Compression ratio
Thread Starter
Burning Brakes
Joined: Sep 2016
Posts: 946
Likes: 266
From: McMinnville Oregon
Compression ratio
Well I did a compression check on the old Hemi/Vette. It came out to 130-135. I think the original engine had about 9:1 compression ratio. Does that look about right. The engine was supposed to be 325hp and based on the dyno run I did a year ago that looks about right. Then my next question would be, could you run regular or that mid grade gas? I know one response is listen for it pinging. However at my age 76 and after flying airplanes for 45 years I'm afraid I couldn't hear it if it did ping!!
Team Owner
Joined: Aug 2007
Posts: 58,061
Likes: 7,145
Army
My 63 250hp car has numbers higher than that and the owner's manual still recommends premium gas....
Maybe try a mid-range fuel and see how it goes, don't think I'd run regular - not worth the few pennies difference to me.
Maybe try a mid-range fuel and see how it goes, don't think I'd run regular - not worth the few pennies difference to me.
Race Director
Joined: Nov 2003
Posts: 10,696
Likes: 3,090
From: Cottonwood AZ
C1 of Year Finalist (performance mods) 2019
I run 87 Octane in my stock 1965 300 h.p. without issues. When I convert the engine to a 365 h.p. even with aluminum heads that may be a different story but only time will tell.
Melting Slicks
Joined: Jan 2007
Posts: 2,842
Likes: 622
From: Pasco Florida
If it were mine, I would use a higher octane. Detonation can occur even though you can't hear it happening.
Race Director
Joined: Nov 2003
Posts: 10,696
Likes: 3,090
From: Cottonwood AZ
C1 of Year Finalist (performance mods) 2019
Actually I run 91 (the highest available in my area) in the winter but in the summer I run 87 ethanol free which is only available in 87. I don’t notice any performance difference between the two fuels and I can’t HEAR any detonation.
Le Mans Master
Joined: Oct 2002
Posts: 7,098
Likes: 378
From: Las Vegas - Just stop perpetuating myths please.
Theres some old school/mechanical ways of listening for knock. If your really interested take a look: https://www.enginebasics.com/EFI%20T...et%20Cans.html
Good luck.
Good luck.
Team Owner
Joined: Jul 2001
Posts: 21,372
Likes: 1,003
From: Various places in Southern California.
I would expect it would run just fine on 87 octane. But, just to be safe, I'd use premium.
In my modern cars that can take 87, I use 87. One of my old cars is like yours and I'm sure it can run on 87. I still use 91 (best you can generally get here) in that car (as well as my other old car with 11:1 compression).
In my modern cars that can take 87, I use 87. One of my old cars is like yours and I'm sure it can run on 87. I still use 91 (best you can generally get here) in that car (as well as my other old car with 11:1 compression).
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Thread Starter
Burning Brakes
Joined: Sep 2016
Posts: 946
Likes: 266
From: McMinnville Oregon
Ok thanks I wasn't sure if 9:1 would still give me 130-5 compression. Like you say as much as I drive the car just running premium isn't a big deal.
I did find something interesting. As I said part of the history of this Hemi/Vette is it's build in a shop that may have been building drag race engines. Well it looks like the Transmission was also built for that purpose as the 4th gear isn't 1:1 but closer to 1:2, hence my poor gas mileage. Now I have a Tremec 5spd on order so I should notice a major improvement there.
I did find something interesting. As I said part of the history of this Hemi/Vette is it's build in a shop that may have been building drag race engines. Well it looks like the Transmission was also built for that purpose as the 4th gear isn't 1:1 but closer to 1:2, hence my poor gas mileage. Now I have a Tremec 5spd on order so I should notice a major improvement there.