True Twin Scroll Turbo & Manifold Design Discussion

[brad 110]

Many manifolds are built and sold as split pulse using one gate, if the waste gate pipe work isn't separated with tube work and a file fit devider right to the gate valve, then it's not true split pulse just as Micheal suggested full stop. He too is correct re two gates if one flows sufficiently to control turbine speed there are as many down sides as up in using two gates over one.

[bradsm87]

cant remember but i heard that a few times. with a merge collected mani like a 6boost, the exhaust is not clashing tho is it ? coz its merge collected ?

If it was a 3 cylinder engine, that would be true but with 6, there are more than 1 runners trying to have access to the "shared flange" at the same time, regardless of how good the collector is.

[mico]

3 is more than 1 too

[The Dan]

As the highest pressure point it makes sense to me to run the gate off the housing which is why I talked Artz into it. The idea for my setup, (if I ever get around to making it) is to get the flow straight through the turbo, cutting out the back of the scroll and making the wastegate the priority when it is open. With twin scroll just run the splitter up to the gate and the same will apply.

Too many setups I see favour the turbo at the expense of the wastegate flow which would mean too much power is lost up top imo.

^^ This

You also need to be careful how far around the scroll you put the pipe and try to avoid making the pipe flow the same or similar direction as the scroll of the turbine housing. The idea is to create a high speed pressure drop at the high pressure area but avoid restricting the flow by making an easier path while the gate is shut. By doing it almost 90deg to the scroll you will achieve that.

We don't have back to back results to share unfortunately, but we have a brilliant view from up here standing on top of all the failed attempts at manifold designs we have seen and had tuned when people supply manifolds to us.

Sean at EFI started noticing more hp on the cars that they ran gates off housings and better boost response and control than other identical setups. We started doing it (a little sceptical at first for sure). The results spoke for themselves and we just do it that way every time now. There have been a couple I've done where we actually had another manifold made for the customer and binned their 'namebrand' steam pipe manifold as they got a much better result that way.

GTR_Joey - the only reason it's better than 2 gates is because it works just as well (2 gates works extremely well) but you only have to buy 1 gate. Premium gates aren't cheap. That's a nitrous kit worth

*No manifolds were harmed in the making of this post

[brad 110]

Split pulse is about grouping multiple pulses in two banks (in the case that the turbo is twin scroll) 123/456 (as one cylinder fires in pulse group 1 then 1 fires in group2 and so on) in the case of an rb. Nothing to do with individual cylinders having access to a shared flange nor trying to keep cylinders individual (other than grouped).

[mico]

the gate on my falcon is about 10 o clock on the ex housing (single scroll tho). works beautifully no matter how many springs i cram in there. screamer pipes are so loud off there.

[bradsm87]

3 is more than 1 too

Gas isn't constantly flowing out of each exhaust port. Each exhaust pulse happens over a period of about 220 degrees of engine rotation. it takes 720 degrees for a full cycle through all of the cylinders. 3 cylinder engine has. 220 x 3 = 660 which is pretty close to 720 so there is no overlap of exhaust pulses and pretty much no gap between them either. 6 cylinders into 1 means that most of the time, there are 2 runners flowing into the merge collector at the same time.

[The Dan]

This isn't a difficult excercise. Too many of you are worrying too much about wtf is happening inside your engine or manifold. If anyone worried as much about fuel choice or correct injector/pump sizing instead, most would not need to worry about their manifold design because they would be out smashing v8's all over the place and pulling chicks because their shit is so awesome.

steam pipe, good merge collector, lots of boost - there! I just designed all your manifolds.

If you've spent 100k on your setup, are going to WTAC and need to worry about every tenth of a second and beating the guy next to you that spent 101k, split pulse is the way to go. Spend hours, if not days, pondering the length of the runners and the internal dimensions of the collector to make sure at 10,000 magnification, you have no raised edges anywhere to disrupt flow.

1. Most manifold makers don't understand the true physics behind the design or even how the engine works

2. Most split pulse manifolds (if done correctly int he first place) are going to give you 100rpm response gain over your standard run of the mill CRG/6Boost manifold

3. More time can be spent consuming alcohol than worrying about something that is going to give you 2/5ths of f**k all benefit. I'd rather shorten my life by alcohol than by stressing over manifolds

4. Tomei did back to back testing - split pulse vs single entry and tuned length vs normal runner manifolds in every possible combination and the results were basically nil gain or so minimal it wasn't worth the extra coin

[bigmikespec]

Favouring the wastegate means you can get better boost control with a smaller gate. As mentioned most setups are turbo placement first wastegate after... should be the other way around. Twin wastegates will always work well because the placement can be less than ideal and still control boost, it masks the design problem of the wastegate outlet being in a poor position.

A turbo always looks nicer under bonnet as the showpiece, not a dirty great big wastegate and a turbo hidden under a manifold!!!!!

