OK...lets talk about high octane fuels and your car

[FNBADAZ06]

Very, VERY, cool.

I know I'll need to ultimately get HP Tuners to get a complete answer on some of the things we've talked about regarding fuel, but what I've seen so far in my limited logging, the performace numbers at the track, and your detailed response on the subject...I'm comfortable in knowing I'm extracting everything I can out of the stock tune, and with a few minor tweaks in the fuel mixture I'm putting in the tank...I'm probably sneaking a few extra ponies out of her as well.

[Two Fangs]

The technical term for that is a "Happy Accident". Good job, and congratulations. They are much less frequent than the "unhappy" variety. I am very impressed with your exploration of the "why" behind the "what". I'll see you tomorrow at lunch.

[Blk n Blu]

Thanks for the good read V & P.

[FNBADAZ06]

Check this out......

All were mixed roughly 1 gallon 100 octane VP fuel (R+M/2=100) to approximately 2+ gallons of 91 octane pump gas. I try to keep my fuel load to 1/16 tank...1/8 max.

My best ever 60' times

Pay attention to the 1/8 split numbers

My previous record run of 11.11@124 set at SW earlier this year on a 1.63 60'. I'm #57

Density Altitude: 320 feet

Relative Density: 99.07 %

My 2nd best run (IIRC) with HOXXOH that same weekend race when I went 1.59 60' and 11.16@122 ...I'm #57, and Tom is #79 when he set his then PB of 11.06@124.72

Density Altitude: 524 feet

Relative Density: 98.48 %

My best run at Sacramento on 1/15/2011 at 3:30 p.m. of 11.203@124.408 ....granted, I was having shifting issues for the 1-2 shift. Car had the passenger seat removed, which saves me an additional 40 lbs.

First time I touched 99 MPH in the 1/8 mile split

Density Altitude: -943 feet

Relative Density: 102.79 %

60'-----1.706

330'----4.765

1/8th---7.273

1/8th---99.110 MPH

1000'---9.413

1/4-----11.203

1/4-----124.408 MPH

Now, November 2, 2011.....2 gallons of Sunoco GT+ with a R+M/2 octane of 104, mixed with approximately 2 gallons of Shell 91 octane pump gas. This gave me just between 1/8 and 1/4 tank of fuel. New PB on 1/8 split , new PB on ET and MPH.....all on totally inferior air by a long shot !!! I was well above 99 MPH on 4 of the 7 runs I made that night...even with 60' times of 1.66 to 1.73

Density Altitude: 1595 feet

Relative Density: 95.41 %

My best 1/8 MPH that night was a 99.62.....nothing slower than 98.72 MPH that entire evening, and that was because my ECT's were well above 215* on that particular run

The 1000' MPH wasn't working that night, and my higher MPH trap speeds are due to that I can carry 4th gear thru the traps now...instead of running out of MPH in 3rd gear on the rev limiter at 7100 RPM.

I don't know if this fueling strategy would work for LS1/LS2/LS3 cars, as they have lower compression, a smaller bore, maybe even the lower red line (shift point) may contribute....but it definetly works (IMHO) on the 11:1 compression, 7000+ RPM, big bore LS7 car

[Two Fangs]

That is some very interesting data. I would be interested to see how it worked in other LS engines.

[FNBADAZ06]

That is some very interesting data.

I would be interested to see how it worked in other LS engines.

I'm still searching for my data logs for the SW January runs to show the comparison on the IAT, ECT, RPM, and Timing...as compared to my runs the other night. I can tell you the IAT and ECT were well below the temps I was seeing on November 2's runs.

Timing the other night maxed at 24.5 or 25 total....I'll have to look at the log again. Too bad I can't monitor MAF in g/sec like you suggested.

[Two Fangs]

While I log much more data than this when I am tuning, here is what I have set up as my gauges in HPT for at-a-glance capabilities.

[FNBADAZ06]

Uh, yeah....that's a wee bit beyond Rev But, for a cheapy program it does pretty good....still need to step up to HP Tuners to really get the lowdown on my car's operation.

[Z06_Mir]

Bijan has HPTuners and we have spent some time logging my car and its tune (he didn't do the tune). Yes, it pulls quite a bit of timing, and some of that timing pulled can probably be attributed to the 91 octane that we get here. One of these days I will see if he will log it with 91 first, then a mix of 91 and unleaded race fuel. I know it would be more helpful with a stock tune but it would still be interesting to see. My butt dyno told me that last time I mixed race fuel with 91 the car was a lot quicker, especially in the heat. In a nutshell, I have very little to add but I'm enjoying learning from you smart folk!!

[Two Fangs]

Uh, yeah....that's a wee bit beyond Rev

But, for a cheapy program it does pretty good....still need to step up to HP Tuners to really get the lowdown on my car's operation.

