Added a Cat, Now Car Runs WAY Better?

[rico05]

So, my car has been out of inspection since 4/05 (D'OH!) So I ordered a Magnaflow bolt in cat ($72 shipped off eBay) so I could pass visual (small town Texas pwns! No Smog!), and I hop in, and BAM. Car runs better than ever! Pulls sooooooo smooth and idles better than it EVER has. I even have fouled plugs in, and it still pulls AMAZING. It even sounds better. I really think I am going to leave it in. Backpressure is not such a bad thing it seems. Unless someone else has a better explination...

[Ca_Silvia]

Keep in mind that these cars were originally engineered to have the cat in place. Which mean closer to perfect operation with them installed.

Personally ive owned a Silvia with 3in ex. and no cat. And a Silvia wih 2.5in ex. with a cat. The Silvia with the cat heats up faster and idles way smoother. My .02cents

[rico05]

Good point. I think I will leave it in. I mean, this is a street car.

Anyone want to buy a ProjectSilvia 3" test pipe?

[BACARDI_DWB]

well think of it like a sink. when you take the screen out of the end of the faucet where the water comes out then the water rushes all over the place. now when you put that screen back in it evens out the flow. your turbo can have alot of turbulance in that exaust housing and when you introduce a little backpressure (however slight it may be) it can actually even out the pressures and nuetralize the gasses trying to escape creating a more even equal flow also creating a better response for your wga flapper..... any comments

[rico05]

I also noticed a lot less boost spike. See, I already have a sizeable resonator and muffler can (HKS HiPower) but I guess it makes less backpressure than I thought. I didn't get a chance to do any boost runs (need to go do that tonite), but I bet that I will see a little less top end....A trade off I am willing to make for a daily. I do notice a lot more exhaust shake....I need to find a way to hook up the downpipe to transmission mount (I have a SR O2 housing and dp, so the angle is off so I can't bolt it up directly).

I wonder how long it will take to kill it

[davidricardo86]

It could be the type of catylitic converter? You said it was a Magnaflow? Arent these usually known to be "performance" type cats? Most than likely it flows better than stock but not as freely as your test pipe. Have you tried a stock cat?

[r34 gtr]

i abuse the stock sohc ka cat ive got on my car on a daily basis. its the only thing that dampens noise in my exhaust system (basically straight piped!) and my car sounds silky smooth (if you ignore the idle issues).

- Tim

[rico05]

No, I chunked my stock exhaust (the entire thing) when I did my swap and ran open downpipe for about a month. Then I put on my current setup (ProjectSilvia 3" O2 housing, downpipe, test pipe and HKS HiPower catback), so no comparison to stock. This cat is WAY smaller compared to what I remember the stock cat being. The stock one, I could hardly even lift it, but this one is TINY. My resonator on the HiPower is like 2x the size...

Also, my car has a new smell. Really weird one too. Do cats "break in"?

[BACARDI_DWB]

yes cats have a break in period of like 100 miles

[davidricardo86]

Weird smell? Maybe its the cat doing its job by reducing NOx, HC, and CO and you just got so use to the smell of pure exhaust? lol. i never heard of a break-in period with a cat. but a lot of parts seem to have a break in time so i wouldnt be surprised.

[kapower06]

What kind of weird smell is it? Like sulfur or rotten eggs? lol. No joke buddies bonnevilles' cats used to smell horrible until he changed them. Dunno from what though.

ANyways I was wondering what kind of boost spike you were seeing? Because I have a full 3in. turbo back exhaust, no cat, no resonator. And I have a steady 8 psi after it spike to around 12-14psi when it initally spools up then it settles back down. I was wondering if the cat would help or not?

Thanks agian

[nissan_blood]

Eh if his exhaust smelled like sulfer when he passed by was probably because he was given his car a little of that bottled love joo joo

[ccasey645]

Good point. I think I will leave it in. I mean, this is a street car.

Anyone want to buy a ProjectSilvia 3" test pipe?

Still tryin to get rid of this test pipe?

[rico05]

Yeah, rotten eggs. Pretty awful actually.

Boost spike is 2psi. Boost is set w/ a MBC @ 10psi, but spikes to 12psi.

No, I actually decided that the reduction in boost response (but the increase in engine response) was not worth it. I swapped the test pipe back in Thursday.

[biosehnsucht]

Try a Random Tech high flow cat perhaps? Thats what I have.. although a quick look around, they seem hugely more expensive than when I got mine a few years ago.

how was engine response better but boost not? less top end?

[rico05]

Exactly. The engine seemed to have a noticable bump in torque, and seemed to run a bit smoother. But boost response was WAY off. I am used to being able to put my foot into it at nearly any RPM and have immediate boost. Now, the turbo felt like it was fighting to get to full spool. I think that for autox, the cat may be the way to go. I need to get to an event before the season is over and test it out...