1991Z07

I'm cursed to be one of those people who always think outside of the box.

I'm building a C4 ZR1 racer and the motor is going to be a 427 SBC set up to run E85, so the C/R is going to be fairly stout at around 12.5:1. Octane ratings for E85 are 105 - 115, so I was thinking that since I'm going to be using an aftermarket ECU anyway, why not get one that can use the GM sensor that reads the ethanol content of the fuel and automatically change the fuel maps accordingly.

If I can get E85 at the track...fine. If not, get some 105-110 octane race fuel and I don't have to screw with changing the fuel maps manually.

This car will be mostly track only...so I thought I'd ask if anyone else has gone down this path. I've found a lot of references in the turbo world for this...like a 60 RWHP gain using E85 over race gas because of the cooler intake/fuel burning capabilities of E85 and the higher octane allowing them to advance the timing even more.

Seems to me it's a no-brainer. Just need a road map to follow now.

Thoughts?

Aardwolf

If I'm understanding correctly you would use E85 if there is some at the track or race fuel if not? The fuel table will be vastly different with E85 compared to race fuel. The timing table may be similar.

When I started tuning my rebuild I found knock scattered throughout the timing table and decided to switch to E85. It was fairly easy to do. E85 uses much more fuel than gas though. You would need two different tunes or bring E85 to the track.

1991Z07

Well the beauty of using the flex-fuel ECU is that once tuned it uses a fuel composition sensor in the fuel line to adjust the fuel curves & timing automatically. Tune it for straight E85, then tune for straight 105 Race fuel. The 2 tables are separate, and the sensor tells the ECU what the ethanol content is and the ECU takes care of it all.

I'd never need to worry about "which" tune I was using...ever.

Even if I had a 1/2 tank of E85 and filled it with 105 race fuel...the system would scale everything to where it needed to be for optimal performance.

I understand there is about a 35%-45% increase in fuel usage with E85...but the cost of E85 compared to 105 race fuel ($3.50/gal vs $10+/gal)...the cost savings is well worth it.

I can't help it...I am just one of those "outside the box" people.

FAST XFI has this option...but I'm hoping to do it with a GM computer so everything in it can be bought from my local parts house vs. waiting for FAST.

Just soliciting ideas here to see what would be needed.

Aardwolf

I would be very wary of trusting my engine to that. They have been around for street cars awhile but I haven't seen that used for a track car. I suppose you could mix the fuels and data log to see if it gets everything working fine.

1991Z07

That was the plan...testing to confirm the tune is working as intended with mixed gas/E85 conditions.

GM has had flex fuel vehicles on the market since 2006. Not sure how many iterations of ECU they've had in that time, but from what I've been reading it takes the ethanol content by % and adapts the A/F ratios and spark timing dynamically. It'll need some close watching, but in the end it would be a very clean burning race car with some flexibility to run on another high octane fuel if E85 wasn't available.

A lot of the very current generation have additional things like selective cylinder cutoff for highway use...but I'm not interested in that. A V8 ECU with the basic stuff should be good for this. Injectors will need to be sized about 50% bigger to account for the additional fuel needed with E85.

Some of this is uncharted territory...other parts are old hat. Quite a few reads out there on doing this conversion for Mustangs as well...using GM ECU's (how do you make THAT un-holy marriage work )...

I COULD do this manually...but where's the fun in that? Something different & unique will be much more fun.

In the end, the reward will be so much better. I already know what a FAST system will run...I just need to make sure the GM version doesn't exceed it (by much) and then work out the bugs.

Aardwolf

My friend Brian works at tuning and uses E85 too, he may have some insight. bjankuski here on the forum.

mcar00

I sort of did the same thing. I've got a separate tune for 93 octane, E-85 and 112 race fuel. Whichever fuel I plan to use I just download the appropriate tune. However, I drain all the old fuel out before introducing a new fuel. I would not trust any type of "Flex Tune" on a race track with my motor at stake. There are just too many variables depending on the volume of each different type of fuel in the tank.

