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Do i have too much overlap?

Jussi Alanko

Member
Joined
Jun 5, 2020
Location
Finland
I finally found a cam card, and i put the values to summit racing camshaft calculator, and this is what i found out:



Camshaft is designed to work with my head, but overlap seems to be huge, cam is designed for turbo use.

Does this work ok with this kind of overlap.

I have a holset super hx40 with 18# exhaust housing, which is biggest that you can get. I also use a good tubular exhaust manifold and i only put something about 23-25psi of boost, so i think that i have more boost than backpressure.

Do i worry too much which this overlap thing?
 
Yes, that is good turbo application overlap. The lobe separation goes down as overlap goes up. A typical n/a cam overlap in a red block would be 109 like in enem V15. However, the turbo version of the V15 uses 112 lobe separation. The 278 duration will be an upper rpm band cam even for a turbo. For example the duration on a V16 is 268 and it's power band is 2500-6500 rpms.
 
278 sounds like gross (almost zero lift) duration. That calculator needs duration from .050? to .050? lift.


I put to the calculator following things: Lsa, both centerlines, and open and close at BTDC and ABDC. both exhaust and intake, then calculator calculates durations, i dont insert those.
 
Now i had a good info about this camshaft, a shop where i buy my head and camshaft was dynoing a redblock engine with a v camshaft, in engine dyno and max power was just shy 400hp, when he installed same camshaft that i have power jumps to 540hp in 7000rpm, and this come with lower boost than a 400hp with v-camshaft.

I don't know actual boost figures but with v-cam max power was at 5800rpm and with this cam what i had max power came out at 7000rpm. That means that actual power curve in v-cam was about 3800-6000rpm, so useful powerband is 2200rpm when with this camshaft power curve was useful at 3500-7200rpm (rpm limiter) so useful powerband is 3700rpm.

This is a huge benefit and shows off what a good designed turbo cam with a good head can do. This application uses a twin scroll Holset hx40 super turbo, i had the same turbo, my power goal is 400-500hp at flywheel.
 
If I had to guess I'd say that performance cam is a 3k to 7k or even 7.5k rpm cam. That's a huge power jump from the better flow. Sounds like it'll be a lot of fun.
 
yes, now i found the head flow specs, if engine was NA it will make most power at 7840rpm (cylinder head wise), here are the flow chart.


It will flow 216.5 at 13mm and 214 in 12mm, exhaust flow is 66% of intake flow.
Camshaft is as i was saying before 278 degrees at 0.050" and 12mm lift.
Flow numbers are measured with an intake manifold in place (dual 2*45dcoe)
 
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