for the 461 and run them on the 400. Your CR will be lower on the 400, but as long as it isn't too low, it should work OK. Only other thing that may change would be valve spring choice for whatever cam you are going to run. Keep in mind that a cam that would be considered as pretty aggressive in a 400 will be milder in a 461.
> 
> One thing to consider here is it will be way cheaper in the long run to build the engine you want than to build up a 400 and then a 461. Many of the components won't/may not be transferable. The added costs will add up.


Yea I get that about building what I want but since it is apart I was wondering what I could do to get buy until I can afford to build what I want. 
I like the idea of getting a set of heads for the stroked build and use them now in the 400 with no other changes.
Regarding the value springs would it be a problem to run the higher spring rates on the 400 stock cam I would not think so.


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## BearGFR (Aug 25, 2008)

The only concern with running more spring than what you need is the increased loading on the components, including the cam. If you go really crazy with spring pressure on a flat tappet cam, you can end up wiping out lobes and ruining the cam.

If you change springs, pay very close attention to coil bind height and installed height. Published spring pressures for any spring are very dependent on these measurements. You may need a tool for measuring installed height (I use this one - it's made out of stainless steel instead of aluminum which I think makes it more accurate and reliable. Note that there are different models for different ranges of installed height.), and changing installed height may require either shims or machining the spring seat to lower it. 

Bear


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## Sick467 (Oct 29, 2019)

I'm in a similar situation, 400 with 670 heads and I cannot find an out-of-the-box stroker kit to work with pump gas (91 octane) and the 670 heads. Not That I am trying to run the current 400, but I would love to re-use the 670 heads. Partly to save the money, but more to just have the "670" numbers under the hood. Me and those heads have been around the block a time or two together...

Butler seems to have stroker kits that allows you to input your desired CR along with the other options and it kicks out a kit that could be 670 friendly (I think). It basically offers custom dish pistons that could work with the 670 heads work with pump gas. I have run some numbers and the 487-495 cu in kit seems to be an option, more so than the shorter stroked 467 kit. The custom-built piston kits are towards the bottom in the following link...



https://butlerperformance.com/c-1459542-engine-components-internal-rotating-assemblies-stroker-kits-400-blocks-406-495-cu-in-butler-custom-rotating-assemblies.html



I have not called them to make sure I am interpreting their website correctly. So long as the custom pistons can be dished enough...this may be an option. I'm certainly going to look into it when the time comes. I hope that the money thrown at the custom kit will be somewhat saved on not buying new heads.


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## Jared (Apr 19, 2013)

One thing you could do here is figure out how aggressive of a cam you would want to run in the 461 and see if it'll be tolerable in the 400. That should eliminate the risk of coil binding the valve springs. Personally, I wouldn't take a cam out of one engine and install it in another, but if you went with the same profile in both engines, or even one profile in either direction, it should work. Take a look at cam and lifter kits that include valve springs and see how much overlap there is where the same springs are used. 

6X heads may be the way to go. The right cc will work on both engines. Maybe dial in exactly what you want for CR on the 461 and just be running a bit lower on the 400.

I get the budget thing. I went through this a couple years ago with mine and know first hand that these builds get expensive really fast.


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## Baaad65 (Aug 29, 2019)

goat671 said:


> Yea I get that about building what I want but since it is apart I was wondering what I could do to get buy until I can afford to build what I want.
> I like the idea of getting a set of heads for the stroked build and use them now in the 400 with no other changes.
> Regarding the value springs would it be a problem to run the higher spring rates on the 400 stock cam I would not think so.


I tell you what I'll sell you my ported 7K3 heads built by Butler with screw in studs and 92cc chambers and then I'll have enough for one KRE head 😉


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## goat671 (Apr 13, 2019)

Baaad65 said:


> I tell you what I'll sell you my ported 7K3 heads built by Butler with screw in studs and 92cc chambers and then I'll have enough for one KRE head 😉


Ok how much?


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## geeteeohguy (Feb 2, 2008)

92 cc chambers on a 400 for the win, IMO. Go for it!!!


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## Baaad65 (Aug 29, 2019)

goat671 said:


> Ok how much?


