rpm when towing

[bbaker2001]

When towing with my ram diesel how do I tell when I should downshift.
it seems to tow so easy, but slows when going uphill
at 60 what should my rpm show.

[Espee]

Wow
So complicated
Very unscientific as compared:
Home is at the base of the Grapevine
Learn by watching water temp if only factory guages
Steep hill temps will climb fast with rpms in the lower 2k's...
so downshift and spin it mid to upper 2k's... Life is good
YRMV

[bbaker2001]

Thanks everyone. Have got my answer
I think we can close this thread because the last 2 pages have nothing to do with my rpm question. Maybe we can start a new thread
Happy passover Easter

[ShinerBock]

4x4ord wrote:
Wikipedia explains how the air fuel ratio in direct injection gasoline engines can vary from ultra lean (as lean as 65:1) to stoichiometric to slightly richer than stoichiometric during full power.

Click


Edit: I copied and pasted the part that of the write up that explains ultra lean operation:

Ultra lean burn or stratified charge mode is used for light-load running conditions, at constant or reducing road speeds, where no acceleration is required. The fuel is not injected at the intake stroke but rather at the latter stages of the compression stroke. The combustion takes place in a cavity on the piston's surface which has a toroidal or an ovoidal shape, and is placed either in the center (for central injector), or displaced to one side of the piston that is closer to the injector. The cavity creates the swirl effect so that the small amount of air-fuel mixture is optimally placed near the spark plug. This stratified charge is surrounded mostly by air and residual gases, which keeps the fuel and the flame away from the cylinder walls. Decreased combustion temperature allows for lowest emissions and heat losses and increases air quantity by reducing dilation, which delivers additional power. This technique enables the use of ultra-lean mixtures that would be impossible with carburetors or conventional fuel injection.

I am aware of these engines and even knew someone who had a Civic with a lean burn system. However, these engines were dumped in the early to mid 2000's because they could pass upcoming emissions since you cannot put a three way catalyst on lean burning engines. You can only put a two way catalyst on lean burning engines and have to have another way to deal with NOx which would more than likely negate any of the benefits of a lean burning gasoline engines over a diesel.

As I said before, I don't know of any DI engine in production today that are designed to run on an air/fuel ratio too far outside of stoich at 14.7:1. I know that it can be done, but I am more concerned about real world not would-a, could-a, should-a land that doesn't currently exist.

[4x4ord]

Wikipedia explains how the air fuel ratio in direct injection gasoline engines can vary from ultra lean (as lean as 65:1) to stoichiometric to slightly richer than stoichiometric during full power.

Click


Edit: I copied and pasted the part that of the write up that explains ultra lean operation:

Ultra lean burn or stratified charge mode is used for light-load running conditions, at constant or reducing road speeds, where no acceleration is required. The fuel is not injected at the intake stroke but rather at the latter stages of the compression stroke. The combustion takes place in a cavity on the piston's surface which has a toroidal or an ovoidal shape, and is placed either in the center (for central injector), or displaced to one side of the piston that is closer to the injector. The cavity creates the swirl effect so that the small amount of air-fuel mixture is optimally placed near the spark plug. This stratified charge is surrounded mostly by air and residual gases, which keeps the fuel and the flame away from the cylinder walls. Decreased combustion temperature allows for lowest emissions and heat losses and increases air quantity by reducing dilation, which delivers additional power. This technique enables the use of ultra-lean mixtures that would be impossible with carburetors or conventional fuel injection.

[4x4ord]

ShinerBock wrote:


I haven't heard about DI engines no longer being regulated to 14.7:1? What engines are these?

Every DI I have hooked my OBD Torque App up to from my Ecoboost truck to my wife's old Audi(both turbocharged) have been regulated to an A/F of around 14.7:1 with a very narrow range. The only time either engines ran lean was the brief instant after going WOT it would add too much air before the injectors could compensate. It would go no more than 15.0:1 though. After that it would run rich at 13.2:1 if you left your foot into it and then start to go back to stoich as you picked up speed. In normal driving or idle they always stayed around 14.7:1 +/- .5. My diesel on the other hand will go anywhere from 20:1 to 80:1 depending on engine load. At Idle, it will go even higher than that to upwards of 100:1.

I know some DI engines have high compression ratios like the 6.2L Ecotec with 11.5:1(probably why 93 octane is recommended), but I have not heard about any mass produced DI engine getting to the 15:1 and up compression ratios of diesels or the 17.3:1 of my Cummins.

I might be wrong regarding DI engines no longer needing to be regulated to around a 14.7:1 A/F ratio. I'll look into that before I say anything more.

[Redwoodcamper]

Newer vgt turbos are a big part of the torque curves these days too. And tuning ability.

[ShinerBock]

It seams that Mazda is doing the reverse to diesel engines by lowering the compression ratio of their diesel to 14:1(which lowers combustion temps) so they don't have to have any emission devices.

SKYACTIV-D

[ShinerBock]

wilber1 wrote:
Mazda Skyactive gas engines are using a 14:1 compression ratio. The are planning on going to 18:1 with gas engines.

