# Engine and heads?



## bobthewelder (Jun 26, 2010)

My engine seems to be a 1973/4 engine. The heads are 11's, which are 1970? It has a 2 barrel on it. I read somewhere that Pontiac kept the 400 short block the same and used different heads to achieve different compression ratios. Is this true? If so, could I find a better set of heads, intake, carb and cam and have a good strong engine?


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## jetstang (Nov 5, 2008)

Yes.
A set of later 6X-4 heads will wake the car up, then an aluminum intake, cam and headers and you would be good to go. I would think a 73 engine is a smog engine, so it may have dished pistons in it. The early high compression heads will give you compression, but they would have to be 67 or later because of the valve relief location. But, early heads didn't have hardened seats for unleaded gas, so that would be extra money to get them installed, that is where the 6X heads would have an advantage.


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## 68greengoat (Sep 15, 2005)

Heads - 16, 62, 12 ,13. Basically 72cc heads. Q-jet/Edelbrock 4barrel, 650/750cfm...


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## jetstang (Nov 5, 2008)

68greengoat said:


> Heads - 16, 62, 12 ,13. Basically 72cc heads. Q-jet/Edelbrock 4barrel, 650/750cfm...


72CC, cool stuff, I think the 6X-4s are 94 CC. Any of the heads you listed have hardened seats? 72s and flattops will give 11:1 or what?


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## Thumpin455 (Feb 17, 2010)

I have yet to tear down a Pontiac engine from any year that had factory dished pistons, they made the chambers bigger rather than dishing the pistons. The 11 head is a decent head despite the small valves. There are no 72cc heads with hardened seats, and unless you are road racing or towing with it you wont have a problem with them.

A 455 with 72cc heads will be over 11:1 but a 400 is a bit lower, it depends on the head gasket, valve reliefs in the piston, overbore, and actual chamber size, but it is still too high for pump gas unless the pistons are down the bore a good distance or some other thing makes the chamber larger. The 400 with .040 TRW pistons and zero deck was 10.58:1 with the 670 heads I had on it. It had inaudible knock and flattened the upper rod bearings. If you are a higher altitude in cooler temps you can get by with more.

6x is a good head, but the 11 isnt far off from it, the compression is about the same. A set of 96 or 7K3 will have a slightly smaller chamber, big valves and screw in studs. They are 71/72 heads and are kinda hard to find, and the 7K3 has no end exhaust manifold bolts so headers will leak unless you fix that. Some can be drilled, others simply dont have metal in that area.

For the most part D ports all flow about the same, the big differences is in the chamber volumes and if they have screw in studs or not. All the 4 barrel heads had screw in studs, some of the other heads did, some didnt.


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## 68greengoat (Sep 15, 2005)

jetstang said:


> 72CC, cool stuff, I think the 6X-4s are 94 CC. Any of the heads you listed have hardened seats? 72s and flattops will give 11:1 or what?


Just because they didn't come from the factory with hardened seats doesn't mean they haven't been converted, or, that you can't have them converted.... A friend of mine runs '68 #16 heads on a 400 while using 91 octane.. Been doing it for years..... Maybe we're in a good location and can get away with 72's(at least he can, I have a 455 which wouldn't work) better than other locations..


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## jetstang (Nov 5, 2008)

68greengoat said:


> Just because they didn't come from the factory with hardened seats doesn't mean they haven't been converted, or, that you can't have them converted.... A friend of mine runs '68 #16 heads on a 400 while using 91 octane.. Been doing it for years..... Maybe we're in a good location and can get away with 72's(at least he can, I have a 455 which wouldn't work) better than other locations..


I had hardened seats put in my 11 heads, they charged $120 for the set. It's just excess expense when building heads. I talked to a guy with a machine shop and he says for a limited use car you don't have to install hardened seats, but a car that is getting road tripped and used should have hardened seats installed. Lead additive is about $10 a tank, so don't want to have to use that all the time at 10 MPG.


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## bobthewelder (Jun 26, 2010)

I see on charts that a 400 with 11 heads yields 8.6cr, isn't that kind of low for a performance engine? I know with an AL head you can run more cr with 91 octain, but can't you run an iron head around 9.5+- without detonation or ping? I'm a newbie to Pontiac, been a Mopar man for over 20 years, but I love the GTO's and had to have one. Can I build a healthy combo with this base engine assuming all is well inside? Add a good cam matched to the Muncie and 4.11's with a streetable dual plane intake and good carb? I don't want a pooch, I want something that wakes up and is maybe capable of 12's on the occasional 1/4 mile strip pass. Am I dreaming here? Advice is very much welcomed. This will be a long (4-6 year resto) but I want to play even while it's still ugly, so the drivetrain planning is paramount here.


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## jetstang (Nov 5, 2008)

Yes Bob, the 11 heads are not performance oriented, large CC, small valve. My motor is number matching 350, and low perf, but cammed to sound good. Just a nice cruiser that won't overheat and run AC. Dropped the heads off at the machine shop for a light redo and hardened seats and ended up spending $400 to get them redone! I was pissed, as they didn't call with a quote. But, the motor is a good cruiser motor, so oh well.


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## bigdogs (Jul 7, 2010)

Hi Guys. Im looking for some big chamber heads (66, 96, 7M5, 4X (1H), or 455 16's for a stroker project. I have a set of 13's and 62's Ill sell or trade. I also have a low mileage 
LS2 wit the 6 speed auto, harness, and gas pedal. Thanks Kevin


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## bobthewelder (Jun 26, 2010)

I have a set of 11's I'd trade you.


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## TDInewguy (Jul 29, 2010)

I have a engine I took out of my 66 GTO - the engine is a YA code with a D296 date code and the heads are a 96 code - with a D181 date code.

It's all put together and runs, and I've got another thread on it, I'm considering selling... any idea what it's worth?


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## Eric Animal (Oct 28, 2007)

I am not that up on the mix and match stuff....if you are not going to make over 400 HP consider RAM AIR style manifolds, they flow well and will solve a lot of "header issues". My humble $.02 Eric


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