Hey all,

I have had a helix downpipe on my car for about 8 months now.

I have dyno'ed on a dynodynamics at 247.9 with it and I thought it was pretty good but I didn't know how useful the cat was until today.

I am doing some apprentice work at a shop that does smogging, and we hooked my car up to the sniffer, and with the helix downpipe at idle the car was at 58 HC and at 2500 RPM no load I was at 89. I don't have the NOx numbers but that is pretty damned good.

I thought I would relay this to you guys since a lot of us are interested in having performance and environmentally friendly cars.

Cheers,
Austin

 

Do you have an uppipe cat? Are other catted dp's and high flow third cats comparable?

 

The up-pipe cat is what in the business known as a "pre-cat", so before the 2 main stock cats are heated up, the precat is working to keep emissions low on startup. That being said, at any smog station the car will be tested hot, so that cat is nuetral at that time and does no work. That being said, no I do not have one

I do not know about other catted downpipes but I am guessing they would work ok but I have done no research on them.

High flow catted midpipes are like **** on a nun, they do nothing, if you still have that far too restrictive primary cat, or downpipe then the midpipe makes no difference.

Austin

 

is there a significant difference in performance with the catted dp vs. noncatted?

 

There is supposedly somewhere around 8-10 HP added with no catyletic convertor.

Rush

 

is it worth the $ to get the catted, in your opinion

 

I think it was worth the cash, at idle and low RPM's I am still passing california emissions, which are really hard. Now since it is high flow, from what I have heard from people behind me, I get a smog cloud at higher rpms and load. But at least I know I am not a gross polluter, in my mind it kinda makes me drive a little more easy

Austin

 

well a smog cloud isn't too bad compared to a fireball (although those are cool)

 

running same setup. helix flex up. helix catted down. borla hush catback. pro tuned AP stage 2.
there are no smog clouds or any other clouds behind me. its a great setup and the hp lost is worth the low emissions for me.

 

In all honesty, I dont think its restrictive at all... Maybe at very low rpm it may show a bit of a difference between between catted and non, but under load, i REALLY doubt it matters... im thinking MAX 1-2 WHP difference... unless a dyno can prove me wrong, logically it just makes sense...

 

Passing the sniffer test is good and all. But wouldn't you still fail visual?

 

I kinda wish I went this route....oh well

 

Yes you would fail visual, but this thread kinda isn't about passing smog, it is just about feeling less guilty about pulling power and having a "gross polluter".

Cheers,
Austin

 

This is the same dilemma I'm in right now. I think I'll go catted. Not so much for the environment, but for the smell or rather lack of.

 

Wait, so say I have a aftermarket DP w/out a cat. However, i also have a midpipe with a high-flow cat. I should see somewhat of the same results, correct?