Head Flow vs. Max HP

plev72

Registered User
Hey all, I'm hoping to get some educated responses on this... personal experience would be great if you've got.

Assuming all else being equal and head flow being the limiting factor on HP, anyone have any ideas where the flow points vs. hp/tq might be at?

For example,

If stock (per the apten page) heads have peak flow at
int exh
.650 183.1 129.3

and for the sake of argument if we add on all of the go fast goodies, a more aggressive cam, roller rocker, etc. We should top out somewhere around 350 +/- rwhp (w/out nitrous)

I don't see optimizing for .650 lift... but that aside, if we assume that these numbers are roughly correct... what kind of max hp could we expect w/ say:

int exh
220 160

or

int exh
230 220

etc. etc... any of you high hp guys mind sharing what kind of flow numbers you've got?

Thanks,
Paul
 
My head's peak flow numbers (@ .500 lift) are 232 CFM In & 218 CFM Ex (w/header pipe) and 194 CFM Ex without pipe.

David
 
It could easily make as much as 100hp difference, but the heads are not the biggest bottle neck in the motor.

IMO, the 3.8 could make 600hp with all the right parts. Replace those heads with stockers and you would be looking at about 500hp max.

Replace the cam with a stocker and you can drop about another 100hp off of that.

Yes, I think it is totally possible for a bone stock 3.8 with the right parts and turbo(s) to make 400hp at the flywheel. (at 18psi and with pump gas)

Most of the fast SC's you see around here are WAY over engineered while overlooking the biggest HP obstacles (mine included). For example, I believe that a good motor like Dave N or Gary Kuhn have is capable of 550 HP with nothing more than an efficient way of getting air into the motor.

The fact that my Whipple fed stock 3.8 has made almost 290rwhp by 4500rpm should give you a hint of what the potential is. I know that the V6 Mustang guys hit over 300rwhp with a twin turbo on a stock 3.8. Food for thought.....
 
XR7 Dave said:
The fact that my Whipple fed stock 3.8 has made almost 290rwhp by 4500rpm should give you a hint of what the potential is. I know that the V6 Mustang guys hit over 300rwhp with a twin turbo on a stock 3.8. Food for thought.....

I aghree, these motors can make serious power as the whipple showed instock trim. The guy that may over 300 RWHP with twin turbo's on a stock motor is a little misleading to us though, it was done ont he split port 99+ motor, the heads on that motor flow a heck of a lot better then our single port style heads.
 
The air capacity is a product of RPM & Displacement.
In a 4 stroke motor.the volume displaced on the intake
strokes during each crankshaft revolution will be 1/2 of
the overall cubic capacity.So to find the air capacity
in cubic inches per minute.Multiply the RPM by the
displacement in cubic inches and divide by 2.
.................... RPM X DISPLACEMENT
AIR CAPACITY=---------------------------
.................................2

To calculate this to cubic feet per minute or CFMs
You divide the displacment by 1728,the number of cubic in in a cubic foot.
..........RPM X Displacement 232cid
CFM =--------------------------------
.................3456
===========================================================quote
Assuming all else being equal and head flow being the limiting factor on HP, anyone have any ideas where the flow points vs. hp/tq might be at?
==========================================================
Paul;You need a dyno sheet or the max torque and the RPMS that you expect
max torque.Like other measurement of motor efficency,volumetric effiency is highest at that point,and max RPM, because thats where the air capacity is
its greatest.

If you know that max torque is delivered at 3600 RPM with your SC.
so to find the air capacity.
...........3600RPM X 232 CID
CFM=--------------------
............3456


If you understand this so far.I will try to explain CFMs you need for A HP
rating of each cylinder.Or CFMs you need for each port to flow for HP YOU
want. I know how to do it but writing it down,so someone will understand
is not my great thing in life.I am not the greatest communicator in the world.
typing or talking.

Thanks Randy
 
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