I wouldn't say it's always wrong, because there was a noticable difference with and without the cat. Since I'm running a stock motor with a TPI computer, the car runs better and gets rid of that awful gas smell. Also, it set off an SES light every time I drove it without the cats. I figured the the stock TPI motor was engineered to run with the Cats. So unless you are highly modifying the motor and the computer, then it might be worth removing the cats imho.

I have been messing with these cars a long time and have never had an issue running with out a cat.

The only way I ever had a issue was with longtubes with the 02sensor real close to the edge of the outlet and no Ypipe

well then, what worked for you didn't work for me. I installed the cats back on my exhaust, never had a problem since. I used my car as a daily driver everyday for a 70 mile drive, and it would always set off a light halfway during the trip. I'm not going to argue much further about the benefits of having or not having a cat installed. It's nice to not smell like gas where ever you go, and I'm not running a high horsepower setup that would benefit from removing the cats. Even the ferrari that drives around has to have cats installed.

Lets say your running a single cat/pipe exhaust system that has all the upgrades. How much HP is lost with a high flow Magnaflow cat on ?
It dose not have to be exact, just a ballpark figure.

1-3hp

Why not stock? Have you ever tried this exact combo? The car does have dual 2 1/2in cats. And I did say with a tune custom chip.

Sometimes its not about the power gain, it's about the size gain. Like my car originally is a single 2.5 inch outlet cat. Well I am going with Hooker Headers with Y-pipe and a Borla Cat Back. that stock 2.5 cat won't work for me

You guys have to remember that the RS and low HP TPI's has 2 1/4 cats to a 2 1/2in cat back system. It makes a big difference when installing the right headers, cat(s) and 3in cat back exhaust systems. If your tach redline at 5000rpms, you have a very restricted exhaust system with a 2.5 cat back and the pipes from the manifolds are 2.0-2.25.

Not saying it's impossible, but it's just VERY impressive numbers for what is a mostly stock car.

I've got better heads, better intake/fuel distribution system (as far as airflow, I would love to go to EFI for all the otehr good reasons), and a larger exhaust system with smaller primary long tube headers. I dont buy that LT headers are better for peak power, or that the larger 1 3/4 primaries on the Dyno Don shorties dont make a difference, I've seen the dyno charts that point out the differences.

However... with better heads, better intake, and a GOOD exhaust system, with a larger cam (albeit flat tappet, unfortunately) I'm only hitting 102mph. Now I think it has more in it... might even hit 103-104 with the new gears and in better tune next time I get it out there.

Its HARD to get these Gen I blocks to 300-400 hp levels at the flywheel. You need to know what you're doing. And I just dont see how a stock L98 with exhaust is going from 245fwhp to ~320-340fwhp, even with a tune. You've got to admit that's pretty crazy.

Either way, very impressive numbers and times. Not saying your car isnt really that fast, but I just dont see how it can do that with only headers and exhaust. Thats pretty drastic.

Maybe it's something to do with the T5? May not sap quite as much power out as the 700r4. And my T56 is much heavier, more moving parts, etc, so you're probably at least 75 lbs lighter than me based on that alone.


Edit: I see you have a miniram, is that the car/build you're referring to? I dont normally consider a 350 with 083 heads and a miniram a "stock L98". I see what you mean, just not what I was imagining.

My car was an auto at the time posted and stock with factory runners.

I did Hooker 2055's, 3" catco cat & 3" dynomax cat back on my LO3. I noted a BIG difference.

I was reading an article a while back not sure if it was hotrod or chevy high perform. Anyways these guys were trying to build up a 305 i believe. They bolted on headers w full exhaust a new air cleanee assy and i think a cam and new fuel rods. They saw little improvement on their third gen. Eventually they brought in someone who told rhem they werent getting enough fuel. The stock thirdgen fuel pump is hardly capable of handling the engine as it is and bigger fuel rods will do nothing with an inadequate supply of fuel. I was curious if the 350 stock pumps may have the same problem or perhaps you have a 305 pump? With all these mods they hardly made 15a hp after getting a better pump and adjusting the carb rhe gains jumped up by 50+ hp i was curious to see if maybe youre experiencing the same problem. Are you maybe running too lean? Im consideeing getting a new catback on my 305car which only has a new cam so far and have had very little luck in researching the gains on a stock 305thirdgen w. New cam

from my own experience i have recently in stalled headers an a obx catback an the ebl flash ( i'm tbi ) i run out of fuel at 3275 rpm . i added a external fpr an maxed out the fuel pump ( only 14 psi ) but the car is like night an day difference . my a/f stays 12.4 all the way to redline wot but my injecters go 100 % at 3700 rpm .so i need 15% more fuel psi to get them down to 85% . which will support 231 hp . at that rate i'm up 61 hp . but i'm also running lots of timing 34 degrees at wot . i'm gonna buy a tpi pump which will run 60 psi . i'm adding a t70 turbo an a 454 tbi with 80 lbs. injecters to be sure i got plenty fuel . an my gas mileage went up from 15 mpg highway when i bought the car to 24.5 highway as of right now . just my experience i thout i'd share .

Most of you guys are confusing muffler flow with pipe sizing. A single 2.5" straight pipe with NO bends and NO muffler is NO restriction for an engine making 260 HP at the crankshaft. But none of the bolt-in mufflers flow that well, not even the 3" offerings. And it's the same deal with cats, but back to mufflers: There are a few aftermarket mufflers that do flow that well, but installing them means some cutting and some welding, and they're rather loud.