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Discussion Starter #1
What flex plate have you guys used to go from the 8.1 to the th400 converter. Or is it so dang obvious I don't see it?
 

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Vertical Limits
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Post pics of your build:flipoff2: if not, email them to me, I wanna see the progress. I'll then post them up.
as far as the flexplate thing, I don't know. I'm using the allison attached to the one sitting in my shop:flipoff2:
 

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does the 8.1 have the same as the LQ4 6.0?
ill i had to do is egg out the holes on the flex plate, and bolt it up :D



i went thru a ton of bullshit from
A) you need a converter built for it
B) you need a flexplate built for it
C) you need a spacer and it will bolt right up
D) you need nothing, it will bolt right up
E) wont work :rolleyes:


heres the EASIEST thing to do:


measure the distance from the mounting surface of the bellhousing to the mounting pads on the converter.
measure the distance from the mounting surface of the block to the pads on the flexplate.
remove the flexplate, and sit it on the snout of the converter, see that is is supported w/ no slop.
align the holes, or make new ones.
bolt it up :D

hope that helps, cause thats the only way i was gonna get it figgured out :)
 

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Vertical Limits
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he did a 5.3 in his last rig. the guy that helped him build it was the one that turned me onto gen III's 3 years ago. He has been through the small block stuff. knowing that he knows that it leads me to believe that the big block is different. pure speculation right now, though.
 

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Discussion Starter #5
8.1

Hey Kelly, I will email you some pics tomorrow I'm getting ready to hit the sack. Just wired it. Fuel lines, o2s, Radiator hoses, and a flexplate is all that is needed!:D
 

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Not any help....but wow after tonight I hate that motor. I spent 4 hours dropping a 8.1/TH400/203/205 into a 72 Blazer and its still not fitting correctly. You have to build the vehicle around that damn monster......if I not mistaken the flex plate and converter looked stock.
 

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I got a 8.1 out of a 06 silverado, and the flex plate it came with bolted right up to the torque convertor that came in my art carr trans... Th400. 4 bolts and done. Dont know what else to tell you.
 

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4 bolts? 4? you sure?

my t400 was 3 bolts if im not mistaken.
That might depend on the TC itself more than anything. Many flex plates have the 3 and 4 hole TC pattern in them already. Seems like most TH350 TC's are 3 bolt and most TH400 TC's are 4 bolt. There really isn't anything stopping someone from building a TH400 TC with 3 bolts.
 

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Discussion Starter #14
flex plate

Thanks for the replies guys, but still out of luck. My flex plate has a bolt pattern for the allison converter. I already have a built th400 and converter waiting to go in. My converter has the 3 bolt pattern, and yes my rig was built around the motor and axles.
 

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so go see if a LQ4 6.0 liter flexplate will go on your engine. if thats the case, it will work as i said
I'm swapping an 8.1 into my CJ. It will be mated to a SM465 so I can't help much with the auto swap. But I do know that my '88 TBI350 flywheel bolts right up to the 8.1L. That tells me you could run an old school 350 flexplate with an 8.1L. It's an internally balanced motor and the crank has the same bolt pattern as the 350.

I doubt the LQ4 flexplate will work (different crank offset I think).

Edit - Removed the bit about a 454 flexplate working. The 454 is externally balanced but the 8.1L is internally balanced so the 454 flexplate won't work. A 350 flexplate will though.
 

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I'm swapping an 8.1 into my CJ. It will be mated to a SM465 so I can't help much with the auto swap. But I do know that my '88 TBI350 flywheel bolts right up to the 8.1L. That tells me you could run an old school 350 or 454 flexplate up to the 8.1L. It's an internally balanced motor and the crank has the same bolt pattern as the 350.

I doubt the LQ4 flexplate will work (different crank offset I think).
I thought that was not true. I coulda sworn they are externally balanced. They require a $$ flywheel?
 

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Discussion Starter #19
flex plate

Thanks guys again I'll try what J Bruce said. Just going off what the gm parts guy said the flex plates for the 8.1-allison and 8.1-4L80 were the same. He also said the offset on the 6.0 flex plate isn't the same? I'll let you know what I end up doing:D
 
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