My JPS has the EJ 2.5 Subaru motor. I have been using 91 octane . Subaru says regular is all a stock motor needs-don't know what if any mods JPS did. Am I wasting my money running 91
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You're wasting your money
Might be good when you store it 
Try this:
Run your current tank down to less than 1/4 (as low as you dare). Re-fill to 1/2 with 89 octane and drive it. Get it just under 2,000 rpm in 3rd or 4th gear and hit the gas. It should acclerate with no “pinging”. Pinging will sound like rattling from the engine, like you’re grinding up walnuts back there or something. If it doesn’t ping on acceleration, then it’s OK with 89 octane.
Run your tank down to under 1/4 again and fill half way with 87 Octane and do the same test. If it still doesn’t ping I would stick with 87 Octane in your car.
John Steele is a cheapskate. Unless he (or the PO) made a big deal of all of the wonderful “improvements” made to your engine, it is most likely very stock and a stock Subaru will happily run forever on 87 gas. That’s what they recommend because the engine computer detects pre-ignition (pinging) and backs off the spark advance to compensate for it, automatically.
Higher octane gas simply has a higher flash point to prevent pre-ignition of the fuel/air mixture before the piston stroke and ignition is ready for it. It won’t give you any more power than lower octane gas, it just prevents pinging.
Supposedly higher test gas also has more detergent additives - at least with name brand upper tier gas. A 2.5L Subaru is 9.6-10:1 cr so bet 89 is right octane. I have Miata that is 13:1 cr - it takes 91 but 87 and 93 are typically available, It does get better mpg with higher but that is because it was designed for the higher octane.
I've run 87 in my EJ22 and it doesn't ping. All stock with stock ECU though. Gordon's idea works. You could skip the middle step, probably.
Jerry Freeman/N.J. posted:My JPS has the EJ 2.5 Subaru motor. I have been using 91 octane . Subaru says regular is all a stock motor needs-don't know what if any mods JPS did. Am I wasting my money running 91
Yes.
IaM-Ray posted:Might be good when you store it
I haven't found it necessary. If it makes you feel good though, go for it. I never use Stabil and have left 89 gas in my car over the winter inside my dry, semi heated garage and it fires right up next spring. Maybe your gas is different.
Actually, not totally true. My buddy down the block reminded me of a time we were at his house for a new years eve party and about 2 am I gave several people a couple of laps drifting around the neighbourhood on that mild, clear night. Top down of course and only about an inch of snow on the road.
So, yeah. Maybe better to go with high octane and Stabil.
the ecu can back off for lower octane so long as the knock sensor is working. .... I have seen engines with a completely loose knock sensor ... duh
You all need to back up a little here. Most Subys have factory ECU except Stroud who is running a carb.
Indeed, Subaru has designed most EJ-25s to run 87, excepting 1995-1996 DOHC 2.5. That one took higher octane fuel.
JPS uses the Stinger aftermarket ECU. Not a single one of you(including me) has any inclination of what the spark and fuel maps and programming are, or if the Stinger uses a knock sensor(I suspect not).
So if Steal says to use 91, I'd use 91. Or follow Gordon's advice on filling with lower octane and running it HARD on a hot day. Pinging sounds like a shaking a coffee can filled with steel balls. Pinging is bad.
Since some people busted my hump about cheap oil, how about here? How many miles do you drive a year? How much extra does it really cost to use premium?
Danny, your right, If JPS uses the Stinger ECU, and they have mapped the powerband using 91 octane you need to stick to it I would think.
I also have no clue if Stinger uses the knock sensor.
I just read the stinger specs with no mention of a knock sensor.
thanks for the info--- also just learned about top tier gas when I was reading the manual for my C7 vette- around here (N. New Jersey) only Exxon, Sinclair are all over and some Sunoco and Mobil are on the top tier list--- I know what pinging is, even my stock 390 in my 61 Caddy runs very well on regular
Jerry Freeman/N.J. posted:thanks for the info--- also just learned about top tier gas when I was reading the manual for my C7 vette- around here (N. New Jersey) only Exxon, Sinclair are all over and some Sunoco and Mobil are on the top tier list--- I know what pinging is, even my stock 390 in my 61 Caddy runs very well on regular
Your suby engine is not on the same level as your detuned c7 but if you feel better running 91 octane I say do it!
Stinger with wire harness is like $2,000? That's more than I paid for my engine—with the whole car attached to it—plus the Shiels wiring harness mods.
Good to know!
Looks like the PLUS with the Stinger is you can install any fuel-spark map you want, even custom make one. That seems like it'd be worth the premium if you're into tuning.
Yes sir that is why a stock ECU is attractive and a 240hp turbo with stock ECU also is inexpensive in reality compared to a N/A 2.5L 200hp engine even though you get the turbo kick, it is the best bang for your buck in spite of the extra plumbing.
Ed did you know that some people sometimes do not use the VVT on their engines when they use the ECU from a different year. My Subie Tech guy says he has seen people swap engines and use the wrong ECU and not use the VVT... Why I do not know but you lose quite a bit of hp... just saying.
Because variable valve timing is a GOOD thing. Advanced camshafts at low revs adds torque, retarded cams add high rev oomph. Overall more power than you can get with fixed camshafts.
There was a trick on the earlier Ford 2.3 liter engines (used in just about everything, it seemed) where you removed the cam drive pulley, filed the key slot wider by 50 thousandths and re-assembled it with a shim next to the key to advance the valve timing 10º - 15º (depending on how aggressive you got with the file). Instantly added 15-20 foot pounds of torque, low-to-mid revs and slightly better gas mileage. And it was FREE!