# Rookie question: What heads would you recommend?



## tk421 (Sep 20, 2011)

Hey guys, newly registered to the site but have been lurking/reading for some time. 

I have a 400 block marked "531293 YX", "481988", and "F231" that Id like to put in my 67 Lemans. From what ive read, this should be a 1971 block that was originally a 265hp car with a 2bbl. 

The heads are marked "98", which corresponds to the 71 block. The valve sizes are 1.96/1.66 and they are 98cc. 

Ive got it torn down and it was pretty rough on the inside. Dropping it off a the engine shop this week, having it cleaned up, done .030 over and reassembled. the owner asked if i was going to have the heads reworked but i told him i wasnt sure. 

Should I have the factory heads worked or is there a better option to consider? The car will be just a summer cruiser, no racing or drags or anything. 

Thanks!


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## Instg8ter (Sep 28, 2010)

Welcome to the reservation....you will want a set of heads that will get your compression down to around 9:1 for pump gas to avoid detonation, also those are the small valve heads with push in rocker studs, you might want to find a set of big valve heads with screw in studs. not up on my head codes for the 400 i know the 6x-8s are a favorite maybe someone will jump in and tell you what heads would work best on the 400. BTW that HP was underrated from the factory so don't go by it, a nice streetable cam should get you in the 350HP range with some big valve heads and around 400 ft. lbs. torque. And make sure your engine builder is familiar with Pontiac motors.


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## NEEDLEZ (Oct 21, 2009)

I am in the same boat as you and I am in the process of gathering parts for a complete rebuild. I am diligently looking for a pair of 6x heads and from all of the resources I have gathered up on the subject those are the best bet in post 1970 Pontiac 400s. I am new to the hotrodding scene but am learning tons everyday. I have read countless articles over at Pontiac High Performance and I would search "6x heads" and read what makes them breath so much better in comparison to what you currently have.


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## freethinker (Nov 14, 2009)

tk421 said:


> Hey guys, newly registered to the site but have been lurking/reading for some time.
> 
> I have a 400 block marked "531293 YX", "481988", and "F231" that Id like to put in my 67 Lemans. From what ive read, this should be a 1971 block that was originally a 265hp car with a 2bbl.
> 
> ...


its really a waste of money to repair those heads. i would buy a good set of large valve 68-70 gto heads and since you are boring lower your compression with dished pistons.


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## Instg8ter (Sep 28, 2010)

Its not necessarily the breathing as pontiac made a bunch of large valve heads, and there are actually three forms of the 6X heads. What is unique about Pontiacs from 66' on is that all the blocks are the same physical dimensions, and bolt patterns hence no Big Block/Small Block in the Pontiac family. What this means is that all the heads from any motor will interchange with any other (with very few exceptions 301's). So by using different heads (different chamber volume) we can taylor the compression ratio to the desired 9:1 for pump gas. The 6-x 8 heads have the correct volume to put a stock 455 right at that number with no machining. so a good set of cores and a three angle valve job and new seats and your in business running on 89-91 without the dreaded spark knock (detonation) that kills these motors prematurely with the camel swill they are passing off as gasoline these days.


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## BearGFR (Aug 25, 2008)

Welcome tk,
Like lots of things a lot depends on what your goals are and how deep your pockets are  and/or how much of the work and time you can put into it yourself.

Like Mr. PBody would say, there are lots of ways to skin this cat. If you're after power, then a set of the larger valve heads would be good,a nice pair of ported aftermarket aluminum heads would be "the best". You also of course want to be mindful of compression if you intend to run pump gas. With iron heads, "generally" you want to treat 9.5:1 as an upper limit. I say generally because other things have an influence, notably the cam - because it controls when the intake valve closes and compression can't begin until that valve is shut. That said though, .2 to .5 worth of compression ratio is only going to make a difference of less than 15 peak HP so pushing the limit generally isn't worth the risk on a street motor. You can usually get away with a little more compression with aluminum heads because they don't "hold" as much heat as cast iron does.

Also, it's best to cc those chambers yourself. Pontiac head chambers can and do vary quite a bit from factory published volumes, and just a few cc's can make a significant difference. The heads you have can be modified to have larger valves, screw in rocker studs, etc. but usually it's more expensive to go that route than it is to just swap heads.

