Rb26 oversized itb's... has anyone actually done it?

[LaurelPWR]

Hey lads,

As the title states, RB26 oversized 45-49mm throttle upgrade...

The best known company that offers this service is NAPREC in Nagoya, Japan.

I believe it's around $1.2k+postage and tax and also (if you use Streeter) Streeter's postage fees and commission etc. And that's just for the throttle machining and rebuilding and you have to supply your own set of throttles. Then you need the 50mm gaskets.. more $$

 

NAPREC link:

 

http://www.naprec.co.jp/product/t001

 

There is also the Garage Ito option which is cheaper but still $1100+postage+gaskets etc. etc. and you still need the set of throttles to send them.

 

Nengun link:

 

https://www.nengun.com/garage-ito/rb26-big-throttle-body

 

Interestingly enough, HyperTune now offer their itb intake manifolds with the 49mm oversize runner option to mate with NAPREC throttles. Both company's promote each other in regards to these products now too.

 

NAPREC link for HyperTune plenum:

 

www.naprec.co.jp/product/rb26dettサージタンク

 

There's also this Facebook post I saw with what I assume is a customer of Top Secret and someone who has done the upgrade. I'm not 100% if these claims are of the oversized throttles and the plenum combo or just the 49mm runner plenum...Anyways he's claiming around a 40ps gain from the upgrade which I think (if at all true) is actually a pretty substantial gain for an intake mod...

 

Here's the link:

 

https://m.facebook.com/masahiro.takemura/posts/921436694600562

 

And a screen shot of the link:

 

 

Some more screen shots of the products in question:

 

 

 

So, has anyone on here actually done this mod or know of anyone with first hand experience on this and that has done the 49mm itb's ?

Would love to hear and or see some graphs or real world results.

[KiwiRS4T]

The trouble with this sort of mod is that almost no-one does it in isolation - they do it as part of a rebuild/upgrade so you will be very lucky to find anyone able to offer a before and after comparison.

[WantGTR]

Whats the point really? Everyone is going  aftermarket plenum these days. Extra money, extra bling, extra likes.

If youre looking to squeeze more power might just be easier to go single throttle and plenum anyway otherwise leave as is and screen in a few more psi

[LaurelPWR]

Whats the point really? Everyone is going  aftermarket plenum these days. Extra money, extra bling, extra likes.
If youre looking to squeeze more power might just be easier to go single throttle and plenum anyway otherwise leave as is and screen in a few more psi

The whole single throttle more power thing is a myth... I believe both single & itbs have their individual uses and purposes so it's not something that really can be compared.
Not to mention there's the car in the article above built by Top Secret running itbs making well over 900hp...
But anyways that's an argument that could go on and on hahahaha
So yeah, aside from all that, I kinda just really wanted to know if anyone on here has actually done it..
I've always seen it as one of those glamorous mods that is there for the high end and elite types and big workshop builds.. Would be cool to hear from just a lad who decided to take the plunge on it.
But as said above^ it's normally done with a whole host of other high end fruit so probably never going to see a before and after but it's worth a shot asking (:

[WantGTR]

6 hours ago, LaurelPWR said:

 

 

The whole single throttle more power thing is a myth... I believe both single & itbs have their individual uses and purposes so it's not something that really can be compared.
Not to mention there's the car in the article above built by Top Secret running itbs making well over 900hp...
But anyways that's an argument that could go on and on hahahaha
So yeah, aside from all that, I kinda just really wanted to know if anyone on here has actually done it..
I've always seen it as one of those glamorous mods that is there for the high end and elite types and big workshop builds.. Would be cool to hear from just a lad who decided to take the plunge on it.
But as said above^ it's normally done with a whole host of other high end fruit so probably never going to see a before and after but it's worth a shot asking (:

 

 

Absolutely, i agree with you. I think one of the big advantages of going single throttle is using electrontic throttle and the options it gives you. Really brings the ol Rb into the new century.

I remember reading a thread on here about someone actually getting oversize throttles done but they were stolen before they were used.

Have you looked at what efi hardware have to offer?

https://www.efihardware.com/products/2521/Nissan-Skyline-GTR-RB26DETT-Enlarge-Throttle-Bodies

[Leroy Peterson]

ITBs are more trouble than they're worth for turbo application IMO.
If they're anything like the GTiR ones: more effort, less room, harder to reach stuff (which I guess is just business as usual for a GTR) more shit that can break/leak.

