so i removed the air pump and ACV on my 87 t2 and was wondering do i also have to change the precat to a downpipe or could i just get away with just changing the main cat to a straight pipe because that's where the air is injected any help is greatly appreciated

 

they're separate but related systems. The air pump actually doesn't normally put air into the cat. Most of the time it puts air into the exhaust ports through the ACV.

Do you think either of those cats are clogged?

 

No not yet but its been run without the air pump for a while already plus I just did the acv delete and just wanted to get ahead of the game before they do plug up how long does it normally take to plug them up without the acv and air pump

 

so my downpipe just came in today its a 3" i wanted to take out the cat also but keep the stock mufflers for now is there any ill affects from keeping the stock exhaust from the y pipe back has anybody done this that has any input

 

No air pump = no cat . No air input means no catalyzing so it will clog . My T2(87) is perfect with a straight pipe . However, 3" is wAy overkill . Do you have a 3" tid ? The inlet size should be relative to exhaust id

 

well i got the downpipe for a pretty good price here on the forums the turbo is a stock s5 turbo so no its not a 3" i was thinking of keeping the stock exhaust from the y pipe back i could make a pipe at work reducing it from the 3" to whatever the id is on the y pipe
thats why i was asking is anybody runnin full 3" straight pipe to stock y pipe and mufflers

 

I'm not sure, so this is for the turbo guys: Is there a danger in boost spiking with what OP is doing?

 

I am not a turbo guy, but I can answer your question...

...the answer is yes.

 

well just talked to racing beat and they said it should be fine if i run three inch from the turbo to the stock Y pipe as he explained that pretty much from the y pipe back the exhaust flows about the same as stock the only difference would be the sound


as far as the boost spikes i know its more likely with a bigger exhaust that's why i went to a s5 turbo and ported the wastegate on it so not really too worried about it

 

Basically you have your down pipe acting as a messed up resonator . Tid is turbo inlet duct . The tube from the inlet side of the turbo to the AFM . Which is 2.5" , so should your exhaust be on an ht18

 

it will probably just sound kind of tinny

 

just got it on and it actually doesn't sound too bad a little louder turbo spools a lot faster still maintains 8psi with a manual boost controller i have a aftermarket intake on the turbo not running the stock air box any more