ANOTHER SBC STROKER QUESTION 377-

[joespanova]

I wonder how much different the cam requirement is for 50* vs 45* seats, according to CI??

As for Bischoff, I was curious as to what his prediction was with regards to ET change.
Was he optimistic it would be better?
Did he suggest a different cam would be required before any benefit from the 50* seats would be realized?

Yes and no..LOL

[PRH]

I take that as, yes he was optimistic, and no on the cam recommendation.
Fair enough.

Was there any discussion about the cam at all?
As in, did you ask if it might need something different now?

And to Stans point....... yes, it would be great to hear Mikes take on the cam situation re: 45* vs 50* seats.

[novafornow]

If the flow before .500 declines, then I will guess that Mike would suggest a different cam. I assume that he asks for a complete flow curve for a reason.

[joespanova]

I take that as, yes he was optimistic, and no on the cam recommendation.
Fair enough.
Was there any discussion about the cam at all?
As in, did you ask if it might need something different now?

There was never a discussion about cam....

[PRH]

If the flow before .500 declines, then I will guess that Mike would suggest a different cam. I assume that he asks for a complete flow curve for a reason.

But if you have the same flow numbers at each lift increment for both 45* and 50* seats, if you were basing the CD off the “valve seat area”, the 50* seat is more efficient and the velocity is higher....... which is not reflected in the flow number itself.
So, it would be interesting to know if there were any “generalities” that could be applied towards the cam selection when taking the valve seat angle into consideration.

[SpeierRacingHeads]

I think what gets lost in the seat debate is the steeper seat "pulls" harder on the port. So if you have a localized velocity issue, your making it worse. And if you didn't have any issues, you might have just created one.

Nothing wrong with steep seats, if it is designed or ported to them.

[ClassAct]

I think what gets lost in the seat debate is the steeper seat "pulls" harder on the port. So if you have a localized velocity issue, your making it worse. And if you didn't have any issues, you might have just created one.

Nothing wrong with steep seats, if it is designed or ported to them.

You say it way better than I do. It's always better to start with a plan in mind and work to that. It's pretty tough to take a set of heads that are developed with a 45 degree seat and then go to a 50 and not be able to change the port for the valve job.

I don't want to speak for anyone but myself, but if Chad doesn't mind I'd like to say that I think he's posted where he has developed his ports and seats to work with a 45 degree seat and bowl percentages over 91% IIRC (Chad please correct me if I'm wrong about that) and I do know others who run bowl percentages like that. Me personally, I'm not likely to go over 88, maybe 89% on a 45 just because of the way I port, and how my eye and my mind see the end result. I know that sounds strange, but that's about the best way I can say it.

I've developed a couple of cutters that I used and any time I tried over those percentages I lost power. So I base what I do off how my eye sees the port and the finished work.

[SpeierRacingHeads]

Tonight I just finished up my v2.70 which is a 250cc, v2.70in pinch, 2.125 valve.

This cylinder head has a 1.940 diameter throat = 91.3% throat and a .311 valve

It has a 2.170 bowl = 102% of valve

It has a 40 degree top cut and a 45 degree seat

[MELWAY]

I think what gets lost in the seat debate is the steeper seat "pulls" harder on the port. So if you have a localized velocity issue, your making it worse. And if you didn't have any issues, you might have just created one.

Nothing wrong with steep seats, if it is designed or ported to them.

I think this is spot on. I’ve seen plenty of big throats make big numbers on the bench and kill TQ on the dyno. I’ve been guilty of it


You say it way better than I do. It's always better to start with a plan in mind and work to that. It's pretty tough to take a set of heads that are developed with a 45 degree seat and then go to a 50 and not be able to change the port for the valve job.

I don't want to speak for anyone but myself, but if Chad doesn't mind I'd like to say that I think he's posted where he has developed his ports and seats to work with a 45 degree seat and bowl percentages over 91% IIRC (Chad please correct me if I'm wrong about that) and I do know others who run bowl percentages like that. Me personally, I'm not likely to go over 88, maybe 89% on a 45 just because of the way I port, and how my eye and my mind see the end result. I know that sounds strange, but that's about the best way I can say it.

I've developed a couple of cutters that I used and any time I tried over those percentages I lost power. So I base what I do off how my eye sees the port and the finished work.

I think this is spot on. I’ve seen plenty of big throats make big numbers on the bench and kill TQ on the dyno. I’ve been guilty of it

[ClassAct]

Tonight I just finished up my v2.70 which is a 250cc, v2.70in pinch, 2.125 valve.

This cylinder head has a 1.940 diameter throat = 91.3% throat and a .311 valve

It has a 2.170 bowl = 102% of valve

It has a 40 degree top cut and a 45 degree seat

Thanks Chad. I appreciate you posting numbers. BTW, I love how you get atop cut in. I'll say it again, I've seen many valve jobs where the top isn't in or only partially in. That's a big deal on any valve job.

[joespanova]

Since, the 50 degree seat hurts the flow below .500" and helps the flow above .500", tightening the LSA 1 degree could help. And the only other remedy would be to increase the profile area by accelerating the valve harder on opening.

Which falls right back to " was the cam ever discussed".
Somehow , without thinking about it , I was under the impression WIDENING the centers is the remedy.

[PRH]

If the CD were calculated for the “valve job area” for the lift vs flow of the 45* vs 50* seats, it’s possible that even with a little less flow at a given lift point, the steep seat while flowing less still has higher velocity between the valve and the seat.

Imo, that would be more relevant than the flow number itself as to what kind of adjustment might be made to the cam.

[GARY C]

If the flow before .500 declines, then I will guess that Mike would suggest a different cam. I assume that he asks for a complete flow curve for a reason.

But if you have the same flow numbers at each lift increment for both 45* and 50* seats, if you were basing the CD off the “valve seat area”, the 50* seat is more efficient and the velocity is higher....... which is not reflected in the flow number itself.
So, it would be interesting to know if there were any “generalities” that could be applied towards the cam selection when taking the valve seat angle into consideration.

I don't know that these would be excact numbers but this is just changing the valve size to try to compare 2.08 valve 45 vs 50 to 52ish seat but leaving everything else the same, note the number on the left under the lift numbers gives you an idea of the change in CD.

[ClassAct]

Since, the 50 degree seat hurts the flow below .500" and helps the flow above .500", tightening the LSA 1 degree could help. And the only other remedy would be to increase the profile area by accelerating the valve harder on opening.

I don't agree with your statement that the 50 hurts flow all the way to .500 lift because in my experience it doesn't always hurt flow in the lower lifts.

Sometimes the flow is the same from as low as .200 lift. That arbitrary .500 lift number makes people think that if you are not running .800 lift the 50 degree valve job won't work. Myself and others have used much lower lifts (some as low as .480) with 50 degree seats with success.

Again, it's all about the shape. The shape of the port and the shape of the valve.

[Stan Weiss]

Doesn't the max lift that the valve angle change effects also have to do with what the valve diameter is?

Stan