Downpipe: Stillen or ATR?

I have a Stillen dp that I put on after replacing the clutch last winter. Like someone said earlier, the Stillen is very nice, stainless steel with flex section, larger diameter than stock tubing, flows nicely into a large collecter, and eliminates the front pre-cat and main cat. It also bolts right up to the stock exhaust, flange that the main cat bolts to. I gutted the rear pre-cat while the engine was still in the car, but it took me several night of CAREFULL surgery with a powerdrill and 18" extension. I used a 1.5" diameter spade type drill bit that helped to knock chunks of the cat out. WEAR SAFETY GLASSES AND A GOOD DUST MASK!

The Stillen is made for 1st and 2nd gen. 3SI's and the rear exhaust flange has two sets of holes drilled in it. If you have a '94 or newer vehicle, save your rear exhaust gasket because the ones that come with the kit are for first gen. models. At first I didn't think the bolt holes were going to line up but they did (it has to be just right).

The nice thing about the Stillen is that it's all one piece. No extra sections needed to eliminate the front cat. It all stainless and the welds are very nice. The flex section will help to eliminate vibration and make the rest of your exhaust system less prone to failure (I'm a metallurgist, trust me). It's also got two bungs welded onto it for EGT or O2 sensors, so when the time comes I won't have to drill/tap any holes in it.

That's my 5 cents. Sorry so long.

Jeremy

The Stillen is made to mate to the stock exhaust. That gives it a little bend right at the exhaust side. It didn't mate up properly with my Borla.

I expect you to have the same problem mating to the ATR exhaust.

The Stillen is a nice piece and it gets rid of the front pre-cat, so that should save you some money (unless you gut it yourself). However I like the idea of being able to swap a cat in and out which the Stillen can't do.

So in conclusion:
Stillen pros:
- no front pre cat
- flex section
Stillen cons:
- can't put a hi-flo main cat
- doesn't mate well with aftermarket exhaust

ATR pros:
- test pipe + cat option
ATR cons:
- no flex section
- doesn't get rid of front pre-cat.

I hope this helps.

later,
Amir

I have the ATR on my 94 VR4.

I have ATR's high flow cat (it is OEM'd by the same people that make the unit for Random Technologies) and I ordered it to mate to a Borla exhaust (I got the downpipe and cat from MVP Motorsports on a group buy). I installed mine using stainless steel band clamps instead of the U clamps that ATR supplied (which create a crush fit). This allows more "float" in the system while creating a perfect seal. I've seen no problems in the system and installation was very straightforward.

Mine did not replace either pre-cat. When the time and money are right I'll get the pre-cat eliminators and be done with it. Nice thing is that even after the pre-cats are gone it will still pass emissions after a complete warm-up and the high flow cat delivers at 98% of test pipe so no having to put the main cat back in to pass emissions while getting all the performance you're going to be able to measure. I also feel better about not belching emissions into the air (I'd like my kids to be able to breath decent air too).

I'm very happy with the ATR. Sounds good, works well. No complaints.

Chris
1994 VR4

All have good comments regarding the two dp's. RE: the flex section...I'd be wary to go with a system that doesn't incorporate a flex section. There is a reason why its there in the stock set-up. I think we all might be surprised at how much the engine and exhaust move in realation to the body of the car. Rubber hangers still aren't going to isolate the movement b/w the exhaust system and the engine/dp....that's where you're going to have problems (long term anyway). There is also the matter of thermal expansion of the system. blah, blah, blah....fatigue cracking of high stress areas may be a problem (longterm).

It does eliminate the main CAT so if you love kids and the environment, or if you hate kids and the environment but have to go through emissions testing, go with the ATR. The Stillen system has a badge welded right to it that says something to the effect of, "For Racing Use Only Which May Never Be Used ON Highway".

Attached is a side by side comparison of the Stillen and the stock system. I've got lots other pictures too. PM me and I'll email them to anyone interested.