FWIW, I gained 10 RWHP switching from QTP standard collectors to their HVMC with no other changes. It wasn't on the same day, but it was in fact warmer on the day we dyno'd with the HVMCs and the numbers were not corrected for either pull.

I've had experience, on my car, and on my brother's car, with three sets of QTPs. The only reason I sold my first set (standard collector), bought a second set, and convinced my brother to by a set of them was because of the HVMCs (not a factor in the first set) and because of the merge in the Y-pipe. I don't think the fitment argument is really applicable (regarding the LTs themselves) because every car is not the same. In addtion, ALL LTs have had fitment issues pop-up from time-to-time. I believe Kooks can better suit a persons needs because they offer varying sizes. I believe it is doubtful that there is going to be a significant difference, in terms of collector style, until the power numbers get higher. In addition, the farther the restriction is away from the exhaust port the less effect it will impose on power, and with both Y-pipes being 3-inches, on a mostly bolt-on car, I doubt there would be an appreciable gain with the QTP Y-pipe.

Now if my HVMCs and my modified QTP catd' Y-pipe were destroyed, and I were seeking replacements, I would likely go go Kooks because of the Y-pipe, more than anything. I've seen cars with Kooks, and the owners are as happy as I am with my QTPs. I have almost as good a clearance but it was after a little cutting and fab'ing, so it certainly didn't come as easy as it could have with Kooks.

Regardless, Kooks would be able to answer any questions you have. I'd talk to him ;D

 

I thought my QTP's fit great and I love the way they look and perform. Their ypipe sucks though hangs very low. It took me about 4 times of adjusting it to get it tucked up close to the floor. I am lowered and scrape here and there, but its no big deal. My only rant about QTP is their customer service. Both of my HVMC are leaking the drivers side quite bad I can smell it in the car and hear it when driving, and when I contacted QTP about this I was told thats the price you pay for performance which I think is a horrible way to do business. I was not alone on this issue either there are other who have this same problem. This is why they do not get my vote. If the time comes for me to get a new set of longtubes im going with Kooks

 

I have Kook's. They should both be equally good.

 

My Kooks 1 3/4s are on order now. I ordered them for the following reasons:

-I don't recall ever having seen a single complaint about them, every Kooks owner has only had good things to say about them.

-When I saw their product in person, what I had read about them regarding fit and finish was confirmed, and then some.

-George R. hangs out here. He seems like a good guy, he actually does answer questions personally, and that gives me a lot of confidence in the company and the product.

The fact that I was able to buy high-quality, good fitting headers and a Y-pipe from the same company didn't hurt either.