Cutting out the cats will it mess anything up?

[Jakethesnake73]

So ever since i got my blazer i have had an intermittent lean oxygen code and im thinking the cats are bad. I already have no mufflers and want to make it a true straight pipe. Will it mess anything up to have no cats? The check engine light will turn on right? Can i bypass that check engine light temporarily untill i have to get emmisions again? Will it hurt power in any way?


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[Irish_Alley]

yes and no. if you just cut them off you can experience lack of power if you dont tune the engine.
read this
and this

[Jakethesnake73]

I cut the cats out and put about 3ft of pipe on the ends and defiantly lost some low end. And its loud. I now have a dual input and output muffler coming in the mail. Will that fix my back pressure issue?


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[Irish_Alley]

im no exhaust expert. but does the muffler run a true dual path or does it combine the two pipes exhaust gasses like a x or h pipe would?
if so it will help, how much idk. im kind of waiting to hear from your experience to see the outcome.
do you have any bends in the pipes?
what size?
headers?

[Jakethesnake73]

im no exhaust expert. but does the muffler run a true dual path or does it combine the two pipes exhaust gasses like a x or h pipe would?
if so it will help, how much idk. im kind of waiting to hear from your experience to see the outcome.
do you have any bends in the pipes?
what size?
headers?

I get the muffler in tomorrow afternoon. Ill post how its setup. I just bought it because it was cheaper than buying 2.  I just have the stock exhaust manifolds and theres no real bends in the pipe. Just what it takes to get from the manifolds to the right level and a few little bends to get around the drive train. When i get the muffler ill weld in some pipes so ut bends out and exits before the rear wheels. Ill post pics tommorow as well


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[Jakethesnake73]

I think its 2.25" pipe my previous mufflers had an id of 2.125 but the pipe seemed bigger than where i hooked up the last mufflers


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[Irish_Alley]

now where do you plan on meeting the exhaust pips to joint them at the muffler ?

[Jakethesnake73]

now where do you plan on meeting the exhaust pips to joint them at the muffler ?

im not sure yet. As close to the transfer case as i can. Idk if it would hurt to use a 90 degree joint to bring the pipes together


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[Irish_Alley]

this is just for grins but you doing a 45 before the tire or a 90? i think its going to be tight cause you have to pass the t-case then the muffler is going to take up some space then you have a tight bend before the tire. i think your power wont be hurt too bad and you should do just fine

[Jakethesnake73]

this is just for grins but you doing a 45 before the tire or a 90? i think its going to be tight cause you have to pass the t-case then the muffler is going to take up some space then you have a tight bend before the tire. i think your power wont be hurt too bad and you should do just fine

returning the muffler. Theres not enough room to get everything where it needs to be. Ill probably be putting my glass packs back in. Fyi the muffler im returning isnt a straight through


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[philo_beddoe]

I was told my 77 c-10 is loud after a new system for three reasons; large pipes, no cats and dual exhaust, no H or Y pipes. So its real dual.  Should i be concerned about power and back pressure?

[Irish_Alley]

concerned? no. but you will notice some power loss without a proper tune

theres a formula you can use but its based off your hp. youre intake need to flow 1.5 cfms per hp and your exhaust needs to flow 2.2 cfms per hp. so lets say you have a 400 hp engine. your exhaust needs to flow 400x2.2=880 cfms. a 3.25" pipe has a pipe area of 7.67 and a pipe can flow 115cfms per in². so a 3.25" pipe can flow 882.5 cfms. anything more than 3.25 is over kill and if you run true 3.25 duals it can support a 800hp motor.

but like we said before theres more to exhaust than back pressure you also have scavenging and velocity. scavenging is a good thing its the pulses in the exhaust that help pull the gasses out of the head. back pressure is bad but running too big of pipes is just as bad cause it screws up the velocity and scavenging effect.

[philo_beddoe]

Interesting, i just installed a new system, true duals, and it still sounds like my muffler has holes in it, too loud i think.  I have no cats, what should i do to make it quieter, the right way.

[Irish_Alley]

what size pipe? any bends? if you can play a video

[philo_beddoe]

I'll have to measure. But probably larger than stock.  My friend who did the work had to do a little cutting and welding but nothing crazy. He said its loud for three reasons.

1. Dual system
2. No cats
3. My pipes are large