SirKnightTG

How come these guys with smaller engines, like 4 cyl or 6 run turbos pushing 20psi or more on pump gas? Where I work, there's a guy with a subaru pushing 20psi through his turbo on pump gas. Of course he completely built his engine his self, stock wouldn't handle that. He's been driving this car pretty much every day for years and races it. If those little 4 bangers can handle the boost on pump gas, I don't see why built V8's can't.

modaddict

Bingo.

Phya

A lot of those built 4 bangers have rod/piston combinations that result in a low compression rates, 7.8:1 or so..

That lets them run much higher boost.

SirKnightTG

That makes sense. So in that case, in theory we could lower the compression A LOT like that and run mad boost on pump gas.

If I only had a second 8 banger that's not my DD to experiment on... Not that I know a damn thing about building engines of course...

CataclysmGT

"However, for guys pushing 14+ boost levels, they are crazy if they think they are not hurting their motor (detonation or not) running around on pump gas or even 100 octane in some cases."

This doesn't make sense. If you are not detonating with pump gas, running race gas isn't going to make your engine last any longer. In fact, it will actually wear the engine even more since your cylinder pressures are higher (hence more power with race).

modaddict

Ah - but the question is are you sure you are never having any sort of detonation? Our drive by wire alllows for a lot of paramters to happen when detontation occurs and usually long before you'll notice it (thus knock sensors) - but it occurs AFTER the detonation occurs, not before so some detonation is actually happening before your computer or tune does anything about it.

I'm not saying it's going to blow your motor, just something to think about. I don't know what the actual numbers are for our car (boost = ratio) and trying to learn myself...

fastford20

haha way to stir the waters modaddict... even though i completely agree with the concept you are talking about but maybye a diff chart would be a wise decision just trying to back you up

Phya

I might have it twisted, but as far as I know, the higher the octane rating, the more resistant to pre-mature detonation it is through compression. The OP's concerns are worth listening to.

CataclysmGT

Thats obvious....but if you are not getting any detonation with pump gas there is no extra damage occuring to your engine.
Its very easy to tell if you are getting detonation: datalog, and see what the knock sensors are doing.
There are many factory cars running 10+ psi, and of course they all use pump gas.

jaguarking11

One very small thing that does not appply to the chart is fuel enrichment. The reason our cars dont detonate with pump gas and a good tune is due to fuel enrichment, this lowers the charge temp as well as efectively increases fuel octane.

If you go backward into carbed days where fuel was delivered linearly through the jets of carbs, then the above is true. It would also be true that a nearly 10:1 compression car should ping and knock with 87 octane as well. Leaded fuel allowd 13:1 compression in the 60's through carbs.

Also e85 for example if used with a good tune, you can efectively run 500rwhp withough an intercooler and stock internals. But thats another story.

The above does not apply to our cars, higher presure will reduce engine life, unless built for it and thats a fact. Also boost is not going to be at lets say 14 psi on idle. at most it will be 0 boost and vacum with a turbocharger. With a supercharger, your engine will be at vacum.

The whole trick of the matter as far as fuel is concerned is, enrichment values that increase almost exponantioaly as the revs increase and boost increases and temp. If someone can figure out how to produce boost at lets say 0c @ 14psi you can efectively run lower octane. Its another reason our cars get heat soked. Heat soak makes the ecu enrich to the point of diminishing returns. In a carbed car, the engine would knock.

appleas and oranges.

The real weak link in our cars is not the piston, its the rods and crank. The rods are no good at above 440whp and the crank is not much better, if you are going to boost then a forged cobra crank and some good rods will make 650hp stretable to wheels on pump gas given a very good tune. Hell another manufacturer using terminator engines have built a reputation of being one of the worlds fastest cars, Koineseg does this why not a good tuner?