Is this a correct '63 300HP Harmonic balancer?

[Paul B.]

Hi,
Is this the correct balancer for a 300HP manual '63, the OD is about 6 1/8" ?
The manual says that there should be a "step" on the balancer, but there is no picture to confirm exactly what the balancer looks like.

Many thanks,
Paul


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[Timothy B.]

Re: Is this a correct '63 300HP Harmonic balancer?

Paul; I have a early 63 engine with 300hp and my damper looks like your picture except does not have the small holes around the outer ring. I believe these were added maybe in late 63, I always thought they were used for some sort of balance.

[Paul B.]

Re: Is this a correct '63 300HP Harmonic balancer?

Thanks Timothy, my car is a late January build, I wonder when they began with the holes?
Paul

[Timothy B.]

Re: Is this a correct '63 300HP Harmonic balancer?

Paul,

I'm sure someone can give you a more accurate answer, check the archives because I think this was discussed years ago. I have noticed even the flywheels for (I think) 64-up engines have a ring of holes similar to what your picture shows.

If it's in nice shape I would put it on and use it.

[Harry S.]

Re: Is this a correct '63 300HP Harmonic balancer?

1963 Harmonic balancer (ncrs.org) Some additional details.

When I redid my April 63. 250hp engine, but the balancer should be the same.

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[Duke W.]

Re: Is this a correct '63 300HP Harmonic balancer?

The equal spaced drilled holes around the circumference must have been to "retune" the balancer. There is a "dimple" at the 5:30 clock position, and this is for balancing.

The responsible engineer must have decided to "retune" what is more correctly called a torsional damper, probably based on testing in a dyno test cell.

I was also thinking that since the 30 pound OE flywheel is heavier that the flexplate and converter housing maybe a different damper was required with Powerglide, but the P and A catalogs make no such distinction. The converter itself likely provides some torsional damping.

Torsional vibration can range from annoying vibration to crankshaft failure. I recall reading that the early 240Z engines suffered crankshaft failures due to under damped torsional vibration issues. The longer the crankshaft the more critical torsional vibration can be, so inline sixes and V-12s usuallly need more damping than flat sixes, inline fours, and V-8s.

Typical dual-mass dampers like what was installed on early 327s are "tuned" to one fairly narrow RPM range where peak torsional vibration occurs and this speed is usually determined by testing on an instrumented engine on a lab dyno.

The forged pistons on SHP/FI engines are heavier than the cast pistons on lower performance engines so the crankshafts are heavier because it takes more balance mass to balance he reciprocating mass and the first order rocking couple caused by the reciprocating mass. This is why SHF/FI cranks have a different forging number than the 250/300 HP crankshafts. They are somewhat heavier than 250/300 HP cranks. They could have used the SHP/FI for the lower performance engines, but that would have required more machining time of the hardened steel for a much higher volume part, so it was cheaper in the long run to make difference forging dies for the SHP/FI cranks.

Due to the heavier SHP/FI reciprocating mass and higher rev range a more robust torsional damper was required.

Duke

[Paul B.]

Re: Is this a correct '63 300HP Harmonic balancer?

The forged pistons on SHP/FI engines are heavier than the cast pistons on lower performance engines so the crankshafts are heavier because it takes more balance mass to balance he reciprocating mass and the first order rocking couple caused by the reciprocating mass. This is why SHF/FI cranks have a different forging number than the 250/300 HP crankshafts. They are somewhat heavier than 250/300 HP cranks. They could have used the SHP/FI for the lower performance engines, but that would have required more machining time of the hardened steel for a much higher volume part, so it was cheaper in the long run to make difference forging dies for the SHP/FI cranks.

Due to the heavier SHP/FI reciprocating mass and higher rev range a more robust torsional damper was required.

Duke

Thanks Duke, but now I think I may have opened a new can of worms... The engine is the original to the car, I will be having a refresh/rebuild done, so I purchased a set of forged Sealed Power flat tops (with reliefs), I was just going to have the assembly balanced, but are you saying that my 300HP crank will have to be changed? The balancer now on the car is the one below, about 6 1/2", should I also go to a larger balancer?

Paul

[Duke W.]

Re: Is this a correct '63 300HP Harmonic balancer?

Forged pistons are overkill for a medium performance engines that will probably not be driven very aggressively.

For 300 HP rebuilds I recommend the KB 156 hypereutectic pistons with a measured CR of no more than 10.1:1 if you have 93 PON fuel available and reduce 0.1 for every one point PON reduction, so 9.7:1 for CA 91 PON premium.

One thing you can do is get the piston mass for the pistons you mentioned and the KB pistons from their Web sites.

I advise you to call me on the phone so we can have an interactive discussion about the involved issues and what path you should take. It's not rocket science complicated (but be prepared to take notes), but you need to understand the underlying issues before you commit and few "engine builders" have good advice.

Duke
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[Paul B.]

Re: Is this a correct '63 300HP Harmonic balancer?

Hi Duke, thank you for the detailed reply, my apologies for the delay in responding, I've been traveling.
I will call for sure this week.

Many thanks,
Paul