Seeing that Mike D is tuning the Gen3 for 93 octane I have a question. Here in my neck of the woods I seldom see 93 octane if ever and am most likely to see 91 octane. So my question is if I mix 3 parts 91 octane pump gas with 1 part 100 octane Avgas do I come up with 93 1/4 octane or is there some other formulas for mixing octane ratings to achieve approximately 93 octane?

Answered my own question with a Google search. It appears to just be a straight forward percentage 1 gal of 90 octane and 1 gal of 100 equals 95 octane.

A question for Mike D is, will there be a benefit to using higher octane than 93 and also will we still require supplemental regulations with the Gen3 for the witches brew (hot gas) that seemed to give some a few HP advantage a few years back?

It was an Enterprises BOD decision to tune the GEN3 on 93 pump gas and I agree…it’s not in the best interest of our class to use 100 octane or higher race fuel.
So at least with the R&D program cars, the tuning has been dialed in so to speak to use 93 octane.
We do all of our dyno and track GEN3 testing in the Denver area with 90 or 91 octane. Shop 5700’ HPR is 5500’, PPIR 6000’ and Pueblo 4800’ it’s not a pure linear equation Altitude vs Octane requirement. In the current state of tune, 85 octane is not enough in the Denver area, it mildly knocks and takes a couple degrees of timing to clear it up.
So far, I’ve done a handful of test @ see level with brand name 93 octane has proven to be plenty safe.

As the GCR fuel rules have changed, it’s been harder and harder to blend a hot pump fuel. In most cases OEM tune is rich at the top RPM range. So the hot pump fuel made a nice improvement with minimal tuning changes. SRF 1.9 needed a special or rich set of EFI parts to take advantage of hot pump fuel. Not cheated, just the outliers in the rich range.

The GEN3 engine management is tuned right @ optimal A/F from 2000 to 6700 RPM. That’s not the case with the Roush 1.9 tuning. It is also running in closed loop, small tuning changes are adjusted on it's own in closed loop. It’s not dummy proof…you will still need to buy good quality 91 / 93 octane fuel. If you are not sure, a mix with 100 octane unleaded will be safe. 1 Gal of 90 and 1 Gal of 100 = 95 Octane.

One of our goals with the GEN3 update was to run the engine in safe optimal state of tune across the entire rpm range. We will never be able to eliminate dyno tuning, but the improvements will be nearly nonexistent.

I thought we were detuning the motor a bit? Why do that then set it up to use more expensive gas? As a minimum tune for 91 so people in part of the country without 93 don't have to mix gas. And if we are detuning the motor anyway, tune for cheap standard 87 (which is what the stock 1.6L Duratec uses to begin with).

I hear recuring rumors that the government wants to take the standard "gas" from an E10 blend to E15. It would be nice if we had enough margin to deal with that without having to buy/mix race gas again.

The beauty of the new engine management system is; we are building the Engine Calibration or Tune from scratch. If it becomes necessary to make an update it’s in our control, that was not the case with the OEM ECU. The question in your mind is why base the tune on 93? People already mix 100 with their pump fuel now as a reassurance. It's just the starting point, as more GEN3 R&D cars are run my sample size will increase and the locations around the country will be wide spread. That is the purpose of the R&D program, to develop the best possible compromise across the country.

We just received the first official batch of engines late last week. We should have R&D kit #3 out by the end of the week.

If the fuel standards across the country change, we will update the Calibration.
But at this minute we are well over a year from the public release of GEN3 kits and my sample size is 3….I write little updates to let everyone know how the project is progressing.
Tuning is fairly easy up to about 80 / 85%, it’s much more difficult to get the last 15%. I would say I’m in the 85 to 90 % range right now. Still lots of things to improve on.
Here is a link to some laps at the end of Sunday 8-18 test @ PPIR…all of the laps are 2.5 seconds or better than the current 1.9 lap record of 1:05.0

https://vimeo.com/72786775

We mix 100 & 93 (or 91) because you (enterprises) told us we needed to to be safe with E10 pump gas. As you are building a new calibration, I say calibrate it so we don,t have to do that anymore. Even of we are in an area with only 91 instead of 93 octane. And further if we are purposely detuning the engine (which was my understanding) then I see no reason to calibrate it to use more expensive premium fuel.

Your plan for potential use of E15 in future street fuel seems reasonable.

I am in complete agreement with Bruce's comments. I left EP to try and restrict costs. But regardless Mike is doing what he has been directed and SCCA has made the call that 93 is the way to go apparently. I don't understand why 91 couldn't have been used and then the spark tables get restricted so it won't adapt to higher octane fuels, seems like that would have been most economical (although I would suspect high altitude locations could be penalized for it).

Bill almost all TC BP stations have 93 octane with ethanol. I know you have been running non-ethanol and most are at 91.

I agree with the BoD decision to not require racing fuel, but 93 is not the answer. If the intent is to reduce the need for using 100 octane fuel, we need it to work at 91 in California There may be exceptions at some tracks but for the most part we've blended 91 street with 100 track at 50/50 to be safe. While it won't take as much to blend to get from 91 to 93 (let's say 2 to 1 to make it easy), it's still a cost and effort issue. Can't believe it would matter that much to calibrate appropriately for 91...

I'm with Bob. We don't get 93 out here, that's why we've been blending. It's almost impossible to find non-ethanol fuel in California, too.
Dave

Hey everyone, Thanks for the input, I don't want to get in a tit for tat with you guys..! We have a long time till the public release of GEN3 kits. The sample size is now 4 and #5 should ship next week. I write little bits and pieces so all of you have an idea of GEN3 progress.

We all hope the R&D program will bring any weak links to the surface, so we can update parts or systems and provide a taste of GEN3 performance before the kit is delivered to you.

I promise, we are doing our very best to make SRF GEN3 the most Hassle Free / Fun, Spec Racer to date.

If you feel you have valuable input, contact your CSR they should be your first point of information, we have monthly CSR conference calls to try and keep up with current events in your area.