AH64ID wrote:
Farmerjon wrote:
AH64ID Check out what your own truck's compression ratio is. CTD 5.9 24v has 16.3:1 to 17.2:1. How high does a gas engine have? 9.0:1 to 10:.1.
Compression braking has nothing to do with compression ratio. Diesel engines generally, until EGR, have an unrestricted intake. That means there is nothing slowing the air in/out. It does take energy to compress to 17:1, but that energy is released pushing the piston down with equal force.
Gas engines have butterfly valves in their intake, which restricts the intake flow. This is where compression braking comes from, the vacuum created in the intake stroke slows the engine.
A compression release brake, Jake Brake, uses the compression stroke to build pressure and then releases it to the atmosphere, or exhaust, before it can push the piston down on the power stroke. So the 17:1 is the braking at that point, but only when the pressure isn't kept in the cylinder.
Farmerjon wrote:
The diesel trucks and tractors that we have hold a load back on a hill much better than our gas engines. That has been my experience with all the gas vs diesel engines I have driven or ridden in.
Your experience is not consistent with the industry, or companies like Jacobs would never have been created.
AH64ID.
I have done some research after reading your post and I stand corrected . Thank you for enlightening me.I'm not being sarcastic.
we were absolutely convinced that our 460 didn't hold our speed down as well as our 7.3 or the 6.7 (without using the exhaust brake).
I can't explain why we were so sure. Maybe we drive more cautiously with the diesel and there is less speed to get rid of?
We will pay more attention.
Two of our tractors are identical except one is diesel and one is gas. Coming down a steep road with the diesel I start in second gear and am still in 2nd when I get to the bottom. With the gas tractor on the same hill and same size load I start 1n 1st and when I get to the bottom I am in 5th which is road gear and I'm close to being red lined.
The governor is slow on closing the throttle all the way and maybe the butterfly is cracked open enough to prevent a good vacuum?
