Sxynerd

A friend has just completed a forged short block 2v and has a chance to get a blown (as in broke) 99 cobra motor for almost free. I know we can physicaly swap the short blocks but will this increase or decrease the compression of the engine with the different heads and short block that was made for a 2v?

Sxynerd

everything would be included that would be needed for the swap... just to make it clear, I know how some of you get! lol

ASUSMC

DECREASE. 2V's with the same pistons have a higher compression ratio.

01Steed

My question would be, "why would youchoose the '99 motor over a forged shortblock?"

Also, without knowing what the forged piston's dish size is, no one can tell you whether it will increase or decrease the c/r.
Your post is kinda confusing. Is it your friend's intention to swap the short blocks? If so, assuming his forged pistons are of stock dish volume (or even close), his c/r will INCREASE if he installs 2V heads on the cobra block. The 4V block has smaller dish volumes than the typical 2V (PI).

Sxynerd

I don't think it's confusing... I'll break it down third grade style.

I have a new PI shortblock with the same specs as a 01 2v. I also have a 99 cobra motor that the bottom end went boom. When we take the cobra heads and "stuff" and put them on the short block. Will it increase or decrease the compression?

Whats hard about that?

Sxynerd

Does anyone know any numbers? If it decreased then this might be better for pump gas/high boost aplication, wouldn't it?

adam_ferguson

well if it decreases of course it will be better for a f/i application. the more shallow the dish volume the higher your compression will be. you need to look up and find what the depth is on the stock piston on the 99 block .

01Steed

Nah, you don't need that. His 15.8 cc 2V piston ('01 spec) coupled with the 51 cc chamber volume will net him 8.6:1 c/r or so.

Your original post confused me because you had mentioned "swapping short blocks". You don't have to be condescending with me. I'm not a third grader. I just honestly had trouble sorting out what it is you wanted to know. My bad. And if I've mistook your tone, my bad again.

If you want, I can send you an Excel spreadsheet that breaks it all down for you. You just enter either your desired c/r or your piston/chamber volumes, and it does the math for you. It has all of the factors already plugged in. We use it all the time here at work.

Sxynerd

My apologies, my GF pissed me off and I had my panties up in a bunch... Sorry.

With that low of compression would that affect low end power (before boost) at all or would it be not enough to really notice? He'll be running about 20PSI from a Vortech.

01Steed

Hey, no prob! I know how that cookie crumbles.

Well, theoretically he'd be losing some low end power, but like you said, with that much boost I don't think he'll be missing anything, LOL! He'll prolly develop some boost (translated into low vacuum) down low anyway with an impellerasaggressive as that would have to be.

That thing is going to scream!! Be sure he upgrades his valve springs, uses ARP head studs, and good gaskets!