94xj5spd

Ok if I use the 4.2 rods and crank with the 4.0 pistons bored. 0.60 over. What kind of compression would I be looking at?

DeathWobble

Probably close to 10:1. Will cause detonation on pump gas without dishing out piston heads and some machine work to the head. On the interweb theres all kinds of info on this subject

SeriousOffroad

Use this:

http://www.madxj.com/MADXJ/technical...rokerCalcs.xls

94xj5spd

What is a safe compression ratio for pump gas?

SeriousOffroad

You can't use stock 4.0L pistons with a 4.2l rod.

There's a lot more to know before you start woryring about compression ratios and pump gas.

Get your Read on....

http://www.angelfire.com/my/fan/stroker.html
http://www.jeep4.0performance.4mg.com/stroker.html
http://www.naxja.org/forum/showthrea...ght=crankshaft
http://www.jeepstrokers.com/forum/

94xj5spd

with this combination do i have to mill the block?
Jeep 4.2L 3.895" stroke crank
Jeep 4.2L 5.875" rods
Speed Pro H825CP +0.030" bore pistons
9.6:1 CR
CompCams #68-231-4 206/214 degree camshaft
Ported HO 1.91"/1.50" cylinder head
Mopar/Victor 0.043" head gasket
0.081" quench height

94xj5spd

?

94xj5spd

Would a 4.2 cam be benefical in a 4.6 stroker

94xj5spd

Anyone know ?

SeriousOffroad

oops...nevermind.

CoffeeCommando

With this combination milling the block is YOUR choice. This is the exact way I built my stroker minus the ported cylinder head. More compression means less room for error in your engine, and shorter engine lipe-span. If it was me I wouldn't mill jack. I don't want it lasting for 30-40 thousand less miles because I wanted to increase compression in order to gain ~2-3% horsepower.

I recently looked into having some milling done because I was having some new valves/guides/seats installed (FYI, make sure your 02 sensor is hooked up. it's a costly mistake).

In the end I found that if I milled it enough to jump my compression up to 11:1 i could gain 4% horse power (9 HP). But that's rediculous. That cuts life off the engine.

You are much better off going with bolt on mods like this guy (this guy doesn't even have a stroker and he ran a 10.7 or something close to it at the track) :
Or supercharging like this guy: http://www.4wheeloffroad.com/techart...kit/index.html

DO NOT COMBINE HIGH COMPRESSION AND SUPERCHARGING. Just google it. That's all I have to say about that. It's a stupid, and stupid-expensive, move... unless you love tearing engines apart after spending thousands on a build and breaking it a few thousand miles later.

94xj5spd

where did u get your head gasket from

CoffeeCommando

Felpro at Autozone.

94xj5spd

Does it matter about the bore of the engine on the head gasket

CoffeeCommando

Nope. You should already know this though if you are stroking the engine.. .. . .