Little background:

1)I have a used Greddy 18g twin kit I purchased used. Not sure if I have the Greddy downpipes.

2) Recently my employer of 15 years forced me to relocate away from Nashville (where I shared custody of my child) to Mississippi. As a result I am considering a HUGE drop in income and am thinking my TT will have to wait for a while.

3) Before deciding to go FI, I purchased a Fast Intentions Intimidator catback exhaust that I absolutely love and therefore plan to keep when I finally go forced induction.

It is my understanding that 'Downpipes' connect the turbo manifold to the exhaust system, deleting the cats. How do they differ from 'Test pipes'? Only that downpipes are specifically made to connect to the greddy turbo manifolds while test pipes are designed to fit the stock exhaust manifold?

If the above is true, would HFCs need to be modified to fit the Greddy manifolds? I understand that downpipes would allow the exhaust gases to exit quicker and therefore helping to acheive the most power gains, but Tn has a visual inspection during the yearly testing.

I am also thinking of getting HFCs and then getting a flash, which will hopefully satisfy my mod bug for a year or two while I try to get the job situation worked out allowing me to build my engine and get the twins installed.

Would HFCs be a total waste of cash and perhaps I should try to find some used test pipes and switch them out with the stock cats when I get tested?

Kinda screwed and looking to make the best of my situation.

thanks,

george

 

Downpipes are basically the same as test pipes except that they have the flange that mounts directly on to the turbo.

Test pipes are basically straight pipes which mount just like a cat to a turbo system using the provided elbows that come with the kit.

HFC are good for NA/Low power Fi applications if you do not like the fuel smell and would like to stay semi legal as far as emissions standards.

Downpipes would be the optimal choice out of the 3 for any Fi application.

Test pipes I would rate as 2nd on the list for Fi application and last in a NA application.

HFC Would be my first choice in a NA application and last in a Fi application but again its a compromise if you do not like the fuel smell.

This is my personal opinion since I feel for a NA application back pressure is needed.

 

I went with 3" downpipes and HFC's. Minimal losses; still hitting 400+whp with ease...your car not smelling like a gas station...priceless.

 

Huh..I was told that the downpipes take the place of the cats/test pipes. Sooooo.........do you just cut/splice the cats/testpipes into the downpipes?

Thanks

 

I have 3" AAM 'catted' downpipes. They are custom made for my car and tt setup, so yes most likely they took their regular 3" downpipe design and welded the cats in.

I think everyone is getting overly critical on the diff between test pipes and down pipes.

test pipes means a pipe that replaces your cats. you can only use test pipes on sc or na setups...basically anything that would normally utilize the stock cats.

down pipes are only used with tt setups and can exist with or without a cat. a down pipe with no cat in my book can also be called a test pipe, its just a matter of how you want to think of it.. for a tt with no cat, you've replaced a catted downpipe with a 'test pipe'. There ya go. LOL

 

Down pipe






The elbows from the turbo kit that need to be removed to install downpipes


Test Pipes



High Flow Cats






That should give you a better idea of what we talking about

 

Hey Thanks Guys!!!!!

much appreciated

 

This is good to know. I want FI but definitely don't want the gas station smell going on

Plus I already have HFCs so I figure its best to leave them on there for my FI goals anyway