Just trying to hit you with the hard sell, LOL

Bijan has HPTuners and we have spent some time logging my car and its tune (he didn't do the tune). Yes, it pulls quite a bit of timing, and some of that timing pulled can probably be attributed to the 91 octane that we get here. One of these days I will see if he will log it with 91 first, then a mix of 91 and unleaded race fuel. I know it would be more helpful with a stock tune but it would still be interesting to see.

My butt dyno told me that last time I mixed race fuel with 91 the car was a lot quicker, especially in the heat. In a nutshell, I have very little to add but I'm enjoying learning from you smart folk!!

Interesting, more data for the pool....

[FNBADAZ06]

Bijan has HPTuners and we have spent some time logging my car and its tune (he didn't do the tune). Yes, it pulls quite a bit of timing, and some of that timing pulled can probably be attributed to the 91 octane that we get here. One of these days I will see if he will log it with 91 first, then a mix of 91 and unleaded race fuel. I know it would be more helpful with a stock tune but it would still be interesting to see.

My butt dyno told me that last time I mixed race fuel with 91 the car was a lot quicker, especially in the heat. In a nutshell, I have very little to add but I'm enjoying learning from you smart folk!!

Actually, Mir...I would think your car could take GREATER advantage of the high octane fuels, as you have a modified tune already.

Remember....my two points I was trying to stress were this:

1) When you can identify that 91 octane pump gas is NOT suffiecient to ward off KR when ECT, IAT, and other mitigating factors are controlled, a mix of high octane racing gas can be the solution. You only need as much octane as needed to keep from getting pre-ignition or knock/ping....high octane in itself does NOT produce any additional HP.

2) On a STOCK tune, the use of highly oxygenated "racing fuel" has the potential added benifit of leaning the pig rich A/F at WOT when the LS7 motor goes into open loop operation, while simoltaneously providing AKI protection....I just can't read A/F with a WB yet to see exactly where I'm at. Your modified tune may already be configured for a different A/F from stock, and depending on how leaned out your current tune is, running highly oxygentated fuel like I'm using may create a dangerously LEAN condition for you .

Log the data and see where you're at with your current tune and go from there

[Buccaneer]

Neat stuff guys. I'd love to see what your A/F is at WOT with both mixes since around 12.6 would be about ideal with a few other things thrown into that figure. But its what ever the motor wants/needs which would be correct. BTW...Is this thread considered a HIGH TECH post?

[Cross]

For those mixing, I am jumping in here on the second page as this is where the view new content put me, why not mix E85 instead of Race gas? Just curious on why your going with Race gas when its so much more expensive than a cheaper alternative like E85.

[Z06_Mir]

For those mixing, I am jumping in here on the second page as this is where the view new content put me, why not mix E85 instead of Race gas? Just curious on why your going with Race gas when its so much more expensive than a cheaper alternative like E85.

E85 is a different fuel all together. You can't mix E85 because it combusts differently and it actually takes more fuel to equal the same amount of race gas..... if that makes sense. That's why when you go to E85 you usually need larger injectors and a fuel pump.

[Buccaneer]

For those mixing, I am jumping in here on the second page as this is where the view new content put me, why not mix E85 instead of Race gas? Just curious on why your going with Race gas when its so much more expensive than a cheaper alternative like E85.

E85 is a different fuel all together. You can't mix E85 because it combusts differently and it actually takes more fuel to equal the same amount of race gas..... if that makes sense. That's why when you go to E85 you usually need larger injectors and a fuel pump.

...unless you can run FlexFuel.

[Z06_Mir]

For those mixing, I am jumping in here on the second page as this is where the view new content put me, why not mix E85 instead of Race gas? Just curious on why your going with Race gas when its so much more expensive than a cheaper alternative like E85.

E85 is a different fuel all together. You can't mix E85 because it combusts differently and it actually takes more fuel to equal the same amount of race gas..... if that makes sense. That's why when you go to E85 you usually need larger injectors and a fuel pump.

...unless you can run FlexFuel.

But for the purpose of this discussion we're talking about our LSx motors, which are not FlexFuel capable from the factory ;)

[Cross]

