I just received a spare set of throttle bodies in the mail today. I am going to send them to maxbore.com Monday to be overbored, have the throttle shafts thinned and then filled with larger butterflies. I will be then port matching the boots to the throttle bodies and intake ports on the heads to the boots. Here's what we are starting with, I'll post up the new dimensions in a week or two when I get them back. I'm hopping for at least 42mm (as the entrances are already 40mm) but really anything over 36mm will be an improvement. (As the exits are only 32mm x 35mm)
I've had a number of two-stroke snowmobile engines that responded really well to enlarged throttle bodies. This is a very well named thread; really curious what lowering the pressure drop through the intake system will do for mid-range torque.
Well 42mm is a pipe dream, not enough material in the lower sections where it meets the engine boots. The man Larry followed this on mr RC45 & lost power everywhere. Larger throttle bodies have only been shown to work at very high revs. They kill gas velocity at any normal revs.
Either way without a before & after dyno run we won't see what effect it has.
Larry didn't bore out his throttle bodies, he machined larger intake trumpets for inside the airbox.
Without the HRC race kit, that mod alone was useless.
VFRpwr
I've had a number of two-stroke snowmobile engines that responded really well to enlarged throttle bodies. This is a very well named thread; really curious what lowering the pressure drop through the intake system will do for mid-range torque.
And snowmobiles operate very well at high rpms, with a narrow powerband, and have the clutching to take advantage of it.
I have a set of '09 I'm going to use on my 5th gen and I'm playing with the same idea...
These are also off of an 09. They look brand new :)
Switchblade
Hmm thought about the starter valves but i guess it want have much of a affect .
Right my name is George . Needs bigger print on his web site :goofy: .
How are you going to re-sync the two half's ? Are you doing the disassembly or is he ? I guess if he does it he will re-sync.
I am really not concerned over the starter valves. Their use is only in the 0-5% throttle position range. If I get super bored, I will sync them.
Veefer800Canuck
Probably gain some HP up top, and lose some down below.
I have heard that before.... Basically what you have said with every modification that I have done, to date lol.
triharder
Okay, i'll bite.
Doesn't "goes into" have to match "goes outta"?
If you don't inlarge your exit bores (which i believe is dictacted by the valve size) aren't you just fluiding the cylinders?
Just curious.
Huh?
Mohawk
Well 42mm is a pipe dream, not enough material in the lower sections where it meets the engine boots. The man Larry followed this on mr RC45 & lost power everywhere. Larger throttle bodies have only been shown to work at very high revs. They kill gas velocity at any normal revs.
Either way without a before & after dyno run we won't see what effect it has.
Yeah we all know 46mm is too big for a 749cc engine 118hp engine. But 40-42mm should do the trick nicely on a 782cc engine.
Yes Larry did just create wider velocity stacks, but the pion was it did NOTHING for power delivery or cylinder filling, as he lost torque & HP everywhere.
As I've said before the bandit 1200 uses 36mm TB's so they are capable of flowing more than enough air. The journalist that created the bio blade told me it uses standard TB's & airbox, plus a set of cams & a one off akrapovic exhaust.
Two strokes & 4 strokes react differently to carbs sizes. Not saying it won't work, just that it's Not an area that is considered restrictive on the current rev range, as Larry proved. Without the full HRC kit & the extra 2000rpm.
It's not the HP, it's the air flow. The bandit is in a far lower state of tune ! But it still pulls 50% more air through the same TB's over a comparable rev range. I believe the CB1300 uses the same size & is in a better state of tune than the bandit.
All are well under our hp goals. Sure you can pull more hp through those tiny throttle bodies, but not as much or as easily as you could through say 42mm throttle bodies. Our bench mark should be more along the lines of the gsxr750. Those have 42mm throttle bodies, are rated at 150 crank hp and have a wonderful powerband.
The stock TB seems to funnel down from entrance to exit (40 - 35mm ) based on your measurements... are you going to maintain some sort of taper... idk, 42=> 40 mm?
The taper is important to maintain a good gas flow pulse. But too big & the depression caused by valve opening & piston travel is not sufficient. Gas velocity is the key, that's why if you look at TB size, its more related to RPM than to HP, HP being the result of same torque at higher rpm, but usually results in poor low end drive & fuelling.
The intake pulse is caused by piston depression, so try breathing in slowly with your lips just open. Now try if fast. Do the same with your mouth wide open, you can tell difference in gas velocity. Now imagine what happens when you run flat out breathing hard, mouth wide open & rapid breathing. That's why the GSXR750 has larger throttle bodies, because it revs much higher, the 90's versions had 13.5krpm limit & the early 2k's had 14,250rpm limit. If you look at this comparison of 2K -v- 2004 models the only reason the newer one has a higher HP figure is because they retuned where peak torque occurs thus the point it decays.
