Done some searching but I'm more confused now than when I started. I have a couple of questions. The 350 I just pulled from my car has always had some vibration at highway speeds. It's a 1 piece rms mated to a flywheel from an '84 305 (wouldn't that have been a 2 piece rms?). Was this a mis match?

Next,

 

Done some searching but I'm more confused now than when I started. I have a couple of questions. The 350 I just pulled from my car has always had some vibration at highway speeds. It's a 1 piece RMS mated to a flywheel from an '84 305 (wouldn't that have been a 2 piece RMS?). Wouldn't this amount to a mis-match?

Next, the replacement engine is a 383 from GMPP which is "externally balanced". I have a new 153 tooth flywheel that I originally purchased for the 1 piece RMS 350. I asked the place that I bought the flywheel from if it was still appropriate and they came back with "yes".

While the 350 used a neutral balanced damper the 400 crank in the 383 requires an externally balanced one. Would it not be logical that the flywheel would also need to be somehow different to balance at the rear?

I'm keeping my T5 bellhousing so I can't use a T56 flywheel.

Thanks,
Jon

JSD MOD 03/08/09

 

Are you sure that the flywheel you pulled was from an 84? The two piece and one piece don't have the same flywheel pattern.

The one piece seal cranks have a counterweight on the flywheel/flexplate. This is needed because the offset weight on the crank was removed when the swtich was made.

As for the 383 needing a differnt flywheel, you may want to check the GMPP website (Summit of Jegs might even have it). Some 383's use a 350 flywheel, others use a 400. This seems to be independant of the balancer used. If it was just a 400 crank turned down...then a 400 balancer/flywheel would be needed. But I doubt this is the case since you said it was one piece rear seal.

What is the part # for the crate motor?

 

I am pretty sure that it is impossible to interchange components for the 2 types

 

305 and 350s are balanced differently.
you need to put the right flywheel in the car .
the wrong one will either just cause a small vibration or it can tare your motor apart .
in time the wrong one will still hurt the motor even with just a small vibration so get it changed.

 

305/350 are not balanced differently the only difference is internal and external balance either of which could be done to either engine... it depends on how yours was balanced... the norm is internal which means you need a flywheel that is a neutral balance and 153 tooth for the T-5

 

The part number for the motor is 88962517 GMPP ZZ383. The new flywheel I have is a Hays 10-530 for externally balanced engines. I called Hays and they think that this should work. Certainly, it is for a 1 piece RMS SBC requiring external balance. The gentleman I spoke to was unsure as to wheather there might be a difference in balancing between the crank used in a 350 versus the 383.

Now, the booklet that came with the engine actually specifies a GM flywheel pn 14088650. When I look up Hays 10-530 on Jegs it offers... "Similar Items - You May Also Consider... GM #14088650". So Jegs, at least, thinks that these are interchangable. That leaves me reasonably comfortable in thinking that, in the GM crate motor scheme of things, 1 piece RMS SBC motors require the same flywheel.

One thing though, I honestly can't remember why I chose to go with the after market flywheel when the GM one is half the price. Does anyone think that the Hays one is worth the extra for a street only, roughly 390 HP car?

 

just seems odd that they would sell you a short/long block that would require you to completely disassemble it in order to get running properly... as the only way to use that externally balanced flywheel would be to have it balanced along with the rotating assy.