lower octane in California

[Venom Lover]

Hmmm, I just noticed that as I was fueling up on the way home last night. I figured it was just Chevron, but are you saying all premium has gone to max 91 octane in CA???

Now I, too, am curious if this is going to be a problem.

Fortunately, the Union 76 by where I live offers 100 octane unleaded. Perhaps I'll have to start blending my own gasoline cuvee...

 

[Vreracing]

For some reason because of where I am located (something to do with altitude(3800ft) and how far west we are) the gas stations only provide 90 octane fuel. I've been driving my car and would occaisionally put 104 unleaded racing fuel in it. I didn't notice any difference at all. When I drove the Porsche 993TT if I went from 90 octane to 104 there seemed to be a big increase in power. (The turbo bar would only hit .6 with 90 and would hit .8 with the 104)

Maybe some of the "tuners" in this group will have a different opinion but my seat of the pants assessment (I have a pretty sensitive behind) did not note any difference.

 

[AndyR]

My owners manual (1993) says use a minimum of 91 octane fuel and that light spark knock at low engine speeds is not harmful to your engine. However, continued heavy spark knock at high speeds can cause damage that may not be covered by warranty.

Is it harmful to use 100-105 octane fuel in these engines or just wasteful (money and fuel) with little or no benefit?

 

[treynor]

I spoke with a Chevron representative about this yesterday. The basic scoop: ALL California premium gas will be 91 octane by the 1st of August. Only stations which specially blend (like race pumps) will be able to offer >91 octane. This change was evidently done as a result of the MTBE ban coupled with the continued requirements for reformulated gasoline.

I am concerned that this will not work well with my Venom 550 heads. I'd be very interested to hear of any other experiences with tuner cars running on 91-octane, especially at sea level. I'd hate to have to start ordering 55-gal drums of 100-octane race gas to mix into the local fuel every time I fill up...

 

[LTHL VPR]

This is not good news at all!
I know several other people in regions where 91 was the highest Octane rating, they were forced to go with colder plugs. The problem is that I have seen colder plugs cause a loss of 10-15hp&tq+.
In addition, even when adding simple bolts on like headers and exhaust slighltly leans out the mixture. Again, I know of others who had to go to colder plugs to eliminate pinging. Lost even more HP too.
Looks like I will be carrying around a bottle of Octane Boost everywhere I go now. This seem to eliminate the pinging/detonation problem I had in my 96 Cobra Must. when 92 wouldn't do.

 

[JimDavis MT 97GTS 650R]

I don't get it, what's the problem here? The higher the altitude, the more I need a higher octane fuel in most of my vehicles in order for them to run properly. (Thin Air) When I go down to sea level, they run strong on less octane. This is true of both my "low" compression and "high" compression engines. When I take my Venom "high" compression 650R out to the west coast, it runs like crazy. It is much stronger at sea level compared to back here in Montana where it is 3700 + ft. You should try 10,000 ft. With 91 octane your computer should compensate for the small difference. You folks at sea level should have a barometric advantage. Sure, 93 octane is nice, but you won't damage a street engine on 91. You probably won't loose any street advantage ether, as the other "high" compression cars will be running the same fuel! Save the racing fuel for the track where you can actually justify the difference!

 

[JimDavis MT 97GTS 650R]

91 Octane works just fine in my 650R here in Montana. My local altitude is 3671 ft. of very dry air. Octane boosters have shown no perceptible improvement here when added to premium fuel. I do find that the use of a slightly cooler NGK spark plug helps with detonation under full load, however if you do lots of stop and go slow traffic, you would probably be better off using the stock Champions. These engines love cool dense air. If you live on the coast at about sea level, I doubt you will have much problem with 91 octane. The computer should compensate for the change. (My 2 cents.)

 

[treynor]

I filled up with 91-octane from Chevron last night, and headed down to the dyno this morning. There was no heavy knocking, and no audible knocking or pinging at the RPMs where the car was still quiet enough to hear it

However, the dyno A/F revealed evidence of mild pinging in the 4000 - 4800 RPM range (the car's torque peak). Adding a bottle of AMSOil octane booster cured the problem.

Sooo.... for as long as CA continues to offer only 91 octane, it appears those of us with high-compression heads have the following options:
(1) carry octane booster around in our trunks for use every time we fill up;
(2) buy gas at one of the Unocal 76 stations which sell 100 unleaded;
(3) move to a different state.

Argghhhhhh!!!

The good news -- my car makes just as much power as it did a month ago.

 

[JimDavis MT 97GTS 650R]

mjr, The "implications for using octane booster on a regular basis" are spending big bucks for little or nothing if you are just driving on the street. Excessive use of additives may actually harm your FI system. (imo)

 

[Jerry Scott[CO]]

Be careful with octane boosters, since many of them contain lead. Lead will destroy or damage the cat. converters and some of them simply do not work.

Here in Denver, we have had ethanol diluted 91 octane fuel for several years. It does not seem to be a problem in the Summer when the percent of ethanol is very low, but in the Winter we have experienced high rpm (4K up) detonation in the Viper, when the ethanol content goes up. We have accepted it here as a way of life and I'm sure that in the future it will be happening in your area as well.

Texaco claims to have the lowest percent of alcohol here in Colorado, so that seems to be the fuel of choice for most performance car owners. You might want to check your brand to see what percent of alcohol it contains and try and buy the lowest.

Vipers here, with headers and other mild modifications, all seem to have the detonation problem with the stock plugs. The solution seems to be - use a colder plug, especially in the Winter.

 

[treynor]

Having now had a couple days to consider my options, I've done the following:

(1) ordered a case of Torco unleaded gas accelerator (octane booster). I'll keep a couple bottles in my trunk in case I'm caught out on the road and need to refuel;
(2) ordered 15 gals of Unocal 76 100-octane unleaded race gas. One can buy it in various quantities with prices from $4.50 - $6.25 / gal. 2.5 gals of 100 mixed in with 16 gals of the local 91-octane sludge will keep me above 92 octane, at which level there's no detonation present in my car.

One other note: with a properly-running computer-controlled fuel system, the mixture will not lean out at higher altitudes. However, the lower air pressure will (on a NA car) translate to less cylinder filling, and thus less compression, reducing the octane demands of a given engine. Thus the prevalence of 91-octane premium gas at higher elevations.

 

[treynor]

One other interesting note -- I pulled one of my plugs to check for any signs of detonation. I found none, but I also found:
(a) they were stained red from the Octane booster I used (common);
(b) they were two heat ranges colder than the stock plugs -- our local Viper wizard Ted May had tossed in a set of his favorite race plugs in prep for my upcoming roadrace event, and had forgotten to mention it. What's interesting about this is that I dyno'd exactly the same with these plugs as with the stock plugs which seems to contradict other reports that colder plugs lose HP.
(c) there were absolutely no signs of detonation or other ill events on the plugs.