My OSSA dealer gave me both stock 5-degree and an "experimental" 15-degree butterfly along with Btwice throttle body. Looks really interesting: 15-degree butterfly is oval with angled edges and thus starts from more off-angle position and regulates the air flow in a more "progressive" fashion vs stock. I wonder with TPS having larger starting angle yet the engine gets less air (= theorethically richer mixture on low-rpms as it gets more rapidly leaner when opening up the throttle) if it improves bottom end delivery as well?

 

 

 

Anyone has Btwice throttle body and experimented with a 15 degree butterfly? Is it worth experimenting with different custom EFI maps or it required designing my own custom map for it?

 

I have the diagnostics kit from people who designed the OSSA EFI with lots of different mappings, so maybe should go through some of those first I guess.

Ossa made the 15 degree butterfly for the 125 motor to obtain a power increase over the standard 125 motor fitted with a 5 degree disc. The theory behind the 15 degree disc is that this allows more air flow at low revs, and therefore can acept a relative increase in fuel. This required a new map specific for the motor size and the 15 degree butterfly. I was told the 125 with 15 degree disc had a similar spread of power to the Beta 125.

The 15 degree disc was made using a mandrel, say a 25 dia round bar with the top machined at 15 degrees, drilled and tapped to accept the blank brass disc, then turned down to size on a lathe. I was told they worked well on the bigger motors too.

Bye, PeterB.

Big thanks Peter, that's a very good info! Makes sense too. Sure the 125 requires more to be sqeezed out from the small motor.

280 is already very nicely balanced in the power and delivery department. I guess 15-deg butterfly is a good upgrade when one would require more progressive power out of this engine. Other interest is a very high altitude (3000 + meters) behavour, this TB mod may acctually be beneficial there with the right maping. I'll experiment with it when I have more time.

Cheers,

Margus

The 15 degree butterfly is on my 250 and I like it. In comparison with the 280 (rode that one a bit more than a year) the 250 picks up a bit quicker, making it easier to lift the back wheel on obstacles. It has a bit more go than the 280

I do not have the cables and software to map so mapping was done by the dealer.

Edited February 14, 201610 yr by tcrhino

Sounds interesting. Inspecting the butterfly motion in TB it does visually look like the 15-deg opens the aperture more "progressively" vs the stock 5-deg. The latter is probably more mild and predictable.

 

Looks like 15-deg is a good mod when you need more rapid "pop" from the engine. I'll see into mapping compatibility once I get there and have an actual need for it I reckon.

I have a BTWICE throttle body (and cables) but I have no idea which throttle plate it has.

Seems to work well - a little stiffer spring, but I don't really notice it.