I've seen a lot of back and forth on running a higher compression ratio with E85, like even in the 12.X:1 area, boosted. I see others arguing against the safety net of E85 and run a high 8, low 9:1 compression.. So what's the most optimal CR for a boosted E85 setup? I've never found a straight answer.. My build will consist of a fully forged 370ci. iron block, PRC heads (68cc Chamber), Tick ground cam, Hi-Ram with twin 69/68's.

 

My opinion is that you can run damn near 12:1 compression on FI without having to worry about meth injection. The issue you will run into is actually finding a good grade of E85. Gas stations very seldom sell actual E85 consistently. Some place around st louis sell as low as E40.

But my theory is that you can run more compression on E85. Its similar to running alcohol. If you wanna run 8:5-9:1 compression I dont think E85 is even needed. Unless your going for 30+lbs of boost. I run E85 because im 10:5 compression and I would be able to make decent torque at lower rpm and potentially make same hp on 8lbs as opposed to another car on lower compression that has to make 14-15lbs of boost to match my hp. JMO

 

The only argument I have against it as a "safety net" is what was mentioned above...lots of pumps advertise E85, but I'd say most of them aren't selling fuel that's 85% alcohol.

If it's a race car, you can just get a test kit, and order the fuel by the barrel, and know what's going on...if it's something you're filling on the street, you're going to run into inconsistencies, but it's still going to be better than E10 (pump gas) every time you fill it up.

 

It's gonna be a street truck, but I plan on trailering it to big events due to my tendencies of breaking ****.. So worst case I can carry a barrel around in the bed of my big truck. However, if I do need to fill up at the pump and I get a bad batch, will it throw the whole tune off?

 

Honestly my next motor I build I'm shooting for a 10.5 or 11:1 CR. e85 is so damn knock resistant that I think you can get away with so much more than your typical pump gas setup. Currently i'm at 9.5:1 and wouldn't go any lower IMO

 

I can't even tell the difference in my tune from summer to winter blend, I live in CO though so who knows we may never get summer blend. Regular 91-93 pump gas is inconsistent as well. If your tuned for %85 ethanol and fill up with a batch that's %50, it will run rich. You lose some of the safety net of the cooling effect of ethanol but its not going to go lean on you.

 

I am pretty sure it will screw up the tune. Thats like saying your truck is tuned for pump 93 but you run 87 octane. Thats why I was saying to test every batch before filling. Thats great cheap insurance. And it could potentially destroy your setup if you do not test and get a bad batch.

My opinion if you are a serious roll racer I would run lower compression so you could through more boost at it so it would perform better in upper rpm. But if you do more digs than rolls, I would bump up the compression some so you could have that lower end torque. Maybe Im wrong though.

 

My motor with -3cc dish pistons will come im at 10.8:1 compression, roughly, which seems like a good in-between zone

 

If I leave it four-wheel drive, I'll be digging all night long, but I feel like that's a system that'll take a lot of money to beef up and maintain, so I most likely will be yanking the four-wheel drive out. But compression makes the world of difference in power and I'd rather more power on lesser boost.

What turboventura said about it just running rich sounds a little safer, and maybe I can figure out a tune for rich *** E85 if somehow possible. I know there's no consistency with the inconsistency, just trying to look at the pro's and con's and what the best way of going about this will be. Obviously a lot of people are on E85 and are making it work, but never know if that's pump or barrel or what.

 

From what I have seen most people run between 10.0-11.5 with much success. As noted above the issue is having your tune setup for a specific blend of fuel. Thats why I loved my ProEfi 128, the tune was setup for "E85" but the parameters were input between E60 and E90 so that the ethanol analyzer would adjust accordingly. I am a complete newbie regarding the tuning capabilities of Holley but heard some of their units can also do the same with the ethanol analyzer. Being from NY I have seen blends range from E67 in the winter to E89 in the summer depending on the station and time of year.

 

That’s because there is no "straight" answer. It will vary.

