Topic: 2.5L Rebuild using a commercial 3.0L stroker?

[Jeffy]

Well, I think the only option for a crank is to locate a Mopar Performance Crank.  It's listed in the FAQ.  I've never seen one though.

[RNandKT]

are the belhousing bolt patterns on that gm 3.0 the same as the amc 2.5?

[Jeffy]

I'm not positive but I'd suspect it uses a standard 60 Degree Bellhousing bolt pattern.

[RNandKT]

Hmmm i am going to have to do some more research into the 3.0 L engine and see whats common etc.

I do know the the GM 2.5 and the 3.0 share the same bellhousing pattarn.

How much is common between AMC's 2.5 and GM's? Anything swappable? Heads, distributers etc etc?

[Jeffy]

If the 3.0L shares the 2.5L Pontiac Duke's pattern then it will match the 2.4L AMC bellhousing.  Like I said before the AMC and GM do not share anything.  For the GM, the exhaust ports are on the passenger side.

[RNandKT]

The amc 2.4L?

The "marine" 2.5 and 3.0 have the exh and intake ports both on the drivers side. perhaps that could work. <--- slim chance.

but is there a possibility you could put a head from a fuel injected GM 2.5 and have it be a simpler wire up to the jeep?

[RNandKT]

maybe I am just beating a dead dog here, but I just want to look at it every way.

[Jeffy]

Whoops, that should have been 2.5L.

Like I said before you're best chance is to use a stand alone EFI.  I believe the RBI's of the 2.8L and early 5.7's are like this.

The only other concern would be if the engine runs in reverse or not.  I'll have to dig out that article about the CJ with the Mercruiser 3.0L and see what they say.

[RNandKT]

Well almost all boat motors do, but that is a matter of a different cam and so on. I believe the 3.0 was also used in commercial things such as tractors whatever, where it ran normal rotation. Plus you should be able to use a cam from a chevy 2.5L to run normal rotation ... right?

I'm starting to think I'm pushing this too far though. My best guess is that it would bolt up to the tranny but getting the intake to work and still keep the MPI would be near impossible.

[RNandKT]

Another question though, the "Mopar Performance crankshaft" does it actually increase displacement? I.e. is it actually a longer stroke requiring longer con rods?

[creepyjeepy]

if the mopar crankshaft did increase displacement via a longer stroke, it would require shorter connecting rods.  

what about simply using the 3.0L engine and doing away with the 2.5L entirely?

i was looking at how some guy in canada put 4.2L parts into his 4.0L to stroke it.  someone correct me, but given that the connecting rods are shared between the 2.5 and 4.0--according to what i've found on the net--then it would be possible to use the shorter 4.2 connecting rods on a 2.5L.  then it is a matter of getting a longer stroke 2.5L crankshaft.  i've been wanting to see if the 4.2L and 2.5L share similar patters (assuming that the 4.0 and 2.5 are the same with the exception of 2 more/less pistons, though i've read that they're not).  nonetheless, it would be great to simply machine a 4.2 crank to be a 2.5L pattern.  if possible, then it would be possible to stroke the 2.5L slightly.

i did some calculations and the displacement increase was small (maybe 2.7 or something), and you would still need a spacer between the head and the block.  then again, it would be cool to weld a machine a different stroke on the 2.5L crank and use shorter rods--4.2 or another?--and get more out of the engine.  on some mopar site, it says that the 2.5 is already stroked from the smaller 2.-something, and that stroking it would be impossible or very difficult.

[RNandKT]

Yeah wasn't thinking about shorter not longer con rods. But yeah that would be awsome. So do you think it would be possible to have a 2.5 crank custom machined to a longer stroke?

I don't know about the 2.5 and 4.0 rods being the same? But I do believe other than the length the 4.2's and the 4.0's are the same. So maybe it could be done. Who would you talk to about finding out?

Assuming all that could be done, do you think that as long as you didn't deck you block or head (at least very little) that you'd have enough clearance? It would probably push the commpresion up with out having to deck it anyway .. right?

[creepyjeepy]

right, i think that increasing the deck was to keep the compression right.  it's been a while since i tried computing the stuff out.  i contacted a machine shop and they wanted 2-grand to grind a crank with a longer stroke.  too much for me.

maybe getting shorter rods, a longer crank, and off-set pistons, you can stroke the 2.5L.

i'll look up my notes to see what scheme i was trying to create.  also, try this formula: piston size x piston size x crank stroke x .0031416 equals displacement in cc's.

so, 88mm pistons and 90 mm crank would be: 88x88x90x.0031416 or about 2040 cc's or a 2.0L engine.  

i started with this to figure how much more stroke and piston size would be required to get to a given displacement.  you can also apply factory specs to figure what is the least that can be modified to get the most increase.  

then, i got this formula to determine TDC for pistons (can't recall for sure right now), and using it i got the deck height increase needed to keep everything in line.

[Jeffy]

if the mopar crankshaft did increase displacement via a longer stroke, it would require shorter connecting rods.  

what about simply using the 3.0L engine and doing away with the 2.5L entirely?

i was looking at how some guy in canada put 4.2L parts into his 4.0L to stroke it.  someone correct me, but given that the connecting rods are shared between the 2.5 and 4.0--according to what i've found on the net--then it would be possible to use the shorter 4.2 connecting rods on a 2.5L.  then it is a matter of getting a longer stroke 2.5L crankshaft.  i've been wanting to see if the 4.2L and 2.5L share similar patters (assuming that the 4.0 and 2.5 are the same with the exception of 2 more/less pistons, though i've read that they're not).  nonetheless, it would be great to simply machine a 4.2 crank to be a 2.5L pattern.  if possible, then it would be possible to stroke the 2.5L slightly.

i did some calculations and the displacement increase was small (maybe 2.7 or something), and you would still need a spacer between the head and the block.  then again, it would be cool to weld a machine a different stroke on the 2.5L crank and use shorter rods--4.2 or another?--and get more out of the engine.  on some mopar site, it says that the 2.5 is already stroked from the smaller 2.-something, and that stroking it would be impossible or very difficult.

The guy's who are stroking their engines are using the 4.2L crank.  This engine is in the same family as the 4.0L and 2.5L.  This is wht Mopar was able to make an EFI kit for the 4.2L.

The problem with the 2.5L is that there are no other engine's that share the same profile.  If you bored the engine to .060" you'd get a 2.74L.  

Honestly, I don't think it's worth it to use the 3.0L unless you're going to use it stock.  I'm not sure if the 3.0L shares the same parts as the 2.5L either.  The more common 2.5L is a Pontiac engine and usually a bit different like the Buick's.

I think the 3.0L is a dead end.

[RNandKT]

Well thanks guys for all the info, I don't think spending 2000 to get like .2 more liters is worth it. I suppose if I want more displacement I will either have to just bore it, or go the old fasion way and swap in a bigger motor. If anyone does come up with a way to stroke it a little more affordably, I still love to hear about it. It would make a great compliment to the .060 bore.