Exhaust, Custom or order?

F

FluxCapacitor

Member
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2003 Mazdaspeed protege
I currently have a stock exhaust with a downstream o2 out. I'm going to replace the exhaust and o2 sensor. I would love to get deeper tone with just a tad bit louder. Previous owner knocked cat out which is probly the cause of my o2 sensor failure. My questions are, Can you get a 3" cat and a 3" downpipe weld them up and go custom exhaust from there which I figure $100 - $150ish or less for custom piping and welding, plus Muffler, downpipe, and cat cost. I'm probly looking at $400 or less for a 3" exhaust or maybe even 2' 3/4" and everything to match?. This would repalce sensor and full exhaust from turbo back and with cat so no cel. Is this possible or do I have to run a stock 2.5" exhaust with at least 1 stock sized cat to no throw a cel for it. So this method over ordering one which would be best. Not to mention installation of ordered exhaust and o2.
 
i havent found a down pipe thats cheaper then 350 for our cars so your budget is way off, you can get o2 sensor simulators so you wont throw a cel code, or get the spacer thats what i run on mine and dont get codes, i have no cat at all just straight pipe from the j pipe back whick i need to change!!
 
Yea ive been doing some more reasearch and there pretty expensive. I go to a high performance college and its a great college I recommend it, But anyways I was thinking about custom making one myself but it would also be a hassle lol. Its alright I have some mroe cash for an exhaust, I just got the msp last weekend and a great car. I think I alos have the piece your talking about. I will add a pic here in 10 min or so. It's like a piece that screws onto your o2 sensor and then your screw it back into the exhaust. Is this the piece your talking about??
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Yup that's the piece.


As for making the exhaust. I would say buy a downpipe, and custom the rest. (for me) it was fun making the exhaust. It was a good learning experience. I went with 2 resonators, with 2.5" piping and an N1 type muffler, deeper tone without the rice.
 
Yea i think thats what im going to do. Coming from the dsm world here, how does the adapter piece work?? Does it just restrict the flow of exhaust gases that meet the o2 sensor? Because if you think about it, the o2 measures presence of unburnt fuel, wouldnt it still detect the richness or lean in exhaust just as much. I mean i understand theres a whole in to to restrict it but, for me its kind of confusing a little bit. Let me know im looking to learn something new today haha.
 
The O2 sensor actually does not measure fuel, it measures the amount of oxygen in the exhaust stream, hence the name. An unburnt mixture will have more free oxygen than a burnt charge. The sensor, whether narrow or wideband, can't tell that there's also fuel in the mixture, so it's tricked into reading leaner than it actually is. I'm guessing the spacer just reduces the amount of air passing the sensor, so it reads less oxygen.

A word of warning: with a straight pipe, you get less backpressure, which scavenges more air/fuel mix out of the cylinders during the overlap period. Some of that is good, obviously, but too much causes our cars' hesitation/misfire problem to get worse; you can read jdwk's writeup on why here, but the gist is the #1 sensor reads lean as the turbo spools up, the PCM trims rich to keep it stoichiometric, then when it kicks over to open loop at ~4k the stock rich fuel map plus that rich trim causes the mixture to be so rich that the spark plug can't ignite it, so you get misfire. This happens intermittently on the stock car, but the lowered backpressure makes it worse, since that unburnt mixture makes it look even leaner to the O2 sensor. Basically, if you get even a 2.5 inch exhaust (stock size is 2.25), I'd reccomend getting something like the SSAFC; I don't have mine yet, and my car with a 3 inch CS straight pipe bucks like crazy at about 4500 in 2nd gear, every time I put the hammer down.
 
Thank you for all the info carlinator, very helpful and usefull. I have a Ssafc, it came with the car, I got the car, with motor rebuild with new tranny less than 40,000. Extra motor and trans both in good condition with 120,xxx, and a brand new head with some mods and all is good for only 4500. I got lucky and am very pleased with the car and would love to make this my nice project daily. Future plans are 300 daily and 400 to 450hp for fun. What all would i need besides for a fullybuilt bottom end. If u were to build for 400. what would you do? I will be getting the car tuned here soon after i get all the cel to go away. Buying 1 sensor at a time b/c there expensive as F**K(boom08),(nailbyt)
 
I'm not too sure about 400hp...im sure its acheivable but my car running 14lbs of boost is probably making 210ish and i was pulling Trans ams pretty good, i pulled a car on a sti that had boltons, for me a good goal would be 240-250 wheelhp cause its a realistic goal and I'll be stomping on most people i pull up too!
 
Oh and i cruise around with my cel light on it doesnt bother me, i know exactly why its on, and periodically i get my friends code reader and check it and clear it, Cel is emissions based so i know that as long as im runnning good afr's and check the codes once in a blue moon it wont be hurting anything
 
Yes I wish I knew how to use the split second a/f controller, I don't have a wideband yet ethier, so as far as I know it'son stock tune, Im getting lean bank 1 and no downstream o2 sesnor activity, car will be getting tuned here soon. I have stock motor, bored .020 over, custom ic piping, manifold, wastegate, stock exhaust, stock fuel, fmic, vtcs and vics removed, port and polished intake, a fuilly built head is going on soon, and soon to come is injectors fuel pump, exhaust, and some few other mods and a tune should put me right around 230 which is what I would like for now.
 
Another thing is running the car with the cel on does affect the cars performance I have dyno proven this so it's not a good idea, as for exhaust if I were you this what I would do... 2.5 downpipe then after that custom 3 inch back to stock muffler with no resonator and make sure the piping is as straight as possible with the least amount of bends for better flow.
 
14 pounds of boost and only 210? that can be reached with like 8-10 pounds with bolt ons. You should be well above that
 
i was just throwing a number out there based on what other msp's have run but yeah i realize that number was way low balled now, i plan on getting the pope cast piece for the downpipe and then just making a 3" all the way back with an electronic cutout right before the front seats, for the price of the whole pope pipe with the flex section and flange i can buy the cast piece get a flex section and the cutout for the same price we have a place here local we can pick up the 3" pipe for reasonably cheap so next mod on the list after i get my ssafc in.
 
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