72_nova

iTrader: (1)

my 99 LS1 is going in my nova, I bought the crank spacer and it fits right up, but the Flex plate does not. the bolt holes don't line up on the flexplate to the spacer/crank. I ordered a stock replacement for a 99 TA A4 flex plate. went back to my parts guy and he says the part number of the plate I have is what is supposed to go on my engine but they don't match up. is there something I'm missing here?

speedtigger

iTrader: (16)

Which transmission are you using? What type and brand of spacer are you using?

72_nova

iTrader: (1)

I have a TH400 transmission. and I bought the spacer directly from GMpartsdirect.com. the spacer lines up perfectly with the crank holes the flex plate is the problem.

speedtigger

iTrader: (16)

There are two style flexplates. One style is an offset design for the 4l60e transmissions. The other style is the flat flexplate for 4l80e transmissions.

When using a TH400, you need to use the flat, 4l80e flexplate. These flat flexplates come with the appropriate spacer from GM. The whole set up is about $60 new.

72_nova

iTrader: (1)

do you have a P/N? or an application that I can use to come up with a P/N?

speedtigger

iTrader: (16)

GM part # 12621399 Flywheel & spacer assy (used to adapt LSX motors to old school automatic transmission)

This information was taken from my swap parts list. You can see everything I have used for my swap at:
https://ls1tech.com/forums/14092457-post4.html

Two extra bits of information. You will still likely have to slot the torque converter bolt holes about 1/8th of an inch. And, if you are going to be making big horsepower and drag racing, you would be better off running an SFI approved racing flexplate from a company like Hughes. Hughes makes an SFI flexplate and adapter for LS motors using older transmissions. Theirs is considerably more expensive, but I don't remember how much.