97stanger

Well, within the next few weeks I will buy the forged rotating assembly, just have to decide the right kit with the right price. I know for a fact I am going with forged h beam rods, arp bolts, forged pistons (stock compression), rings, and bearings. My next step are the heads. Keep in mind I already have crower stage 2 non pi cams with valve springs/steel retainers sitting in the garage. Should I port/polish my non pi heads? run another head? Keep in mind I am planning on running some pretty good boost so compression will be a factor.

MikeInCape

Build your motor for the boost, so yes compression is a factor. Go talk to some local machine shops to get a good idea of what you are looking at.

More boost=lower compression

97stanger

yeah, thats what i figured. I would just hate to work up my non pi heads, and have them be my restricting factor, ya know?

MikeInCape

Get a set of PI heads... Then you won't have that worry.

97stanger

but before power is my worry, compression is way more important to me. I'll have to talk to some race shops to see if P/P PI heads would be too high of compression for my setup

MikeInCape

Either will work. PI or non PI... PI is just a better platform to start with.

Remember, there are a few ways to raise/lower compression including piston shape and head work - among other things.

97stanger

okay, thanks for the advice man. I'll talk to some shops and see what I can work out here

Sxynerd

Ported NPI heads flow the same as Ported PI heads.


if you're running a big blower and plan to up the boost go with 8-8.5:1. If you're running an S, Si, P1, 1.7, 2.1 go with 8.5-9:1. npi's are 9.6:1.(year depending) That .6 equates to about 10hp before boost. You'll never be able to fell the difference in your seat. The Boost builds to quick

Smaller blowers wont make up the difference and your boost will drop with the lower compression.

"More boost= Lower compression" is kinda true but misleading. It's the fuel that's the problem not the compression.

your npi intake going to be your only restriction at that point but then you can just swap that out when ever.

97stanger

well if thats the case, i dont see the need to buy the PI heads if I can just use my NON PI heads for some work done to them.

I already run a SQ trim, Paxton front mount, PI manifold, full bolt ons, built AODE, 3500 stall, walbro 255, 42# injectors...and will be forging the bottom end, heads, and installing my crower stage 2 non pi blower cams

Sxynerd

What's your boost and hp goals going to be at? That single intank 255 is going to limit you past 400rw. (through an auto)

At minimum, add an inline hv255 and relay wire both your pumps to get 14v. Injectors will help out tremendously as well. My intank and inline 255 has taken me to 600rw with 60# injectors and run at 70%