Bike EFI

Rucastle rucastle at silk.net
Tue Mar 25 17:35:42 GMT 1997


Hi guys, with regards to my statement below   "my old BSA 500cc single cyl.
makes 1.86 hp  per cubic"  I was over tired when I wrote this. It should
read .86 Hp/in3. 
>From the original post I took "throttle body" to mean a manifold with
runners and a throttle body injection unit at the beginning of the manifold.

I said:
>> I'm one of the people that would like to FI a bike engine. I know dick
>> about electronics, but personally I would not consider throttle body FI.
>> Bikes to my knowlage, with the exception of Harley Davidson, are designed
>> around indiviual ports and carbs for each cylinder.  Throttle body on a
>> Harley yes.  On the rest, unless you have a hair drier on it, I think you
>> would probably lose out if you used throttle body FI.  I don't mess around
>> with new bikes but my old BSA 500cc single cyl. makes 1.86 hp  per cubic
>> inch at the rear wheel, this is from Superflow dyno runs I have made.
>> Check out the HP the new super bikes produce.  I'll bet by the time you
>> made a manifold etc. to run a throttle body you would not gain back from
>> EFI what you lost to manifolding.
>
>Most bike systems I've seen use an individual throttle body for each 
>cylinder, which has a injector boss as part of the assembly.  The systems
>use port injection and individual throttle bodies for each cylinder, so 
>the whole EFI system is about the same size and location as the OEM 
>carbs.  From a performance and packaging standpoint, this is about the 
>only way to do it.
>
Michael, what I meant was that if you look at the intake tract of most bike
engines, from the carb air horn to the valve is usually a straight in
'shot'.  The jet needle and, on CV carbs, the throttle shaft/butterfly are
the only restriction to air flow. Most (read modern) bikes have air boxes.
What would stop someone from making the air box act as a plenum and having
the throttle body at its opening?  With a properly designed air box the air
should be slow and non turbulent by the time it reached what used to be the
carb air horn. And the throttle shaft/butterfly restriction would have been
eliminated, not to mention the possible problems of butterfly
synchronization.  We would also have no need to find or build multiple
small throttle bodies.  Although I suppose one could use the original CV
carb bodies, but the shaft would still be there.On the BMW this is not such
a big deal, they have lots of room for the throttle bodies and can spread
the cost of making them over a ton of bikes.



Tom Cloud said:

>I don't think anyone claims you're going to make more HP with EFI.

If I didn't think I would get more torque and horse power from EFI I would
not go to the trouble to install it.

>EFI is about control .... things like fuel distribution; 

Fuel distribution is not really a problem with bikes except Harley, most
bikes have for each cylinder, one carb, one port, straight in.

>and rapid throttle response; 

Find a GSXR or other high horse oriental bike and wick the throttle a few
times

>and better fuel control over the complete operating range, etc.
Carburetors still >work great if you're interested mainly in performance

Sentence 2 above answers sentence 1

>and don't care about emissions and optimum performance over the entire rpm
range.

See sentence 2 above. Way cheaper (but ugly) to fit a cat.

I can see where my thoughts may not be easy to apply to a stock bike.  My
judgement may  be clouded because I'm building a frame for the engine I
would like to EFI and will not be limited to how the factory placed there
components.  

The engine I would like to EFI is a 1974 Triumph 750cc 3 cyl.  The Amal
(anal) carbs on this bike originally cost Triumph something like 2 pounds
sterling each.  They ware out fast because the bodies and slides are made
of like materials. Milage and power is not as good as it could be with
modern Mikuni or Keihin (s?) carbs.  By the time I buy up-to date carbs I
could probably install a EFI system and have an adjustable advance curve
ignition thrown in for good measure

My biggest problem still lies in the fact that I may not have enough
current to run an EFI/electronic ignition system.

Hylton





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