Pontiac 400 heads

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mag2555
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Re: Pontiac 400 heads

Post by mag2555 »

Exactly my point Geoff!
No one seems to have kept in mind the detail in the OPs post as to his usage and the level of work he was stating he was comfortable in doing to his heads.

Most everyone replying back here has launched straight into race motor world which the OP clearly stated is not what he’s after!
If your only running no more then .500” lift and you Cam pick holds your valves open for the longest amount of time at 1/2 of that .500” lift, then that’s where you want the biggest flow gains to be.

And hey ClassAct, I am not making this a personal attack on you and calling you names so stop doing that in terms of your comments with me!
You can cut a man's tongue from his mouth, but that does not mean he’s a liar, it just shows that you fear the truth he might speak about you!
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Re: Pontiac 400 heads

Post by EDC »

Geoff2 wrote: Sat Jul 17, 2021 3:20 am Yes, some need to polish up on their reading skills. Street car, minor porting. These words are in post #1 by the OP. It is NOT a race engine, where multiple things would be changed from stock.
Because performance enhancing valve jobs don't work on anything but a racing engine. OKAY....
"Quality" is like buying oats. You can pay a fair price for it and get some good quality oats,
or you can get it a hell of a lot cheaper, when it's already been through the horse.

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Re: Pontiac 400 heads

Post by Ken_Parkman »

To be honest the OP application is the exact one I do recommend changing to a 45 degree seat from 30 on the intakes.

A race engine is a different discussion and goals.

To directly answer the question on back cut assuming the engine is getting some kind of a performance street cam, say more than 220 degrees, I would not do a back cut. For street use you want to minimize very low lift flow to clean up the intake reversion, and that is the sure thing about 30 degrees seats is they flow more at low lift as the effective opening is greater for a given lift particularly just off the seat. Depending on the cam this is bad cause the piston is going the wrong way and at street cruising you do not have the intake system "in tune".

A 45 with a 30 back cut might be a good compromise.
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Re: Pontiac 400 heads

Post by mag2555 »

Here’s my flow test results.

The head in this test started life with a 1.960” intake valve with a 30 seat.

In the first test listed here I the head for a 2.11” valve with a 30 seat.
This seat OD was 2.04”, so still way way under the 2.10” that could have been used and it’s available curtain area!

The seat width is .075”.
Throat diameter is stock.

For the test of the 45 seat the seat OD was taken up to 2.075”.
The seat width was kept at .075”

The test of the 45 seat version was given the added benefit of the valve having
1) a 30 back cut.

2) a necked down stem.

3) greater curtain area due to the 2.075” seat OD.

4) .023” bigger throat due to the 60 bottom cut narrowing down the 45 seat to .075”.

Both flow test where conducted within 30 minutes of each other.

The first column list the flow with the 30 seat , the second column the 45 seat.

.100”. 76.5. 74.9

.200”. 139.3. 136.8

.300”. 174.3. 176.7

.400”. 184. 187

.450”. 186.6. 188

.500”. 189.1. 188.5

Total CFM with 30 seat up to .500” lift = 949.8

Total CFM with 45 seat up to .500” lift = 951.5
You can cut a man's tongue from his mouth, but that does not mean he’s a liar, it just shows that you fear the truth he might speak about you!
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Re: Pontiac 400 heads

Post by HDBD »

Now flow the head backwards and report. For anyone interested these is a ton of information here and on the web written by Larry Meaux and Larry Widmer on the "Low Lift" topic.
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Re: Pontiac 400 heads

Post by ClassAct »

mag2555 wrote: Sat Jul 17, 2021 7:34 am Exactly my point Geoff!
No one seems to have kept in mind the detail in the OPs post as to his usage and the level of work he was stating he was comfortable in doing to his heads.

Most everyone replying back here has launched straight into race motor world which the OP clearly stated is not what he’s after!
If your only running no more then .500” lift and you Cam pick holds your valves open for the longest amount of time at 1/2 of that .500” lift, then that’s where you want the biggest flow gains to be.

