Let's talk octane...
 

Admittedly, I am not a gearhead or anything really even close. I know a little about engines, how they work... just basic stuff.

Obviously when a person goes to the track, some will run race gas, I don't know how many here do, but that usually requires the tune to be for the higher octane, correct?

What is the increase in power with the increase of octane?

Some will run E85, others on here say on an NA engine it doesn't do much for the car in terms of power output. With the Evo's and being on the Evo forums for so long. They just switch to E85 and gain like 30 or 40 whp. How unfair :mad:

So what are the ins and outs with all of this? Can we make more power this way or not?

Higher octane is used on turbo cars to turn up the boost safely. I ran 27psi on a stock f20 by running c16.


On an NA app, you can advance the timing some, but there aren't usually huge gains t be had from adjusting timing.

ok, well what about the VVEL? Can the Z's timing even be adjusted because of that? How much NA power could be had by running 100 or more octane?

I haven't spent a lot of time checking out datalogs for the Z, but I highly doubt there is much to be gained by running high octane gas-- probably not enough to make a substantial difference.

When you're switching from one octane to another, you need to siphon out all of the previous fluid correct? Mixing the two = vewwy bad??

not necessarily. Of course, running your high octane tune and getting a load of 93 into the engine can be risky.

I ran mixes of C16 and pump gas with no issues.

With that being said, is there say a noticeable difference you could sense that you knew it was time to switch from say a 93 octane map to the racing fuel octane map or vis versa?

:confused: Why would mixing high octane with a regular octane be possibly risky?

Octane is nothing more than a measurement of a fuels resistance to detonate. Higher the octane, higher the resistance.

You could, in theory, cruise around in a 370 with 87 octane...but if you even think about putting a load on the motor, your odds of running into trouble are high.

E85 is great if your car is setup for it: it burns cooler, has a higher overall octane, and its cheap. Assuming you make sure your source is ACTUALLY E85 (and not, for instance, E70 or whatever they run in the winter in many places...), then in essence, its race gas on the cheap. However, its downside is obvious: to get the same amount of energy from E85, you need to burn something like ~30% more fuel to get the same effect as pure gasoline of the same octane. None the less, E85 will still be cheaper overall, over race fuel.

So, when your running forced induction, you can keep raising your boost thanks to the higher octane, and go for a more aggressive tune with E85. Obviously, raising boost is a very quick way to gain power, hence why anyone who has a 335i, WRX, or Evo do these mods very quickly (along with the good breathing mods, of course).

On the 370, all you could do really is advance your timing and squeak out a little bit of extra horsepower, but (like Zed's already said), you wont be seeing a huge gain at all in our car - its pretty efficient as it is.

some fuel formulations don't blend well together. And running the aggressive map when it's not suitable puts you at risk of detonation.

On my car, it wouldn;t run on 93 with the c16 map.

If your tune is for...say....93 octane and its a VERY aggressive tune...but you can only source 91 octane at the time? That could be risky.

Other than that, with a comfortable tune, I see no reason why it'd be risky.

So your range per tank goes down considerably using E85 due to needing more fuel per cycle? So larger injectors are a must?

Correct.

Gotcha. I've run FI before, but I've never tuned for anything above what I could get at the local pump.

Since larger injectors will come with any Z TT kit, could you theoretically convert to E85 at the time you went TT? Or would you need even larger injectors than the ones that come with the kit being the kit has already compensated for the extra fuel needed for TT?

If I were running FI, I'd make sure my system I had could handle multiple tunes on the fly, based off boost/octane. That way I can change to whatever I have available at the time...

Fuel saver tunes are nice, too :)

Depends on the injectors, but I'd hazard to guess you'd need to go even BIGGER. I dont know how close we are to maxing out the stock injectors with only basic breathing mods off hand, but I doubt any FI kits are going to come with HUGE injectors - just enough to handle the max HP of the kit. Whereas with an E85 setup, you'd need injectors 30% bigger than THAT, really.

Also, cant forget the fuel pump...one that can at least keep up w/ those injectors...

Of course, once you know how much you'll be 'injecting' then you know how much fuel you need, in terms there is your pump size required so you get that as well. Interesting... Soooo much involved with just switching gas lol.

Theres a lot of science behind setting up a proper fuel system. You'd think you can just add a pump, but sometimes even just one pump isnt enough for an E85 setup. I should see if I can find my friends crazy *** home-made pump setup for his garage built, TT 427. He already had a 1100HP/1000Tq twin turbo Silverado, and sold it...

so back to my other question... since the VVEL cannot be changed, can the timing of the engine still be changed? Basically i'm saying... if I wanted to run race gas for a run down the 1/4 and I needed to tune for it, can the timing be advanced due to the higher octane to maximize power? OR is that all part of the VVEL?

When you get into a situation like that, do you have 2 pumps in line with eachother, a smaller one to feed the larger one? Or would that give you starvation issues? Would you instead have 2 separate fuel lines, 1 for each bank with their own pump/filter?

There's many ways to handle it. Sometimes 2 inline pumps is one way. Other times, 2 pumps maintaining pressure is another way, sometimes multiple fuel lines going into rails is another. Like I said, lots of science :)

You can advance timing within certain limits.

like most things, it depends on what you are doing. the other thing you have to watch for when setting up for e85 is corrosion in your fuel system, which often requires running different components than what TT kits come with (not that familiar with Z kits though)

I dunno, but all of it sounds really cool, the R&D of it.

Would be crazy to see.

Would the VQ37 be a platform that you'd wanna see in E85, or the fact that it's not boosted and VVEL limitations would make it a waste of time?

