Dynamic comp on 390

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OLFOOL

OLFOOL

OLFOOL
Joined
Jul 27, 2021
Messages
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Location
New South Wales, Australia
Just wondering if anyone could work out the dynamic comp on the 318 stroker we are about to build using a Comp Cams Xtreme Energy 242/248 Hydraulic Roller I normally use the UEM calculator but it asks for inlet ABDC @.050" and the roller is at .006". Any help appreciated.
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View attachment 1715772244
 
Comps web site should have all of that information for you. They post the cam card on there site when you look up the cam itself.
 
Use the Wallace Calculator. My ASSumptions include an elavation of 366 feet.

Camshaft, Rod Length, Boost and Altitude Correction to Compression
Static compression ratio of 11.7:1.
Effective stroke is 2.92 inches.
Your dynamic compression ratio is 8.81:1 .
Your dynamic cranking pressure is 183.51 PSI.
Your effective boost compression ratio, reflecting static c.r., cam timing, altitude, and boost of 0 PSI is 8.74 :1.
V/P (Volume to Pressure Index) is 157.
Edit , I see Comp Cams aren't being clear on their timing figures on the cam card. Those #'s are not at .006 there at .050 on their illustration.
Is there not a "value" given for piston valve reliefs?
 
Last edited:
OLFOOL said:
not @ 050" only at .006" as I posted.
Click to expand...

Sorry, my bad. Thought I read different.

The advertised numbers are 292/300 but at what exact lift point Comp uses for that XE Hyd roller shaft is IDK. You could try those numbers. I’m not 100% on this, but *I Think* Comp uses the .006 on there other cams along the similar lines. As in not there race cams.

Xtreme Energy 242/248 Hydraulic Roller Cam for Chrysler 273-360

I see your location. Perhaps a phone call would work? I know the time difference is huge.
 
I don't get the numbers they post on their site. The intake timing events at .006" lift are shown, but actually add up to their duration at .050" (15+180+47 = 242*). I'm guessing it must be a misprint and those are actually the events are .050"??

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I initially started to write what you have discovered but decided to bite my counts and figured a call to Comp would clear things up faster and more accurately since it’s there cam and web site. LMAO!

Expert time!
 
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