GTR inlet/throttles on RB25 NEO

[RoboPope]

Hi Goddard,

I’m intrigued by this as I thought about fitting an RB26 head and or engine in to my GTSt before popping an RB30 with the gtst head in (not that I got my hands dirty you understand I just got RSI from all signatures). What do you see as the potential of this modification as apart from aesthetics and marginal delay / lag improvements etc.

That’s not to say I'm detracting from anything you are doing and I am very much in the same boat in terms of doing things you want because it’s what you want I have built exactly what I wanted because I wanted it I’d just like to know why

Thanks

Pope

[Goddard]

Hmm, what do I want from this?

Asethetics (I want to tidy the engine bay up, and use RB26 engine covers, much nicer!).
Ease of front mount intercooler (I really don't like the long pipe runs you get with a GTsT/GTT).
Better arrangement imo than a Greddy inlet (No big nasty GTT throttle hanging off the end in the way of the battery - packaging should be easier).

Performance wise,

Better response - One thing I don't like on a turbo car is the lack of response. In the reviews I've read comparing GTT to GTR it is always said the GTR is so much more responsive, feels like it has more urgency about it.
Better noise - I love the way throttle bodies sound, I like listening to the engine as much as enjoying the acceleration.
Possibly more power - Less heat radiation into inlet pipes from top of engine or them running back across the top of the rad.

Downside I'm kinda expecting is a reduction in low end torque due to shorter inlet runner length, but with a bigger turbo that is to be expected anyway.

And finally it gives me something to do in my spare time

[RoboPope]

In that case space the whole setup 15 - 20mm off the head with some machined spacers and you will get the torque back. like I said I did look in to this and I am an engineer so have a reasonable grasp of the fluid dynamics.

I have the GReddy inlet on mine and it does the same thing give or take. I am now toying with the q45 throttle body etc but i find grip a big enough issue already and I can only really plant it in 5th with any real safety where it takes off like a scalded fighter pilot so how much power do I "need"? i can have it dynapacked to silly levels but they are not tractable for road use

spool time on the turbo is the only thing you will really notice and a big single really sucks compared with a pair of smaller GT cored turbos. I have a GTR too and that picks up so much better with GT cored N1's for a similar power output despite being smaller capacity / displacement wise but it is still so boring to drive

Porsche did a really interesting thing with variable throttle tracts where they got shorter with increasing revs, that is the place to go as length will cause issues with high rev power

The gearing on the GTR is somewhat different which tends to lead to the increase in urgency as you get better "time" in gear. I have a 6 speed box to go in mine and that will solve the short gearing problem as well as giving me a monster top speed should I want to melt something.

Pope

[Goddard]

Yeah I don't want rediculous power for mine as I want to be able to use and enjoy the car.

I don't think I can be bothered with the hassle of a twin turbo set up, or the expense of a variable vain turbo. I did some work on variable inlet runners on a dyno for a few months, makes good improvements, but it's only when you get into big rpm (>9000) that you start to notice any benefit of having short ones I found. I did see a nice system once though which had essentially a short trumpet mounted on throttle bodies, with a larger trumpet sat down the inside of them, which was lifted out of the way for higher rpm. Looked trick, but didn't see any figures for it. I was only planning on making the adaptor plate about 12mm thick. Anymore than that and I would be worried the injector being in completely the wrong place. The GTT inlet isn't just 20mm longer either, it's more like another 200mm longer.

The only reason I would conider making the adaptor plate any thicker would be to help clearance around the VCT solanoid. Which might not be a bad idea.

[RoboPope]

I'm not so clued in on the GTT side of things, i thought hat had dual tracts already? I looked at VNT too but it only seems to be reliable on the 996 at the moment and is very susceptable to heat and I was going to wait for turbo core technology to improve or the sustainability / reliability of VNT technology to get better.

If you are going to run big rpm moving the injectors back is a good thing in terms of fuel dispersal

Pope

[simon]

don't misundertsand me, I think it is a very cool project and only cost/capability prevented me for carrying it through.

You won't be the first to do it by any stretch, as for the mapping again I can only go off the research I did and that was mapping on mutil TB's can be trickier than singles.

