I was wondering the otherday about a downpipe if i were to get a downpipe without a cat or a offroad pipe and would use a O2 Sim will this hurt gas milage or would it be better to run a downpipe with a cat? also which would give me more power without loss of gas milage a 2.5 or a 3" ? i just had these coupple of questions on my mind and i figured i allways get great help on here

The 2.5 vs 3" is a classic debate over on cxxxGP. I personally say 3" just because you will barely notice any torque that you might lose, but your car will feel stronger up top. If you plan on modding further, a 3" is your best bet no doubt.

Probably with both you won't really gain or lose gas mileage depending on your driving habits.

would it be better to have a cat or not... yes i know to be legal and stuff but im thinken about performance and gas milage

there is no performance difference with a cat its just for legal purposes which is why its so darn expensive....i got a 3" with no cat and love it....the o2 sim does nothing to gas mileage

allright i just had those questions i didnt know how all of that would work out

go 3" without a cat. unless you have emissions testing

nope no testing... so zzp gives you 50$ for your downpipe and cat... do they pay for the shipping does anyone know also is it worth getting the extra coating on it ?? and how hard are they to change out your downpipe what would all be needed ... i have air tools so if that helps out at all... in the future i just dont want to get in over my head.... would a 3" bolt right up to the manifold and to the rear section??

3" DP when my GT was N/A still felt pretty good.

The only point of the rear O2 sensor is to see if the cat is doing its job. So if you take out the cat, you'll either want to get the O2 sim or have the code removed via aftermarket PCM (need to request this feature) or tuner. Otherwise your check engine light will be on.


Yeah, just make sure that rear section of the DP is 2.5, cause thats what the rest of the stock exhaust system is.

Its not really hard to do unless your bolts are rusted on good. I had to take mine into a shop because my old one needed to be torched off.

crap... because i dont really want to take it to the shop because he charges an arm and a leg for everything. ok then thanks for the help

x2

for the DP just get some PB blaster and soak the hell out of it and let it sit for a little....you just need a long extention but your air tools would make the job a breaze just dont snap the bolts cauz its a pain in the but....if you cant get it right away heating the rear manifold is also a tip but not the DP itself beacuse that would heat the bolts and allow them to twist instead of loosen.....as fot the o2 sim i have a spare.....could throw it in the rest of the kit for you 4drgt

....PS heating the manifold would be with a blow torch

ok thanks gteisele ... let me see how graduation all works out... and if i can pocket most of my money without the banker (mom) seeing how much i put in savings for school lol but i am looken forward to getting the nitrous and all new exhaust and then soon powertuner... then a coupple sets of tires lol

no problem hope everything works out ok with your banker haha.....where you going to school?

Hawkeye community college in waterloo iowa.... i am going to be doing auto collision repair.... they have a huge shop for a coummity college i am pretty excited to start. i am also ready for this summer so i can start buying some mods!!!!!!!!!!!

i have to treat my banker like many people treat there wives when they get back from vages you just dont tell them how much you spend or lost lol..... so no problems no worries lol

so wait a 3" dp wont fit on a stock exhaust?

they said it would but you have to get a 2.5 end on it ... i think

Correct. The connection is for a 2.5 bolt-up end. Would need to either weld a bigger end on, or just weld it together isntead of having a connection.

so whats the point of having a 3" inlet with a 2.5" outlet? that doesnt seem to work... but are all after market exhaust like the borla have a 2.5 outlet

Because a 3" catback is pointless unless you have really high horsepower.

You want bigger pipe to clear the exhaust closer to the heads, but as you move farther away, the exhaust gas loses velocity, so you can go with smaller pipe.

oh ok.. that makes sense haha well i was looking at the togs and there are 2 types of dp one eliminates the flex pipe the other doesn't im thinking that the one that doesn't eliminate it is better... correct?? it would eliminate any KR..

high horse power were talking like 6 or 7xx's right

I do'nt know where some of you get your imfo but the gain from a stock cat to no cat=9whp and the gain from a hi-flow cat to no cat=3-4whp, as far as a DP 2 1/2" vs 3" on a GT I would have to recommend the 2 1/2" unless you plan on going boosted or are going to go heavily modded N/A now the difference may be small but you will retain a little more low end torque with the 2 1/2" .Chico.