So, I'm looking at turbocharging my NSX and have decided to build my own system (the available kits on the market are either too expensive and aren't "ideal" in my opinion). Right now, I am planning on running a GT3582R (tons of turbine housing options), but don't know what to do about an exhaust manifold.

I plan on using my current aftermarket headers as "pre-manifolds" and just going from there. The main issue I am having is whether or not it will be worth my time/effort/money to use design a true twin scroll manifold.

I see three options right now.

1) Run a GT35R with a divided T4 (1.06 A/R) turbine housing and fabricate my own fully divided manifold with two Tial 38mm wastegates. (Already have gotten an awesome quote for this turbo).

2) Run a GT35R with a divided T3 (0.82 or 1.06 A/R) turbine housing and fabricate my own fully divided manifold with two Tial 38mm wastegates.

3) Run a GT35R with an undivided T3 (0.82 or 1.06 A/R) turbine housing with STMPO's production manifold and a single 38mm wastegate. (I have asked STMPO about a fully divided, dual wastegate manifold, but haven't yet received an answer....my guess is that it will be VERY cost prohibitive).

At this time I do not plan on building the motor, am only looking for around 400whp, and will only be running around 8psi or so. So I guess the question is...is going twin scroll worth it in this case? Also, any other comments/advice is always welcome.

 I realize it is for faster spool, but I am assuming that you see more of the benefits when you run higher boost. Since I am planning on running less than 10 pounds of boost, I'm not sure if I will really see that benefit. Also, I have read that running twin scroll in I6 setups isn't all that beneficial...so I'm wondering about my V6.

I currently have a twin scroll T04Z setup on my RX-7 and can definitely tell the difference at 15psi (compared to my previous car with a non-divided exhaust manifold), but 2-rotor rotaries are quite possibly the absolute best application for twin scroll turbos.

As for the other question...this is a 100% street car that will never see track time (RX-7 is the track car). I drive it a lot...at least 10k miles per year.

 The latest BMW inline-6 engine, the N55 I believe, has a single twin-scroll turbo.  I'm a big fan of twin-scroll as it really improves transient response and spool-up.

I see two options:

1.  Keep it simple with a non-divided setup and get a GTX3576 which will have quicker spool and reponse than the GT3582, but a little less power potential.  T3 flanged, 0.82 A/R turbine housing.  Tial 44mm wastegate.

2.  Divided setup with the GT3582, twin Tial 38mm wastegates.  Garrett is releasing newly designed T3 divided housings later this year with 0.61, 0.83, and 1.01 A/R sizes.  I'd go with the 0.83.  I'm not sure on the release date, so you could always run a regular T3 undivided housing in the meantime.

So the GTX3576 is ~$230 more than a regular GT3582.  With the twin-scroll setup, you CAN run a single Tial 44mm, you just have to keep the wastegate flows separated all the way up to the valve surface.  Either way you go with these two scenarios, I think it'll cost roughly the same.

Therefore, I think it's worth going twin-scroll with the GT3582 if the difficulty level in fabrication isn't much different.  Back when I had my turbo SE-R, the wastegate pressure was only 7.5psi, but I still wished it had better spoolup and response.

Posted By Mike Kojima on 01-23-2012 11:04 AM
Twin scroll doesn't work on a 6 cylinder. We actually have measured less power with no change in lag. It needs more distinct pulses to work. Read Watson and Genoda, their work backs up what we have experianced as well.

This is what I was afraid of....if this is true...my decision will be very easy...just buy the T3 undivided manifold that STMPO currently sells.

Also, I would love to read Watson and Genoda...if I could find a copy. Only one I can find is $575

http://www.ebay.com/itm/Turbochargi...3a4d013f31

 

Mike, are you sure about that?  While I do not think it has the same magnitude of benefit as compared to a 4-cylinder (separation of pulses from valve opening events for a pair of cylinders thereby improving cylinder fill, doesn't work the same if you have 3 cylinders), I think there is still some benefit in keeping the exhaust gas velocity up all the way to the turbine wheel.  In the undivided setup, the gas flow exits the manifold runner into a larger merge area and into the larger volute of the undivided turbine housing.  With the divided setup, the gas flow exits the runner into merge and volute areas half the size of the undivided setup.  So the gas velocity should stay higher up to the turbine wheel helping spoolup and response.  A lot of the big diesel inline-6 engines use divided housings.

One way to know for sure is to have a divided manifold, and run both a non-divided housing and a divided housing on it.  Given the same A/R housings (assuming they are truly the same flow area, and that's often not the case), less power from the divided housing can certainly be expected due to the greater surface area in the flow path.  Anyways.... the BMW engineers are pretty damn smart.  I don't think they would have gone with the extra cost of a twin-scroll setup on their inline-6 if it didn't have a good beneft.  Well, as they saying goes, there's only way one to find out.

Posted By spdracerut on 01-23-2012 12:41 PM

Mike, are you sure about that?  While I do not think it has the same magnitude of benefit as compared to a 4-cylinder (separation of pulses from valve opening events for a pair of cylinders thereby improving cylinder fill, doesn't work the same if you have 3 cylinders), I think there is still some benefit in keeping the exhaust gas velocity up all the way to the turbine wheel.  In the undivided setup, the gas flow exits the manifold runner into a larger merge area and into the larger volute of the undivided turbine housing.  With the divided setup, the gas flow exits the runner into merge and volute areas half the size of the undivided setup.  So the gas velocity should stay higher up to the turbine wheel helping spoolup and response.  A lot of the big diesel inline-6 engines use divided housings.

