anyone running higher compression?

[Vigo]

is anyone running something close to 9:1 compression in their turbo engines, if so why and what does it get you?

[85glht]

Quote:

Originally Posted by Vigo is anyone running something close to 9:1 compression in their turbo engines, if so why and what does it get you?

A friend of mine is. It wasn't planned that way. Something was missed, either the cc of the head or not enough dish in the piston. It runs fine but he cannot run the boost as high. I would just stick with 8.0-1.

[Dave Sigman]

I'm using a tbi shortblock its working out good so far spools the turbo real fast. 9.5:1 isn't a very high comp ratio to me. with enough fuel and easy timing any compression will work. it feels stronger out of boost and with higher cylinder pressure you get more power throughout the entire rpm range. in my opinion 8.0 is just too low of a compression for performance and I'm thinking chrysler used it to keep the low buck mitsu turbo streetable. with the higher compression its just too small its into boost so fast its kinda hard to drive.

hth

Dave

[turbovanman]

I ran tbi pistons for 3 days, at 12 psi of intercooled boost before it melted down, badly.
But it had great throttle response, less turbo lag, and the power was more linear. This was with a stock TIII turbo and a 50 trim compressor wheel and matching housing.

[ozonekiller]

You can get away with higher compresion if you take a few precations. Such as polishing the chambers, ceramic coatings pistons, valves, and chamber walls. Chrysler kept compression low partly to keep the overly bright general public from cooking the motors with low octane fuel. With a good cooling system and intercooler and the right preperation some honda guys are runing 9.5:1 with 20 pounds of boost. It just takes doing your home work.

[Vigo]

im thinking of running 14 psi or so, intercooled, on a 2.5 tbi, with a stock garrett.. seems like with the timing pulled back it shouldnt have any trouble there??

along the same lines, has anyone noticed a big difference in how much boost you can safely run based on water or oil temp?

[turbovanman]

Quote:

Originally Posted by Vigo im thinking of running 14 psi or so, intercooled, on a 2.5 tbi, with a stock garrett.. seems like with the timing pulled back it shouldnt have any trouble there?? along the same lines, has anyone noticed a big difference in how much boost you can safely run based on water or oil temp?

Theres more than timing involved. Inorder to safely run 14 psi, you will have to pull the timing back alot, enough that it will be gutless without the turbo. Need a big ass intercooler and lots and lots of fuel. Mine got so hot at 12psi even with my airfuel gauge reading perfect that I melted and bent the spark plug electrodes.

[Una]

I'd bet that tossing a G head onto a TBI block would do wonders towards pulling this kind of stunt off. You get a .5 compression ratio drop (so I've been told) and combustion chambers that are less prone to detonation.
Me, I'd run 6:1 compression if I could.. heh, scare the kids with 50psi of boost. ;>

[Vigo]

Quote:

Theres more than timing involved. Inorder to safely run 14 psi, you will have to pull the timing back alot, enough that it will be gutless without the turbo. Need a big ass intercooler and lots and lots of fuel. Mine got so hot at 12psi even with my airfuel gauge reading perfect that I melted and bent the spark plug electrodes.

so, seeing as how some t1s with mitsus run 12-14 psi non intercooled and dont melt their pistons in a matter of days, you're saying that a cooler running turbo, an intercooler, less timing, and possibly some colder spark plugs just plain dont make as much difference as 1 point of compression?

ive run my 2.5 tbi as 4 degrees base timing and it ran about the same down low as a stock 2.2 tbi, so i dont think running maybe 8 degrees instead of 15 would hurt me too much.

[turbovanman]

Quote:

Originally Posted by Vigo so, seeing as how some t1s with mitsus run 12-14 psi non intercooled and dont melt their pistons in a matter of days, you're saying that a cooler running turbo, an intercooler, less timing, and possibly some colder spark plugs just plain dont make as much difference as 1 point of compression? ive run my 2.5 tbi as 4 degrees base timing and it ran about the same down low as a stock 2.2 tbi, so i dont think running maybe 8 degrees instead of 15 would hurt me too much.

But thats a tbi, I see what yuor getting at, all I can state is what happened to me, tbi pistons, 12 psi, intercooled, TIII turbo with 50 trim compressor, air fuel gauge showing good, no EGT at the time, timing at 10 deg. I lasted 3 days, melted down 3 sets of plugs then melted #3 piston badly. At the time, couldn't figure out why until I took it apart, and someone had put tbi pistons in a turbo block, dumbass's but it gave me some more learning.

[DocFish]

I had a 2.5l tbi in for 4 months but had to light pedal it. It would ping above 5psi @ 14 degrees advance. Ran GREAT with race fuel, not a hitch, but finally holed a piston on the street against an STS. I had a swirl port head, though. A buddy had a Rampage with a 2.5l with a G-head and never had any trouble. No intercooler either at 13psi.

[Vigo]

Quote:

But thats a tbi, I see what yuor getting at, all I can state is what happened to me

not trying to offend or anything, i do appreciate your input.

but it sure sounds worse than i would imagine.. i cant see the tbi pistons being so much worse than the turbo pistons that they'd fall apart under such mundane conditions as 12 psi intercooled. i know a guy thats run a 75 shot of nitrous on a tbi motor for over a year and hasnt had problems, i would think 12 psi intercooled wouldnt even be as harsh as that.

but im not the one whos done it, which is why im asking


heres another question (still want input on the 1st one tho!)..

will turbo pistons/rods bolt right into a tall block 2.5? 87 pistons/rods in this case?

[glhsken]

Yes, people are running higher compression

[turbovanman]

Quote:

Originally Posted by Vigo not trying to offend or anything, i do appreciate your input. but it sure sounds worse than i would imagine.. i cant see the tbi pistons being so much worse than the turbo pistons that they'd fall apart under such mundane conditions as 12 psi intercooled. i know a guy thats run a 75 shot of nitrous on a tbi motor for over a year and hasnt had problems, i would think 12 psi intercooled wouldnt even be as harsh as that. but im not the one whos done it, which is why im asking heres another question (still want input on the 1st one tho!).. will turbo pistons/rods bolt right into a tall block 2.5? 87 pistons/rods in this case?

No offense taken,

To run higher compression, you need to take in a bunch more variables, thats all I am trying to say. 12 psi 8.7:1 is easier and safer than 12 psi at 9.5:1.

Yes, the pistons and rods work, as I found out. Tall deck? 2.2L's and 2.5L's have the same deck height!

[Vigo]

i was under the impression the tall deck 86-88 block was only used on 2.5s, so that it could use the same pistons and rods as the 2.2??
i know they had the same deck height when they went to the common block (hah, what a coincidinc).

also, im talking about using the tbi pistons 8.9:1 compression ratio, not 9.5:1.. turbo motors have 7.8:1.