[horsepowerjunkie]

Roughly how much boost can you run on 91 octane pump gas? 8.2:1 compression 331, 66mm Turbo.

[302Army187]

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[JBIGBOOTSY]

Originally Posted by horsepowerjunkie Roughly how much boost can you run on 91 octane pump gas? 8.2:1 compression 331, 66mm Turbo.

At 8.2.. alot depending on timing. prolly up to 16-18.

[BAD98GT]

with a 8.2:1 compression 15 lbs is fairly safe, as jbig said also depending on you timing you can go a lil more

[horsepowerjunkie]

My orignal plan was to run E85 and run 18 psi saftly, but they stopped selling E85 locally, so I'm stuck with 91 pump gas! I can't decide what to do?

[robturbo331]

Originally Posted by horsepowerjunkie My orignal plan was to run E85 and run 18 psi saftly, but they stopped selling E85 locally, so I'm stuck with 91 pump gas! I can't decide what to do?

Thats a good thing because you can't trust e85 from the pump. The octane varies a lot depending on who their vendor was. Hard to lock down a tune.

You can safely run 15 lbs boost with 91 octane. Y0u will need to keep your timing under 25 degrees full advance with that. To keep you from popping headgaskets shoot for 21 degrees full advance with boost. If running factory fuel injection use a MSD Boost timing master or equivalent. Set your full advance timing to about 34-36 degrees then set the boost timing master to take one degree of timing out per pound of boost. The Boost timing master can take 15 degrees total out so if run 15lbs you will take 15 degrees out and will be around 19 - 21 degrees total with full boost. This setup will be safe and make good power.

If want quick spoolup and running a carburetor lock your distributor to full advance all the time at 35 or so degrees and hook up the timing master. This will smooth out your idle a lot and give you a quick rev as well as help spool the turbo up. Will not increasel horse power or torque in high RPM but will increase a great deal in the lower RPM range.

[robturbo331]

If you are running the F.A.S.T system then set your idle timing to say 750 to 2000 rpms to 30 degrees. Then advance the none boost part of the map starting at 2000 rpms to 35 degress all the way up. Once you are in the 100 KPA and up start taking timing out. Convert the KPA to PSI and start taking one degree out for every one pound of boost increase. For you info 100 KPA is 0 lbs of boost. You want your fuel and AFR to be set before you start messing with the timing when tuning on the DYNO. For the Acceleration map ramp it up for a quick swing. You want it dumping fuel fairly quick when you hit the throttle. This will make it rev quick and help build boost.

I'll tell you like this. With 11 lbs of boost 6 years ago I had a pump gas 93 octane car running 5.90s in the 1/8 mile and low 9's in the 1/4 with a 331 c4 and 3.73 gears with Victor Jr. heads and intake with a .680 lift cam. 3200 lb car Here are a few video of the car in 2004 threw 2006

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[horsepowerjunkie]

Thanks for all the info and the video, Robert. I am going to use the classic fast system and this car will see alot of street time also. I hope to get into the 9's. We'll see what happens. Again, thanks for the info.

[robturbo331]

Originally Posted by horsepowerjunkie Thanks for all the info and the video, Robert. I am going to use the classic fast system and this car will see alot of street time also. I hope to get into the 9's. We'll see what happens. Again, thanks for the info.

Anytime horsepowerjunkie!! If you want to push the car hard at some point you can either add another turbo to your setup and keep a pretty quick spool or if can deal with a little lag you can jump to a 91.5 turbo. Throw c16 race fuel in it and about 25 lbs boost and it will show you 1000+ hp at the tires. 22lbs and better with at least an 1800 cfm blower or turbo is the key to making 1000+hp at the tires. Have done it a lot. All the tunes are almost all the same. A little tweek here and there are all that is needed. Make sure if go this far with it you have it on the DYNO so can see if the timing is helping or hurting your torque. Don't worry about the horsepower it is not important just the torque.

If need help with your AFR #s just remember no more than 11.5 with full throttle and full boost and no less than 12.5. Keep it in that range and will never hurt the engine unless the mechanical components can not handle the stress!! When not in boost or low boost say under 5 lbs you can run it around 12.5 to 13.5 and be safe. No matter what anyone tells you do not lean it out anymore than this and will be fine. Only professional tuners can lean an engine out more than this and not blow an engine unless you just have a lot of luck and I will tell you a lot of pros have blown a lot of engines so do not let them talk you into putting the engine tune on the very edge because they don't care if it blows they will be paid regardless.

If you start having issues with not being able to hook the car off the line start dropping 2 degrees of timing at a time at your launch RPM and 500 RPMS after your launch RPM and then smooth the timing curve out into the rest of the timing map. A little trial and error and you will have it flying in no time. Good luck!!

[robturbo331]

If know anyone who wants two 67mm ball bearing precision turbos for $1000 for them both let me know. I am trying a 393w all motor car at the moment with a hydraulic cam. 6.90 1/8 so far looking to get it down to 6.70s then will put a plate NOS system on it and hopping for some 5 sec runs and low 9 sec 1/4 runs. When I have that setup working right I will have some tunning info if anyone is having issues in that department. Its my street car and a pump gas only car until it sees the NOS!!