Captain_Kaboom

I've got headers, true duals and 2.5" pipes with and H pipe running into 2 cats before hitting the flowmasters. Legality/enivronmental concerns aside, would I gain anything by replacing those two cats with straight pipes?

Disco_Mike

I dont know. I will ask a similar question. How many horses does a cat eat up?

zwede

Depends on the cats. If they are modern high flow cats and you have two of them they rob very little power. Saw some tests a awile back where a 500 hp engine dynoed within 1 hp with and without cats.

rob75383

First of all, I don't have dyno #'s to back this up, but...
I did feel a good increase in power through the whole rpm range, and a noticeable change in the sound of the exhaust. I have hooker headers, and 2.5" true dual going into 2 1/4" repro- turbo mufflers (soon to be replace by a set of SS 2.5" summit mufflers)
Years ago, I had my muffler guy install a pair of walker 3-way cats I ordered from summit or jegs, and then two days after passing emissions, I had him remove the cats, and replace them with 2 3/4" pipes. The car was definately suffering with the cats on, but probably if I'd tweak the tuning, I could've gotten her to run good.
Last year, I decided to gamble, and took the sniffer test without cats. At the time, I had just installed the adjust-a-jet kits from holley on both sides of my carb, and just leaned it out a bit. I passed with flying colors, although it was only a sniff test at idle speed. I did have a problem driving her to and from the test, since she was set for a close to perfect mixture at idle, instead of running her rich like I usually do. Good thing the test station is only about 2miles from my place.
My local emissions stations stopped using the mirror to check for cats, and they do no vehicle inspection other than checking your gas cap. Check your local laws to see what you can get away with.

Captain_Kaboom

Both cats are new high flows. I'd hate to go through the time and expense to remove them if I don't get a significant gain. The car is exempt from emissions & inspections, and I know she runs clean and don't feel guilty about removing them- I just want to know if it will make me some HP....

Boofers

Something else you may want to consider - some people have said in previous posts about this subject that without cats your exhaust smells really bad.

Larry B.

One GOOD thing the cats do is take away odors caused by some of the additives (octane ingredients) used to replace the lead. That's why all of the older cars without cats smell from the exhaust.

81' Corvette Guy

Who the heck is going to be smelling my exhaust....the ricers and vette wannabes ...as I fly by them??? I know I sure wont be smelling anything with my hair on fire...(tops off). Maybe when I go to put her in the garage..but for what, a couple of seconds till I get in the house....? Thanks!

Schmucker

If they are high flow modern cats, and you have two of them, then there should be no cause for alarm. They won't eat power like old ones do. It should be a fairly small loss. Hardly noticable.

corvtt1969

the no cat smell never bothered me nor did i really notice it when i first got the car. 69s dont have any cats and never did. plus people put up with it all the time pre 70's

The Dude

So the converters are after the H pipe? The converters, in a perfect world, would be the next component in line after the header collectors. Preferable attached directly to them. Catalytic converters need lots of heat to work. They're not doing you any good where they are so you may as well take them off.

wgc_3

Here is the real question....

Are you or are you not a green thumb?!

Captain_Kaboom

I drive two V8s- a gas chugging Corvette and a gas doesnt-even-taste-it-going-down swallowing 5.8L Bronco. Do I look like I'm a tree hugger??

Actually I got into an eco discussion this weekend with a buddy that is buying a Hybrid. My vette has a new engine that I bet runs cleaner than a lot of cars on the road.. my big question however is: Is driving a 27 year old car more eco-sound than a new car??

1) You're keeping a car on the road instead of turning it into a junkyard piece
2) How much damage does the manufacture of a new car damage the environment vs keeping a current vehicle?

Anyway, my lame arguements....have to check where the cats are under the car.

Bobchad

Greg,

Hadn't seen you around in a while. Hope all is well.

If you have replaced the single stock cat with two, as I did as well, technically you are not in compliance with the emission laws. You can't make any changes to the stock config.

Bob

billlambeer

Who checks emissions?!? I mean really, i have never even heard of having to go get mine checked around here, im sure its not legal since it isnt too old(79), and has just straight pipes. Just wondering if its like a law that you have to get it checked, or you do it willingly to get the cops off you butt if they pull you over for being too loud?

TTop Tony

I took my car two years ago with duel exhaust,stock manifolds and no cats to the drag race. My mph at the end was 98. The next year I put two free flowing cats on to pass emmissions and got 96 mph at the drage race with the same times of around 14.8. I didn't feel any horsepower loss but I did eventually go from ultraflows to no mufflers just for the sound.

Captain_Kaboom

Tony-
Thanks for that info- I like your stinger hood, btw. Do you have any info on how you did that pop out rear window? I'd kill to have that....

Bob- Yeah FINALLY back on the road and loving it. Glad to finally have a few days of no rain to drive it!

Based on what I've heard I think I'll keep them for now- doesn't sound like they are holding up much power.

Since apparently having two cats is breaking the law as no cats..I guess it really doesn't matter which way I go, huh? I mean, if I get pulled over and a cop wants to make an issue out of it and sees two cats under the car, I stand on getting a ticket just as well as having no cats?

TTop Tony

The popout window was as easy as it gets. I got the window off ebay along with new headliner pieces. The new headliner has a notch cut out for the latches. The latches and weatherstripping are from Paragon reproductions. I pulled the old window out and the surrounding pieces. All the old connecting points are still there for the latches. One of the easiest mods I've done and the nicest too. With the top up the back window out and the windows down you hardly miss not having AC. If you need pictures I'm sure I could take some if you get ready to do it.

Captain_Kaboom

Yeah I'd love some pics! So you just had to buy an older window, and the rest from Paragon? What is the headliner piece?

I have no AC either and it's dang hot here in GA during the summer...