I have a 1987 iroc 5.7 with a Paxton SN93 blower on it. The engine is stock, and I have the stock fuel injectors. What FP should I be running? right now I have it temporarily set to 50psi, and it's running rich as hell.

Also, for those of you who ran or run this or a similar combo, what timing did you run? I currently have it backed off to around 4 or 5 to be safe. I have an MSD 6al with a BTM that's going to be installed this week.

Thanks guys.

 

I would not even begin to take a guess at what fuel pressure would be correct for your car. The only "true" way is to tinker with it while on a dyno. The only other alternative albeit a distant one, would be to invest in a scanner and observe O2 readings at WOT. I say this because I have proven to myself (others have done this too), that O2 readings are not as accurate in determining air/fuel ratio as people believe it to be. I have run as high as 54 psig and low as 47 psig with no effect on O2 readings.

Initial timing would depend on the amount of advance built into your PROM. Optimum total advance would be 38 degrees. Again with a scanner (or timing tape adhered to the harmonic balancer), determine how much advance the PROM is burned for, then subtract that value from 38 degrees. This should be where your initial timing should be set.

Retarding timing is only one method of preventing detonation. If you do not encounter detonation, retarding timing is not necessary. I am a strong believer that other methods to prevent detonation are far better than retarding timing and will never resort to a method that reduces power (timing retard). I have successfully run a Carroll Supercharging 100 psig water injection pump for years to prevent detonation with great success. I have run as high as 10.5 psig boost without timing retard. In fact with the Paxton kit, you're already plumbed for water injection. Just don't use that cheap Anco pump (in reality, a windshield washer pump) that Paxton supplies. It cannot produce the anywhere near the water pressure needed to fully atomize the water/alcohol mix.

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Willie

Supercharged 1987 305 IROC-Z, Daily-Driver, Emissions-Legal.
12.57 @ 111 mph.
12.04 @ 114 mph (50-hp nitrous).
http://members.optushome.com/au/downunder1/rides/willie/willie.html

1987 "20th Anniversary Commemorative Edition" Z28 Convertible -- Super Chevy Show Class Winner, 1998.

My custom front marker lamp assemblies:
http://members.optushome.com/au/downunder1/misc/lens.html

 

I have a 92 Z28 305 w/Paxton sn2000 and many mods. With the stock 19# injectors I ran 59psi.
Since then I installed Bosh 22# inj. and have the fuel pressure set at 49psi.
What's your o2 readings at WOT under boost.
Mine are .860 - .900
It runs a little rich when first started until closed loop operation.

Louis
Home Page: http://www.lbsz28blown.cz28.com

 

thanks for the responses.

I don't have the tools for the O2 readings yet, I will definitely need to pick up a scan tool though.

Willie, i'm not running the water injection setup. That may be something to look into for the future. The 6AL is just in case i need it. I don't think i'll encounter any detonation when it's 20 degrees out, but when it's 90 in summer, i probably will.

Also, I have 2 proms, stock and a hypertech. I'll have to figure out the specs of them both and figure out what to do with the timing.

Thanks for the help!


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DeathMobile, aka TheWraith

 

You will definitely need the 6AL or any comparable aftermarket ignition (I prefer Jacobs Pro Street). I've tried running only 6 psig boost with the stock ignition and it starts misfiring at ~4,500 rpm. What I personally wouldn't use is the boost retard function on the box.

On the timing issue, you can also install an MSD adjustable timing module, so you can experiment while driving. It's a whole lot easier than turning the distributor, running the car and repeating the process -- over and over. It's also good to use to compensate for atmospheric conditions. I have one and love it.

Willie

[This message has been edited by Willie (edited December 26, 2000).]