If those heads really are 98 cc's, then if I assume everything else about the motor is close to "factory nominal" with flat top pistons that'll put your static compression ratio at 8.059:1 That's too low for good power. Even "zero decking" the block at going with a thinner (.030) compressed head gasket would only raise that to 8.513:1 - still low and very safe for even the crappiest regular gas. Take that same block and put a stroker kit in it, turning it into a 461 (4.155 bore, 4.250 stroke), zero deck it, run 'normal' head gaskets and you're at 9.334:1 --- right in the sweet spot for a strong street motor. Point is... you've got options. Tell us in a little more detail what you want to do with the car, about the rest of the drive train (transmission and rear), and how rowdy you want to get with it?

Bear


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## tk421 (Sep 20, 2011)

Hey guys, thanks for the replies and all the info. 

Basically, im just looking to make the car a nice cruiser for the summertime. It will be a street car only, no racing or trips to the strip. I pulled the motor (chevy 350) and sent the body off to get painted and in the meantime i picked up this 400 block. Eventually the whole car will be restored (so to speak) as far as suspension, rear end, interior, disc brake conversion, etc. 

Id like to say that my goal is 350-400 hp, but thats a number more than anything. Ive also got a muncie 4 speed that came with it that i intend to re-use. Rear end is undecided at this point, the factory non-posi is still in the car. 

Id definitely like to have a nice lope to the engine, but not too crazy, i still want it to be streetable/driveable. 

So basically i should be looking for a set of heads that have larger valves, like 2.11/1.77, with a CC somewhere in the mid to upper 80s?


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## freethinker (Nov 14, 2009)

tk421 said:


> Hey guys, thanks for the replies and all the info.
> 
> Basically, im just looking to make the car a nice cruiser for the summertime. It will be a street car only, no racing or trips to the strip. I pulled the motor (chevy 350) and sent the body off to get painted and in the meantime i picked up this 400 block. Eventually the whole car will be restored (so to speak) as far as suspension, rear end, interior, disc brake conversion, etc.
> 
> ...


since you are boring .030 anyhow just use dished pistons to lower your compression then you can use any of the plentiful 68-70 gto heads and your compression will be good for pump gas.
i would then suggest a comp cams xe 274 for a nice lopy idle.


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## tk421 (Sep 20, 2011)

freethinker said:


> since you are boring .030 anyhow just use dished pistons to lower your compression then you can use any of the plentiful 68-70 gto heads and your compression will be good for pump gas.
> i would then suggest a comp cams xe 274 for a nice lopy idle.


Thanks! Any recs for a piston to use?


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## freethinker (Nov 14, 2009)

tk421 said:


> Thanks! Any recs for a piston to use?


look for a guy named mrpbody on this site. he has a pontiac engine shop and he has a ready made kit with the right pistons.
http://www.centralvirginiamachine.com/facilities.aspx


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## geeteeohguy (Feb 2, 2008)

tk, follow Bears advice here. You may want to contact Mr. P-body, as well. For what you say you want, I think an XE274 is too much cam, especially if you have an auto trans and highway gears. An XE 262 would be my choice. Small valve heads aren't necessarily a bad thing on a street driven engine. They made them by the millions back in the day, for a reason. They worked very well on heavy, lazy geared, street driven cars. I'm running small valve heads on my '67 GTO (87cc chambers/9:1) and it produces a ton of torque, has great low end throttle response, and gives great fuel mileage. I did upgrade to screw in studs, though. You could run stock spec pistons (get the good forged ones) that are cheaper than customs, and mill a little off your heads to get about an 82-90cc chamber, and have a responsive, 8.5-9:1 engine "on the cheap". Do as much research as you can. The more you know, the more money and aggravation you will save


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## jetstang (Nov 5, 2008)

I agree with GTO guy.
I swapped a set of ported peanut port BBC heads for a worked set of BBC heads, LS-5, big valves. Heads don't match my combo and lost a lot of low end torque. Drag strip proved it, same ET, less torque.


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## BearGFR (Aug 25, 2008)

Ok that helps. I hear 4-speed, street cruiser (limited if any highway driving), some "attitude" but no serious racing, rear gear ratio/type still "to be determined".

