Rogor

Reading some more about E85 (Ethanol 85% + gasoline 15%). I came to this math, which is all approximately, I didn't draw my calculator of spreadsheet.
I see that:
- the calorific value is 30% lower than gasoline
- for a stoichiometric burn there is 30% less air needed, so 30 more e85 (which I know is not the correct calculation, because 30% of a big number differs from 30% of a small number. e85/air = 1/9.7 and gasoline/air= 1/14.7 [kg/kg])
This means the energy output of a stoichiometric mixture of e85 is approximately the same as the energy output of the same amount of stoichiometric mixture gasoline.

But air input is the limiting factor for power output of an engine. The more air you can put in a cylinder, the more fuel, the more power (until you reach the knock limits). That's why volumetric efficiency is so important for natural aspirated engines. That with a high compression ratio determinate the energy output.

Air input in a turbo engine is somewhat easier, more boost = more air, so you can inject more fuel which leads to more energy.

What this means for the transition from gasoline to e85 is that if with the stock turbo's you load it up to max boost, you need 30% more fuel (e85) for a stoichiometric burn. So there is you're new mapping comes in, which makes the mixture richer for e85 than for gasoline. The energy output stays the same.
What happens is that the stock injectors can't deliver 30% more fuel (e85), what means that the amount of air has to cut down to stay stoichiometric. With maximum e85 injection you only need 70% of the maximum air input so you lose 30% energy.
That means a stock 997 turbo on e85 is far less powerfull than running on gasoline.

If you can increase the fuel amount from 100% to 130% with e85. You still can use the stock turbo's for the stock 100% air amount an have the same 100 % energy delivery than the same engine of gasoline.

Why then e85?
Maybe because e85 has a higher knock value then gasoline the engine can cope with the higher pressures and temperatures and there is also no engine knock. Now I'm fantasizing, in this calculation, with stock turbo's and 30% more fuel flow gives more exhaust gasses, pumps up the turbo's which give more boost, so more e85 can be injected...

PS With energy I mean delivered energy in a stroke. Multiplied with revs is power output.
PPS Sorry for my long story, my wife is looking Madman and I had nothing better to do that fooling around with my daughters laptop.

roncooper

As I read this and having obtained my engineering degree and taking all the chemistry classes required, while are your calculations seem reasonable I feel there is something fundamental that is missing. I do not currently run E85 however I believe they are upgrading the injector size so I would assume the duty and volume has increased. Thus they are increasing spark and moving more air all while burning cooler. As parasitic heat is a big issue for these cars as they want to pull timing and cut boost down I can only assume they love burning cooler. I'm not sure they are increasing boost as most threads I've read they haven't mentioned that. From a progressive stand point e85 is just a smarter fuel. It's no wonder these cars respond so well to it.

Igooz

E85 also has the 100-105 Octane...so you get into detonation at a later time...cheap high Octane fuel.

(OT: However it is 85% ethanol and I would never that much alcohol in my car..no way...E85 has been used in drag racing for at least a decade and you should read about the fuel system/rubber/and havoc that it creates.)

Team Plutonium

If you run it occasionally (since it's hard to come by) your lines should be fine. Most folks who run it (on other cars, GT-R's for example) change everything out. But I think we've established that the 997.2 won't be able to handle the fuel demand if I'm not mistaken....

A418t81

Hey guys, I just happened to stumble across this thread. The 6speed thread is about my car, and I'm happy to answer any questions you may have.

As speculated earlier, the boost is not increased over my 93 octane levels, but I do run a fair amount. It is around 21-22 psi across the board whether on 93 octane or E85.

I also ran a 6.7 60-130 on pump gas 93, which from what I've been told is also a 60-130 record on gasoline for this platform. Both custom tunes are from Dzenno @ PTF who just recently introduced himself here. Both calibrations are incredibly powerful and the torque is just insane. There's a huge difference just going from a canned (one size fits all) flash to one specifically tailored for your individual car.

