# A question about heads...



## HaloPlayer (Jun 22, 2013)

A local shop is advertising 2 sets of heads on Craigslist. Both sets are listed as rebuildable. Both are the same price.

The first are 1967 670's, the second are 1969 YS 62.

I have not seen them so lets assume both are bare and in need of rebuilding.

Since I am not doing a numbers matching restore, which set would be better for a medium performance build?


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## BearGFR (Aug 25, 2008)

The 62's. They have open chambers and don't need as much timing to make decent power.

Be careful though, both have relatively small chambers and on an otherwise "stock" 400 build will result in a compression ratio that's too high for pump gas.

Tell us more about what you're planning to do?

Bear


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## geeteeohguy (Feb 2, 2008)

X2. The 670's would work better if it was 1967 and you could buy 100 octane fuel for 30 cents a gallon. They need super high octane and a lot of timing, but they worked very well back then. Now, you need open chamber heads of about 85-90cc or dished pistons to run on today's poor fuels.


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## 68greengoat (Sep 15, 2005)

Yeah, both those heads are 72cc and wont like pump gas very well.........


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## HaloPlayer (Jun 22, 2013)

BearGFR said:


> The 62's. They have open chambers and don't need as much timing to make decent power.
> 
> Be careful though, both have relatively small chambers and on an otherwise "stock" 400 build will result in a compression ratio that's too high for pump gas.
> 
> ...


I'm not sure if you followed the other threads, but I have a '75 400 in need of a rebuild (557 block casting). Factory specs are either 170 or 185 hp; I have not pulled any more numbers off the block yet to see what it came out of. I know I can NOT do a high performance build on this block due to thin web castings but everything I read says you can go up to 400 hp.

So, my plans....

No stroker for this one; just a standard crank. 

A mild cam and a bigger exhaust (2 1/2" with x-pipe).

I was thinking these heads would help it breathe better but it appears the'll just raise compression. The current heads should have 101 cc chambers but still have big valves. Dished pistons would allow me to use the 62' but would there be any benefit? Save my money and just buy domed pistons to increase compression on the existing heads? There is 0.11" difference in size on the intake valve between my heads and the 62's. Will it make that much of a difference?

I've made no decision yet about an intake. Thoughts?

MSD distributor, electronic ignition. Anyone have opinions on mechanical advance vs vacuum advance?

Muncie 4 speed (m-20 or 21).

Dark blue paint, blue interior. 

Power steering, power brakes, a/c (factory a/c car, a necessary evil living in Florida).


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## geeteeohguy (Feb 2, 2008)

Domed pistons are a no-no. They tend to increase detonation and are poor in the quench area. If your current heads are 101cc, you can have them milled to about 90cc and you'll be right where you need to be. You'll need to do the math, but I think about an .060" cut will do it. The intake may need a shave to fit the heads, but this is all cost effective and will work just fine. I ended up spending $1400 for some 87cc iron heads to lower the compression on my '67 GTO. They work fine, but had I known the hidden costs of re-habbing old heads (they needed EVERYTHING), I would have just bought a pair of KRE or Edelbrock aluminum heads.


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## BearGFR (Aug 25, 2008)

As far as port flow, _in general_, D-ports are D-ports are D-ports. There's not a whole lot of difference between them as long as you go with the "performance" (i.e. 2.11 intake valve, 1.96 exhaust valve) heads.

For the level of power you're talking about, there's no reason to be afraid of the 557 block as long as it's sound now. Building a stroker making over 500 HP night be cause for concern, but not with what you're planning.

If we assume it needs a slight bore to clean it up, say +0.030, and also assume everything else is "nominal", then I'd still go with the 62's to get the bigger valves (yeah, it matters) and the screw-in rocker studs. Add a set of dished pistons with 12 to 13 cc's total dish volume and you'll have a 406 and be in the neighborhood of 9.3-9.5 to 1 static compression - right where you want to be for 93 octane.

Running a manual transmission frees you from having to worry about the effects of "too much cam" with an automatic and a stock converter. That leaves the power brakes as the main limiting factor on how rowdy you'll be able to get with the cam. I'd recommend not pushing it any lower than 15" idle vacuum, unless you're also willing to add either a vacuum assist pump or convert to hyrdoboost braking.

If you want to go a slightly different route, then go ahead and have the block "zero-decked" and run pistons with at least 16 cc's total dish volume. That'll still have you with the same compression ratio, but you get the added advantage of better quench characteristics in the chambers which both helps combustion efficiency and does a better job of resisting detonation.