[image: post-24524-0-43974300-1410721944.jpg]
That's why I had my cams made & have made the various intake mods to try to push peak RPM higher. I hope to have a dyno pull done this week, to see if those mods made any difference before I fit the TBR & rapid bike race when it arrives. Target rpm for peak torque is 9500-10k & just to put that in perspective the current 107rwhp is the result of 57.5ft/lb @8500rpm, with a residual of 53.8@10500=107.5rwhp.
Now if we push those same numbers 1500rpm up the range to 10k, then 53.8@12,000rpm=123rwhp with no other changes to the engine. That makes the same torque look like 16hp more ! is it anymore drivable, no, will it achieve a higher top speed yes even in a drag scenario.
The taper is important to maintain a good gas flow pulse. But too big & the depression caused by valve opening & piston travel is not sufficient. Gas velocity is the key, that's why if you look at TB size, its more related to RPM than to HP, HP being the result of same torque at higher rpm, but usually results in poor low end drive & fuelling.
The intake pulse is caused by piston depression, so try breathing in slowly with your lips just open. Now try if fast. Do the same with your mouth wide open, you can tell difference in gas velocity. Now imagine what happens when you run flat out breathing hard, mouth wide open & rapid breathing. That's why the GSXR750 has larger throttle bodies, because it revs much higher, the 90's versions had 13.5krpm limit & the early 2k's had 14,250rpm limit. If you look at this comparison of 2K -v- 2004 models the only reason the newer one has a higher HP figure is because they retuned where peak torque occurs thus the point it decays.
[image: attachicon.gif]image.jpg
That's why I had my cams made & have made the various intake mods to try to push peak RPM higher. I hope to have a dyno pull done this week, to see if those mods made any difference before I fit the TBR & rapid bike race when it arrives. Target rpm for peak torque is 9500-10k & just to put that in perspective the current 107rwhp is the result of 57.5ft/lb @8500rpm, with a residual of 53.8@10500=107.5rwhp.
Now if we push those same numbers 1500rpm up the range to 10k, then 53.8@12,000rpm=123rwhp with no other changes to the engine. That makes the same torque look like 16hp more ! is it anymore drivable, no, will it achieve a higher top speed yes even in a drag scenario.
Is that why the R6 has smaller throttle bodies than the R1? Because it revs higher? lol
To answer his question, CandyRedRC46 did the R6 conversion a long time ago. I have an R6 equipped airbox on mine. I'm not feeling it (yet)
but I'm running small tube headers with a CAT. just sorta waiting on the good header to get built. the rapidbike2 is here and installed with the timing booster, and 93octane. the 1000RPM limiter extension is working as well. first gear goes absolutely berzerk now with the -1 front. 6th gear pulls quite easily into the high 11k range, 162 thereabouts indicated. and yes, while that is still about stock top speed, it's pulling TO it, at a much higher rev range. I'm not entirely sure a stocker would carry enough topend steam to pull 6th into the limiter on a -1. BUT. I have no proof.
I have a speedo corrector coming in the mail, with some other delicious upkeep bits. new (stock) brakes/pads, a new rear sprocket, ect. my last chain before I changed it knocked the tip off of a few teeth out back, so I'm changing it out as soon as I can.
Candy are you also going to R6 velocity stack on the VFR ? I alway thought the 6th gen un-equal ones are FU.
When I get the rapid bike racing I will tune each cylinder individually, so I will be ditching the staggered velocity stack arrangement. I will probably need some bigger stacks after the overbore. As I do not know how much the throttle bodies can be overbored yet, I do not know which velocity stacks I will be going with yet.
Yes Larry did just create wider velocity stacks, but the pion was it did NOTHING for power delivery or cylinder filling, as he lost torque & HP everywhere.
As I've said before the bandit 1200 uses 36mm TB's so they are capable of flowing more than enough air. The journalist that created the bio blade told me it uses standard TB's & airbox, plus a set of cams & a one off akrapovic exhaust.
Two strokes & 4 strokes react differently to carbs sizes. Not saying it won't work, just that it's Not an area that is considered restrictive on the current rev range, as Larry proved. Without the full HRC kit & the extra 2000rpm.
Keep in mind, Larry has no way of adjusting the air/fuel ratio or ignition timing or cam timing on those RC45's ;)
End of thread · 26 posts recoveredWayback Machine snapshot 8 Jul 2017