Team Plutonium

Awesome! Congrats & thanks for chiming in! Any info on running E85 would be much appreciated. You load just a different map?

A418t81

To run E85 on the 997.1 Mezger motor and actually make more power than you can on pump gas, injectors are needed. I have injector dynamics 1000cc injectors, but the recommendation from Cobb is to go with the 1300cc injectors if larger turbos are in the picture. I'm not very interested in going with anything bigger, so the 1000cc option has been fine for me (they are also much less expensive, fyi).

E85 mapping involves changes to the fuel scalar as well as cold start changes, and a few other odds and ends to getting drivability correct. As far as tuning to make more power, you can run more boost if you setup allows, but the big changes are leaning the air fuel mixture out as well as running a lot more timing than you can on 93 octane. The peak torque, particularly with the OEM VTGs on E85, can get out of hand with regards to the stock rods, so a bit of care has to be taken to keep torque in the midrange down to more reasonable levels (we are talking less than 700 ft/lbs at the wheels, so still quite a lot).

The midrange power on E85 is just insanity. The car has factory rubber sizes (305 on the back) and traction is definitely an issue in second gear. In second gear particularly, the power is absolutely explosive once the turbos spool. It's quite a lot of fun

Team Plutonium

^ Ah, thanks! You have the wonderful Mezger block, I have the DFI motor, was hoping you pioneered and ventured into that territory with E85. Since it looks like that won't be an option I ended up rebuilding my VTG turbos to run more boost.

Thanks again for the write-up and info. Hope you keep pushing.

proTUNING Freaks

E85 is really great and works very very well on the 997.1 Turbos just like many other forced induction motors/tuning. Direct injection motors such as the one in the 997.2 and 991 Turbos will see an even greater benefit with E85 once we've got fueling sorted out.

FYI, effective octane of E85 when direct injected at high pressure into the combustion chamber is 160+ points! Now all we need to do is find a way to satisfy these motors 30% higher fuel craving over conventional gasoline

Let me know if any questions on this topic at all guys.

Dzenno@PTF

Team Plutonium

Can you provide any info on how you approach this issue and plan on resolving this? I'm very interested.

proTUNING Freaks

Its still very much work in progress and unfortunately we don't have anything significant to share at this point publicly. What we can say and have posted in the past is around the flow capacity of the OEM fuel pumps which showed that they should be able to support quite a bit more power than anyone is making today on the Porsche DFI platform.

Here are the results we've gathered through 3rd party independent fuel testing on a flow bench as posted on 6speedonline.com recently:

Team Plutonium

Very cool, and very exciting! Thanks for sharing. The second you guys have something I'll be all over this.

A418t81

Hurry up and figure out the high pressure fuel pump limit so I can upgrade. I've been eyeing the 991 Turbo S pretty hard lately. Give me a reason

elite1

Physically, the 997.1 can handle a mild E85 conversion with new injectors.

On the E85 topic, exactly what this thread has turned to. Fuel volume and octane efficiency. 105Oct. is great for performance but, expensive when daily driving the car. (At the track, Awaiting the results this coming weekend.) I really don't think that the track situation differs much. With E85 in comparison to 100oct., I feel that the car is truly stronger with the right tune, resulting in a better result. Not to mention at half the cost.

I have installed the Cobb (Injector Dynamics) 1000CC injectors along with their custom tuning. Car is an animal on the street but, need to keep logging this particular tune for track use to fully understand if this environment is completely safe.



My only recent concern is due to the black coating that Porsche put on their fuel lines. I recently replaced my fuel filter and noticed that this film had "bunch or slide" along the input connection tube.

I managed to cut any excessive film off the fuel line prior to filter input.

Yogi911

Is e85 safer than 91 in really hot environments like Phoenix or Vegas.

Same quest for cold places like the great north.

Same question for high alt like NM, CO, or Utah