The Split Pulse Turbocharger Thread

[h2k]

The link to OBX Racing homepage: OBX Racing

But it's under construction and doesnt contain anything usefull

Otherwise it's easily found on webshops and ebay

[discopotato03]

Hi all , I've had an E mail back from Geoff Raicer to say that he read these TS type threads here . He said the only way to show the difference is to experience both because the difference is really noticable .

In about 6-8 weeks he is going to do some dyno testing in the following configs .

The engine will be a "stock" RB25DET except for the GRedy (sp ?) inlet manifold and a GT3071R turbo so .

1) Std exhaust manifold with a single scroll GT3071R , not sure which A/R housing , tune and dyno .

2) Change to Full Race manifold with same turbo , retune and dyno .

3) Change turbine housing to twin scroll , retune and dyno .

The results should be very interesting though how well the graphs relate to the real world experience is hard to say .

I'm going to ask him if he can log exhaust manifold pressure (turbine inlet pressure) and compare or overlay the numbers to the inlet manifold ones . I don't know if they'll get the chance to try a twin scroll GT3076R and GT3582R but it would certainly answer the question of can bigish (not hugeish) turbos be reasonably responsive without being restrictive on the exhaust side (ie resorting to small A/R's) .

I think also more TS turbine housings are going to be made available but no details yet .

Cheers A .

[Warpspeed]

Warpspeed, i would be very interested in knowing some more about the VNT turbo's that you have played with. I spoke to garrett australia about these a year ago, and they told me that they had not yet reached the development level for high performnce petrol engines, as they could not get the VNT to be reliable with the ex temps.

I have heard that too, but I ran one for three years without any problems with the movable vanes. Porsche now use these turbos on the current 911, so reliability cannot be too bad.

Why is there a problem with also runnung a wastegate if necessary,

Fitting a wastegate is no problem, but what sort of control strategy would you use to control both vane position and wastegate. Think about all this very carefully, and figure out a simple way that does not require full electronic control by the engine management system. There is no simple way, that is the problem.

Just use a tuned size exhaust housing, and then use the vnt to spool it up nice and early. Have you considered the possibility that the overall size of the ex area was too small and thats why the top end sucked?

Yes obviously. You could fit an enormous turbine and housing, but then even with the movable vanes, a GT ball bearing turbo would leave it for dead response wise.

I havent looked into these 100% yet, due to the lack of range of availability, but i can say for sure the vehicles i have driven with VNT turbo's(BMW X5 and Merc 4wd diesel thing)i have been incredably impressed with given their small capacity diesel motor.

Yes, they are good arent they ! But they are diesels not petrol engines, the air (andexhaust flow) is not throttled as it is with a petrol engine. Why don't BMW use it on their turbo petrol engines if it works so well ? Their current turbo petrol engines all use wastegates.

I believe these have totally revolutionized diesels along with single rail direct injection. I believe the ideal turbo for a petrol engined car, would have VNT, possibly a wastegate if necessary

It is nice to speculate. Why do you think Garrett have never fitted variable vane turbines on their GT ball bearing turbos ? If it really worked, companies like HKS would be selling premium performance VNT turbos in all sizes to the hot rodders.

If it was all that good why have the drag racers and rally cars not bothered to use VNT technology ????

The answer is, it has been tried by almost everyone, and it is a real BUMMER. It creates far more problems than it solves on a petrol engine, but works wonderfully well on an unthrottled diesel.

But getting back on topic. I have even tried using a split pulse turbine housing with a second wastegate to block one side of the turbine. Use half the a/r to spool up, then open the wastegate to double the effective a/r to reduce turbine back pressure while holding full boost. A second wastegate then works in the normal way.

I have actually tried this too, and it works. But the improvement is barely noticeable, and it is just not worth doing.

[Dale FZ1]

Applause from the side-line.

Yes, it will at least give us some idea of what happens under full load.

Thank you for pursuing this one Adrian, thought the trail had gone cold...

[discopotato03]

I don't think you'll be disapointed .

Cheers A .

[Cubes]

Can't wait to see the results Disco.

[BHDave]

same here, as personally, i think the 3071 should be the weapon of choice for stock bottom end 25's. funnily enough i'm looking at a greddy manifold aswell.....

[discopotato03]

I think I did see a pic of those once , do they have the stud holes for RB25 and 26 heads ?

Also possibly a 52 comp trim 3071R may better suit those not after lots of revs and high boost .

[BHDave]

Sorry, greddy inlet manifold.

I already have an hks low mount exhaust manifold.

I think it was the apexi ex manifolds that have the multi flange on the rear 2 ports.

56T 3071 in a .78 twinscroll housing should be good for very high 200's with bullshit good response. I have a battle with a 2835proS/rb25 equiped cef tomorrow evening. We have the same cams, stock bottom ends. It should be interesting to see if the 56T/71mm compressor can knock over my old 52T T04s in the power stakes (assuming he hasn't cheated)

[Devils_Advocate21]

Hey wondering about those obx manifolds above, are the tuned length or guesed length? Plus cant wait to get closure on the results of the difference

[swanny180]

Fascinating topic, will keep watching this with interest

[Dale FZ1]

Sorry, greddy inlet manifold.

56T 3071 in a .78 twinscroll housing should be good for very high 200's with bullshit good response. I have a battle with a 2835proS/rb25 equiped cef tomorrow evening. We have the same cams, stock bottom ends. It should be interesting to see if the 56T/71mm compressor can knock over my old 52T T04s in the power stakes

Well I'd guess the pro S will make it up to around 265-270rwkW tops.

Yours will be good for another 20 (duh!! knowing it has already cracked 288+) at max. Full load figures will be in your favour, but the transient response difference might be different.

