need the correct flex plate for a 400 sbc for a 6 bolt converter on a 4l80e trans

Grumpy

The Grumpy Grease Monkey mechanical engineer.
Staff member
Hey everyone, I'm in the process of sticking a 4L80 in my Van...this has been in the works for almost 8 years now as I started the project in 2014, the same year I was getting married. Needless to say the swap never happened (but I did get married)
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I'm picking up where I left off though and one of the pieces of the puzzle I need is a flexplate for my 406sbc. I did technically buy one back in '14 that I thought would work with a dual pattern so it will only give me 3 bolts in the converter / leave three holes empty. I'm not sure if this is a great idea though so I'd like to see what other options I have with a 6 bolt pattern.
I've done a bit of digging and it sounds like some flexplates that came with TH400's are compatible, but I was wondering if in the last 7 years there is now more aftermarket support for swaps like this and maybe there's a part number just waiting for me
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. I (embarrassingly) can't remember if my motor is externally balanced or what tooth my current flexplate is, but I think it is typical 400sbc stuff (externally balanced??). I can and will confirm this but wanted to throw the question out there and see what comes up. all 400 sbc engines are externally balanced. and two piece rear seal engines
the one I purchased was a 168. but its dual bolt pattern and only three of the six bolt holes align correctly with the 4l80e converter mount bolt holes

Its this guy here:


SB Chevrolet 400 168 tooth external balance. 10-3/4" & 11-1/2" converter bolt pattern. SFI 29.1 approved.
FPW400-SFI-2.jpg

https://www.performance-world.com/SFI-Flexplate-p/...


Thanks and good to see so many familiar names still on here. Blast from the past!


summit suggest the SUM-101G SFI should work
https://www.summitracing.com/parts/sum-g101sfi

its obviously a dual bolt pattern, 168 tooth flex plate also
sum-g101sfi_xl.jpg

you'll need the correct ARP bolts
http://garage.grumpysperformance.com/index.php?thr...
remember to use ARP grade 8 bolts with loc-tite in the threads RED SUGGESTED 271
I talked with the tech guys at summit,
I don,t really trust them to much because I also asked for the part number for my gen 6 BBC one piece rear seal 454,
and the guy acted a bit confused when his computer said the same flexplate fits my one piece rear seal 454 BBC engine,

looking at the picture it looks like only three bolts line up,
so you would need to have a machine shop drill three to match
this is hardly a new or unique issue, most universal parts are not ideal,
but many can be TWEAKED to fit and function correctly, for that mater, your existing flexplate might be used if re-drilled,
most experienced machine shops will have done similar mods dozens of times,
and if you explain in detail what you need they should do the mod at a reasonable price
personally ID tig weld a small grade 8 washers on the three new bolt holes to re-enforce the location,
as the new holes may partly be compromised being next too the old holes
I doubt the balance would be effected, as the difference in weight is evenly spread and minimal
 
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