Ok so I recently purchased a 1986 928s manual tranny with 108k miles on 'er

Now my question, is it worth putting the premium gas 91+ octane in the car?

this is my first car and my parents say its not worth putting in that kind of gas in a 22 yearold car, they say i won't be able to afford it etc etc especialy with the prices in my region (canada). I say i should be putting in the gas porsche recomends regardless how old the car is because the higher compression ratios and the robbing of power lower octane might do.

So am i right? should i still be putting in premium octane?
will the car be "harmed" with lower quality gas?

I personally love the car and its in great shape for what i payed for it and i would love to keep it for aslong as i can.

my parents also say the regular octane gas is much better then it was 22 years ago so it would be fine..

 

Using lower octane gas than what's recommended can rob you of power through retarded ignition and potentially cause other problems, like pinging. Using higher octane gas than what's recommended for your car is a waste of $$$. It doesn't buy you any extra power because your car isn't designed for it. If your '86 calls for 87 octane (regular), that's what I'd use.

 

It works out to about the same cost per mile I think. You'll get slightly better mileage with the premium, but not enough to offset the cost. Off the top of my head, I don't think your car has knock sensors, so if you're going to be driving hard in summer heat it might be worthwhile insurance against detonation.

And FWIW, gas quality seems to be getting worse, not better.

 

You can't afford not to. The car will not compensate for low octane.

 

OK, you now know not to trust your parents regarding things automotive. Your car has a high compression engine (10.0 to 1) and it will experience detonation if you don't use the highest-octane (i.e. premium) gas. And detonation will gradually erode metal from the combustion chamber, which is a bad thing for sure. At least you can take comfort in the fact that, with gas prices so high, the extra percentage cost for premium is almost negligible.

 

search is your friend! This is the definitve thread on gas for our cars. You should run premium....https://rennlist.com/forums/showthre...ht=regular+gas

 

Remember that carbon build-up over the years will up the compression ratio requiring a higher octane.
You could connect the low octane loop located on the LH. Look for a green wire with a white connector hanging off of the 25-pin connector. Just connect it this will will pull back your timing 3 degrees.

 

That's true, but the trade-off in performance is not worth it. It will run sluggish. If one is worried about 10 or 20 cents a gallon difference for a high performance car like this, then you have the wrong kind of car. Honda's get good gas mileage and use regular

 

Compression and timing are what causes you to have to run premium. It takes more heat to ignite premium, so it won't detonate, or light up before the spark plug fires.
Higher timing will generally give you more power at the higher rpm range, taking away from the lower. Now if you have a car such as an Porsche 928 with it's relatively high compression engine, and you put 87 in it, it will detonate. Then the knock sensor will have signal the ecu to retard the timing, causing you to lose power and put a pottential danger to your engine (detonation= super bad).
So don't put 87 in your sports car, thinking that there is no difference, engines are designer for specific octane rating so, as said before, put whatever is recomended by the manufacturer. Hope this helps!

 

The S³ engine is high compression, but the cams are long duration, so the effective compression is lower. These engines can take a lot of ignition advance without pinging.

You can run the middle grade without issue, if you have the stock ignition chip. If you don't drive on the track, run the A/C much, and the fan clutch is working, you could run regular and may never hear a ping.

IME, even with a performance ignition chip, the medium grade works fine, but for extended full throttle, high rpm driving.

You can do some simple things to lower the engine temps, too, which will make it safer. Colder spark plugs (WR5DC), covering the radiators to keep hot air out of the airbox, and removing the rear hood seal in summer, to name but a few.


thread

 

I stand corrected.....learn something new everyday! As Emily Litila always said..."NEVERMIND"

 

That is an interesting thread

I always thought that Premium would do better job at keeping the fuel system and injectors clean.

So if for .20 cents per gallon I can keep my fuel system clean, then I guess I am in for Premium...............

Plus I think we all like to treat our Sharks to the best (of everything right?), so if spending the extra $50 per year for Premium makes me feel good about making my Shark feel good .................then so be it right?

Shawn
84' 928s Pewter Met
74' Triumph TR6 (Summertime Top Down Fun)

 

Although base gasoline all comes down the same pipe, the additives make a difference. (I would never buy Arco, for example.)

Chevron/Texaco has Techron in all grades.

 

Your parents are probably thinking of the modern detergents in gasoline that (depending on brand) ARE better than older formulations. But octane has fallen considerably over the years. So they do a better job of keeping your engine clean but have lower octane ratings.

 

Yep, I think Exxon is bad too. I did some research on this when I bought my 928 and found that all the major name brands available here (So. Cal) have the good techron-like cleaners in them except Arco and Exxon.