Skyactive 2

Interesting! Thanks for the link.

[wilber1]

Mazda Skyactive gas engines are using a 14:1 compression ratio. The are planning on going to 18:1 with gas engines.

Skyactive 2

[ShinerBock]

4x4ord wrote:


The DI gasoline engines are no longer regulated to a 14.7 air/fuel ratio nor is the compression ratio limited. Preignition can't happen without fuel being injected.

I haven't heard about DI engines no longer being regulated to 14.7:1? What engines are these?

Every DI I have hooked my OBD Torque App up to from my Ecoboost truck to my wife's old Audi(both turbocharged) have been regulated to an A/F of around 14.7:1 with a very narrow range. The only time either engines ran lean was the brief instant after going WOT it would add too much air before the injectors could compensate. It would go no more than 15.0:1 though. After that it would run rich at 13.2:1 if you left your foot into it and then start to go back to stoich as you picked up speed. In normal driving or idle they always stayed around 14.7:1 +/- .5. My diesel on the other hand will go anywhere from 20:1 to 80:1 depending on engine load. At Idle, it will go even higher than that to upwards of 100:1.

I know some DI engines have high compression ratios like the 6.2L Ecotec with 11.5:1(probably why 93 octane is recommended), but I have not heard about any mass produced DI engine getting to the 15:1 and up compression ratios of diesels or the 17.3:1 of my Cummins.

[wilber1]

A point here is that DI and turbocharging has made the old adage that the gasser needs to rev like crazy to produce power no longer holds true. The 3.0 Audi gas example that was given has an extremely flat torque curve, one any diesel would be proud of. It produces that 364 lb ft from 1370 RPM all the way to 4500 RPM.

BTW that 3.0 diesel in European S trim is now putting out 340 HP and 516 lb ft but we know it won't meet NA emission standards. Wish it did cause it must be a hoot.

[Redwoodcamper]

Some good points explained clearly here. Modern diesels have come so far that alot of preconceptions and myths are still out there about them. So many people make the blanket statement, "diesels cost so much more to maintain..." When this isn't always the case. It boggles my mind why people still tow 7k+++lb trailers with gas trucks. I love gasoline engines. I have raced several of them. My wife's last two daily driven cars have had over 350whp and run high 11s in the quarter. But that being said, I would never choose to tow with a gasoline vehicle. Once you buy a reliable(Cummins) modern diesel and live with it for several years you learn to appreciate them.

[4x4ord]

ShinerBock wrote:



What each fuel does outside of the engine is one thing. How each engine uses that fuel is another. Gasoline engines are regulated by air and add a certain amount fuel to stay around a stoichiometric air/fuel ratio (14.7:1) while diesel engines are regulated by fuel and uses all the air available to burn lean most of the time. The more air you add to a diesel engine, the more efficient it becomes. The more air you add to a gasoline engine, the more fuel it consumes to stay around stoich. This is one of many reasons why diesel are way more efficient than gas engines under load and are used for towing applications.

Yes, with the same compression ratio gasoline engines would be more efficient, but I don't live in unicorn would-a could-a should-a world so I go by what the real world has. Diesel fuel itself allows for much higher compression ratios making the diesel compression ignition more efficient at utilizing more out of a drop of fuel than spark ignition.

I disagree on the emissions thing. As technology increases, I see less emissions devices on future diesels. Cummins has already deleted the EGR on their current ISL engines and only utilizing SCR making the engines more efficient and better performance. they already have plans to do the same for other engines on their line up including the ISB 6.7L.

The DI gasoline engines are no longer regulated to a 14.7 air/fuel ratio nor is the compression ratio limited. Preignition can't happen without fuel being injected.

Hopefully emission equipment for the diesels will become simpler and less taxing on fuel economy but until they can get rid of the DPF and the DEF there is an efficiency tax that the diesel has to pay.

[4x4ord]

ShinerBock wrote:
If you want to compare a diesel and gas engines with similar displacement, bore/stroke, duty cycle, and technology then you can compare the Audi 3.0L turbocharged diesel and gas engine.

Audi 3.0L Diesel
240 hp
428 lb-ft


Audi 3.0L Gas DI
354 hp
369 lb-ft

That is a good comparison.

I believe the potential is there for making higher torque with a gasoline engine but it becomes kind of futile. For instance say Ford decides they want to make a gasoline engine to put in a F350. They will consider how fast it needs to be able to pull a 20,000 lb trailer up the Ike and determine the truck needs to make say 450 HP. The operating rpm range of a gasoline engine easily allows for that HP to be made at 5000 rpm. Therefore the size of the engine and level of boost is determined to be much smaller than a turbo charged diesel designed for the same use. If they were to decide to make a 6.7 liter turbocharged gasoline engine with a peak torque of 900 lbft of torque at 1700 rpm they would have a 900 HP monster that would require a radiator larger than the one on our Kenworth to keep things cool. So in other words because the nature of gasoline engines so easily allows for them to make HP at a higher rpm it is unlikely that the manufacturers will ever build the gasoline engines to produce the same gobs of torque they design into the diesel.