A technical question about a jake brake.

he was talking fuel/air ratio not compression ratio...

 

I doubt that but many a rocker arm has become victim to high RPM jakeing. C-15 cats seem particularly susceptible, more so on the earlier ones.

 

What is considered 'high RPM' ? I run my 3406E up to the governed 2100 and maybe a little more on some grades... it's made to do that.

What is amazing is watching guys descend a grade with their Jake on at 1200 RPM's... and smoking the brakes. A Jake needs more RPM's to work at it's peak...

 

The answer is actually yes...

An engine without a jake will cost alittle bit less to run the overhead.

The cost between the two would be minimal, but yet there would be a difference.

An engine brake will do damage if a driver runs them wrong.... too high RPM.

Jakes and guns are the same, sorta..... Guns don't kill people, people kill people with guns, same goes for Jakes. They don't do damage, people use them to do the damage...

 

The only reason I brought up the compression ratio is because I have never heard of an actual air/fuel ratio spec listed for a diesel... I understand technically it has to exist but I have never heard of or dealt with it. I am never ashamed to learn something new..

 

Sheesh......You all are all over the place with this subject!

Jakes: GOOD to have and use accordingly! No sense in using at a lower RPM.....most are set to kick out around 1200-1000 rpm anyhow. Dont use ANY jake above 2100 rpm. At 2100 rpm, the engine is at pretty much top speed and valve train is moving VERY fast meaning easily damaged if not adjusted correctly. Jakes work the best between 14-2100 rpm along with the right gear.

Running overhead on one with Jakes will cost you more due to the fact you have and extra gasket on some and you have to bar the engine twice (longer time frame) to get all your adjustments. Detroits have internal (under valve cover) engine brakes as do most Macks, Cummins, Cats.

As for the guy who said a cat runs better at 2100+ rpm.....your askin for trouble. Cats are like Macks, They are made for LOW rpm pulling power. Thus is where Caterpillar got the slogan "Cat Power". Cat originally started out with off road engines for dozers and other construction equipment. They didnt fly up a hill side in a dozer. They were made to have low rpm torque and they stuck with that idea with the truck engine. Older C15's are ok, but watch out for newer models and C15 acerts. Acerts are TROUBLE and expensive! C15's are also BAD for blowing head gaskets.

ANY QUESTIONS???? Im a mechanic.....Ive seen all this junk for the last 15 years!

 

I was quoting the air/fuel mixture ratio at idle. Not the compression ratio.

 

Hate to tell you this but all Diesel engines burn Diesel to air at 15 to 1 ratio. That is 15 parts Air to one Part Fuel. Higher air than that they will not run right they miss and will burn pistons. Below that and your getting Black Smoke out the stack. Electronic engines have a sensor that is simalar to the O2 in your Car that tells the Computer if a Cylinder is running lean or Rich.

 

15 to 1 at idle, cruise, or under load?

 

All the time that is the required air to fuel Ratio. you start dumping more than that your going to get black smoke. Less than that you risk burning a pistion.