Custom tunes safe for track usage?

[dradernh]

Originally Posted by ddeflyer

...other engines are still likely to benefit from higher octane gas when on track.

I've got an 11.3:1 BMW Motorsport engine in my race car with cams, headers, an intake, a MoTeC ECU, and it's tuned on 93 octane. I've put in higher octane when at the track and I didn't want to go into town for more fuel. I can tell you it makes no difference in how that engine performs.

I think if what you're suggesting were generally true, the line at the race gas pumps at the track would be seriously backed up; instead, almost no one is using them. Not back here, anyway. If BMW and Porsche drivers thought they could get a performance boost from race gas, they'd be lined up for it - the cost isn't going to stop them.

Originally Posted by CSG Mike

The only other car I know of this high is a 458 Italia, and I'm willing to bet a 458 owner isn't going to track on 91 octane

I seem to recall that 93 octane is not available at the pump in Southern California - is that correct?

[ddeflyer]

Originally Posted by dradernh

I've got an 11.3:1 BMW Motorsport engine in my race car with cams, headers, an intake, a MoTeC ECU, and it's tuned on 93 octane. I've put in higher octane when at the track and I didn't want to go into town for more fuel. I can tell you it makes no difference in how that engine performs.

I think if what you're suggesting were generally true, the line at the race gas pumps at the track would be seriously backed up; instead, almost no one is using them. Not back here, anyway. If BMW and Porsche drivers thought they could get a performance boost from race gas, they'd be lined up for it - the cost isn't going to stop them.


I seem to recall that 93 octane is not available at the pump in Southern California - is that correct?

CA only has 91 and it is supposed to be shitty 91 at that.

I am a little surprised that other cars don't benefit from higher octane, I've read about people wanting higher octane for some BMW engines. In the end though, I can only speak to my own experience that a little race fuel gives a small boost in power.

[ddeflyer]

Originally Posted by Sleepless

12.5:1 is not a big deal for a direct injection engine. I have not problem running 91 at the track. I tried a tank with 50/50 mix of 91 and 100 and found no performance advantage.

Our engines are both direct injection and port injection. DI can improve things by later introduction of fuel and also more controlled flame front via the more refined/controlled fuel dispersion cone. High load conditions make more use of port injection which does not have those knock resistant properties.

Also, the manual says that you can run 91 without damage. When they say this it is going to be a probabilistic statement based upon some number of cars having their lifespan shortened by a tolerable amount. These conditions are almost certainly considered with fairly normal driving patterns, not race track conditions. With the introduction of higher heat loads you very well might shorten you engine's lifespan by an appreciable amount. If you are not running an oil cooler the extra stress is even more pronounced.

Remember also how the engine deals with knock; it pulls timing. Pulling timing reduces the dynamic compression ratio of the engine (and with it charge density and associated heat). This reduces the amount of power you get. I absolutely can feel that difference. It could be my engine is more prone to knock than yours, it could be CA gas, it could be that my driving is more sensitive to small power changes or maybe I am more sensitive. I really don't know. It is noticeable to the point that I have forgotten that I put a half tank of 100 in before lunch and then wondered in the next session why I am picking up extra speed out of a corner when general conditions should be reducing my speed.

[OkieSnuffBox]

Originally Posted by CSG Mike

It's a twin specific thing; we have REALLY REALLY high compression for a gasoline engine.

The only other car I know of this high is a 458 Italia, and I'm willing to bet a 458 owner isn't going to track on 91 octane

Add forced induction into the mix, and you really should be running 100 octane.

Mazda SkyActive 13:1 in the US, 14:1 in the rest of the world.
Ferrari LaFerrari 13.5:1
458 Speciale 14:1

[CSG Mike]

Originally Posted by dradernh

I seem to recall that 93 octane is not available at the pump in Southern California - is that correct?

That is correct. It's also laced with Ethanol (10-15% depending on luck of the draw...), and tuning for CA 91 requires you to take that into account.

[CSG Mike]

Originally Posted by OkieSnuffBox

Mazda SkyActive 13:1 in the US, 14:1 in the rest of the world.
Ferrari LaFerrari 13.5:1
458 Speciale 14:1

The SkyActive is an economy engine; both output and redline are significantly lower than the FA20. If we lowered the FA20 to those specs, we'd have no issue either...

[ddeflyer]

Originally Posted by OkieSnuffBox

Mazda SkyActive 13:1 in the US, 14:1 in the rest of the world.
Ferrari LaFerrari 13.5:1
458 Speciale 14:1

As much as I love the idea of being comparable to a Ferrari, I don't think we can realistically compare the FA20 to those engines.

