TimmyGt

how much hp would it add to a 97 GT with PI swap. Take into the fact I would have to do all new internals and change the compression somehow. I just want to see vs just droping in a rebuilt cobra engine.

tcuallstar

why would you have to do all new internals? or change the compression? the supercharger is going to run you about 5 to 6k installed and from what i hear the pi isnt too cheap either, you would see much greater gains out of that setup than a rebuilt cobra engine (unless it was from an 03 cobra)

yoteehunter

^the pi swap makes the compression ratio up around 10.5/1 wich aint to good for FI.

You could skip the internal rebuild part and just pull the heads again and use cometic head gaskets that are .090 thick. that would bring down the compression to normal and almost be as good as oringing the block as these gaskets are made for boost. A supercharger will add about 100hp or so depending on the boost used.

yoteehunter

http://forums.modulardepot.com/showt...threadid=51255
Here is exactly what Im talking about. Read this it will probly answer your question, and If I were you I would skip the cobra swap just because of cost issues. Cometic head gaskets are like 200$ I think. Do the work yourself and your good to go. Also you can get them in any thinkness up to .130.

TimmyGt

from the looks of it even with the stock compression just by adding the PI head he got to 377 ! I was looking at the procharger or vortech I dont know what would be best! when I get the new charger with the diffrent head would I get the setup for 99-04 or would I still get the 96-97? I was looking at the cobra block (97) and for how much it is I dont know if it would be $$$ for what I would get out of it because I wouldnt try to make the car much faster after I hit that 400rwhp mark. I just dont know if I would want to spend that much for the new block because then I would most likely not supercharger it because all my money would go into getting the block and the rebuild. what does everyone think I should do supercharger or rebuild cobra?

ShadowDrake

I love how many people have compression ratio wrong. Higher compression is ALWAYS better. Cylinder pressure = power, and compression ratio raises that the most. What's the down-side to high compression on a boosted motor? Much higher cylinder pressures, so if your engine isn't built to take it, it will break.

Atmospheric pressure is around 14.7 PSI... so on a 10:1 compression motor, you have 147 PSI at the top of the stroke. On a motor boosted with 9psi, the new "atmospheric" pressure will be 23.7 psi, so cylinder pressure will be 237 psi... an increase of 90 psi just from 9 lbs of boost. That's a 73% increase, so you can expect a 73% increase in power in the perfect world.

On an 8.5:1 compression motor, N/A you'll have 124 PSI at the top of the stroke... with 9 lbs of boost you'll have only 201 psi. 62% increase. You won't have as much power as if your compression was higher, but you see, there's less cylinder pressure.

I personally am a fan of getting power first, then building up to support more later (then if you're boosted, add more boost)... that's what I would suggest. Contact Vortech about what kit to buy, the biggest difference in them is just the mounting hardware, they can suggest what you need.

TimmyGt

but I dont want to high of a compression because I am scared I would put a hole in my block. I just want to make sure then when its all said and done I wont have parts always giving out on me. thats why I was looking into a new engine (DOHC) but for the money I can rebuild my block with some new parts and still make my car fast.

ShadowDrake

The 4.6 block isn't the weak link, as it is with the 5.0s, your block will very likely be fine... You could put 6lbs of boost through it and be fine for a long time. Get forged internals and some dished pistons to bring compression back down to a standard level for the 4.6 and bring your boost back up to max out your supercharger. That's just one way of going about it.

yoteehunter

Hello!.......... he is trying to save money here, and get the most bang for his buck. Look....... if you have to high of compression with your current set up you wont be able to make as much power as you would with the lower compression. The reason.........you cant run much boost. A PI swap does bring the compression ratio up to 10.5/1. This is a ratio! In naturally asperated form for every point gained in this "ratio" you will gain about 15hp. NOT true for FI motors unless it is built for this purpose and normaly will have to run race gas. Use the thicker gaskets and dont feel bashful about running 10psi of boost. You will gain way more than 6psi on 10.5/1 compression. Hince MORE BANG FOR THE BUCK. Plus those gaskets are made for boost. Also it will open up the horizon for better tuning and longlivity. ^what the other guy said is about half *** correct. The weakest link in the 4.6 is #1 the rather small wrist pins and #2 the connecting rods.