Engine balance on a Series 3 top swap (Page 1/2)
olejoedad FEB 17, 08:34 AM
As the title highlights.

Series 3 3800 NA shortblock
Gen 5 supercharger top swap

Getrag trans

Any insight on balancing this configuration?
pmbrunelle FEB 17, 11:48 AM
In my understanding, engine balance is related to the flywheel, crankshaft, connecting rods, pistons, harmonic balancer, and balance shaft.

How are the heads or supercharger related to this?
olejoedad FEB 18, 08:15 AM
Your understanding of engine balance is correct.

The heads have nothing to do with balance, however the S/C and N/A heads are different, as the N/A heads do not have provisions for the injectors and the S/C heads do.

The 3800 S/C and 3800 N/A engines use different rotating assemblies and are balanced differently.
The S/C is externally balanced and the N/A is internally balanced.
With that said, there are still balance weights on the N/A flex plate and the harmonic balancer also has balance weights. The counter weighting is different between the two engines, and is different between the Series 2 and Series 3 variants.

I'm looking for info from people that have done a Series 3 3800 N/A top swap and have successfully balanced the engine, using a flywheel for the Getrag transmission.
cam-a-lot FEB 18, 08:24 AM
Not sure if this helps. The previous owner of my car did the swap, and it is a Series III N/A with top swap Gen III blower and Getrag 282 5 speed. I think he describes the balancing process somewhere in the thread

https://www.fiero.nl/forum/...160323-1-079530.html

He has been out of Fieros for many years and is not around to answer questions, but hopefully there is some useful info here for you

[This message has been edited by cam-a-lot (edited 02-18-2024).]

pmbrunelle FEB 18, 12:36 PM

quote
Originally posted by olejoedad:
I'm looking for info from people that have done a Series 3 3800 N/A top swap and have successfully balanced the engine, using a flywheel for the Getrag transmission.



So, you want to know how to balance a Series 3 3800 N/A with a flywheel?

Top swap has nothing to do with this topic, correct?
olejoedad FEB 18, 01:35 PM

quote
Originally posted by pmbrunelle:


So, you want to know how to balance a Series 3 3800 N/A with a flywheel?

Top swap has nothing to do with this topic, correct?



The top swap (heads, LIM. supercharger) requires the use of the supercharged balancer.

So yes, the top swap has everything to do with balancing, as the S/C balancer is balanced differently than the N/A balancer.
pmbrunelle FEB 18, 03:16 PM

quote
Originally posted by olejoedad:
The top swap (heads, LIM. supercharger) requires the use of the supercharged balancer.

So yes, the top swap has everything to do with balancing, as the S/C balancer is balanced differently than the N/A balancer.



Now I understand.

Well then, it seems like duplicating the balance of the NA balancer in the SC balancer is a way to do it.

You could make a shaft with two keyways 180° apart, and then install both the SC and NA balancers on the common shaft (180° apart).

Then, send the shaft+balancers assembly to a crankshaft balancing shop, and have them bring the assembly to zero static imbalance by adding/removing material to the SC balancer. When the assembly has zero static imbalance, that means the SC balancer has become equivalent to the NA balancer.

You could use a similar approach for the flywheel / flexplate.

[This message has been edited by pmbrunelle (edited 02-18-2024).]

pmbrunelle FEB 18, 03:27 PM
Other idea, perhaps slightly more invasive (not sure if the project in question involves complete engine disassembly):

Assemble crankshaft + balancer + flywheel + bobweights together, and then get assembly dynamically balanced to zero.
olejoedad FEB 18, 03:47 PM
Thanks for the input.

S/C balancer have already been balanced to Series 3 N/A spec.

Spec aluminum flywheel for Series 2 S/C has a removable weight, but engine still exhibits imbalance in either flywheel configuration.

Looks like I need to dig up a Series 3 N/A flex plate to match balance to the Spec flywheel.
olejoedad FEB 18, 03:48 PM
Has anyone else dealt with this problem and found an off the shelf solution?