Pontiac 400 heads

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Re: Pontiac 400 heads

Post by steve cowan »

ClassAct wrote: Fri Jul 23, 2021 7:38 am
Geoff2 wrote: Fri Jul 23, 2021 4:50 am It is about the application. You might run 16:1 CR on a race engine, but not on a street engine.....
Very true. But that low port Pontiac head is no different than any other low port wedge head. It will respond to a 45 degree seat. As I posted long ago, I can’t think of an application where a 30 degree seat is better than a 45. Not one.
i have never done a set of those heads but just curious
the chamber looks pretty horrible,what top cut would you use
on the valve job?i suspect it would have to be a shallow angle like a 30 deg top as an
example,i am all for a steeper seat angle but i think top cut to chamber transition is key.
again just curious thats all :)
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Re: Pontiac 400 heads

Post by PRH »

30* intake seats in a 400 Pontiac.

Maybe not the “best”, but certainly not the kiss of death either.
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Re: Pontiac 400 heads

Post by GARY C »

steve cowan wrote: Fri Jul 23, 2021 12:54 pm
ClassAct wrote: Fri Jul 23, 2021 7:38 am
Geoff2 wrote: Fri Jul 23, 2021 4:50 am It is about the application. You might run 16:1 CR on a race engine, but not on a street engine.....
Very true. But that low port Pontiac head is no different than any other low port wedge head. It will respond to a 45 degree seat. As I posted long ago, I can’t think of an application where a 30 degree seat is better than a 45. Not one.
i have never done a set of those heads but just curious
the chamber looks pretty horrible,what top cut would you use
on the valve job?i suspect it would have to be a shallow angle like a 30 deg top as an
example,i am all for a steeper seat angle but i think top cut to chamber transition is key.
again just curious thats all :)
Considering the flat chamber roof, a cam with no lift and trying to feed 400+ inches with a head less desirable than a SBC DBL Hump head my guess it that GM didn't just run a 2.110 valve on a 30 degree seat for the hell of it. :) With modern day valve train and higher lift cams I don't know that a 30 would be the best option, although I think the 35 degree seat in this test did provide the best average over the rpm of the pull if I remember right. https://www.motortrend.com/how-to/1203p ... valve-job/

I don't recall a top cut on my 6x heads, I wish i had taken a photo but most people that I know who ran 30 degree seats did not run a top cut.
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Re: Pontiac 400 heads

Post by steve cowan »

Some guys are saying 30 degree seat ,others are saying 45 on these heads,if we are talking about the early cast iron head
If you use a 45 deg seat can you put a 30 degree top cut in ?
If you use a 30 deg seat cut and no top cut like Gary is saying then I assume a 45 seat with a 30 tc is feasible but if you sink the valve it might be difficult to shape the SSR to the seat or (bottom cuts)if any.
Again I am just trying to visualise the valve job,I found only 1 picture of a early V8 pontiac head.
I am not saying one is better than the other just wondering how people would do a valve job on that type head.
GARY - I do have some 23 deg sbc heads with 50deg seat and they run :D
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Re: Pontiac 400 heads

Post by GARY C »

steve cowan wrote: Sat Jul 24, 2021 1:56 am Some guys are saying 30 degree seat ,others are saying 45 on these heads,if we are talking about the early cast iron head
If you use a 45 deg seat can you put a 30 degree top cut in ?
If you use a 30 deg seat cut and no top cut like Gary is saying then I assume a 45 seat with a 30 tc is feasible but if you sink the valve it might be difficult to shape the SSR to the seat or (bottom cuts)if any.
Again I am just trying to visualise the valve job,I found only 1 picture of a early V8 pontiac head.
I am not saying one is better than the other just wondering how people would do a valve job on that type head.
GARY - I do have some 23 deg sbc heads with 50deg seat and they run :D
My guess is most shops would redo them with a 45/30 and is probably better with modern day faster higher lift cams, mine already had work done to them and port work looked good so I didn't pay much attention just checked one on the bench so I would know what I wanted for a cam.

A 50 or 52 with modern cams and chamber shapes seems to work pretty good.
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Re: Pontiac 400 heads

Post by Geoff2 »

'Pontiacs have machined, very flat combustion chambers. Plus the heads that had the 30* seat used nail head valves. The two work together. The Pontiac Ram Air engines had more valve lift, & went to the 45* seat AND tulip shaped valves. Pontiac knew what they were doing.
I am surprised David Vizard's very positive comments on 30* seats has not been mentioned....
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Re: Pontiac 400 heads

Post by GARY C »

Geoff2 wrote: Sat Jul 24, 2021 4:49 am 'Pontiacs have machined, very flat combustion chambers. Plus the heads that had the 30* seat used nail head valves. The two work together. The Pontiac Ram Air engines had more valve lift, & went to the 45* seat AND tulip shaped valves. Pontiac knew what they were doing.
I am surprised David Vizard's very positive comments on 30* seats has not been mentioned....
Thats not allowed here... :)
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Re: Pontiac 400 heads

Post by mag2555 »

All Pontiac ram air production heads had 30 degree seats, I know as I own them, or have owned them all.
There are,
The 1968 RA1 D port exh cast number 31

The late 1968 round port exh cast number 96.

The 1969 and 70 round port exh cast number 722 and 614 respectively.
Even the round port exh 1971 and 72 455 cid HO heads had 30 degree seats.
The only factory production performance head that had 45 degree intake seats was the 1973 and 74 casting number 16 ( car of the year motor in the F body ) 455 SD motor.

