Reduced low lift flow from porting...

[ClassAct]

One thing I found interesting around me is that the reputable shops that are known for good power don't even own 50 or steeper cutters, the main guy I deal with does have a 55 for exhaust that he does for some Mopar teams based off what they found doing testing with Allen Johnson, probably a Super stock kind of deal but they found a 45 intake and 55 exhaust to be best at least for that combo.

Some people are so afraid of going backwards, they never go forward. Their fear of failure paralyzes them. I know I was absolutely shocked at the amount of blowback I got from every quarter about steeper than 45 degree seats. I know some of them still won't budge. I get what Chad is saying. There are going to be times where a 45 may be better. Don't know how many times I've made more power and the car is slower. The power showed up chassis/tuning issues. Yet, the customer says the dyno lied. It's never their car or tuning or both is the issue.

I'd be leery of any shop today that isn't at least testing with other than 45 degree seats. I know that some teams were using 58 degree seats and some bullshitters were claiming 60 degree seats were being tested. I believe the 58, because I know who was doing that. The 60 I can't say. Could never verify that.


It's all about the SHAPE and always has been about SHAPE. The SHAPE of a correctly designed 50 or 55 degree seat has a far better shape than anything else.

I suspect some who are not finding results with steeper seats are not using the correct size and/or shape of valve to go with it.

I had heard the same about 60 degree seats, what you never hear is how as valve train got better guys started reducing seat angels and some back to 48* I think this is why you hear so much now about 50 and 52 but little about 55.

Everything in my shop right now is 45 (personal stuff) and I have yet to see a big enough gain to justify changing anything I have for what I am doing but I think that is why this discussion keeps coming up. If I do any future projects and am willing to test I would like to do ex first and then int just to see.

If you are looking to find flow number improvements to wow you with steeper seats, you usually don't. You see it on the dyno, and then on the time slip. I've said it before and repeat it now...gross, or bulk or whatever you want to call it on the flow bench means very little.

[GARY C]

Some people are so afraid of going backwards, they never go forward. Their fear of failure paralyzes them. I know I was absolutely shocked at the amount of blowback I got from every quarter about steeper than 45 degree seats. I know some of them still won't budge. I get what Chad is saying. There are going to be times where a 45 may be better. Don't know how many times I've made more power and the car is slower. The power showed up chassis/tuning issues. Yet, the customer says the dyno lied. It's never their car or tuning or both is the issue.

I'd be leery of any shop today that isn't at least testing with other than 45 degree seats. I know that some teams were using 58 degree seats and some bullshitters were claiming 60 degree seats were being tested. I believe the 58, because I know who was doing that. The 60 I can't say. Could never verify that.


It's all about the SHAPE and always has been about SHAPE. The SHAPE of a correctly designed 50 or 55 degree seat has a far better shape than anything else.

I suspect some who are not finding results with steeper seats are not using the correct size and/or shape of valve to go with it.

I had heard the same about 60 degree seats, what you never hear is how as valve train got better guys started reducing seat angels and some back to 48* I think this is why you hear so much now about 50 and 52 but little about 55.

Everything in my shop right now is 45 (personal stuff) and I have yet to see a big enough gain to justify changing anything I have for what I am doing but I think that is why this discussion keeps coming up. If I do any future projects and am willing to test I would like to do ex first and then int just to see.

If you are looking to find flow number improvements to wow you with steeper seats, you usually don't. You see it on the dyno, and then on the time slip. I've said it before and repeat it now...gross, or bulk or whatever you want to call it on the flow bench means very little.

I am interested in the data if you have any to share, I only know of a cpl of on track comparisons and they were pretty much the same, not enough info to narrow it down to either valve job.

I only look at the flow bench or the dyno as a tool to measure change at that time to that piece... not the potential outcome of the combination as a whole.

I have seen added power slow down a car probably as many or more times as I have seen it make one faster.

[PRH]

But does that address the OP's issue or mine in regards to throat and flow on a 45 degree seat low runner head?

I gave my thoughts about that on page one.

