Yes I know there are a million threads out there already but I just want to compile what I'm looking for.

Ok so I'm trying to think of xmas ideas and I started looking at zzp downpipes (catted). The 304 seems a little too much, but how do the reg. 409 or whatever they use compare? I mean the car already has 160k on it so I don't really need top of the line.

Also, is there any difference between bolt in and weld in, besides the obvious?

What type of gains will I see with a basically stock GTP? From the info listed it seems that you lose out a little low end torque, but gain in the high end. If I'm not racing at all then would this really be worth it to lose low end torque?

And I'm assuming I should get front and rear gaskets as well?

Thanks.

With a GTP getting a 2.5" you should lose no torque. The gains will be more noticeable on a GTP than a GT. You want a bolt in with cat and yes, get both gaskets. For a few days prior to doing the DP. Spray the upper and lower bolts with PB Blaster or similiar so they come off without breaking when you do it.

Do you have aftermarket muffs? A high flow DP which has no u-bend will make your car louder and give you drone and rasp if you have chambered mufflers.

As for gains, besides a louder exhaust note, maybe 10 HP on a good day, but definitely less knock retard which is GOOD for your motor.

Approximately 50% of us with high flow DP get P0420 after install. You will either need a O2 sim or code delete on your PCM. Read the very bottom of the DP page at ZZP.

Add a Plog now and you are off to making power.

http://www.performancepeddler.com/detail.asp?PRODUCT_ID=MAG23405

Best DP for $140.

Nobody should be getting a 2.5" downpipe. Especially not a GTP.

Can't you get the O2 holder/bung or whatever that holds the old 02 sensor?

And Zalfrin, why no on the 2.5?

And what about the 304SS compared to the reg steel ones they offer?

There is already a bung for the o2, it's just that the high-flow cat may cause a code to trip.

3" is superior.

I think losing like 1 ft lb of tq at like 2k rpm is worth the hp you make everywhere else.

Never do a 2.5" on either a GT or GTP.

x2

I do not know how that myth got started, but a 3" DP is the best for every application of these cars.

Ok so 3" it is, what about the two material types they offer?

You're up north, so go with the 304.

From ZZP's website:
2.5 inch downpipes are designed for naturally aspirated applications where no loss in low end torque is desired. They can also be used in supercharge applications when the lowest possible cost is important.

How much do those 304 DP's cost? you could get stainless headers for the price of that DP with a little more

I guess that answers my question as to where the myth began. That statement is completely false and there is dyno proof of it.

Actually that statement isn't false lol. The 2.5" was designed for N/A cars and you deff won't lose torque haha. But what they forgot to mention is that a 3" is the best choice for any GP from N/A to S/C to Turbo. 2.5" is death on any setup because it holds back power.

lol. I guess you're right. They just leave out the important part.

This argument has come up so many times that it is fool hardy to even have to prove.

Hes not wrong and his statement is quite true and there is a idk how many page post on CGP proving this to be right with loads of dyno proof.

It just gets annoying to have to keep going back and looking up info and having to prove a point over and over again.

Tell me about it...
I guess that answers my question as to where the myth began. That statement is completely false and there is dyno proof of it.

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Since you brought it up. Do you have dyno proof to back up your claim? If not, then your statement can be considered completely false also.

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http://www.clubgp.com/newforum/tm.asp?m=4571652&p=1&tmode=1&smode=1

There is some reading. I'm not going back to find the dyno charts again. They are over there somewhere, but it's finals week and I really don't have time to spend an hour searching.