What psi will the stock 4.2 handle...safely...?

Used the search function, couldn't find a definitive answer.

More questions coming pending answer(s).

 

That's a very vague question, but in general the "safest" extreme seems to be around 300-350 bhp. That's pretty much the same for all non forged Mustangs, V6 or V8. Sure some can go as high as 450 bhp, but for how long is the question.

 

hmm. i figured asking for a psi rating wouldn't be vague.

More elaborate question...
Will a stock 4.2 rotating assembly with windstar upper, p&p lower, stock 9.2 compression, long tubes to 2.5" prochamber dual exhaust handle 10 psi boost from an intercooled procharger blower?

Or will i need to decrease compression to run that much boost?

My estimates put that setup at between 320-350bhp... am i close?

 

With no cam or head work you should be fine. But keep in mind, there is no real certainty when it comes to FI. There is always that possibility for some type of catastrophic failure. It's rare, especially when the job is done 100% right, but it does happen.

Centrifugal S/Cs put a little less strain on the internals than twin screw/roots blowers do, so that's a plus for the motor.

 

yes, stock cam.
Head work, if any, would consist of a valve job, better gaskets, and heavier springs if needed.
Plan on keeping the stock 3.8 on hand in case of one of those failures. haha
Does my hp estimate seem close?

 

Well stock you have around 160, given the mods you would jump to around 180-190 N/A. Depending on the quality of the head work and the extent it is taken, maybe 200 rwhp. Now adding in 10 psi would jump you to around 320-350 rwhp. Based off the flywheel numbers that's pushing you to around 400 bhp. That's well beyond the extreme "safe zone" however with the proper tuning, and work done it shouldn't be a problem because of the manner in which centrifugal S/Cs work. The 10 PSI would only create maximum hp and load for a short period of time which reduces the strain on the engine.

 

Well that's nice to hear, all my math and reading is becoming useful. I don't plan on racing it so it wont be under boost for long durations and its and auto so redline duration should be minimal especially with a j-modded tranny.

 

I don't recall seeing anyone post more than 8 psi as safe for an old engine.

 

PSI is just a measure of restriction.... the number to base it off of is hp/tq.
Say you run the 10 lb pulley on a ProCharger on your stock 3.8L. Say you make 300 hp (just for the use of this example). Port the intakes, heads and swap a cam. You will see less psi (7-8) with the same pulley, but be making much more power because you've opened up the air path.

The 4.2L set up you talked about would be pretty safe (assuming you have a good tune) with the Pro Charger. The thing to keep in mind is the bottom end breaks at big hp... but how often are you really making full power from an engine on the street - slim to none. Just be smart with it and you'll be ok.

 

Thanks for the input guys. I'm still in the planning stage right now. I'll keep updates and questions coming as i have them.