Outer Limits 4x4 Board

Hi, I'm converting my Jeep 4.0L 6 to lpg-only this April and want to complete a long-overdue 4.7L stroker project at the same time.

From my research it appears the ideal CR i'm after is 12:1 to 14:1 (stock is just under 9:1)

Has anyone done this (ie a high/er CR, naturally-aspirated lpg stroker either v8 or 6) or know of any good links for info ?

I mainly want to clear up whether the stock 4.0L bottom end (currently 140k on the motor) will like such a raise in CR or if big $$ are needed to prevent kaboom or spat head gaskets.

tia

sounds way too high ( 14:1 ) to run on pump fuel unless
you are running a fuggin huge cam.
But I'm more holden than jeep.


Rather than fork out thousands on the stroker, force some air into
it with better results allround.



.

hahaha....my bad (the gas thing)
I should learn to read properly.



But still go for the forced induction (with less cr).




.

12 or 14 to one is too high, even for straight LPG.

you can easily run 12: 1 comp on LPG, but it will be much more tempremental to LPG with a low butane content.

you should at that compression run proper gas cam and set your ignition timing curve properly.

jes

I would consider 12 : 1 on a propane engine, but not LPG, the butane is no good for fuel.

I'm building mild Cleveland with 224 @ .50 cam on straight gas... I asked around and general opinion was 10.0 to 1 compression, even Gas Research said that. Originally was hoping to go a bit higher than that the quality of LPG isn't so great anymore I've been told.
BTW if running alloy head(s) 11.0 to 1 would be acceptable.

mmm thanks for the feedback

I guess the 12-14:1 range I was looking at was more propane-based. Is there really that much extra non-propane in our lpg ? I guess so...

Have got a gas cam ready to go and was keen to up the cr a little as the pistons have to be custom made anyway so can order to suit.

Dismissed the idea of either super/turbo charging long ago for a million reasons - main one... I'm a tightarse

aint keen for the $$ alloy head. am just going to run a flowed stocker cast one with bigger valves.

as part of the stroker install an adjustable map sensor is going in for fine tuning but I'm keeping the factory computer. may have to address this later with an add-on chip.