We have used the common gear drives on a lot of engines in the past and I assume you are talking about the less expensive dual idler gear drives. My experience has shown that the quiet ones are noisey and the noisey ones are very noisey. It is annoying to some people and some people love it. You will probably need to shut your engine off at drive-thru windows and such. However.....

I will share some experiences with some of the ebay junk that is out there. I am a distributor for Cat and Pro-Comp (I pick and choose very few items that I use from them!) and I can buy their gear drives for about $35 per set which sends a bad vibe already. We got a few of them in and the gears looked OK but the hardware was crap. I did not want to use them in any of my engines so I sold them off on ebay just to get rid of them. From that time on, we were critical of all this Chinese garbage that is being sold on the internet.

I did have some customers use them on engines that they assembled themselves and two of them had failures within a very short period of time. One had a failure caused by the junk hardware and another had the idlers come apart. A few bent valves and the aggrevation of pulling the motors back out was the only major setbacks but it is something I choose to avoid upfront.

Gear drives have one plus and that is the accuracy of the cam timing. What I set it to today will be the same 10 years from now. Aside from that, it robs horsepower and it transfers a lot of harmonics from the crank into the valvetrain. A good quality roller timing chain set is the way to go on the street and I prefer a belt drive on a drag engine.

If you have a burning desire to have a gear drive, the only ones worth using is the Milodon or any other American made single idler gear drive. They require more skill to use and set up but they are worth it. They are the only ones that I will install on my engines.

Hopemy 2 centshelps!