The only way one would really “know” how the different flow curves would affect the power output is....... to test it.

Of course, any time low lift flow is mentioned the thread turns to the benefits of 50* seats and their reduction of low lift flow(and how that’s what you really want).

In the particular situation of the OP’s heads....... we don’t have the benefit of looking at the comparison between what those heads would have flowed as delivered from Ford, vs what they are now.
Only what they flowed after the bigger valves were installed vs what they are now.

For this type of mild street build, I don’t like to have the low lift flow be less than it was stock.
And, if larger valves are installed I don’t like it when the c/d is less than the original c/d.

Without knowing what the flow was in the OE configuration....... we don’t really know if there was a “reduction” in low lift flow or not.

[digger]

It's about the combination of parts and how they work together to be greater than merely the sum of the individual parts

[GARY C]

But does that address the OP's issue or mine in regards to throat and flow on a 45 degree seat low runner head?

I gave my thoughts about that on page one.

The only way one would really “know” how the different flow curves would affect the power output is....... to test it.

Of course, any time low lift flow is mentioned the thread turns to the benefits of 50* seats and their reduction of low lift flow(and how that’s what you really want).

In the particular situation of the OP’s heads....... we don’t have the benefit of looking at the comparison between what those heads would have flowed as delivered from Ford, vs what they are now.
Only what they flowed after the bigger valves were installed vs what they are now.

For this type of mild street build, I don’t like to have the low lift flow be less than it was stock.
And, if larger valves are installed I don’t like it when the c/d is less than the original c/d.

Without knowing what the flow was in the OE configuration....... we don’t really know if there was a “reduction” in low lift flow or not.

Thats why I would like to see that subject move to lift at TDC or some other relative term so people could start learning how it correlating it to the engine and not the Flow Bench... But that is why it is important to keep having these discussions is so we can find a way to quantify the results to engines we have not tested. Kind of like how people have moved away from CFM and CC's to cross section and shape, that has only taken 2 decades of repeated discussion...

[PRH]

It's about the combination of parts and how they work together to be greater than merely the sum of the individual parts

This is it exactly.

For example, a 455 Pontiac with some typial bowl ported D port heads and 2.11” 30* valves will tolerate quite a lot of cam duration without any real noticeable loss of low end power or throttle response.
Theoretically a double no-no, 30* seats with their inherent high low lift flow, and a long duration cam.
Yet, because the ports in the heads are so grossly undersized for the motor, the momentum of the column of fuel/air in the intake runner is high and does a good job of combating exhaust dilution during the overlap period.

One of the cam swaps we did in my friends bracket race 400 Pontiac was going from a 247/255-108 SFT to a 263/271-108 SFT......... listening to it and driving it around....... you could barely tell we changed anything.
It did pick up .25 in the 1/4 though.

[digger]

People on this forum seem to make the erroneous assumption that everyone works on the same engine combos and applications as themself. There are a lot different combos, priorities, applications so rarely do any of the details becomes absolutes. What works for one may not work for another.

[travis]

But does that address the OP's issue or mine in regards to throat and flow on a 45 degree seat low runner head?

I gave my thoughts about that on page one.

The only way one would really “know” how the different flow curves would affect the power output is....... to test it.

Of course, any time low lift flow is mentioned the thread turns to the benefits of 50* seats and their reduction of low lift flow(and how that’s what you really want).

In the particular situation of the OP’s heads....... we don’t have the benefit of looking at the comparison between what those heads would have flowed as delivered from Ford, vs what they are now.
Only what they flowed after the bigger valves were installed vs what they are now.

For this type of mild street build, I don’t like to have the low lift flow be less than it was stock.
And, if larger valves are installed I don’t like it when the c/d is less than the original c/d.

Without knowing what the flow was in the OE configuration....... we don’t really know if there was a “reduction” in low lift flow or not.

From multiple flow tests of stock D0OE’s and C9OE’s I have found on the ‘net, I am still better at all points. I’m also better than any of the better stock heads...iron GT40’s and GT40P’s. Especially on the exhaust side.

