Are bored throttle bodies beneficial?

[Cycle Concepts]

In our testing we have seen power gains with our bored 47 mm throttle bodies on stock zx14 engines of 8hp.
On a built 1570 we have seen 13 hp.   Dan Millholland among many other people will confirm this.

On the gen 2 busas replacing the 44 mm units with our 47mm units will pick up about 6 hp on a stock motor and 13 hp on a busa motors with a ported head and cam. Cecil at HTP is one of many that will verify this as well.

Now here's the deal.  All bored throttle bodies are not the same.  Ours are bored all the way threw and are never smaller than the butterfly diameter. There are at least two laces selling "bored" throttle bodies out there that have the stock size blades or they leave a huge lip in the bore.  Don't even waste your time with them.  We tested them and they don't do a damn thing.
If there is any part of the bore that is smaller than the dia of the blade then don't waste your time with them.

With that being said,  the gen 1 busa throttle bodies are 46 mm stock and there is very little gain with going to a larger bore on the gen 1 busa throttle bodies ON A STOCK MOTOR.  However, on a built motor of 1507 or bigger there is a gain with going to the larger throttle bodies.  And the more radical the head and cams are the more power you gain. 
Again, they have to be done properly and have smooth bores of no less than the new over sized butterfly diameter.

so you are boring oem gen2 throttle bodies now? Send me some info or call me at the shop..803.285.8093

[Cookie]

your ? is flawed.
it is like asking is a thropy wife benefical?

You could stand a 'THROPY' wife next to a 'TROPHY' wife and I don't think anyone would be bored! 

Unless it was 'beneficial' as being "benefical" 






  No one has ever called me a Jakcass either! 

[Competition CNC]

hey Jim, great info.

The Montgomery OS TB setup i have is:

52mm top of the Hartley stacks where they start to bell out

51mm at the TB/stacks connection

49mm at the blades

below the blades there is a tapered section, goes  from 49 down to 44.8

44.8mm where they go into the head.

You think that config will work any better than stock TB/stacks with Carpenter's short intake/big exh head & 465/425 cams, 18.3-18.5:1 CR??

One of these days, i'd like to try yr new big exh head 

Karl, the taper needs to be constant.  Basically the intake port starts at the bell mouth and ends past the valve in the combustion chamber.  Any hour glass shape is detrimental.
We would have to try it to know what the results are in the real world.  Computer simulations only tell you so much.
Let me know if you want me to update your stage 3 head.
FYI  Were testing another revision of our latest cams and port designs as we speak. I guess you would call it rev 4. So far each revision has matched the computer simulations almost perfectly.  Thats scary. We are really getting into one off custom cams playing with cam ramp acceleration rates and the results are very positive.   If i had more customers for these big busa motors with stage 3 heads the pace of development would be much faster.    Richard said there expecting over 315 hp from this engine on the dyno.  Which is what were seeing for crank numbers in the simulations.  Should know very soon.

Dwayne, it was nice chatting, looking forward to working with you.

[entropy]

Jim, there is no way to get a constantly decreasing bore by boring stock TB's below the butterflies.  Best that can be done is a section with a taper.

I don't know antone who makes full custom Busa TB's.

315 at the crank???!!! YIKES!
What do you figure that is at the wheel?

[Penianator]

What about turbo applications?? How much hp could be expected??

[Competition CNC]

Jim, there is no way to get a constantly decreasing bore by boring stock TB's below the butterflies.  Best that can be done is a section with a taper.

I don't know antone who makes full custom Busa TB's.

315 at the crank???!!! YIKES!
What do you figure that is at the wheel?

Yea they are tapered to the port manifold.... I shoiuld take some pics... hard to describe....

Jenvey makes custom busa throttle bodies but they are small, 42mm? I believe. 

We should know what it makes for power very soon Karl. 

Richard said the head he had on the bike (our medium port stage 2 head intended for a 1507-1580cc engine) made almost 300 on the dyno.
He sold that head and he now has the stage 3 gen4.

[Competition CNC]

What about turbo applications?? How much hp could be expected??

turbo application?  I dont think you would see much if any power with them on a turbo.  Maybe if you were running huge boost... but i really dont know for sure.

[speedduck]

I have 49mm throttle bodies, and it starts with 50mm, 49mm at butterflies, then quickly tapers to 45mm, rest is 45mm. So, is there a flaw in design ? I don`t know who made these, they were in the bike when i bought it.

[TrickTom1]

I have 49mm throttle bodies, and it starts with 50mm, 49mm at butterflies, then quickly tapers to 45mm, rest is 45mm. So, is there a flaw in design ? I don`t know who made these, they were in the bike when i bought it.

the 45mm is an orifice

[Competition CNC]

Basically the port reduces in cross sectional area from the bell mouth to about where the port divider v is in the intake port. That's where the ports minimal cross sectional area is.  Then the port gets larger again to the valve seat.
The port is like a funnel.  you want the area of the port to steadily get smaller to increase the velocity to xxx feet per second.  The rate of area change should be consistent over the length of the port.  This area A vs area B vs length is the ports overall taper.
Any abrupt changes in cross sectional area absorbs port kennetic energy (air mass energy) as well as reflects a portion of the postive and negative pressure wave's amplitude (sonic).  This hurts power when you reduce the positive pressure wave's effect on the intake charge.

