Cobra4B

Here's my latest dyno graph after getting tuned post cam.



Should I be fine on pump gas or add some 100 octane for summer track events?

Does't the car richen itself up as it gets hot anyway?

Any input from tuners/experienced people would be much appreciated.

Bink

You should be fine. You're fattened up before peak torque and leaned out to 13 after.
If your knock sensors are active they'll pull timing if needed - I doubt they will need to. If I remember correctly - didn't Jeff at Carolina Motorsports tune your setup?

Lawdogg

I don't know it this helps much, but mine was tuned to 12.0 due to its use at hpdes. Tuner said better safe than sorry.

0Randy@DRM

13.1 is just fine. But there are a ton more things to it then just A/F.
3 gallons of race gas is cheaper then a set of pistons.

Randy

Last C5

I'm tuned at 12.7 average for HPDEs, you should be fine.

Cobra4B

Yep... Jeff Creech tuned it for me.
Thanks Randy... I'll throw in some 100 octane in the summers at HPDEs.

davidfarmer

low 13's is my goal, you are fine.

DoingOK

It's gonna explode Brian.....parts everywhere.

John Shiels

Cobra4B

Suck my back... seriously... just suck it.

ScaryFast

Randy, why run race gas? Unless the compression on the car is high isn't that a waste of money and a loss of power?

Miguels

Richer is safer than lean correct.

I know my car is running rich....

on the race gas question.....

0Randy@DRM

I agree, it will lose a little power. But if it lives to fight more track days then I guess it's good. When running anything on the edge it's good to have some safety, 3 gallons in a tank is worth about -5 horse power.

Hot inlet temps during long use is hard on the motor.

Did you guys know that it is ok for the gas stations to have up to a 10 percent cross contamination per pump??? So that means you can have 10 percent e85, disel, 87, 89, or even water.

Randy

davidfarmer

Randy, I didn't know about the 10%, but I DID know they pump all of the fuel through the same pipelines (with no definitive break in between), so mixing certainly occurs at various stages of the processes.

Even a stock car can have some detonation, especially at high temps, so a little race gas is never a bad idea. Whether it's worth the money these days, well that's another question....

0Randy@DRM

Most of the problems are with the transport and storage of the gas.

Randy

ScaryFast

Thanks for the explanation, that's what I assumed you meant. Actually, this is something I've been wanting to talk about. If the original poster objects I can start a new thread as it's not really related...

The higher octane helps eliminate pre-ignition, but does not necessarily add power unless the engine is built for it. So my question is - what makes a higher compression engine more prone to pre-ignition and detonation, and why can't a lower compression motor get more out of higher octane?

I have a 383 motor built for track use with lots of high end power and a flat torque curve, but stock compression for longevity. It actually seemed to have more power when I ran it Saturday on 93 with a bottle of OTC octane boost. Sunday I filled up with 100 octane and it seemed to have the same or less HP...

My imprecise measureing stick is a buddy's car, we always run together and i can differentiate by how much I pulled on him on the back straight.

Timz06

Depends on how much silicon gasket maker and other junk fell into the engine during the cam change

Timz06

Gases will explode at a certain compression without a spark. With a high compression engine and lower octane fuel, the fuel reaches this point before the piston is at the spark point. Adding octane basically makes the fuel less volatile, avoiding the ignition without the spark. Thus adding octane to fuel that does not need it will do nothing, the fuel will ignite when the spark reaches it.

kelp

You could even lean it out a bit at lower RPMs.

13.1:1 is fine across the board, speaking of HPDEs specifically. Keep in mind stoich is 14.7:1. I datalogged mine and had "0" knock retard all over the maps. You can even try advancing your timing 5% at a time and see if you get any knock. But I would avoid race gas regardless.

ScaryFast

Makes sense. Thanks for the explanation.