Max Dynamic Compression Ratio on 91 pump gas
11-18-2011 | 04:52 PM
#52
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From: IBX
No all forged now. I can honestly say though I melted a forged engine down while the hyper engine next to it lived on with no issues with the exact same setup(and abuse that day). It did turn out tho that the forged engine had about 4* more timing in it due to a slipped balancer. Now I degree in the balancer along with the cams. Nonetheless, hypers are way underrated and actually superior in most ways. Its the destruction on failure that is unacceptable which is why I run forged now. If the engine with the hypers had the same timing issues that engine would most likely have been catstophically destoyed when the piston failed.
Last edited by blue thunder; 11-18-2011 at 05:07 PM.
11-18-2011 | 04:57 PM
#53
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From: IBX
Agreed, thanks for sharing!
Mine is;
"Your engine summary is as follows: Bore 4.53 inches, stroke 4.5 inches, rod c-c length 6.7 inches, with a static compression ratio of 8.3 :1. Your camshaft specifications call for an inlet valve closing of 54 degrees ABDC (after bottom dead center).
Your chamber volume is 162.81 cc's. With this camshaft your dynamic, or effective stroke is 3.82 inches. Your dynamic compression ratio is 7.20 :1 corrected for cam timing, altitude, and rod length. Your dynamic cranking pressure, corrected for cam timing, rod length and altitude is 138.55 PSI. Your dynamic boost compression ratio, reflecting static c.r., cam timing, altitude, and 7 PSI is 10.63 :1."
To add, I see my cranking pressures usually pretty darn close, within say 5-7% give or take.
Mine is;
"Your engine summary is as follows: Bore 4.53 inches, stroke 4.5 inches, rod c-c length 6.7 inches, with a static compression ratio of 8.3 :1. Your camshaft specifications call for an inlet valve closing of 54 degrees ABDC (after bottom dead center).
Your chamber volume is 162.81 cc's. With this camshaft your dynamic, or effective stroke is 3.82 inches. Your dynamic compression ratio is 7.20 :1 corrected for cam timing, altitude, and rod length. Your dynamic cranking pressure, corrected for cam timing, rod length and altitude is 138.55 PSI. Your dynamic boost compression ratio, reflecting static c.r., cam timing, altitude, and 7 PSI is 10.63 :1."
To add, I see my cranking pressures usually pretty darn close, within say 5-7% give or take.
)Straub cam, I'd love to see the output from the calculator on one of those just to put fact to all the stone thrown.
11-18-2011 | 05:04 PM
#54
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From: IBX
Actually if you look at the original calculator we are discussing, it uses abdc intake valve close * to calc the cranking pressure we are talking about.
11-18-2011 | 05:23 PM
#55
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From: Vancouver BC
11-18-2011 | 07:39 PM
#56
Frank's Marine Service
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From: Elkton, MD
I've got 4.530 bore, 4.5 stroke, 8.3:1 comp, 6.70 rod, 7psi and 54* ABDC @ .050 (Crane 138631)
Last edited by Panther; 11-18-2011 at 08:09 PM.
11-18-2011 | 08:12 PM
#57
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Ya got me, I just plugged in the numbers they asked me for and that's what it spit out. I'd have to assume the chamber volume is the cc of the head, plus the dish in my pistons and then a head gasket etc??? If I were add all those cc's together it doesn't seem that far off??
11-19-2011 | 08:57 PM
#58
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I run the 525sc blowers with 3.25" pulleys and make 6.2psi. Edelbrock rpm performer heads. 9.5:1 compression on 93 octane. Much care is put into my engines though to ensure the setup is right (quench, a/f, timing, valves, mls, ect. so that may be a little much for you. Certainly 9:1 on 91oct, 30* all in, 11.8 wot a/f and a cool running alum headed engine would be doable (12.7:1 dynamic). To be aggressive, last season I ran 9.6:1 compression and 6.2psi for a 13.4:1 dynamic ratio. Rule of thumb is supposed to be 12:1 total but I have debunked that, at least with my junk. This year I am going to add a bit of margin and run 9.4:1 with 6.2psi on 93oct.
Blue Thunder how much hp did you get out with your setup?
