2.8 versus 3.8 L36 imbalance

[cpom]

Are the pre-1988 2.8 rotating assemblies built with the same weight of imbalance as the 2002 3800 L36?

Meaning, if I were to mount a pre-88 2.8 flywheel on a 2002 L36 3.8, would the weights balance out? This is all assuming I redrill the flywheel and orient it in the same way as the 3.8 flywheel. Ignore transmission issues since this is for a motor swap application.

Reason I need this info is that in my application I need a .5" thicker flywheel and I heard the pre-88 2.8 flywheel was 1.5" thick (same thickness as the 3.4 flywheel) and also externally balanced.

Any help on this one?

[Nikos95]

Erm I don't know if I would even try to re-drill the flywheel, you will weaken it by doing so. I haven't ever done it nor do I know anyone who has, so I can't say for sure the outcome. But a replacement light aftermarket flywheel shouldn't cost too much anyways round what $100 or so if you don't go nuts on it.

[cpom]

People fill-weld and redrill flywheels. The center hole is teh same 32mm which is what is locating the flywheel, the bolts don't have to be 100.00000% accurate since they are just applying a clamping force.

Do you know where I could get a 3800 flywheel that is .5" thicker? If I could and it was under $200 that would solve all my problems. I have two other ideas if the 2.8 flywheel doesn't work...

[3.4 slow to go]

check http://www.l67swap.com/ I know there is someone swapping in an l67 in an Amigo, but I think he's reusing the cars tranny. It could help

[cpom]

Thanks, but he went with an AW4 auto trans so he didn't run into the issues that I have with the R150F.

[3.4 slow to go]

can you get an spacer made?

edit: late & it'd tired. try going to parts store & have them pull both & compare/measure. It shouldn't be any trouble for them to do so.

[ March 14, 2006, 09:09 PM: Message edited by: 3.4 slow to go ]

[AZ3.8Camaro]

The 2.8 is a 60 degree v6 right?
If so, the flywheel difference will be extreme as far as balancing.
But on the 3.8, the balance shaft does the work, so you would be ok running whatever you want as a flywheel.

[CDNFB]

The vast majority of balancing is not accomplished by the flywheel. It is accomplished by the counterweights of the crankshaft. And destructive harmonic frequencies are dampened by the harmonic balancer. If the flywheel was the primary means of balance it would have to be indexed to the crank flange and it is not.

The primary function of the flywheel is to lend mass to the recipricating group, storing rotational energy from the previous power stroke and providing energy for the next compression stroke. The heaver the flywheel the smoother the engine runs because there is more stored energy to aid the next compression stroke, but the cost to that is a slow accerlerating engine. To achive a quicker reving engine, go to to a lighter flywheel. Your engine will also vibrate more. Remember, this vibration is not a rotational inbalance, but the inability of a light flywheel to absorb and transmit the power pulses efficiently.

The major issue facing you is the attaching bolt holes. Weld them up, pick up your new holes, bolt it in place. Hopefully the diameter of the flywheel will be such that all you have to do is some shimming to install your starter. (I would also check the pitch of the ring gear to make sure they match the starter gear).

DZ

[AZ3.8Camaro]

Originally posted by CDNFB:
The vast majority of balancing is not accomplished by the flywheel. It is accomplished by the counterweights of the crankshaft. And destructive harmonic frequencies are dampened by the harmonic balancer. If the flywheel was the primary means of balance it would have to be indexed to the crank flange and it is not.

The primary function of the flywheel is to lend mass to the recipricating group, storing rotational energy from the previous power stroke and providing energy for the next compression stroke. The heaver the flywheel the smoother the engine runs because there is more stored energy to aid the next compression stroke, but the cost to that is a slow accerlerating engine. To achive a quicker reving engine, go to to a lighter flywheel. Your engine will also vibrate more. Remember, this vibration is not a rotational inbalance, but the inability of a light flywheel to absorb and transmit the power pulses efficiently.

The major issue facing you is the attaching bolt holes. Weld them up, pick up your new holes, bolt it in place. Hopefully the diameter of the flywheel will be such that all you have to do is some shimming to install your starter. (I would also check the pitch of the ring gear to make sure they match the starter gear).

DZ

He is exactly right. Don't forget the fact that the 90* V6 CANNOT be balanced out by the crankshaft alone, and so it needs the balancer shaft to elimanate shake. Some flywheels are indexed to the crank. Ours is not (I forgot) so it is not an issue.

[cpom]

My 02 camaro L36 is externally balanced with the flywheel and does not have a harmonic balancer. The flywheel is indexed.

Either way, the main point I learned here is that the odds of the 2.8 and 3.8 flywheels having the same weight of imbalance is next to impossible.

I had my friend turn a "shouldered" spacer out of 6061 Aluminum 3" round stock on a lathe. I am going to make the starter engage via welding another ring gear behind the original.

[AZ3.8Camaro]

It should have both a harmonic balancer (crank pulley) and the internal balancer (above the lifter galley.)

[cpom]

I thought for a pulley to be a harmonic balancer it needed some absorbing rubber material injected near the weights or something similiar. This crank pulley is definetly weigthed as it is drilled out so I assume we are on the same page just calling it different things.

[3.4 slow to go]

Originally posted by cpom:
This crank pulley is definetly weigthed as it is drilled out so I assume we are on the same page just calling it different things.

sounds the same, as the 3800 pulley/dampner is different than all the other dampner's I've seen. It's more like an integrated unit.

[AZ3.8Camaro]

Mine has rubber in it..

[black34v6]

Re: 2.8 versus 3.8 L36 imbalance

all 60* v6's are internally balanced and as a result use neturally balanced flywheels / harmonic dampers.