1.) E85 itself varies a ton in my town. I've seen as low as e50 and as high as e90 depending on the pump and time of year. Yet the gas stations label it "E85". Also the base fuel used to blend "E85" will vary in quality. Inconsistent fuel makes it very hard to give definite answers.

2.) Each engine combination will vary. Backpressure, Intercooling Efficiently, Turbo Efficiency, CC Design, Ambient Temperature, Vehicle Weight, Gearing Loads... etc... all vary between setups. This makes it impossible to give a blanket statement like "On E85 a 12:1 370 can run 25lbs".

As a general rule lower compression will net you a larger more forgiving tuning window. IMO the engine you described doesn't need a high SCR. 8.5 to 9:1 would allow for great easy to tune setup. A full point of compression is only worth 4% Na power. So if you're making 450crank HP NA. You'd only lose 18hp dropping a full point of compression. Though if you only plan on running 6 lbs of boost there's no reason to run low compression either.

IMO build a turbo motor to make power with the turbo...screw NA performance. Why anyone needs more than 300 HP "NA" to cruise the streets out of boost makes no sense to me. I'd rather have lazy NA performance, a wide tuning window, and retardo HP at big boost levels.

I've ran as low as 8.6:1 and as high as 10:1 on my E85 LS 5.3 setups. The 10:1 was snappy and mean sounding, defiantly more fun in "NA mode", but performed about the same at the track. I was still able to launch at 24lbs if I wanted on the 8.6:1 motor. Once boost came in the higher SCR seemed to make little difference. The higher compression motor was finicky to tune, whereas the low compression motor was not. For a novice like myself I prefer relatively low SCR builds.

 

Ethanol is VERY forgiving. If you leave some room for error in the tune, you can run E70 without a problem. You start running into issues when you tune with a really high ethanol content, e90+, and then squeeze it for all its worth tune wise, and then later end up with a batch of e70.

Pumps around me have gotten as high as 90% ethanol and as low as 70%. My car was tuned on 85% and there was definitely some room left in the tune, but i had no issues when it dipped below 85%.

That being said 10ish:1 will leave you room. I'd love to go 11.5+:1 if i knew i was always gonna have E85 around me

 

Im running damn near 11:1 this season. But it was an accident. Long story. Ok its really not long. My used heads were cut .060 and I didn't notice till the intake didn't fit. Put it together anyhow. We shall call it a learning adventure. Tuning on C12 which has treated me great for years.

 

C12 VS inconsistent pump E85 is a big difference. I'm sure you'll be fine if you keep the boost reasonable.

I'm in a similar boat. Found a block and forged rotating assy pretty cheap local. Ended up around 10:1. Not the SCR I would have chosen, but i'm going to roll with it. Picked up a drum of Ignite 114 to try. Basically E90.

 

If at find myself around a pump with unhealthy E85, is there any sort of "octane booster" so to speak? Or can I spray a little more meth to compensate?

 

Nice let us know how you like the fuel. I have loved C12 and we have it on pump right around the corner from my work!

 

Can someone explain the difference in C16 and E85? Is it more expensive compared to E85?

 

My setup with the -3.2cc pistons bring it around 10.0:1 static compression. That to me seems to be a good compression for tuning and allow for safety if it's a bad batch of E85. I'm afraid to run too high of a compression in case I need to switch to 93 for some stupid reason, and to keep the power coming in more on the top end of the rpm range with more boost, and not so snappy.

 

I have NO experience with E85. I've been trying to get my dad to run it in his TT WS6 but he doesn't believe in it. I'll show him

 

11:1 compression 378ci forged motor on e85 running a stock $100 ls1 crank making over 1000rwhp for a few thousand hard miles. No issues. Spools a T4 88mm turbo with minimal lag. In out area it varies from 78-85% depending upon station and time of year. I have an ethanol content meter to always let me know what I'm running. Typically you find a good station and they will consistently have high levels. Midwest in the winter the content goes down more then west coast as colder weather makes it harder to start an engine on a purer blend.

Just a little over $2/gal for 106 octane fuel is the best! If you buy a quality injector that can operate well at low DC then tuning is easier and idle/low end response is good until you really need the DC at higher boost levels.