compression

Skyman · 08-12-1999, 03:38 AM

whats the highest compression I can run on 92octane pump gas?

I was lookin to go 11.42:1

thanks

Clark Rodgers · 08-12-1999, 09:58 AM

I know that will be too much, most of the time 10.5 is about as high as you can go. Maybe 11 but I think you will be pushing it!

------------------
69 351W Sportsroof deluxe

gofishing · 08-12-1999, 02:42 PM

Forgive me for the silly question,

What happens if the compression is too high?

Learning something new everyday in life.....

Skyman · 08-12-1999, 03:50 PM

There are no stupid questions..... everyone has to learn.

You engine will detonate, unless you use a higher octane fuel. Basically it will ping to death.

Sky

David Gagnard · 08-12-1999, 06:12 PM

I'm running 9.75 to 1 in a 351-W, have to use 92-93 octane. Once when running low all I could get was 89 octane and when trying to accelerate she pinged pretty bad. I would not go higher han 10-1 without some sort of additive or racing gas(expensive).

David

66fastback · 08-13-1999, 01:40 AM

What you're really concerned with in the end is running cylinder pressure. The more static compression you run, obviously the more running pressure you make. You can control this somewhat with your cam selection. More duration and overlap will bleed off the running pressure. Overlap is affected by how much duration you have, and what lobe seperation angle you use.

Make good friends with the cam company, but I wouldn't run anything over 10.5 comp. on the street. I think that's pushing it pretty good unless you use a monster cam.

351w67MustangGuy · 08-13-1999, 08:05 PM

I've got a question because i heard a couple of my friends talking about it... Do blowers work better at a high compression ratio and nitrous work better at low (or vise versa) or does it not make a difference? also does it matter for a super charger and does anyone make a supercharger for a 351w?

------------------
67 Mustang Coupe w/351 Windsor 405hp 2.79 gears & street tires ran 13.01 @ 105.9 mph

thunderbolt · 08-13-1999, 10:41 PM

Two things are going to impact this dramatically. Do you have aluminium heads. If so they loose heat much faster than iron and typically resopond to about a point more compression than iron. My $.02 is around 9.5 on iron, and 10.5 on Alum. Two, what elevation are you at? I can run 86 octane no problem at 3000 feet but have to have 90 or higher at sea level. One more thing, Fuel injection will allow about .5 higher compression because all cylinders will be equally balanced. Carbs tend to lean out some cylinders relative to others and hence lower compression must be run so as not to detonate in the lean cylinders.

[This message has been edited by thunderbolt (edited 08-13-1999).]

08-12-1999, 03:38 AM	#1
Skyman I need 110mph Trap Speed! Join Date: Feb 1999 Location: So, CA Posts: 4,315	compression whats the highest compression I can run on 92octane pump gas? I was lookin to go 11.42:1 thanks

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08-12-1999, 09:58 AM	#2
Clark Rodgers Registered Member Join Date: May 1999 Location: Rowlett,Texas Posts: 306	I know that will be too much, most of the time 10.5 is about as high as you can go. Maybe 11 but I think you will be pushing it! ------------------ 69 351W Sportsroof deluxe

08-12-1999, 02:42 PM	#3
gofishing Registered Member Join Date: Apr 1999 Location: Seattle, WA, US Posts: 33	Forgive me for the silly question, What happens if the compression is too high? Learning something new everyday in life.....

08-12-1999, 03:50 PM	#4
Skyman I need 110mph Trap Speed! Join Date: Feb 1999 Location: So, CA Posts: 4,315	There are no stupid questions..... everyone has to learn. You engine will detonate, unless you use a higher octane fuel. Basically it will ping to death. Sky

08-12-1999, 06:12 PM	#5
David Gagnard Registered Member Join Date: Jul 1999 Location: Marksville, Louisiana Posts: 17	I'm running 9.75 to 1 in a 351-W, have to use 92-93 octane. Once when running low all I could get was 89 octane and when trying to accelerate she pinged pretty bad. I would not go higher han 10-1 without some sort of additive or racing gas(expensive). David

08-13-1999, 01:40 AM	#6
66fastback Registered Member Join Date: Mar 1999 Location: Dallas, TX Posts: 208	What you're really concerned with in the end is running cylinder pressure. The more static compression you run, obviously the more running pressure you make. You can control this somewhat with your cam selection. More duration and overlap will bleed off the running pressure. Overlap is affected by how much duration you have, and what lobe seperation angle you use. Make good friends with the cam company, but I wouldn't run anything over 10.5 comp. on the street. I think that's pushing it pretty good unless you use a monster cam.

08-13-1999, 08:05 PM	#7
351w67MustangGuy Registered Member Join Date: Jul 1999 Location: Bay Area, California Posts: 103	I've got a question because i heard a couple of my friends talking about it... Do blowers work better at a high compression ratio and nitrous work better at low (or vise versa) or does it not make a difference? also does it matter for a super charger and does anyone make a supercharger for a 351w? ------------------ 67 Mustang Coupe w/351 Windsor 405hp 2.79 gears & street tires ran 13.01 @ 105.9 mph

08-13-1999, 10:41 PM	#8
thunderbolt Registered Member Join Date: Oct 1998 Location: Houston, TX, USA Posts: 380	Two things are going to impact this dramatically. Do you have aluminium heads. If so they loose heat much faster than iron and typically resopond to about a point more compression than iron. My $.02 is around 9.5 on iron, and 10.5 on Alum. Two, what elevation are you at? I can run 86 octane no problem at 3000 feet but have to have 90 or higher at sea level. One more thing, Fuel injection will allow about .5 higher compression because all cylinders will be equally balanced. Carbs tend to lean out some cylinders relative to others and hence lower compression must be run so as not to detonate in the lean cylinders. [This message has been edited by thunderbolt (edited 08-13-1999).]