sorry I'm new at this and did some research but I got confused.
If i were to change my up pipe would it give me a increase in turbo lag or will it decrease my turbo lag, and would it increase the hp? sorry i got confused because some people say with a smaller diameter up pipe the turbo lag decrease while with a bigger diameter it will increase my lag time? but then someone also said the opposite. So I'm a bit lost, is bigger better? or smaller is? Oh and what would a gutted up pipe do?

Help please!

 

A catless uppipe will typically decrease your lag times and give you a slight increase in HP. You won't see the full results unless you go with a turbo back or at the very least a catback. With that said, the very first exhaust modification I did to my car way back when was an Uppipe and I could tell by the boost gauge that I was spooling faster. Seat in the pants was hardly noticable though.

Bill

 

Oh thats about right i guess... but the sizing of the pipe, does that matter?

 

hahah dude that is the same question i posted: https://www.i-club.com/forums/engine-power-ej20t-pre-2006-wrx-jdm-60/up-pipe-hks-vs-helix-139939/

something too big is bad, i would still like some more technical info, comparing different diameters

 

the uppipe diameter being good or bad boils down to velocity through the pipe. I am not 100% sure about larger than stock turbos and what size you should use with them but for the stock one I am gonna pick up Cobbs uppipe. smaller uppipe=higher velocity=quicker spool and vice versa but you dont want something the size of a straw obviously. . I think the Cobb uppipe is the stock diameter minus the cat.

 

any uppipe without the oem cat should basically give u less lag. Typically a non-flex (gives less turbulence or disruption) uppipe in the 1.6-2.0" in diameter is good enough and the differences are negligible.

The purpose of the change in the uppipe is to take out the cat and decrease your spoolup times. You'll get better torque than hp, but with just an uppipe alone u won't feel much difference.

But as for your original question, going smaller in diameter with the uppipe is better for faster spoolup times.

With the downpipe, some say going bigger (3") is better, but in reality 2.5" is good enough if u plan to run with the stock turbo in place for quite some time.

 

oh... I get it.. heres my other question that came up as i read your post. Correct me if im wrong please. The smaller diameter give faster spoolup because it cause restriction right? if so then wouldn't adding a 2.5-3.0'' Downpipe be kind of weirded because your already restricting the uppipe but then all of the sudden you making it flow faster...? a little lost in the concept. Oh and if i go catless on downpipe or uppipe maybe even both would i still pass smog?

 

u want little to no backpressure on turbo cars. Hence the reasoning for 3" piping for downpipes. But like I said before, if you're on the stock turbo, which is pretty small in size, 2.5" is good enough.

You won't pass smog going catless or with only the uppipe cat. If you removed the uppipe cat but left the 2 other cats, u could pass smog.

 

basically: the exhaust flow has already gone through the turbo compressor and you want that stuff out, you wanna make the turbo spool up quickly, hence the different sizes of aftermarket up's and dp's

 

But If i want the stuff out quickly then why would the smaller diameter of the uppipe help spoolup faster?

Sorry guys I hope I'm not asking much, BUT i really APPERICATE this!!

 

A standard rule in fluid dynamics is that when you take a fluid in motion (which is what hot air behaves like) and narrow the diameter it is traveling through, it increases in velocity. This is why the nozzle on your hose makes the hole smaller when you adjust it for a stronger jet of water. Thus, a narrow up-pipe (or a tapered one, like the APS pipe) squeezes the exhaust gas and makes it increase slightly in speed as it enters the hot side of the turbo.

 

ah physics, my true love

 

2.5" sounds perfect for the stock turbo witch is pretty small.

 

Ohhh I got it... So basicly the uppipe is use to increase the velocity of the flow to get the air OUT fast and not to cause restriction. I see, before I was thinking that having a smaller uppipe was to hold back some air. But I get now. Thx guys! Oh btw What do you gut out of a stock uppipe? b=Because I heard that is better then buying a new uppipe.

thankz !!!!!

 

just spend $160 on a up pipe and dont bother with guttin it, its easier, plus youll have you stock up pipe intact in case you ever need it again, maybe smog inspection or somethin

to gut means to remove the precat from the up pipe