One thing to keep in mind is if you use O2 sensors the race fuel will destroy them quickly. Also, the E85 tune produced more horsepower than the race fuel tune which I thought was interesting.

1991Z07

I'm not too worried about the tune in various mixtures. If the turbo guys can use this stuff and not sweat it, I can with no problem.

Turbo tuning is much easier to get wrong and finish a motor...these guys are getting 1200+ HP and mixing the fuel up and still having no issues.

And only when you run leaded race fuels will it adversely affect the O2 sensors. Every manufacturer has unleaded high-octane mixes in their arsenal...the question is does the track happen to have them there.

My "plan" is to bring enough E85 that I don't need to worry about it. But the option of being able to use something else WITHOUT going to the trouble of changing the programming intrigues me because your "tune" in particular would never be 100% correct unless you drained the tank and put the other fuels in.

I hear you on the E85 and more power than race fuels. White Racing Marine generally gets 50-60 RWHP gains with E85 over race fuel on turbo motors...



Pretty significant when you consider the cost for the E85 is ~1/3 - 1/2 that of race fuel

VetteDrmr

True, but remember that GM's engines aren't running the CR that you're wanting to use to take advantage of the E85 octane rating. The engine is set up to run on 87 octane, the E85 just has to run smoothly, not efficiently. That's why you lose about 30% mileage when E85 is used.

I do like your idea, though. Hope it works out!

Mike

1991Z07

The reason you lose 30% mileage on E85 is due to the air/fuel ratio...

Typically “pump” gasoline is burned at a Stoichiometric A/F ratio of about 14.5:1 A/F where E85 would be 10.0:1 A/F. The lower O2 levels to burn the ethanol results in lower efficiency.

Ethanol's lower energy content (76,100 BTUs/Gal.) is a big contributor to its reduced fuel economy compared to gasoline (114,100 BTUs/Gal). Even though Flex Fuel Vehicles burn E85 (81,800 BTUs/Gal) and the energy penalty isn't as severe, it still requires more fuel to do the same work. On paper, according to this GGE chart, it takes 1.39 gallons of E85 to move a flex-fuel vehicle the same distance as 1 gallon of gasoline.

The flex fuel computer cares not what the fuel is...the fuel composition monitor is testing the fuel continuously to determine the levels of ethanol and the ECU calculates the delivery level and then testing the results with the O2 sensors, making adjustments as needed.

I don't think the "penalty" will be as much with the higher C/R, but it should be interesting to see where it falls. As a WAG (wild assed guess) I think it will fall somewhere in the middle around 1.20 but I'll have to wait & see.

I highlighted part of your reply because it isn't exactly correct. The EPA control it all, and efficiency with low pollutants expelled is their primary concern. It is one of the biggest reasons they encourage flex fuel vehicles to be on the market.

From Wiki:So it makes a difference to the EPA, and manufacturers have had to account for that in the programming inside the ECU's.

It's going to be a fun experiment. Maybe I can use it as a road map for others...we'll see. It isn't going to be an easy change...at least I think that way but who knows? It could be a very EASY swap as well, and the PITA will be the two separate tunes that will need to be done for both fuel types.

VetteDrmr

Good point. Also good explanation about E85; I knew all that info, but you put it together nice and clean.

Really looking forward to your project!

Have a good one,
Mike

1991Z07

You too Mike...

boltvette

I once asked Wil Cooksey why Chevy didn't build a flex-fuel Corvette. It would seem to be the perfect vehicle for flex-fuel technology, if they were really serious about it. You could run E85 at the track and take advantage of the much higher octane rating and the cooler combustion temperatures. Yes, the lower energy content of the fuel means you'll be filling the tank after each session, but so what? Then put pump gas in it for the drive home. And if you really want to sell flex-fuel technology, how better to showcase it than with the Corvette?

When I made the case, Wil just smiled - and retired about 6 months later.

EVAN&MONICA

Any update? Did you ever get this all figured out? very curious!

Evan

forbiddenvette

Me three,, i was pondering this idea as well. My strung-out LS2 hates 91. What about PRO-EFI?