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Are you guys going using much more lift on your cams then you heads flow at 28”?
My heads do 300cfm on the intake side...240 on exhaust. Two cam outfits are giving me recommendations of 250/255 @ .050 and 257/262 @.050 both with lifts of .560-.570.
Then my drag race friends are running anywhere from .620 to .700 @ 28” with the same flow numbers on the same heads.
I know we have different needs for our engines but that much?
Very normal thing to do.
Basically, the area under the curve is greater and more than offsets the peak lift flow. Even more of a difference when the small port is the restriction so as a stock head class. The trade off is valve train stability and longevity. Even that is easily delt with with today's choices in springs and valves.
Flow means nothing on the surface without knowing the demands of the engine. A 300cfm head might run like a turd at 1200rpms on a 120 cubic inch engine. The cross section of the port for the rpm requirements of the engine to produce the maximum velocity the port shape will handle is far more important.
A drag race engine likely runs in a narrower rpm band *also higher* and can utilize more cam. A dirt car runs in a wider rpm range and to maximize the numbers in that rpm band it could require less cam area to make it happen.
I'd like to keep the duration around 255-260 intake/exhaust but with lift around .620 or a bit higher.
I found an Erson with a bit more duration with .650-.670 lift. I could advance the cam a bit to adjust for the extra duration. Done that before.
The port speed in my heads is real good. I had one on the flow bench last month and the operator was impressed. He said they should handle 650 HP pretty easy from his experience... more with the right cam and tune.
Can you just add more ratio to the rockers, create more lift, and a faster ramp?
.560 - .570 based on 1.5s? You could go to 1.65's and get .627" lift and a wider bell curve higher up in the lift range.
Unless i got it all wrong in my head, which is entirely possible...
You're right Krom. That's exactly what I've been thinking. I'll call T&D this week to ask about the cost of rockers...
Right now I'm waiting on my pistons to be built and delivered. I should have had that taken care of in November but Santa stole all my $$$.