Engine/Transmission (1998.5 - 2002) 3cyl question...

[Alphacowboy]

no, not your typical "how do I engage it" question, as I already have it, and love it!



Anyway, so just for sh!ts and giggles ya think there would be a way to activate this on the fly? Sounds odd, but think about it, if you were crusing the freeway at 60-70mph unloaded, I would think that 3 cylinders should easily keep you moving, correct? Basicly in a sense, kinda like the MDS system on the Hemi, but then again, not really the same, but basic premise behind why to do it.



Just an idea, be pretty sweet if it worked, could you imagine if it worked and you ended up getting 25-30mpg with it? :-laf Oo.

 

[Hoefler]

It would wind up costing you power and mileage. You would have to some how keep the valves open to keep from having a compression stroke, which will rob power.

 

[johncameron]

Just think, my truck idles just under 500F when on 3cyl. Could you imagine what the EGT's would be at 70MPH, and could the engine produce enough power?



JC

 

[WestTN]

Just think, my truck idles just under 500F when on 3cyl. Could you imagine what the EGT's would be at 70MPH, and could the engine produce enough power?



JC

Just think, my truck idles just under 500F when on 3cyl. Could you imagine what the EGT's would be at 70MPH, and could the engine produce enough power?







I think the EGT would not increase too much because there would be some boost at that speed. However, there would be pumping losses from pushing air through those cylinders unless the intake valve remained closed. In that case, the loss of power due to the compression stroke would be mostly returned on the power stroke.



Aren't theories wonderful?

 

[obert]

... . having a compression stroke, which will rob power.

Sooooo... lets shift gears. Would we be on the fore front of a primitive copression brake??! It wouldn't work very well, but its' fun to think it!!! Oo. Oo. Oo. Oh wait, that'd just be the same as LETTING OFF THE THROTTLE, huh? Too bad.



OHHH I cant wait for the camless B model... .

 

[obert]

on second thought.....

Maybe we (I) shouldn't make light of that idea. Stepped out for a moment there and thought af a big massey tractor I drove once. Had a Cummins 555 V8, true dual stacks with raincaps Thing is, when the engine was unloaded, the pump cut off one side of the engine. Left bank, if I remember right. Of all things to do, I was using it as a pull back for a tractor pull sled. Headed back to the start line, once you got rolling, even in the heavy classes, one stack went dead. A completely mechanical engine that did pretty much what WestTn said on the powersroke.



Our engines are electronic. If stock software allows the engine to cut 3 at idle, I bet somehow Marco could write that into the smarty software by the time I can get one... ...

 

[benhall]

I would go for a compression braking feature on my Smarty.



Ben

 

[cojhl2]

It would wind up costing you power and mileage. You would have to some how keep the valves open to keep from having a compression stroke, which will rob power.

Not quite correct Except for some irreversability you get back the work it took to compress the cylinder charge.

 

[obert]

Not quite correct Except for some irreversability you get back the work it took to compress the cylinder charge.

Think of tipping over your small lawn mower, and turning the blade (sp plug unhooked of course). You feel resistance as the piston comes up on compression, cross TDC and the blade flips over on its own.

I would go for a compression braking feature on my Smarty.

Exh. valve timing is changed alot for a comp. brake. Soon it will be possible. I dont know where Cummins is at on camless technology, but it is inevitable.

Chevy trail blazers with the inline 5 or 6 cyl use solenoids for the ex. valves now. (So why did they leave the cam for intake?? who knows. It is GM after all) With electronic valves, duration and timing are at our will, and FINALLY we can complete the "big rig" sound from the ISB. I could only imagine how long brake linings would last.

 

[benhall]

If I remember right, when the 3 cyl feature is enabled for cold weather start-ups, it is another version of compression braking. I doubt it would take much to have another option built into the Smarty to stop fuel from going to 3 cyl when your foot comes off the go pedal.



Ben

 

[obert]

Maybe I inadvertintly started somthing. oops

It wouldn't work very well, but its' fun to think it!!! Oh wait, that'd just be the same as LETTING OFF THE THROTTLE, huh? Too bad.

When off the go pedal, fuel is cut to 6 cyl's, so the 3 cyl thing as far as fueling is concerned cannot be used for braking. I like the premis of 3 cyl hyway cruising, it might just work.



You see, a "jake brake" really has nothing at all to do with fuel. Basicly, the engine coasts up on compression, but instead of the energy returning to the crank, the ex valve opens just past TDC to release the energy thrugh the exhaust system. Early systems used a hydraulic solenoid to push open the valve befors the cam lobe hit it.



That was a half-4S5ed idea, mostly intened as a joke, I appologize for any confusion. So far we are limited to exhaust brakes, which seem to do well and cummins even says its OK for the engine. But a compression brake would be cool, huh?

 

[cojhl2]

When off the go pedal, fuel is cut to 6 cyl's, so the 3 cyl thing as far as fueling is concerned cannot be used for braking. I like the premis of 3 cyl hyway cruising, it might just work.

Before Exhaust Brakes or Jake Brakes were avail we were taught to use a little foot feed once in a while to keep the cylinders warmed up, so the shock would not be so great at the bottom of the hill. This was because as obert says, fuel is completely shut off when the foot feed is released and the engine is running at greater than what the governor is set for idle.



Most of these threads vary somewhat from the original question or comment, so as this one. .



I have never understood (although I agree it must work cause others say it does) the shutting down of some cylinders to save fuel. If one considers it takes so much power to move the vehicle down the road, and approx 1/3 of the BTU's entering the system is used to do that why is it more efficient to burn it in a reduced number of cylinders and drag the shutdown ones along anyway?



And what happens to the cylinders that are still absorbing friction horsepower? They must be running cold. Is that good?