[PRH]

So....... as long as the remaining parts selection is appropriate for the way the engine is intended to be used....... they should work fine.

I don’t recall the details of the individual heads that were tested, but those tests that DV did with the SBF and the different ported stock heads...... how did the power output correlate to the flow curves of the different heads?

[SpeierRacingHeads]

I have 3 different sets of heads in the shop with 60 degree seat.

I recently had some DRCE PS heads in the shop, no 60 there..

I feel I can make as much power with a 45 as I can with a 50 with my 23 degree stuff. Most of the Comp, big valve sportsman, are all 50 degree.

My 265cc 23 degree has a 50 degree seat.

These aren't some catalog cutters I use. I'll also say all of my 45 cutters have a 40 or more top cut. 35 is old news.

[GARY C]

It's about the combination of parts and how they work together to be greater than merely the sum of the individual parts

This is it exactly.

For example, a 455 Pontiac with some typial bowl ported D port heads and 2.11” 30* valves will tolerate quite a lot of cam duration without any real noticeable loss of low end power or throttle response.
Theoretically a double no-no, 30* seats with their inherent high low lift flow, and a long duration cam.
Yet, because the ports in the heads are so grossly undersized for the motor, the momentum of the column of fuel/air in the intake runner is high and does a good job of combating exhaust dilution during the overlap period.

One of the cam swaps we did in my friends bracket race 400 Pontiac was going from a 247/255-108 SFT to a 263/271-108 SFT......... listening to it and driving it around....... you could barely tell we changed anything.
It did pick up .25 in the 1/4 though.

Thats interesting, my 10.2 Chevy 2.05 headed 350 with a 262 XE vs my 9.2 Factory Pontiac 2.11 headed 412 with a 268 AH have almost the same overlap, 54/56 respectivly but my Pontiac is a bit more radical at idle at 2" lower in vacuum and requires at least 150 more rpm to idle despite being 62 ci bigger? both with 1.65 rockers an around .511 lift and similar head work around 240 CFM?

[Charliesauto]

I have 3 different sets of heads in the shop with 60 degree seat.

I recently had some DRCE PS heads in the shop, no 60 there..

I feel I can make as much power with a 45 as I can with a 50 with my 23 degree stuff. Most of the Comp, big valve sportsman, are all 50 degree.

My 265cc 23 degree has a 50 degree seat.

These aren't some catalog cutters I use. I'll also say all of my 45 cutters have a 40 or more top cut. 35 is old news.

At this very moment, I am looking at a set of NASCAR SB2.2 heads from a many time championship team, they are 60 degree exhaust, probably 13-14 year old stuff.

[GARY C]

I have 3 different sets of heads in the shop with 60 degree seat.

I recently had some DRCE PS heads in the shop, no 60 there..

I feel I can make as much power with a 45 as I can with a 50 with my 23 degree stuff. Most of the Comp, big valve sportsman, are all 50 degree.

My 265cc 23 degree has a 50 degree seat.

These aren't some catalog cutters I use. I'll also say all of my 45 cutters have a 40 or more top cut. 35 is old news.

Yes that was something DV told me years ago was that people were looking at 35 to 38 top cuts and the old 30 was out, the AJ cutters my shop uses are 38 top 45 seat and multi angel to the bowl, looks almost like a radius. It does how ever kill some low lift as opposed to an OTB 45 seat.
EDIT, with this set up it tends to dyno best with a non back cut valve even though the bench shows a back cut valve to flow better.

[BradH]

... I'll also say all of my 45 cutters have a 40 or more top cut. 35 is old news.

Can you comment on what you want to see as a transition from that type of top angle into the chamber?

[SpeierRacingHeads]

... I'll also say all of my 45 cutters have a 40 or more top cut. 35 is old news.

Can you comment on what you want to see as a transition from that type of top angle into the chamber?

Here are a couple pictures of a 15 degree Ford with a 40 top 50 and a 23 degree Dart with a 40 top 50. Same cutter. Then the third picture is a 40 top 45. I want to not feel any transition.