Idk I'd have to see what a dressed 290 cfm KRE head costs 😉


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## goat671 (Apr 13, 2019)

Baaad65 said:


> Idk I'd have to see what a dressed 290 cfm KRE head costs 😉


let me know when you figure it out


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## PontiacJim (Dec 29, 2012)

Baaad65 said:


> I tell you what I'll sell you my ported 7K3 heads built by Butler with screw in studs and 92cc chambers and then I'll have enough for one KRE head 😉


Keep in mind that the 7K3 heads do not have all the exhaust bolt holes unless Butler added them or studs?


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## Baaad65 (Aug 29, 2019)

PontiacJim said:


> Keep in mind that the 7K3 heads do not have all the exhaust bolt holes unless Butler added them or studs?


Not to worry I have the brackets 👍


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## Baaad65 (Aug 29, 2019)

Ok I'm coming clean because I didn't think this would get serious, I can't tear my motor apart now and just slapping on the KRE's isn't going to net me much for the high cost, I confirmed that with Butler when I got the motor. If I get aluminum heads they're going on something much bigger and better than I have now. Sorry for ever misleading you or getting your hopes up.


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## Bopman (7 mo ago)

LATECH said:


> the 670 heads are 72 CC too tight for pump gas with a 400 or a stroker crank.
> Some body will likely want them so hang on to them.
> Get some aluminum heads with chambers around 80-82 CC . That will put the CR around 10 .5 ish on a 462 CI.
> 85 CC would be at 10.0 to 1 so that would give some wiggle room for octane /hot days/etc
> safe enough for aluminum heads as long as your cooling system is top notch and you have the right curve on the dizzy/timing (93 octane of course)


670's could be used with a dished piston....could they not ? Also....I used .125 dome piston with '75 model 6x on our 72 lemans runs on 87 Octane with out any issues ! Just some thoughts !


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## Bopman (7 mo ago)

BearGFR said:


> You're in a really good spot with it right now because you (presumably) haven't bought your stroker kit and pistons yet. 670 heads are closed chamber designs and generally need a little more than the usual 34-36 degrees of total advance at WOT to get the maximum performance out of them. They have relatively small chambers. Some reference pages on the 'net list them as nominal 72 cc's, others at 70 cc's, and that will apply only if you're positive they've never been surfaced/cut/milled. Even then, untouched from the factory, chamber volumes on heads have been known to vary some so it's always best if you cc them yourself to find out what your chamber volumes actually are - and that means all 8 of them.
> 
> 670's have been very popular for performance builds for years because even though they need more timing, they flow as good if not better than any other Pontiac D-port head.
> 
> ...


I used an online calculator to figure out what my conglomeration came out to.....😂😂 came to right at 9.2:1 👍


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## goat671 (Apr 13, 2019)

Baaad65 said:


> Ok I'm coming clean because I didn't think this would get serious, I can't tear my motor apart now and just slapping on the KRE's isn't going to net me much for the high cost, I confirmed that with Butler when I got the motor. If I get aluminum heads they're going on something much bigger and better than I have now. Sorry for ever misleading you or getting your hopes up.


I know you were not serious I was pulling your chain


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## armyadarkness (Dec 7, 2020)

goat671 said:


> Looking for some options on what I can do with my engine.
> 
> Background: I needed to pull the heads to determine the condition of the internals due to the engine not being turned over for a very long time.
> Future: I will at some point be replace/rebuild engine more than likely looking to get to a 461 stroker.
> ...


Im running a 67 400, with born-with 670 heads, a big cam, and 93 octane E10 fuel. My base timing is close to 18 and my total timing is almost 40 degrees. And I drive like a cat with its ass on fire.

My car is 100% street driven and I put at least 100 miles a week on it, often 200, and this weekend, 400.

Your geographic location can affect your ability to get my results, but it's an old-wives tale that 670's cant be used on pump gas/ E10


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## armyadarkness (Dec 7, 2020)

BearGFR said:


> 670 heads are closed chamber designs and generally need a little more than the usual 34-36 degrees of total advance at WOT to get the maximum performance out of them


Hence my almost 40


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## armyadarkness (Dec 7, 2020)

LATECH said:


> the 670 heads are 72 CC too tight for pump gas with a 400 or a stroker crank


But for the record, Ive been doing it since 93. However, I do always tell everyone that Im in a humid state at sea level.


