Just got a GTP, have a few questions for the experts

**blueguy** · 05-26-2009

Yup...LS1 needs a cam, headers, rockers, intercooler, stuff like that...things you don't want to do. A Ported Supercharger and Stock Throttle Body are great mods though that in perfect conditions might net you MID to HIGH 13's.

**LSXHP** · 05-26-2009

Hmmm...sounds like mid to high 13's is more realistic for the money im willing to dump into this car. How restrictivw are the stock mufflers, and how many cat converters are on these? (storming like crazy out cant go look for myself today lol)

**LSXHP** · 05-26-2009

Also can anyone answer my question about what down pipe I should go with? there is quite a selection on ZZP like 3" or 2.5 or "Shorty? whats that? Might as well eliminate the one cat if its a significant increase.

**superv6** · 05-26-2009

Let's see. Anything after the cat is ok for ur application. Changin muffs would only change sound not performance. And u have a gtp so most people would say 3" catless downpipe. That will give u a much better flowin dp and get rid of the crappy u-bend whwre the o2 sensor is. U only have the one cat on ue car so ur good there

**Sabrewings** · 05-26-2009

Shorty is a weld in version.

**blowfishRus6** · 05-26-2009

i dont think shorty takes care of the ubend either.

**Sabrewings** · 05-26-2009

Originally Posted by blowfishRus6

i dont think shorty takes care of the ubend either.

No, but if you're welding it in you're not going to weld the u-bend in are you?

**blowfishRus6** · 05-26-2009

then you would have to cut the ubend out and weld in a straight pipe in its place.

**Sabrewings** · 05-26-2009

Originally Posted by blowfishRus6

then you would have to cut the ubend out and weld in a straight pipe in its place.

That's the point to a shorty...

**blowfishRus6** · 05-26-2009

well you said weld the u bend in. its already in, you have to take it out

**Sabrewings** · 05-26-2009

You don't have to take it out since it's already removed when you remove the old DP. Most people just cut the whole thing off and weld it to the catback directly.

**blowfishRus6** · 05-26-2009

Shorty pipes weld directly to your factory converter. They do not replace the Ubend. They are generally used for custom applications and defective OEM downpipe sections.

sounds like you weld it to the factory dp after the cat and aperently it stops before the ubend because it does not take it out.

but thats just going by zzp

**LSXHP** · 05-26-2009

K...so sounds like I should go with the 3" DP...is this thing gonna be much louder without the cat? How restrivtive is the cat on these cars?

**blowfishRus6** · 05-26-2009

its not really going to make a difference with or with out the cat.

yea i would go with a 3in bolt in.

**LSXHP** · 05-27-2009

So i'm thinkin of ordering the 3" cat less down pipe,3.4 pulley,180 t-stat and those autolite 104's this afternoon. would that combo be safe if i run 93 octane on the stock pcm for a while? Then when i decide who i want to get the pcm from ill gef it tuned for that and probably get that power log too.

**blowfishRus6** · 05-27-2009

ehhh you might wanna wait till you get a tune. stock tune is not going to put in enough fuel for the extra air of the 3.4

**98SilvermistGTP** · 05-27-2009

Hey man, one more thing, if you get a catless downpipe, either get a PCM with the rear O2 trouble code deleted or get a rear O2 simulator. I did not notice any difference whatsoever going from an RT 3" bolt in downpipe with cat and a ZZP 3" bolt in downpipe without cat. Getting a downpipe with a cat will be about the same price as a downpipe with no cat and getting a simulator.

**superv6** · 05-27-2009

That's true it would b about the same price. I don't think thwres much if any of a difference. I would wait to get the pulley till u get a tune and at least a dp and a plog or headers. I got the dp without cat and got the o2 simulator. I think I sounds great. Deeper tone u know

**Bio248** · 05-27-2009

catless downpipes suck. the cat helps with a deep tone and less rasp. if you have enough money, get one with a cat.

also, youre not going to want to run a 3.4 without a good tune. do all of the flow mods first, then buy a pulley later. your car will feel awesome after you open up the intake and exhaust.