View Full Version : To much boost?

08-30-2003, 10:14 PM
What is the max amount of boost I should run with 9.89 to 1 compression. The block is o-ringed and all the internals are forged. Is 16 pounds to much?

08-31-2003, 10:37 AM
I would doubt you will see any problems. Compression will generaly raise 1 point for every 3lbs of boost. I ran 15-17 with no problems on my 89. However, you can just run headers and ported heads with the full exhaust and get the boost pressure down some.

MIKE 38sc
08-31-2003, 10:54 AM
You better run racing gas in that engine because your static compression is too high for pump gas.;)

08-31-2003, 11:00 AM
Should I change pulleys and get the boost back down a tad? I dont want to have to run $4.00 a gallon gas.

08-31-2003, 11:09 AM
I always ran 94 Octane in mine at 15-17 lbs of boost with no problems and that should have been around 13:5- 14:1. I never had problems with detonation. I would think you should be ok with 94 octane from sunoco. If that does not work, CD2 has a new octane booster that raises the octane 20 points (two full octane numbers) that would put you at 96 octane, which would be more than enough to compensate for the little extra compression you are running. Or you could simply run the stock blower pulley and stay around 12-13psi.

MIKE 38sc
08-31-2003, 11:14 AM
Unfortunately they dont make a pulley that large. With a stock setup on the pulley and a freeflowing exhaust you will end up in the neighborhood of 15-1 to 17-1 effective compression ratio and thats way to high for pump gas. You would have to cut your boost back to about 4 psi to stay within the limits of pump gas.

Could I ask why youre running such a high static compression ratio?:)

08-31-2003, 12:22 PM
I went to a higher compression so I would have power when not on boost. It went to 16 pounds of boost with a 10% od. pulley on the blower. I also have a early model pulley that came stock on the engine and a newer style pulley that is supposed to slow the blower down even more. If I go to the stock 1990 pulley wont it bring the boost way down?

MIKE 38sc
08-31-2003, 12:36 PM
The #'s I posted are for an early model pulley that if the exhaust is freed up like it needs to be will produce 8 psi of boost and those #'s are too high for pump gas.
The route you have taken will have you activating the knock sensor and pulling ignition timing out of the motor so youre not going to get a big jump in power, in fact you may produce less power or detonate the engine into destruction on pump gas.

Your set up would be good for an all out drag car running good racing gas. But its a recipe for destruction and a tuning nightmare on a street engine.

08-31-2003, 01:10 PM
Perhaps you should consider a water injection system. I'm not sure if a unit was ever made which could be retrofitted to these cars, but I know they are available for some applications.

08-31-2003, 01:33 PM
I have a 5.0 sport with a centrifugal blower. I run it at 13# of boost on 93 octane pumpgas.
I have an Alcohol/ Water injection system on it which completely eliminated all my detonation problems.
It's actually for a 94/95 Mustang but I modified it slightly to fit under my passenger's side front fender.
A drill and a tap to install the spray nozzle before the Throttlebody is the hardest part of getting this thing to fit.

08-31-2003, 02:09 PM
I don't think you should have anything to worry about as long as you run the proper gas. I'm running a ported 95 blower with and early model pulley. I make about 16~17 pounds of boost with no problems. I've run this setup for about 8 months now. I have a 255lph fuel pump and stock injectors.


08-31-2003, 02:41 PM
Time to go see Brian at aptune. I have one of his chips set to the specs of the car. I guess I better get down and get on the dyno. Anybody have a good source for a water / alcohol system. I didnt build this thing to not make horsepower.

08-31-2003, 03:13 PM

This is where I got my system. I understand that there are several manufacturers out there and opinions vary as to who is best.
This system works fine for me. Don't set it to come on too low or it will quench your spark. I'm engaging mine at 6#.

Do a google search to find others.

Good luck.

08-31-2003, 04:49 PM
Thanks for the information. This really looks like a good solution. Is it set to come on at a certain boost pressure or is it on all the time?

08-31-2003, 07:41 PM
I have mine set to come on at 6# of boost. At first I had it set to come on at a lower boost and found that it was quenching my spark. At higher boost levels this system behaves differently. Mine came with 2 different sized spray nozzles for low, medium, or (both) high levels of injection. You would have to fiddle with yours to find a happy place but I'm pretty sure you would not need more than is provided for.

My mix is 50/50 ethanol and water. I observe about 100'F intercooling effect at 10# boost. I would question the claims of 60 HP however.

Nice, Cheap crutch for pump gas