[LaurelPWR]

Absolutely, i agree with you. I think one of the big advantages of going single throttle is using electrontic throttle and the options it gives you. Really brings the ol Rb into the new century.
I remember reading a thread on here about someone actually getting oversize throttles done but they were stolen before they were used.
Have you looked at what efi hardware have to offer?
https://www.efihardware.com/products/2521/Nissan-Skyline-GTR-RB26DETT-Enlarge-Throttle-Bodies

Yeah man I just received my 49mm throttles from them last night [emoji87][emoji12]
They only offer a 48mm service though...they like to keep a minimum 1mm of housing "meat" between the inner bore wall and the shaft bearings on each end of each set of throttles...but after a long phone call explaining that there's other company's that offer 49mm service albeit for a higher cost, I convinced them to go to 49mm and they do it by moving the centre of the bore inwards .5mm to retain the 1mm of "meat" at the shaft bearings.

I would post pics but I went and dropped them off at the machine shop with a nismo plenum to get the plenum cnc port matched to the throttles.
I don't need the injector plate machined as I run the throttles on my rb25 using a custom made adapter that used cut and shut lower rb25 runners which are 50mm ID.
Will be interesting...

[LaurelPWR]

ITBs are more trouble than they're worth for turbo application IMO.

If they're anything like the GTiR ones: more effort, less room, harder to reach stuff (which I guess is just business as usual for a GTR) more shit that can break/leak.

 

That's a matter of personal preference my dude.

I personally love the snappy on/off throttle response I get from them. It was a nice upgrade from the forward facing "Greedy" plenum and also surprisingly increased boost response.

Another thing is, I don't know any other car in the world running an old GT28/29 frame, internal gate turbo making the figures I make so I strongly believe they help me achieve that also.

 

So yeah they have cost me a lot and continue to do so, but to me it's well worth it haha

 

As far as room to work on them goes, well rb's are mounted north/south so naturally they would be a s h i t l o a d easier to work and because mine are in an s13, my strut towers are further away from the motor (s chassis McPherson strut VS unequal double A-arm R chassis) so I may have a little more room again to access them over a skyline.

 

Then if I compare to the factory rb25 intake manifold... NO COMPETITION AT ALL haha

You can't hardly access the injectors and a few other sensors on the factory long plenum because of its curl-over long runner design. Then add the fact that the throttle body sits smack bang in the middle of the plenum, feeds from the cooler cold pipe that goes up past the top of the turbo, over the rocker covers... just to chance plugs and coils you have to pull half the intake system off...

 

Give me throttles over that any day haha.

Easier, snappier, faster for a given purpose.

[LaurelPWR]

 

^^49mm bored out throttles with new 49mm oversize butterfly's, cnc port matched nismo plenum & cnc cut plate to match the new centres of the throttle bores that will be welded to the rb25 runners

 

 

 

^^finished cnc machine work inside the nismo plenum.

The origional ID's inside the nismo plenum runners are 43mm from the bell mouths all the way to the last 10mm before the throttle, then it tapers to 45mm.

I've had the runners cut to 46mm from the bell mouths, but then started the taper from halfway along the runner which tapers out to 49mm to match the throttles.

 

[Snara]

For how many horsepower stock ITB is good? Or how much bhp u have/seen on stock ITB?

[LaurelPWR]

For how many horsepower stock ITB is good? Or how much bhp u have/seen on stock ITB?

 

There's some old videos and articles around of jap built gtr's doing 8 sec 1/4 passes with itbs so I would assume they can support anything one can throw at them..

Also, a google search shows results of 1000hp cars running itbs so I guess it's all about how much you want to spend for your personal goals and desires which is pretty much the outcome with all these sorts of questions...

[GTSBoy]

The factory ITBs are HUUUUUUUUUUGE compared to any reasonable size single throttle.  At least the equivalent of a 100mm single, taking some extra wall friction and extra throttle plate obstruction into account.

[Mick_o]

ITB's are the ONLY good thing about RB26's lol! KEEP THEM! Big single throttle plenums make 26's even doughier than they already are! 

