Replace the catalytic converter.
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Good point.
Many bench racers without first hand experience. If ppl actually examine the location and construction of the cat on the A4, they'll realize how big a restriction that is. From first hand experience, replacing the cat with a high flow unit or a test pipe makes a huge difference.
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I'm with you. I don't like the idea of eliminating the cat when other things can be done to...
increase power and remain green. I was contemplating on the turbulence of that honeycomb cat right after the spinning exhaust stream from the turbine.
I took a quick peep under our TTRQ a while back. It splits the work on to 2 cats mounted further downstream like @--<=>--D--[
Now if that doesn't help make 225hp stock, I'll be damned
But that twin intercooler setup has to go.
I took a quick peep under our TTRQ a while back. It splits the work on to 2 cats mounted further downstream like @--<=>--D--[
Now if that doesn't help make 225hp stock, I'll be damned
But that twin intercooler setup has to go.
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Agreed, except for the 3hp part.
you might see 3hp on a NA car (if you're lucky) but you'll see more on a turbo car, plus quicker spoolup. Depending on the cat (and the mileage) I bet the average gains are 5-10hp accross the board, plus more power sooner.
I noticed a big difference on the top end, not so much on the
If there was a 4-wheel dyno around here (MI) I'd have no problem doing a before/after test (I could test my WI setup too) I wonder if I can dyno with the driveshaft disconnected?
I noticed a big difference on the top end, not so much on the
If there was a 4-wheel dyno around here (MI) I'd have no problem doing a before/after test (I could test my WI setup too) I wonder if I can dyno with the driveshaft disconnected?
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RIf you read the MacInnes book on turbos he talks about the exit flow...
from the turbine housing. Several to 10" of straight pipe, or even gently expanding conical pipe help smooth the rotational aspect of the flow. At certain flow regimes the exhaust plume rotates in the same direction as the turbine, then will stall straight out, then actually begin to counterrotate. Having the cat right behind that tends to bollux up the flow of the exhaust gas and is bad. A long straight pipe, angling down to go under the floor near the firewall, with the cat attached under the floor is probably the best approach.
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you need to block the center diff...
there are guys who have used a welded up center diff to make their cars FWD for dyno reasons. Just taking the shaft off means the rear output shaft will soin, lots of heat will get used up in the Torsen, and generally bad things will happen.
I'd love to see some numbers.
About catalysts: I think you are still using old-school catalyst theory. Cats used to plug up as they got older when they used a pelletized catalyst matrix (like a bed of gravel) which were also very restrictive. If they were overheated (common when hotrodded from overrich mixtures) and just from age the catalyst pellets broke down until you had a sand bed. Monolithic cats came next with a porous brick of catalyst that the exhaust flowed thru. These were great on Mercedes diesels because they trapped particulates well.
Modern catalysts use a metal matrix catalyst which doesn't tend to plug or break up with time, so I don't think catalyst age is a factor.
Metal matrix cats are also miles ahead in reduced backpressure compared to the older styles, which is why I stick to my guns with the 3-5 hp figures. You can go look it up in VW Performance Tuning, if you like, they give actual dyno numbers. Granted its not a turbo car, but I don't think you will get more than 5 hp mas out of it, and its still illegal as hell.
Thanks for the spitired debate!
I'd love to see some numbers.
About catalysts: I think you are still using old-school catalyst theory. Cats used to plug up as they got older when they used a pelletized catalyst matrix (like a bed of gravel) which were also very restrictive. If they were overheated (common when hotrodded from overrich mixtures) and just from age the catalyst pellets broke down until you had a sand bed. Monolithic cats came next with a porous brick of catalyst that the exhaust flowed thru. These were great on Mercedes diesels because they trapped particulates well.
Modern catalysts use a metal matrix catalyst which doesn't tend to plug or break up with time, so I don't think catalyst age is a factor.
Metal matrix cats are also miles ahead in reduced backpressure compared to the older styles, which is why I stick to my guns with the 3-5 hp figures. You can go look it up in VW Performance Tuning, if you like, they give actual dyno numbers. Granted its not a turbo car, but I don't think you will get more than 5 hp mas out of it, and its still illegal as hell.