And hey ClassAct, I am not making this a personal attack on you and calling you names so stop doing that in terms of your comments with me!


Yeah, you called me out like you are a God or something. No matter what I post, it won’t change your mind. If you want to be treated with respect then you need to be respectful.

I don’t care if it’s a street car. The 30 degree seat is past obsolete. For anything. The reverse flow is horrible. And the shape of the seat is terrible. There is no reason to use it. But you will continue to argue the point based on a stupid, arbitrary lift number.

It’s all about the shape. If the OP is dead set on not spending any money for valves and is wanting to reuse his OE valves then go ahead and leave it a 30. I wouldn’t do it for him. I’d have him buy valves and cut it for a 45.

Just ridiculous that the 30 degree seat gets so much love.
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Re: Pontiac 400 heads

Post by ClassAct »

mag2555 wrote: Sat Jul 17, 2021 10:34 am Here’s my flow test results.

The head in this test started life with a 1.960” intake valve with a 30 seat.

In the first test listed here I the head for a 2.11” valve with a 30 seat.
This seat OD was 2.04”, so still way way under the 2.10” that could have been used and it’s available curtain area!

The seat width is .075”.
Throat diameter is stock.

For the test of the 45 seat the seat OD was taken up to 2.075”.
The seat width was kept at .075”

The test of the 45 seat version was given the added benefit of the valve having
1) a 30 back cut.

2) a necked down stem.

3) greater curtain area due to the 2.075” seat OD.

4) .023” bigger throat due to the 60 bottom cut narrowing down the 45 seat to .075”.

Both flow test where conducted within 30 minutes of each other.

The first column list the flow with the 30 seat , the second column the 45 seat.

.100”. 76.5. 74.9

.200”. 139.3. 136.8

.300”. 174.3. 176.7

.400”. 184. 187

.450”. 186.6. 188

.500”. 189.1. 188.5

Total CFM with 30 seat up to .500” lift = 949.8

Total CFM with 45 seat up to .500” lift = 951.5


So what? Like someone said, flow that port in reverse. Then up the test pressure to 40 inches and see what happens. You can’t live and die by flow bench numbers.
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Re: Pontiac 400 heads

Post by tjs44 »

First of all,all 69 factory GTOs got 2.11 intake valves.I would not use the factory 2pc valves in ANY rebuild.JMHO,Tom
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Re: Pontiac 400 heads

Post by dfarr67 »

If edelbrock makes a head for this app- that's where I'd be at.
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Re: Pontiac 400 heads

Post by GARY C »

A conversation with Pro Stock engine builder Jon Kaase seemed to indicate it might not be worth it. "We tried different valve jobs a few years ago, and really didn't find much there so we just stick to the same one we always use [on the high lift engines]." Kaase mentioned he ran a 30-degree valve job on the potent Pontiac he entered in the Engine Masters Challenge a few years back, but was unsure whether that was a good or bad thing. "If the seat ID is the same when you got all done below the angles, I don't know if it's going to make a real big difference." For the most part, Kaase recommended a common 45-degree valve job for "normal" lift engines.
https://www.motortrend.com/how-to/1203p ... valve-job/
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Re: Pontiac 400 heads

Post by Geoff2 »

EDC,
Wrong. OKAY!
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Re: Pontiac 400 heads

Post by Walter R. Malik »

Geoff2 wrote: Sun Jul 18, 2021 4:57 am EDC,
Wrong. OKAY!
I thought he was being sarcastic ... at least I hoped so ... LOL.
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Re: Pontiac 400 heads

Post by 1980RS »

If a 45°is bad for a Pontiac head makes me wonder why someone would want to run a 50 to 55° seat on a SBC head :mrgreen:
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Re: Pontiac 400 heads

Post by Geoff2 »

It is about the application. You might run 16:1 CR on a race engine, but not on a street engine.....
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Re: Pontiac 400 heads

Post by ClassAct »

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.
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