Reqfuel question

[tech3sandcars]

I have a Microsquirt running on a Vtwin kawasaki motor, it was about 105 HP at the flywheel. I have now built a 1000cc Vtwin motor lots of go fast goodies, estimated flywheel HP to be about 145-150. Thats about 45% increase. Is it a good assumption to raise my Reqfuel the same 45% as a good starting point?

[Matt Cramer]

How much have the engine displacement and the injector size changed? If these two are constant and the change came through more RPM, you'd actually want to leave that number alone.

[tech3sandcars]

I went from 840cc to 1000cc, 10:1 to 12:1 compression, bigger cams, biggers valves, cnc ported heads, etc. Same injector size and same RPM range. The guy I get parts from said I was going from about 105-100 HP to about 145-150 HP.

[24c]

OK, but even if you left it alone, assuming the engine started and idled on the old settings, you could just adjust your VE numbers upwards. Anyway, if I compare a typical engine before and after tuning, the run up the initial horsepower slope is pretty similar, then it will keep climbing until it peaks/flatten and then should decay a lot less with your mods over stock. You might find the upper rev limit horsepower might be double what it was.

You'll also be using wideband sensors? so you can watch your AFRs etc and adjust your fuelling that way. You will also probably want less total ignition advance with the higher compression, and port job.

[tech3sandcars]

Ya makes sense, was just trying to figure out a good starting point, if I was at Reqfuel of 8 and I add 40% more power to the motor is it realistic to think that I up my Reqfuel 40%?

[Bernard Fife]

t...,

No.

The req_fuel should be related only to the displacement and injector flow rate. See: http://www.megamanual.com/v22manual/mfuel.htm#reqfuel

What does change with increasing horsepower is the VE table, and the highest VE will go up by about 40%. However, the rpm at which the peak VE is reached will increase (if naturally aspirated), and the VE table itself will likely be more 'peaky'.

So you have to retune, you can't just adjust a number like you might do if you were only changing injectors.

Lance.

[tech3sandcars]

makes sence, thanks guys.