# Can I or not?



## Boomstick (Sep 13, 2021)

I just picked up a 400 with 6x-8 heads. I only got the motor to put the heads on the 350 ho in my 69 lemans since someone put 1971 #94's on it. The guy I bought the motor from said I can not put those heads on the 350. Is this true? I don't see what would cause an issue.


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## BearGFR (Aug 25, 2008)

It can be done, but you need to be careful with valve clearance. You might have to chamfer the sides of the cylinder bores, both so that the valves don't hit them AND the votes don't "shroud" them. By that I mean that it's possible for the valves to clear but still be so close to the cylinder walls that it has a significant impact on flow. 

Bear


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## PontiacJim (Dec 29, 2012)

Boomstick said:


> I just picked up a 400 with 6x-8 heads. I only got the motor to put the heads on the 350 ho in my 69 lemans since someone put 1971 #94's on it. The guy I bought the motor from said I can not put those heads on the 350. Is this true? I don't see what would cause an issue.


The '69 HO 350 block will have the needed chamfers at the top of the block for the valve clearances.

1970 and up 350's had chamfers, but it can also be hit or miss.

The 6X-8 heads will have a 100CC combustion chamber. The factory #48 heads were 68CC's and the 1971 #94 heads are 89CC. You are going to kill engine compression and lose a bunch of power if that is your goal? You will have a 7:1 compression ratio - should be able to pee in the gas tank and it will run. Don't even think of adding the HO cam and Q-jet.

Your 350 should look like this when you pull the heads. This is a 1970 350CI:


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## Boomstick (Sep 13, 2021)

Pontiac Jim, Wallace's website says the 94's are 96cc, so I didn't think the 4cc increase would make that much of a difference but if you're right, I'd be better off just dropping the 94's on the 400... I was just now wondering if the 2.11/1.66 increase from the 1.96/1.66 would even be worth the hassle of switching heads unless the 6x flow better but 7:1 compression on my 350 is out of the question...

My thought was put the 6x heads on and a 67 cam in and my flowtech headers (I don't know what cam is in the 350 now) combined with the rpm intake already on the car and 750 Holley, I'd have a fairly impressive street combo. It's already running a 3:23 rear with a th400 and scoots pretty well even with the 600 summit carb (my 750 needs rebuild). Now I'm rethinking this whole idea...

Dang I wish someone didn't change the heads...


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## BLK69JUDGE (Jun 10, 2010)

nice heavy duty bench


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## pontrc (Mar 18, 2020)

I would keep the 400 for a future project. But at least work on that carb. Factory Quadrajet on some are 800+ CFM


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## PontiacJim (Dec 29, 2012)

Boomstick said:


> Pontiac Jim, Wallace's website says the 94's are 96cc, so I didn't think the 4cc increase would make that much of a difference but if you're right, I'd be better off just dropping the 94's on the 400... I was just now wondering if the 2.11/1.66 increase from the 1.96/1.66 would even be worth the hassle of switching heads unless the 6x flow better but 7:1 compression on my 350 is out of the question...
> 
> My thought was put the 6x heads on and a 67 cam in and my flowtech headers (I don't know what cam is in the 350 now) combined with the rpm intake already on the car and 750 Holley, I'd have a fairly impressive street combo. It's already running a 3:23 rear with a th400 and scoots pretty well even with the 600 summit carb (my 750 needs rebuild). Now I'm rethinking this whole idea...
> 
> Dang I wish someone didn't change the heads...


You are correct, 96 CC's. Not sure where I got 89CC's, I think form the line above for 455's which was 87CC's..

With the #94/96CC head, your compression is 7.2. Still bad.

Using the Wallace Compression Calculator, you will need a combustion chamber of 72CC's to get around 9.0 compression. There is a 1969 350 HO build that used 66 CC chamber #48 heads, zero decked the block (factory is typically .020") and got 9.85 compression. The 1969 350 HO is rated for 10.5 compression - which is probably an NHRA Super Stock prepped block using all the legal tricks to do so.

So 72 CC's are basically a standard head of the 1960's and you can look at the Wallace chart to see the head numbers. The small valves will not hurt the 350 as the larger valve with shrouding won't flow as best as they could. I would install 2.02" valves as a compromise.

With the lower compression, you can still make a snappy engine using a 110 LSA which will build cylinder pressure.

The RPM will be too much intake. The Performer would be a better choice if you have to have aluminum, but the best choice will be the factory cast iron/Q-jet combo.

Of course the 400 will out perform the 350, but the 350 can still be a sporty rival with the right parts.


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## Boomstick (Sep 13, 2021)

Thanks for the info!

I wish I could get two a websites that say the same thing.

https://www.pattersoncoachworks.com/pontiac-cylinder-head-id-numbers

Patterson says the #94's are 90cc with screw in studs, Wallace says they are 96cc and no info on the studs.



Pontiac V8 Cylinder Heads



I guess I have to pull the valve cover and look at the studs myself...

I might just stick with the 94's and store the 400 until I blow up the 350... Besides, I just figured out is not the HO motor, it's an xs code and according to Wallace it's 265hp and what I assume is a 2 barrel motor.

I wish I knew what cam was in it...


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## PontiacJim (Dec 29, 2012)

Boomstick said:


> Thanks for the info!
> 
> I wish I could get two a websites that say the same thing.
> 
> ...


 "XS" coded 350/265HP is for 1969 and a 2 Bbl. Correct heads should be #47 which puts the advertised compression at 9.2. The stock cam is the factory "254" or "U" cam - Duration 269/277, Lift .374"/.406"

My '68 Lemans came with the same 350/265HP engine and 3-speed manual trans on the floor. Did a fine job, but was tired.

The #94 heads are 350CI heads and the _*advertised*_ compression is 8.0. But, as Pontiac does, the advertised compression and actual compression can be different. If I look at the1971 #96 400CI heads with 96CC for 1971, the blueprinted NHRA chamber volume is 85.8 CC's. This is achieved by milling the heads. The calculated compression with 85.8 CC's is 8.0 - just as advertised. With 96 CC's, 7.3 compression - what you actually have off the showroom floor.


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## Boomstick (Sep 13, 2021)

So I have a line on a set of #15 heads, but I see they are pressed in studs. Do you know if the 94's are pressed or screw in?


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## PontiacJim (Dec 29, 2012)

Boomstick said:


> So I have a line on a set of #15 heads, but I see they are pressed in studs. Do you know if the 94's are pressed or screw in?


They are press-in studs. Typically the small valve heads are press-in. You can have screw-in studs added, but that adds cost to the head work. This is why most will locate a set of heads with the screw-in studs. 1974 and up, Pontiac began using screw-in studs on *most* all heads, but there are exceptions of course. With screw-in studs, you have to be careful when using a cam with larger lifts that require heavier valve spring pressures - they can pull up.


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## Boomstick (Sep 13, 2021)

i found a set of 46's for sale i might be picking up... have them ported and screw in studs put in...


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