OEMs and Fuel Economy

In reply to DaewooOfDeath:

Sure seems like it- now that we have 2.7l V6s.

Many years ago, when the electronic overdrive was introduced, the theory stated by engineers, that an engine got better fuel mileage at lower rpm and a larger throttle opening.

This theory seems to be still in effect. Multi gear transmissions with a high top gear. Automatics with an overdrive gear.

This goes back to the climbing a hill question. Highest gear that will maintain speed.

rslifkin wrote: Being speed density, there's no VE tables or anything, so the fuel table is just raw injector pulsewidth values that it then applies various adders and multipliers too.

That's not what speed-density means.

Speed-density is what has VE tables, mass-air doesn't. Or doesn't need it.

Knurled wrote:

rslifkin wrote: Being speed density, there's no VE tables or anything, so the fuel table is just raw injector pulsewidth values that it then applies various adders and multipliers too.

That's not what speed-density means. Speed-density is what has VE tables, mass-air doesn't. Or doesn't need it.

I think what he meant was there's a map sensor, that that goes into a engine speed- MAP table, which directly outputs the injector pulse width. Which is even simpler than "speed-density". Our first controller for our challenge car had that- interesting to calibrate. Dumped it as fast as I could find a cheap alternative in 2003.

alfadriver wrote: I think what he meant was there's a map sensor, that that goes into a engine speed- MAP table, which directly outputs the injector pulse width. Which is even simpler than "speed-density". Our first controller for our challenge car had that- interesting to calibrate. Dumped it as fast as I could find a cheap alternative in 2003.

It bases everything on RPM vs MAP with modifiers for coolant temp, intake temp and a few other things. Accel enrichment is based on MAP change and TPS change.

From my understanding, speed density was any system that used MAP and intake temp versus engine RPM to calculate the incoming air charge (compared to a MAF setup or one that just works based on rpm and throttle position). Is that not a correct assumption?

In reply to rslifkin:

I would not call it correct, but it's not that wrong... To me, speed-density suggests that some calculation of how much air is in there takes place. And the direct calculation of PW skips that step. But that line can be drawn in other places, too.

alfadriver wrote: In reply to rslifkin: I would not call it correct, but it's not *that* wrong... To me, speed-density suggests that some calculation of how much air is in there takes place. And the direct calculation of PW skips that step. But that line can be drawn in other places, too.

Makes sense to me. When tuning this thing, it always seems easiest to just think of stuff in carb terms because of how primitive the ECU is.

kb58 wrote: Two other side notes: 1. In this day and age of super exacting ECU measurements, it amazes me - in a bad way - how the ECU's MPG estimate vs the measured value always "happens to be" off in the direction that favors the mfg. My truck regularly claims 19.8 mpg but measured it's consistently about 10% less. 10% is a lot when ECUs are measuring things in microseconds.

Have you ever checked your speedometer/odometer calibration? If the car thinks it's travelling 10% farther than it really is (some of them are that bad), the MPG calcs will be 10% high.

BrokenYugo wrote:

kb58 wrote: Two other side notes: 1. In this day and age of super exacting ECU measurements, it amazes me - in a bad way - how the ECU's MPG estimate vs the measured value always "happens to be" off in the direction that favors the mfg. My truck regularly claims 19.8 mpg but measured it's consistently about 10% less. 10% is a lot when ECUs are measuring things in microseconds.

Have you ever checked your speedometer/odometer calibration? If the car thinks it's travelling 10% farther than it really is (some of them are that bad), the MPG calcs will be 10% high.

That error would also appear in the 'calculated' fuel economy.

alfadriver wrote: In reply to DaewooOfDeath: Sure seems like it- now that we have 2.7l V6s.

Last time I looked around, small sixes were very rare.

The only recent ones I can think of are higher cost options to four cylinders. Like the Hyundai Delta, which was always more expensive than the 4g and beta engines.

In reply to DaewooOfDeath:

That depends on what you mean by "small". 2.5-3l sixes were the norm for the longest time for just about everyone who wasn't GM of North America. You could get down to 1.8l (1.6l?) and up higher, of course.

DaewooOfDeath wrote:

alfadriver wrote: In reply to DaewooOfDeath: Sure seems like it- now that we have 2.7l V6s.

Last time I looked around, small sixes were very rare. The only recent ones I can think of are higher cost options to four cylinders. Like the Hyundai Delta, which was always more expensive than the 4g and beta engines.

Well, our aluminum pick up is powered by a 2.7l V6. For now, it appears to be our smallest V6, while the biggest I4 is 2.5l

ProDarwin wrote: Huge cylinder volumes are efficient (better chamber volume : chamber area ratio than more smaller cylinders), but they have a negative effect on NVH. From a vehicle NVH standpoint, we should all be driving 2 liter V12s. For mileage we should all be driving 2.0L Thumpers :) Revs - Cruising RPM seems to make a much bigger difference than the RPM the motor is capable of. I don't think the **peak** BSFC of ICE engines has gotten *that* much better over the past 25 years, but the size off the sweet spot has grown a ton.

I was about to reply, but Darwin pretty much summed it up for me. A 5.0L V10 has far more cylinder surface area than a 5.0L I4, but a 5.0L I4 would be an NVH nightmare. Friction is the big thing in that scenario. There are also other issues to consider like parts reliability, packaging, etc. Another big factor is marketing. No one is going to buy the new mustang with a V-twin regardless of how big it is.

An example: Vehicle #1, a commercial box truck with a 6.6 Duramax and Allison 1000 making 250hp. Vehicle #2, take the same truck but with a 5.9L Cummins at 235 hp and Allison 1000. Both trucks are in the same hp/tq range, but the Allison behind the Cummins will not last as long by a fair margin. The Cummins makes bigger "hits" of power every 120 degrees of crank rotation while the Dmax makes smaller "hits" of power every 90 degrees. The V8 is a much smoother way to make grunt without rattling drivetrain parts to smithereens.

curtis73 wrote: No one is going to buy the new mustang with a V-twin regardless of how big it is.

Actually, I'll bet a Harley Davidson package Mustang with a V twin would sell like crazy.

Keith Tanner wrote:

curtis73 wrote: No one is going to buy the new mustang with a V-twin regardless of how big it is.

Actually, I'll bet a Harley Davidson package Mustang with a V twin would sell like crazy.

All the obnoxious sounds, none of the motorcycle problems! I can't see how that wouldn't sell like crazy.

Keith Tanner wrote:

curtis73 wrote: No one is going to buy the new mustang with a V-twin regardless of how big it is.

Actually, I'll bet a Harley Davidson package Mustang with a V twin would sell like crazy.

The paintshaker version of the V8 seems to be doing okay sold at a premium

(No, I haven't driven one. Reviews I have read said "Everything shakes and buzzes. But when you actually DRIVE it, you stop caring")