Certain non performance 2 BBL motors over the years with 1.96” intake valve came with both 30 and 45 degree seats, and the reasoning for this at this point in time will likely never be known !

With the Pontiac flat chamber floor and the 30 degree seat if you add a 15 degree top cut, you will pick up low lift flow, but that will cut into higher lift flow numbers above .480” lift, and such a change will greatly cut into potential high lift numbers the more you port the heads!

On one D port Head I was porting early on in my grinding days I had it flowing 280 cfm with the 30 degree seat , I added a top cut of 15 to get closer to the much flaunted full radius seat form and I lost 15 cfm from that peak flow number .

Of course back then I did not realize what was taking place as I heard the sound from the intake port change.
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Re: Pontiac 400 heads

Post by ClassAct »

steve cowan wrote: Fri Jul 23, 2021 12:54 pm
ClassAct wrote: Fri Jul 23, 2021 7:38 am
Geoff2 wrote: Fri Jul 23, 2021 4:50 am It is about the application. You might run 16:1 CR on a race engine, but not on a street engine.....
Very true. But that low port Pontiac head is no different than any other low port wedge head. It will respond to a 45 degree seat. As I posted long ago, I can’t think of an application where a 30 degree seat is better than a 45. Not one.
i have never done a set of those heads but just curious
the chamber looks pretty horrible,what top cut would you use
on the valve job?i suspect it would have to be a shallow angle like a 30 deg top as an
example,i am all for a steeper seat angle but i think top cut to chamber transition is key.
again just curious thats all :)

I had a cutter made and I don’t recall the top cut but it’s not a 30.
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Re: Pontiac 400 heads

Post by cpmotors »

I've never done a 30° seat on any Pontiac head, nor did I worry about flow testing them.
The worst example I can offer is this 404ci 670 headed example. All stock intake, RA exhaust manifolds with crappy head pipes, and a little 225°@ .050", .525" HR cam.
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Re: Pontiac 400 heads

Post by Walter R. Malik »

Yesterday I looked-up the last pair of Pontiac heads I used on a customer engine with a high performance valve job; which worked very well with .650" valve lift.
They were casting number 216 from a 1968 - 428 engine; 2.11" intake & 1.77" exhaust. Valves were S.I. stainless replacements.
The intake valves got sunk with a 45 degree seat and 2 topping angles 36 degree and 25 degree; 56 degree bottoming.
They had mild bowl blending on the short side.
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Re: Pontiac 400 heads

Post by 65mustang393 »

mag2555 wrote: Sat Jul 24, 2021 7:40 am All Pontiac ram air production heads had 30 degree seats, I know as I own them, or have owned them all.
There are,
The 1968 RA1 D port exh cast number 31

The late 1968 round port exh cast number 96.

The 1969 and 70 round port exh cast number 722 and 614 respectively.
Even the round port exh 1971 and 72 455 cid HO heads had 30 degree seats.
The only factory production performance head that had 45 degree intake seats was the 1973 and 74 casting number 16 ( car of the year motor in the F body ) 455 SD motor.

Certain non performance 2 BBL motors over the years with 1.96” intake valve came with both 30 and 45 degree seats, and the reasoning for this at this point in time will likely never be known !

With the Pontiac flat chamber floor and the 30 degree seat if you add a 15 degree top cut, you will pick up low lift flow, but that will cut into higher lift flow numbers above .480” lift, and such a change will greatly cut into potential high lift numbers the more you port the heads!

On one D port Head I was porting early on in my grinding days I had it flowing 280 cfm with the 30 degree seat , I added a top cut of 15 to get closer to the much flaunted full radius seat form and I lost 15 cfm from that peak flow number .

Of course back then I did not realize what was taking place as I heard the sound from the intake port change.
mag2555, first thing I want to do is thank you for the help you’ve offered on this forum in shaping difficult short turns (old school Pontiac, LSX) and explaining their relationship to the sizing of the throat in order to achieve a clean sounding and stable flow curve.

The second thing I want to do is say that many years ago a very well known cylinder head porter in the Virginia Beach area mentioned that he didn’t follow most posts on speed talk but… he took the time to read yours…

High praise indeed, considering his head work is some of the best in the business.

I don’t know you or who you are, but sincerely thank you for taking the time to offer help on this forum.
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Re: Pontiac 400 heads

Post by mag2555 »

I am flattered beyond words, all I can say is thank you!
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Re: Pontiac 400 heads

Post by mag2555 »

Well let go back to diving in here a bit with all this talk of Pontiacs horrible chambers and other comments.

Let’s look at LF4 400 cid model SBC with a 4 bbl as installed in trucks, this motor and the Pontiac 400 have the same bore and stroke ( I guess Chevy new a good thing when they saw it! ) the Chevy was only making 185 hp at the end of its years of production and the Pontiac was making 200 to 220 hp as in the TA cars.

Just sayin!
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Re: Pontiac 400 heads

Post by Stan Weiss »

mag2555 wrote: Sun Aug 01, 2021 4:42 pm Well let go back to diving in here a bit with all this talk of Pontiacs horrible chambers and other comments.

Let’s look at LF4 400 cid model SBC with a 4 bbl as installed in trucks, this motor and the Pontiac 400 have the same bore and stroke ( I guess Chevy new a good thing when they saw it! ) the Chevy was only making 185 hp at the end of its years of production and the Pontiac was making 200 to 220 hp as in the TA cars.

Just sayin!
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