SEADave HalfDork
4/23/17 8:22 a.m.

I'm trying to put an LT1 (93-97) style T56 behind a cheap SBC. Looking into it and to use a pre-86 block with the stock set-up requires a ~$450 special flywheel. 

So I have a line on a newer crate motor with a one piece RMS.  This should allow the use of a standard $80 LT1 flywheel.

My only hang up is that from what I can tell the crate motor is external balance, which I think means balanced by the flexplate - is that right?  Because if so, then maybe my plan to just bolt on a flywheel and go isn't so great.  In any case I'm trying to avoid having to have the engine rebalanced or trying to find someone to match-balance the flywheel to the flexplate. 

Am I even understanding this right?   Can someone clue me in on how this whole external balance thing works?

patgizz UltimaDork
4/23/17 9:04 a.m.

It's exactly how it sounds. Internal balancing takes the whole rotating assembly and adds weight or removes weight(drilling crank throws, adding weights to them, moving things around, take a little material off here or there). external balancing uses the damper and flywheel to balance the internals.

Your lt1 flywheel should work on the 1pc 350 engine.

GTXVette HalfDork
4/23/17 9:45 a.m.

400's or 383's if you will are External Balance ALL Sbc Smaller Or that don't use a 400 crank are Internal balance. One piece RMS flywheel or Flexplate is different from two piece RMS and up front on the 400 is also Different. and for more fun the earlier two piece RMS engines Have the Harmonic Balancer in three diff. design's as to where the Timing mark is located so don't lose track of what you have if several engines are apart of different year model.

Connecting rods for all sbc engines except 400's are 5.7" long, 400 use a 5.5 inch long rod.

pre 67 sb have a smaller Diameter crank throw than Post 67 the best Factory rods pre 67 Have a Green dot painted on, the post 67 is a pink dot and also an x molded into post 67 rods is a good rod.

SEADave HalfDork
4/23/17 12:09 p.m.

Thanks guys. So I can just bolt on the flywheel in place of the flexplate and go? Or am I needing to find someone that can match the balance?

I'm looking at a low miles version of this: 350 HO; it's a 350 but the specs say it is externally balanced.

BrokenYugo MegaDork
4/23/17 1:33 p.m.

From what I'm reading it seems the one piece rear main cranks are all slightly external balance on the flywheel/flexplate end only to make up for the loss of the funky flange on the 2 piece cranks. It looks like the LT1 uses the same crank as a one piece 350, so the flywheels should interchange without upsetting balance.

Streetwiseguy UltimaDork
4/23/17 3:10 p.m.

I'm a bit confused why a flywheel for a traditional SBC is expensive. Is it a weird stepped design, or what?

81cpcamaro Dork
4/23/17 4:09 p.m.

To Streetwiseguy, the LT1 used a special clutch/flywheel setup with the T56. That flywheel fits the 86-later one-piece rear main seal engines. So if you have an older SBC with 2-piece rear main seal, you are stuck buying the special flywheel. Sucks that it is cheaper to buy a later engine than the special flywheel.

9/9/18 9:03 p.m.

Hey everyone had a question I’ve been looking for a flywheel for my sbc  with a 1 piece RMS to bolt up with a T56 from a LT1. I got this Chevy 350 from blueprint and it says this for the balance kinda confusing “Internal Front/ External Rear” I got a MCL 460260 flywheel with a stock clutch for a T56 # is SUM-700830 and they don’t fit. Called summit and they told me it has to fit . I’ve also tried flipping the clutch the other way but the hole in the middle of the flywheel it too small which prevents the clutch to sit right

Matt New Reader
9/9/18 9:17 p.m.

I got a GMPP SP350 5.7l crate motor and bolted a T56 to it. It’s external balance and I have no idea why they did that - until this motor showed up at my door I’ve only ever seen external counterweights on 400 sbc...My flywheel has a counterweight in it. Flywheel came from GM,  Everything else came from a 95 LT1 camaro donor car...

APEowner Dork
9/9/18 10:55 p.m.

Your best bet is to call blueprint and ask them what you should use for a flywheel.

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