Also anothother thing to keep in mind. If you do indeed run 87 octane. I'd run a full tank of 93 through it before you get on it again, and reset the pcm.

 

Why even mess with your car like that. You can pick up an old used honda or toyota for ~$500 with A/C. they get 30+mpg around town and close to 40 mpg on the hiway. If the motor blows, you can get a new one at the pet store or ebay for less than $400.

It would suck *** to have to daily drive an old beater, but it would save you the gas money and make you LS1 that much more fun to drive when you do drive it.

 

I've always wondered if compression is a little over rated. A friend that does a lot of bracket racing says going from 10.5 to 1, down to 9.5 to 1 compression only looses 15 horsepower on the dyno. It seems like haveing a car that could run well on less octane would in some cases perform better than one that was pushing the limit on compression and always triggering the knock sensors. A side benefit would be you would save enough money over a year or two to buy a N2O setup.

 

It would be like $150 extra per year. considering you fill up once a week with 15 gallons of gas.

 

I think this is the best post so far. Saying $0.20 a gallon is nothing to worry about vs $150/year come across differently.

So, who wants to lose potentially dozens of horsepower, which thousands of dollars was spent to obtain, for $150/year savings?

Even if you drive a LOT, it would take so many miles to make that number something noteworthy. (BTW: I got $156 )

 

who cares

 

See signature.....87 octane always, heads are ported, milled 0.012 for 10.5:1 compression, swirl dam left in......shitcan the 2.73 gears and you'll get another 0.1 off the 60', and 0.2-0.3 in the 1/4...., so you're basically
talking about an all motor car running 10s on 87 octane....tell your '03 Cobra
friends to think about THAT!

Never knocks, even when its over 100 degrees outside here....7.24 at 94+
in the 1/8th seems like decent performance for a 2.73 geared car to me.

I agree though that the yearly "savings" in gas is not worth mentioning. The
actual problem I had here, is we only have 91 octane pump gas, not 93. So,
I shot a little too low on compression and ended up with an accidental 87 octane combo... Car made 399 HP locked on the dyno, and trap speed has increased 2 MPH since then via tuning, so I assume it makes 410+ now...

Long story short - it is possible - but not really much point in doing it....

 

Rob: That's interesting and good to see that it's possible, but you have some ricer calculations saying that it's basically an all motor car on 87 octane running 10's. You should know how difficult it really can be to improve by even one tenth when you are already pretty fast, so please don't say it's basically a 10 second car.

 

400rwhp and 2.73 gears won't net you 10's on any day. I'm suprised you are running an 11.42. I'm actually completly shocked that you aren't getting knock on 87 octane. ESPECIALLY with a heads/cam car.

 

Plain and simple you got to pay to play the game, we want power out of our toys and now that gas is ungodly high priced we are all feeling the pinch. It would be great if we could take a stand and say have the nation as a whole sat nd and say I am not paying these prices by taking one day where as many Americans as possible just didnt go to work. Shut down the workforce for a day and see how big buisness and the gov't like it. But in reality I doubt it would have any real effect !!!

 

777, I said GET RID of the 2.73 gears and then 10s blah-blah-blah.....

Heck, I never even got serious about weight reduction...A/C and 12 disc CD
changer were still in on the 11.42. I built the short block (stock, made from junk I bought from ebay and Valvegod ) 5 years ago, and the heads have been on for over 3 years. The head porter tells me he can give me another 20 HP now.....I never really have tried THAT hard yet, I'm sure a real pro tuner could pull another tenth out of it....

What I AM saying is, drop a motor like mine (preferably something designed SPECIFICALLY around the 87 octane goal, rather than it being a bit of an accident .....) in one of the 3000 lb lightweights , and it would go 10s easy....something to think about

 

Get rid of the 2.72's....still 11's. I really, really doubt a gear swap will net 0.43 or more in an 11 second car that is already pulling a 1.59 60'. And no way will they take 0.1 from the 60's.

Feel free to try and prove me wrong.


Point about the 3k pound lightweights is noted. Would be interesting....but in the end being able to save $0.20 a gallon isn't really reason enough to worry about it.

 

Enough, on the woulda-coulda-shoulda's of my car. If you read what I said, I think you see I'm really saying about 11.10-20 would be maxed out for it, without getting creative or back into the motor

Point is, such a motor is possible, and could deliver excellent performance with the heads and proper cam design to support it. Ragtop is spot-on to mention dynamic cylinder pressure is the key.

 

Read, I said this discussion is about the possibilities of running low compression not MPG. I never said I wasn't concerned about gas mileage. Believe me, if I wasn't concerned about saving a buck(MPG) then I wouldn't be concerned about the possibility of an 87 octane friendly set up.

It's easy to say just go get another car or it's not worth the savings. I was kinda hoping someone would have some insite that was a little more technial or a real life experience such as Plum Crazy Rob.

I highly doubt I would ever do a low compression set up. I just thought it would be interesting to discuss the potential to run low octane and maybe save some money. I just switched from 93 to 89 on this tank and I'm taking it easy. So we'll see how bad the mileage gets with the lower octane. I currently have 230 miles on this tank and have a little under half a tank left. So we'll see how the second half does...you know how quick it goes on the second half

Larry