Minimum amount of BOOST for a supercharged 383?

[JohnBlazeLTZ]

Can you guys show me a way of determining the minimum amount of boost for a supercharged 383? I have a blower that is capable of pushing between 6-10lbs and I am thinking that probably isn't enough for a stroker.

[Packard V8]

FWIW, being a stroker has nothing to do with boost. Manifold pressure or boost is an absolute measurement of how much pressure generated by the supercharger DID NOT get into the cylinders. The longer the camshaft duration, the greater the overlap and the better flowing the cylinder heads, the more generated flow will get into the cylinder (and some right out the exhaust) and the lower will be the boost pressure reading. Thus, a reading of ten pounds of boost on factory heads, intake and cam will usually generate less horsepower than six pounds of boost on good flowing aftemarket heads, intake and camshaft. With the performance heads, intake and camshaft, more flow generated by the supercharger can get into the cylinders and less will be left trapped in the intake thus giving a lower boost pressure gauge reading.

Bottom line, ten pounds of boost will be all your 383" will want on the street. You will need a top-of-the-line ignition with good boost-retard program. Spend the bucks on an MSD or J&S Safeguard, otherwise ten pounds on a stock distributor is a death sentence. Racing is a whole different discussion, but it does not seem you are going there.

thnx, jack vines

[JohnBlazeLTZ]

Thanks Jack.

No this is not going to be a race engine...just for street. I have a Centrifugal supercharger by Vortech. Its an older design. Its meant for the old GM TBI injection system but I have since decided that if I want to use it...I should just put it on the 383 I want to build and just avoid the TBI if possible. Some of these Natural Aspirated TBI 383's are equipped with Vortec heads and they are getting 275-330hp at the wheels with 400+ ft/lbs.

I would not be using pure stock parts but it won't be the cutting edge either. I was considering World/Dart Cast heads at best and a 4 barrel intake of some sort with a blow-thru TBI and probably a Multi Port FI system like the MPFI from Affordable Fuel Injection. This isn't going to be bleeding edge but I was just shooting for 400hp at the flywheel but 500 ft/lbs of TQ. Its for a 1993 Caprice...so it has to have the TQ to get it up and moving quickley. Some guys have said that a heavily modified GM TBI system could Actually work but I haven't bee able to find to many people interested in helping me determine the right combination of parts. I think its possble too but because I am not as good with this stuff...I am not sure what to do.

John

[big_G]

FYI..I am running an inter-cooled ProCharger D1SC blow-thru carbed 383. 8.3:1 scr, 242/248/110* cam, (now running 230/236/114*) Vic. Jr. heads. Had it pullied up for 16 lbs. of boost @ 6,500. Never a problem. No timing retard. No detonation. Blow-thru carb. set-ups (inter-cooled) are more forgiving on boost v. timing, imo. You will need to pull timing on an injected motor. Make sure you have good rods/bolts and forged pistons. They will save you in event your tune is off. G/L

[JohnBlazeLTZ]

OK bigG Thanks man.

I will only be able to get 10lbs max...I believe that 10lbs is with using an inter-cooler as well. The stock Vortech A-Trim is the weakest Centrifugal Vortech offered at the time when this kit came out.

Can anyone tell me if an A-Trim is even strong enough to work on a 383 vs. a S-Trim or a T-Trim?

John

[big_G]

Originally Posted by JohnBlazeLTZ

OK bigG Thanks man.

I will only be able to get 10lbs max...I believe that 10lbs is with using an inter-cooler as well. The stock Vortech A-Trim is the weakest Centrifugal Vortech offered at the time when this kit came out.

Can anyone tell me if an A-Trim is even strong enough to work on a 383 vs. a S-Trim or a T-Trim?

John

Call Vortec...see what they say. When I was building my ride, I called ATI/ProCharger and they said the P1SC (the smallest they sell) would be too small for a 383. Me thinks you need at least an S-Trim.

[Packard V8]

Since you've got the A-trim, use it to set up and get running. If it only makes 6PSI, that will be a huge horsepower increase. I know a guy who is a TBI-blow-through-guru. Send me your e-mail off list and I'll ask him to contact you.

big_g is the exception.

Had it pullied up for 16 lbs. of boost @ 6,500. Never a problem. No timing retard. No detonation. Blow-thru carb. set-ups (inter-cooled) are more forgiving on boost v. timing, imo

No one else I know has been able to run 16PSI of boost through a regular NA ignition timing. Usually that boost level would require half the ignition advance of the NA, say 18 or 20 degrees versus 36 NA. This month's Car Craft had a supercharged draw-through article and they said the max on 91-octane was 19 degrees. Yes, a blow-through with an intercooler will have a cooler charge, but are you really running 36-38 degrees of ignition advance with 16PSI?

thnx, jack vines

[big_G]

Originally Posted by Packard V8

Since you've got the A-trim, use it to set up and get running. If it only makes 6PSI, that will be a huge horsepower increase. I know a guy who is a TBI-blow-through-guru. Send me your e-mail off list and I'll ask him to contact you.

big_g is the exception. No one else I know has been able to run 16PSI of boost through a regular NA ignition timing. Usually that boost level would require half the ignition advance of the NA, say 18 or 20 degrees versus 36 NA. This month's Car Craft had a supercharged draw-through article and they said the max on 91-octane was 19 degrees. Yes, a blow-through with an intercooler will have a cooler charge, but are you really running 36-38 degrees of ignition advance with 16PSI?

thnx, jack vines

No, I am running 32*...have tried 34* and no detonation, verified by plug examination. Keep in mind this was with a big overlap cam and 8.3 scr. 93 octane is available here in Austin, Texas. Engine Masters did a write-up a few years ago with almost the exact engine build I have. They also ran a D1SC at 16 lbs. They ran as as much as 30* timing, no retard. This was with 9.5:1 scr motor.

FWIW, fron the ProCharger site:

"For engines that are experiencing detonation problems, the primary options are the use of ignition/timing retard systems, higher octane fuel, or intercooling. While ignition retard systems can be helpful in certain situations, they can also greatly reduce the horsepower output of an engine, as any reduction in timing will reduce horsepower. And while a reduction in timing can save a motor from detonation, the excessive heat which was causing the detonation is still present. Intercooling, on the other hand, actually removes the heat which causes detonation, and allows higher boost levels to be safely run with full timing on pump gas. This produces the maximum benefit in terms of both horsepower gains and engine protection, without any additional maintenance or hassle."

[Packard V8]

Hi, big_g,

Yes, I'll believe your low SCR (8.3), lots of cam overlap, an intercooler and 93-octane can run 16 PSI and 30 degrees of timing. However, that is not the combination on which we were asked for recommendations. John was asking for a much milder combination to street-drive a heavy car and probably max 91-octane. Giving

Had it pullied up for 16 lbs. of boost @ 6,500. Never a problem. No timing retard. No detonation.

without all the above detail can get a first-timer into lethal detonation trouble.

thnx, jack vines

[big_G]

Originally Posted by Packard V8

Hi, big_g,

Yes, I'll believe your low SCR (8.3), lots of cam overlap, an intercooler and 93-octane can run 16 PSI and 30 degrees of timing. However, that is not the combination on which we were asked for recommendations. John was asking for a much milder combination to street-drive a heavy car and probably max 91-octane. Giving without all the above detail can get a first-timer into lethal detonation trouble.

thnx, jack vines

Absolutely. Best to approach F/I with caution.