It requires more but the PCM is smart enough to see that need as I understand it. Once the PCM see's the changes in the fuel system once combusted its making adjustments same as it is with you running Race gas. The difference here being it will add more fuel. Now mixing should be fine and there is a lot of data on many different cars as well as just on LS1tech about mixing in amounts of E85 and how much the stock tune can take. Remember our stock PCM will make adjustments up to 25% before it throws a code (Fuel Trim Adjustments). Since your not doing the full switch like I did (And I think I found a way to get the Vette to be a real Flex Fuel vehicle using a 411 PCM, the sensor and running the wires) you should be able to do a mix, gain the higher octane and possible better characteristics against Knock and not spend 6-8 a gallon on Race gas. Its not something I am trying to bash at but frankly many things said about E85 turn out to be speculation. Such as my use of E85 NA got a lot of negative feedback here with locals (Not on this forum per-say) However once put on the Dyno next to an LS6 with a much bigger cam, Fast 92 and Nic Williams TB he put down 365 I put down 385. He had a lot of nicer items than I did. We both want to go again and I am playing with the tune now as I still think its too rich. I have been trying to tweak it on my own this time though as even with me not being familiar with HP Tuners with Megasquirt and Tuner Studio I have always done my own tuning and all the cars I have done are not only still on the road today but the owners love them. Tuner Studio compared to HP Tuners is a big change though... I have a lot to figure out to accomplish the little things I want to. (Idle, Leaner running etc) Anyway just where my experience and bases for my input is coming from.

[Two Fangs]

I am intrigued to know where you are setting your stoich values when you are doing all of this mixing. Additionally,could you please explain "Once the PCM see's the changes in the fuel system once combusted its making adjustments same as it is with you running Race gas." Because I am not following. Cheers Parker

[Jon]

The GM flex fuel vehicles have a sensor that tells the ECM what it's getting. There is a GM Hight Tech that I noticed an aftermarket version you can add on. I'll have to see if I can dig it up. Let me see if I understand some of what's been said. If you use a fuel with a lower stoich, like 13:1, you effectively lean out the mixture because the computer is still trying to maintain it's rich value of 11.5:1(or whatever GM puts it as) against the programmed 14.7:1 stoich value. So if you stay at 11.5:1 and stoich is 13:1, you are closer to stoich and thereby leaner?

[Two Fangs]

Yes and no. The PCM can adjust during most normal driving conditions, because the O2 sensors will adjust (to a degree). Where things get sticky is when the vehicle goes into open loop during hard accel (the PCM then ignores the O2 sensors) and the fueling is then controlled by preset data and multipliers known as EQ ratios. What we have ruminated about in this thread is how a slight change in stoich has indeed created a slightly leaner, yet knock protected condition that has enhanced performance. I think this is where Cross got confused, in that we are talking about subtle changes in stoich, but big changes in performance. E85 requires very large changes in stoich and different engine management protocol. E85 is cool enough, but that discussion probably deserves its own thread.

[Ted Y]

I definitely recommend starting a separate E85 thread to keep this one focused.

[Cross]

I wasn't talking about adding large amounts but I can link the threads I spoke of. What I took that we are talking about here is raising the Octane level to provide a safety net and possibly net more power. Race Gas is very expensive and your mixing what amount I would say around a 40% amount correct? The most I would mix of E85 would be 4 gallons in a 18.46 gallon C5 (According to the information from GM and HP Tuners preset for my vehicles tank sizes put together) thats 14.46 91 + 4 E85. So that would be less than 25% . What you gain would have to be calculated going beyond that well since I run complete E85 I never really tested this on the Vette only on other vehicles. However What we have here is the ECU see's a condition that it does not expect as the O2's are still trying to compensate for the set afr in the PCM stock tune were saying is being used here. (Which I mentioned being what were sticking with as well, a completely stock tune and injectors if I need to specify) Once is see's that number change it will compensate for it. Now the Open Loop under WOT issue was honestly one I have never seen a PCM do but again my experience tuning with HP Tuners and how this PCM reacts is not nearly extensive and I would have to research that this actually happens. In MS this does not it goes by the tables and AFR the whole time. With adding E85 to raise the Octane you probably will see a loss of gas mileage to a degree but then it costs less than 3.25 a gallon vs race gas's cost and you can use it for the same purpose. I can go look for the threads of actual tests running this on a stock pcm with no changes but it would mainly be F-Body's doing it. I read through quite a few threads on this before I made my switch. I am by no means an expert this just started out with asking a simple question, I have seen many methods such as Xylene and other chemicals used to raise octane levels. I asked based off that because well... the limits of finding race gas and the cost make it rather... annoying.

[FNBADAZ06]

