10% Ethanol Added 91 OCT vs. 88 OCT No Ethanol Added for 92 JDM Stock Tune
 

Hey all. Searched, only found this thread that wasn't very definitive: https://www.rx7club.com/3rd-generati...s-jdm-1136700/

I am picking up a 92 RHD FD less than a week from today. The current owner of the car (a private party importer, essentially) texted me this morning and said the car would need to run no-ethanol-added/ethanol-free gas "for safety reasons" on the stock tune, as gas in Japan does not have ethanol added.

The highest octane ethanol-free gas in my area, to the best of my knowledge, is 88 octane. Wouldn't it be better to run 91 (higher octane fuel) with 10% ethanol added, even on the stock JDM ECU tune?

Coming from other non-rotary cars, forums and tuners have always recommended ethanol-added 91+ over non-ethanol 88 because of the increased knock resistance and lower burn temps of ethanol-added fuels. I've even talked with tuners when I switched between e85 and 91 maps (never had a flex tune), and they've told me switching tanks from e85 to 91 was safe, because higher ethanol fuels partially mixed with regular gas acted, in many ways, like an octane booster. Again, burning cleaner, cooler, and offering more knock resistance.

However, they told me to be extremely careful when switching back from 91 to E85 though, as 91 burns hotter than E85, has worse knock resistance, etc. I know a lot of guys run e85 tunes on FDs and there's a mixed discussion about deposits and buildups from ethanol.

But I suppose my question is: wouldn't ethanol-added fuel, especially at a higher octane (91), offer increased knock resistance, more safety, and no big downsides on a JDM stock ECU car tuned to run non-ethanol fuel? PS: I do plan on premixing at .05/gal, the factory OMP is working, not sure if that makes a difference on fueling.

i've run a JDM ecu in my car on California 91, and its been totally fine. we had have 10% ethanol for ~30 years and it just isn't a problem, if you try both you would see about a 1% difference in mileage

to run E85 you need more volume, larger injectors, different ecu, it wont work on a stock car

My JDM car runs fine on E-10 93 octane.

I think the importer is over-thinking things. Also probably just saying that as a CYA for them. "Oh, you blew up the engine a week later? Sorry, it may have been an old engine with problems, but you didn't run the exact right fuel, so no refunds".

If the car is fairly stock and running 10psi, you will be plenty rich and you will be fine. Run the high octane 91 you can get.

Big thing with any JDM car is give the car a THOROUGH tune up and fluid change. You don't know the history of this car, anything you can do to help things out is well worth it. All new fluids, new plugs, inspect hoses, inspect EVERYTHING.

Dale

Awesome man, thanks for the insight. I wasn't saying I'd run E85 – I know what it takes to set a car up for that. Was just comparing the two fuels using E85 as a benchmark!

Thanks everyone else for your replies as well. Good to know 91 octane will be fine. I plan on making sure the car hits the trademark 10-8-10 when I test drive.

@DaleClark It's actually a pretty unique situation where it's a smaller importer and they have a YouTube video series documenting the car from being purchased at auction and its refresh. I have compression videos, as well as video documentation of fresh coolant, plugs, wires, lower rad hose, and a few other things.

Is the car stock? If it's completely stock you should be fine with 91. There is a knock control system. E10 makes no difference.

@arghx The car has some basic bolt-ons, but the turbos are stock and engine is stock. Only mods are:

- ARC Intake
- HKS Charge Pipes
- Samco Radiator Hoses
- GREX (Trust / GReddy) Oil Relocation kit
- Apexi Muffler

I know modifying intake/exhaust can sometimes cause turbos to spike or run higher than 10-8-10 factory boost levels. I plan on watching that closely during my test drive and if it's overboosting, will be extra careful until I can get the car tuned. Assuming those higher boost levels could cause it to run lean.

Sounds like you have the main cat still and probably the stock downpipe. You will be fine there.

The ARC intake isn't a great design, long term you may want to swap that out.

Dale

Sightly OT, but which version JDM ECU are you running?

i have two, a stock N3A7, and a chipped N3A7. both run just fine, the stock one passes smog easily.