I was wondering if anyone who has a turbo II runs a straightpipe. I have a T04 compressor housing with a stock turbine on the exhuast for my turbo setup and was thinking of runing my 2.5 inch downpipe to a straightpipe, or downpipe to presilencer to straightpipe. My only concern was lack of backpressure. I know turbo cars do not need as much backpressure which allows the turbo to create more boost, but I am not sure if a straightpipe will create enough. This setup will be mainly for at the track or for street racing on the weekend nights. Eventually I would like to get the money together to do a 3 inch downpipe to two 3 inch magnaflow mufflers setup. But I need something cheap for short term. I have a decent set of mufflers now but they aren't high enough flowing. They sound deep, but are not loud enough.

 

On a turbo you want as little backpressure in the exhaust as possible. The turbo provides any backpressure the engine requires, and the less backpressure after the turbine the faster the turbo will spool. The best way to do that is with a full 3" system, however on a Series 4 FC like yours the wategate is far too small for that and will overboost. The wastegate needs to be ported as much as possible, or even better, the manifold and turbo be swapped for Series 5 items. Your upgraded compressor would bolt onto this turbo.

 

hey, i'm about to have a 91 jap spec turbo and manifold for sale

 

I know Mazdatrix has a complete racing series exhaust system for $789. I have heard that this is one of the best setups to run on a T2. It is 3" from turbo, 3"pre-silencer and a pair of 2 1/4" pipes into the mufflers. One thing to remember (as you have stated above...) this is intended to be racing use only. It will not pass certification as emissions compliant. (no cats at all) I have also heard that it increases the sound level but not to the extent that it is obnoxious. Then again, last week at the local Dragway, a guy had a 12A peripheral port in a Toyota Starlet with a straight pipe. He was revving it to around 12,000 R's and I think that was only borderline obnoxious. You can't go wrong with Mazdatrix, they are great guys and really know their stuff.

 

One other thing to remember: If you run an exhaust with less restriction, your turbo will boost higher. You will need to run a FCD. I also recommend a larger fuel pump too so you don't lean out the intake and get the dreaded........DETONATION!!! I merely hollowed my cats and I hit the boost limiter frequently. I also realize it is there to save my engine so I work around it.

 

Actually, a full 3” front section with a long 3” straight-through presilencer, splitting into two 2.5” pipes with 2.5” straight-through mufflers (with large diameter cans, that’s important) is not too loud. It’s a quite common configuration over here. If a cat is legally required (3” again), it’ll be even quieter.