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What is the max safe overbore on a 3.8?

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jjvites

Member
Joined
Jan 25, 2004
Messages
164
Was wodering what is commonly the largest overbore on a 3.8 motor. What are common size pistons that are available? I have a spare block I picked up but it's at .030 now.What is the safe overbore size for 3.8?
 
every block is different .. theres probly plenty that would take .100 over

but without sonic testing .030 to .040 is plenty safe :cool:
 
I'm at 40 over but due to leaking fuel, I have not yet had a chance to run the motor yet - I do not believe there will be any trouble
 
Wall thickness ... how much

If sonic tested what can one expect to see on a production3.8 block for wall thickness. Anyone know what it is for stage 2?
 
I ran one at .040 over. It ran many low 10's without any problems. A stock rod broke and killed that block. I remember an artical in a GS Extra that said they havn't seen a 109 block that wouldn't except a .040 overbore. But if it is for a race motor I would have it sonic checked.
 
Phil,
Thanks, just wondering when sonic testing what is good wall thickness on these motors. Need a reference point.

Thanks,
Marty
 
I found the GS X-TRA that had the article (Sept-Oct 2003). The recommended wall thickness is .250" on a major thrust side and .150" on the minor thrust side. Also in a seperate article " Mid To Low 11-Sec. T-R Buildup" they say " All the 231's that we've sonic checked have been able to take a .040" overbore."
With all that said, I'll throw this in, on my last motor I had 2 cylinders crack and it was bored .020" over. Good luck!!!
 

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aftermarket blocks are only .250. I had a stage1 sonic checked and most thrusts were .170-.190. Between the cylinders is were things got tight .077,.090,.120. Production blocks including stage1's were mass machined were stage2's were done by buickmotortsports. 3/16 is a good number for stage2 blocks,doubtfull to find a stocker that thick.
 
chevyII said:
aftermarket blocks are only .250. I had a stage1 sonic checked and most thrusts were .170-.190. Between the cylinders is were things got tight .077,.090,.120. Production blocks including stage1's were mass machined were stage2's were done by buickmotortsports. 3/16 is a good number for stage2 blocks,doubtfull to find a stocker that thick.

Thanks, good reference point.
 
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