93 Octane losing ... octane?

[Lex]

I get to see a lot of data logs and a lot of cars from different areas. I've always emphasized how the same octane rating in different areas of the country or continent can actually be quite different in terms of knock resistance.

For example, here in the west of Canada, our 94 octane is on par with California 91.

In general, 93 octane is fairly decent in most areas of the US from what I have seen in the past. Lately, I've noticed that the 93 fuel starts to knock quite a bit earlier in a few cars. Even though we are not in the swing of summer yet and temperatures are still low, I am picking up on a trend where 93 fuel (in general) is less resistant to knock.

In Canada the reason our 94 was so poor is because there was no ethanol blending. Ethanol does wonders for knock resistance and E10 fuel is probably underrated in terms of octane. The 93 probably had a little extra ethanol in it for good measure to raise its octane since ethanol was cheap. At the end of 2011, the ethanol subsidies in the US were stopped so the price for ethanol fuel went up. This can be speculation, but perhaps the 93 fuel contains less ethanol these days.

U.S. ethanol subsidy expiration may be driving up gas prices

Question is - have you guys noticed more KR lately when using the same fuel on the same tunes?

[Nliiitend1]

Don't know if it's related, but I had some KR at WOT where I'd never really had it before when I did some logs last weekend. I don't log very regularly (especially now that I've been running a nice solid Stratified Tune), but I figured maybe I had a "bad tank" and was simply going to try to flesh that theory out the next chance I got (which might be tomorrow)...

Again, this post of mine is by no means a post that is based on much evidence, but it's kinda funny that you started this thread just as I noticed this happening with my car...

[Lex]

If KR is above 2.0 I can feel it in the seat of the pants even if I'm not logging. It's like a slight hesitation.

[Nliiitend1]

Originally Posted by Lex If KR is above 2.0 I can feel it in the seat of the pants even if I'm not logging. It's like a slight hesitation.

That's what prompted the logs I took last weekend...

[UnknownSuperhero]

I was just thinking this same thing Lex.

We have been running the same tune since it was finalized when you were down for dyno day.

It might have something to do with the summer blend/winter blend as well. During the summer time there was little to no KR which I think would be opposite, since ambient temps are 100+.

Now in the winter, at wot we have been seeing frequent KR events.

I wonder if it will go away once the summer blend fuel comes into town.

[MS3-a(sore)ASS-rex]

You should also remember they advertise fuel as containing *up to* 15% ethanol. So while one fill up may contain a blend rated near E15 another could contain almost no ethanol.

The inconsistencies vary greatly.

It's a generalization that during winter less ethanol is added to promote easier cold starts for a vehicle because of the lower ambient temperatures. And vice versatile for summer months. This is where the terms "summer and winter blend" stems from.

[Lex]

These kind of inconsistencies really do suck when running a high performance tune. Let's keep an eye on this in the hope it is a winter/summer blend thing.

[sidekick]

Originally Posted by Lex These kind of inconsistencies really do suck when running a high performance tune. Let's keep an eye on this in the hope it is a winter/summer blend thing.

They really do. Same goes for ethanol blends, sometimes it may be E70 and others it may be E85, but we really have no way of knowing unless we take one of those testers with us and test it at each fill-up. It's unfortunate, but there's really nothing we can do.

IMO, if you're having an issue with KR once in a while due to inconsistencies in the gas, it may be a good idea to have your tuner make you a second map with timing retarded by a degree or two. This way you could quickly load the other map and be KR free.

[Dimenus]

I'm not sure if I'm one of the people you are referring to, but this is very interesting.

Do you keep track of (or ever ask) what brand of fuel people are using @Lex;? Maybe the larger companies might have a bit less variation vs those stations that only get the leftovers.

[phate]

Lex, are you increasing the bat/ect ignition comp tables from stock/ots values? We have consistently top notch fuel out here with Shell 93, but it still doesn't like high bats. Even a difference of 20-30* or so will cause it to ping a little bit on an aggressive tune.

My engine seems especially sensitive to bat's. On the same tank of fuel in warmer weather, it was hating the same tune and I've had to pull timing. [Now on e85 which, of course, changes the ball game.]

[sidekick]

Originally Posted by phate Lex, are you increasing the bat/ect ignition comp tables from stock/ots values? We have consistently top notch fuel out here with Shell 93, but it still doesn't like high bats. Even a difference of 20-30* or so will cause it to ping a little bit on an aggressive tune. My engine seems especially sensitive to bat's. On the same tank of fuel in warmer weather, it was hating the same tune and I've had to pull timing. [Now on e85 which, of course, changes the ball game.]

That's pretty normal for a high compression engine, I'd think. You're already compressing the air/fuel mixture more, which would put you closer to the detonation threshold. Those slightly higher BATs/IATs could definitely put it over the edge. .

Now that you mention it though, I need to look at my ECT/BAT ignition comp tables, because I'm sure I will have issues once we start getting into the 90s/100s this summer. I guess that's the downside to tuning in 40° weather. Lol.

[Lex]

Originally Posted by phate Lex, are you increasing the bat/ect ignition comp tables from stock/ots values? We have consistently top notch fuel out here with Shell 93, but it still doesn't like high bats. Even a difference of 20-30* or so will cause it to ping a little bit on an aggressive tune. My engine seems especially sensitive to bat's. On the same tank of fuel in warmer weather, it was hating the same tune and I've had to pull timing. [Now on e85 which, of course, changes the ball game.]

Yes, this is a useful strategy to have as much performance as possible in all climates especially where fuel quality is not the best.

I always recommend going to well frequented stations where the premium fuel gets used. Not mom and pop stations.

Any tune, especially a performance one, will show some KR in certain conditions. It should however not have consistent KR at WOT. If there is a significant drop in octane in general tunes that saw 0* KR will start to see some. What I am noticing is that the 93 is less tolerant timing advance. Just a general trend and wanted to get more feedback.

[rolanblack]

filled up on sunday with shell like usual. had some fun with mimmiz, brain86 and saw 2.5 kr. usually i see .3. i didnt do a log afterwards to see if it was mechanial noise though. so, this might not help your findings