it will make more power into higher rpms with the full size than you will with the underdrive....
it takes Mass to absorb vibrations....and the underdrive pulley has less mass than the full size.

 

10% won't make a difference. ATI said themselves the 10% would be perfectly fine for my application, and they know I'm going solid roller to at least 72 - 7400 RPM. It was however built with their better dampening material (no extra charge)

 

I wouldn't but that just my opinion. Gains are so minimal with 10% if any I don't see much point.

 

While that is remotely true no one is using metal to dampen vibrations. Hell in that case why even use rubber or synthetic materials? Just make balancers out of solid steel. If the rubber material is doing its job, which by ATI's design it should then the hub material will do NOTHING because the rubber dampens all that is needed.

Again how can you argue with real world results? Have you PERSONALLY experienced this happening? Show me one that has caused a failure. I can show you multiple times the stock STEEL/IRON one caused timing chain failures. Till then I'll keep spinning mine to 6900 and waiting for it the balancer to take out the timing chain.

As whigham said, I think I'm gonna trust the engineers at ATI instead of someone telling me that a stock dia balancer will make more power and that ATI doesnt know what they're saying when they recommend the 10% UD. Are you also aware that they offer different polymers that dampen differently in all their pullies depending on how you will be racing the car?

 

Well I should have wrote down his name but I called in to ati and asked which dampener I would need and he said at bigger power levels 800-1000hp I need the bigger stock diameter balancer. "It will provide better dampening".

 

That makes sense. No mention of steel there, the stock dia balancer comes in alum or steel. You get better dampening because there is more surface area of the rubber polymer not because its steel

 

Well idk im just stating what the guy said. I told him I have part # 917242 and will be around 800-1000 hp and he said that will do the best job of dampening.

 

There is a lot of bad info in this thread. The OP should listen to ATI or an experienced engine builder. You will get different suggestions but they should be close. The actual damper ring in ATI units is steel and commonly the same size. The only things commonly changed are the shell size, shell material, and o ring durometer. The full size steel shell will dampen more than an equivalent aluminum shell. The aluminum shell weighs less and will translate into a slight power increase. Your dampener needs to have enough mass to do it's job. Low power doesn't create strong vibrations while big power does create big vibrations. The o rings change in durometer for the intended rpm range. Soft rubber for lower rpms while harder rubber for higher rpms. The aluminum is great for a majority of applications and will live for years on the street or drag strip with an occasional rebuild with new o rings. The steel does have it's place for economics or durability.

 

For my engine Rob recommended 917073, 7.53" no UD, aluminum, 6rib shell w/70 rubber. I already had the steel hub.

 

There's 2 things I would say...

10% underdrive isn't bad, accessories usually work out fine for power steering and charging systems...especially since most likely you're idling the engine more than 10% higher RPM than the stock one did. If you idle down at stock RPM, the underdrive might cause you to get annoyed with power steering and your charging system when the engine is idling...25% you'll definitely be annoyed, 10% might not be.

Short of that...if it's a stick shift car, and you street drive it, and you've got a lighter flywheel/clutch assembly, it might benefit you a TINY bit to run a heavier material on the damper...it's effectively another flywheel...it's a small diameter though, so it's fairly insignificant in that regard...but in some cases that little bit of rotating mass can help.

 

I've spent a great deal of time taking all the rotating mass I can out of my car. I'll never understand why people want roatting mass? Its parasitic and hinders performance. The only thing it helps with is a launch, which can be negated with a variety of other things. Everywhere else it hurts performance

 

Agree!

 

a heavy harmonic balancer will save the stock crank in these cars, lots of people run stock shortblocks up to 700+hp and are running a stock balancer or a heavy ATI

actually the stock harmonic balancer isn't that bad if your staying in the 6500-6600 range, many people keep them.

I actually talked to kurt urban a long time ago about this and he said to keep the stock balancer if staying under 7000 rpm, the main reason ATI is a good upgrade is because most tracks require an SFI rated balancer at faster speeds.

once again, my opinion backed up by someone who knows a lot about timing chain failures, harmonic balancer and dampers etc...