Thanks for the spitired debate!
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hey bob
have you tried a before and after on a 1.8t with and without a cat?
there IS a large diffirence esp in the top end.
it is much more than 3hp, and i have no DTC's.
if i were using a straight pipe then i might get a code, but if your aftermarket cat runs at least somewhat efficiently you wont have a problem
look at my pics above, then tell me there wont be a noticibale diffirence. i couldnt even get any light to shine through the stock cat, thats why the pic was taken with the light behind it
there IS a large diffirence esp in the top end.
it is much more than 3hp, and i have no DTC's.
if i were using a straight pipe then i might get a code, but if your aftermarket cat runs at least somewhat efficiently you wont have a problem
look at my pics above, then tell me there wont be a noticibale diffirence. i couldnt even get any light to shine through the stock cat, thats why the pic was taken with the light behind it
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I did the light test too, but.....
the stock cat is all black inside. The Random cat was shiny. The black vs. shiny will affect the light test tremendously, so I don't think it's accurate, especially given the fact the outlet of the cat is curved. The shiny surface will reflect the light around the curve. The black surface will not.
I think my dad has (or has access to) a pressure gauge that you screw in place of the O2 sensor to check for a clogged cat/exhaust. If possible, I'll try to see if I can get my hands on it, although I'm not sure how well the car will run with the primary O2 sensor unplugged (although I could make the second O2 sensor the primary one, but it still might cause problems)
I think my dad has (or has access to) a pressure gauge that you screw in place of the O2 sensor to check for a clogged cat/exhaust. If possible, I'll try to see if I can get my hands on it, although I'm not sure how well the car will run with the primary O2 sensor unplugged (although I could make the second O2 sensor the primary one, but it still might cause problems)
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I'm always up for a good debate :)
The cats are specified as cells per brick or something like that, right? Stock is 400, Hi-flow is 100 (no cat would be 0 obviously). If you look at CharlieG's pics, you can see the difference in the bricks. They are also more orderly arranged.
Since the exhaust is very turbulent coming out of the turbo, the first thing it will hit is the cells. Less cells = less restriction, and I'm curious if the more orderly arranged cells help by straightening the flow (much like a MAF screen does)
This would be an even bigger advantage on a K04 as opposed to a K03, since it flows more air and more exhaust.
Since the exhaust is very turbulent coming out of the turbo, the first thing it will hit is the cells. Less cells = less restriction, and I'm curious if the more orderly arranged cells help by straightening the flow (much like a MAF screen does)
This would be an even bigger advantage on a K04 as opposed to a K03, since it flows more air and more exhaust.
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Yes, yes, yes, yes and yes.... but...
Hi everyone,
The point here is every post that claims removal of the cat gives a big increase is not backed up with numbers.
The only test that would satisfy myself and the other critics is this:
Audi/Passat dyno - stock exhaust/cat vs. stock exhuast/no cat (or aftermarket cat)
Audi/Passat dyno - aftermarket exhaust (+downpipe)/cat vs. aftermarket exhaust (+downpipe)/no cat (or aftermarket cat)
Then this argument would end once and happily for all! ;-)
My instinct says 3-5hp on the stock dyno comparison, and maybe 5-7 on top of the aftermarket exhuast comparo.
Take care,
Michael
The point here is every post that claims removal of the cat gives a big increase is not backed up with numbers.
The only test that would satisfy myself and the other critics is this:
Audi/Passat dyno - stock exhaust/cat vs. stock exhuast/no cat (or aftermarket cat)
Audi/Passat dyno - aftermarket exhaust (+downpipe)/cat vs. aftermarket exhaust (+downpipe)/no cat (or aftermarket cat)
Then this argument would end once and happily for all! ;-)
My instinct says 3-5hp on the stock dyno comparison, and maybe 5-7 on top of the aftermarket exhuast comparo.
Take care,
Michael