Cross , Unfortunately, you can't mix enough E85 with 91 octane pump gas to raise the AKI properties of the fuel without really throwing the A/F ratio WAY off, AND, you're dropping the amount of potential power in the fuel mix because the BTU/lbs value per volume of fuel drops significantly with the addition of ethanol. The stoich value of E86 (at 9.76) is SO far off the values of standard pump gas (14.7), that any GM car tune that's expecting a standard pump gas fuel is going to be very lean, especially when operating in open loop. By contrast, VP 109 or Sunoco GT+ racing fuels have a stoich value that's in the general ballpark of standard pump gas...around 13.7, so while the A/F ratio will be leaned out slightly at WOT, it's not going too far outside the norm that the ECU's stock tune can't handle it. The VP and Sunoco fuels will also carry as much, if not more, power potential because of the higher BTU/lbs ratio per mass of fuel over regular fuel.....ethanol has a much LOWER BTU/lbs ratio than standard pump gas. We will start a new thread discussing E85 fuels, and it's benifit when the ECU is tuned for the proper stoich value and the added timing that can potentialy extract more power. E85 really shines when you add any type of forced induction, or add a lot of compression, as it's ability to staive off pre-ignition and engine knock at these extreme cylinder pressures is where the magic of high octane fuels like E85 are. The denser air/fuel mixture that is packed into the cylinder via FI, and the associated bigger "bang" during combustion when compression is increased, is where you're getting the power from....not because of the fuel octane. But, let's reiterate that octane in itself does NOT create horsepower. Octane's sole responsibitlity is to reduce pre-ignition and engine knock/ping while allowing full ignition timing....that's it. If your engine can run on 87 octane low grade fuel and not experience pre-ignition or engine knock at various engine loads (to include WOT operation), a higher octane fuel serves NO PURPOSE. One more thing I should mention about the 91 pump gas and racing fuel mix I'm using......this mix is only used when I'm at the 1/4 track where every bit of horsepower I can find helps me achieve the performance numbers I'm aiming for. I don't use this mix for my day to day driving needs in the Corvette

[Cross]

I was never under the impression Octane had anything to do with power in any other relation than the ability to control Knock. Oddly enough I spoke with another tuner about this who uses E85 a lot and we shared the same hands on experience that I just put into action tonight tuning a 05 C6. We started the tune on 91 that while watching HP Tuners turned out to be really crappy 91... So I had him put in 4 Gallons of E85 and top it the rest of the way off with Shell 91. (He was at half a tank to start with). After a few minutes of driving the issue had gone from really worry some to almost non-existent. I tweaked things a little and it was completely gone and the owner was very happy with the results. The conversation between myself and another tuner was along the same lines, while it will require more fuel because of the lower BTU that only means a drop in Gas mileage to account for the extra amount of E85 being used to compensate. Basically the rating goes from a 91 Octane E10 to a 93 or so Octane E30 or so. It may take more E85/Ethanol to reach the same power output in terms of BTU but thats something the O2's will show you as they will correct for any fuel to the ratio they want to see no matter what, the issue comes in when the injectors can not keep up and/or the ECU goes above a 25% change in the tables to run such a mix. On that note watching his tables tonight he went up less than 8% but to error on the high side I will say 10% in his long term fuel trims. Well within the norms. Again I am talking about using it as an Octane booster we can talk about E85 specifically in another thread but this thread was about boosting Octane to drop the amount of Knock seen and reclaim power already on the table being lost due to our current available 91 Octane and its questionable quality at times. Just like the Xylene I mentioned and many other methods of raising Octane. Somehow this drifts from my center on this topic to else where and I think its just in the spirit of gear heads being gear heads. Hopefully this provides some tested proof of it in action I even have the logs saved I believe of his first run and then with the E85 Mix. However on the Open Loop return on WOT the more I think about tonight's logs this makes a little sense as each time the knock dropped off until it was gone and of course unlike MS, you can not make changes on the fly so this was all the ECU learning on its own. The same would be said for any race gas you mix it would take a few pulls WOT for the ECU to learn the new abilities it has with the higher octane if its not listening to the O2's at WOT. So to me an important point would be to monitor and ensure the ECU has learned the abilities of this higher octane rating (No matter what kind of a mix it comes from) before going for that better run at the track to maximize your results. The ECU prelearns to your driving habits and changes those when it see's it can such as with this fuel with a higher octane rating but it does so over time not all at once unless it somehow knows now the Octane has gone up.

[FNBADAZ06]

You have made several great points about E85 and it's use in staiving off KR, and there's no doubt that E85 and it's greater octane can be a cheaper alternative to mixing race fuel with regular 91 pump gas......BUT......

You have to TUNE for it.

This thread was about getting around the issue of knock when using 91 pump gas, and the potential of leaning out the A/F when at WOT and open loop operation, while NOT touching the GM factory tune....therefore keeping your GM drivetrain warranty intact

I'm going to start a whole new thread on E85, and it's benifit's when it comes to using it as a fuel for our LS engines. The thing with E85, and extracting the most efficient use of it as a fuel, is that it requires you to change GM's factory tune by modifying some key tables, therfore killing your GM drivetrain warranty.......something many people aren't willing to due or risk.

We have several E85 user's on this board, and several tuner's who use it on their personal rides as well. I have a few personal friends that are not board members that use E85 exclusively on their modded, 13:1 compression LS7's and make crazy power But these guys have no concern over a GM driveline warranties. That's the difference :

I have plans of switching to E85 myself, so believe me, we have a common goal in understanding the E85 "mystery" fuel !!!!