I ran the SLP's on my 96 WS6. With no changes other than the headers, I went from 12.7@109 to 12.4@111. Both days had roughly the same DA and short times.

 

Yeah but what do you know!?!?! Like you got a fast car or something...

 

I wish they just put a mirror under the car or something. But when I went they got on the ground on both sides of the vehicle and verified both cats. I am not sure on the location of the cats, but they do check for them, in there general location. It seems the SLP's are possibly the way to go. As for the stock y-pipe being restrictive.... how? It is 3"'s with high flow cats. I mean look at the example of LT1's and even LT5's that Lingenfelter modified, which retained stock cats, and only made a 3-10hp difference when removed. I believe the stock y-pipe is plenty, and is always something that can be changed. Probably after emissions are checked, I could switch in a catless y-pipe if I wanted.

 

IMHO a 2mph gain isn't worth the money for those headers.

Dougie!
I've been thinking about you. Ugh... sorry I didn't catch the phone. I'll call you this week dammit!

 

It was to prove you do gain with them. But that was back then when we still had the sniffer for emissions testing. Only way to stay legal.

If I were to do it now, long tubes with some cats. Since we just do plug in testing, you don't necessarily have to be 100% legal to pass. Heck you don't even need cats to pass when you lock that code out

 

Most E-test stations check the monitor status of the test. I have found that all a computer program does is disable the monitors or tests run, which in affect turns the codes off. Most E-test stations will recognize this when plugging into OBDII. Just some FYI for ya.

I loved my SLP shorties, but was unable to use any type of aftermarket valvecovers. The passenger side header creeps up over the head just enough that taller valvecovers do not fit well, if at all.