BMW K100 with single carburettor.

I built everything from scratch, some parts had to be re-made as I understood the system better, but it was an interesting project.
I never had it on the dyno, maximum boost used was 0.65 bar, (9 psi), so you can do a quick calculation.

patzx12 said:

I wouldn't mind trying one of mt CBX1000 with twin carbs. it would make setup and access so easy.
I bet it would run ok as well.
Not many car engines ran with individual carbs an they went down the road ok.
A bit of reading here:
http://www.randakksblog.com/single-carb-conversions/

Click to expand...

The single carb on my K100 is excellent, mid-range is really good, servicing is now really simple, adjust the mixture screw, re-set the tick-over if necessary.
No fuel pump or filter or throttle bodies to balance, if any changes are made to the exhaust system it's just a matter of carb adjustments, no re-mapping, etc.
Plus it uses about 10% less fuel than the standard set-up.

Look at the power figures from an Alfa Romeo twin spark. Per cc they are not far off a BMW bike output. Having to drive a car they will be tuned for torque more than a bike would be. This is in spite of just one throttle body and power sapping precats in the exhaust downpipes which the bike does not have.
The multi carb setup on bikes minimises the time for atomised fuel to evaporate in the inlet manifold. And it's space efficient on the old air cooled engines with back inlet front exhaust setups.
These days, multiple throttle bodies look like a bike fashion thing though they must benefit absolute top end power with race cams (as in a sports bike).
The old A Series Mini engine had two inlet ports merged inside the head. A good well designed single inlet manifold with 1.5" SU carb was down only a few bhp over twin 1.25" SU carbs that had a direct line to the cylinder head. The single gave better efficiency with more torque at low to medium revs.

These days it's easier to fit an injection system because the fuel and exhaust data can be logged and the map adjusted accordingly. Multipoint injectors deliver fuel over the inlet valves - better atomisation with less evaporation - more power better efficiency.

I can't talk about the Ks but likely to be similar. I suspect the BMW boxer with injectors close to the cylinder head and a single throttle body under the fuel tank would make the same power with less complexity. Alfa engines are responsive and quick so why not a bike with similar setup.?
The tuned A Series was notorious for fuel starving the middle two cylinders. So much that special "scatter" cams were cut for race engines. What's to say that BMW with an angled TB close to the head are not also favouring one valve? It's not harmful in our case but unbalanced valve flows can't be having a positive effect.