should i start putting in 93 octane?

[niq_nak]

i just recently got everything settled to where im able to drive my car so im starting to use up some gas. it has 87 in it now.. and i believe has always had 87 in it. would it really be worthwild now to start putting in 93? could it do any harm since the engine probably has never run as hot as it would with 93? also, would putting in 93 effect my gas mileage for the better?

oh, the car has 160,000 miles on it btw.

thanks

[EverWiser]

Okay...Your engine will not run hotter with '93 octane gasoline but it CAN run hotter without detonation...The octane rating is simply the gas'es resistance to detonation. If you are running a "chip" that advances your timing or have done other work that may have uped your CR, etc. sometimes the gas will "light-off" before the spark plug fires. When this happens you will get two burns (one from pre-ignition and one from the spark plug) and thus two "wavefronts". When these two (or more) wavefronts collide you get the shock or "SLAM" called detonation (also called, sounds like, pinging) and it is very hard on the engine, especially piston rings and lands. The higher octance gas will resist this premature ignition through addtives and such therefore eliminating detonation/pinging. If you don't get any pinging under load now, higher octane gasoline will only cost you more money...Just my .02.

[nando]

unless you have a chip or a lot of engine work, anything other than 87 octane is a complete waste of money (except if you drive a M3 or 318is, then premium is required).

and high octane fuel doesn't "resist" detonation. It just burns slower, if you have a high compression engine and you run low octane fuel it can sometimes ignite before the spark goes off just from the heat and pressure.

[///M Powered]

unless you have a chip or a lot of engine work, anything other than 87 octane is a complete waste of money (except if you drive a M3 or 318is, then premium is required).

and high octane fuel doesn't "resist" detonation. It just burns slower, if you have a high compression engine and you run low octane fuel it can sometimes ignite before the spark goes off just from the heat and pressure.

excuse my ignorance but why does the 318is require premium, my freind has one and was telling me how it sucked filling up.

[EverWiser]

I'm not one to argue with a moderator but higher octane fuel does not "burn slower". Check this link out: http://auto.howstuffworks.com/question90.htm. Higher octance "resists" "pre-ignition" and pre-ignition causes detonation/pinging. I agree with you that higher compression ratios (and even carbon deposits that get hot even to ignite the compressing air/fuel mixture) can cause pinging. High octane fuel resists ignition due to compression.

[niq_nak]

thanks for the input. i just filled it up with 87. maybe down the road ill get a chip and have to start using the 93.

[hamann318is]

unless you have a chip or a lot of engine work, anything other than 87 octane is a complete waste of money (except if you drive a M3 or 318is, then premium is required).

and high octane fuel doesn't "resist" detonation. It just burns slower, if you have a high compression engine and you run low octane fuel it can sometimes ignite before the spark goes off just from the heat and pressure.

excuse my ignorance but why does the 318is require premium, my freind has one and was telling me how it sucked filling up.

I'm pretty sure it's related to the high compression ratio of the M42.

[Rob]

the compression makes it almost necessary. My m42 knocked on the dyno running 87 octane

[Ryan Stewart]

yes, that rattling noise was your engine consuming itself. Make sure and run 91-92 and hope the fire rings on your gaskets hold.

As for people with M20s only run a higher octane if your engine starts rattling like that. Mine would knock on hot days so I had to jump to 89 which solved the problem. I look foward to finding LOTS of carbon when I start pulling this engine apart.

[///M42 sport]

so using 93 would prevent carbon buildup on the m20?

[Ryan Stewart]

no, I suspect that carbon buildup caused my compression to rise and insulating the cylinders so they couldnt dissapate heat as well which would have lead to the detonation.

The carbon was the problem.

[Rob]

I've got an M42, and when I advanced the valve timing to 5 degrees advanced on the intake sprocket I heard ratteling.

for shits sake put that cam how it was factory then before you destroy your motor

[EverWiser]

In extreme cases of detonation/pinging, the ring-lands (piston ring grooves) and or the piston rings can be broken which then can severely score your cylinder walls past the point that a rebore can fix. It can also lead to premature failure of your rod and main bearings. If it's pinging you're destroying your engine.