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Author
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Topic: 11.1comp
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the last dive
Gearhead Posts: 147
From: sydney australia
Registered: Dec 2001
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posted 04-29-2002 07:57 AM
  
does any body know what octane fuel is required to run 11.1comp?
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jkilroy
Gearhead Posts: 1719
From: Vicksburg, MS
Registered: Dec 99
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posted 04-29-2002 10:23 AM
It is not nearly that cut and dry. New Corvette's run 11 to 1 on the street with nothing but pump gas and do fine. If I run anything less than 93 in my 68, which is right at 10 to 1, it will ping like crazy.Aluminum heads can generally use a half a point more than iron. Big cams bleed off pressure allowing you to run more compression. Advanced cams tend to ping more than those installed straight up. How about some detail on your combo? ------------------
Jay Kilroy
68' Fastback GT 390
"No such thing as a cam thats too big"
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cpmaverick
Moderator Posts: 1564
From: Auburn, AL.
Registered: Jan 2000
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posted 04-29-2002 11:25 AM
Yeah, it really just depends on the camshaft (cylinder pressure). The new Celicas run 11:1 also. ------------------
-Charlie Ping
1970 Maverick Grabber
[email protected] with AC and overdrive.
http://www.maverickgrabber.com
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Dusty Kiser
Gearhead Posts: 126
From: Bethel,Oh USA
Registered: Mar 2002
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posted 04-29-2002 08:50 PM
quote:
Originally posted by the last dive:
does any body know what octane fuel is required to run 11.1comp?
Like the guys said, it isn't at all cut and dry. Cylinder pressure is the key word. Cylinder pressure is affected by, static compression, valve events, ambient air pressure, engine temperature, combustion chamber configuration, ignition timing, engine speed, engine load, fuel mixture, Fuel quality ( vapor pressure, true octane rating, what additives are used to achieve octane rating etc.) SO, let's assume you are carbureted, no PCM management for spark knock control etc. and you have an engine with a calculated compression ratio of 11to1. You want to run it on the street using 93 octane pump gas. If you have a cam with much overlap for a nice rump rump idle, keep the engine under 180 degrees, use a low cog, say 4.5 with normal street tire so the engine doesn't labor at all, and resist the temptation to want to crank in a bunch of timing at low engine speed, keep the fuel mixture slightly rich and your foot out of the carburetor, you'll probably be OK!
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steve'66
Gearhead Posts: 6522
From: Sonoma,CA,USA
Registered: Mar 2000
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posted 04-29-2002 08:57 PM
quote:
Originally posted by Dusty Kiser:
You want to run it on the street using 93 octane pump gas. If you have a cam with much overlap for a nice rump rump idle, keep the engine under 180 degrees, use a low cog, say 4.5 with normal street tire so the engine doesn't labor at all, and resist the temptation to want to crank in a bunch of timing at low engine speed, keep the fuel mixture slightly rich and your foot out of the carburetor, you'll probably be OK!
Very well said Dusty, especially if he's using aluminum heads.  We're putting the 408w around with 11.7-1 compression and pump gas breaking it in with aluminum heads and timing locked out at 35btdc. Haven't hear a ping yet! Of course the converter stalls at over 4000 rpm. SteveW
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