I keep wondering what it is with aftermarket heads NON ported that people are having issues with getting RPM from them.
They then assume the runner volume is the culprit as to why it is RPM limited.
I run ported l GM cast iron heads and even the mild ported ones that do not seem to flow well on the intake side they still RPM to 7000 and then some with mild cams [email protected]
.050. or [email protected]
I did stick large valves into a small chamber 601 casting come with 1.84-1.50 and I went 1.94 intake valve and the cam was 292H [email protected]
The engine was done right before 7000 rpm.
That was not right as I have ran the small 1.84 valve to 7000+ and it pulled harder with the 280H cam.
Off came the heads after 2 days of tweaking the tune to no avail.
The 1.94 valve was too large and I was getting a washed out spot in the chamber near the spark plug right across from the intake valve.
I unshrouded the chambers and only in that spot.
The engine now pulled hard past 7500 and we just set shift point at 7400 for safety sake.
115 MPH. It did hit 117 once.
I ran some Edelbrock 5089 heads on an FS600 flow bench and at .500" lift they got noisy and the flow was not clean.
I ported them and things smoothed out.
Those heads are on a 355" with a 280H cam ground on a 106LSA.
.050 and .480" lift best shift point was 7000 RPM.
I slightly opened and smoothed the push rod pinch also.
I open that up quite a bit on all my iron GM heads.
Could it be the cross section is the limiting factor or could it be the unported bowls or the chamber shape holding out of the box heads back???
I will never know as I can't stick heads on without porting them.
I ran the 280H cam on a 110 LSA in a 385" ported 601 heads 1.84-1.50 valves and not any good porting either.
Intake runner was left stock size and I did not raise the exhaust runner either.
Flow was way less than an RPM head 220cfm intake and in the 150 on the exhaust.
Lapped stock valves no fanyc 3 angle valve job either.
It still pulled to 7000 rpm really quick.
11.9 compression on that one. Runners are under 170CC
If you ask me the 180cc runner is fine. Is the rest of the head up to the task at hand.