-K- wrote:Ok, first the best thing you can do is get rid of the cat and get a straight through muffler. Back pressure on a turbo is crap. My experience is that turbos run best on just a downpipe and no other exaust. The turbo itself is all the back pressure (and more) that is needed. I don't care about the velocity out the tailpipe because that is for scavenging and I don't see how much of an exaust pulse makes it through the impeller. Velocity doesn't have too much to do with the turbo, heat it what drives the turbo. So if you have never run just a downpipe and felt the difference... I'd say 3in DP 2.5 back with a straight through muffler and high flow cat if you have to is the way to go.
Heat is not the driver for a turbo. Heat is the measure of the turbo's efficiency. Velocity and volumetric expansion are the main drivers. Myself, several other engineers, and an engine guru discussed this to end. The turbo guro from Kansas state told us what I just said.
There may not be much exhaust gas pulses getting through the turbine.....but I would still suggest not going too big. Bigger is not better.....you WILL loose lower end power, and turbo lag WILL increase.
Bigger exhaust or as you mentioned, no exhaust WILL give you the best flow at higher rpms.......however it is not the best setup for driveability on the road.
Last edited by Legacy777 on Sat Oct 26, 2002 5:33 pm, edited 1 time in total.
k, i have heard the phrase '' the best exhaust for a turbo is no exhaust at all". i personally don't fully believe that. i was thinking of comprimising. instead of getting a catless 2.5inch turboback and maybe regretting it down teh road or getting a catless 3inch turboback and it being too big. how about a custom 2.75inch catless turboback, the happy medium. what ya think?
Have you ever run no exhaust on a turbo? Anyway, 2.75in all the way would be just fine but I would run a 3in DP. I think you would be happy any way you go, it is not as big a deal as some would make of it. Oh and before you take it in cut off the exaust just before cat, drive it, then see if you get more low end after you put the exhaust on. Heat is what causes the expansion that drives the turbo, so I think we are close on that one. Turbos do run hotter though, more fuel/air in, more heat out.
not to ruffle anyone's feathers but the gains you get in hp from not having a cat are so little and anything that helps keep the air cleaner is such a big plus that keeping a cat seems like a good choice. Of course this kind of talk gets me the nickname "hippy" and "tree hugger" But if you lived in any of the many cities like Salt Lake where we often have a brown sky you would probably make this argument too. Then again you may live in a brown sky city or town...
I don't have any direct experience with cat-ectomy, but from all the people I've seen do it, I've come to the same conclusion: Leave it there.
The minute HP gains aren't even worth getting your impact wrench out... Plus my friend's 95 Civic seemed slower with his cat removed, due to loss in torque, I presume...
I have been to Europe where diesel is all the rage, and I had trouble breathing, so suberboy, you're not alone
"Der Wahnsinn ist nur eine schmale Brücke/die Ufer sind Vernunft und Trieb"
Agreed on the cat situation...at least as far as bolt on turbos for our cars are concerned.
As for the just running the Do theory, I did this the night I did the TD05/top mount install..NOT RECOMMENDED AT ALL...car ran like utter crap..zero power down low, took forever to spool. But sounded lke one baddass '69 Nova though
what car did you toss on the TD05 and topmount? So you highly recommendhaving a cat on our cars. What kind of exhaust did that car have? Are the TD05's still $375 US, I may give in soon
Mark,
1991 Turbo Sedan, Aspen White 5MT, Sold RIP
1994 Turbo Sedan, Crimson Pearl 5MT, from British Columbia-no rust!
I'm thinkin with that wicked high-flow turbo, having no cats gave him like no backpressure so his low end had teh sux0r. and with the added IC, until his turbo spooled at 4000 or whatever, the air has a very long complicated pathway.
IggDawg is cool.
-IggDawg
1994 Barcelona Red SVX LSi.
1990 CRX Si (for sale)
You need to understand what subaru does with the cats. They are not your normal cat. They use a 2-part system where the front cat takes care of a certain set of pollutants, and the rear takes care of some others. I don't remember exactly what the exact pollutants are, or which does which, but most high flow or even replacement universal cats you buy will take care of all the exhaust gasses.
Essentually, you're getting a 2-for-1 deal.
It's possible the two cat setup is a tad more efficient.....but I certainly don't care......it's more costs, and more hassle.
Just get one high flow cat.....put it somewhere in the mid pipe or after the downpipe.
Passenger car emissions are a very very small amount of your brown sky, but if it makes you feel any better run a cat. Not a restriction, ha! Scoobysport catless up-pipe DP for WRX is worth 20-25hp. just look through a cat. Getting a high flow cat might not hurt you very much at all at the power level we have so if you have to or want to it's not a big deal.
ummm stock cats & high flow cats are two completely different things.
No kidding stock cats are a restriction. High flow cat......not that much of a restriction for the application we have. Maybe if you're making tons of HP.......but you're not making 400-500 hp are ya?
Yeah car emissions are not a huge part of the smog and crap in the air.....industry is definitely the biggest contributer to pollution. However for what you can do to help why not....plus....do you want a ticket for no cat.......it's pretty steep.
But if you lived in any of the many cities like Salt Lake where we often have a brown sky you would probably make this argument too. Then again you may live in a brown sky city or town...
