shadopadla

Hey all,

New to the board, and not driving a porsche right now, but I hopefully will be in the near future.

My question, my father has had his 91 Turbo from inception, and has only run about 33-34,000 miles on it, but for most of that time, he's been using low grade unleaded gasoline. I know he's tracked it a few times and most likely used high grade fuel for that, and my mother and I fill it with highest grade whenever we get to take the car out, but whenever he fills it's with the lowest grade.

My question is what kind of damage does this cause, both short and long term, and can it be cured without too much headache and wallet-ache? Since the mileage is still fairly low, can it be cleaned and if stick to high grade, no unfavorable effects?

Thanks, and hoping for good news. Besides the fuel thing, my dad keeps great care of his baby and refers to it as a work of art. I agree and love the bug nose and whale tail!

SonnyV

I would say that it depends on how the car was driven while with low grade of gasoline.

In Turbo car, it is very much depending if you are on full boost or not. It is during full boost (and some people increase boost level too by springs or electronically) that pinging can occur with low grade gasoline.

This is the reason why turbo charge engines have low and lower compression ratio as compare to a normally aspirated engine; to prevent ping/knocking.

You need to ask your dad how he drove the car during that time.

Regards,

Sonny

shadopadla

Thanks Sonny,

I asked and he said he's always used unleaded low grade because he's read papers that there isn't any real difference besides price. He has only tracked it a few times, and besides that, has driven it very behaved on the roads. Always within 5-10 miles of the speed-limit and not to heavy on the pedal. He was a driving instructor so while demands a lot from cars, knows what to do and not do. He's used track stuff a few times as well and said that while it gives a slight power boost, he always uses the lowest grade no matter the car. I need some kind of site and papers/ research that show that's not true?

On his side however, is that his porsche has never pinged or knocked that I've heard of, and he has stock boost. I think the only thing he modified was springs/ suspension on the turbo. He takes really good care of it besides the gas issue, and I'd love to buy it off of him because of how well he's taken care of it.

SonnyV

Personally, I would not worry about it if everything else about the car has been cared for.

As for high octane gas is concerned, in the manual of my '94 Acura Integra GSR, it states that if I were to use low octane gas, the performance will be reduced. The thing is modern cars with electronic ignition managements have a much better control over CIS system on the C2 Turbo. I think that older cars, especially turbo charged cars, don't have much tolerance of various octane levels. I might be wrong here.

Good luck and I hope you get the car. It is one fun car to drive.

Regards,

Sonny

shadopadla

Thanks Sonny,

I'm crossing my fingers too, it's a very nice car. Want to have a ppi done though because just a good thing to do, even with service history and such. My dad takes it to an import that specializes in german/ bmw mostly, but he used to take it to a gas station/ garage for minor work. Most recent debacle was he got a flat tire and took it to a corner gas station for the fix...ended up the station goofed his rim and he had to get a reconditioned one that doesn't match the other 3. I want to get it checked to see if they tried an "original/ replica swap" don't think they did, but that's the only real concern. On the good side, the "goof" stopped him from selling it a month ago, and now he's thinking of selling to me instead of outside the family.

I know it's very fun to drive, first thing I'll do is get a speed detector, otherwise I have to keep within 5 miles of the speedlimit because cops see and hear it and love to pull it over.

Thanks again,

Tyler

Adrian

Dear Tyler,
The 964 Turbo was "designed" according to the Porsche documentation I have to run on low octane fuel, 91 RON over here in Europe. However the recommend fuel is 98 RON. Using lower octane fuels in the 964 Turbo will as Sonny says, reduce performance but not damage the engine. They had to be sold in California remember.
Ciao,
Adrian
964C4

SonnyV

A PPI is a must and don't take it to the same place your dad used to take it.

About the wheels, check to see if the "new" one is original Porsche item. It should have the offset number near the valve stem, and the porsche part number somewhere on the inside of the rim. The replicas are not of the same quality and weigh a whole lot more. I assume you are talking about the 5 spoke Turbo wheels that come standard on these cars from '91 to '92, which should be 9" in the rear and 7" in the front in 17"

I am not sure I understand the matching issue with the rim. They should be the same color - silver, painted. Unless the condition of the "new" one is not the same as the rest of the other rims.

Radar detector is a good thing to have. If you have the money go for a Valentine One. Do a search on this website on 993 or 996 board to find more about this and other radar detectors.

Best of luck,

Sonny

shadopadla

Adrian,

Thanks for the added info, some friend maybe pulling my legs by saying that using the lower octane gases actually dramatically decrease engine life, not just performance differences. This was actually said by my friend who works at a toyota dealership, but then again, she works at a dealership, and it's toyota, could be true for them

Sonny,

Thanks about the rim, I am itching to check but will have to wait a week or two. Most likely a good one since would probably notice if two different rear wheel weights were being used. In regard to the paint, there is a noticable difference between the reconditioned and other ones. The new one is more of a flat silver, where the stock rims are brighter. You're right on the wheel sizes, and style is cup 1. Nice porsche look.

Will check around for a place my dad doesn't take his porsche for servicing for the PPI, but he's switched between quite a few over the years! If anyone knows of a nice reputable shop in the Rochester, NY area, I'm all ears!

Edit: Looking forward to the release of your book Adrian! I have a copy pre-ordered, and look forward to learning more about the 964. Also looking forward to eventual release of the 911SC book, as that was my father's first porsche and the car I learned to drive on! Great memories.

fc-racer

I don't think that you would see reduced performance with low octane fuel, just reduced headroom for detonation. Reduced performance from low octane fuel in modern cars comes from the knock sensor providing input to the ECU to reduce timing due to potential or existing knock.

The 964 Turbo has no such knock detection, therefore performance cannot be adjusted based upon fuel quality and knock feedback.

It can be tough to remember that this car has no electronic fuel injection considering this was a $100k car in 1991 and it was 1991!!!

fc-racer

shadopadla

School Finals so been busy.

Thanks for the additional info fc, didn't realize it wasn't an electric fuel injection system. But then my butt doesn't care whether what it uses, so long as it works and works well.

Doing the PPI, are there any questions I should ask, areas that this particular model (91 C2T) should have checked or looked at? It's been well maintained and low miles but has seen track use, Dad used both his old porsche and this one down at Watkins Glen in NY. Much fun :-)

Also, he was thinking about selling it to someone besides me, what is price ranges for these cars? He is going by KBB and that says between 35-40k. Is difficult because he's been through this before and backed out because didn't want his car in the hands of someone else. He also has an 83 911SC that's on semi-permanent loan to his sister, my aunt. Either one are great cars, but then, when it's 911's to choose from, you can't go too wrong. Oh, price on the SC? It is high miles and probably suffers a bit more from stagnation, my aunt and uncle don't use it very often, the battery has run flat numerous times over the years they've had it. PPI of course, but KBB and edmunds had prices around 3-6k even for good condition ones... What are the real market prices if anyone knows them?

Thanks!
Tyler

Adrian

Dear Tyler,
No the 964 Turbo does not have electronic control over the fuel injection but it does have electronic control over the ignition. This is a mapped or programmed system.
The knock system installed in the 964 is a detected knock system. It cannot detect potential knocks. Specific frequency vibrations pick ups are used.
Reduced performance cuased by using the low octane fuel is caused by inefficient burn of the fuel air mixture. Remember that when it comes down to performance, it is directly proportional to the big bang every time the spark ignites the mixture. When the bang is not quite so big or inefficient the amount of energy transmitted to the top of the piston is less and engine output is reduced. The bigger and better the bang the more you get out of your engine.
Ciao,
Adrian
964C4