Using 91 octane gas in a 930?

javadog · 10-24-2005, 04:21 PM

The local gas stations have quit serving up 93/94 octane unleaded and all that I can buy now is 91 R+M/2. I have seven cars that would like much higher octane, so I have some adjustments to make. For a stock 1980 Euro 930 that would really like 98 RON, I figure my choices are:

1. Use some form of octane booster.
2. Blend in some higher octane race gas with the cheap swill.
3. Back off the timing and/or boost.
4. Screw a thick block of wood under the throttle pedal. (just kidding)

I briefly looked at the octane booster choices in my local auto parts emporium and most appeared to be snake oil. Only one, Berryman, indicated what they used (methylcyclopentadienyl manganese tricarbonyl, or MMT for short) and approximately what to expect from using it (up to three points for 16-20 gallons per bottle.) Ever the pessimist, I would be surprised if the crap actually worked but I thought I'd ask.

I know other states have to put up with crap gas (California, for instance) so what's the best solution?

Thanks,

JR

look 171 · 10-24-2005, 05:04 PM

I mix 5 gallons of race gas if I know I am going to hammer on it for a while. Union 76 also sells, I think it is unleaded, 100 octane gas. A bit hard to find around here. Yes we have **** gas in CA. I heard with 1 bar of boost, 91 octand should be ok. All of that booster stuff from auto parts store are snake oil.

Jeff

cnavarro · 10-24-2005, 05:10 PM

Torco sells cans of race gas concentrate. I am pretty sure that each can will probably do maybe 5-6 fill ups and boost your octane from 91 to 94 octane. It's most definately cheaper and easier than trying to blend 104 at the pump :-)

look 171 · 10-24-2005, 05:18 PM

[QUOTE]Originally posted by cnavarro
[B]Torco sells cans of race gas concentrate.

Where do you get this stuff and how much? Is this stuff bad for rubber parts?

Jeff

9dreizig · 10-24-2005, 05:34 PM

the guys over in AudiWorld use Touline (sp) they get it from the paint store...Not sure of the mixture though

cnavarro · 10-24-2005, 05:53 PM

You can get it right from the manufacturer at http://www.torcoracefuels.com/catalog/product_info.php?cPath=22&products_id=80. I used to stock it and bring it to shows every once in a while. I would sincerely try to find a local speed shop to purchase it from to save on the shipping. They make both a leaded and an unleaded version.

89turbocabmike · 10-24-2005, 06:33 PM

javadog, what boost are you running? If your completely stock, .7 bar, no worries. As look171 has mentioned, you should be fine up to 1 bar. This info comes from more than a few notable experts including Steve@Rennsport and Stephen from Imagine, though it can't hurt if your going to be running hard to mix in some unleaded race gas. FWIW, I've run 1 bar, K27-7006, Headers and Kolkeln IC for 40K miles with no problems on mostly California 91, which with the special formula for our California emissions standards, is supposedly worse than the 91 oct. you've got.

TerryH · TerryH's Garage

You can add toluene or xylene at about 5:1 and gain a whole lot more than those otc octane boosters that say they can add points. What they don't tell you is those 3 points are decimal points. It boosts 91 octane to 91.3 octane.

Anyway, all this fuss will get old pretty quick and you may as well just detune your car a notch and use the gas available. Unless you can find a local Unocal that pumps 100 unleaded, there are several here in SoCal.

My '81 Row demands 98 Ron also and it lacks a turbo. It runs fine on 91 octane, but I'm sure it could run better on 94.

look 171 · 10-24-2005, 09:53 PM

Hey Mike,

are you at 1 bar boost in your cab? Do you get any pinging at all up top of your rev range?

Jeff

javadog · 10-25-2005, 03:56 AM

Mike;

The 1980 Euro car I was talking about is bone stock and it does ping on the stock .72 bar boost on 91 octane gas. I also have a modified 1986 US-spec car and haven't run it since the switch to 91 happened, so the jury is still out on that one. It runs a Garrett turbo, different exhaust, 964 cams and a Fred Garrettson intercooler. Boost is up a little, to .8 bar. At any rate, I also have 5 other cars that need higher than 91 octane and some of them are going to be harder to deal with than the 930s.

I was hoping to find a solution other than blending race gas (which is impractical when I am re-filling the cars away from home) or detuning them. I suppose I could retard the ignition timing on the Euro turbo 3 degrees or so and get close to what the US cars ran, which ought to solve the problem for that car. I can change the Motronic chips in a few of the other cars to deal with the problem. There are still a couple that I may have to blend gas for.

In Oklahoma, we have no Sunoco or Unocal stations. There's avgas at the airports and race fuel at a track 45 miles away. That's it.

JR

89turbocabmike · 10-25-2005, 06:33 PM

Quote:

Originally posted by look 171
Hey Mike,

are you at 1 bar boost in your cab? Do you get any pinging at all up top of your rev range?

