98Zeric

From what I'm understanding from reading this thread, To use a motor with higher compression, with the addition of boost comes down to the fuel and the octane of it. If i want to run 11.5:1 i could, however a minimum of 93 octane would be needed, but E85 is ideal and should be safe and able to run it at10-15# safely.
If i drop the compression to a 10.0:1 i will have less of a concern of fuel octane, min 91, but of course the better the octane the better off i am no matter what compression. But i can run higher boost with the potential of making more power, while using the same octane rating for both scenarios?

NicD

iTrader: (7)

Mainly in regards to your, "What you dont wanna listen to trolls that say lower compression makes more power" comment and gave an example of where it does. And it does every single day as I hear from a LOT more people who just want to be able to run pump gas and not worry about their engine vs guys who want to push the limits because they run junkyard motors and don't give a ****. It has nothing to do with the tuner and everything to do with physics.

E85 is not the be all end all of fuel and it still has limits and when you find that limit it's usually catastrophic as with all alcohol based fuels. Not a single engine builder out there is going to recommend a high compression setup for boost even with ethanol no matter what ls1 tech says.

As I said above, not a single engine builder out there is going to recommend a high N/A compression ratio when throwing lots of boost at a motor.

Yes that's the just of it.

gsteele

Thanks. You did clarify "when throwing lots of boost at a motor" in a later quote so I wanted to be accurate. Should have used that quote.

SLOW SEDAN

iTrader: (13)

I get your crap fuel in a crap engine example, but that's not what we do on our side of the country since we aren't stuck with 91 octane. E85 is pump gas here, so a LOT more people want to take advantage of it.


Just have to define the variables, what is "lots of boost", what is "NA compression"? E85 has been perfectly happy on 10.5:1 and "higher" (NA?) compressions at 30+ PSI. Seen plenty of methanol engines run 60+ PSI (lots of boost?) over 11:1 as well.


Basically, yes. 93 or E85 will run 11.5:1 just fine, especially if you are only going to run 10-15psi then almost anything will work. If you want to run 40psi then 93 isn't going to cut it unless you drop the compression, but 91 octane isnt going to magically work at that boost even if compression is lowered.

They way I run mine is keeping boost/timing lower on pump gas, you can cruise around just fine and even beat on it and still be fairly quick. But when you fillup with E85 or even E50 boost and timing go up, still cruises fine, its just a lot faster when you mash on it.

The BallSS

iTrader: (9)

Just to add one more element to this, I've been told many times that not all boost is created equal as well.
For example 10 lbs. from a 78/75 turbo will be different than 10 lbs. from a billet S484, I'm guessing the S484 will make considerably more power at the same boost level.
Is this fairly accurate?
My old car had an old 7875 at 13-14 lbs. w/ pump fuel and I've got a couple guys saying I don't need to turn the S484 up that high to make the same power even though I intend to lol.

SLOW SEDAN

iTrader: (13)

True, and its not just the compressor making gains, going to a larger turbine makes more power as well. Car I tuned went from an S484 to a 94mm Garrett, Borg took almost 30psi to get over 1000whp, Garrett took 20psi and it was already over 1000. Garrett keeps gaining more power per pound over 30 PSI as well. Opposite is true with a small turbine, you can take that 7875 from 25psi and crank it up to 35psi and its not going to make that much more power.