Harmonic Balancer 6" or 8"?

[TheBMan]

1970 350ci small block. From the factory, did it use a 6" or 8" harmonic balancer? My Assembly Manual doesn't show the balancer, unless I'm missing it. I see the pulleys but not the balancer itself. I want to be sure I get the correct balancer and accompanying timing cover with timing marks tab. Does anyone know the correct size and perhaps have the part number?

I would rather get an OE style cover with the timing tab welded on rather than a separate cover and tab.

Thanks guys!

[jft69z]

2 or 4 bbl carb? There are a couple different part numbers for the balancer.

One appears to be 7", the other 8"

[Scott S.]

Joe...

Are there different balancers for 2 and 4 bolt main blocks as well ?

[jft69z]

14 hours ago, Scott S. said:

Are there different balancers for 2 and 4 bolt main blocks as well ?

 

Scott,

It doesn't appear in any research, that is a factor. Mainly they want to know if it's a 2 or 4bbl. Also turns out that 1969-70 seems to be the years of timing cover with the welded on timing tab, where the other years will use a bolt on tab, for the 8" balancer.

Timing cover for 1969-70 with 8" balancer would be a GM part number 3946870, (later years would be 3991433 and would need additional pointer).

Parts manual lists Harmonic balancer number 3947704 for the 350-4bbl, which is 8". The one for 350-2bbl is 6 3/4" diameter.

I talked with Bryan (naturally) and he already has this info now.

 

[TheBMan]

@jft69z Thanks for the call, Joe! Always good to talk to you. I appreciate the research and clarity on the 2bbl vs 4bbl parts difference!

[Scott S.]

So the size is actually dictated by the RPM range..... I'm assuming ?

[jft69z]

1 hour ago, Scott S. said:

So the size is actually dictated by the RPM range..... I'm assuming ?

Whatever the GM engineers deemed was the correct balancer for the application. Could have been RPM, internal harmonics, torque loads, ...I don't know.

[420ponies]

All that I can remember about SBC balancers is that the 4 bolt main or 4bbl used the 8" balancer. Back in the day, we always looked for motors with that 8" balancer in junkyards for our next build small block chevy.

[Michael Boyte]

1 hour ago, 420ponies said:

All that I can remember about SBC balancers is that the 4 bolt main or 4bbl used the 8" balancer. Back in the day, we always looked for motors with that 8" balancer in junkyards for our next build small block chevy.

That and the Vega torque converters was always on our list of items to hunt for also . 

[Marks71]

3 hours ago, Michael Boyte said:

That and the Vega torque converters was always on our list of items to hunt for also . 

Need to get my “learned something new today fix”. What was special about that converter?

[jft69z]

32 minutes ago, Marks71 said:

Need to get my “learned something new today fix”. What was special about that converter?

Smaller diameter, higher stall speed.

[Michael Boyte]

29 minutes ago, Marks71 said:

Need to get my “learned something new today fix”. What was special about that converter?

This converter would work with the turbo 350 trans and would give you a higher stall . I used to pick them up for $50 or less 

[420ponies]

Best 2500Rpm stall converter for guessed it ! $50 

[Marks71]

Got it. But how did it live behind, say 400 hp when a Vega would be lucky to put out 85?

[Michael Boyte]

35 minutes ago, Marks71 said:

Got it. But how did it live behind, say 400 hp when a Vega would be lucky to put out 85?

Fairly well, I would say. I probably went through 3 or so between the age of 16-20 and that was with a 250 HP nitrous kit.  I certainly beat it up as a kid. However, for $50 it was very affordable for a person with limited finances 

[Scott S.]

That's why you picked them up in bulk..... There were always lots of Vegas/Astras kicking around back then.... Even the Monzas had them until '82.

[420ponies]

Well , to let everyone know we installed a 400 hp 350 motor in a'73 Vega ( Don Hardy) 12 bolt 4:10 gear , with that same converter, drove it around and to the drag strip, no problems 4 nights a week , won a lot of stop to stop light racing. Had alot a fun on the street racing anything that came up on us. This thing would " rock" at the lights , just idling. And launch, oh yeah, " hang on dude " We are Gone" 3 rd gear over 90 mph at 4,000 rpms , shut it down !! 

[Scott S.]

Had a buddy in the '80's that put a Vega torque in a four door '75 Impala with a hopped up 350/350..... There wasn't much that could beat him out of the light. 

Mind you, after about 300', he'd used up all the RPMs he had.