Compression ratio

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12-04-2016 | 09:56 PM

#11

outonsafari

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Joined: May 2009

Posts: 1,941

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Quote:

Originally Posted by BenPerfected

Our 500 ci 3.80 stroke engines are 9.5 CR with Valako/Dart I.E. 308's ported to 320ci. We run 92-93 pump gas and have never had any signs of detonation including totally inspecting the recent complete rebuilds. The timing is locked at + 40 degrees and we have a very smooth valve train w/55mm cam cores. Total package gives us 780 HP @ 6800 RPM. Water conditions being reasonable, we regualrly make extended runs at 6000+RPM.

for fun and laughs, define reasonable water conditions and stop being modest and post the speed at those 6000 rpm extended runs, boats' incredible

12-05-2016 | 06:10 AM

#12

BenPerfected

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Joined: Dec 2002

Posts: 2,195

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From: Dallas, TX

28P Bravo 1 props.... 90+ MPH in 2' or less water.....balls are getting smaller

12-05-2016 | 06:12 AM

#13

Eliminated572

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Joined: Aug 2011

Posts: 526

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From: US of A

If running locked in timing it will be a bit less than a mechanical or digital curve... The lighter the boat the less difference mind you

12-05-2016 | 07:23 AM

#14

MILD THUNDER

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Joined: Jul 2004

Posts: 11,332

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From: chicago

Quote:

Originally Posted by abones

these comp #s are a great starting point, but the real deal is to know your VE at operating RPM. I would that a 9.6 at 125% VE over a 10,0 at 95% VE of equal CID. Meaning the combination of parts in the build will ultimately determine your running CR and fuel requirements. Cam valve timing event, induction system and air flow volumes and speed, exhaust scavenging and so on. my point is static CR is no more then a good starting point.

Good point. The OEM's have been going to higher compression for years, once they figured that out. Engine Management is the big factor. I remember having old Pontiac 400's that were 7.6:1 static, that would spark knock.