Pontiac 400 heads

[ClassAct]

ClassAct, when you have the time put your flow sheets where your Mouth is please.

I will respond in the same.

LOL. Another dick measuring contest I see.

[ClassAct]

Valve lift has everything to do with seat angle. Pontiac used low lift cams, just over 0.400" with most engines, where the 30* gave superior flow up to about 0.450" lift. I know of an Edel head for a Pontiac that had the intake converted to a 30* seat from the as delivered 45* seat. It had substantially more flow at lower lifts [ eg, 164 v 139 cfm @ 0.200"lift ] & was on par up to 0.550" lift

If the 30 degree seat was optimal, then everyone running less than some arbitrary lift number would be using the 30. Low lift numbers don’t impress me. In fact, flow numbers don’t impress me. Shape, size, sound, air speed...those things are what counts.

If you read my posts, you’d know I’m a big proponent of 50 degree seats. On anything even remotely performance oriented. I never consider lift. I’ve never seen a power drop using a 50 over a 45. Not once, regardless of lift. I’m going to deliver a street/strip car to a customer this Sunday. It’s a .508 lift solid, and a 50 degree seat. I know what they flowed, and I know what the dyno numbers are. I will ask him today if I can post his numbers. If he’s good with it, I will post them up.

What I will say is on a third party engine dyno, it made more power under the curve than anyone thought it would. And it had a flatter torque curve than they dyno operator said it would. When I told them what the heads flowed he immediately started bitching the “low lift” numbers we way down for that low lift. He said the engine would be a pig. Then I told him it was a 50 degree seat. His guesstimate for horsepower was off. By 46 HP.

It’s not the 1970’s anymore. Pontiac had a bad idea. It’s time to move on.

[Ken_Parkman]

The AMC's I work on also had 30 degree intake seats from the factory. I have tracked a significant improvement in intake reversion contamination and idle quality going to a 45 degree intake seat. I have made the distinction duration, and anything more than a stock type idle duration I change to 45 intakes. My conclusion is good very low lift intake flow is bad and I kill it by going to a 45 seat.

[mag2555]

It would seem then that you do not have a flow bench to support your claims.

[Walter R. Malik]

The AMC's I work on also had 30 degree intake seats from the factory. I have tracked a significant improvement in intake reversion contamination and idle quality going to a 45 degree intake seat. I have made the distinction duration, and anything more than a stock type idle duration I change to 45 intakes. My conclusion is good very low lift intake flow is bad and I kill it by going to a 45 seat.

On almost every engine I have tested on a dyno or at the track, whenever I need to take camshaft duration out of the engine in order to make the torque return ... it makes less horsepower, regardless of valve lift

Low lift flow is only a good thing when very small camshafts need to be used; by rule or whatever other reasoning.

[EDC]

Valve lift has everything to do with seat angle. Pontiac used low lift cams, just over 0.400" with most engines, where the 30* gave superior flow up to about 0.450" lift. I know of an Edel head for a Pontiac that had the intake converted to a 30* seat from the as delivered 45* seat. It had substantially more flow at lower lifts [ eg, 164 v 139 cfm @ 0.200"lift ] & was on par up to 0.550" lift

Our old 400 inch Pontiac Trans-Am NHRA Stocker picked up changing from the factory 30° to 45° seat. Flow bench numbers be damned.

[Stan Weiss]

I am not going to get into which is better 30 or 45. But let me say looking at low lift flow numbers is not a really oranges to oranges test.

Why is that. Because flow area is not really valve lift * pi. At lets look at .100" valve lift. The 45 has less flow area than the 30. So when using that area the 45 may actually have a better CD.

Stan

[PRH]

For a mild build like is being discussed by the OP, I wouldn’t work very hard at changing the intake seat angle.
If he’s going to run OE type valves that have the extra thick margins, I’d reface them steeper....... as much as the valve will easily accommodate....... and make the seat match.
Whether that’s 35, 37, 40....... whatever.

Before the rules in stock allowed changing the seat angles, plenty of Pontiacs were running in the 10’s with 30* seats.
It’s really not a deal breaker IMO.

[ClassAct]

It would seem then that you do not have a flow bench to support your claims.

Sure do. But I have nothing to prove to you. You aren’t important. Keep doing the wrong thing and trying to bully people who don’t follow your bad advice.

[408swinger]

Call my brother ....lol he just dynoed this 400 for his 69 Bird a few days ago . Stock intake and heads. Ran near identical numbers with a Qudrajet but ran too lean and he didnt have extra jets with him so they plopped the shop Holley on it . Still lean but better . Could have spent more time tuning but he was really just breaking it in and leak checking .
file:///var/mobile/Library/SMS/Attachments/dd/13/D05BAF0C-0365-42FD-A7C6-105875D54EC2/Resized_20210714_150518.jpeg

file:///var/mobile/Library/SMS/Attachments/21/01/48C8037A-DAD5-4303-9436-18A89CF9D3AD/Resized_20210714_204823.jpeg

[408swinger]

Doh !

8E1968AB-ABD3-433A-9C64-51FAE0AA371D.jpeg

7FBCDF11-B2EA-45F4-8459-5A53D45FB080.jpeg

[pastry_chef]

Valve seats
http://www.eng-tips.com/viewthread.cfm?qid=84437

[ClassAct]

Valve seats
http://www.eng-tips.com/viewthread.cfm?qid=84437

Interesting. That’s worth reading.

[68corvette]

https://www.google.com/amp/s/www.motort ... e-job/amp/

Not the best test going fom 45 to 35 to 50deg.. but still shows some trends.

[Geoff2]

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.