I’m not really looking for suggestions on reworking the combo...... I’m asking “why” the lower flowing 50* heads on a combo like this are supposed to be superior.
Not examples of what happened on some other combo when the seat angles were changed, but specifically what about using steeper than 45* seats would result in the engine making more power, in a combo that has grossly undersized heads, in terms of area and flow...... when utilizing the steep angle results in less flow across the board.
The new 50* heads were done to be a bolt on upgrade by the extremely well known and highly respected engine builder........ to replace the existing heads with 45* seats, also done by the same engine builder.
Discussions about whether or not the current cam was suitable or not were had....... a new cam was not deemed a requirement for the new heads to work.
So far, they have not shown any improvement on the dyno or in the car.
After I flowed them my response was....... well, they don’t flow as good.
But, I keep being told that despite the lesser flow at all lifts...... they are better.
So, my question is.......”why” is that better?
Somebody fibbed. If I call and give flow numbers to a cam grinder for two sets of heads (especially for a well known head) and one has a steeper seat, it will call out for a different cam. When I bought the cam for the example I first posted of my DD, the first conversation I had was almost an hour going over why the numbers looked odd to him and why. And why the smaller valve.
Eventually the cam ended up being way off from what he originally thought he would use.
Can you post the cam specs for that 540? I find others results fascinating. Come to think of it, the cam in the 2.3 Ford I mentioned ended up being a Jones or a Bullit I think. It may have been a Bullit because IIRC at that time 2014ish getting cores was a bit of trouble. But the two identical 2.3 engines had quite different cam grinds. I wish I still had the numbers on the two becuause they were quite different. The 50 took quite a bit more duration and the LSA was tighter, yet they both ran close in RPM. We thought we might need more RPM and gear with the bigger cam, but we never felt the need to change either.
I’m not really looking for suggestions on reworking the combo...... I’m asking “why” the lower flowing 50* heads on a combo like this are supposed to be superior.
Not examples of what happened on some other combo when the seat angles were changed, but specifically what about using steeper than 45* seats would result in the engine making more power, in a combo that has grossly undersized heads, in terms of area and flow...... when utilizing the steep angle results in less flow across the board.
The new 50* heads were done to be a bolt on upgrade by the extremely well known and highly respected engine builder........ to replace the existing heads with 45* seats, also done by the same engine builder.
Discussions about whether or not the current cam was suitable or not were had....... a new cam was not deemed a requirement for the new heads to work.
So far, they have not shown any improvement on the dyno or in the car.
After I flowed them my response was....... well, they don’t flow as good.
But, I keep being told that despite the lesser flow at all lifts...... they are better.
So, my question is.......”why” is that better?
Was the cam changed? If not I could see why there was no improvement.
Was the cam changed? Was it right to begin with? if not was it changed to what was needed? If not I could see why there was no improvement.
You could ask these questions if one was going from a 50 to a 45 seat and saw now change.
Please Note!
THE ABOVE POST IN NO WAY REFLECTS THE VIEWS OF SPEED TALK OR IT'S MEMBERS AND SHOULD BE VIEWED AS ENTERTAINMENT ONLY...Thanks, The Management!
Very true, but what does the flow at tdc really have to do with?
So the lift during overlap, at tdc, is what defines the low lift flow point?
Why not 10* btdc?
Why not 5* btdc?
Or these same values atdc?
I feel people put too much concern in overlap itself. To me it is just kind of a necessary evil.
I know some like DV use it as a basis for cam selection but......?
Jay,
TDC is just a reference point and you can choice what ever one you like.
I picked TDC because it is a transition point / the piston is no going up and the piston is not going down and is seating there with zero velocity.
How in the world did overlap and DV come into this discussion?
Stan
Ok, I understand now, was just asking for clarification, as I really didn't know where you were going.
The reason I brought overlap into it, is because it seems to be uber important around here, and figured that was what you were referring to. I gave the DV example of how it is sometimes used, both by him and others.
Is that ok?
Jay,
It is not for me to say what is OK or not OK. It just confused me as the overlap thing came out of nowhere.
If both sets of heads had the same seat angles, and all the pertinent measurements were the same(pinch, bowl diameter, throat, area at ST, etc), and one set flowed more at every lift....... while still being used on a combo where they are seriously too small for the application........ most would agree that the better flowing heads should make more power.
But once the steeper seat gets added to the equation, then it’s like the poorer flow gets a pass.
I don’t think I’ll ever get a satisfactory answer to this question........ but I’m quite confident if I installed a bigger, higher flowing set of heads on this motor...... with 45* seats....... it would make more power.
I’m sticking with my initial assessment of the situation.
The motor is severely restricted for flow........ and the new heads just flow less than old ones...... and the result is...... less power.
Sometimes....... the flow does matter.......and the motor responds to less flow, like it’s less flow.
I understand (and agree with) the point about steeper seats reducing low-lift flow during the overlap period in applications that need a bunch of duration and the benefits of seat velocity as you come up to IVC but I don't think Chad's point about getting the top cut to jive with the chamber walls gets the attention it deserves.
RevTheory wrote: ↑Thu Jul 04, 2019 11:43 am
I understand (and agree with) the point about steeper seats reducing low-lift flow during the overlap period in applications that need a bunch of duration and the benefits of seat velocity as you come up to IVC but I don't think Chad's point about getting the top cut to jive with the chamber walls gets the attention it deserves.
Again, application, IMO.
