question on octane
03-29-2010, 03:47 AM
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question on octane I am very interested in a car that has a big block chevy .60 over with 12:5:1 compression. The owner is running 110 octane . I never had a chance to ask him ,but does that mean he is mixing his fuel ?
03-29-2010, 06:38 AM
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yea most likely your gonna have to buy race gas for it all the time...i could be wrong....anyways if your really interested in the motor either run the race gas or you can always just put in new pistons or change the heads and run pump gas
03-29-2010, 09:33 AM
#5
Last season when I was buying 110 for the racecar it was $9 a gallon.
Depending on the CC size of the heads that are on it, just changing those may not bring it down enough to run on pump gas. Also, a lot of pistons that have a dome like that to get the compression up that high only work with certain shapes of combustion chambers.
To lower the compression properly, your looking at pulling the motor apart and changing pistons.
$45-50 for 5 gallonds of gas gets expensive quick.
Depending on the CC size of the heads that are on it, just changing those may not bring it down enough to run on pump gas. Also, a lot of pistons that have a dome like that to get the compression up that high only work with certain shapes of combustion chambers.
To lower the compression properly, your looking at pulling the motor apart and changing pistons.
$45-50 for 5 gallonds of gas gets expensive quick.
03-29-2010, 09:45 AM
#6
What do you plan to do with it? I use to daily drive my 1976 TA with a 455 I built for it. Compression ratio was 12.5:1 and I would lower the timing allot, run super unleaded, add a little extras valve lash (solid roller) to make the cam act smaller, and I had to remind myself not to go wide open throttle while detuned and on pump fuel. Heck I realy just eased it around town. You can run it on pump fuel if you never hammer into it and de tune it. But those were the days my race car was my only car. I would suggest if you want a good daily drive not to runthat much compression. If you are planing to put this in your race car, go for it and run racing fuel.
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03-29-2010, 02:27 PM
#9
LSx's run lower timing and that helps reduce detonation. Also the aluminum heads help too. It realy depends on several other factors too. Lower engine coolant temp helps. Lower oil temps help cool the piston helps, more valve overlap tends to help by bleeding off some of the dynamic compresion at lower rpm, as well as the scavengine effects help to cool the cylinder which helps control detonation too. Not to mention the LSx's have knock sensors, even though that does not insure no damage from knock, it does lower the chances. Lower intake air temps help, the right spark plugs will help too.
I personaly would rather run higher octane race fuel and a higher compression ratio with more timing to make the power. It all depends on what you are doing. My current build is a 10.25:1 408 with a PT-88 turbo, running 30+ degrees of timing off boost and 22 degrees of timing under boost. I am working my way up to the 36 degree range under full boost. I might not make it that far but I will see. I run VP-113 or VP16 while doing this with lots of methanol injection. Ofcourse, I would never do this on super unleaded. Nor will I have it tuned that radical while running it on the street.
10-15 years ago we would run out to the local air field and buy all the Avgas we wanted for like 2 bucks a gallon when race fuel was like 4 bucks (I got my liscense when gas was less then 1 buck a gallon! Older then the hils huh!!!LOL). It is 100 octane leaded. We would run it on the street in our old school engines. But new laws and what not pretty much stopped that around our parts.
I personaly would rather run higher octane race fuel and a higher compression ratio with more timing to make the power. It all depends on what you are doing. My current build is a 10.25:1 408 with a PT-88 turbo, running 30+ degrees of timing off boost and 22 degrees of timing under boost. I am working my way up to the 36 degree range under full boost. I might not make it that far but I will see. I run VP-113 or VP16 while doing this with lots of methanol injection. Ofcourse, I would never do this on super unleaded. Nor will I have it tuned that radical while running it on the street.
10-15 years ago we would run out to the local air field and buy all the Avgas we wanted for like 2 bucks a gallon when race fuel was like 4 bucks (I got my liscense when gas was less then 1 buck a gallon! Older then the hils huh!!!LOL). It is 100 octane leaded. We would run it on the street in our old school engines. But new laws and what not pretty much stopped that around our parts.
03-29-2010, 02:54 PM
#11
What do you plan to do with it? I use to daily drive my 1976 TA with a 455 I built for it. Compression ratio was 12.5:1 and I would lower the timing allot, run super unleaded, add a little extras valve lash (solid roller) to make the cam act smaller, and I had to remind myself not to go wide open throttle while detuned and on pump fuel. Heck I realy just eased it around town. You can run it on pump fuel if you never hammer into it and de tune it. But those were the days my race car was my only car. I would suggest if you want a good daily drive not to runthat much compression. If you are planing to put this in your race car, go for it and run racing fuel.
Fix it the right way if you wanna drive it on the street.
Aluminum heads will generally allow you to run almost a full point in compression more on pump gas than a cast iron head. Im not sure how much more an aluminum block helps as well.
03-29-2010, 04:01 PM
#12
I did not advise to do this, and sorry but never hurt a damn thing in that build. Took it apart only to make it better. Drove it all the time, and made several 8 hour trips to Dallas in it, tuned it up and went to the drags like that, then de-tuned it and drove it back. Dead heat of West Texas Summers too.
Keep in mind the OP is talking about a Big Block Chevy, not an LS with EFI, I was speeking of my Pontiac 455 in particular.
I love it when people like to jump in and try to make others look like an idiot.
Keep in mind the OP is talking about a Big Block Chevy, not an LS with EFI, I was speeking of my Pontiac 455 in particular.
I love it when people like to jump in and try to make others look like an idiot.
03-29-2010, 08:35 PM
#13
Wouldn't increasing the lash make the cam seem smaller and therefore lower the overlap, and increase the cranking compresion of the cam? Maybe I misread or maybe I don't understand. I would think, the bigger the cam, the less likely to detonate. Just asking.
03-29-2010, 08:42 PM
#15
For the OP - not sure what part of the country you are in, but a couple of fuel system upgrades and a new carb could have you running that engine safely on E85. You could run it on the street at part throttle as posted above. As long as the throttle stays closed a fair bit, you should be ok (think restrictor plate motors).
If you don't have that kind of restraint, or if you live somewhere that E85 isn't readily available, you might see what you can find out about the engine before you get a hold of it. Large chamber heads and pop-up pistons have been fairly common in BBC engines, and that setup doesn't leave you an easy downgrade. That type of combustion chamber is also pretty sensative to detonation - lots of places flame front to reach.
If you don't have that kind of restraint, or if you live somewhere that E85 isn't readily available, you might see what you can find out about the engine before you get a hold of it. Large chamber heads and pop-up pistons have been fairly common in BBC engines, and that setup doesn't leave you an easy downgrade. That type of combustion chamber is also pretty sensative to detonation - lots of places flame front to reach.
