would runing high octane gas make my car quicker and have less hessitation than runnin on the cheap stuff?

its a 1971 so what about a lead substitute?

 

The level of octane you need to run depends mainly on the compression ratio of the engine and how much timing you are running.

I'd say anything above 9:1 with a decent amount of timing should have premium.

I always ran premium in the '85...and did notice a difference. The LB9 had 9.5:1 compression and I did run a little more timing than stock. When I ran regular unleaded, I would get some Knock Retard.

What are the specs of your motor?

Also...this would be better in the tech/gen engine board.

-Doug

 

Well, the thing about octane is that some people automatically think that higher octane= faster. That's not necessarily true, the octane number is the fuel's ability to resist detonation, not ability to make HP, so in a new computer controlled car it really doesn't make much difference, because the computer can retard the timing and play with the spark (just look at the new LS1's). The only time it's worth increasing your octane number, and this probably applys to you, is if your engine is knocking (or you've retarded the timing to compensate for that), like 85transamtpi said. You want to run the lowest octane number you can that will not put you in detonation range. If you have very low compression, that's probably 87 or 89 octane, but if you have a performance engine with higher compression, you'll probably need 93 or maybe even higher to prevent it from lighting the fuel off early at high rpms (knocking), it depends on your combo. Also if you have a car like an LS1 (I know you're talking about a '71, but I'll toss in a little extra knowledge), you can run 87 if you don't drive it hard, if you plan on zoming around at high rpm's like most people, that's when you'll want the 93 so the computer doesn't have to retard the timing and the motor can make full power.

Oh, and leaded fuels was just a cheap way to boost octane rating until the EPA outlawed it, its not any sort of high performance fuel. Hope some of this helps.

 

Exactly what these guys have said, don't waste you're money on higher octane gas if you car doesn't have higher compression.

 

I only use 92 octane ethonal blended pump gas. I don't need anything higher.

There's no more BTU energy in 92 octane as there is in 87 so you get the same amount of power out of each. The higher octane burns slower so that it doesn't preignite (knocking) when subjected to higher compression or power adders.

Using too high of an octance fuel can decrease performance because the fuel won't burn completely in a low compression engine.

You only need enough octane to resist detonation. With the newer cars that have knock sensors, it's hard to tell what octane works best. You need to see realtime data from the computer to know if the timing is being retarded. Having an LS1 running 87 octane then finding out they have more power running 92 just means the 92 isn't causing spark knock and the computer isn't retarding the timing giving them poor performance. With the computer controlled fuel management systems now, you could still run 87 octane in a 9:1 engine with no problems. Just a little lack of power.

 

Out of curiosity, what should an '89 L98 be run with? I have put both 93 and 89 in and cannot tell any difference, however, I have been driving fairly lightly. I use my TA mostly for commuting, though I don't want to be caught out if, for some reason (say, if I was to race someone), I need full power. I don't have any data acuasition(sp?) equipment, so there is no way I know of to find out about any retardation.

 

If you can't tell the difference, then there's no difference.

Actually, most regular gas these days contains more heat energy than "premium", most of which of merely regular with some additives; most of the additives that are used contain oxygen, so you're literally buying extra air by the gallon at gasoline prices. Kind of like the beef at the store that's been pressurized with water and red food coloring so that you pay $6.99 a pound for water.

The only time that "premium" will make more power is if your ECM sees spark knock on regular and retards the timing. As long as that doesn't happen, the engine will make more power on regular.

So, unless you just like spending extra money for nothing, use the cheaper gas if it runs the same.

 

its a 1971 AMC 360 2bbl 285hp@5600 rpm

it runs like total crap on cheap gas, and diesels when you shut it off, the valves ping like a bitch. It runs alot cleaner on the premium

 

I'm wondering if I should try 87 octane (much cheaper), but I don't want to buy a tank full of gas that's bad for my engine, yet if it isn't mostly 87 it's not really an accurate test. Quite a catch 22, don't you think?

 

Vavles don't ping. Combustion does.

The flip side of my earlier comment is that if you can tell a difference, then there's a difference. Apparently your car has enough compression to require the slower-burning fuel. However the "premium" fuel by itself doesn't make your car faster. It's possible though not likely that it might be faster on racing gas, there's only one way to find out.

It's kind of a shame that there is no pump gas available today for older, higher compression engines. Your predicament is one of the reasons that engine building choices have been forced to change over the last 30 years, and why the cars that were fast in the 60s aren't practical any more.

 

well, tonite the strip is open for test&tune, im going to run 1/4 tank of 92 octane and mix it with 2 gallons of the TURBO BlUE racing fuel (109 octane?) heard it might shave maybee a few .1's of the time

also what about adding a lead substitute to my fuel?

im alredy running on a back up carb so i need the best fuel

the original carb is currently being rebuilt at the shop, so i have an undersized (compared to the original) ford motorcraft carb on the motor, it stuters at high RPMs and doesnt dump enuff fuel, so i have a few things to fix.

I recently embarrassed my self in the ole AMC by taking a former 14 second car (stock with original carb) and runnin low 18's (with junk carb and low octane)!!

thanx for the help

 

right now im running 93 octane in my lo3 because the base timing is way up there. like 12 degrees base compared to the 0 stock setting car runs so much better now

 

DO NOT ADD LEAD!! It is completely unneccesary on modern cars, it would make no difference to your car except that it clogs the catalyticv converter. So, unless you have a way of circumventing the cat, don't do it at all, even if you can, I highly doubt it would help anything.

I think you have much more to gain by tuning your carb than anything else at the moment

 

he said he has a 1971 AMC.........not a new car lol, and those cars originally burned leaded gas, and unless he had the heads redone the additive wont be a problem..

 

I keep forgetting that we're talking about a 1971 AMC on thirdgen.org, my bad. ah well, we all make mistakes . I suppose adding lead would be something that might be useful. I don't know if those cars were designed for lead or not, I'm only 21, a little before my time. As I recall from hs auto class, there were only a few years that lead was added to gas (mid 60s to early/ mid 70s?). Don't you need to put harder valve seats in if you want to run unleaded in a lead era car? I know that my great aunt's '73 chevelle (307) ran fine on unleaded.