Throttle sizing?

Bitza · 24-12-2022, 08:57 AM

Hi seasonal greetings to all, well I've recently obtained a bargain throttle body assembly off a ST4(?). Which I'm thinking should be 50mm, but when
I measure the dia on the out (inlet valve) side it measures 45mm dia. Can anyone shed any light on the matter?

Mr Gazza · 24-12-2022, 09:56 AM

Hello Mike and I don't think you can beat a bit of seasoning whatever time of year. (Or season?)

I think you'll find that 45mm is pretty universal from 750 through 900 and ST4.
Dacs was concerned about using his 750 throttle bodies on the 944, but a bit of research revealed the above.
I do remember reading somewhere or other at the time that 50mm tb's were no particular tuning advantage, but I can't remember what engine in particular was being discussed.
It's all in the mapping these days!

Perhaps it would be interesting to look at what size the M1100 uses and also the 1100 Scramblers? I wouldn't be at all surprised to find they are 45mm.

Edit.. M1100 are 45mm TB. 2018 1100 Scrambler Special is 55mm but with full ride-by-wire. Probably goes beyond what can be conventionally mapped? And is a much more modern engine.

Albie · 24-12-2022, 10:34 AM

[QUOTE=Mr Gazza;596419

Perhaps it would be interesting to look at what size the M1100 uses and also the 1100 Scramblers? I wouldn't be at all surprised to find they are 45mm.

Edit.. M1100 are 45mm TB. 2018 1100 Scrambler Special is 55mm but with full ride-by-wire. Probably goes beyond what can be conventionally mapped? And is a much more modern engine.[/QUOTE]
But as like the 800 scrambler it uses only one throttle body per engine due to the size of tank and available space.

Bitza · 24-12-2022, 01:54 PM

OK, so I've kind of jumped the gun, because I didn't really measure the dia it was more of a case of offering up a rule. So the actual dia is 46.5mm and I have also measured a set of 45mm throttle bodies and they came out at 41.5mm dia. SO I guess it's just a matter of where you measure.
750, 900, 944, 1000 1100 all use 45mm throttles. 916 engined bikes 50mm, with later variants going up to 55mm. Have just looked up the 1100 scrambler special which like Gary says has 55mm plus fly by wire.

Mr Gazza · 24-12-2022, 03:04 PM

S4, S4R and S4RS, 916, 996 and 998 all have 50mm TB's.
They clearly breath differently with 4 valves as distinct from the 2 valvers.

Kato · 24-12-2022, 07:32 PM

As has already been said the TB's are pretty standardized across the range, fitting bigger TB's will work after setting up but will not deliver any benefit at all unless you have very heavily modified cylinder heads with race cams and are pushing the very upper limits of power output at the top end of the rev range

50mm TB's were worth 5-6 bhp on 1000/1100 motors in the 115bhp upwards below that sort of power there was zero advantage to be had other than bragging rights

24-12-2022, 08:57 AM	#1
Bitza Bronze Member Join Date: Jul 2006 Location: Poole Bike: M900ie Posts: 470	Throttle sizing? Hi seasonal greetings to all, well I've recently obtained a bargain throttle body assembly off a ST4(?). Which I'm thinking should be 50mm, but when I measure the dia on the out (inlet valve) side it measures 45mm dia. Can anyone shed any light on the matter? __________________ Bitza

24-12-2022, 09:56 AM	#2
Mr Gazza Lord of the Rings Join Date: May 2013 Location: Norwich Bike: M900sie Posts: 5,807	Hello Mike and I don't think you can beat a bit of seasoning whatever time of year. (Or season?) I think you'll find that 45mm is pretty universal from 750 through 900 and ST4. Dacs was concerned about using his 750 throttle bodies on the 944, but a bit of research revealed the above. I do remember reading somewhere or other at the time that 50mm tb's were no particular tuning advantage, but I can't remember what engine in particular was being discussed. It's all in the mapping these days! Perhaps it would be interesting to look at what size the M1100 uses and also the 1100 Scramblers? I wouldn't be at all surprised to find they are 45mm. Edit.. M1100 are 45mm TB. 2018 1100 Scrambler Special is 55mm but with full ride-by-wire. Probably goes beyond what can be conventionally mapped? And is a much more modern engine. __________________ Last edited by Mr Gazza; 24-12-2022 at 10:03 AM..

24-12-2022, 10:34 AM	#3
Albie Fanactical volunteer Join Date: Oct 2003 Location: Kent Bike: M900 Posts: 9,030	[QUOTE=Mr Gazza;596419 Perhaps it would be interesting to look at what size the M1100 uses and also the 1100 Scramblers? I wouldn't be at all surprised to find they are 45mm. Edit.. M1100 are 45mm TB. 2018 1100 Scrambler Special is 55mm but with full ride-by-wire. Probably goes beyond what can be conventionally mapped? And is a much more modern engine.[/QUOTE] But as like the 800 scrambler it uses only one throttle body per engine due to the size of tank and available space. __________________ http://albies93m900.blogspot.co.uk/

24-12-2022, 01:54 PM	#4
Bitza Bronze Member Join Date: Jul 2006 Location: Poole Bike: M900ie Posts: 470	OK, so I've kind of jumped the gun, because I didn't really measure the dia it was more of a case of offering up a rule. So the actual dia is 46.5mm and I have also measured a set of 45mm throttle bodies and they came out at 41.5mm dia. SO I guess it's just a matter of where you measure. 750, 900, 944, 1000 1100 all use 45mm throttles. 916 engined bikes 50mm, with later variants going up to 55mm. Have just looked up the 1100 scrambler special which like Gary says has 55mm plus fly by wire. __________________ Bitza Last edited by Bitza; 24-12-2022 at 02:17 PM..

24-12-2022, 03:04 PM	#5
Mr Gazza Lord of the Rings Join Date: May 2013 Location: Norwich Bike: M900sie Posts: 5,807	S4, S4R and S4RS, 916, 996 and 998 all have 50mm TB's. They clearly breath differently with 4 valves as distinct from the 2 valvers. __________________

24-12-2022, 07:32 PM	#6
Kato Dismantled Join Date: Feb 2006 Location: East Molesey Bike: Multiple Monsters Posts: 2,222	As has already been said the TB's are pretty standardized across the range, fitting bigger TB's will work after setting up but will not deliver any benefit at all unless you have very heavily modified cylinder heads with race cams and are pushing the very upper limits of power output at the top end of the rev range 50mm TB's were worth 5-6 bhp on 1000/1100 motors in the 115bhp upwards below that sort of power there was zero advantage to be had other than bragging rights __________________ "Political correctness is just intellectual colonialism and psychological fascism for the creation of thought crime" Last edited by Kato; 28-12-2022 at 02:22 PM..