My pre cats are clogged and last saturday took the front pre cat off the exhaust manifold. Was a easy process, took about 1 hour without removal of the stock y-pipe. The precat was clogged terribly, the honeycomb pattern was filled and a huge chunk of it broke off the honeycomb fillment, which i am suspecting (1) it either disentigrated or (2) it broke off and is stuck at the main cat. Because of inclement weather i wasn't abale to get to the second precat by the firewall which will need removal of the stock y-pipe. Total time only took 2 hours. Notice a improvement right away, regained some flow as i put my hand next to the tail pipe. Before i was getting a weak flow with a near silent tone, now you can actually feel the exhaust coming out with a mellow tone. MPG went from 16.2 -20.0. Also redline went from a brickwall 4k rpm to 5200 rpm. Almost there , but not quite....

Tomorrow i will pull the second precat out . One thing i notice the car pull extremely hard to 5200, then chokes.
So i think the removal of the precats will definitely help in overall performance when totally removed. Also engine sounds beefy...

 

I would have just gotten headers 2 birds with one stone!

 

mine was never clogged but i developed a pretty large leak right before the precat and it showed a pretty decent loss on the dyno. after the headers went on, it felt much better as all the precats were removed as opposed to just one with the cattman y pipe. if it was clogged then you should definetely notice some power difference and increase in mpg if you can restrain from feeling the difference all the time. i would definetely check the main cat for damage from the parts of the precats.

 

Yeah i will be under there tomorrow. I want to do headers, but i am going to lay low now , as my money has to go to more important things at this moment. I was amazed how huge the honeycomb fillmet is, it really is a huge restrictor in exhaust flow. Amazing how the VQ3.5 can produce so much power and flow so well with these restrictive road blocks in the way. I definitely think the mid to top end power should increase dramatically, although the low end response is very responsive then stock as i took it out for a little WOT romp. Although i can't push it to hard because fear of blowing a head gasket or worse, so much pressure with a clogged cat. Seen it happen to my friends honda prelude....pushed it to hard with a clogged cat then boom!

 

Daily Driver, I spoke to Dallas at Warpspeed after reading your post and he said that the precats are made of metallic substrate. I was thinking of punching the radiator side precat but he said since it is metallic substrate it may not be worth it. Are you sure it's honeycomb?

 

My main cat did that at around 50K miles, and my precat did the same bout 70K miles. It was deff honeycomb inside as I punched the precat out and had it like that for a long time. Watch out for a check engine light now- for catalyst efficiency below threshold. It will take sometime for it to detect it and throw a check engine lite. U will need a 02 simulator to take care of the light.

 

do you know where i may be able to get an 02 simulator black bird?

 

But you had no problems with driving like that for a while? Also did you notice gains in the low to mid, or mid to high when you took out the pre-cats? Also where could i find a 02 sensor simulator?

 

www.o2simulator.com. I noticed some gains from removing the cats, as they where melted and restricting the exhaust flow. I have no cats on my car, havent had any for the last year or so, no check engine lights for me. For 01-up you need the dual output version of the simulator.

 

Thanks....for your response...also thanks for the link too. Nice max ... love those wheels , your car is very stealth looking.