At what engine build level does something like this become necessary?

 

Whenever you can afford the expense. High quality dampers are considered a benefit to any engine, even stock. It helps protect the engine, any engine.

No one can say when something like this becomes 'necessary' because nobody is measuring the kinds of harmonics/frequencies and running the sorts of tests necessary to determine which parts create what dangerous conditions, and then reporting about it on a public forum. Even if they did, it would be a coincidence if you happened to have the exact same parts with the exact same weights and shapes as the engine which was used in the test. And even then, the way the drivetrain is configured and how the engine is mated to the drivetrain components may affect the outcome.

 

I considered it necessary with my 99 TA's heads & cam install as an extra measure of security for all of the above reasons. I was concerned with stock bottom end not really sure how well it would really hold up back in 2002 - extra security.

On my 91 RS's custom built LS1 383 stroker, I didn't feel it was necessary because we knew exactly what went in to the motor and how well it was balanced. If I road raced the RS it defiantly would have got one. My driving is pretty tame these days so I passed on the ATI for now this time.

 

The stock damper is usually more than up to the job on a stock engine running stock RPM's, The issue is when you start making more power and turning more RPM's that stock dampers don't always hold up to the torsional stress applied and they fail usually destroying everything in it's path. I've seen them exit through fenders/hoods and take out radiators/waterpumps and just about anything they come in contact with.

 

ATI has other advantages. It can be rebuilt by the factory (buy once). It is keyed and can be easily pinned with the ATI kit. You don't need to remove the hub to remove the damper itself.

 

NHRA requires an SFI balancer to run 10.99 or quicker.

Over the years I've seen very sporadic enforcement of this though.

 

Thank you for all the responses. I have been given many mixed answers on the subject over the last few weeks, so its good to hear some more knowledgeable insight. I have never used one and almost ordered one from a respectable site, and was told it wasn't really necessary on an engine which had been professionally balanced and to opt for a cheaper higher % underdrive pulley instead, so I decided to put some more thought into it before making a decision .... I have also been told that any higher HP or stroker engine it is highly suggested by others .... So I guess it really comes down to personal opinion/preference as well as how strict your local track can be.

 

ATI is the best harmonic damper out there that I know of, so you can't go wrong other than it costs a bit more. I would spend more time on the ATI web site and talking to their technical staff rather than other vendors. ATI, more than any vendor, know their product. When Motorola cup cars had harmonic issues GM called in ATI. Looks for posts by Kurt Urban for more information and history, he goes under the name on this forum of "427". His recommendation is either ATI or the stock GM, so that should give you an indication. Lighter weight and smaller diameter also reduces the effectiveness of the damper's primary job. Whatever you do, stay away from ASP, documented as responsible for a number of broken timing chains and trashed motors.

Here is a good link with information:--->Link

 

It has nothing to do with how well the rotating assembly has been balanced...

it has everything to do with the resonance of the crank twisting and untwisting on every combustion event...

the ATI damper does a very good job of shifting the harmonic frequency to outside the engine's operating range.

 

Agreed. Either leave it stock or go with the ATI.

Freeing up 5HP at the expense of the motor is not what I would recommend. That's not what the harmonic damper is for - it's to balance out the harmonic pulses. And in the LS1, the harmonics are right around 4400 or so. That's where Vettes were jumping their timing chains with aftermarket balancers. So either leave the stock piece on or get the ATI. They do a good job of being a damper.

 

Does the rpm of the resonance change for cranks with different strokes or different materials? Would the same 4400 rpm apply to both 3.62, 3.90, 4.0, 4.1 & 4.25 cranks?

 

I don't have the resources/time to chase that down (GM would have many man-years into this subject);

the resonance would depend on many things, including physical geometry (stroke), mass (rotating assembly), crank material/alloy, manufacture method (cast vs forged), and a few other things...

all of those things influence where (what rpm) the crank resonates, but it would still be in the vicinity of 4000-5000 rpm, right where the engine makes torque.

Would be interesting if someone could capture high-speed video of damper/pulley while running on engine dyno, with help of strobe light, you would see some "strange" stuff occurring.

 

If you want to see when an ATI damper becomes necessary, take a look at the Chevy performance parts catalog. Check out the crate motors and circle track motors. Any LS-based crate motor that spins to 6500 or more has an ATI, not a GM, damper on it. If the factory goes to the aftermarket at 6500, then that's good enough for me.

 

Sorry to hijack but I was just curious as to what percentage most guys are running on the ATI some say 10% some say 25% I know it depends on the accessories you plan on running but just say for the average car. The most accessories I would ever do is a stealth box and small amp. Thanks for any input I've searched this a few times haven't gotten a defiant answer.

 

I did 10% since I still need power accessories. And it's funny... at idle at 850 I see good voltage from my alternator. But if I idle it down to 700 or so, it goes in the toilet with the 10% underdriven. Power steering and other things bog the motor more too if you're not running a higher idle.

I may switch to the supercharger one which is not underdriven at all.

 

The critical parameter for determining the crank pulley size is your car's idle speed. The alternator has to spin fast enough at idle to run the average car's accessories. Think about sitting in traffic, waiting at the drive through, etc.

Having said that, if your car idles at the stock setting, you can probably go 10% under without hurting anything. Not only will you free up some hp but you will also reduce wear on your accessories.

For a modified street/strip car that idles at higher rpm, the 25% reduction pulley makes sense. The stock idle is 650 rpm, but my car idles at 950 rpm - 50% faster than stock. So I can get away with the smaller crank pulley and still get charging from the alternator and cooling from the AC.

One more thing to consider is your water pump. If you road race or auto cross, or just live in a really hot climate, you might not want to go with the full 25% reduction because it will reduce the capacity of your cooling system by 25% as well. I'm new to the LS engines, but I was a serious drag racer for 10 years or so back in the 90's, and we sometimes ran into cooling issues using electric water pumps. GM usually over-engineers the cooling systems of its cars, but it's something to think about.

 

ok again are you saying any aftermarket balancer other than ati is junk????? doesnt SFI mean its been tested to 12k rpms? how many of us rev over 7k rpm???? please give accurate info!

 

All I'm saying is that GM puts ATI dampers on all their high horsepower LS-based engines. Including the COPO Camaro race engines. I have no experience with either Fluidampr or TCI, I'm merely basing my choice on what GM Performance chose.

 

http://www.enginelabs.com/news/katec...o-performance/

 

I don't remember if someone already posted this url:
http://www.enginelabs.com/engine-tec...damper-advice/