Theoretical gains from weight reduction and aero improvements

[saand]

MetroMPG, i am logging using a home made fuel consumption meter. It uses the same principle as the MPguino by measuring off the injector pulses.
The logging is done by the fuel consumption meter which logs straight to a USB thumb drive when one is plugged in. It writes a new line to a file every second with the duration of the injector being on in that last second along with the speed of the car.

It would be very easy for the MPguino to send out this information out of a serial port if others want to log a trip. Alternatively i believe logging to a flash card is fairly easy.

[99kleansi]

Originally Posted by SentraSE-R

I doubt that starting and stopping a warm engine a few times in a minute causes as much wear as running that engine at 2500 rpm for the same minute.

Well thats where your wrong. Starting and stopping an engine is horrible on the starter, electrical system and engine bearings.

500 revolutions on a surface thats relying on a risidual lubricant film does cause pitting in soft bearing surfaces creating internal friction equal to wind resistance on the outside of a car. This parasitic drag can severly reduce MPG's no matter how you drive as all RPM's are affected.

On the other hand 2500 rpms with your crank floating on a bed of lubricant causes almost no wear at all because thats what it was intended to do then the left .008" inbetween your bearing surface and metal surfaces and then added 50 psi of oil pressure.

I seriously hope your vehicle is not idleing at 2500 rpms as you may have a hugh vacum leak that will cause a sever mechanical failure if you do not fix it soon.

Instead why not tune your idle to a lower RPM and leaner AFR. Most manufaturers stick to around 15:1 or 16:1 in closed loop at idle with no load. You can easily tune this to a leaner 17:1 as long as you adjust for throttle tip in to ensure you do not damage your pistons under load. Assuming gasoline is being used for these AFR's

At these leaner ratios the top of the piston expands more then the shirts of the same piston and could cause scuffing under load. The tip in should compensate with additional fuel to act as a coolant on the piston before timing were applied to increase power.

[MetroMPG]

Originally Posted by 99kleansi

Well thats where your wrong. Starting and stopping an engine is horrible on the starter, electrical system and engine bearings.

Better tell that to every single major manufacturer deploying the engine start-stop feature.

Most use a beefed up starter vs. a conventional engine, but I have a feeling they've investigated engine wear and determined it's a non-issue when start/stop occurs in a warmed-up state.

[99kleansi]

Originally Posted by MetroMPG

Better tell that to every single major manufacturer deploying the engine start-stop feature.

Most use a beefed up starter vs. a conventional engine, but I have a feeling they've investigated engine wear and determined it's a non-issue when start/stop occurs in a warmed-up state.

Agreed but I am almost positive that different bearing composites are being used. This can also be accopmlised by allowing the engine to continue to rotate keeping oil pressure but opening the valve so the compression doesnt act as an engine brake. An electric oil pump also maintains that protective oil layer.

[MetroMPG]

Any references for the unique start-stop bearings?

I'm not talking about hybrid "EV mode", eg. Honda's version where the engine rotates while the electric motor propels the vehicle on its own.

I was referring to otherwise "regular" cars where the engine stops every time the car stops (assuming proper operating conditions are met - probably temp primarily & 12v state of charge) and restart when the driver releases the brake (or uses the clutch) again.

[99kleansi]

Originally Posted by MetroMPG

Any references for the unique start-stop bearings?

I'm not talking about hybrid "EV mode", eg. Honda's version where the engine rotates while the electric motor propels the vehicle on its own.

I was referring to otherwise "regular" cars where the engine stops every time the car stops (assuming proper operating conditions are met - probably temp primarily & 12v state of charge) and restart when the driver releases the brake (or uses the clutch) again.

No specific reference to any manufactureer using these bearings. Do a quick search of engine bearing and you can quickly learn that there are different materials to be used. I myself use a softer bearing then normal. I would rather use a softer bearing and replace more often then have the crank turned.

Bearings are usuall comprised of three layers each have a specific function. You can find the rest.

[NeilBlanchard]

I think the Start/Stop systems on new cars use the alternator and the main belt to start the engine?

[SentraSE-R]

Of the potential hazards mentioned by 99kleansi, the only one I find credible is possible bearing journal wear. Starting a car by kissing the clutch adds no electrical or starter load at all, obviating the supposed "horrible" wear on those components. Similarly, cylinder wall scuffing from a warm start is negligible in comparison to coasting down a long downhill in gear in DFCO, which most cars do.

[Frank Lee]

I'd think such "wear" would disappear in the noise of the varied conditions engines see under normal use i.e. city car will see 10x? 30x? 100x? the amount of start/stop cycles, and accels from a dead stop as an identical car model based in South Dakota yet both deliver acceptable lifetime intervals.

It seems to me that chassis' rust away and owners simply get tired of driving a car after, say, 250,000 miles, and it gets junked and yet... many of those cars have never had an engine teardown...