101 cc's in the heads is way too much for a 400 and running domed pistons to fix that is no solution. Yeah, you can get compression up that way but what you gain in compression you'll turn right around and forfeit because the domes will destroy combustion efficiency and flame travel.

In either case, I'd run aftermarket forged rods even though you're not pushing "that much" power. They're relatively cheap insurance, especially when you consider that the rods tend to be the weak link in Pontiacs and by the time you pay to have a set of factory rods prepped and reconditioned you'll be very close to what a set of forged rods would cost anyway.

Run the factory intake but make sure you port match it to the heads and clean up the various bumps and rough spots in the runners. For what you're proposing, nothing will make as much power as the factory piece will.

I wouldn't fool with an MSD ignition if you don't already have one. A good HEI, or even the factory points unit will work just fine. There's a lot to be said for the realibility and "side of the road" serviceability of the points system and for what you're planning, even the most expensive MSD box isn't going to make any additional power.

Either route ought to get you a fun and reliable 400 build that will make respectable power.

Bear


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## HaloPlayer (Jun 22, 2013)

BearGFR said:


> If you want to go a slightly different route, then go ahead and have the block "zero-decked" and run pistons with at least 16 cc's total dish volume. That'll still have you with the same compression ratio, but you get the added advantage of better quench characteristics in the chambers which both helps combustion efficiency and does a better job of resisting detonation.
> 
> Run the factory intake but make sure you port match it to the heads and clean up the various bumps and rough spots in the runners. For what you're proposing, nothing will make as much power as the factory piece will.
> 
> ...


I've read enough about 400 engines the past couple of days to make my head swim (this forum and others). Keep in mind I have built a total of 2 engines in my entire life, and nothing I have 'thought out'.

For the above mentioned reasons it seems zero decking is the way to go.

Couldn't the same results be achieved by a taller piston / connecting rod? Does anyone offer such an item?

Seems to me if you shave the block, the heads will sit lower throwing off the alignment with the intake manifold. So then you have to custom fit the manifold to the newly lowered heads?

Or is the 0.030 to 0.040 shaved off just not enough to make a difference when lining up the intake?


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## geeteeohguy (Feb 2, 2008)

I've never had a deck shaved to zero (because I only recently learned about the benefits), but my understanding is that it's maybe a .010-.020" cut at the most. Not enough to alter your intake/pushrod fitment. You could have custom pistons made in any configuration, I would imagine.


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## BearGFR (Aug 25, 2008)

HaloPlayer said:


> I've read enough about 400 engines the past couple of days to make my head swim (this forum and others). Keep in mind I have built a total of 2 engines in my entire life, and nothing I have 'thought out'.
> 
> For the above mentioned reasons it seems zero decking is the way to go.
> 
> ...


"Most" Pontiacs have the pistons located 0.020 "down the hole" from the factory. You're correct, slightly longer rods or pistons with slightly relocated pins could also be used - in theory. However doing either one of those would put you in the realm of having to have them custom made and would be very expensive - much more so than just having the block decks shaved a little.

Having that piston crown "squish" really close to the head creates all sorts of turbulence in the chamber, and that turbulence is very beneficial for promoting combustion, keeping air/fuel nice and mixed, getting good flame travel, and the like. Another benefit is having the pistion top "covering" the sharp edge at the top of the cylinder. Those edges tend to create hot spots in the chamber and hot spots lead to detonation. Detonation-resistance is a good thing, and may even allow you to get away with slightly more compression than you'd otherwise be able to.

Bear


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## HaloPlayer (Jun 22, 2013)

BearGFR said:


> If you want to go a slightly different route, then go ahead and have the block "zero-decked" and run pistons with at least 16 cc's total dish volume. That'll still have you with the same compression ratio, but you get the added advantage of better quench characteristics in the chambers which both helps combustion efficiency and does a better job of resisting detonation.
> 
> Bear


Would one do this when the block is being 'cleaned up' or would you wait until the new pistons arrive then have them measured so the machine shop knows exactly how much to take off?


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## BearGFR (Aug 25, 2008)

I'd wait until you can measure. Zero-decking is a precision operation and you want it done correctly.

Bear


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## HaloPlayer (Jun 22, 2013)

Well, the 62's have been at the machine shop since Tuesday. I'll go pick them up next week. I think I've beat the heads question to death, so now a new topic.......


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