How much??
 

I'm trying to find out how much boost I could throw at a NPI 4.6 and not worry about it goin boom. Most of the kits you see are something in between 6-8 psi, but could I safely run 10psi on the stock internals?

I wouldnt go above 9 psi, you would be pushing it with 10

It should be the same as the PI, the only difference is heads/cams/intake. The shortblock should all be same internals/rings/etc. But yea, usually nothing more than 8-9PSI if you like to get on it a lot.

8 is my max...
9's knockin on the door, kinda iffy...
10 you're just askin for it...

No because the PI engines have diff. internals and the heads are very different. PI motors have higher compression than non PI cars because of a smaller combustion chamber made by the different heads.

Just curous, what would the HP gain approx be with 8psi?

youd be sittin around 360-385 hp

I knew the heads were totally different, but that shouldnt have to much of an effect with how much boost. It mostly is within the internals. But thanks for clarifying that, I learn something new everyday!

At the wheels? with 8psi?..... i was figuring about 330...

yep at the wheels


well up here it might be closer to 350

No way! From a NON-PI engine!

With a Vortech blower, NON intercooled and on STOCK engine, they're website says it will produce 323HP (in engine). So thats like 300RWHP, but with his full exhaust set up it would prolly be around 335-340RWHP. Change to PI and boom, 390RWHP

Thats where I would run into problems tho. When you swap a NPI motor to PI heads it jacks the compression to 10.5:1 And with that high of compression I would have to lower the boost to somewhere around 6+/- PSI.....its a bummer.

Jon when you said 360-385 you were referring to a PI car right.

You can lower the compression jump on a PI swap by porting out the combustion chambers a bit. Make sure this is done very carefully and get the heads cc'd once it's finished to make sure you've got everything correct.

I run 10psi on stock internals and so far...all good!!

actullay u can run 12 or 14 psi - depends on your tune - u maily have to worry about the hp rating not so much the boost - about 400-420 rwhp is all u want with a stock block to be "safe" - however you can pull 525-575 rwhp out of it but - it could blow at any second - or last for years but that the gamble.