Flex Fuel is pretty awesome....

[Speedy!]

I started a thread a while back as Mike from OST and I started playing with Flex Fuel tuning: https://www.hellcatforum.org/threads/those-running-flex-fuel-get-in-here.5711/

Car setup for those not following along:
2016 Hellcat A8
Original motor threw a rod so I replaced that motor with a Demon/RE long block.
2.72 Hellraiser Pulley makes about 17psi of boost
ID1000 Injectors
Dual Pump drop in fuel system (this is what allowed me to start playing with ethanol as I had lots of overhead on the fuel system with this setup)

Results have been way more than I expected honestly. I'm not going to give specific timing advance numbers as I don't want someone just throwing those values in their tune as all cars are different, but what I will tell you is based on my 93 octane timing map, I went all the way to plus 9 degrees more advance than I had on 93 at full tilt E85 in the tank. I never got any STKR once I figured out a couple things about E85 and how it's 30% more fuel volume and resulting cylinder pressures impacted the knock sensors. It got to the point that the car was making too much power for the street to be honest, so I actually backed it down a tick or two in the end and will save the mojo for when I need it at the drag strip. To put that in to perspective when I was dialing in 93 octane I'd make a rip in 4th and shift to 5th to test and log. On E85 that was a bit hairy so I had to back that down to a rip in 3rd with a shift to 4th. Once I had things all dialed in I did do a few pulls 4th - 5th but I had to go way out on my "closed test course" for that.

It's been very cool to just roll up to the gas pump, drop in E85 and watch the car adjust and add power automagically. It's a pretty complicated tune so be sure to work with someone that has done them. Mike from OST did mine, Curt Dusterhoff has done a bunch as well. I've got some video I'll put together on my YT channel when I have a few minutes.

For the past several years I have been using Renegade Race Fuel RM109 unleaded at the track. It has a R+M/2 rating of 107 octane.

Octane – R+M/2 107
Motor Octane 100
Research Octane 114
Specific Gravity 0.723
RVP 6.7
Oxygenated 9.6%
Unleaded Yes
Stoich Ratio 13.04%
Color Blue

With the results I've seen from regular o'l pump E85 I'm going to try out some Renegade ethanol products in the future like this: https://www.renegaderacefuel.com/product/pro-e85/

Octane – R+M/2 100.1
Motor Octane 91.6
Research Octane 108.6
Specific Gravity 0.778
RVP 3.72
Unleaded yes
Stoich Ratio 9.91 : 1
Color Orange

 

[DGatzby]

Great report @Speedy!

With E-85 literally all over the place around here, that flex tune is something that may very well interest me. My problem is I probably CAN’T use 100% E85 on the tracks, because it may not leave enough gas to complete a session on a couple of these long courses! Damn near burning a gallon a lap here at BIR and at RA, with gas! The world of tuning will be really kool once I decide to do it. Thanks to all of you pioneering that for us.

 

[Confuzed1]

It's been very cool to just roll up to the gas pump, drop in E85 and watch the car adjust and add power automagically.

Like your vids, been watching them on/off for a year now. Very informative. I'll catch up with the vids and have questions I'm sure....lol

 

[Hpindy]

Do you ever worry about testing the fuel every time you have to get some? What about the integrity of all the fuel system components ?

Asking for a friend
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[Speedy!]

Fuel system in all cars are ethanol compatible these days I believe. As for testing, no that's not a concern with flex fuel and one of the reasons I wanted to go that route over a dedicated E85 setup which would require testing fuel.

In my testing of the flex fuel tune I have been testing the E85 at the pump just so I know what's going in the tank to confirm it's calculating properly. Mike and I had to work on that a bit to get everything accurate. I've tested going from a couple of gallons of 93 in the tank and adding 5 gallons of E85, to going from full on E85 and adding in 5-7 gallons of 93. Within about 5-7 minutes the car figures it out and within about 7-12% accuracy (sometimes as close as 3%).

There's an algorithm that determines how much of a blend between the 93 timing table and the alcohol timing table based on the ethanol % reading the car picks up. Same for the fueling. It's pretty slick. After about 65-70% ethanol I'm getting full mojo, and mojo it is.

 

[fubar569]

Curt tuned mine in and the guy knows his stuff when it comes to flex.

Pretty much same boat as speedy...it's so far always within 10% after getting my sending unit fixed and making sure the trims stay put and injectors are accurately scaled.

It will start blending between fuel tables around 20% inference I think...at least that's when I noticed it start to affect the in-dash wideband reading...which curt sets up to read properly as the content changes.

I test my stations for the first handful of fills and then again when the seasons change. So far my chosennfew (sheetz and speedway) have been no less than E75 and speedway off barkeyville on I80 was true E85 last I tested it 13 days ago.

 

[Speedy!]

It will start blending between fuel tables around 20% inference I think...at least that's when I noticed it start to affect the in-dash wideband reading...which curt sets up to read properly as the content changes.

From a fueling perspective mine starts to blend at about 15% ethanol, but the timing advance doesn't start until almost 60% (safety).

I think this is an important point. Mike gave me a choice to have it read normal AFR like stock, or have it read actual AFR depending on fuel in the tank. I chose the latter since it allows me to know the ethanol blend at a quick glance. On pure 93 the AFR gauge reads high 13s. AT 20% ethanol it's high 12s, 30% high 11s to low 12, 40% low 11s, etc. On full E85 it's low 9s. If I ever fillup and the gauge doesn't match what I think it should be I know something's up.

I use Speedway E85 here and during the winter, very early spring at least, the lowest I ever saw was E80. Now that it's summer I've seen E83 - E90.

