Determining balancer size?

[65dragster]

For a small block Chevy, say an internally balanced 350, how do you decide which size/diameter balancer to use? Street-Strip motor, stock forged crank and rods, flat top pistons (10:1), 185 cc heads, using a .550 SFT cam. What brand—am thinking ATI.

[Kevin Johnson]

http://www.atiracing.com/pdf/converter_sheet.pdf

Edit: Fill out the sheet above and email it to ATI. This is what they say to do on their website. Good luck.

[Alaskaracer]

Call ATI and see what they recommend. They will ensure you have the correct part for your combo....

FYI, I run a 7" damper on my BBC, 5" stoke.....8000 rpm at times...

[cardo0]

Most sbc dampners are neutral balanced with only a few exceptions. So size does not affect balance. The larger the dampner the more effective it is so you want to use the larger dampner though many times this means moving/replacing the timing tab and re-verifying TDC on #1. Now some owners use a smaller dampner in an effort to reduce weight and that would be rotating weight on the rotating assembly. And there are some that will even race w/o a dampner at all. So the choice is yours as it would be difficult to use a new/functional dampner no matter what the size and hurt the motor.

[engineguyBill]

For street high performance and bracket racing, large diameter dampener is optimum. For high RPM maximum effort race engine with lightweight rotating components and high stall torque converter or stick shift, then the small diameter dampener is the best choice. My opinion . . . . . .

[MadBill]

Bingo! Exactly what David Vizard found when he did extensive tests a number of years back:
https://books.google.ca/books?id=kmTNub ... ng&f=false

[65dragster]

Good suggestions. I’ll call ATI and review the David Vizard information. If the motor won’t see over 7500, maybe it isn’t significant. Probably makes more difference choosing the good brand and fit. It’s hard biting off $300 for a balancer, but I don’t want something relatively small to cause engine damage. Thanks, all!

[falcongeorge]

Bingo! Exactly what David Vizard found when he did extensive tests a number of years back:
https://books.google.ca/books?id=kmTNub ... ng&f=false

"...these tests showed that for an engine turning up to 6000 rpm, the best stock balancer was the largest and heaviest available."
Interesting. I was going to use an 8" balancer on the present motor I am building, because "thats how I have always done it" for a basic, street driven "TRW motor", now I am having second thoughts. Building a basic hyd cam 327 street motor that will make around 420-430hp, and be shifted at about 6800 rpm, now I am wondering if I should actually be using a smaller balancer?

[ProPower engines]

The manufactures like GM specifically started out with an 8" balancer on most applications where a 350 was used
but as time has gone by they have reduced the size to 7" like on the newer vortec type engines. But from about 1988 till
when ever they stopped the sm blk production they used a 7" balancer including the LT-1 in the mid 90's in the firebird/camaro and the full size vehicles as well.

While we think about the thought of more/heavier is better why did GM switch to the smaller size. Or is the 7" just barely enough and the weight reduction was for over all vehicle weight not dampening ability?

Makes one think about what is good enough to just get by or is the larger balancer better overall.

While the balancer manufactures will suggest difference to use based on application and rpm usage but is it over kill or is the manufacture way off base with the dampening requirements they provide?

[rfoll]

Buy a Powerbond 8" with a nodular iron or steel outer ring. This stuff isn't that complicated. Higher rpm or external balance is where the rules change. I have never had a problem with the GM stuff up to 7000 rpm.

[PackardV8]

The manufactures like GM specifically started out with an 8" balancer on most applications where a 350 was used
but as time has gone by they have reduced the size to 7" like on the newer vortec type engines. But from about 1988 till
when ever they stopped the sm blk production they used a 7" balancer including the LT-1 in the mid 90's in the firebird/camaro and the full size vehicles as well.

While we think about the thought of more/heavier is better why did GM switch to the smaller size. Or is the 7" just barely enough and the weight reduction was for over all vehicle weight not dampening ability?

Makes one think about what is good enough to just get by or is the larger balancer better overall.

While the balancer manufactures will suggest difference to use based on application and rpm usage but is it over kill or is the manufacture way off base with the dampening requirements they provide?

It's all about packaging and the available space. A reciprocating engine really wants a large diameter damper on both ends of the crankshaft.

[ProPower engines]

The space is the same in the newer vehicles. Either an 8" or a 7" can be used with no interference issues based on
components mounting area and available space. Then you look at some of the earlier engines that used the hollowed balancer. The inertia ring while wider is not the same thickness as the other. Yes there is more rubber in them but they
are used in a lighter duty application and the timing mark is in the worst possible place behind the water pump
in some cases.


I get the point but its funny why the OE's did not follow suit with the aftermarket train of thought. While they have to have as little vibration emitted as possible in OE form they still sub out the balancer production to some one else where cost would be a concern the better quality unit would be must cheaper if they were getting millions at a time for production of the same engine. This is of course based on the balancing technology used to balance factory engines.

Where we all try to get the rotating assembly balanced better then the OE would do it again based on application and useage of vehicle RPM etc. For most of us not flying apart and having the balancer do the job it is intended for and have the timing marks stay in place for the life of the engine is all we really ask of it. Regardless of brand.

[Bill Chase]

Interesting, the timeline also coincides with the 1 piece rear man seal cranks, I can see the 86 switch, but running all the old stock out in another 18 months. So maybe the bigger balancer had something to do with the weight on the back of the old 2 piece seal cranks? Just a thought.

The manufactures like GM specifically started out with an 8" balancer on most applications where a 350 was used
but as time has gone by they have reduced the size to 7" like on the newer vortec type engines. But from about 1988 till
when ever they stopped the sm blk production they used a 7" balancer including the LT-1 in the mid 90's in the firebird/camaro and the full size vehicles as well.

While we think about the thought of more/heavier is better why did GM switch to the smaller size. Or is the 7" just barely enough and the weight reduction was for over all vehicle weight not dampening ability?

Makes one think about what is good enough to just get by or is the larger balancer better overall.

While the balancer manufactures will suggest difference to use based on application and rpm usage but is it over kill or is the manufacture way off base with the dampening requirements they provide?

[Lizardracing]

The only times I've had trouble with a 8" damper is on the cast steel cranks with the 350 hub. That's a lot of weight for the material to handle hanging off the front of the crank. Especially when things like pulleys and belts and such drives off the same hub.