2.9 vs 4.0 crank

[59flatbedford]

so i was wondering what all was different between the 2.9 and 4.0 as far as crankshafts are conserned. basically can i take a 4.0 crank put it in a 2.9 block and gain some stroke.

 

[fastpakr]

It's been discussed here in the past. General result was that it would require significant mechanical alterations to make it all work together, and at the end of the day you'd have a low revving 3.4(ish, not exactly sure) liter engine, rather than a factory engineered 4.0, and you'd spend more in the process to get those reduced results.

 

[volrath]

3.5 to 3.7 liters. there was a uk company that made the 2.9 into a 3.7.
you would have to rebalance the 4.0 for sure. and custom rods for sure. even if you used 3.3 chrysler pistons(same bore, shorter comp height of 1.173 campared to 2.9 comp height of 1.527) you would still need a rod that is about 0.161" shorter(can't remember the true number but close) and the 3.3 mopar has a smaller wrist pin(0.9009 compared to 0.945). clearance is an issue as well as material would have to be removed from various locations to get the crank to spin freely. as far as the revving goes it wouold revv about the same as any other 2.9 or 4.0. i personaly think my 2.9 can sure scream

also newr 4.0 cranks have 8 bolt flywheels so you would have to use older 4.0 ohv crank. preferably a gen 1 (90-94?) cranks. but they do share the same main and rod bearings as well.

2.9 stroke 2.80"
4.0 stroke 3.32"

2.9 bore 3.661 max over bore ive found is +0.060 = 3.721
4.0 bore 3.95


max bore and 4.0 stroke would give you roughly 216.7 CID (3551cc)
stock bore and 4.0 stroke would be 203.97 CID (3342.5 cc)
stock stroke and max bore 182.76 CID (2994.98 cc)
stock bore and stroke would be 176.91 CID (2899.17 cc)

2.9 piston has roughly a 13cc dish in it as well.
2.9 heads have 42cc combustion chambers
small chamber 4.0 has 48cc

just my 2 cents
~mitch