octane question

w0158981 · Post by **w0158981** » Wed Nov 05, 2008 5:28 pm

soo i'm interested in the motor thats in the for sale section and have been doing sum research and i'm trying to get my head around the octane thing i read the sticky already and igot no clue lol. I'm trying to figure out if i can use that motor with 12.5:1 compression and run the highest pump gas - supreme or premium u no wat i mean anyway if anyone can point me in a direction or give me a hand it would be greatly appreciated

bone-yard-racing · Post by **bone-yard-racing** » Wed Nov 05, 2008 6:28 pm

21# injectors and or E85 would be best

Wenuden · Post by **Wenuden** » Wed Nov 05, 2008 7:50 pm

that's over his head.

simple answer is yes, but you'll end up messing up the motor. 100+ octane would be better.

w0158981 · Post by **w0158981** » Wed Nov 05, 2008 8:58 pm

Wenuden wrote:that's over his head.

simple answer is yes, but you'll end up messing up the motor. 100+ octane would be better.

lol yea it was, but when he said 21 injectors i'm assuming injectors like srt ones, hopefully i'd get better mileage then an srt lol as i'm in decision between the motor or turboing mine mpg is a huge factor

Post by **occasional demons** » Wed Nov 05, 2008 9:35 pm

MPG and turbo don't mix well, unless you do a very conservative setup. Granted for the power to fuel used the turbo is efficient, but that is if the power is also used conservatively. If you were serious about fuel mileage, 10.5:1 would be as high as I would go (N/A)and use the stock cam. That would be if you were (re)building the engine. But just how much better mileage that bump in compression would amount to IDK. Or what it would do to the NOX emmisions. Over the long haul it would prolly pay off, but how long the haul need be is the ?

Post by **racer12306** » Wed Nov 05, 2008 9:57 pm

To put it plain and simple...

A 12.5:1 motor needs A LOT of cam to be able to run pump gas. Even at that the tuning window is so small that a variance in weather could throw off the tune. For a daily driver, that engine is not for you.

Unless you have the ability to run E85 which is a mix of 15% gasoline and 85% ethanol. In which case a 12.5:1 motor would be ok on the street. You would have to do a few things to run E85, but the benefit would be great.

10.5 or 11:1 is as much as I would want in a daily driver.

Nutmeg · Post by **Nutmeg** » Wed Nov 05, 2008 10:12 pm

Could someone explain compression? What does the number mean exactly? I feel dumb for asking, and I don't really want to search around on the intraweb.

Nutmeg · Post by **Nutmeg** » Thu Nov 06, 2008 9:11 pm

occasional demons wrote:In the most basic terms, it is the difference of the volume in the cylinder/combustion chamber at the bottom of the stroke VS the top of the stroke. So a 10:1 would mean the volume at TDC is one, and the volume at BDC equals ten times the volume at TDC.

Ah okay, that makes sense. Thanks

asanti · Post by **asanti** » Fri Nov 07, 2008 4:05 pm

Can anyone sticky OD's and Racer's reply?? That's good info to know, especially for the noobs out there!

But to the OP, 12.5:1 is typically NOT a streetable mix unless you have access to race fuel and can tune the car on the fly (i.e standalone or MS). 10.5:1 is definitely streetable, 11.0:1 is kinda pushing it in most cases.

Later
Allex

Post by **racer12306** » Fri Nov 07, 2008 4:14 pm

This is about the only way I could do that....

viewtopic.php?t=36903

asanti · Post by **asanti** » Fri Nov 07, 2008 4:48 pm

That works! I'm sure it'll help someone, somehow!