Here is a good pic of a 40 top just touching the chamber and the transition it makes to the deck. The beauty of this is for THIS chamber I have a 45 and a 50 with the same 40 top, same width, that will lay in any of these chambers. You can also see how the exhaust seat has a 47 top 50 degree radius.
RevTheory wrote: ↑Thu Jul 04, 2019 11:43 am
I understand (and agree with) the point about steeper seats reducing low-lift flow during the overlap period in applications that need a bunch of duration and the benefits of seat velocity as you come up to IVC but I don't think Chad's point about getting the top cut to jive with the chamber walls gets the attention it deserves.
Again, application, IMO.
I get that....... but sometimes the chamber wall is pretty darn far away from the top cut.
Like in the case with the Stocker head Chad posted the pic of.
So, the conventional wisdom is....... change it over to a 50* seat, it’s going to flow less at all accessible lifts....... most likely lose power(otherwise it would already have the 50* seats)........ then your going to swap the cam to not only make up the difference in the power you lost by changing the seat angles....... but then exceed what the motor made before?
If that’s how it always played out........ they’d all have 50* seats in them already.
PRH wrote: ↑Thu Jul 04, 2019 11:59 am
I get that....... but sometimes the chamber wall is pretty darn far away from the top cut.
Like in the case with the Stocker head Chad posted the pic of.
So, the conventional wisdom is....... change it over to a 50* seat, it’s going to flow less at all accessible lifts....... most likely lose power(otherwise it would already have the 50* seats)........ then your going to swap the cam to not only make up the difference in the power you lost by changing the seat angles....... but then exceed what the motor made before?
If that’s how it always played out........ they’d all have 50* seats in them already.
I know what you're saying; I'm with you here.
Here's the crap I've got to figure out at some point. Pic stolen from the net but AMC 304 chamber. Which compromise makes more sense; 40* top cut with a 50* seat or a 35ish* top cut and a 45* seat? They both dump into a flat chamber roof quite a bit away from a wall with no meat between the valves to thwart crossflow during overlap.
IMG_4365.jpg
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Last edited by RevTheory on Thu Jul 04, 2019 12:42 pm, edited 1 time in total.
I’m not really looking for suggestions on reworking the combo...... I’m asking “why” the lower flowing 50* heads on a combo like this are supposed to be superior.
Not examples of what happened on some other combo when the seat angles were changed, but specifically what about using steeper than 45* seats would result in the engine making more power, in a combo that has grossly undersized heads, in terms of area and flow...... when utilizing the steep angle results in less flow across the board.
The new 50* heads were done to be a bolt on upgrade by the extremely well known and highly respected engine builder........ to replace the existing heads with 45* seats, also done by the same engine builder.
Discussions about whether or not the current cam was suitable or not were had....... a new cam was not deemed a requirement for the new heads to work.
So far, they have not shown any improvement on the dyno or in the car.
After I flowed them my response was....... well, they don’t flow as good.
But, I keep being told that despite the lesser flow at all lifts...... they are better.
So, my question is.......”why” is that better?
Both you and Chad brought up two instances where a steeper seat may not work, in a grossly undersized head. Is this 540 engine your giving ad an example also severely cam limited?
PRH wrote: ↑Thu Jul 04, 2019 11:59 am
I get that....... but sometimes the chamber wall is pretty darn far away from the top cut.
Like in the case with the Stocker head Chad posted the pic of.
So, the conventional wisdom is....... change it over to a 50* seat, it’s going to flow less at all accessible lifts....... most likely lose power(otherwise it would already have the 50* seats)........ then your going to swap the cam to not only make up the difference in the power you lost by changing the seat angles....... but then exceed what the motor made before?
If that’s how it always played out........ they’d all have 50* seats in them already.
I know what you're saying; I'm with you here.
Here's the crap I've got to figure out at some point. Pic stolen from the net but AMC 304 chamber. Which compromise makes more sense; 40* top cut with a 50* seat or a 35ish* top cut and a 45* seat? They both dump into a flat chamber roof quite a bit away from a wall with no meat between the valves to thwart crossflow during overlap.
IMG_4365.jpg
That head is a perfect case of where I "sink" the valve to get a top cut on it. No matter the seat angle, you can get a top cut on it, and it will need it.
I'd the bowl is as steep in real life as it looks in the picture, I'd use a 50 degree seat.
Theoretically (and zero experience with seriously valve limited heads), I can see a scenario in which a port flows less at every lift yet makes more power if the low lift reverse flow is eliminated. This is because one can use more duration with the less flowing head and that additional duration allows more lift. I’m thinking this as the CFM(lift(degrees)) against degrees curve, which you want to get to something like a rectangle on the intake side.
Example, If you’re running a late 70’s Pontiac 400 low hp combo, and the factory lift is like .375...... then you’re stuck with .375 lift.
If you’re running a 68/69 Mopar 383 with no valve pockets, and a 245@.050 cam leaves you .00” intake V/P clearance...... then too bad. No flycutting allowed.
Move the cam, sink the valves, don’t mill the heads as much as would be legal(and give up some CR), etc.
Surely how much the engine demands factors into it. If it demands 350 and you have 400 then a loss of flow is probably less important than if the engine wanted 400 and you had 300.
I wonder if the steeper works better at high depressions, in my mind it should.
As for reducing reversion the exhaust port with its ever shrinking size and increase in efficiency often said to use steeper seat angle. This is an outflow problem and somewhat similar to the reversion up the intake. This at first glance seems counterintuitive
