ok just got a 40 series flowmaster put on and i replaced the cat with a straight pipe and it seems a bit sluggish on bottom end. Just wondering if removing the cat would do this or if its more from the muffler, or both. Also, anybody have any experiences with lower gas mileage after removing the cat? it made my exhaust about 10 times louder but i didnt think it would affect the mileage. just curious, thanks

 

Did you up the size of the piping?

Removing the cat could cause loss of low end power but will free up the high end power. Its a trade off. I would recomend putting in a freeflow cat to see if that helps.

 

yeah went to 2 1/2 inch pipe and it is pretty sluggish on the bottom end. It was running fine all day today and then just a few minutes ago i drove it and all through first gear i was hardly even moving and it took untill about 2500 rpms in second gear to finally feel the truck get up and go. I hear a rattling sound too, dunno whats up. Ill check it out in the morning and post up what i find out.

Im deffinately thinking about a aftermarket cat, it just has been a hassle since i ended up paying 60 bucks to replace the cat and dont want to spend more money putting a new one back on, but thats a whole different story......

 

what engine do you have?

22re or 3vze

If you have the 22re then that noise might be your timing chain.

In any sence a 2.5" straight pipe is way to open for these engines..

 

why would his exhaust effect the timing chain?

 

yea its the 3vze, and if a straight pipe is too open then would it be better to add in an aftermarket cat or adjust the mixture (If that would even help? i know nothing about EFI....)??? But i race motocross and i know on my bike i have to rejet the carb when i get a new exhaust, so im assuming the same would hold true for a truck, but like i said, i know nothing about EFI.

So which do you reccomend is easier, if this is my problem, im still going to check it out today and see what i can find.

Thanks

 

EFI tends to adjust the mixture for you (within limits)

 

2 1/2" is on the larger side of exhaust pipes for the 3vze. Increasing your exhaust pipes just a 1/4" in diameter adds 23% more volume to your pipes if they are all the same length roughly. That's 23% more volume that your exhaust gases must remain hot in to move. As soon as they cool they start to slow the flow which hinders exhaust flow and works against your engine. But when you rev the piss out of it you are getting more exhaust pulses which starts to move the exhaust again.

 

well thanks for the help so far, i took the truck out for a drive this morning, it seems to rune fine. The noise was coming from up front towards the fan, either a bearing or a belt, but i sprayed it down and it stopped for now, ill keep an eye on it.

as far as the exhaust goes, truck is sluggish on bottom end but i can deal with it, it runs better than before im just wondering if it was a mistake to up the size of the pipe. It seems to have destroyed my gas mileage though, which sucks because it wasnt that good to begin with.

just one last question, will placing a cat back in instead of having a straight pipe help boost my mileage a little bit?? something like a flowmaster aftermarket cat or something

 

I still think 2 1/2" is too big for this engine, but in the meantime put your cat back in. Cat's heat up as they cook/burn off excess unburned fuel from your engine. This will keep your exhaust products nice and hot and may help them flow better, as remember exhaust gasses are under pressure and the hotter they are, the more pressure they have, as the gases seek to expand to areas of lower pressure i.e. out your tailpipe where there is atompsheric pressure. If they lose their heat, they don't expand as well, cool down, and slow the flow of exhaust until you rev the engine more which gets more exhaust pulses moving. If the cat still doesn't help, I would consider downsizing your pipes to 2 1/4" max. In fact Thorley has their 2 1/4" Mandrel bent system with the Jardine muffler which is a good overall bet for this engine. You know I honestly think that if somoene made a 2 1/8" full mandrel bent exhaust system from exhaust manifold, to cat, from cat to muffler and from muffler out, it would be absolutely perfect for this engine. But 2 1/8" is more of an exotic size and good luck finding an exhaust shop that has the dies to bend that size. I have the Borla catback on my truck and it's 2" and lots of guys have praise for the 2 1/4" jardine system. My Borla system is aimed more at torque and the torque improvement is awesome and it revs a bit better up high. If I had another 1/8" I think that would help a bit for the overall power band.

 

thanks, that makes sense, i trashed the cat but i might end up buying one soon. I just checked my codes and got code 21. When it cools down at night the truck runs pretty bad, so im thinking the o2 sensor is out, is there a way to check the sensor before spending the 60 bucks for a new one?

Ive checked my wires and they dont seem to be melted/damaged. The sensor is stock as far as i know and i have about 204k on the truck so im sure its prob worth getting a new sensor.

i want to see how it runs after working out the o2 sensor first, and if i still have similar problems i may reduce my pipe size and/or add a cat.

 

A new O2 sensor wouldn't hurt, but in most cases it should throw a code (is code21 an O2 sensor). I think there is some way to check the conductivity of the sensor but I'm sure someone with more experience will chime in.
Put a high flow cat on and get a new O2 sensor and you should be set. If it still sucks bottom end wise, consider going to smaller pipes, OR going with some headers as they may help with scavenging/movement of exhaust a bit.

 

thanks alot coed, you've been a big help. The truck is throwing a code, and yes 21 is an o2 sensor. Im not too concerned about the loss of low end power at the moment, i just really want to fix my mileage.

My gas mileage dropped from 17mpg to about 12mph.
Is this from the muffler, larger pipe size, or removing the cat... or a lil of all i guess.

 

o2 sensor can have that negative effect on gas milage

 

how so?? even when replacing with an OEM part??

 

Also, flowmasters have one of the best sounds, but there are definately a lot of better flowing mufflers out there.

 

He ment when an o2 sensor goes bad it can effect gas milage pretty significly ( around 5mpg )
You can get one from www.sparkplugs.com for pretty cheap, I got my NTK for 38us or so.

But I would slap on a cheap cat at the same time, magnaflow's are pretty cheap.


Drew303:

I ment the rattle might be his timing chain, but since he sprayed the front of the engine down and it stopped, I would assume its not..

Sorry if I wrote it confusingly. (is that a word?)

 

that rattle could also be the muffler tapping the frame when going over bumps or whatnot... if you dont do anything else for a while i'd at least butt weld in a peice of pipe thats the same diameter as the rest of the exhaust(instead of the bigger piece you put in place of the cat.), for the time being..

 

well i drove the first time on the highway today with the exhaust, deffinately get better highway mileage, but my city milage dropped about 5mph. whatever im over it. Ill get a new o2 sensor and be good to go.

the thing runs great when warm, but ive noticed after sitting all night it runs terrible, so im worried how it will run in the winter haha. guess ill have to get a cat on there before hand.

thanks for all the help