Carbureted LSX forum - Stock flexplate or SFI

Im building a 500 hp 6.0 and was wondering what flexplate to use ( stock or SFI rated). I will be running a th350 in a pro street pickup. Also will I need a crank spacer for the torque converter.

I went with the TCI.

will I need a crank spacer for the torque converter.

depends which year crank you have.
99-2000 6.0 LQ4 cranks have .400" longer flange which does NOT need the spacer. all other LS need the spacer if using an older SBC/BBC trans

I would go sfi if you are breaking 700 fwhp.

http://sdparts.com/details/tci-automotive/tci399753

Think this is the one I ordered....I was told it had eveything needed and was dual pattern for newer and old school transmissions ?

I'm a stick shift guy, so I got a thicker flywheel , and a pilot bearing that goes into the outer register of the crank to deal with the difference in crank length on my '07 crank.(.400" shorter than old sbc/bbc, relative to belhousing flange on block)

But with an Auto I beleive you need to put a crank spacer between the crank flange and the flexplate. If you dont the converter will not engage the pump completely. front pump damage is the result.
I think the starter will still work properly with the flex plate spaced away from it, maybe someone who has connected an auto trans to a 2001 and newer engine/crank can chime in.
Barrett

SFI all day long. For the $ difference and peace of mind alone. Have you ever seen the damage of a flexplate letting loose and shoothing thru a floor pan.... not pretty.

I'm a stick shift guy, so I got a thicker flywheel , and a pilot bearing that goes into the outer register of the crank to deal with the difference in crank length on my '07 crank.(.400" shorter than old sbc/bbc, relative to belhousing flange on block)

But with an Auto I beleive you need to put a crank spacer between the crank flange and the flexplate. If you dont the converter will not engage the pump completely. front pump damage is the result.
I think the starter will still work properly with the flex plate spaced away from it, maybe someone who has connected an auto trans to a 2001 and newer engine/crank can chime in.
Barrett

That is what i have been wondering. I have the spacer and will be using it on my swap to my 1994 4L60E. I was curious how the starter would be effected.

The spacer, when needed for TH350/400 specific converters, goes on the converter side of the flexplate, not between the crank flange and flexplate. That is why the starter ring position is unchanged with the addition of the spacer. In this case, the spacer is used to move the crank pilot closer to the back of the converter to meet up with the shorter "snout" on TH350/400 to SB/BBC converters.

The factory vehicles (4L80E combo's I think) that had the same type of spacer between crank flange and flexplate had flat flexplates instead of slightly bell-shaped ones like 4L60E (and other) combo's had. So the spacer put the starter ring of the flat flex plate where it would have been on a bell-shaped flexplate without a spacer behind it.

So bottom line........if you have a bell-shaped flex plate from a 4L60E combo, you'd run the spacer on the outside (converter side) of the flexplate). I THINK you can also run a flat 4L80E flexplate with the spacer behind it and achieve the same results with a TH350/400 but I've never tried it. OR.....if you need a new converter anyway, have one built with the LS-specific snout on the back of it and use no spacers with a regular bell-shaped flexplate. For what it's worth.....the popular SFI plates are of the bell-shaped variety. The last scenario is what my combo is (TCI flexplate and LS specific TH400 converter from PTC).

Thanks for clearing that up

Thanks for clearing that up

No problem. Always lots of confusion surrounding this issue. It took me actually having a variety of the different parts in my hands during my build to finally wrap my head around it all.

Thanks to all for the info.

I just spaced the flex ages out if I needed to make them mate between the flex plate and converter. Never worried about the snout side of things.

Im using the hughes hp4004x. IIRC it retails for around 145 dollars. Im running the spacer between the flexplate and transmission. I.E. Crank, flexplate, spacer. That way it properly spaces the dished hughes flexplate and supports the snout of the converter. Eric L

yep....thats the one I got....

Part Number: 399753
Brand: TCI Automotive
The new TCI LS1 Flexplate is made from billet steel plate and is
SFI 29.1 approved. The Lightweight design provides quick engine
response. Dual bolt patterns allow for stock LS1 and small GM bolt
pattern torque converters.

Fits ’98 and newer F-bodies with LS1 engine as well as ’99 and
newer GM trucks with 4.8L, 5.3L and 6.0L LS based engines

Includes Mounting hardware

The spacer, when needed for TH350/400 specific converters, goes on the converter side of the flexplate, not between the crank flange and flexplate. That is why the starter ring position is unchanged with the addition of the spacer. In this case, the spacer is used to move the crank pilot closer to the back of the converter to meet up with the shorter "snout" on TH350/400 to SB/BBC converters.

The factory vehicles (4L80E combo's I think) that had the same type of spacer between crank flange and flexplate had flat flexplates instead of slightly bell-shaped ones like 4L60E (and other) combo's had. So the spacer put the starter ring of the flat flex plate where it would have been on a bell-shaped flexplate without a spacer behind it.

So bottom line........if you have a bell-shaped flex plate from a 4L60E combo, you'd run the spacer on the outside (converter side) of the flexplate). I THINK you can also run a flat 4L80E flexplate with the spacer behind it and achieve the same results with a TH350/400 but I've never tried it. OR.....if you need a new converter anyway, have one built with the LS-specific snout on the back of it and use no spacers with a regular bell-shaped flexplate. For what it's worth.....the popular SFI plates are of the bell-shaped variety. The last scenario is what my combo is (TCI flexplate and LS specific TH400 converter from PTC).

I agree 100%. I tried it both ways on my truck. Ran with the flat plate for about 2 years, then this year switched to a bell-shaped one with spacer on the converter side. No problems yet.

I have a question. Why is it everyone is running the TCI flexplate for $250, when Hughes makes one for about $150? Am I missing something. They are both SFI approved. The hughes part number is HP4004x. It is a dished one that you use with a spacer. Eric L

I have the stock truck flex plate on my car. It was about $50 brand new with the proper spacer and bolts included. My 3700 lbs runs mid to low 11s with no problems so far.

If I were going much faster than I am now, I would opt for the SFI.

I have a question. Why is it everyone is running the TCI flexplate for $250, when Hughes makes one for about $150? Am I missing something. They are both SFI approved. The hughes part number is HP4004x. It is a dished one that you use with a spacer. Eric L

I bought my TCI used for $125.....otherwise I would have considered the Hughes piece.

Wasn't offered and I didn't look well enough :( damnit

http://static.summitracing.com/global/images/prod/large/tci-399753_w.jpg

Now after looking..... I like the TCI better anyway.

http://www.jegs.com/images/photos/500/512/512-HP4004X_3.jpg