desertsubaru Posted July 1, 2004 Share Posted July 1, 2004 I have read alot of threads that say octane dosent change peformance or gas milage. My 1986 N/A ea82 gl wagon likes 89 octane over 87 i get 100 more miles a tank and my power pics up greatly when i use 89. I know this has been gone over abit but i would like to know if anyone else gets better power and milage out of higher octane. In my oppinion it depends on the car its self! Link to comment Share on other sites More sharing options...
All_talk Posted July 1, 2004 Share Posted July 1, 2004 If a engine is designed/tuned to run correctly on 87 octane using a higher grade will make little to no difference without retuning to take advantage of the better fuel (typically at least a timing adjustment). Since you are seeing a substantial difference your car obviously has some issues with the 87 (detonation and such), another test would be to run 92/93 in your car and see if you gain anymore, I doubt that you will. In my RX I recently switched to 90 octane, I was getting some mild detonation as the boost came on with the 87. With the 90 the detonation is gone, engine is smoother, power is better but no noticeable change in mileage. But its possible that could be due to me enjoying the power… Got Boost? Gary Link to comment Share on other sites More sharing options...
mcbrat Posted July 1, 2004 Share Posted July 1, 2004 ea81's at least, are designed to run 90 or better...... I would assume the same for ea82's but don't know for sure..... the owners manual should say..... Link to comment Share on other sites More sharing options...
NV Zeno Posted July 1, 2004 Share Posted July 1, 2004 ea81's at least, are designed to run 90 or better...... I would assume the same for ea82's but don't know for sure..... the owners manual should say..... Y'know Mick, I seem to remember way back when my '83 California-spec EA81 was new (I know the original owner), I was told that her car "likes premium gas". Shortly after I got it in 1990, we adjusted the timing so there was no pinging on 87 gas. 200 thousand miles later (285 on her now), there have been absolutely no engine related problems. As a matter of fact, one of the guys at the local Soob shop commented on the "nice power" it has. Go figure. My 2 bucks Link to comment Share on other sites More sharing options...
Guest taprackready Posted July 1, 2004 Share Posted July 1, 2004 Octane requirements are also altitude sensitive. The higher the altitude the less octane required. I run 87 Octane at 4200 ft. in Klamath. When I go to Medford which is down under 2000 I start getting a ping.Bill Link to comment Share on other sites More sharing options...
NV Zeno Posted July 1, 2004 Share Posted July 1, 2004 Octane requirements are also altitude sensitive. The higher the altitude the less octane required. I run 87 Octane at 4200 ft. in Klamath. When I go to Medford which is down under 2000 I start getting a ping.Bill I guess I'm lucky. I've taken that car from sea level to over 9000' passes, no pinging or problems..the only difference I see that's elevation related is that my mileage is significantly better at the higher elevations (6000-plus) than at sea level. Link to comment Share on other sites More sharing options...
Zefy Posted July 1, 2004 Share Posted July 1, 2004 ok so if a EA81 is best run at 87 octane then what would my EA71 be run at??? just a side note but you can buy this fuel additive stuff that will make 93 octane into 106 octane... i saw it on trucks and thought it was cool... i wonder how much of a power gain there will be if you ran 106 if any power gain??? Link to comment Share on other sites More sharing options...
Guest taprackready Posted July 1, 2004 Share Posted July 1, 2004 ok so if a EA81 is best run at 87 octane then what would my EA71 be run at??? just a side note but you can buy this fuel additive stuff that will make 93 octane into 106 octane... i saw it on trucks and thought it was cool... i wonder how much of a power gain there will be if you ran 106 if any power gain??? The only real power gain on any engine would be the ability to advance the ignition timing beyond the factory specs without the danger of pre-ignition. You could also run higher compression pistons with no worries. Bill Link to comment Share on other sites More sharing options...
GeneralDisorder Posted July 1, 2004 Share Posted July 1, 2004 My EA81 in the Brat is running 87, and with the shaved heads now pushing 9.1 compression, and the timing at 10 degrees (stock should be 8) I get just the slightest amount of pinging under load. Very subtle. I will probably reduce it to 9 degrees, and maybe back to 8 once I get the 1600 pistons in, and the compression goes up to around 9.5. Seriously - I have crazy power for an EA81, and 87 runs just fine in my rig - even with higher than stock compression. I don't know why Subaru would have sugested 90 or more - I have read that also in my manuals. Maybe the quality of gas in the 80's wasn't as high. I know they have made progress in 20 years..... I have experienced EA81's that ping - the one in my parts car (which has MAD power) pings going up hills. It has 330k miles on it, and my guess is that it has serious carbon build up in the chamber - probably pushing the compression up in the mid to high 9's. We put the timing at 7 degrees but it still does it up hills under load... The engine runs awesome and has insane power, so we have just left it alone for now. GD Link to comment Share on other sites More sharing options...
