mongoose87

I am doing an upgrade to my 1972 L48 which will use vortec heads and new hydraulic roller cam. From what i read, the needed harmonic damper size pertains to the desired RPM range, compression, and crank material used. I am using the same stock bottom end with cast crank. I know the L82 engines use forged crank and 8 inch damper, but not sure if the reason for the increased damper size was because the crank was forged or if the engine was designed for higher rpm.
The cam I am installing is intended for low end torque, so I don't think high rpm use should really be a factor for my application
.
I'm leaning toward the stock 6.75 inch damper, but also wondering with me changing the compression of the engine, should I install a larger damper?

Has anyone ran into engine harmonic issues after a vortec upgrade?

Thanks in advance for all your advice.

cv67

The bigger (stock) one is better for a street car believe it or not
They absorb more harmonics, remember that crank wants to twist too. I run a tiny light one but dont expect more than 5k out of mine and want every last bit.
Your heads and cam wont change anything

Jebbysan

Internally balanced 350 does not require a large balancer. 8" balancer is heavy....not really sure why GM decided the L-82 needed this but it is heavy. Heavy is not conducive to quick revving.......this is a good place to save weight. Not only that but it opens up an already tight area down there.......
Look at and read the reviews on this list: https://www.summitracing.com/search/part-type/harmonic-balancers/engine-balance/internal/make/chevrolet/engine-size/5-7l-350/engine-family/chevy-small-block-gen-i/outside-diameter-in/6-750-in?N=4294943542%2B4294949313%2B429495139 9%2B4294951398%2B4294951388%2B4294951379 %2B4294906826&SortBy=Default&SortOrder=A scending

The Summit balancer is a ProStreet brand made by PowerBond in Austrailia......pretty good piece.
I recommend the corresponding Moroso timing tab too...I have used the tab out of the package with zero adjustment and it was spot on zero on three different engines. This is measured with a piston bridge and indicator. A bargain here.

https://www.summitracing.com/parts/mor-60110

I have run the the Professional Products and the ProStreet unit......both are quality pieces for street engine to 6000 rpm.
After that I would think about an ATI.

I don't like auto parts store balancers because they do not have the marks on them......this requires a dial back or digital timing light.....which are inaccurrate when using an MSD box.

Jebby

jackson

if you deviate from 6.75 you must also change the timing TAB.

jackson

Pioneer makes very good dampers at good value. I recall the last one I bought was USA made.
For 1972 C3 350
6.73" standard is pn DA-3071
6.73" heavy duty pn DA-3071-HD
6.73" hipo street pn 872002
6.73" bonded steel SFI pn 872022

7.99" standard is pn DA-3502
7.99" heavy duty pn DA-3502-HD
7.99" hipo street pn 872003
7.99" bonded steel SFI pn 872023

http://www.pioneerautoinc.com/wp-con...06/HB-2011.pdf

Old dampers' rubber deteriorates and bond between iron & rubber loosens.

Jebbysan

The 872002 is made by Powerbond....has the PB symbol on it. Nice piece for $100

Jebby

jackson

The last one I bought was heavy duty 8" for a sbc 400 ...nice piece and a T&D maker pal scribed about 90* of timing marks ...God bless him and keep him.

If I had to do it again but with a stick, i'd probably go with a light bonded 6" (327 style) ... that's what I ran in circletracker.

jackson

Clearly Dayco owns PowerBond … seems there's also a relationship with Pioneer but not clear.

jackson

same Mexican company which owns Pioneer also owns Perfection

mongoose87

Thanks for all the advice.
As part of the upgrade i also got one of those cloyes timing covers with the built in end play button, so not too concerned about the marker, as i will have to do something about that anyway.
I'll be going with with the stock size 6.75 damper because it sounds like the earlier 327 motors had them as well, which were higher compression, so the compression bump I'm doing should affect much.

REELAV8R

Vette5311

mongoose87

I don't really understand this logic of intertia/momentum being advantageous. I guess it makes sense if you are doing burnouts/launching and you are dropping the clutch after raising the engine rpms, but I can't see the advantage if you were...say...doing a rolling start.

REELAV8R

REELAV8R

CanadaGrant

The same thing also applies to a heavier rather than lighter flywheel with standard trans cars in drag racing. The heavy flywheel stores more torque than a lighter one and produces lower 60 ft. times because of this.

mongoose87

So i read the article by HotRod magazine citing David Vizzard saying the 8 inch damper has better 60 ft times and almost all street applications, although I still don't understand why, physics wise. I like to understand the science behind these things, but to be honest, I'm not sure I will ever understand how crank harmonics could contribute to the gains from a larger damper. Torque and hp are about accelerating the car, the crank, and of course the wheels, so if accerlating the crank is easier with a smaller damper...
Is there a condition when the 6.75" damper would be advantageous? Higher rpms?
I know most of use aren't concerned with mpg, but I'd imagine greater crank momentum also helps with highway cruising where you are staying at the same speed.
Has anyone done any testing on this?

I just read the fine print for the cloyes end play button timing cover, and it says the bolts may cause interference with the larger 8" damper.
Has anyone installed the timing cover with a 8" damper? Maybe use screws with a filet on the head?

Jebbysan

A larger heavier part has more stored energy. But the flywheel on your car is 40 lbs. anyway. Get the smaller one and live happily ever after. For my builds....it is just a more open area to work on stuff later.
Another thing about the 8" deal is how wide it is.......you can't see behind it and that can be a problem if there is a leak of any kind......you cannot see where it is coming from. IDK.....I just see zero need for a large balancer and if you look at later LT-1 (late model) engines....there is no balancer at all....just a hub with a serpentine pulley on it......
Fact is if you have an engine that is balanced right.....the harmonics are low to non-existant anyhoo.......so use the smallest balancer you can find.
My own 406 has a tiny balancer on it because it makes about 400ft/lbs. torque off idle........the available torque much out weighs the spinning inertia from a large balancer.

Jebby

REELAV8R

mongoose87

I agree with this rational if you are dropping the clutch, the torque converter isn't locked up yet, or launching in general, but with more stored energy/momentum/inertia it should also require more force to accelerate to a higher rpm. If i'm on the highway going 65, then goose the throttle to 85, I would think the smaller damper would be better, no? (i imagine by a very small amount)
Maybe I'm just looking at his too simply, as mass/momentum as a whole rather than mass of the crank related to all the rest of the drive train.
Again, I know it was tested by Vizzard, but just looking to educate myself.

Jebby you bring up some solid points about repairability, and I'm not going to be racing the car, so it more about seat of the pants feel rather than reducing my times by 0.1 seconds.

I guess a better question would be is it worth it to upgrade to a 8" damper, performance or reliability wise with the increased compression after the upgrade?