FAQ Board This board is where some of the most informative and helpful Frequently Asked Questions we get here at ThirdGen.Org are put for easier reference. This IS NOT a general question board.
Thanks for the info, I can't believe how much I learned about my car today reading on the message boards. This site is awesome. Thanks again for your help.
Ive always been iffy about removing my cats, ive had people tell me it can actually be a hp loss and can result in low backpressure which can lead to other problems and trouble codes my local speed shop said they put a firebird on theyre dyno the owner took the cats off and brought it in a second time and it resulted in a 9hp loss. Is there any truth to this is it possible to actually lose hp even though your improving flow.
ur friend is smoking crack..there is no way removing the cat takes away horsepower either way u put it. and arent u gonna get a little bit mroe back pressure when u lose the cat since it can breathe easier.
well, i have read that w/o the cats or air system, the computer doesn't get proper feedback, from these components, and richens or leans out the air/fuel ratio, causing a loss of power.
Loss of back pressure would not cause a power loss, but losing too much backpressure, and having too large an exhaust will cost you torque in some cases
For example, 1 3/4 headers, no cat and 3'' exhaust would probably not be the best choice on a stock 305
IMO, if you have emissions, get a high flow cat, and get computer tuning if you are going to rid your air sys.
No cat here for 5 years. Always passed Mass smog tests. Never ran rich or lean. Never had a problem with back pressure (people remove them just to lessen back pressure, why else would you...?)
Until 2001, I lived in a rural area in MO, so the inspection was visual only, no sniffer. Over a period of a couple of days, my car started losing power, and eventually wouldn't go over 45 mph. Started fine, idled fine, no codes, just a really choked sounding engine. A "free flowing stock cat" fixed the problem. .
In 2001 I landed a job in Dallas TX, so I packed up and moved. Eventually I decided I wanted my car to be 100% TX legal. I knew the "condition" of my cat, but decided to push my luck anyway. The smog check at the time was a test that included idling and a simulated cruise test (the rpms were upped, thats all, no load.) I failed miserably. I had a new cat installed, and passed the follow up test with flying colors (only emitted like 25% of the allowable limits across the board.)
Sometime in 2003 (I think) the whole metro Dallas/Fort Worth area stepped up to the dyno style tests (I must say that if these types of tests help, I'm all for it, as the air pollution here is BAD -- red ozone alerts for consecutive weeks.) My first dyno smog check went horribly. I failed across the board.
Back to the drawing board. I completed a full ignition tune up, oil change, and found a small crack in the vacuum hose to the EGR valve. I also filled up my tank with premium after adding a bottle of RXP fuel kicker (I figured it cant hurt.) The follow up test went smoothly and I passed. I was amazed that my the 15 year old IROC was only puffin out like 1/6 of the allowables, and was low on NOx as well.
Always fully warmed up before testing.
Was the answer to my problem the cat (obviously it was early on), the vacuum/EGR issue, the tune/oil, or maybe just that little red bottle of additive?
IMO, on a relatively stock engine, the cat causes a mere loss in hp for quite an improvement in emissions. I would not remove it unless you are putting a new one in its place. Performance gains vs. Air Quality/Legality is a no brainer for me. Its nice to jump out of my car, hand over the keys, and walk away from inspections and not sweat it.
FYI-
86 IROC
LB9 TPI
summit "TPI" cam 204/214 @ 0.050 .420/.442
3.42 auto
GM performance fast chip
ram air
screens removed on MAF
Last had it on the track in 1996 -- 9.5's in 1/8th(stock) before the cam/chip/engine rebuild/intake mods
Go with high-flow cat and keep the environment clean. A properly tuned engine with a good cat will burn clean and have output almost as high as no cat.
I live in CA. where the smog Nazi's rule. I flanged my exhaust where the cat resides and had a free flowing cat made:
I kept my smog pump in and cut the air injection tube. When I go to smog, I hook up the cat and the tube with rubber fuel line. BTW, it really makes your exhaust louder!
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Here's my project '54 Chevrolet P/U: http://67-72chevytrucks.com/vboard/s...d.php?t=212753
'54 5 window TPI 5.7/700R4/10 bolt posi w/3:73
'88 IROC TPI 5.7/700R4/ 9 bolt lim.slip 3:27
'99 Tahoe Vortec 5.7/4L60E/ 10 bolt posi w/4:11 Doing my part to warm the globe
I guess under the tires is better than the cubby where the windsheild washing fluid tank used to be. God what a mess that made after I started the car.
BTW, it really makes your exhaust louder!