desertsubaru Posted July 1, 2004 Author Share Posted July 1, 2004 Wow if an 8.7:1 engine was designed to run premium as per the owners manual that really sucks. Just goes to show what 4 valves and a well designed combustion chamber can get you, with the new cars running 10.5 points or higher on 87 all day long. Dem EA81's can be tuned to run on 87, at least I would hope so! I'm not a big fan of running expensive fuel if you don't HAVE to, so I'd cut timing in an instant to kill detonation on 87. If they had better tuning on the EA81's than a mechanical dizzy and a hitachi they might have gove with more conservative recommendations in the manual, but alas it was the 80's.My car is carbed set up for high altitude from factory. No pings on 87 runs good but not like it does on 89! my timeing is set forward a little as my belts need a change. allso i live at 3500 feet and work at 4500 feet. Does dry air affect milage? In my oppion im not wasteing money on the higher octane becase off the better gas milage and if i do back off the timing it wont run as good ive tried factory specs and it just likes to be advaced. My car has 170.000 miles on it and burns no oil. Thanks for the input every one.I know the original post is 86 ea82... my 86 was a carb'd model, is yours SPFI or carby? I know that SPFI's are ping happy it seems, that's about all you ever read on the newer Loyale's and such. I'm with Alltalk if your engine is tuned to run 87 and you 'upgrade' fuels, your just going to loose power, unless you change the tune to take advantage of the better fuel. The peak pressure point will move with octane and won't be optimized any longer if you up octane on an engine that ran correctly on the lower stuff. A lot of folks will say they gained 'mad' power by upgrading fuels even if they had no audible ping on lower grade, but in that case they were probably too advanced for the lower fuel and the PP was before the optimal 20' ATDC so power sucked, the slower burning high octane likely put it into the correct band for thier ignition curve. One BIG thing to consider is that if your burning oil, as these are old cars, that radically changes the percieved octane rating. Just think of motor oil as really, really low octane fuel, or aka explosives for your combustion chamber. If you don't want ping, fix the burning oil problems first! Link to comment Share on other sites More sharing options...
subynut Posted July 2, 2004 Share Posted July 2, 2004 Wouldn't the quality of the fuel make a differance too? It is for me, if I go to say, Gas City, Shell, or Texeco suby pings real bad at low rpms running at 8 deg BTDC. However, if I use Chevron, the ping is completely gone and I also advanced the timing to 10 deg BTDC! Both were 87 octane. What gives? Link to comment Share on other sites More sharing options...
WJM Posted July 2, 2004 Share Posted July 2, 2004 The 89 DL i had, SPFI, didnt matter what fuel, or what timing setting, it ran fine. Max timing on the dizzy and 87, great fuel milage, good power (for its stock and tiny flowing stuff) and no detonation. Teh 88 RX...it runs OK on 87....does fine, no det, but its kind down on power. I run 93 in it, its much stronger. Fuel milage is really unaffected by octane....but the 93 is less due to my lead foot with the added pull under WOT!! The GL-10, it hates 87. Loves 93. Wont take 87, cant get it to move its self, even playing with the dizzy, makes it worse! Only thing it likes is max/close to max timing, and 93...and cool dry weather. It hates the hot and humid. DL didnt care, RX is sensitive about that as well....but way more tolorant of the 87. Octane DOES matter...higher performance requirements means you need more octane. The DL, just driving....87...RX just diving...87. DL autocross...87...(im telling you these SPFI dont care what gas, just max the dizzy, pour in 87 and GO!) RX autocross, better have 93, garuntee 0.2 sec could be gained on a 30 second course! GL-10....93 at all times....run race fuel for autocross and what so. LOVES it. I remember asking.... ME: where can I get race fuel? Them: Whats compression are you runnin' boy? Me: 7.7:1. Them: HAHAHAHAHA!!! Its amazing that it runs! just use regular. Me: its turbo, no intercooler, and its hot outside, lets be serious. Them: Turbo? whats that? Listen boy, just run regular. Me: Ok guys, w/e....seriously, Ive got a winston cup engine in my late model. Them: oh, finnaly telling us the truth! Go to the corner of *blah blah blah*. You'll have to go inside and pay first tho. Good luck at the track tomorrow night! Me: Sure thing. See ya'll.....them I mutter *dumb *****'es* Link to comment Share on other sites More sharing options...
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