[LaurelPWR]

I'll have a before and after dyno result in the next months but unfortunately won't be a straight up comparison between the 45mm and 49mm throttles as I'm also installing a crank trigger kit, r35 coil kit, 1000cc injectors and re tuning with a new link G4+ instead of the power fc but will be the same turbo set up so might still be relevant enough for some [emoji848]

[jnoor]

On 11/29/2017 at 11:47 PM, LaurelPWR said:

 

^^49mm bored out throttles with new 49mm oversize butterfly's, cnc port matched nismo plenum & cnc cut plate to match the new centres of the throttle bores that will be welded to the rb25 runners

 

 

 

^^finished cnc machine work inside the nismo plenum.

The origional ID's inside the nismo plenum runners are 43mm from the bell mouths all the way to the last 10mm before the throttle, then it tapers to 45mm.

I've had the runners cut to 46mm from the bell mouths, but then started the taper from halfway along the runner which tapers out to 49mm to match the throttles.

 

Apologies to resurrect such an old thread, but I'm planning on sending my throttles to Garage Ito for the 49mm enlargement, but I'm having difficulty finding out how to perfectly machine the plenum runner diameters to match.

LaurelPWR how did you go about CNC machining yours, did you have to get a jig made up for it to keep it straight and true? And just to clarify, is it a gradual taper from the 46mm to 49mm? i.e. it increases bit by bit from 46mm until it become 49mm at the throttle end.

Starting the taper from halfway, what kind of distance is that from the throttle end?

Apologies for the many questions, would be incredibly grateful for any info.

Edited March 1, 2019 by jnoor

[RICE RACING]

http://www.riceracing.com.au/rides/DatsunR34_Charles.htm

 

This attached graph is on the stock RB26, with Nismo intake ITB, turbo system fitted but in NA form to calibrate the engine (noboostbro), and all other aspects are done with custom tables to account for map/tip, bap, fuel equivalence ratio, WM50 etc etc.

There is minimal pressure drop overall, though what is ascribed to the throttle plates themselves is not known, either way its minor. This is obviously not an issue when you are running under turbocharged conditions thus we never felt the need to 'increase' the size of them even when running the 3.15lt engine that revs to 9k rpm.

FYI, Most people ditch the ITB cause its hard to set up. I on the other hand love them On other engine types with respect to increasing the size again when the motor is at 3000mB + its really the most pointless money spent ever, may as well put some stickers on the car they give comparable power gains honestly. If however you are going to run the car at 1500 > 2000mB map and are limited say by racing class etc then this is an area worth looking into, but its for the last 1/5th of the power band mostly nothing more.

[LaurelPWR]

Apologies to resurrect such an old thread, but I'm planning on sending my throttles to Garage Ito for the 49mm enlargement, but I'm having difficulty finding out how to perfectly machine the plenum runner diameters to match.
LaurelPWR how did you go about CNC machining yours, did you have to get a jig made up for it to keep it straight and true? And just to clarify, is it a gradual taper from the 46mm to 49mm? i.e. it increases bit by bit from 46mm until it become 49mm at the throttle end.
Starting the taper from halfway, what kind of distance is that from the throttle end?
Apologies for the many questions, would be incredibly grateful for any info.

Hey man apologies for the late reply....
I had an engineer shop cnc my nismo plenum.
He clamped it the the bed and made a program to suite....he probably still has that program and could do the same for any plenum depending on if garage ito offset the throttle centre slightly like efi hardware did for mine to retain more meat around the shaft seals.

Even if the ito centres are slightly different to mine, I’m sure he could slightly modify the program to cut any centre...

[LaurelPWR]

http://www.riceracing.com.au/rides/DatsunR34_Charles.htm

 

This attached graph is on the stock RB26, with Nismo intake ITB, turbo system fitted but in NA form to calibrate the engine (noboostbro), and all other aspects are done with custom tables to account for map/tip, bap, fuel equivalence ratio, WM50 etc etc.

There is minimal pressure drop overall, though what is ascribed to the throttle plates themselves is not known, either way its minor. This is obviously not an issue when you are running under turbocharged conditions thus we never felt the need to 'increase' the size of them even when running the 3.15lt engine that revs to 9k rpm.

