3.4 to 3.1 swap

[Luke]

I just purchased a 92 Z34 with rod knock. Car is perfect otherwise. I would like to know if anyone has any experience with swapping out the 3.4 for a 3.1. I am not so much interested in performance as in reliability. The 3.4 is costly to rebuild or replace. I need to know about motor mounts,cradle, PCM, trans., etc. Would I need a donor car or just an engine. Any input would be greatly appreciated. Lucas.

[Baddflash]

basically everything is different between the two motors, a donor car would be a good idea if you really want to swap to 3.1L. If you're going to swap why not go to a 3.8L they're very reliable and have more power than 3.1L, if your're going to go through all that work make it worth the effort.

[Luke]

How much fabrication is required for the 3.4 to 3.8 swap? Exaust? Harness? PCM? I would like to rebuild the 3.4 to keep it original. I found a crank kit/gasket set for $350. I don't know what caused the failure. No oil in coolant, and no visible leaks. The car belonged to my sister, and she has no idea what happened. I have built race engines for Mopars, but this seems like a sensitive operation. Any input is appreciated. Thanks. Luke.

[patgizz]

keep the 3.4 if you can

 

otherwise the harness, pcm, cradle, everything will work just need a 3.1 with its specific 3.1 mounts and the rear right mount for the tranny

[99RegalGS]

If you want reliability the 3800 is the way to go.

 

How much fabrication is required for the 3.4 to 3.8 swap? Exaust? Harness? PCM?

You will probably need all of those and the engine and tranny mounts.

[Luke]

This car has 72,000 miles. I will take engine out soon as weather permits. Is replacing crank/bearings staightforward deal? Is there anything I should check during disassembly/reassembly? Has new starter/fuel tank/pump. I really appreciate all the help/comments. This is a great site! Luke.

[J]

i have a motor for about $1300 if you want, brand new 3.4 DOHC with everything on it but t.b. Let me know

 

0 miles

[DaveFromColorado]

I'd try to drop the pan and see how bad the bearing is, sometimes* you can get away with putting in a new bearing and then "plastigauage" the thing to check clearance, assuming the bearing didn't score the crank too baddly, otherwise you'll be pullin' the crank too ...

 

I tried doin' a 2.8 to 3.4 swap, it was the worse expirence of my life, and I'll never* attempt it again.

[sonyman87]

you could also try the 3400.. its alot faster the the 3100 and more fuel efficent then the 3800

[99RegalGS]

you could also try the 3400.. its alot faster the the 3100 and more fuel efficent then the 3800

I looked up the mpg difference on a 2004 Monte Carlo. the 3400 gets 21city/32highway with a 2.86:1FDR, whereas the 3800 gets 20city/30highway with a 3.29:1FDR.

 

IMO the 3800 is as efficent as the 3400 and the 3800 gets 20 more horsepower and 20 more pound-feet of torque.

[Luke]

Thanks for all the input. I have located a 3.4 dohc from a 95 Monte Carlo. It should be a direct bolt in. When I am done with the swap, let me know if anyone is interested in the knocking 3.4. Luke.

[EurosportZ34]

Granted the 3.1L is a great motor, but why in the world would you want to swap that with all these other better/faster choices?

[Luke]

The initial reason for the swap was availability. The 3.1 is plentiful where I live, whereas the 3.8 is pricey and the 3.4 was not available. Finally locared a 3.4 w/65,000 miles from a wrecked Monte in Ohio. It will be delivered by the end of the month. Luke.