1BadGTA

We all know abou the benfits of doing it. I was wondering if there were any cons to doing it. About all I've heard is that the car may backfire.
Thanks

84TransAm

It will sound louder, if that's bad.
Oh and if you get caught during inspection, or have to be smogged, you have to replace it.

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--Steve S--
1984 Trans Am 305 LG4, 5 speed
Daily Driver, Flowmaster 80 Series
Holley 600 cfm & vacuum advance

MrJ

yeah it will take away some low end, that much I can assure you.

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91 Trans Am WS6
Bright White
5.0 TPI auto
Flowmaster 3" 2 chamber catback
Trans Go shiftkit
2000 stall converter

Built on Wednesday

327 firebird

Just make sure after you gut it out to put a section of pipe inside the cat to reduce turbulence. This way you won't lose so much low end. You just may not have enough back pressure. Besides the smog police there really isn't that many cons about it. If you need to get tested, keep a good one around (preferably a bolt on) And put it in when test time. I know around here if you are missing a cat though, its a 5000 dollar fine for each one missing. Sucks for those mustang owners who's cars can have up to 4! 1 more point fpor the f-bodies who only have 1!!

idrag2

I remove my cat and run a soild 3" pipe into a 2 chambered Flowmaster and everyone told me I would loose low end? BUT GUESS WHAT befor I had all the work done you could stand on the gas and it would not spin a tire not even a chirp, after the work I can white smoke the sh#$ out of both tires for about 30 feet, and I also gained alot of upper RPM too, Man if you live in a small town and can get away with taking it all the way off do it........YOU WILL BE VERY HAPPY, also try to get 3" pipe run!!!!!

84TransAm

Foolish of them to say that. Mufflers cause backpressure, only a large leak or open pipes that are unmuffled (ie not having a source of scavenging pressure)
You can run without backpressure, I have done it, but off the line power really does suck without it.

82camaro

What 84 said, the muffler causes plenty of back-pressure. The Cat is an emission piece, not a low end power booster.


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82 camaro--original steering wheel, brake/gas pedals, seats--everything else modified
82camaro

1BadGTA

Does removing it affect your gas mileage in any way? So, from what I'm hearing, is there a low-end power loss, or is it just with some cars?
Thanks

Rob P

iTrader: (1)

I gutted the stock, single cat on my 92 Z28 convt. I lost no low end torque, and the car still passed the old Florida e-check.


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Rob P
89RSconvtZZ4TPI
Edelbrock Hi-Flow Intake
SLP Dual Cold Air Intake
1 5/8" Headers
Semi-Siamesed Runners
MSD6AL/relocated MAT/ AdjFPR/IROC frnt@rear swaybar/wonderbar/steeringbox/alum drvshaft/ Alston SFC/3:23posi disc rear/MAC LCA/H.Adams Panhard Rod/KYB struts/ shocks/
92Z28convt5spd
71Impala convt 402BB
BETTER DRIVING THRU SUPERIOR HORSEPOWER!

theformula

I'm really wondering about this too. I've heard it can be even more beneficial for forced induction vehicles. After inspection this year I think I"m going to do it.

kiztope

I gutted my cat last year... even on a 6 it made a difference..

Gut it!

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http://kiztope.50megs.com

92 Rs 3.1/T-5
Its slowly but surely coming along....

AIM : Theonekiztope
ICQ: 8787542
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"If it can be better than it is, make it so!" Leon Calrinsky (00)

Ed Maher

No, you absolutely cannot have too little backpressure. That is one of the biggest and dumbest fallacies that exist in relation to 4 stroke IC engines. Why? I'll tell you.

Pumping Losses The concept of backpressure means that there will be a high pressure area at the exhaust port. When the valve opens, the escaping exhaust gases have to push against that high pressure area. How can a parasitic loss be good for your engine? The only engines that NEED backpressure are various small engine designs, mostly 2 stroke. The problem with them is they have the tendency to be too effective at driving the exhaust out, loosing compression. I assure you that on a big 4 stroke engine such as an SBC you want the exhaust to have the free-est path possible. In fact, it would be ideal to have a low pressure zone at teh exhaust port. A low pressure area would help to pull the exhaust gases out. Freeing up more power that your engine would have wasted pushing the gases out...which brings up the next topic beautifully.

