jgsx

Ok guys. I was keeping quiet because I was expecting this to be my secret weapon, but it didn't work out.

I dyno'ed my car as is. I then removed the secondary cats and redynoed. zero hp gain.
Then I removed the primary cats. zero hp gain.

You heard right, you will not gain any hp by removing the cats.

advans

was it just "louder"?

jgsx

Yup, significantly louder.

rlee02135

did you put the cats back on?

Eurocharged Rick

how long did you give the computer to relearn after the removal of the cats?

Eurocharged Rick

also, this must mean that we have the best in terms of high-flow cats if there is nothing to be gained...did you gain any torque?

jgsx

The car was driven for about 20 miles, mostly WOT after removing the primaries. I don't have the graphs in front of me, the car is still at the shop.

jgsx

Not yet. The primaries are gonna go back on soon.

Eurocharged Rick

interesting, let me know when you get the graphs, i will be curious if you gained or lost any torque....

RawAMGpower

Isn't your dash flashing check engine with the primaries off? Damn your car must be super loud. All I noticed when I took the secondaries off was the the car sounded much better. I don't think I lost or gained any power from it, but the sound improvement was well worth it. The shop that took them off for me told me I might gain like 5hp with them off.

jgsx

I used spacers on the o2 sensors, so no check engine light.

Zeppelin

I thought some people warned you that there was no power to be gained by doing this.

SilverBulletAMG

I posted this in another topic where you said this, so I'll just copy and paste it here as well...

I assume you are talking about the stock front and rear cats vs. running straight pipe around? One thing I was told was that if you just run a straight pipe (up front) you could "lose" hp and tq. There needs to be larger diameter tubing in place of the front cats, which I assume is for backpressure.
If you are talking ZERO gain when using a high flow cat vs. a stock cat, that makes ZERO sense. The stock front cats are pretty restrictive. Freeing that up has got to make more power. Maybe not a ton, but it has to at least pick up 5-10hp overall??!
What does everyone think? How can there be no gain?

jgsx

I did not switch to high flow cats. I replaced the 4 cats with pipe. I was at least expecting to gain a few hp, so I'm scratching my head too. The car is still at the shop, but I'll share the dyno graphs when I have them. I'm not sure if I lost torque yet, but I wouldn't be suprised if I did

jgsx

They did? I was the one saying that the gains would be minimal. Different people were talking about very different gains, so instead of keyboard racing, I decided to actually try it and back it up with dyno data.

RawAMGpower

So you think replacing the secondary cats with straight pipe you will lose hp or tq? Or is that only if you replace the primaries with striaght pipe?

jgsx do you know if you lost anything when you took the secondaries off?

SilverBulletAMG

I was talking about replacing the front (primary) cats. That is what "supposedly" needs the larger diameter pipe and not just a straight pipe. I am by no means a pro in the exhaust field, but that is what I was told by a few exhaust guys. The dyno doesn't usually lie though, so hard to argue with that.

jgsx

you def should not lose any hp, but I wouldn't be suprised if you lost tq. I don't have the graphs yet, so I can't give you a confirmed answer yet. All that I know so far is that the hp level remained the same with all 4 cats on, just the 2 primary cats on (2 secondaries removed), and all 4 removed. The front cats were replaced by flex sections.

RawAMGpower

Well, I'm hoping jgsx dyno results show no hp or tq loss with the secondaries off. However, doesn't evertime you dyno a car the results can be slightly different depending how hot or cold the engine is and how fast you rev the rpm's? Also does a dyno's software correct for temp, humidity and what not?

jgsx

It was a dyno dynamics dyno, so it is pretty accurate. The car was run with the same conditions each time.

RawAMGpower

So was your hp the exact same each time or was there a 1-2hp difference at all?

jgsx

I'm going to pick up the car late this evening, so I'll have a better answer for you then

jgsx

Ok, I went to pick up the car last night. While at the shop, I looked at the various dyno graphs. I was supposed to get an email with them last night, but I haven't got it yet. I'll post the graphs as soon as I get em

Ok. The graphs for all 4 cats vs no cats were not the same. The car did gain a few hp in the mid range, but max hp was about the same. I don't recall how the torque curves were off the top of my head.

I drove the car around for a bit with no cats, and let me tell you, it was awful. The car sounds SO bad! At part or full throttle, the car sounds like a riced out Civic -- only louder. It is very high pitched and raw sounding
Also, my ride was following me, and she said that it smelled AWFUL the entire time she was behind me. I could smell it a little inside the car. Needless to say, I made a U turn and took the car back to have the primaries put back on.

Also, my car was being weird again. It seems like whenever I make a change, the car becomes a total slug and takes a week to recover. That's how my car felt, so I'm not sure if the dynos are even useful

CynCarvin32

The cats are not a bottle neck with stock tuned ecu (or even a car win an ecu upgrade. Now if you were to buy a set of kleemann V8 headers that have a collector chopped off and closed off (they will make them for a V6k) and run no cats you will see a HUGE incrase in power.

Kleemann runs car without the first set of cats and without the cats you can advacne the timing a great deal and see a very nice increase in power. The ECU's designed to run with the cats do not advance the timing enough to see any real increase in power by taking out the cats.

Now yes it is not legal to run around without cats and at your next smog check they will have to go back on the car (at least the main cats) but buy some headers for 3-4k and see maybe a 45 hp increase in power.

Now I really dont know how kleemann gets away with this since any of us could call the EPA and get them shut down and fined up the rear end for selling parts that are known to going on cars for street use without the first set of cats.

RawAMGpower

So are the primaries back on now? If so how's the car running with just the secondaries off? Oh your getting me worried like I should get my secondaries put back on. When you fine out the numbers with just the secondaries off please post them up. I hope there is no torque loss.