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Old 10/09/2006, 08:56 PM   #1
p51
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About a month back I had my car tuned. My mechanic did a great job advancing the spark such that he maxed the power output - I could feel the diff. Anyway, about a week later I accidently put 89 octane unleaded (the engine has been rebuilt so it can handle unleaded). Anyway I got some slight pinging on hard acceleration on an incline. Immediately I went back to premium (91 octane in CA) and the problem went away. However, I then actually looked at the manual and it recommends a ~94 (R+M)/2 pump octane rating (= ~99 R octane rating according to the manual). So, I went down to the local Kragens and bought some octane booster. It only boosts ~4 points or 0.4 in (R+M)/2 octane but I swear that the engine ran smoother (note that not all detonation is heard as pinging) - but this may be just psychological because I had just spent $8

Anyway, it raised some questions in my mind.

What do you guys and gals do in CA for premium >91?

Specifically, if anyone lives in the San Francisco south bay (Sunnyvale, Santa Clara) where can you get gasoline with >91 octane? I gotta believe with all the Porsches, etc running around here that there's got to be some high octane gas (or possibly all the Porsche people just in general suffer from severely retarded spark and not know it??)

Has anyone *hypothetically* used toluene (the stuff they use in Formula 1 racing) to boost octane? It seems like a very cost effective way to do so.

Here's an interesting webpage about it.

http://www.gnttype.org/techarea/misc...explained.html

Thanks

James

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Old 10/09/2006, 11:03 PM   #2
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Here are a few threads where high octane fuel is discussed.
http://www.californiaspecial.com/for...ghlight=octane

http://www.californiaspecial.com/for...ghlight=octane

http://www.californiaspecial.com/for...ghlight=octane

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Old 10/09/2006, 11:05 PM   #3
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Ah , now this link answers a lot of questions i had relative to US v OZ regarding octane ratings -------- here all our pumps are in RON.

So James have you used the regular hardware store Toluene yet ???????

I am considering it , as our summer is pretty Hot 100f + on most days and i want my performance not to suffer.

68 J/R code special - 2007 Turbo Territory - Mercedes CLK 2008
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Old 10/09/2006, 11:51 PM   #4
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Quote:
Originally Posted by p51
About a month back I had my car tuned. My mechanic did a great job advancing the spark such that he maxed the power output - I could feel the diff. Anyway, about a week later I accidently put 89 octane unleaded (the engine has been rebuilt so it can handle unleaded). Anyway I got some slight pinging on hard acceleration on an incline. Immediately I went back to premium (91 octane in CA) and the problem went away. However, I then actually looked at the manual and it recommends a ~94 (R+M)/2 pump octane rating (= ~99 R octane rating according to the manual). So, I went down to the local Kragens and bought some octane booster. It only boosts ~4 points or 0.4 in (R+M)/2 octane but I swear that the engine ran smoother (note that not all detonation is heard as pinging) - but this may be just psychological because I had just spent $8

Anyway, it raised some questions in my mind.

What do you guys and gals do in CA for premium >91?

Specifically, if anyone lives in the San Francisco south bay (Sunnyvale, Santa Clara) where can you get gasoline with >91 octane? I gotta believe with all the Porsches, etc running around here that there's got to be some high octane gas (or possibly all the Porsche people just in general suffer from severely retarded spark and not know it??)

Has anyone *hypothetically* used toluene (the stuff they use in Formula 1 racing) to boost octane? It seems like a very cost effective way to do so.

Here's an interesting webpage about it.

http://www.gnttype.org/techarea/misc...explained.html

Thanks

James
I made the mistake of trying to run CA 91 octane plus a NOS octane booster (black can) with a 347 with cast block/cast heads with a small cam and 11:1 compression with a 670cfm street avenger carb and not alot of advance and the pistons were hypereutectic and i destroyed them completely.

The next motor i had built, was built to fun safely on CA 91 octane with forged pistons and a bigger cam and 10:1 compression with a 750cfm Holley, MSD and 10degrees initial stepping up to 32 degrees total....no pinging...lots of horsepower...when i race on hot days i pour in 101 octane from a pump in the SFV, makes it run just a little stronger without changing the timing.

The EFI on Porsches with the computers and everything say that the minimum octane to run is CA 91 Premium, at least for the 2004 Porsche Cayenne Turbo which makes 450 Engine HP and 460 Engine Torque on that CA 91 octane. I think there is a knock sensor that retards spark accordingly...porsches that are tuned on high octane gas do make a hell of alot more power but $6 a gallon.
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Old 10/10/2006, 08:22 AM   #5
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Quote:
Originally Posted by gt bandit
Ah , now this link answers a lot of questions i had relative to US v OZ regarding octane ratings -------- here all our pumps are in RON.

So James have you used the regular hardware store Toluene yet ???????

I am considering it , as our summer is pretty Hot 100f + on most days and i want my performance not to suffer.
In the US octane seems to be all measured as (R+M)/2. Also seems that in CA the highest you can get at almost all gas stations is 91 (a few places have 100 octane but they seem to be few and far between). Other states seem to have premium at 93. Not sure why CA only has 91.

Have not tried toluene yet. If I do I dont plan on adding more than 5% - if a bottle of octane boost (which only raises octane by a few tenths) does the trick then a small amount of toluene should be sufficient.