[scotty nm35]

Favouring the wastegate means you can get better boost control with a smaller gate. As mentioned most setups are turbo placement first wastegate after... should be the other way around.

Not only better boost control, better exhaust flow which means more powah.

No-one can see my turbo so I guess looks are out of the question.

[wolverine]

4. Tomei did back to back testing - split pulse vs single entry and tuned length vs normal runner manifolds in every possible combination and the results were basically nil gain or so minimal it wasn't worth the extra coin

They should have borrowed my bum dyno. I reckon that the hairs on my arse cheeks rise just a bit quicker than with the single scroll.

It makes all the difference when you are racing......

.......from the traffic jam at one red light to the next on the fine roads in Sydney's North Western suburbs.

[Dose Pipe Sutututu]

is there a reason why I never see exhaust housing like the below for RBs?

I'm all in for the mount waste gate on exhaust housing, but prefer if it was cast like that instead of an mod (mainly due to cost & future possibility of cracking)

[The Dan]

They should have borrowed my bum dyno. I reckon that the hairs on my arse cheeks rise just a bit quicker than with the single scroll.

It makes all the difference when you are racing......

.......from the traffic jam at one red light to the next on the fine roads in Sydney's North Western suburbs.

Lol. The traffic light racing scene from Ali G came instantly to mind

[Lithium]

1. Most manifold makers don't understand the true physics behind the design or even how the engine works

Agreed

2. Most split pulse manifolds (if done correctly int he first place) are going to give you 100rpm response gain over your standard run of the mill CRG/6Boost manifold

Not so much agreed.

3. More time can be spent consuming alcohol than worrying about something that is going to give you 2/5ths of f**k all benefit. I'd rather shorten my life by alcohol than by stressing over manifolds

I half agree with this Don't make a decision, just get drunk - go onto the net and order a twin scroll manifold from a reputablable dealer.

4. Tomei did back to back testing - split pulse vs single entry and tuned length vs normal runner manifolds in every possible combination and the results were basically nil gain or so minimal it wasn't worth the extra coin

That is very strange, I rate your opinion and experience high on most topics and if I hadn't seen otherwise with my own eyes I'd take that fully on board - and I am still taking note, but the amount of times I've seen results personally which are completely to the contrary is overwhelming.

Alternatively, taking that to its logical conclusion we'd say that unless we are racing at top level there is no point modifying our cars full stop - but that completely misses the point of our hobby, we'd just buy cars to get from point A to point B and be more than happy with a stock GTR/GTS. Rationally that makes sense, but we aren't doing this because we have to.

[scotty nm35]

is there a reason why I never see exhaust housing like the below for RBs?

I'm all in for the mount waste gate on exhaust housing, but prefer if it was cast like that instead of an mod (mainly due to cost & future possibility of cracking)

It wont crack if the weld is done right as there is very little expansion on such a small part. I prefer to buy the stainless Tial or Tial copy housings and modify them with stainless schedule 10 as welding cast to mild steel steampipe is a little harder. Cost wise, if you get a Tial copy housing and get me to cut a port, it would work out cheaper than a Garrett rear and flow much more freely.

There have been no issues so far with any of the housings I have modified, even with track work and hard dyno tuning. It's a great budget option as it will save you buying an aftermarket manifold.

[GTR_JOEY]

GTR_Joey - the only reason it's better than 2 gates is because it works just as well (2 gates works extremely well) but you only have to buy 1 gate. Premium gates aren't cheap. That's a nitrous kit worth

*No manifolds were harmed in the making of this post

Excellent, still happy I have the twin scroll with dual gates

[Mitcho_7]

The thing that turns me off dual gates (besides price) is how tight of a fit it will be for everything.

So much so that you would probably have to pre assemble everything to get it in and if you wanna take something off for some reason, it might have to come out as a whole thing as well.

Is that the case with the one you made up Scotty?

Edited July 27, 2012 by Mitcho_7

[KiwiRS4T]

is there a reason why I never see exhaust housing like the below for RBs?

I'm all in for the mount waste gate on exhaust housing, but prefer if it was cast like that instead of an mod (mainly due to cost & future possibility of cracking)

I don't expect mine to crack anytime soon:

[scotty nm35]

The thing that turns me off dual gates (besides price) is how tight of a fit it will be for everything.

So much so that you would probably have to pre assemble everything to get it in and if you wanna take something off for some reason, it might have to come out as a whole thing as well.

Is that the case with the one you made up Scotty?

It was definitely a pita to fit, the turbo had to be bolted to the manifold with the gates and screamer in place then bolted to the head. With a better wastegate placement it would have made the job a lot easier but that is how 6boost manufactures his split manifolds.

[r33_racer]

The new split pulse 6boost manifold with twin 40mm compgates we run on our car was not difficult to fit at all. I actually have alot more access then I was expecting! Rb30det in r33 gtst though whether that makes much difference. No abs either which no doubt helps abit.