Harm from 87 octane?

boomvang · boomvang's Garage

I did a really dumb thing, I fueled up with about 10 gallons of 87 octane in my 85 Carrera. (I'll blame sky high gas prices) I only drove a couple of miles and while it ran OK with no apparent pinging at speed, I did notice a knock at idle. Did I do any harm? Can I dump some octane booster in or should I drain and replace with 92? I had a rough time sleeping last night for worrying.

masraum · 05-05-2005, 04:33 AM

It shouldn't really be a problem as long as you don't push it really hard. Many people have reported running their SC's and Carrera's on '87 octane. Is your tank full? In not then fill it the rest of the way with 93oct and that should help. The biggest danger is from when it's hot, or when you are really pushing it under load. I think you should be ok since it should be cool in NY, and just don't drive it at 100%

And don't do that again.

Formerly Steve Wilkinson · 05-05-2005, 04:36 AM

I'll be interested to see what the experts say. Maybe Steve Weiner will chime in. Certainly I'd drain and refill on my own twin-plug, high-compression engine, just to be safe, but I think if I had a stock engine I'd be lazy enough to simply drive the tank's worth with a light throttle foot and moderate revs. And I should think the octane booster additive would help. But that is a totally uninformed opinion.

Stephan

jmohn · jmohn's Garage

Shouldn't be a problem. Look in your manual, I think your '85 is designed for regular (87 octane U.S.). Remember Euro. octane numbers are higher than U.S. for the same grade of gasoline. You shouldn't notice a "knock" at idle even if your car is meant to use higher octane, octane ratings become a factor when the engine is under load not when it's idling.

Jerry M
'78 SC

SpeedracerIndy · 05-05-2005, 04:41 AM

If there is carbon buildup in the engine, it could increase the octane requirment. Other than that 87 should work fine in a 84-86 Carrera.

jmohn · jmohn's Garage

Stephan Wilkinson bring up a good point, I assumed you have a stock engine. If your engine is modified, and because of the modifications requires higher octane fuel, you may be well advised to add octane booster or drive it gently until you can re-fuel with the proper octane gas.

Jerry M
'78 SC

Paulporsche · 05-05-2005, 04:44 AM

I agree w/ Jerry. I would be concerned about a knock @ idle. Are you sure it's not a miss, or (I hope not!) a chain tensioner or bearing about to go?

boomvang · boomvang's Garage

I am pretty sure the engine is stock, bought it from the original owner with full records which did not include any mods. It is for sure a light knock at idle, the car was not knocking before. I did get it on once, about 3/4 throttle for a quick burst. Boy, I hope I didn't screw anything up.

Paulporsche · 05-05-2005, 05:05 AM

Maybe you could have someone elso listen to it. These cars make a lot of mechanical noises. It could be an exhaust leak, a pulled head stud, or just the fan, or nothing, really. If the car is stock, 87 shouldn't be problematic. I suppose, if you are still unsure, dump some octane booster in (it will help a little) and drive the car easy. You might also check your timing to see if it is advanced too far, and set it correctly, or even retard it a little for this tankful, then set it back.

SpeedracerIndy · 05-05-2005, 05:20 AM

Quote:

Originally posted by Paulporsche
Maybe you could have someone elso listen to it. These cars make a lot of mechanical noises. It could be an exhaust leak, a pulled head stud, or just the fan, or nothing, really. If the car is stock, 87 shouldn't be problematic. I suppose, if you are still unsure, dump some octane booster in (it will help a little) and drive the car easy. You might also check your timing to see if it is advanced too far, and set it correctly, or even retard it a little for this tankful, then set it back.

You can't set the timing on a 3.2 Carrera motor can you?

masraum · 05-05-2005, 05:24 AM

Quote:

Originally posted by boomvang
I did get it on once, about 3/4 throttle for a quick burst. Boy, I hope I didn't screw anything up.

I wouldn't worry. As long as you didn't run the thing up to redline in 4th and 5th you should be fine. I'm certainly no expert, but I think you'll be fine as long as you don't get the engine up to 230* and then flog it or try to redline 5th or something. I think before you do any real damage you'll have to be pushing really, REALLY hard.

boomvang · boomvang's Garage

Thanks for the reassurance. I do think I will siphon at least 5 gal and replace with the best gas I can find. My baby deserves the best!

sammyg2 · 05-05-2005, 06:16 AM

Octane booster is a scam. When they say it will raise the octane 4 points that doesn't mean from 87 to 91, it means it will raise it from 87 to 87.4 don't waste your money.
Top off the tank with premium and don't worry about it.
The knock at idle doesn't have anything to do with the gas, something else is wrong. Get that checked out right away.

vash · vash's Garage

i am with sammy. top of with premium and turn you tankful into "plus" fuel. you know the 89 octane stuff. that is what the gas station does anyways. i think they mix it 60/40.

cgarr · cgarr's Garage

Does your DME have a switch on it like my 86 which lets you retard the timing a bit should you get some bad fuel?

Craig

boomvang · boomvang's Garage

I don't know, I will have to check when I get home. Who knows, maybe my paranoia about my baby has warped my sense of hearing. I do tend to worry about her.

Quote:

Originally posted by cgarr
Does your DME have a switch on it like my 86 which lets you retard the timing a bit should you get some bad fuel?

Craig

Bob's Flat-Six · Bob's Flat-Six's Garage

Quote:

Originally posted by boomvang
I don't know, I will have to check when I get home. Who knows, maybe my paranoia about my baby has warped my sense of hearing. I do tend to worry about her.

You have to watch out for paranoia, really

You'll be fine. How much gas was in the tank to begin with ?
They hold about 20 gallons. So your probably at a higher octane than 87.

I would just add higher grade gas when you have room.

Be very careful if you siphon off gas. And use the proper type of container.

These are noisy motors. My guess is your just hearing the valve train. Maybe they need adjusting?

TerryH · TerryH's Garage

I would not use over the counter octane booster unless you want to coat your combustion chambers in an orange crud. Put in a few gallons of toluene or xylene(paint store) or top off with high octane gas.

ras911 · ras911's Garage

Is it April 1 already?

I think you will be fine , kiss the car goodnight and take two aspirin. Check back in the morning . Try not to lose any more sleep!

qcwang · 05-05-2005, 12:05 PM

Quote:

Originally posted by boomvang
Thanks for the reassurance. I do think I will siphon at least 5 gal and replace with the best gas I can find. My baby deserves the best!

Before you go through all that work. Check your manual and see what grade of gas is recommeded for your model since your engine is stock. If 87 octane is ok, fill it up and enjoy, if premium is recommended top it off with such and enjoy.

When I first got my 83 SC (stock engine) two years ago, I too was in the frame of mind "My baby deserves the best". Still am but with more scrutiny now. I had filled with premium all the time, thinking this is a Porsche and only the best gas will do. From learning on this board and reading my manual carefully that 87 octane was recommended, I switched. I could not tell a damn difference!! I had wasted all this money on premium this whole time. What I thought was the "best" really wasn't. Just my two bucks (inflation)!