Terry Burger

iTrader: (4)

I'm trying hard to resist the urge to sell one of my FBodies and buy a Civic, but with gas prices at all times high, it's getting hard! Sitting at lunch today with a friend, we hit upon an idea. Let's turn the LS1 in to a "displacement on demand" style motor.

I figured the easiest way to do that would be to disable one bank of injectors during steady state cruising (like when the torque converter locks).

As a test, I unplugged the injectors from the driver side of the engine (before I realized I could pull an injector fuse to have the same effect), and to my astonishment, the car ran! (It's not a stock car either, I have a cam, ported heads, etc.) I was even able to drive back to work 6 miles with this arrangement. Acceleration wasn't great, but it wasn't horrible either. I only noticed a slight vibration, about like a normal Honda engine.

Forgetting the PCM/LTRIM ramifications, what do you think this would do fuel economy and longer-term engine longevity?

To accommodate PCM/LTRIM issues (that will arrive via wacked o2 readings on the disabled side), what if while one side was disabled, I gave it the o2 signal from the functioning side? I could even have sides alternate every 10 seconds on a timer, and trigger the entire thing off the torque converter lockup.

What do you think?

WS6snake-eater

Wouldn't that cause an exteme lean condition in one bank, and leave holes in your pistons?

Terry Burger

iTrader: (4)

No, because that one side would have no fuel, so there would be no combusion.

jimmyblue

iTrader: (11)

I ran my Fiat/Buick V-6 project car for maybe
50 miles before I noticed I'd left one side's plug
wires off. That "odd-fire" motor had a pretty
nice natural balance to it. I guess I dumped a
lot of gas out but basically, it had the same
power as the original Fiat motor even so, and
ran very smooth.

You would have the pumping losses but that
is probably better than burning the gas.

Maybe make it a "lean cruise" type of deal
where you drop out the banks only when
above some speed, and alternate banks?
Use relays for the bank-drop and O2-shunting
to the other side, I guess. Wonder about the
actuation time, but I guess if you kept that
down to 1Hz ping-pong it might go unnoticed.

Don't know how all of that might play on an
A4 car; on the one hand, TCC lock would be
a handy cruise indicator. On the other, the
whole scheme might be showing up as misfire
city and unlock the TCC (bad for economy).

An "injector drop box" that was plug-n-play
would be a pretty cute thing. As long as it
gave a significant economy improvement. I
guess you could drive a hundred highway
miles with the left bank plug wires off, and
see what the gas pump says....

Though personally, I just chalk up the 16MPG
to "entertainment expenses".

Terry Burger

iTrader: (4)

As an alternative to relays on the O2 sensor, what if I simply enable a resistor in the engine temp sensor to throw the whole works in to open loop? It will ignore O2 readings (and resulting potential misfire codes) while in open loop, right?

jimmyblue

iTrader: (11)

Yes but you will have to live with the mixture
and timing effects, faking it cold or hot. I think
as an economy deal, you would want closed
loop (though open loop and lean setting is how
countries without a fascist EPA, get high cruise
economy - lean cruise mode is OS-disabled on
US LS1s but the Aussies get some pretty nice
km/liter out of theirs).

Maybe open loop tuning deserves more thought.

Terry Burger

iTrader: (4)

Hmm so you'd want to run like a 15.7:1 AF ratio in open loop for best economy? What is the drawback?

jimmyblue

iTrader: (11)

The rare and endangered speckled tadpole
will cough its rare and endangered lungs out,
I guess, if it has any.

Terry Burger

iTrader: (4)

Heh.. Well, if its simply a matter of running leaner while cruising, why not add a little resistor to the O2 sensor signal to make it read a tad "rich"?

patSS/00

iTrader: (6)

A better way to put it in open loop is to cause the TPS output voltage to go to go high (4.5V will do it). This can be done with a real simple circuit. You might need a delay in going back to closed, loop, when switching to 8-cyl mode, to give o2's time to adjust.

Maybe if you turned off 2 on each side, it would run more smoothly?

HumpinSS

iTrader: (1)

If you have edit or tuners you can change the o2 pivot voltages to effectively lean the car out so the PCM isnt swingng to far in either direction while trying to maintain the AFR...

Other alternatives would be to run the car in open loop with a AFR of 15.5 (best fuel economy) in the lower maps and slowly ramp richer as the tps gets greater and greater

Steve Bryant

iTrader: (1)

Guys,

Here's the fundamental problem with disabling injectors only. The non-combusting cylinders are serving as an air compressor, increasing the load on the four cylinders that are running. This really hurts gas mileage which is what you're trying to increase.

The reason that with displacement on demand causes the lifters (intake and exhaust) to collapse on four of the eight cylinders is that the valves are closed and the engine is not sucking in compressing and pushing out air into the exhaust, consuming power. Instead, the cylinder is pumping up and down against a spring in a manner of speaking. The stable air charge offers resistance on the upward strokes and gives the pistons an equal and opposite push on the downward strokes.

Steve

emarkay

Correct, that compression stroke negates any benefit - it's like a "windmilling prop" on a B24 in WWII.... Also there are stresses placed on the crank and block that have not been engineered into the engine - A few cars have "limp home" mode for low coolant that does just this, but it's not an efficinecy set up and I think it is limited to 50 miles - probablly to save the crank and bearings.

Good thinking - but if you have to worry about MPG, put in a vacuum gauge and use it!

Yes, I have seen 31MPG in my car on a trip.