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## armyadarkness (Dec 7, 2020)

goat671 said:


> Great info
> 
> My question now is can I get a set of heads now that I can use with the stock 400 that I could then reuse in the 461 stroker later.
> 
> ...


Although I dont know your location, Im recommending that 670s are awesome, but as bear said, they wouldnt be good for a stroker. However, most any other modern aluminum Pontiac head would work fine for both setups


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## armyadarkness (Dec 7, 2020)

geeteeohguy said:


> I blazed your exact trail for the past few decades with my '67 GTO with the original 400 and 670 heads. Even in the 80's, the 94 octane pure gas didn't do the trick.
> 670's are closed chamber and prone to detonation. I'm running flat top pistons, installed in the '80's when I overhauled it. Dished pistons were not available then.
> I next tried the #66 455 heads with 114 cc. This let me run on regular fuel no problem. The performance difference from the stock 10.75 to the now 7.25 was huge.
> The car ran ok, but guzzled gas and was a slug. I next installed a set of 1970 #15 heads from a 455. These were small valve 87 cc iron heads. I converted them to screw in studs and have ran them the last 12-15 years with an 068 cam. My car now will run on 91 pump gas and only detonate on days like today (105 degrees) pulling a grade.
> ...


Yes, I know that your experience with them is the exact opposite of mine, which I suspect is even more proof that geography matters.


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## armyadarkness (Dec 7, 2020)

goat671 said:


> Yea I get that about building what I want but since it is apart I was wondering what I could do to get buy until I can afford to build what I want.
> I like the idea of getting a set of heads for the stroked build and use them now in the 400 with no other changes.
> Regarding the value springs would it be a problem to run the higher spring rates on the 400 stock cam I would not think so.


BTW, my heads were updated with better springs and stainless valves, and my 400 is a roller motor


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## goat671 (Apr 13, 2019)

armyadarkness said:


> But for the record, Ive been doing it since 93. However, I do always tell everyone that Im in a humid state at sea level.


yea the 670s may work I am at 800 - 1000 ft elev so who knows. I may just put it back together for now and build the stroker with the other 400 block I have and the other set of 670 heads


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## goat671 (Apr 13, 2019)

armyadarkness said:


> Although I dont know your location, Im recommending that 670s are awesome, but as bear said, they wouldnt be good for a stroker. However, most any other modern aluminum Pontiac head would work fine for both setups


My location is in my profile I am in Minnesota. The 670s can be used in a stroker just need to use the correct cc reliefs in the pistons around 27 - 28 cc


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## armyadarkness (Dec 7, 2020)

My car has the original engine, heads, etc, and as bear mentioned, they flow great. Yes, there are drawbacks, but heck, there are draw backs to a Pontiac engine, when comparing it to an LS, so... only you can know your commitment to nostalgia and balance that against your performance needs. Im sure I could ditch my 670's and grab another 25 hp, but I don't need another 25 hp, and Im proud that my car is sporting a semi-rare, iconic Pontiac head.

Your feelings will vary.


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## geeteeohguy (Feb 2, 2008)

Despite being closed-chamber design, 670's are one of Pontiacs best heads. If I ever re-rebuild the 400 in my '67, I'm doing dished pistons and those 670's are going back on. I've run 670's and #12 Ram Air III heads on this engine before and after overhauling, and the 670's ran every bit as hard as the 12's. A good friend has the original 670's on his '67 with Tripower and gets his gas (100LL) at the airport. It will not run on 91 e-10, which is the highest octane we have at the pump.


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## PontiacJim (Dec 29, 2012)

Baaad65 said:


> Ok I'm coming clean because I didn't think this would get serious, I can't tear my motor apart now and just slapping on the KRE's isn't going to net me much for the high cost, I confirmed that with Butler when I got the motor. If I get aluminum heads they're going on something much bigger and better than I have now. Sorry for ever misleading you or getting your hopes up.


Damn skippy. (a Southern phrase)  Aluminum heads have a better CFM head flow out of the box as compared to a stock iron head. But, more CFM's can be disappointing on some engines as the lower RPM port velocity may be sluggish and the engine will also seem a little flat off the line and at lower RPM's until the mid-to-high RPM's start pulling.

