Engine/Transmission (1998.5 - 2002) Good reason for an exhaust brake

[GMincher]

Hey guys, I have a mechanical question about our diesels. Why doesn't my Cummins have the same amount of holdback on a downhill as say my Jeep gasoline inline 6? The Jeep has the same gearing, granted it doesn't weigh as much, but the truck seems to almost freewheel. With it's much higher compression this doesn't make mechanical sense to me! Straighten me out!! Thanks, Greg

 

[NIsaacs]

Greg,



The difference between the Diesel and the Gas motor is in the intake system. The diesel has a wide open intake vs. the gas motors carburetor butterflys, or in the case of the fuelinjected motor, the "chingus", (can't think whatcha call it), that shuts the air down. This creates the vacume pump effect that slows the gas motor down. If you want to slow the Cummins down, put an exhaust brake on it, you can have about 190 retarding hp





"IF IT AIN'T CUMMINS POWERED, IT AIN'T A TRUCK"





"NICK"

 

[darkhorse]

The energy used in compression is delivered back to the piston on it's down stroke. The "Jake" brakes on the big rigs brake by opening the exhaust valves at the top of the compression stoke.

 

[Forrest Nearing]

LMAO! @ "chingus" (AKA "throttle body")



like they said, no throttle blade to creat engine braking on a diesel. this is part of why they get better fuel mileage also



Forrest

 

[jmeehan]

Originally posted by Forrest Nearing

LMAO! @ "chingus" (AKA "throttle body")

Dang! I've been refering to the wrong part as the chingus all these years A fella can learn alot here on the good ole TDR:-laf

 

[y-knot]

The real difference between a gas and diesel engine, is the lack of Vacuum. Like mentioned before the diesel has a non-restricted intake, it consumes 100% of the available air all the time. Where a GAS engine does not, it has to maintain a strict air/fuel ratio of 14. 2:1 to live. The addition of a carburetors "Butterfly valves" or the more modern fuel injected engines" throttle body valve", closes to create the vacuum. It's this opening and closing of the intake air way that causes the back pressure which causes the "engine braking" or deceleration under coast conditions. The diesel has nothing to restrict it's intake air way, and hence has no back pressure to cause the engine braking. This small difference between the two engine types is also one of the reason diesels get better fuel mileage. There the gas engine is always in a battle to maintain the correct air/fuel ratio, the diesel is not. So while idling along in city traffic, or in the drive, it's air/fuel ratio can go to 200:1 or better. We adjust the fuel to get more power, need to get over that hill step on the peddle and pour the fuel on. The air never changes, it is always consuming as much as it can. In the gas engine, they use an array of metering devices to control that delicate balance of air/fuel. Throttle bodies limit the air intake and Mass air sensors measure the air intake, those along with many other input devices, allow the on-board computer to make the right adjustment in regards to the fuel mapping. The oxygen sensor then reads the exhaust gases and tells the computer if it's current fuel mapping is right, if not it will make the needed changes till the readings are back within specifications. This is called a closed-loop system, it makes changes and then evaluates those changes, always checking itself for the most efficient running condition.

 

[GMincher]

Thanks guys!! I knew there was a simple thing I was overlooking!! The chingus!!! Seriously, good explanation! I'm a died in the wool gearhead, but this was one that I had considered for some time but was having trouble with. Guess I've got to save up some money for an exhaust brake. Thanks again

 

[GMincher]

While on the subject, with that amount of engine braking power, is the exhaust brake attached to the brake lights? Or do you leave the pintle hitch in place and suprise 'em! If it's not wired in I said it first I want patent rights!!! See ya!

 

[tgbol]

No they are not wired to the brake lights. But a member of this board got a ticket once because he slwed so quick the cop wouldn't believe he didn't step on the brakes and had no lights.

 

[Mad Bomber]

Ex Brake

Originally posted by tgbol

No they are not wired to the brake lights. But a member of this board got a ticket once because he slwed so quick the cop wouldn't believe he didn't step on the brakes and had no lights.

Sounds like the #$%^&& COP was following to close and was just not ready for anything that happened in front of him