With a carb no less. The carb is causing 5 to 8 inches of
Hg loss in manifold pressure due to venturis and butterfly
plates despite the fact it is a 58 mm carb. 58 mm is 2.3 inches
in diameter. At full throttle we were still seeing 10 inches Hg
vacuum or an absolute manifold pressure of around 20 inches of Hg.
A fuel injection system with slide throttle would eliminate most
of this loss. We should be seeing close to 29 inches Hg at sea level.
We ran out of time tuning Tracy's fuel injection sys so Dave suggesting
getting some numbers using the carb. Dave and the folks at Mazdatrix
knocked out a carb intake manifold in one day. Not to mention
building a fine rotary engine. I need to depart for the
Paris air show on Friday morning. Will be gone for a week.
I will visit Francois and Mistral in Geneva and try and talk
him into a P-port :)
Much thanks to Dave Lemon and all the guys at
Mazdatrix that helped out. Half a dozen jet changes and we were
up and running. These guys really know their Webers.
These are the pictures and numbers for the 28 inch runner
version. This would make a good engine for the 2.17:1 gear box.
Note the torque peak is 5600 to 5700 RPM which would make a
good cruise setting.
-----------------------------------------------
Here is what it looks like with 24.5 inch runners.
Peak HP was 245. Dave feels there is more there with
a few more jet changes.
Note the torque peak has moved up to 6200 RPM.
This would be a good engine for the 2.85:1 gear box.
Cruising at 6200 would optimize the BSFC. Takeoff and
climb out at 7200 to 7500 RPM.
The exhaust and muffler sys used for the test is nothing special.
Something like you would see on a 2nd gen mildly hopped up street
RX7 with a Racing Beat header.
Dave will probably get another two inches out of the carb runner
length and run some more curves while I am gone.
When I get back we will work on the fuel injection system.
Tracy thinks we are having trouble because we are
not using a manifold referenced fuel pressure regulator.
Makes sense as it is rich on the low end and lean on the high end.
I ordered a high buck Aeromotive manifold pressure referenced
regulator. Should be here tomorrow.
BTW we think we have discovered why the Innovate wide band
mixture monitor was giving us a lot of trouble. We think it was
picking up electrical noise through the common system
supply 12 volts. We reconnected it to a separate battery and
it seems to be working better. It is not wide band enough
however for initial tuning on a new engine with a new fuel system
as it stops working around 9.8:1 on the rich side.
One can be far off that and have the engine still run with
the MSD or Tracy's ignition systems.
Also I might mention we are using Tracy apex seals in this engine
and they are down on compression compared to stock Mazda
seals. Rumor has it they take a long time to break in.
The numbers are 6.7 to 7 (pascals per furlong or some metric
nonsense like that) at 245 RPM and wide open throttle for Tracy's
seals and 8 to 9 for stock seals. Hopefully the engine will
generate even more power when Tracy's seals are properly broken in.
Paul Lamar
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