How much hp will I lose if I replace my presilencer with my stock main cat? I was thinking of just doing a 3rd gear pull from 40-70 before and after to see, but what kind of losses am I looking at?
My reason is that this summer I'm seeing a lot more cops out, and every time I see one I get real nervous, so I want to at least have a legal exhaust. Plus, the noise decrease would be a plus.
One other question: what exactly is the difference (in design) between my stock cat, and a new high flow? Are they really that much better?

 

If you are nervous, take the heat shield off of some junk cat and wrap it around the presilencer so it looks like a cat. Worst a cop is gonna do is get his nightstick and smack it around under your car til he hears what sounds like a cat.

EDIT - Don't know about your other questions though, sorry.

 

i'm nervous because it smells from behind, and it is very loud.

 

um Why are all the cops everywhere so ghey. Here in south texas no one gives a ****. I mean what about those loud hondas???

 

if a cop ever gave me a ticket for exhaust i would ask him why he is not doing the same to harleys which are ten times louder.

 

yeah, but motorcycles don't have to pass emissions.
Anyway, no one has answered my question yet!

 

loud doesn't describe it...a straight piped NA will sound out the voice of God.

Puting the precat back in will no drain too much power. The most serious effect you'll see is a lower top end...but throttle response and low end accelleration will benefit.

 

not the precat, the MAIN cat. My system will be the RB header, to the stock main cat (as opposed to the RB presilencer that I have on there now), to the RP cat-back.
Yes, my car is very loud now.

 

I just wrote it wrong...it's the same either way.

As well as the RB silencer works you should have just left it open...lol.

But anyways...it's the same either way, the loss of power prolly won't be anything you'll notice unless you try to top the car out a lot.

This actually just came up in another forum I cruise all of the time:

http://www.supraforums.com/showthrea...hreadid=120699

 

I know the high end will suffer, but how much slower overall will it get? Let's say I'm perfectly even in the 1/4 with my friend in his Ferrari F50 , and I put on the cat, will he beat me by a car-lenth, two, what?

 

The amount of back pressure the main cat throws on the N/A would prolly not be noticable...again, your low end will probably benefit from it, and beings low end is pretty much what makes/breaks you in the quarter with this kind of car, you will prolly do better...so you would prolly pull a your buddies Ferrari... *cough*cough*fierro*cough*...but not by massive amounts.

Havnig a totally free unrestrcted exhaust helps two things:

Top end
turbos

 

LOUD PIPES SAVE LIVES!

 

That is great news. I have always heard that backpressure helps the low end. The reason I like that is because my system (RB header, presilencer and Dynomax dual cat-back) sounded very sweet but was like a damn Cessna 172 for sound level. So I am planning on putting the main cat back in and possibly the stock cat-back. It will be streetported once that is done and we all know what street ports do to the sound level.

 

yes, this thread is a little old, but I put the cat back on, and here are the results:
no difference . I did a 2nd gear pull from 3000 rpm to 7000 rpm at about 60*F going up a slight hill on the highway with the presilencer on, then with the cat on. With the presilencer the time was 7.73 seconds, with the cat on, it was 7.71 seconds. So basically there was no difference. I'm sure the high end is a little weaker than before, but I'll gladly sacrifice the couple peak hp for the better low end (slightly better anyway), and the smoother, quieter sound.

Basically I'm just reposting to say that the main cat does not rob much power at all! If you are thinking about doing the same, I'd recommend it. The low end is better, making around town driving better, and the sound is significantly better IMO.

 

I need to post my exhaust thread here...too...

 

lets see... If your butt dyno gives you approx 180 Hps, and given that its an N/A, that translates to approx 130 RWHP. So then factor in the restriction for the cat, which through unbelievable scientific research, I have determined, robs you of 28.43 RWHP. This gives you approx 101.57 usable RWHP. Now factor in the fact that you live in Boulder, CO. the rarified air there will rob you of an additional 7.382 RWHP. This leaves you with a grand total of 94.188 RWHP.

What does this mean? You need a turbo!...

Jarrett

 

another boost junkie

 

turbos are cool...but they're one more thing to help my car break...again...I have a hard enough time keeping my NAs alive...

 

through scientific proof (timing acceleration runs) I have determined that there is no difference, or a very small difference in hp. Trust me, I did not lose 30 hp by putting that cat on. This an N/A remember? The cat kills a turbo, but an N/A isn't affected that much.
Anyway, you can throw every stat in the world at me, but when the pedal hits the floor, that's what matters.
I think your calculations are flawed anyway .

 

I think my calculations are complete BS!

 

Using your logic lets take this a step further...TII's are supposed to have some 200hp...wow....considering how restricive the turbo is if you just take that off you'll make 250 easy.

What does this mean? Poor methods of calculating hp loss make you look stupid.
























j/k......I think you're wrong....but that's okay with me.

 

See above post, where I admitted I pulled those numbers outta my A--

 

Yeah, I was kinda wondering about that

 

A good (new) high flow cat (read Bonez) will cost you only 1-5 hp if installed properly (Basically nothing) with very good top end using headers and stock cat-back. An old, 2 or 3-stage, crumbling stock cat will cost you 20-25 hp (vs. presilencer).

 

lol....I was writing mine as you were posting yours...:P