Question

[bh2285]

Can you run pump gas on 11:1?

[ELewandowski]

yes, I run 87octane on my 440ex. Only cause gas is so expensive, I would wun higher if i could.

[AR15 guy]

The new 450r's have 12:1 and you can run pump gas with them. So 11:1 is definetly safe.

I always run 93 octane in mine. It isn't that much more expensive. You are talking about an additional 30 cents to fill up your tank over 87.

[GPracer2500]

11:1 on premium pump gas is borderline. You're probably fine but may still get some detonation under certain circumstances. Many report no ill affects from running 93 with 11:1. I have to wonder though, how many people are experiencing some mild detonation and just don't realize it? I can almost guarantee that 87 w/ a 11:1 piston would detonate pretty heavily. The 400EX engine--being the tough little guy that it is--will put up detonation for a while. But even mild detonation will eventually make itself known by way of heavily worn (if not catastrophically failed) engine parts.

I can't run 91 on my 10.8:1 piston without getting detonation under heavy load. If 93 was available in my area, I think I'd be ok on that.

The variance between how one guy gets zero detonation with 93 or 91 and an 11:1 piston while another guy does get detonation is because that compression ratio isn't the end-all-be-all factor in what causes detonation. Dynamic compression is what really matters, not static compression (static comp is represented by 11:1, 10:1 or whatever). Dynamic compression changes as elevation (as in elevation on the earth--air density is the real factor here) and cam specifications change. Intake valves with lots of duration and higher elevations both conspire to lower dynamic compression. And then there's igintion timing, ambient air temperatures, engine temperatures, and air/fuel ratios: they all play a part in the likelyhood of detonation occuring or not for any given fuel.

The point about the 450s having high compression and being able to run premium pump gas doesn't mean squat to a 400EX. The biggest difference is air cooling vs. liquid cooling. Liquid cooling is so much better at drawing heat away from the edges of the combustion chamber that liquid cooled engines have completely different compression ratio and fueling requirements. It's apples and oranges.

[bh2285]

Thanks alot...your the best.

[jsmith2232]

GPracer2500 has got it down,
air cooled motor can run 93 octain up to 11.1:1 comp
liquid cooled motor can run 93 octane up to 12.1:1 comp

[ELewandowski]

After this new info to me, I think i will start running higher octane, I would hate to mess something up after i finally got my quad running again. Is it better for the engine to run 110 Turbo Blue over 93 octane.

[GPracer2500]

Originally posted by ELewandowski
After this new info to me, I think i will start running higher octane, I would hate to mess something up after i finally got my quad running again. Is it better for the engine to run 110 Turbo Blue over 93 octane.

I mentioned before that compression ratio isn't the only variable dictating octane requirement. But it is the single largest variable. What compression ratio is your piston? If it's over 11:1 than I would be wary of running straight 93. If it's 11.5 or 12 than you could experiment with running a race/pump mix.

An engine only wants whatever octane is needed to prevent detonation. Any higher and the extra octane does nothing. But also realize that racing fuels generally distinguish themselves from pump fuels by more than just octane rating. The addition of lead (usually), faster burn rates, and higher quality control are typical benefits racing fuels offer over pump fuel (and there can be other benefits too). So, extra octane beyond what the engine requires offers no benefit--but racing fuel can be beneficial for reasons that have nothing to do with octane ratings.

For the most part, an engine will tell you if it's getting enough octane rating. The 400EX engine is fairly obvious in announcing the presence of major detonation. It sounds like a "knocking" or "pinging" noise. It kinda sounds like banging two big rocks together underwater. It's also slightly irregular in frequency (i.e. there might be several clatters spaced very close together and then a couple more spaced farther apart). What you're actually hearing is a supersonic pressure wave slamming into the internals of the engine and causeing the whole area to reverbarate. It's quite violent (even compared to what normally happens inside the combustion chamber).

It's most likely to happen when the engine is hot, the air temperatures are warm, and under a very high load (like when you're pulling up a hill at WOT in a higher gear). Usually there will be indications left on the spark plug after detonation has been happening. But it takes an experienced eye to pick up on those clues.

The tricky part is that the sound of detonation is often dismissed as valve clatter or some loose piece on the quad somewhere. The first times I heard it on my 400EX I couldn't figure out what it was. At first I was convinced that it was my exhaust rattling--it wasn't.

So, to answer your question: There might be some minor benefits to running racing fuel, but if your engine is not detonating with 93 under the worst of conditions, than there is no benefit to having 110.