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Old 10/10/2006, 08:55 AM   #6
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Quote:
Originally Posted by davidathans

The next motor i had built, was built to fun safely on CA 91 octane with forged pistons and a bigger cam and 10:1 compression with a 750cfm Holley, MSD and 10degrees initial stepping up to 32 degrees total....no pinging...lots of horsepower...when i race on hot days i pour in 101 octane from a pump in the SFV, makes it run just a little stronger without changing the timing.

The EFI on Porsches with the computers and everything say that the minimum octane to run is CA 91 Premium, at least for the 2004 Porsche Cayenne Turbo which makes 450 Engine HP and 460 Engine Torque on that CA 91 octane. I think there is a knock sensor that retards spark accordingly...porsches that are tuned on high octane gas do make a hell of alot more power but $6 a gallon.
I assume that the spark advance that you're talking about (from 10 to 32 degrees) comes from the vacuum/centrifugal advance - is that correct? My compression is also ~10:1 so based on what you indicate 91 octane should do fine. And I dont have any issue running at low rpms (I can cruise in 5th @~1900rpm @~60mph and *no* issue at all. No lugging, no pinging, great gas mileage). It seems only to occur, slightly, under hard acceleration on incline. So, *maybe* whats happening is that the vacuum advance may be coming on too quickly. Thoughts?

Regarding Porsches (and all new cars, I think): My understanding also is that on all new cars when detonation starts to occur the knock sensor of the engine computer senses it and just retards the spark. So, you can run the car on almost anything as long at the spark can be retarded far enough. One of my friends w/a high-end Porsche has noticed significant difference when he runs with 91 vs half-n-half 91 + 100 octane. All caused by the spark being retarded w/91 octane fuel.

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Old 10/10/2006, 08:56 AM   #7
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Rhonda, thx for the links

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Old 10/10/2006, 03:37 PM   #8
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Quote:
Originally Posted by p51
Rhonda, thx for the links
Your welcome p51, I like helping.

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Old 10/10/2006, 07:06 PM   #9
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Quote:
Originally Posted by p51
I assume that the spark advance that you're talking about (from 10 to 32 degrees) comes from the vacuum/centrifugal advance - is that correct? My compression is also ~10:1 so based on what you indicate 91 octane should do fine. And I dont have any issue running at low rpms (I can cruise in 5th @~1900rpm @~60mph and *no* issue at all. No lugging, no pinging, great gas mileage). It seems only to occur, slightly, under hard acceleration on incline. So, *maybe* whats happening is that the vacuum advance may be coming on too quickly. Thoughts?

Regarding Porsches (and all new cars, I think): My understanding also is that on all new cars when detonation starts to occur the knock sensor of the engine computer senses it and just retards the spark. So, you can run the car on almost anything as long at the spark can be retarded far enough. One of my friends w/a high-end Porsche has noticed significant difference when he runs with 91 vs half-n-half 91 + 100 octane. All caused by the spark being retarded w/91 octane fuel.
Yes i did mean that my car is set up right now, with 10degrees initial advance and the vacuum/centrifugal advance + the initial advance gives a total timing of 32 degrees.

If your having pinging under hard acceleration, you should retard your timing...there are two ways, turn your distributor to retard the initial timing, or you can change your springs inside the distributor to change your total timing.

Are you running Aluminum Heads? If you really want to increase your performance you should put on aluminum heads because they will save you weight, pass more air through and i believe that aluminum heads dissipate head better than cast heads...so you'll be less likely to ping with the same compression ratio and timing having alum. heads vs. cast heads. Mine are Air Flow Research AFR185 heads with 2.02" intake valves and 1.60" exhaust valves and the 185 is the cubic centimeter volume of your intake runners.
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Old 10/11/2006, 12:15 AM   #10
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Quote:
Originally Posted by davidathans
...If your having pinging under hard acceleration, you should retard your timing...there are two ways, turn your distributor to retard the initial timing, or you can change your springs inside the distributor to change your total timing...
Thx David. It seems to only occur during acceleration. I can run at really low rpms and get no pinging even uphill w/load (so I'm guessing the initial offset is probably ok). I can also run it up to 4500rpm+ without any problem (so the centrifugal advance seems ok). Since its happening during acceleration when I tromp on the gas my guess is that the vacuum advance is not coming off fast enough as manifold pressure rises when the throttle opens up.

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Old 10/11/2006, 09:40 AM   #11
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put a timing gun on your crankshaft pulley and put the engine up to 3000 rpm or so....by 3000rpm you should be close to your max total timing...take a reading and if your at like 35 degrees plus then its probably just a little too much timing...while your doing this, check your intial timing at idle just so you know what your timing is set at.

sometimes it can be really hard to read the numbers off your crankshaft pulley...the guys who built my motor had a really expensive, sophisticated timing gun and they could do it easily, but with my timing gun from sears, my dad and i had a difficult time reading the numbers off the crankshaft pulley. So give it a try and if you cant read the #s...i would suggest going to a shop that has a really sweet timing gun and have them check the timing for you.
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Old 10/11/2006, 03:56 PM   #12
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I use bright yellow paint and a toothpick on my pulley. I highlight the timing point I want to set at (i.e. 12 deg.) and when the engine is running, it stands right out. You could do the same at 35 deg. (maybe two marks side by side so you don't mix them up) and that would give you an idea where you're at.

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