4.0L rod V.S. 4.2L rod

[silver03cobra]

Hello,

I have built 3 of the 4.5 "poor man stroker" for clients now that I have a 4.2l yj I see the need for more displacement. We always did 4.2 rods and crank. Now I see you can use the 4.0l rod. *mind blown* what is everyone's opinion. The jeep is a weekend driver needs to run on 87 octane with a Holley 350 2bl.

[SilverXJ]

If you can afford it I would do with the long rod. Piston will be out of the bore less at BDC, longer life, and suppose to produce more torque. If you want something that can run on 87 octane I would check out Bulltear pistons. You can spec what you want.

[silver03cobra]

OK cool... I will check them out

[Cheromaniac]

Hello,

I have built 3 of the 4.5 "poor man stroker" for clients now that I have a 4.2l yj I see the need for more displacement. We always did 4.2 rods and crank. Now I see you can use the 4.0l rod. *mind blown* what is everyone's opinion. The jeep is a weekend driver needs to run on 87 octane with a Holley 350 2bl.

The modified poor man's stroker combination that I came up with has a lower quench height than the original poor man's and this, combined with the longer 4.0L rods and modest 9.2:1 CR, should allow the engine to run on 87 octane unless you live in a hot climate. There's also less reciprocating weight so the engine should gain and lose revs slightly quicker. As far as performance goes you'd be splitting hairs between either poor man's combination.

[silver03cobra]

Lol "hot" I live in az and we really only take the jeep out in the summer.... (no doors, no top, no heater) anything below 60 is freezing...

[Muad'Dib]

I am not convinced its worth the extra money and fuss to go with Forged Pistons and 4.0L Rods.

The length difference between the 4.0L and 4.2L Rods is insignificant IMO.

This is an excellent thread on the topic:

http://www.jeepstrokers.com/forum/viewt ... =15&t=1148

[Cheromaniac]

Lol "hot" I live in az and we really only take the jeep out in the summer.... (no doors, no top, no heater) anything below 60 is freezing...

It's the same where I am. Anything below 60*F is freezing and it's 100+*F for 7 months/year so I just run 91 octane year round.

[silver03cobra]

The longer rod would change the torque curve (raise it) due to piston dwell time...

[JeepFamily]

The long rod only raises the piston pin in the hole. It will reduce rotation angle at the wrist pin and reduce thrust forces against the cylinder wall. In theory it will increase engine life. I agree though the price may not be worth it.

[silver03cobra]

I get pistons at cost..

[Cheromaniac]

The length difference between the 4.0L and 4.2L Rods is insignificant IMO.

I agree but the 4.0L rod does allow you to build in a 0.018" lower quench height on a poor man's stroker without decking the block/head.
If you already have a matched set of 4.2L rods, it makes sense to use them so that you can get the cheaper stock replacement pistons and save on cost. If you'll need to buy a set of 4.2L rods, then you might as well use the 4.0L rods that you already have and just buy a set of IC944 pistons instead. They won't cost much more than the combined cost of a set of 4.2L rods and stock replacement pistons anyway.

[silver03cobra]

I have a full 4.2L and a full 4.0L so its no big deal..

[silver03cobra]

What rod is stronger??? Either way I with polish & beam & shot pin the rods??? And can I use my 4.2L flywheel???

[Cheromaniac]

What rod is stronger??? Either way I with polish & beam & shot pin the rods??? And can I use my 4.2L flywheel???

I can't give a definitive answer about which rod is the stronger of the two but the only rod failures I've heard of in either case were in hydrolocked motors. The 4.2L rod is shorter yet heavier so the iron is more dense, but does that make it stronger? Either way I'd polish the rod beams and shotpeen the rods as you mentioned and use ARP-112-6001 rod bolts.
Since an I6 engine is balanced without a flywheel and harmonic balancer in place, it's OK to use the 4.2L flywheel.

[atias]

ill use the 4.0 flywheel and starting motor if i where you , way better then the old 4.2 junk.