Downpipe And W/g Dilema

[6bangr]

Complete engine and turbo upgrade, new pt70gtq waiting to fired up. Question about using THDP with h/d wastegate or using a larger downpipe with an external wastegate? I want to be able to utilize this combo. Also is it worth the work to enlarge the hole? I know there is other guys out there with this same problem!!!!

 

[RUQWKNF]

Eventho you will be using a HD actuator, if you want to have any sort of solid boost control with your 70 GTQ turbo, you must port the hole just smaller than the OD of the puck. Otherwise if you were to just put the turbo on as is with the hole size being .900+ - it will have boost creep up top.
This starts to become an issue on turbos that are equipped with a P-trim turbine wheel and larger. Some have had to port the housing on turbos that use the T350 turbine wheel as well, but not everyone.

It is also highly recommended to port your TH downpipe flange to the same size as the discharge hole on the turbine housing. The standard TH downpipe flange has a lot of over hang into the exhaust stream flow from the discharge. Although no real world back to back hp tests have been reported, when you see these next pictures you know there is hp being lost due to the restriction.

True these images are of an external wastegate style downpipe, but the flange bolt pattern is the same and the over hang of the discharge hole on the flange is also very similar on the THDP flange. I would recommend you make a pattern of the discharge hole on your 70 GT-Qs turbine housing and transcribe it onto your THDP flange. Once you get up there in the higher boost ranges with this turbo, you will pickup some power going with a 3.5" downpipe vs the 3".
HTH

Patrick

 

[Hot Air]

What happened to the pictures?
Conrad

 

[Hot Air]

The pics finally downloaded.
Conrad