SBC balancer question

[Guest zfan]

This may sound stupid but here it goes anyway.

My 350 chevy 8" balancer crapped out and my friend offered to sell me his new GM hp 6 1/2"

balancer for a good price.

 

Can I use the smaller balancer? What difference is there? I really do not know the difference other than a smaller mass.

 

thanks Mike

[DavyZ]

It should work The only issues are if your engine uses a 400 crank, which uses a specially weighted balancer.

 

Davy

[Guest Anonymous]

dont forget about the timing marks on the balancer. you will need a new timing tab for the 6 1/2

[Guest Anonymous]

Mike usually the 8 inch damper/balancer is for externally balanced engines like a 400 ci SBC and a lot of external balanced stroker 383s. The smaller damper is usually for internally balanced motors (350). If your engine is externally balanced you should stay with an external damper/balancer unles this smaller balancer/damper is a special one (very spendy$$) to externally aid in balancing an engine.

[Mike C]

All early truck 350's got the narrower 8" balancer. Usually these were 4 bolt main engines as well. The high-perf large journal motors (302, LT-1 350, L-82 350) also got the large balancer, but it is slightly wider. There are different balancers/timing tabs depending on a 49 state or California motor (this depends on year as well). Just double check the timing mark is same spot on new balancer as old one and buy a timing tab for the smaller balancer. I thik all 8" balancers had the bolted on tab, but some of the smaller ones had welded tabs.

[Guest zfan]

Thanks Guys!

 

Mike

[RPMS]

So what's the difference between balancers for the same application? Given the ones that work with an internally balanced crankshaft, why would someone prefer an 8" balancer over a 7 1/4" or a 6" one? Do the larger ones work better in a given application?

[Guest Anonymous]

Space consideration ..ie the JTR conversion requires 7.25" or smaller harmonic balancer to clear the steering rack...aftermarket balacers for external balanced engines as the technology expanded can be purchased in smaller diameters than 8 inch.My internal balanced 73 SBC 350 has a 6 3/4 " OEM balancer. 383 stroker cranks can now be purchased as internal balanced models where you can use the 350 parts such as the 5.7 rods,harmonic balancer and flywheel and/or flex plate. In addition to the internal balanced stroker cast crank ($200.00, you only buy the special stroker pistons ($130.00) and a balance plate ($20.00) Cheap stroker afrer it is all balanced and clearanced but keep the RPM to a 5000 minimum

[DavyZ]

Interesting to note, David Vizard claims that the tests he has done confirm that a bigger balancer makes for a faster car in the quarter mile, although I don't think he explained why. One would think that a smaller balancer makes for a lighter rotating mass and that would be better... My theory is that the crank is producing so many harmonic vibrations at the high rpm levels that a bigger balancer helps absorb them better, thus allowing the engine to spin more freely giving either higher rpms and/or more horsepower from less friction.

 

What I just said may NOT be true, but I like thinking about this stuff

 

Anyone that really knows what & why, please clue me in.

 

Davy

[Guest Anonymous]

Davey , I will go with your explaination for big is better!1

[Mike C]

Originally the balancers were designed to be most effective damping within a certain frequency. This usually was dictated by operating range rpm and crankshaft stroke. Max longevity and minimum perceived vibrations were GMs reasoning. Packaging was usually a non-issue, but when I put the Herb Adams front sway bar on my Camaro I had to put 1/4" spacers between the mounts and subframe to clear the 8" Hiperf balancer. It was fine with the stock 11/16 sway bar, however.