Question on Octane ratings for Michael or anyone else familiar with the subject

[The Shape]

When I bought my car about 3 years ago I knew nothing at all about cars. I just pumped 93 octane gas because it is an HO motor so I assumed it needed it. After seeing a few threads about it and reading up on it from some of the links Michael and others have posted I decided it was a waste of money. So I ran about two tanks of 87, but the car didn't seem to run the same. It is hard to pinpoint, but the engine just didn't seem as smooth. I am just wondering if by runing 93 all of this time my engine for some reason now needs it to run correctly? And if so why? And other than the hit to the wallet is there any damage to be caused by running 93 as opposed to 87? My timing is at 10* on a stock enginine by the way.

 

[giddyup306]

Octaine is the rating of resistance of detonation under pressure. A stock mustang would not need high octaing fuel providing the timing is stock.

 

[Rick 91GT]

You want to run the lowest you can with out any pinging, this isures a hot charge and the car will be at peak power.

I found on the stock style 5.o's I work on they do not like 87 but run good on 89, why not 100% sure. I always ran 92-93 in mine when it was stock years ago.

 

[RickyB]

general consensus is to run the lowest octane possible w/o detonation, pinging, etc...if it runs like crap with 87, try 89, if it still does step up to 91/2, if that dont work something must be wrong with your car ...cause im pretty sure foxes werent rated at 93

 

[The Shape]

Yeah the owners manual says 87. But like Rick91Gt said my car doesn't seem to like that. I may try 89 and see what happens. Never seen 91 ocatne. Here we just have 87 89 and 93.

 

[Michael Yount]

Shape - do a search on "octane ratings" in google - you'll learn a ton and can come back and educate us about how the rating system has changed overtime.

My car has a mild H/C/I set up, runs with 18 degrees initial timing, 34 degrees total in by 2800, and I run 87 octane with no detonation at all even in the summer heat.

You can also do a search in Car & Driver - they did an octane test a while back - testing different cars back to back with different fuel. Absolutely no difference except for cars that had knock sensors to allow more timing when higher octane provided detonation resistance.

 

[Rick 91GT]

It also depends on the brand of fuel and if it is SUMMER or WINTERIZED gas, way to may things can cauase it to run rough.

I noticed a little better burn on my plugs with the 89 over the 87, otherwise I would have run the 87. The plugs are your true reading off what is going on.

I think around here you can get 91,92 or 93 depending on what the brand is.

 

[Schlodes]

I run 91 Octane from the 7-11 around the corner. It's decent stuff cause I could run 15 PSI boost in the T Type with minimal [2-3*] knock retard on the scantool. Sunoco 94 would allow for about 17 PSI in that car with the same knock #s.

I run 15* initial timing and no pinging... I've used Sunoco 94, and it doesn't run much diff than the 91. Wonder who supplies 7-11s 91 fuel?? Could BE Sunoco for all I know..

 

[Michael Yount]

It also depends on the part of the country - there are over 130 different formulations required by the EPA all over the country - and people wonder why gasoline prices are high; just keeping the different formulations straight/separate in the liquid pipelines and tank farms is a logistical nightmare.

 

[tmoss]

I run 16* on 89 with no detonation.