Ok, I bought a used rebuilt block w/ forged internals and swapped it for my blown motor. I got a sweet deal on it ($400) since some kid totalled his ride. The only thing is.. he didn't know what compression ratio the pistons were. I did a compression test yesterday and I got 160-170 PSI on all four cylinders. I'm thinkin it must be lower compression ratio than stock cause when i swapped motors, I added an UDP and it didn't seem to make any difference in power compared to the stock motor i had before. He said it was bored .20 over, so wouldn't this add a lil power too?

sounds lo comp to me lower than stock that is. I don't think boring that tiny amount would add any horsepower. It just to make sure the cylinder walls are round or not overworn, which is why I got this wack compression right now I think :(

hmmm... well do these numbers sound good enough to go stage II? I think i remember him saying he had the engine built with a turbo kit in mind.. so maybe it is 8.6:1 compression?

its around 8.6:1 might be 8.8:1

ok.. so i should be all set for some boost?

Sounds like 8.5 or 8.6:1. At 8.8:1, my compression is at 185 all the way across.

Um i got 8.6:1 compression je's and stock bore and my compression is 220-220-210-210? the 170'ish range sounds like something a stock engine has?

_________________
Vinnie Lima
vinnie.lima@jvllogistics.com
AIM: Kiku888
1997 Chrysler Sebring "Silver XTC"
I4 420a w/ HRC Stage 2.45 w/ FMIC
14.7@97 mph@6psi
Proud member of the
ASOG BoOsT JuNkIe Crew

>Um i got 8.6:1 compression je's and stock bore and my
>compression is 220-220-210-210?

Damn, that has gotta be the highest CR for 8.x pistons I have ever heard of. Did you do much milling or resurfacing to your head?

I think stock pistons can have compression of up to 225 or so. After almost 40k turbocharged miles on my stock engine, my compression was at 175 all the way across.

My JE's 8.8:1 are 185 psi accross also... I'd say you have 8.6:1 pistons too...

stock is what? 9:1? So, let's say it's supposed to be stock compression... Could my numbers then indicate anything bad? Would it still be a good idea to add some boost this fall?

EDIT: Could my compression gauge just be off that much? it's the long hose that screws in type.

>stock is what? 9:1?

Stock is 9.6:1

So, let's say it's supposed to be stock
>compression... Could my numbers then indicate anything bad?

Not necessarily good if your compression is that low, yes. At least all the numbers are close to one another. And that's working under the assumption that your pistons are stock.


>Would it still be a good idea to add some boost this fall?

Why not? Even if they're stock, boost on em till they go bad. Then rebuild! :-)


>EDIT: Could my compression gauge just be off that much? it's
>the long hose that screws in type.

A lot depends on if the car is warm or cold, if you had the tool screwed in properly within the spark plug ports, and if you turned the car over until the compression wouldn't raise up anymore.

If someone told you that the internals were rebuilt, I'd take the half hour to drain the oil out, drop the oil pain, and get a good light up into the bottom of the engine. If they're JE pistons, which so many of us use, it'll say so right on the piston bottoms! Check it out!
:thumbsup

hmm.. thanx man... good advise... I just changed the oil a few days ago... next time i change it tho i'll drop the oil pan and take a gander.

EDIT: One more question... how much less power would i be making by droppin from stock 9.6 to ~8.6 compression, with just 3" intake and 2.5" exhaust and obx canister muffler. Only other mod is TopFuel UDP, but that was added after the motor swap.