Mark Hubley

I've owned my car for eight years. For about the first six years, I always used 87 octane gas, and never had any problems. About two years ago I started to hear some knocking on hard acceleration. My first attempt at a resolution was to try different brands of gas. For a couple of months I tried Shell, Citgo, Exxon. All of their 87 octane gas caused knocking. So, I switched to 89 octane, and no more knocking.

Just for grins, I tried a tank of 87 again. Sure enough, the first time I stepped hard on the gas I heard knocking.

An '86 na should, as far as I know, work fine on 87 octane. It worked just fine for me for a long time. Anybody have any ideas on why that should change? Given the increased cost of gas, I wouldn't mind going back to 87.

Thanks,

Mark

SoCal Driver

87 octane may not be 87 octane. You can reset the DME to accept the lower octane gas. Go to www.frwilk.com . The DME section will show you how to use the multi possition switch to set the timing and fuel.

eohrnberger

OK, so frwilk.com says that this switch is retarding the spark timing. I'm thinking that this would have a performance reduction right along with it. Right?

Dave in Chicago

I thought the car required premium. That's what I recall running in my '88 NA. What does it say inside the gas cap and manual on the late 944's?

eohrnberger

I know that it does in mine. On the dash by the fuel gague, and in the manual. I've always put 91 or preferrably 93 in it, but it's a 10.9:1 3.0L engine. The 2.5L may, or may not need it.

yellowline

Perhaps carbon buildup on the pistons, which raises the compression ratio? Or maybe I don't know what I'm talking about.

I've used 89 in my car, never heard it knock. I do want to try a tank of 87, though.

cjeckert

I doubt you could ever get enough carbon build up to drasticly change the compression ratio but carbon build up can lead to hot spots in the combustion chamber that can cause the 87 more likly to preignite.

Porsche-O-Phile

Do you have a euro-spec engine?

Techno Duck

The '88 and '87 had higher compression engines than earlier models i believe. The '88 being even higher than the '87's compression. ...Something like that. Both had higher compression than the cars from '86 and before.

I am pretty sure my manual states i need 91 RON, so whatever that works out to be. Before using FRWilk's chip i ran 87 octane without any problems at all. After using the chip i started out with 93 and over the course of a month or so worked back down to 89 which is what i still use today. My father accidentally filled up (12 gallons) on 87 one week he used the car, to my knowledge he had no problems with knocking and i had no problems running off the remainder of the gas in the tank. But to play it safe i still only use 89.

Robert D

In the 86 we ran regular 87 octane and it did not knock. This was on a rebuilt 2.5L motor with ~30-35k I'd guess miles on it (odo broken). That car idled and drove like a champ with low octane fuel...

Litespeeds

I have a 1988 944 na which I recently bought and the owner had a computer upgraded chip which stated that I run 91 octane and also octane booster but when I put my first tank of gas in, I figured I would go against his words and fill up with 87 octane. Sure enough, you can hear knocking. Since I needed to smog the car since it didn't pass, I decided to remove the aftermarket chip and put the stock one back in. Now there is no knocking at all with the 87 octane fuel. Since then I have filled up with 91 octane when the tank was about 1/2 full with 87. I am planning on putting the chip back in since I need every little bit of power I can get from this car for track use.
Someone mentioned to me to check my spark plugs as this could be one of the reasons why it was pinging with the lower octane fuel.

inactiveuser92616

I run my 87 on the cheap stuff all the time, and up here I believe that is 85. Never a problem.

Mark Lue

I did the same mistake and put 87 octane in when using the Wilk Chip, it does not knock if you drive the car casually but if you accelerate hard or accelerate in too high a gear it will knock and make a sound like you you are shaking "a bag on ball bearings".

Without the Wilk Chip the car runs geat on 87 octane gas no pinging.

Mark Lue

Too HOT a plug will cause the car to ping!

Dirty injectors or too lean a mixture may also contribute as well. Add a bottle of Techron to your gas near empty drive for a little while then fill er up.

M758

83 to 87 944 and 87 924Srun a 9.6:1 compression ratio (US version) If they are working properly and run the stock chip 87 octane is fine.

For 88 Porsche increased compression to 10.2:1 on the 8v NA motors (944 and 924S). These engines along with the 89 require 91 octane premium fuel.

The 944S, 944S2, Turbo and 968 all requrire at least 91 as well.