Better engine braking?

Im not sure of the answer to your question about which one will slow down better, but i can tell you the jakes hold the valves open. So i think you need to have the jakes adjusted you did say how many miles were on the truck or the last time an overhead was ran. I think that if both the jakes were set properly it would come down to where the rpm's are when the jake is applied, the tire size, and wind resistance on each give truck. If i had to guess the lower horsepower truck would slow down quick because it is working harder. I could be wrong just an uneducated guess.

 

So you are saying when you first got the truck the jakes worked to your satisfaction and now they no longer do?

 

The jakes do not "hold the valves open", but rather they open the exhaust valves at the top of the compression stroke in order to prevent the compressed air from acting like a spring and pushing the piston back down the cylinder. The "braking" power is the energy it takes to compress the air in the cylinders.

No fuel is added to the cylinder, and no real boost is provided by the turbo during engine braking....so how would adjusting those settings to improve HP and torque numbers affect the jake's performance? It won't.

 

Different engine manufacturers design their engines differently and incorporate the engine brake in different manners. Something as simple as valve timing plays a large role...how much air is sucked into the engine during the intake stroke? If the intake valve opens or closes a little too late, there is not as much air inside the cylinder to be compressed. How much energy does it take to compress the air in the cylinder? Less air in the cylinder means less energy consumed to compress it. How effectively is the air released through the exhaust valve? If the exhaust valve is opened too early, the air was not fully compressed...and too late, or if there is too much restriction/back pressure, the piston is already being pushed back down the cylinder.

Displacement is another issue...as is compression ratio.

Another variable which could possibly play a role is that Internationals have the EGR cranked way up, too...whereas most other manufacturers dialed back the EGR when they added SCR. Hot exhaust gas introduced into the intake means the air being compressed was less dense (and therefore more easily compressed) than colder and more dense air would have been....and that could also affect the performance of the jake since your braking power is derived from the energy consumed by compressing the air in the cylinder and then releasing it before it acts like a spring pushing the piston back down the cylinder.

There are really too many variables to consider when trying to compare 2 different engines from 2 different engine manufacturers in 2 different trucks and try to determine exactly why the jake works better in one than it does in the other.

Not every truck with an engine brake will put you through the windshield, though...the engine brakes on some engines just aren't all that great. If it doesn't work, have it looked at. If it is functioning properly and/or the shop can't/won't do anything to make it better, you'll just have to adjust your driving to compensate for the less effective engine brake.

 

i don't think upping the hp has any thing to do with jake power my motor was 500 hp turned to 600 jake still works the same

 

2012 Plus straight off the line, Navistar's engine. My jake does good with 46k in the box. Cincy grade ain't a problem. Mainly cause their turning the jake's up. You can hear it now. GRVVVVVVVVVVVVVVvvvv sound dies down with truck speed.