VQ37 in stock form, N/A with E85 is a waste of time, IMHO.

Boosted however, you can get gains. But I question the worthiness of such gains other than flexing the e-penis size...

This is what I was thinking... You'd need a huge budget to R&D a worthwhile E85 TT kit for the Z I'm guessing...

Why do you say that? Bigger injectors, good fuel setup to feed it....thats it. The rest stays the same really...

Hmm. I was thinking there would be more involved, say different sized turbo's due to smaller volume of gasses?? I dunno... :icon17:

Found it...

http://www.neufamily.org/images/67novagallery/

Nope...the amount of air burned for the power remains the same really. Just the amount of fuel required to ignite it properly changes.

Octane refers to how easily the fuel will spontaneously ignite, as in from heat or pressure (which also increases heat); the higher the number, the less likely to auto-ignite.

Ideally, we want the fuel mixture to only ignite when there is a timed spark event. If it ignites at the wrong time, the force can turn the crank the wrong way (bad), and otherwise put tremenous shock and stress on the engine internals -- this is essentially what knock (preignition or detonantion) refers to: unplanned auto ignition of the fuel that can damage the motor from the stresses it creates.

Higher heat and cylinder pressure (affected by boost and piston CR, as well as timing advance -- spark events tend to have flame kernels that keep high heat on the piston, thus more timing, also means more in-clyinder heat that doesn't have as much time to dissipate before the next rotation) increase the likelihood that the fuel will auto ignite, so for applciations with higher CR's, boost (or even excessive heat under load), a higher octane is generally necessary (DI sytems can get around this somewhat, thanks to the super fine atomized high pressure fueling mix it creates and the ability to spray directly and precisely into the cylinder -- but that's another story).

There is a bit of a down side -- really high octane fuels are harder to ignite even when you want to -- thus a 120 octane fuel in a DD might be hard to turn over on a cold morning, and be more prone to misfires, whereas on a boosted, high CR track car that might work very well.

In general, there are no direct benefits running a hgiher than needed octane -- again, octane is all about preventing knock. The extra power is all based on cylinder pressure in the piston or engine speed, so unless you are running more timing, boost, higher CR pistons, etc, that might require a higher octane to run safely, it's not needed.

As a precaution on a very hot day (again, in-cylinder temps increase the chance of knock), running the car at constant high load on the track, the extra octane might be a reasonable precaution, in that it will prevent power loss/damage from possible knock events, but it will not give you any additonal power than you were already capable of making given your tune.

Incidentially, that is also why tuners will find better power on boosted cars by running a bit richer a mixture -- the extra fuel is not fully burnt, rather it just cools the piston, reducing heat, and therefore quenching possible knock.

Anybody want to add to/amend that?

good post... very informative. I started this thread because it seems like the exhaust/intake part of our engines is pretty well maxed out, so perhaps we could look to fuel to somehow add more power. I personally don't want to go FI... I also don't have the money to do so right now and if I did have it I wouldn't spend 10 grand to do it. The intakes are about as good as they are going to get. Motordyne's manifold, while very well made is sort of hit and miss from one car to the next... no cams because there is no VVEL crack... in general there isn't much left to do I guess.

good post, good info. Octane is always one of those confusing specs for most people. Maybe we should try and get a reference thread together for info on fuels if people would find that helpful?

If you cant get more air into the motor, adding "better" fuel is a waste of time anyway.

so any idea on how to get more air?

http://www.roadraceengineering.com/p.../pte_turbo.jpg
Honestly, doing lots of "little things" to add power is just not the smartest path to take. You spend almost as much as you would to go FI, and it leaves the car just as (if not more so) unreliable as it would be with boost.

Ok, I had a GT500 before my Z and have tried every fuel possible. Heres What ive found.

Basics of higher octane, allows you to safely run more advanced timing without the fear of detonation. So it is more valuable on forced induction cars than NA builds because the FI have more to gain off timing changes. So now to the options

1. E85. corn fuel. Its cheap and has and advanced level of octane far exceeding regular pump gas. Advantages = more timing, more power, CHEAP! Disadvantages = very VERY corrosive, upgraded fuel lines, pumps fitting, and injectors required. hard on motor, hard to come by in some places

2. C16. 116 octane. come in 2 variants, leaded and non-leaded. non leaded required by cars WITH catalytic convertors. Advantages = BIG power, smells awesome (opinion i guess), basic fuel system upgrades required Disadvantages = Very Expensive, Terrible economy

3. 100 octane. sold in some gas stations same advantges as above but with basic tuning can be run on stock fuel system.

Know for the curve ball!!!
Methanol Injection! allows you to run advanced timing on pump gas! basically increases the effective of octane of what ever is in the tank. Advantages = Its washer fluid so its cheap! Horsepower. Disadvantages = Seperate methanol system required for us (pumps, lines, tanks etc...) when you run out car can bnecome unsafe (if its tuned for the Meth and it doesnt get it you have problems)

So in conclusion (sorry fo rthe long post) there are advantages and disadvantages for all fuels. You gotta choose whats right for you. But as a rule of thumb, NA cars dont need to super high octane 91-93 is generally good enough

There are a lot of people who will tell you methanol injection on an NA motor isn't going to do a whole lot... i've done a lot of looking into it myself.

It wont for the sheer fact that the timing adjustments where the enhanced ocatane levels that methanol will let you achieve wont make a big difference on an NA car. you could pick up maybe 5-10 WHP MAYBE but with the price of the kit and all the tuning required to make it run well wouldnt be worth it at all. your looking at 500 for a basic Kit then install then who knnows how many hours of tuning. Id never put it on an NA car

maybe with ITBs:excited: