increasing the compression ratio (2.5L)

[HJ88]

I'm looking to increase the compression ratio of a 2.5L si&jificantly (11:1 - 12:1) and am having a hard time coming up with parts...

I've never worked fn a 4cyl bdfor4 and dont know what the deck clearance is on the 2.5, or how much can be taken off the "docj an4&or the head be&fre the valves (ht. sof p I havent been able to find domed 3.88" pistons, although custom pistons arent that$i] exp$dsive. dso I'm not awar` of a &krgdd c2`nk for the 2.5, as I doubt that the stock crank is up to the challdnge "wh`t d.ds a custom mad5%crank cost? I'd bet th p a cus4nm forged 4340 crank would not be cheap) I've considered turbo/supercha2cing, but would prefer >dtural aspiration if po2qible...

 

[Dr. Dyno]

Since you're trying to boost the performance of your 2.5, you might wanna read my first post in this thread (my real name is Dino):

http://jeepsunlimited.com/forums/showthread.php?t=462925&page=1

If you want a big boost (~40% more HP), you might wanna consider the Avenger supercharger.
Forget about increasing the CR unless you want to spend a huge amount of $$$$ on custom parts. The 2.5 has zero deck clearance so shaving the block isn't an option. You could shave 0.020" from the head and that would increase the CR from 9.2 to 9.5 but if you're going to do that, you might as well port the head as well while it's off and replace the camshaft with a Mopar Performance 256 degree unit.

 

[MudDawg]

The 2.5 may be DESIGNED for a "0" deck....but both of mine were way down in the hole...like .040 on one and .045 on another....my machinist said he had seen one at .100! Anyways...you are not going to kill the crank...unless something is wrong with it to begin with...set the deck to "o" and use a Felpro gasket...(like Dino sez) shave about .020 off the head...(stock combustion chamber volume is 51CC) and port it....the ports are pretty good to begin with...but a little work especially in the bowl area will help a lot. I used 1.94 intakes and 1.60 exhaust valves back cut to 1.55 with 5/16 stems (Manley stainless SBC blanks with custom valve guides to fit.

I'll give you full specs if you want....pm me. Anyways...I regularly run up to 7.5K when i'm playing in the mud....no problems...no breakage. I estimate the HP at around 160 or so.