The SkyActiv on the other hand is something worth comparing. For that you should consider that it is a purely direct injected engine which tends to yield more controlled deflagration of fuel than port fuel injection. This combined with (from a quick google I think they have) continuously variable valve timing and valve lift with independent exhaust and and intake controls gives much better control over chamber temperature and dynamic compression ratios than we get with our engines. They might have a higher compression ratio, but they have control systems that facilitate that.

Also, most of the SkyActiv engines are not being tracked. They aren't usually being asked to operate in the 5-7K RPM range for 25 minutes straight five times a day (or worse). Even if you do track those engines I've heard they have a broader torque curve so you don't have to brutalize it as much as the FA20.

[OkieSnuffBox]

Originally Posted by CSG Mike

The SkyActive is an economy engine; both output and redline are significantly lower than the FA20. If we lowered the FA20 to those specs, we'd have no issue either...

My point is that it shouldn't be a problem to make a tune that works on the track with 91/93 octane.


Will you have to give up some power? Yes.
Is 8hp at 7300rpm worth the engine not going "boom?" I think I'd probably answer yes as well.

[CSG Mike]

Originally Posted by OkieSnuffBox

My point is that it shouldn't be a problem to make a tune that works on the track with 91/93 octane.


Will you have to give up some power? Yes.
Is 8hp at 7300rpm worth the engine not going "boom?" I think I'd probably answer yes as well.

Oh it's a lot more than 8hp.

Don't fool yourself into thinking those Ferraris are reliable on track, because they're not.

[OkieSnuffBox]

Originally Posted by CSG Mike

Oh it's a lot more than 8hp.

Don't fool yourself into thinking those Ferraris are reliable on track, because they're not.

How much do the engines have to be down tuned to not "pop?"






(I couldn't care less about Ferrari reliability since I don't own one.)

[CSG Mike]

Originally Posted by OkieSnuffBox

How much do the engines have to be down tuned to not "pop?"






(I couldn't care less about Ferrari reliability since I don't own one.)

That's data that only Subaru and Toyota would have.

[chrisl]

Originally Posted by CSG Mike

It's a twin specific thing; we have REALLY REALLY high compression for a gasoline engine.

The only other car I know of this high is a 458 Italia, and I'm willing to bet a 458 owner isn't going to track on 91 octane

Add forced induction into the mix, and you really should be running 100 octane.

The E92 M3's S65 V8 has 12.0:1
All naturally aspirated 991 911 models except the GT3 have 12.5:1
The 991 GT3 has 12.9:1
The 997 GT3 RS 4.0 has 12.6:1
The 981 Cayman/Boxster (all 3 engines) has 12.5:1
The R8 (all 3 engines) has 12.5:1
The Lamborghini Aventador has 11.8:1
The Lamborghini Huracan has 12.7:1
The 918 Spyder has 13.5:1, as does the LaFerrari (though now we're getting into silly expensive territory)

If you look at motorcycles, it's even easier to find examples:
The BMW S1000RR has 13.0:1
The Ducati 1199 Panigale has 12.5:1
The Suzuki Hayabusa has 12.5:1
The Yamaha R1 has 12.7:1



Admittedly, these are all substantially more expensive and exotic than the BRZ (or are motorcycle engines), but it isn't as outlandish of an engine design as you're implying. I know a lot of 981/991 owners who happily track their cars on 91 octane, and I haven't heard of any problems related to it.

[Sleepless]

Originally Posted by ddeflyer

It could be my engine is more prone to knock than yours, it could be CA gas, it could be that my driving is more sensitive to small power changes or maybe I am more sensitive. I really don't know. It is noticeable to the point that I have forgotten that I put a half tank of 100 in before lunch and then wondered in the next session why I am picking up extra speed out of a corner when general conditions should be reducing my speed.

Interesting... I did my test in CA at Thunderhill. My butt dyno didn't notice a differences and neither did my lap times (3:57 on the 5 mile on AD08s). What I notice the most is the gradual loss of power as the ambient temps go up. I did 91 octane in the morning and mixed with 100 octane in the afternoon which was much warmer (90F) and that may be why didn't notice a difference. I will try again when I get the opportunity.

[ddeflyer]

Originally Posted by Sleepless

Interesting... I did my test in CA at Thunderhill. My butt dyno didn't notice a differences and neither did my lap times (3:57 on the 5 mile on AD08s). What I notice the most is the gradual loss of power as the ambient temps go up. I did 91 octane in the morning and mixed with 100 octane in the afternoon which was much warmer (90F) and that may be why didn't notice a difference. I will try again when I get the opportunity.

You didn't happen to be doing the five mile last Friday with the blue BRZ in group D, did you?