FYI, Most people ditch the ITB cause its hard to set up. I on the other hand love them [emoji6] On other engine types with respect to increasing the size again when the motor is at 3000mB + its really the most pointless money spent ever, may as well put some stickers on the car they give comparable power gains honestly. If however you are going to run the car at 1500 > 2000mB map and are limited say by racing class etc then this is an area worth looking into, but its for the last 1/5th of the power band mostly nothing more.

 

Hey man, interesting data!

I’m fully aware this is 99% a waste of money and will probably have little to no measurable gains....but I’m not worried. My whole setup is overkill....here’s some insight;

 

I’m only aiming for 550whp with my new setup but with every single thing I can do to have as least restrictions as possible to get every single drop of performance out of the setup.

 

I’m also installing a Platinum trigger kit, Platinum r35 coil kit, HKS type R 100mm intercooler, full 4 inch exhaust from turbo back with a throttle/boost activated 4 inch bypass butterfly straight after the dump, hta3076 turbo with a 1.01ar twin scroll turbine housing, R31house equal length runner twin scroll manifold with two TiAl 38mm gates added on + individual runner egt’s and then obviously the nismo plenum cnc port matches to the 49mm oversized itb’s with a port matched Rb25det neo lower runner cut’n’shut itb adapter with Bosch 1650cc’s under a hks fuel rail, hks step 1 staggered cams even doing a Z34 6 speed box conversion hahaha......all being run by a complete custom wire in Link Fury ecu setup..

 

Most of all this gear is considered by majority as being way overkill for my power goal but the most important thing to me is earliest possible torque, boost response and widest fattest midrange and room under the curve.

 

I’ve probably spent approximately $6k+ on just the intake and itb setup alone, let alone the R31house manifold and customisation to it hahah and I’ll continue to throw money at this project until I get my result, which I will achieve.

 

I’m not in the least bit worried about others opinions etc. when I can look at the end result and know full well I’ve done everything I can to get the desired result [emoji1365][emoji4]

[mr_rbman]

3 hours ago, LaurelPWR said:

 

Hey man, interesting data!

I’m fully aware this is 99% a waste of money and will probably have little to no measurable gains....but I’m not worried. My whole setup is overkill....here’s some insight;

 

I’m only aiming for 550whp with my new setup but with every single thing I can do to have as least restrictions as possible to get every single drop of performance out of the setup.

 

I’m also installing a Platinum trigger kit, Platinum r35 coil kit, HKS type R 100mm intercooler, full 4 inch exhaust from turbo back with a throttle/boost activated 4 inch bypass butterfly straight after the dump, hta3076 turbo with a 1.01ar twin scroll turbine housing, R31house equal length runner twin scroll manifold with two TiAl 38mm gates added on + individual runner egt’s and then obviously the nismo plenum cnc port matches to the 49mm oversized itb’s with a port matched Rb25det neo lower runner cut’n’shut itb adapter with Bosch 1650cc’s under a hks fuel rail, hks step 1 staggered cams even doing a Z34 6 speed box conversion hahaha......all being run by a complete custom wire in Link Fury ecu setup..

 

Most of all this gear is considered by majority as being way overkill for my power goal but the most important thing to me is earliest possible torque, boost response and widest fattest midrange and room under the curve.

 

I’ve probably spent approximately $6k+ on just the intake and itb setup alone, let alone the R31house manifold and customisation to it hahah and I’ll continue to throw money at this project until I get my result, which I will achieve.

 

I’m not in the least bit worried about others opinions etc. when I can look at the end result and know full well I’ve done everything I can to get the desired result

love what you're doing and being different, massive props. Love all the mods and the way you are/am/have been going about them...

Just one question, money doesn't seem to be a massive issue so i'm curious why with all the quality of parts you've used in most areas you haven't gone with a nice modern say B/W EFR turbo etc that would almost certainly achieve your desired 'under the curve' results!?!? The HTA definitely has it's positives but in this day and age isn't exactly a modern piece of kit?!?

Edit: some more reading about the HTA turbo's, they seem to be a good thing that I possibly haven't heard too much about being more an Evo turbo upgrade etc...

Keen to see your results...

Edited April 13, 2019 by mr_rbman

[RICE RACING]

Going all out may as well put in a decent computer while at it