Aluminum heads, or even a modified iron head ported to flow big numbers is not always ideal unless everything else is matched to the amount of port flow. Go bigger with a stroker engine, now you can use the extra CFM's the aluminum heads provide. Remember, the RA heads flowed fairly good and used a much more radical cam to take advantage of them, but gave up the low end drivability to take advantage of the mid-to-high RPM range, thus the close ratio transmissions and 3.90/4.33 mandatory rear end gearing.

Aluminum heads do allow for more compression without the worry of detonation. But the difference in higher compression may be small. They are also patterned after the RA IV so the intake ports are taller so a matching intake should be used, and the head bolts are different than non-RA heads, so these will have to be added.

There could also be concern between the differences of the metals - aluminum heads on cast iron block. The metals expand differently and could over time cause a head gasket failure UNLESS you go with an MLS type gasket which are layered to allow for slight engine block/head movement during expansion/contracting periods. The Cometic MLS head gaskets run about $100.00 plus each, so another expense. Not an issue with cast iron heads on cast iron blocks.

You might be better going with a cast iron head prepped by Butler or Nitemare Performance as *Jared* did unless more cubic inches are in the future or you plan to assemble a mid-to-high RPM "race" engine and matching rear end gearing.


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## armyadarkness (Dec 7, 2020)

PontiacJim said:


> Aluminum heads, or even a modified iron head ported to flow big numbers is not always ideal unless everything else is matched to the amount of port flow. Go bigger with a stroker engine, now you can use the extra CFM's the aluminum heads provide. Remember, the RA heads flowed fairly good and used a much more radical cam to take advantage of them, but gave up the low end drivability to take advantage of the mid-to-high RPM range, thus the close ratio transmissions and 3.90/4.33 mandatory rear end gearing.


This really sums up the entire Pontiac philosophy and recipe. It's amazing how drastically my car was transformed by the Tremecs ability to move my rpms to where the engine wanted them to be. An entire year of "blaming the engine" and throwing money at it, when all along, it was the trans/ gearing.

And since I went with the wide ratio, now Im wondering what difference Id notice with the close ratio.


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## geeteeohguy (Feb 2, 2008)

Close ratio gearboxes are best suited to a high winding small block and steep rear end gears. They tend to feel 'mushy' off the line with a regular rear gear due to the ratio of the first gear and following ratios, which are designed for high rpm HP and not a lot of low end torque. With a Pontiac that is driven on the street, a wide ratio is a much better choice.


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## armyadarkness (Dec 7, 2020)

geeteeohguy said:


> Close ratio gearboxes are best suited to a high winding small block and steep rear end gears. They tend to feel 'mushy' off the line with a regular rear gear due to the ratio of the first gear and following ratios, which are designed for high rpm HP and not a lot of low end torque. With a Pontiac that is driven on the street, a wide ratio is a much better choice.


GOOD! Because the wide ratio TKX's were about as rare as jewel encrusted dinosaur eggs, and it was no easy feat to get one! I jumped through many hoops and was one of the few who got one when Tremec FINALLY released them.


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## DustyOldGTO (Jun 26, 2019)

Random comment on close-ratio vs. wide ratio:
In the olden days, the close-ratio Muncie had a 2.20 low and the wide-ratio Muncie had a 2.54 low (or was it 2.56?!?).
TKX: close-ratio = 2.87 low, wide = 3.27 low.
The close-ratio TKX is "wider" than the wide-ratio Muncie.


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## geeteeohguy (Feb 2, 2008)

DustyOldGTO said:


> Random comment on close-ratio vs. wide ratio:
> In the olden days, the close-ratio Muncie had a 2.20 low and the wide-ratio Muncie had a 2.54 low (or was it 2.56?!?).
> TKX: close-ratio = 2.87 low, wide = 3.27 low.
> The close-ratio TKX is "wider" than the wide-ratio Muncie.


The '63 through '65 M-20 Muncies had a first gear of 2.56, the '66-up had a 2.52 first. The TKX close ratio does indeed have a steeper low gear, but the wide ratio would be better moving the car off the line and easier on the clutch with an A-body car. More mechanical advantage.


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