Scavenging We've heard this before, but what does it mean in relation to our discussion of exhaust. Easier for me to use an example. So your engine fires and now it's on the way up on the exhaust stroke. Exhaust doesn't come out at a consistent rate, it comes out in pulses. Each pulse is a high pressure area, and as it moves, it leaves alow pressure area behind it. Aha, there's our scavenging. You want that low pressure area to be at it's peak when the exhaust port opens on the next exhaust stroke. Thats another reason why headers make better power than manifolds. besides just flowing better, instead of all the pulses being dumped in a log fighting with each other, the tubular runners allow the exhaust pulses to stay seperate and create a nice low pressure area behind it. This is also where tuned and equal length headers come into play. Tuned headers are sized such that the length of the tube corresponds the speed of the exhaust pulses so that the low pressure area is maximized at certain rpms. No surprise that short headers are better for high rpms than longtubes.
Problems can surface if you use too large of a primary diameter, loss of torque. The morons are quick to spout 'you lost backpressure and thus torque.' Next time you hear that you will smile and know that that person failed physics in high school. The problem with using too large of a primary is this. The exhaust pulse only has so much gas and energy in it. If the tube is too large, the pulse expands to much, losing energy and thus velocity. When it loses velocity, it can potentially stall and stop moving in the tube, or at least slow down. aha! Too large of a header actually CAUSES backpressure, and thus lost power. We feel this power loss as a loss of torque because usually this effect is much more pronounced at low rpms as much less gas is moving.

The same principles apply to the entire exhaust system, from primaries to collectors to pipes to mufflers. I am too tired to explain it all, books have been written on these topics. I have just scratched the surface, but hopefully you all understand a little better why their is no such thing as good backpressure. I know some of this has been a little oversimplified, but it think it gets the message across.
thank you please drive through...ed

Damon

It sounds like crap, that why!

It's not a "throaty" or "mellow" increase in sound. It's a hollow rushing noise that almost sounds like you've got a small exhaust leak. I hated it.

As for performance (on my 94 LT-1), it lost maybe just a smidge on the bottom end and never really made up for it on the top end. Dragstrip testing confirms this, not just my opinion. Picked up about 1/2 MPH but went no quicker.

Late model cats are not very restrictive at all and gutting them won't get you much (any?) performance usually. However, older cats that were undersized to begin with and have seen thousands of abusive miles could be a different story.

CSkipEaston

I am not sure how many years it will fit,but I put a 1984 Corvette converter on my 1982 -305 which has a 3" ID thru pipe.

I also have Edelbrock TES Headers on it and a 3" DYNOMAX Cat back system.

For the record, I live in California and have to comply with the 50 State smog legalities.

But, if you want to stay legal and reduce back pressure, this works.

FYI, the 84 Corvette converter is a four bolt square flange converter like was used on 1983 H.O. 305's

-Skip

82camaro

http://208.228.34.13/nate/sounds/lowrpm.wav
http://208.228.34.13/nate/sounds/highrpm.wav
Sounds fine to me


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82 camaro--original steering wheel, brake/gas pedals, seats--everything else modified
82camaro

ArnoldBraker

Ed, that was the best explanation I have ever read as to how exhast works and why. It cleared some stuff up for me. Thanks ~Arnold

BigChevy342

82Camaro,

Hey that sounds really good, what type of exaust you running? I am considering doing this to my chev p/u-350, its the same sound that you have, but its just an off brand glasspack. The carberated cars w/o cats sound really mean, different from injection, or thats how it sounds to me, atleast. its kinda got that more hollow sound to it.

Ray87Z

I just got done gutting my Catco 3" cat tonight (apparently I ran rich this last year, and killed the cat, damnit...) Long story short I used my brother's newer Catco cat on my car temporarily, and it passed the emissions dyno. So I gutted my Catco cat and put it back on since it wasn't doing jack for me and I couldn't pass w/ it gutted or not, why leave it clogged...

Anyway, I have to say I think I prefer the sound w/ the cat intact. It still sounds badass, and it may grow on me. It is definitely different sounding, more raspy sounding now I suppose. I did not however notice any lowend loss, I just got on it several tims, and noticed no loss. May have actually picked up some performance, I can't say.

For the record, my exhaust setup is TES headers w/ a hooker cat-back. With a 3" cat obviously.

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Ray87Z
-Vortec headed 350.
86 IROC w/ a cammed 305 TPI.
Formerly Ray86IROC.
www.inter-scape.com/Ray

[This message has been edited by Ray87Z (edited March 27, 2001).]