Either way I will continue to be interested in how you get on

Simon

[Goddard]

If by dual tracts you mean the runners diverge to the two inlet valves then yeah it does it exactly the same as the RB26 (my pictures above show the comparison between a NEO inlet and the GTR manifold. If you mean it has a switchable short inlet tract and a long inlet tract, then no it just has one length. Are you confusing that with the NVCS that the NEO engine has? (and the later R33 RB25s).

Yeah I've been over the injectors a few times with various people (didn't think it would be such a hot topic). I also did some dyno work with injectors mounted close and far away. The difference was negligable, and I believe that the injector phasing needs to be changed to get maximum benefit, which I didn't do. Alot of these things seem to look good on paper and for pub talk, but in reality do bugger all until you go to the extremes (ie. 500mm runner length vs 50mm runners, and injectors 600mm away vs 60mm away, and 5000rpm vs 15000rpm). Runner length is by far the most important, but they need to be huge for it to make a difference (over 400mm for most engines), which you can't package into the bay unfortunately.

[Goddard]

Originally Posted by simon

don't misundertsand me, I think it is a very cool project and only cost/capability prevented me for carrying it through.

You won't be the first to do it by any stretch, as for the mapping again I can only go off the research I did and that was mapping on mutil TB's can be trickier than singles.

Either way I will continue to be interested in how you get on

Simon

That's fair play mate, I enjoy the conversation. If someone has done it in the UK I would love to have a chat to them. I could only find people in OZ that have given it a go. I have mapped single throttle engines and multi throttle engines. As long as you balance the throttles, the mapping is no harder, and because the pulsing along the runners is reduced, cam overlap affects are reduced making mapping easier in fact.

From what I've read on OZ forums and the replies I've got off here, it seems to be a debateable route to take. Everyone has an opinion on how the injectors are affected, or whether multi-throttles are a benefit etc. No one seems to question a Greddy, or Plazaman intake, and just take it at face value. Funny old world isn't it?

[Jay]

A bit off topic, but i`m following this with interest. Pope, you mentioned the torque issues earlier, i`ve always thought the RB to be a bit down on this anyway, with whatever plenum, would a spacer on a standard plenum help to bring this up or am I fighting a loosing battle due to the overall engine design?

[RoboPope]

Jay, Yes a standard plenum spacer will help

NVCS is the oil pressure operated, electrically controlled inlet cam angle control system. I had some work done so it still operated on the rb30 / rb25 hybrid. I have waffled on about how it works at length, its for idle emmisions and smoothness etc etc. I'm sure I remember Sarky going on about how there was a long and short (relative route) on the GTT?

I like NVCS im thinking about some cam reprofiling so I can keep the sensible idle as my GTR sounds likea lumpy tractor at idle. HKS do the VPro for GTR's so there are some benefits

[Goddard]

Yeah longer runners will give you more torque (but not much), but it's probably the mechanics of the engine that are the limiting factor. IIRC the RB engines are pretty over square (86bore x 73 stroke?), so the short stroke is good for revs and power, but doesn't produce the torque you might get from a lazier engine.

Pope, I was wondering about moving the solanoid to have it external to the head, preferably on a bit of braided hose so I can tuck it out of the way. To me this sounds stupid as it must just be a plunger that blocks an oil way, but I thought I read someone had done exactly this. Or if there is a smaller solanoid that will fit and work I'd give that a go too.

[RoboPope]

I cant say I have heard of anyone doing it, when I get home at the weekend I will have a look in the engine manual and see how and what it operates

Pope

[Goddard]

Thank you please.

[Goddard]

Latest updates,

The parts have all been CMM'd (co-ordinate measuring machine for those interested). So I now have the precise data needed to create a 3D CAD model and 2D draft to get a plate water jet cut to the shape.

On the CMM,




an image of the data from the GTR twin throttle,


Parts being cleaned,



Comparison between the spindle/plate blockage on the 45mm GTR throttle and a 45mm Active Technologies patented "blade" or "shaftless" design. The increase in area is the equivalent from going from 45mm to 48mm or even higher as that is a 10mm spindle rather than the more popular 8mm spindle on the GTR side, but the bonus is that because the bore is still 45mm, you don't loose any air velocity, and maintain the torque,





I'll try to get the CAD done this week at work, and get a plate water jetted next week sometime.

[Ahapartridge]

Those blue TB's are very nice, are they RB26 ones?