RB26 Multi throttle to Single Throttle body

[Skyrine-Dave]

Hi,

As the title.

I have a friend who's putting an RB26 head on an RB30 block.

He wants to get rid of the 6 throttle body setup and replace it with a single 100mm item.

We are wondering where he can obtain a spacer plate to replace the 6 throttle bodys? or would we have to get one machined up?

he's aware of that the 6 throttel bodies can provide a larger cross-sectional area and allow better tuning, but i dont think he wants to stuff around with settting them up.

[awurth]

what's there to stuff around with? If you've got it use it. Lad I bought some turbo's off said he had a single throttle body plenum setup for an RB26. I'll try find out.

[Bass Junky]

Speak to Steve Newing at Speed Technology in Melbourne

03 9873 5400

They are doing it to a car now.

[N I B]

WE have the spacer plates.

The 6 butterflys rob 60kw of air flow this is why the japs remove them also allows easy tuning with MAP sensors.

6X 10mm shafts in a small port is a bad thing for airflow and all the fairy tales about throttle area is just that. One large body has much better flow than 6 small ones near a valve then theres the turbulance issue.

[meshmesh]

hmmm, that's intersting Steve. First I've ever heard of this...

Is this something you'd do to any street GTR, looking for more HP, and what cost are involved?

[Skyrine-Dave]

this motor will be in a pretty much drag only car.

the objective is out right power, not street manners.

Steve is there any more info you could give me at all?

I think we found Tomei makes a replacement... waiting on a price from UAS... but i dont doubt that being Tomei they are going to be very $$$!

[Sydneykid]

WE have the spacer plates.

The 6 butterflys rob 60kw of air flow this is why the japs remove them also allows easy tuning with MAP sensors.

6X 10mm shafts in a small port is a bad thing for airflow and all the fairy tales about throttle area is just that. One large body has much better flow than 6 small ones near a valve then theres the turbulance issue.

Hi Steve, at what power level does the 60 kw get robbed?

[mokompri]

yeah 60kw seems like too much, i really dont see a single butterfly freeing up that much restriction over the 6 individual... if its all out drag then its alrite, but on a street or track setup i would keep the 6 butterflies, much better throttle response, but obviously it doesnt matter in this instance

[benjiman74]

Does anyone know the exact size of each throttle body on an rb26? I would have thought that despite the butterfly restriction the cross sectional volume of the six throttle bodies would be greater than the entry to the plenum anyway? The Mines gtr doesn't appear to be too restricted with the individual throttle bodies nor does the M3.

[BU5TER]

great thread any more info??

[Fitzpatrick Speed Works]

throttle bodies are 44mm

[Fitzpatrick Speed Works]

throttle bodies are 44mm and the runner rod isn't 10mm!!!

[Sydneykid]

Thanks S13drifter, I couldn't be bothered measuring them, but doing the numbers is easy;

Butterfly = 44/2*44/2*22/7 = 1,521 sqmm

Spindle = 44 * 6 (from memory) = 264 sqmm

= 1,257 sq mm each X 6 = 7,543 sq mm

Compared to the big single.....

100/2*100/2*22/7 = 7,857 sq mm

Spindle = 100 X 6 = 600 sqmm

= 7,257 sqmm

So, if s13drifters measurements are OK, the standard 6 throttle bodies are 4% larger than one 100 mm single throttle body. :cooldance

But is this the right way to do the comparison? Since each cylinder fires individually (one at a time) then isn't each cylinder getting sole use of the 100 mm throttle body some of the time? Not all of the time because of valve timing overlap between cylinders and the volume of air contained in the plenum. So you would have to know the valve timing and the plenum volume and the engine rpm to work out each individual cylinders share of the 100 mm. :wassup:

My opinion (for what it's worth) is that the main reason the Japs go to a single throttle body is so they can use MAP sensor driven ECU's. Multiple throttle bodies and MAP sensors don't go together very well when you have big cams and lots of boost. Over some LARGE horsepower number, there is probably an airflow advantage, but I have no idea how LARGE it is. :confused:

I could probably write a formula for it..........nah too much brain drain, time for a drink :alcoholic

[meshmesh]

You're a gun SK... I love it when you get all sentimental, and have these deep & meaningful threads of thoughts, that I don't understand WTF you're on about!! But at least it sounds interesting.

[Skyrine-Dave]

You're a gun SK... I love it when you get all sentimental, and have these deep & meaningful threads of thoughts, that I don't understand WTF you're on about!! But at least it sounds interesting.

[Roy]

Is there a reason why turbo cars dont bother with barrel /slide injectio etc. I assume thar forced induction makes the whole induction process less scientific and less sensitive than an NA engine. Unlike the race cars / bikes running NA and big revs.

Still if there is some truth to 60kw loss at very big numbers, perhaps barrel injection maintains throttle response but without the restriction?!?! Do RB26 throttle bodies / inlet manifolds have the same arrangement with coolant passages like the RB20/25

[DoughBoy]

A couple of things...

When you port a head, and then go on to match port the manifold and increase the runner diameter, do you think it is cost effective to get larger individual throttle bodies or get one large single?

When setting the tune up, how easy is it to get all indiv. throttles working in perfect synchronised harmony? When the aim of the game is to get each cylinder identical to the next, how much easier is it to set up a single throttle body?

When you crack open a throttle body, is it open 100%? I mean, is the throttle body more of a restriction than the shaft (slightly ajar), or does it improve airflow somewhat by giving it a more aerodynamic flow path over the shaft?

Hrm...

[Fitzpatrick Speed Works]

there isnt a MAF-MAP ECU in the world that can successfully run a really smooth transition between tps versus boost ignition map, this is WHY the japs run a single throttle body....By smooth i mean no imperfections in afr's or ignition changes, personally i wouldnt care on my car that much especially on a car with a big turbo where response time is slow and tps-boost map change over can be covered in this time, but the japs hate imperfections!!!!

The only ecu that is tunable in real time and can run a tps to boost is a apexi PFC, one because it retains afm's and two becasue it works like the factory ecu!!!

Oh the reason i say tps to boost is casue that is how the standard 6 throttle are set-up!! All this is not relevant on a drag car as you are aiming to keep it on boost all the time!!!

[Fitzpatrick Speed Works]

Werd! Very valid points doughboy!!! You can get bigger throttle bodies i think veilside do them ther are 48mm i even think there are 52mm but i can't remember who makes them!!!

Roy the rb26 doesnt have coolant running through the individual throotle bodies the do however run through just after this very much like a rb20 or 25.... i will post up some pics or the head and throttle bodies tomorow night if anyone is interested!!!