KW87GTA

Does anyway know if I gut my cat and take the belt off my smog pump what will happen in the AIR tubes at the headers? Does this mean that some of the exhaust will have the tendency to climb up the AIR tubes and leak backward towards that solenoid holder into the engine bay, and what about the tube on the Cat too? Will it leak back up that? Thanks.

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87 GTA 350 L98
K&N filters, beefed up TH-700r4, Accel Manifold, Ported Plenum and Runners, Fuel Press. Regulator 49.5psi, air foil, modified MAF, SLP cold air box, Hypertech Thermomaster chip w/160 thermostat, MSD 6AL and Blaster 3, B&M shift kit & megashifter, Moser Ford 9in Rear with Richmond 3.50 and locker, Edlebrock TES headers and Cat Back,Hotchkis setup in rear, Poly suspension and Koni in the front, relocated MAT, bypassed IAC,

Fastest ET's
Stock-0-60 6.8, 1/4 15.0 @ 94
Best-0-60 4.7, 1/4 12.8 @ 112
Norm-0-60 5.2, 1/4 13.2 @ 108

Bort62

1/2 Galvanized Cap will Solve that.



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60 Ranchero - Project ( Money Hole )
85 Sport Coupe LG4 - Daily Driver

Just another Hot Rod kid, or thats what they all tell me.
Livin' the Stereotype

1BadGTA

Does gutting it affect sensors on FI cars? Also I heard that gutting GM cats is a pain in the *** . How do you hollow them out?

Ray87Z

I used a bigass wood drill bit that was around 2 feet long mostly on mine (1/2" bit I guess) in my powerdrill. Along w/ a 2 foot long screwdriver to chop some of it up. Wasn't too hard. I had gutted the stock cat the same way a couple years ago.

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Ray87Z
-Vortec headed 350.
86 IROC w/ a cammed 305 TPI.
Formerly Ray86IROC.
www.inter-scape.com/Ray

SUPER-SPORT-CHEVY

Props to ED! I have been saying what he stated in his Reply! With fewer words of course

Beefy89

I didn't lose any torque after removing my cat,just ask my tires.

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We need Perry Mason

badbird

I'm running a zz4 with no cat and 3" all the way back, and I have absolutely no idea what these guys are talking about when they complain about high pitch. Everyone says my car sounds like a boat with through hull it rumbles so low. And on the 30'th day, god made flowmaster.

Alan84TA

Just gutted mine and put on a hooker catback. It is 10 times louder than stock and with doing both at once I noticed a large power increase. "cat was bad too" I'm sure its mostly from the catback but people can hear me from blocks away now... Gutting it was VERY easy.. took 5min.. used a big crowbar and just hammered it down in middle and then pulled the stuff out in large chunks...

Red Devil

Ed, I would like to expand on your intro a bit. (BTW name off some reading material!!)
There are some things people may want to consider and keep in mind. First, to visualize this stuff easier, picture the waves/pulses as a half bubble traveling in the exhaust. Here goes:
In a two into one exhaust set up, keeping the CC intact, particularly the high flow ones, creates a small amount of low pressure at the CC entrance (still true with a dual exhaust, but it can ultimately be detrimental due to the losses of energy). The Pulses expand in the cavity and are dampened by the structure of the honeycomb catalyst (making reversion negligible). When you gut the cat and do not replace it with a pipe, you are creating resonance waves that travel back up towards the engine (reversion) and can cause a high pressure pulse at the exhaust port that the exiting pulse must overcome.(that was my gist) You also lose the small low pressure area. It is about the same as a nominal flow through design muffler. One other thing to consider, mufflers (the Flowmaster in particular) that dampen by canceling the sound pulses, typically split the pulses somewhere in the body, causing a significant low pressure area just in front of the split area. This does indeed help/add to the scavenging effect of a good exhaust.
Remember the exhaust starts with a disadvantage in that it has to overcome atmospheric pressures at the tailpipe, anything you can do will help, that said, I believe, in these cars, that you would do better to have one on than not. Not many on this board race for cash, professionally or real street racing style, so the losses you may experience by keeping it is so negligible, particularly when you view the potential for damage from increased emissions.
Edit - Spelling!!

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"Education is the art of making man ethical.
-George Hegel

[This message has been edited by Red Devil (edited March 29, 2001).]