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Turbocharged, Supercharged, and Hotrod Motorcycles: [turbobike] home made FI computer

[turbobike] home made FI computer

Dave Morrill (david.p.morrill@fairchildsemi.com)
Mon, 27 Apr 1998 08:36:46 -0400

	Thanks for the reply on the breather valve, can't wait to see the
pics.  Yea, the 800cc motor is a 2 stroke.  I'll take some pics as soon
as I can.

The FI computer is a closed loop system using exhaust temp as the only
feedback.  O2 sensors get ruined by the oil in the 2 stroke exhaust. 
It's really just a timer that varies injector on time based on EGT.  I
was using 320cc/min saturation type injectors, and found I didn't have
enough fuel, then found a mistake in the spreadsheet I used to calculate
injector size.  

I have the same problem as you with the bikes, I only have about 7.14ms
period so the injector on time must be less than 4ms.  Finding
saturation type injectors that can move 750cc/min was not possible, so I
had RC engineering make me some peak and hold type (I should get them
this week).  I could have piggybacked 2 injectors per cyl. like you did,
but making the injector manifold and fuel rail was a pain, and I didn't
want to hack into that. 

I Had to re-design the drivers for the computer, but everything else
remains the same.  I batch fire all 3 injectors at the same time, future
revs will have port timing and throttle position.  I have a lean/rich
adjustment on the steering, an injector on time display that I made, and
a digatron EGT meter for on the fly tuning, in addition to boost and
fuel pressure.

I am blowing through the carbs which are good for 150 hp, with the FI in
series before the carbs providing the extra 150 hp of fun.  I've run up
to 15 lbs on short blasts before I go too lean (ceramic coated pistons
let me run close to the edge, but I melted 4 pistons early on before I
went to FI).  The new injectors should allow me to run wide open for as
long as I want (I hope).

sorry so long winded,