The combo of the 4-speed and still having the rear gear ratio flexible means you don't have to worry about converter choice and could tolerate a little "more" in the cam departement. Still you can't go too rowdy if you want to retain the ability to run vacuum-assisted power brakes and/or be able to operate things like a factory a/c system.

If you're planning to keep the heads you have an just have them "worked" you've got lots of flexibility there too. They're already too "big" chamber-wise for the motor so they'd need to be milled to address that. However, by the time you took those heads and had them milled, larger valves installed, bigger rocker studs, pressure tested, etc. it's very possible you'd spend more money than it would cost you to find a different set that wouldn't need so much work.

Starting with this as a base line:
400 +.030 (4.150 bore)
3.750 stroke
"zero decked"
.042 compressed head gasket (factory stock)
4.160 gasket bore size
flat top pistons (6 cc's volume in the valve relief pockets)
98 cc heads

---- that gives you a total clearance volume of 113.36 cc's
Take that with the swept volume of the +.030 400 (831.55 cc's) and you get a static compression ratio of 8.336:1

To get to 9.3:1 you need to reduce that clearance volume (113.36) by about 13 cc's (per cylinder) to get you close to 100 total. How you do it matters. The best place is to take it "out" of the chambers via milling. You could also run "pop up" pistons and/or thinner head gaskets, but with those you have to worry about piston to head, piston to valve clearances and also changing the shape at the top of the chamber is going to have an effect on flame propagation (probably make it worse) which will affect combustion efficiency.

If you can find them, a pair of 6x-4's should already have the big valves, screw in studs --- and when combined with .030 compressed gaskets would put you at 9.02:1 with excellent quench distance - assuming they measure out to the factory spec of 91 cc's.

XE 274 is probably too much from the standpoint of idle vacuum for brakes and stuff, but would otherwise be ok with the 4-speed and low to mid 3-series gears, drivability wise. It'd sound pretty mean 

Bear


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## tk421 (Sep 20, 2011)

Found a set of 6x-4s with numbers K255 and L015. The valve sized are 2.11/1.66 and are 93 CCs and they have screw in studs. They will need to be redone, but i can get them for around $250. 

If the heads were milled slightly bringing the CCs down to around 87-88, would these be a good option?


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## BearGFR (Aug 25, 2008)

Those heads do tend to be good choices for street-friendly compression on pump gas. Have they been actually measured at 93 cc's? Even if they have, I strongly encourage you to measure them yourself before you "git to cuttin'" on them any.

Plugging all the following into my handy dandy spreadsheet:

4.150 bore, 3.750 stroke, 87 cc chambers, .030 compressed gasket, 4.160 gasket bore size, zero deck, 6cc's in the piston valve reliefs.

That puts you at 9.342:1 static compression and .030 quench distance, which is a great spot to be for a street motor on pump gas.
Note this though: those are .030 compressed thickness gaskets, factory normal is .042", so those are probably going to be custom Cometics. I also assumed you'll zero deck the block so that the piston tops are dead even with the tops of the cylinder bores. Stock Pontiacs are "usually" around .020 down. A good tight but safe quench (.030) is your friend. It promotes turbulence in the chamber which helps with combustion efficiency because it keeps everything nice and mixed, it also helps prevent hot spots in the chamber by 'covering' the sharp edge of the top of the bore --- and that helps protect you from detonation. All good stuff. By comparison, if you were to not zero deck it (assume 0.020 down) and also use factory spec .042 gaskets, your resulting static compression ratio (leaving everything else the same) would be 8.791:1 and your quench distance would be doubled.

Bear


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## tk421 (Sep 20, 2011)

It will prob be difficult, if not impossible, for me to CC them prior to purchasing (they are about an hour away). Are they still a good buy as long as i CC them after purchase to ensure the proper amount of milling is done?


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## BearGFR (Aug 25, 2008)

It's been so long since I was buying used engine parts such as heads that I've got no idea what anything is worth :confused
If you're happy with the price, and if they're not damaged in any way, then it sounds like a good plan to me. A great plan if you've got the resources and time to send them off to Dave 

Yes - the key thing is making certain you know the chamber volumes before you put them into use on your engine. :cheers

Bear


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## likethat (Oct 5, 2007)

I sold a set of 6x-4's for 50 bucks 2 years ago. They needed redone but were still stock. I am sure I sold them a bit to cheap.


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