 

[fubar569]

From a fueling perspective mine starts to blend at about 15% ethanol, but the timing advance doesn't start until almost 60% (safety).

I think this is an important point. Mike gave me a choice to have it read normal AFR like stock, or have it read actual AFR depending on fuel in the tank. I chose the latter since it allows me to know the ethanol blend at a quick glance. On pure 93 the AFR gauge reads high 13s. AT 20% ethanol it's high 12s, 30% high 11s to low 12, 40% low 11s, etc. On full E85 it's low 9s. If I ever fillup and the gauge doesn't match what I think it should be I know something's up.

I use Speedway E85 here and during the winter, very early spring at least, the lowest I ever saw was E80. Now that it's summer I've seen E83 - E90.

It is a nice added convenience to be able to read estimated content this way.

Speedway E85 is legit. I stop there on the way home every time now.

I want to say the spark starts coming in at 30% and gradually increases with inferred content but is softer than straight E85 because of that 10% margin. It's still an extra 50-100hp estimated though for just picking a different fuel. Can't complain about that and the rest of the tune is literally dead nuts. I am 110% satisfied with how curt set her up. Blending in at around 20% makes sense as the factory widebands are set to the stoich of E15 anyways (13.85:1).

 

[Speedy!]

Well, I recently saw a dyno sheet with 4 runs on it. Each one had a degree of timing added and max HP was 830 and 800tq. This was on race gas not ethanol by the way. Each degree of timing at around 800 hp picked up 12 more HP and about 12 ft/lbs of torque. My car made right at 800 on 93 and I've got quite a few more degrees of timing on E85 so yeah that'll add up fast. 5 degrees would be 60HP, 6 would be 72, etc. With the higher volume of fluid with ethanol, and the cooling effect, it probably works out to a bit more than 12hp/tq as well.

AJ has said a bunch of times he doesn't recommend going over 850RWHP on a Hellcat, but I'm not sure if that includes Redeye engines as well. They're supposed to be stronger, but who knows.

I had mine cranked on up there and it seemed to love it, but I backed it down a bit like I said. It was really a lot of power for ripping around town.

 

[fubar569]

Damn son.

That thing is making steam.

 

[Hpindy]

850 rwhp Is a lot of power in a street car never mind a race car !

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[Speedy!]

I'd say so. On my last 4-5 pull it was pretty freaky how fast it was. That's when I thought I'd best back it down some and save the extra for the drag strip.

So funny story. As I was finalizing the timing map and adding 2 deg, ran a test, add 2 more, test again, checking timing and fueling and STKR I was just about finished. I had been testing in 3rd mainly. I decided to run a quick test in 4th just to cross check, on the shift to 5th at what felt like a gazillion mph the car stuttered and stumbled and I was like oh $hit. Pulled over and saw 12 deg of STKR right after the shift in the log. CRAP. I thought I'd bent a rod because it did the same thing at the track when the original motor failed. I thought I'd just put too much power in it.

I get home and start pricing short blocks and drop in rods/pistons just to see what I'm looking at. I called Crew Chief Greg and told him about it and he said no way you've hurt that thing. The next day I pulled some plugs and they all looked perfect. Heat marks on the straps were great, no issues at all. Jack the car up and start crawling around under neath looking at things, check the knock sensor heat shields and bolts, all looked good and I was stumped.

I go to roll out from under the car and my hand hits the bellhousing and I hear "CLANG". Roll back under and the flex plate inspection cover was dangling on the 10mm bolt that holds it. Bolt had backed almost all the way out and if the plate moved just right it would swing away from the bellhousing and bang against it. Loctited the bolt and all was good.

Can you imagine if I'd bought a short block and found that loose bolt as we yanked the motor LOL!

 

[fubar569]

I know on the flex tune on the 2.79 I'm making 16psi and its downright scary on street tires.

On the ET R's on the street it feels even faster yet. Just feel the carrier bearing screaming for dear life (THUMP) and she's off. No squeal. No BS. Dead hook and gone from a 40 roll.

A full pull in 5th is good til almost 140mph. That's insane.

Truth be told...I cruise most of the time when NOT validating changes...in Eco mode

 

[Speedy!]

The car is setup now with the alcohol table pretty much matching my race gas timing map I use at the track. That was really the goal all a long. So I know with what's there now it's a 9.8 - 10.0 car at 140mph on the street. Kinda crazy really when you think about that. Like I said I actually took it quite a bit past that just to see if I'd ever see STKR, and never did so ethanol is the sheezy.

What's this eco mode you speak of?

 

[fubar569]

I'm pretty sure eco is for when I run out of tampons.

 

[DGatzby]

After reading your excellent information (you too @fubar569) I hope I can hold myself back and retain the warranty for one more season. Great discussion gents!

 

[Speedy!]

The fuel consumption would be something for you to consider. My fuel mileage is like 9 mpg right now, but I was able to fillup from empty for $24 on E85 the other day. That was $1.53 a gallon race fuel basically. Way better than the $15 I pay for race fuel.

With flex you could split the difference though and do like E60 and still be ahead and fuel mileage not as bad.

 

[fubar569]

My mileage hasnt been adversely affected given the additional power.

I've been as high as 24.5 stock and 24 modded on 93...typically 22ish. Highway.

I think on the ride to work on 74% tested (82.5% inferred) I made 19.5mpg? I'd have to check...

City has always been atrocious.

 

[BULL]

@Speedy!


In a few bullet points, what is your idea of the path from "stock" to "Flex fuel tune"?

 

[Speedy!]

@BULL pretty simple really

- Proper fuel system including pumps and injectors
- Proper tuner that understands the intricacies of flex fuel tuning
- Access to proper and tested known good E85
- Don't get greedy with the power. Just because you can does that mean you should.