One way to know for sure is to have a divided manifold, and run both a non-divided housing and a divided housing on it.  Given the same A/R housings (assuming they are truly the same flow area, and that's often not the case), less power from the divided housing can certainly be expected due to the greater surface area in the flow path.  Anyways.... the BMW engineers are pretty damn smart.  I don't think they would have gone with the extra cost of a twin-scroll setup on their inline-6 if it didn't have a good beneft.  Well, as they saying goes, there's only way one to find out.

We did a to b testing on an RB26, same turbo, same manifold, different housings. Well designed HKS manifold. TO4Z Turbo. Spool did not improve, power went down. This agrees with Watson and Genoda's findings. However I have seen twin scrolls on low energy inine 6 diesels in OEM applications and i don't think they would do that if it didnt help.

 I'll give it a brief shot.  So on a typicaly 4-clyinder, a cylinder fires every 180 degrees of crank rotation.  So when a twin-scroll turbo is used on a 4-banger, you pair up the cylinders that are opposite of each other in the firing order, or 360 degrees apart.  The firiing order is 1-3-4-2.  So you pair up 1-4 and 2-3.  So when cylinder 1 is on the exhaust stroke, cylinder 4 is on the compression stroke with the valves closed.  If cylinder 2, which would be on the intake stroke, were paired with #1, the exhaust gas from #1 could get blown into #2 depending on how much cam overlap there is and reduce how much of a fresh charge can get into #2.  So that's why you pair up the opposite cylinders to keep the exhaust pulses from interfering with the intake of a fresh charge.

If you have 3 cylinders connected together... well, can't quite separate all 3 like that.  I guess if you had a triple scroll turbo.... On a V6, there's also a long path from the exhaust manifold to the turbo if you're doing a single turbo setup.  So I imagine there's going to be some loss of pulse intensity.  

My thought is that tthere's still some benefit with a twin-scroll setup on a V6 for the following reason.  You need exhaust velocity to spin the turbine wheel.  If you have 6 runners merge into a collector, then the flow goes from the small area of the runner to the large area of the collector which should slow it down some.  Then it goes into the big area of the undivided turbine housing where it goes to the turbine wheel.  If you do a twin-scroll setup on a V6, each set of 3-cylinders dumps into a smaller area at the collector and in the turbine housing which should help keep the velocity up.  If the flow areas of both the undivided and divided turbine housings are exactly the same, then the twin-scroll setup will make less power due to more frictional flow losses due to the divider wall.

So I'm pretty sure given the undivided and divided/twin-scroll setups have the exact same flow areas in the turbine housings, the twin-scroll will have better response, but less power.  Hard to say how much of a difference though as I imagine the longer the exhaust path gets to get to the turbo, the less benefit there will be.  

Yeah, the pipe length before the turbo will be pretty long...probably 3-4 feet minimum with four 90-degree bends. It's looking worse and worse for the twin-scroll setup, but I'm not completely throwing out the idea just yet.

If I were to go with a single scroll setup, would it be more beneficial to go with a T3 or T4 turbine housing? Also, would a single 38mm Tial MVS valve be able to flow enough to keep the boost below 9 psi at 7500-8000rpm in a 3.0L engine?

Also, what are everyone's thoughts on running a Borgwarner Airwerks turbo (something like the S300 8875 or 8375) instead of the GT35R? The compressor maps look to be a bit more "low boost friendly."

I don't know if 38mm is big enough; I'd be safe and go with the 44mm.  Another option is the GT4088R with the smallest A/R housing, and all GT4088R housings are divided.  The Supra and M3 guys seem to really like it on their inline-6's.  The only word of caution is that the turbine housing is made of hi-silmoly which can't handle high temperatures for extended periods of time.  So for a DD with the occassional WOT, ti's fine.  I wouldn't use it on a road course though.  It would spool like the GT35 in the largest T3, 1.06 housing.  I personally think the T4 housings are too big and to stick with the T3.

For your HP level, I'm going to guess you'll need around 50lbs/min and that's still pretty solid in the compressor map on the GT35s.  So personally, I wouldn't go bigger.

I can't speak to the BW stuff 

Don't forget that you'll have 2-3psi of pressure drop from the compressor outlet to the intake manifold, so figure on 10-11psi at the compressor outlet.  Considering how little boost you'll be running, definitely run the bigger 44mm wastegate as you'll be wastegating a lot of the flow, like upwards of 50%.  I would also make sure the wastegate placement gets priority meaning the flow from the exhaust manifold is more direct to the wastegate than the turbo; that enables better boost control.  On setups where the wastegate is placed at a 90 degree angle from the exhaust flow, they can get boost creep because the flowpath out the wastegate is poor.

Posted By Grant on 01-26-2012 08:45 PM
I'm working on a pretty quick nsx currently(there might have been some coverage on here) and you can't have to much wastegate on these cars. Before I started doing their fab work they went from a single scroll exhaust to dual with no noticeable performance increase. It's currently running twin 46mm gates.

I'm litterally going to order parts tomorow to make 2 turbo kits. Shoot me an email grantborman@gmail.com if you want my boss's info. It's not to complicated of a job on the hot side.

Thanks..I'll shoot you an email tomorrow probably.

Just out of curiosity...what turbo were they running when they went single scroll to twin scroll? Did they change the turbine housing? What else changed at this time?

Thanks.

Thanks for the clarification. I have been talking with Raffi, who has been communicating with Geoff about my setup, and that seems to be what I am hearing as well.

Right now I am planning on running a twin scroll T4 setup with dual Tial MVS 38mm wastegates. I just need to make it a priority to have equal length tubing between the engine and turbo for both banks and get the turbine A/R correct. We have been talking a lot about the GTX3576R and the new Borg Warner S300SX FMW (Compressor: Billet 61.4mm inducer, 83.4mm exducer | Turbine: 76mm inducer, 68mm exducer), but no decisions have been made yet. Geoff and Raffi seem to love the BW S300SX turbos and have had great results.