If all the theory works out, and Full-Race Geoff can give us some idea with back to back testing, I'd wonder if the split pulse system 3071 can bridge the (perceived) gap between the mid-range/top end surge of the 3076 and HKS offering. In some respects I think either a 48T or 52T T04S based GT30 unit offers a damn good compromise already.

Perhaps that split pulse system with reduced turbine inlet pressure can show it the way for response and outright power? Either way, bring on some results Dave, and Geoff.

[Dale FZ1]

Seeing as there is a bit of interest around, with a little bit more searching obviously there’s a bit of discussion going on outside of SAU about split pulse. It’s good to see guys trying to get their heads around the concept and how it applies to cars other than Nissans. I reckon it’s a good thing that BMW mirror Nissan’s approach with I6 configuration, so those guys really use the same/similar techniques when chasing good forced induction performance. Check this out for discussion and pics:

http://forums.bimmerforums.com/forum/showt...ght=split+pulse

Given that MHI do produce split pulse housings, I figure that the Subaru focused discussion on MHI TD05 / TD06 is also worthwhile, given that there are other products than the Garrett units we seem to gravitate towards. Just helps to make a bit of sense when the MHI-based Trust units are commented upon.

http://forums.nasioc.com/forums/archive/in.../t-1081261.html

[discopotato03]

By battle do we mean dyno or ah drag race . Still lots of variables .

Probably a moot point but given a choise Id prefer a 52T GT3071R , mainly because mid trim compressors generally give slightly better efficiencies and if I could get away with using something slightly less bulky than a T04E compressor cover thats a bonus . I figure that Garrett have used T04B and T04E comp covers on those 71mm GT35 compressors and if the trim was down a tad it would not be the end of the world . It'd basically be a GT2871R 52T with a GT30 turbine instead of the GT28 . Who knows - maybe an RB25 housing to make it say NISSAN and fit std plumbing .

As for Geoff , its about three days work for his business so many thanks to FullRace Motorsport .

Cheers A .

[Dale FZ1]

By battle do we mean dyno or ah drag race . Still lots of variables .

Probably a moot point but given a choise Id prefer a 52T GT3071R , mainly because mid trim compressors generally give slightly better efficiencies and if I could get away with using something slightly less bulky than a T04E compressor cover thats a bonus . I figure that Garrett have used T04B and T04E comp covers on those 71mm GT35 compressors and if the trim was down a tad it would not be the end of the world . It'd basically be a GT2871R 52T with a GT30 turbine instead of the GT28 . Who knows - maybe an RB25 housing to make it say NISSAN and fit std plumbing .

The dyno comparison is handy, and quantifies numbers. Gives something to predict comparative performance.

The drag race tells a fair bit about full load performance but little about daily driven capability.

For me, the tell-all is in something like a hill climb event and/or a sprint event. Something where the max figures on a dyno sheet aren't the most important, but where response and torque delivery from low to full load become significant. After all, that is what this whole split pulse thread is about.

For a GT3071, there'd be nothing wrong with a TO4B comp housing. More compact but not really lacking in flow capacity for the application. Less physical size might give fewer clearance problems and a tad easier to plumb up.

Edited June 9, 2007 by Dale FZ1

[discopotato03]

Yep they're not as agricultural (the truck type) as people often think . I'm sure people here would have seen the Nissan/Garrett style T04B comp cover , I think its standard on the GT-RS and Garretts marketed GT2871R 52T . Basically 3 bolt outlet and 2 bolt inlet something like I think SR20's have std though there are S13 and S14 variations . Internally its the same as the garden variety T04B .60 A/R housing and there's two variations of that as well ...

Cheers A .

[Devils_Advocate21]

Question, andrew and dale, there is no diffence in the turbine wheels for these turbo's is there its mainly just in the housing

[Dale FZ1]

Heaps of different specs being bandied about in this thread.

The HKS GT2835 range uses a couple of different trim specs in the 56.5mm turbine rotor with the 71mm GT35 compressor:

http://translate.google.com/translate?hl=e...hl%3Den%26lr%3D

http://www.j-w-racing.co.uk/acatalog/GT_Ba...bochargers.html

From memory I think BHDave is running a TA series unit which has little in common with the GT series gear. Still like old Grandad's axe with an edge on it though - it'll take your foot off as good as a sharp new one.

The GT30 series units run a 60mm rotor, while those TD06, HY35, and GT35 units are all around 65mm (give or take).

The couple of comp housing options mentioned by Adrian are just that - options. My understanding is their physical size and shape does impact on mass flow capacity and boost response to a degree, but not to the extent of the turbine housing.

I'd taken the units to be tested by Full Race Geoff will be the 60mm based GT3071, using a conventional housing, and the split pulse housing.

[discopotato03]

Yes anyone with their thinking cap on wouldn't bother with the cropped version and unless it was the Pro S GT2835 it wouldn't bolt up anyway (wrong flange) .

The GT3071R's I've seen Geoff use on SR20's also used his split pulse manifolds and they are T3 flanged . Anyone who looked at the thread I mentioned a while back should also have noticed that their GT3071R's had the T04E compressor housing with the smaller inlet snout or boss . Off the top of my head this boss measures 2.75" instead of 4" so a bit easier to plumb .

Also the cropped turbine at 56.6mm is a bit small to be going into a GT32 turbine housing that had a 64 odd mm turbine originally .

Cheers A .

[Rolls]

Porsche are the only manufacturer to use them, and they also run wastegates, and the whole thing is controlled by the engine management unit.

Thats what I was going to suggest, why haven't they (garret etc) developed any that use a wastegate also?