Thread: 98 GTP Coupe-upgrade questions-exhaust

First off, I would like to say that I am a newbie, so these questions might seem weird or maybe plain old stupid to you. I appreciate any information or opinions that you might be able to provide for me. I have read many of the other posts on this site and have not gotten all the information that I wanted from them so that is why I am asking. First off this is a daily driver car and will remain that way, and I am not taking it to the track to race. I do like to have fun when I drive though. I would like to leave a cat in the system and the O2 sensors in place without throwing any codes and also I will not be putting in a cat-back system and I am going to leave the stock exhaust in place behind the cat. I have read that the most restrictive part of our exhaust is in one side of the motor and the u-bend and stock cat. My question is if I am thinking of going to the 3.4 pulley but want to make proper mods first. I am willing to put in a CAI system and I wanted to know if a PLOG and a downpipe from ZZP are all that I need other than a high flow cat to make this happen the "right way." I am not sure if I can get away with one PLOG, or if I need the manifolds on both sides or if this is sufficient to get to the 3.4 setup. I will also get a tune obviously as well, but on this post just wanted to get a complete list of what I will need on the exhaust side of things. Thank You

I am assuming that the powerlog bolts directly to the downpipe which bolts directly to cat? or is this incorrect? Is the ZZP PLOG and Downpipe w ubend delete sufficient for the mods I will be doing or would it still be beneficial to have the headers? How much HP am I passing up on if any if I would use the PLOG/Downpipe vs. the header set up? Can I use the O2s on either setup?

yea plus if you light is on all the time then if something was actually bad you wouldnt know

Is it worth anything performance wise to use the stainless steel DP that ZZP offers? Is the 2.5" big enough for using due to the fact that the rest of the exhaust is 2.5" anyway? Or is there a benefit to using the three inch even though it has to be downsized at the end of the DP? Remember, I am not doing major mods to this just want to be able to do the standard 3.4 package and get the most out of it. I will have a cat in this system and would like to keep my O2 sensors in the system as well. Thanks..Yes as stated above, throwing codes is bad........

so how much HP gains would I expect to see from the CAI, 3.4 pulley, and the Plog and downpipe changes( I already have 180 t-stat) and the tune? how much torque changes as well........I am just looking for approximate changes not exact numbers. Thanks.

Originally Posted by bluegtp91

Quit thinking about the pulley. That is why I posted that thread up there...you got a bunch of mods to do before you safely drop a pulley size. CAI, Colder Plugs, Plug Wires, 3" DP, U-Bend Delete, Front Powerlog, OR Headers, and a tune.

Then you can drop to a 3.5" or 3.4".

I am not thinking about doing the pulley until last, but I am thinking about doing it in time. I did read that entire 3800 upgrade thread before I started this thread. Since I did not realize exactly what exhaust components there were totally, and what each aftermarket piece replaced on the stock setup. That is why I started this thread to get more info and do the mods in the "proper order" before finally changing out the pulley and getting the aftermarket tune. I just wanted to know what type of HP gains I could possibly expect when I was all said and done with all of those changes(T-stat 180, PLOG, 3" downpipe w/ubend delete and high flow cat, CAI, Tune, and then pulley) I am just trying to see if it is worth the money to me to spend to get how much HP........Is it twenty HP or fiftyHP or what? I just would like a guesstimate of how much it will help in the HP department. Thank You

Originally Posted by bluegtp91

Well...everything in that thread is listed in the order you should do it in, being pulley last, like I had stated above. Pulley alone is said to net you 20-30 crank HP and since you do every other bolt-on 3.4" supporting mods, I would say about 15-20 wheel horsepower from the PLOG, DP, CAI, Tune, etc. and another 15-20WHP from the 3.4"...so expect your car to dyno about 200-210 FWHP stock and about 230-240 FWHP after all of those mods. And yes...every mod before the pulley is worth the money.

I appreciate everything you have said so far, but back to my question that I asked earlier.....is it worth it if I will not do any modding beyond this, to install the headers or can I get most of the power through the PLOG and the 3" downpipe w/ high flow cat? How much HP if any would I be missing out on by choosing the above setup over the header set up. (Just trying how to get the most for the money) Thanks again........

if youre not going past the 3.4, powerlog and ported rear is fine w/ downpipe

Originally Posted by minichopper6hp

if youre not going past the 3.4, powerlog and ported rear is fine w/ downpipe

In blue gtp's upgrading the 3800 thread it does not mention that you need a ported rear(manifold is what I assume you mean)--Is this step necessary or not?

I hate to be a PITA but how does this upgrade change the gas mileage if at all under normal driving conditions......I imagine it will get worse MPG when WOT, but at hwy speeds, or city driving is it any different than stock?