In modern motorcycle engines they use big "pre-chambers" before the
    intake tubes. Such a chamber in a 1200cc Motorcycle can have a
    volume up
    to 4500 cc. And this is really only for tuning (not for air
    filtering) and helps a lot getting out 175HP from a 1200cc
    production bike.

    Reiner Nikulski

    Unfortunately it confuses the heck out of the carburetor.
    I am about to give up on any kind of venturi sensor.
    The automotive industry did it years ago.

    Paul Lamar ...No rotor no motor.




This is also one of the reasons that even a low pressure version of the
direct injection has merit. If we want better economy we need to avoid
spraying the surrounding environs with fuel! This is also the reason that
most modern cars/bikes/boats use large air boxes to contain the
reversion mist if carburetated.


Bill Jepson

Well I had fully intended to do that but I don't think it will
stop the mixture instability of the air flowing  back and fourth through
a venturi. I could be wrong.

Paul Lamar ...No rotor no motor.

Paul,
I'm making my own slide carb (see attached) and the information from some
Aviation carb web site would indicate that a venturi isn't needed - so I
haven't included one. It probably be difficult with this design anyway. I've
made it from a couple of slabs of aluminum and as such you may see some
resemblance to the Aero Carb - for that reason.

From memory the carb your using is a 52mm but the restriction( Venturi) is

46mm. This may be acting as more of a restrictor than you might believe,
although to my mind 46mm should be enough for your needs. I have in my mind
that the venturi will increase the signal ( velocity/ response) but produce
a low pressure area which reduces the air density. If this is correct it
will be adversely affecting the VE.

I was hoping for more HP from your  trials, especially with the Rx8 and it's
higher compression ratio, I was expecting at least 250hp at 7,000 to 7,500
RPM. The larger carb may or may not work as anticipated because of the
venturi factor. Most carb sites suggest an oversized carb don't provide
improvements and in many case give worse results, but may be worth the trail
for confirmation of that theory.
George ( down under)

Well the venturi must be smaller than the runners to work as a mixture sensor
for carburetors. EFI systems use MAP, throttle position, mass air flow sensors
and air temp sensor to controll the mixture. Therefore the restriction of the
venturi is not needed. In our RPM range the bigger the hole the more the air.
The more the air the more the HP. Also I might had the better the BSFC assuming
the mixture is closely controlled and leaned properly. You won't get that
with a carb.

For power check out the latest down load from Dave Lemon at Mazdatrix.

Paul Lamar

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