If you guys are into learning more about this sort of stuff i highly recommend Gordon Blair's book "The design and simulation of 4 stroke engines".  It came out in 1998 I think and its about $100 or $80 if you are an SAE member.  You can find it on amazon.  Its very dry text book type reading with mind boggling mathematical formulas but if you are really really into complex engine dynamics then its for you.
Its considered by most as the most up to date research on engines in the world.  The software based on the formulas in the book is used by F1 teams, cup teams, and just about every top levels of racing.  The software is about $30,000 per year for a licence!!!   But you can buy the book and get a good understanding of whats going on in the entire engine.

[clearblue]

I have a set sitting here on my bench , don't know if they were done by hand or not . I got them from Bill W some time back and was going to put them on my bike (1397 425/425 cams Carpenter Motor)  But was advised that they most likely would do nothing but hurt power

[Competition CNC]

I have a set sitting here on my bench............. was advised that they most likely would do nothing but hurt power

I'm just curious, who told you that?

[speedduck]

Here is the 49mm throttle body, and there is almost a step after blade.
There is markings on throttle body "BMT 02" ,anybody knows who made them ?

[entropy]

what is stamped on the blades??

[speedduck]

Nothing, only the markings on bodies, and numbers for cylinders

[Competition CNC]

Here is the 49mm throttle body, and there is almost a step after blade.
There is markings on throttle body "BMT 02" ,anybody knows who made them ?

That step is exactly what im talking about. I have seen several sets like that.   Also it looks like there a step again at the rubber manifold.  Thats just as bad, it does the same thing.  Any abrupt change in CSA reflects part of the wave and reduce the amplitude of the wave.

[speedduck]

Throttle bodies were not from that head, just put them on, that`s why the rubber doesn`t fit. I have struggled with different cams and compression, power allways stops at certain level, maybe this could be the cause.
Head in the picture is made by Lee`s, is that Lee`s performance(?) , good quality ? It needs all valves and few guides, bought from blown engine.

[Competition CNC]

The lift (valve window area) has to be of proper ratio to the ports MCSA.  Thats very important.  Thats why a one port size aproach doesnt work on a wide range of engine sizes.

The static compression ratio has to be correct for a given duration on tha cams.

so cams have to be carefully matched to the head porting to get the last 10 hp from one of these modern sport bike engines.

Its the difference in making 210-215 hp with a 1397 street motor and making 220-225 hp.

[speedduck]

Jim, there is no way to get a constantly decreasing bore by boring stock TB's below the butterflies.  Best that can be done is a section with a taper.

Yea they are tapered to the port manifold.... I should take some pics... hard to describe...

Can you take pics of the taper design ?
I tried to make the step smoother but ended up wasting my throttle bodies, there is now hole on the side 

[Competition CNC]

Damn, they get pretty thin.  Did it break threw where the boring was done where that step is?  You may be able to epoxy them. That's the problem when they "round" bore them too deep past the blades.

When we are talking constant taper bore we aren't talking about a "round bore".  We are talking about cross sectional area.

You will have a constantly decreasing area creating an ever increasing velocity that's gradual.  I wish I had a set here now so I could take some pics.
We ran into this on the busa gen 2's, breaking threw in a few areas.  That's why we wont do the 47mm on the gen 2's anymore just 46mm.  You have to constantly be checking the thickness.  Its a real PITA. We check thickness using a Dakota ultrasound unit.  http://dakotaultrasonics.com/?gclid=CKqHi7PF_64CFQgRNAodF22e2g We use it on heads, manifolds, throttle bodies, welds, and all sorts of stuff.

[speedduck]

Yes, the step was about the same on outside and didn`t pay enough attention to it 
I think i will take std bodies and make some minor modification, try some taper but smaller diameter.
How much difference would be expected if shortening throttle bodies, or intake tract ?

[surprenant]

How much to do a set GEN1 for a 1441..?....i have tried them before and always gained hp...and we were swapping stockers vs bored ones at the time...and picking up beetween 5 to 8hp...on small motors.

[Competition CNC]

Yep thats a typical hp gain on a smaller motor.

Give us a call at the shop.....

[badass1000]

So what about the head and the intake manifold?  on my 09 busa the bottom of the tb are 44mm.  the head is 42mm.  the manifold goes from 44mm tb side to 42mm head side. Is the bottom of the tb bored out to 46mm or is it 46mm at the blades and 44mm out the bottom? Can't go from 46mm out the tb to 44mm manifold.
Would it be benificial to have the head ported biger to match the 46mm tb?  Why wouldnt you port out the stock manifolds and head to be 44mm strait through instead of 42mm with the stock tb?

Just thinking about the bored tb and working on my engine right now.  these questions came to mind.

thank you
jeremy

[Competition CNC]

The cross sectional area of the port is constantly decreasing from the bellmouth of the air horn to the ports Min Cross Sectional Area.  That's called port taper and its critical for performance.

So its "normal" for the MCSA to be smaller at the flange vs the blade.