<VV> Anyone using MegaSquirt on a Corvair? (long)
FrankCB at aol.com
FrankCB at aol.com
Sun Nov 4 17:19:58 EST 2007
From your description it appears that you are using the stock 180
distributor with the stock pressure retard. If that's true then you could achieve
another 20% improvement in gas mileage by adding in a vacuum advance instead
of the stock pressure retard on the side of the distributor. With the stock
pressure retard, the ignition timing stays CONSTANT from idle to about 4000
rpm or until you develop some boost pressure. So for highway driving under
vacuum conditions, you're losing a lot of economy. You already have the
SafeGuard to provide timing retard as needed to prevent pinging/knocking. See the
description in the Turbo Chapter of the Corvair Basics manual.
Thanks for the good details on your installation.
Frank "timing is everything" Burkhard
In a message dated 10/30/2007 3:12:06 PM Eastern Daylight Time,
chuckriblett at msn.com writes:
I have been driving a turbocharged Corvair with fuel injection controlled by
a MegaSquirt controller for about a year. This is basically a 95 HP engine
with forged pistons, Otto cam, 180HP turbocharger and 180HP distributor with
SafeGuard ignition. I machined a throttle body that fits between the
turbocharger and the original air filter housing. The throttle plate
diameter is 1.8 inches compared to the YH carburetor throttle plate of 1.5
inches resulting in much greater airflow than the carburetor.
I have never driven for best fuel economy, but I have kept records. With
fuel injection and a wide band oxygen sensor the car has been getting 20-22
MPG despite using the increased performance. For comparison, with the YH
carburetor and original metering rod and jet, I got 13-16 MPG. After much
testing using a narrow band oxygen sensor and machining custom metering
rods, I was able to get 17-19.5 MPG using the carburetor.
Setting up the fuel tables is fairly easy if you use a wide band oxygen
sensor for feedback. The baseline tables are created based on the engine
size and the number and flow rate of the fuel injectors. With the
MegaSquirt I controller, you drive around collecting data on a laptop
computer with MegaTune software. Then you use MegaLogViewer to modify the
fuel tables. With MegaSquirt II, AutoTune is available to adjust the fuel
tables as you drive. I believe that you can easily pay for the $200 wide
band oxygen sensor system with the improved fuel economy.
The engine started the first time as soon as the fuel lines were
pressurized. After setting the idle speed, I was able to drive the car
gently and collect data. After a few drives around the neighborhood
collecting data and then modifying the fuel table, I was able to drive the
car normally. I continued to make small adjustments whenever I noticed an
area that could be improved.
The engine now starts immediately every time without any of the flooding and
vapor lock problems of the carburetor. The increase in torque available for
passing at highways speeds is truly impressive.
The hardest part of the installation was routing a fuel return line and
connecting it to the gas tank. The most time consuming task was fabricating
a wiring harness. I mounted the electronics on the shelf above the
transaxle (early coupe) away from the engine compartment heat.
The original version of the throttle body had the injectors before the
throttle plate. This resulted in fuel dripping out at the air filter flange
particularly in cold weather. For the current version, the injectors are
mounted after the throttle plate. Since the injectors are mounted on the
vacuum side of the throttle plate, there have been no fuel leakage problems.
I don't think that a low-pressure throttle body with the injector(s) above
the throttle plate can be mounted sideways without fuel leakage problems.
Future plans call for using a MegaSquirt II controller for ignition control.
I am also working on throttle bodies for a 140HP engine in another car.
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