using chevy pistons in a 4.0 - JeepForum.com
 
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post #1 of 6 Old 04-17-2009, 07:48 PM Thread Starter
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using chevy pistons in a 4.0

i remember reading a while back about it being possible to use small block chevy pistons in a 4.0.

what kind of machine work in needed to make this happen

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post #2 of 6 Old 04-17-2009, 09:12 PM
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A guy did it to a four banger once. He had to bore it .120 over to run 4" chevy flat top pistons. I'm pretty sure the bore is the same fer the 2.5 and the 4.0 so it should work for your motor as well. His write up is on 4bangerjp.com .
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post #3 of 6 Old 04-17-2009, 09:33 PM
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242ci bore is 3.875" - you'll have to bore +.125" (to 4.000") to make the SBChevvy pistons work. I believe the compression height is also different - meaning changing rods, decking the block, or finding a top design that won't let you lose too much CR (I believe the SBC compression height is slightly lower than the 242ci.)

Possible? Yah - certainly! It will just take some planning, and a good block (RENIX and some of the 2001-2007 blocks will take a 4.000" bore - but you'll want to have the block ultrasonically checked to make sure you'll still have the .100" minimum wall thickness that is recommended.)

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post #4 of 6 Old 04-17-2009, 09:45 PM Thread Starter
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what about using the 4.2 crank?

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post #5 of 6 Old 04-17-2009, 10:01 PM
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Quote:
Originally Posted by SuperStreetJeep View Post
what about using the 4.2 crank?
I'd have to look the numbers up and run them. But, I think you'll still run into a small difficulty with the compression height - I just can't say for sure off the top of my head.

Recall that putting the 258ci crank into the 242ci block also involves replacing the 242ci connecting rods (6.125") with the 258ci rods (5.875" - 1/4" shorter.)

And, whatever the difference is, I'm fairly sure it's not a full quarter-inch. However, I've been wrong before...

Quench and compression can be tuned slightly by head gasket selection - but that's usually only worth +/-.015" from stock, without machine work.

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post #6 of 6 Old 04-17-2009, 10:16 PM Thread Starter
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Quote:
Originally Posted by 5-90 View Post
I'd have to look the numbers up and run them. But, I think you'll still run into a small difficulty with the compression height - I just can't say for sure off the top of my head.

Recall that putting the 258ci crank into the 242ci block also involves replacing the 242ci connecting rods (6.125") with the 258ci rods (5.875" - 1/4" shorter.)

And, whatever the difference is, I'm fairly sure it's not a full quarter-inch. However, I've been wrong before...

Quench and compression can be tuned slightly by head gasket selection - but that's usually only worth +/-.015" from stock, without machine work.
id be real interested to know if this combo would work...

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