Jeff

Jeff, I don't have any pinging up top, but I would imagine that if I did at full boost and could hear it, the party would be over! BTW, it was nice meeting you on the last Malibu run.....I was running 10 gallons of Unocal 76 100 oct unleaded for an approximate rating of 95 for peace of mind. Luckily, I have a station just a few miles way.

JR, using the US timing may solve your problem, I should have taken that "euro" timing difference into consideration and asked a few other questions. When is this pinging present? Cold, Hot, light load or under boost? I had a tired '83 euro turbo with Ruf short-skirt pistons that slapped quite a bit when cold and tighten up some when up to operation temp.

rlh930 · 10-25-2005, 06:54 PM

I've run my '87 930 (.8 bar boost) on 91 octane California gas for four years with no problems. No pinging noticeable. I have no idea, though, how the '87's specs compare to an '80 Euro.

look 171 · 10-25-2005, 09:09 PM

[QUOTE]Originally posted by 89turbocabmike
[B]Jeff, I don't have any pinging up top, but I would imagine that if I did at full boost and could hear it, the party would be over! BTW, it was nice meeting you on the last Malibu run.....I was running 10 gallons of Unocal 76 100 oct unleaded for an approximate rating of 95 for peace of mind. Luckily, I have a station just a few miles way.

Do you do this with every fill up or just when you know you are going to hammer on it?]

89turbocabmike · 10-26-2005, 04:42 AM

Only for runs or DE. Just a precaution.

javadog · 10-26-2005, 05:08 AM

Mike, Roger;

The two cars (US, Euro) use different distributors, among other things. The ignition timing is different and the distributors may have diffferent advance curves as well. I haven't looked into that yet. The pinging occurs as the engine comes up on boost, so it starts between 3k and 4k. I haven't tried it at higher rpms, well past the torque peak, which may help as the cylinder pressures are lower. Off boost is fine.

I have researched fuel additives and come to the conclusion that octane boosters are not the solution. Blending race gas isn't an acceptable option for me either for this car, so what I'll probaby do is back off the timing 3-4 degrees and see if it goes away completely. Failing that, I'll look into a different distributor.

JR

89turbocabmike · 10-26-2005, 09:29 PM

JR, my current timing is 26 degrees at 4K, so if your running say 29 like earlier turbos you could back it down. Bruce Anderson recommends 25 @ 4K. The other question is whether your boost retard can (or hose) on the distributor is doing its job. Also, do you know what your CO is, a lean condition either overall or in a particular cylinder(faulty injector) could contribute. These conditions could certainly have been masked by the higher octane fuel. Unfortunately I don't know of any other viable solutions for higher octane. Even with a 100 octane station a few miles away, it just isn't convenient to mix fuels except perhaps for a weekend toy.

VZ935 · VZ935's Garage

My 1983 911 turbo @ 1 bar , never had any problems..ran the car very hard, had a Andial intercooler, electromotive twin plug crankfire with headers and the Powerhaus turbo cams , I believe they were basically an SC grind .Mahle 3.4 Ps&Cs ..... California 91 no problem. Ran the car a little fat..robbed a little HP but it still had plenty.

Steve@Rennsport · 10:01 PM

CIS-equipped 930's are notorious for going lean on-boost beginning at 4000 RPM so if you introduce more fuel in that range, it will reduce its octane sensitivity depending on your final A/F ratio and ignition timing.

Not that you want to hear this, but adding twin-ignition to 930's is one major part of the "recipe" for getting these to tolerate 91 octane fuels. Its a sorry state of affairs, however thats reality.

Remember, never ever rely on one's ears to be the defactor "knock sensors", otherwise you'll buy pistons and ring sets.

These motors are too loud to detect sub-audible detonation.

Some further info can be found at http://www.rennsportsystems.com/2a.html

javadog · 10-27-2005, 08:54 AM

Mike;

The early 3.3 turbos in Europe had a different distributor than the one you are thinking of. The vacuum retard feature wan't added until 1983. The US cars from 1986 use this same type of distributor as the 83-on Euro cars, although it carries a different part number. At first glance, the advance/retard curves look the same. I'll look a little more closely when I get the time. The Euro cars run 3 degrees more advance.

My CO is correct and I am pretty sure I have no air leaks but I'll check that again. The car runs a little richer than a US car and the stock CIS can flow plenty of fuel, on a stock motor at stock boost, so I am not looking to change anything there.

I'll see what retarding the timing 3-4 degrees will do and, if that isn't enough, I'll install a later style distributor and add the associated hoses and thermal/vacuum switch.

Steve;

Thanks for the info. I know twin-plugging the thing would solve my problem but that's a bit expensive. The US cars run fine on 91, so I'll try the distributor first.

It just pisses me off that the oil companies can give us whatever octane they want (Shell supplied a tanker full of 95 octane for an event I went to in Louisianna last fall-they CAN blend it) but some dumbass beancounters somewhere decided that 91 was good enough. It has to do with the price. We had 93 everywhere until gas prices went up after the hurricanes. There are two refineries within 10 miles of my house and pipelines out the wazoo running through town, so you have to figure that we COULD get whatever we want.

JR