Twin Scroll with Single Wastegate

[95_240]

Just seeing if anyone has experience or opinions about a twin scroll manifold on a RB25 that has two wastegate runners that merge into one wastegate. Any problems with spikes etc. and would it need a smaller or larger wastegate than what someone would run on the same turbo setup with a non divided manifold. I've got a hx35 I'm putting on my car so I'm looking at either a twin scroll with one wastegate or a non divided manifold.

[Darius]

I have a T4 twin scroll 6boost manifold with a single 38mm Tial wastegate. There is a gap between the two halves of the manifold. You can't see it in the pic, but the center flange does not connect all the way to one side. There is a 1/4" gap around the side of the center divider plate.



I never have boost creep issues. To help prevent this from happening in the first place, I also plumbed my wastegate dump tube back into the side of my exhaust so it helps scavenge the gases on the back side of the wastegate.

[240z4u]

38mm on a well designed manifold is fine. I have a 6boost as well with an HX35 + Tial MVS wastegate.

[RRRRB]

Werid you guys dont have creep... i had twin 38mm MVS gates and it creeped terribley with my 6766, it was fine with the GT30R

I ended up installing twin MVR 44mm gates and its better, mine are vented externally though..

Manifold design makes all the difference..

[julio]

Werid you guys dont have creep... i had twin 38mm MVS gates and it creeped terribley with my 6766, it was fine with the GT30R

I ended up installing twin MVR 44mm gates and its better, mine are vented externally though..

Manifold design makes all the difference..

Its suprising that twin 38's wouldn't do the trick, I always thought twin 44's were overkill on most setups (although I did go twin 44's with mine). However in some manifold/turbo, I believe back pressure in the manifold is a key contributer to wastegate flow. This goes along the lines that exhaust (fluid) will follow the path of least resistance. If manifold back pressure isn't very high compared to post turbo exhaust back pressure, then exhaust is less motivated to take a sharp turn down a wastegate runner. That being said, I imagine your 6766 flowed quite nicely and had relatively low back pressure compared to your GT30R and therefore you started to see creep issues.

It would be interesting to see a before/after dyno graph with the wastegates vented and recirc'ed to see the difference in boost creep/power.

[Coolwhip]

We are arranging a back to back dyno with our twin scroll top mount manifold redesign with a popular comparative. I'll keep you guys updated with the write up.

http://www.rawbrokerage.com/raw-brokera ... rb26-rb30/

[julio]

We are arranging a back to back dyno with our twin scroll top mount manifold redesign with a popular comparative. I'll keep you guys updated with the write up.

http://www.rawbrokerage.com/raw-brokera ... rb26-rb30/

Ricky, are they 1.25"" or 1.5" sch 10 pipe?

[Coolwhip]

1.25"

[RRRRB]

you guys should do a comparison with the 1.25 vs 1.5.... i believe full race is using 1.5 inch primaries on their manifolds.

[Coolwhip]

they use 1.25" primaries as well. We've did a small batch of manifolds a few years ago with 1.5" primaries. Aside from the increase of real estate those manifolds took up they're torque numbers were down on comparative RB25 sets. Another manufacture does 1.5" (single scroll) but there is no use of either A/C or installing it without jacking up the motor.

[julio]

There is a dyno graph floating around on the web comparing 6 cylinder manifold primaries of 1.25" against 1.5". I believe the 1.5" lost power everywhere except past 600 or 650whp.