Fuel Injectors revisited

[thomasinnv]

I have n65's in my 8v71 so I am assuming it is advanced timed.  what are the advantages/disadvantages to the advanced timing vs. standard timing as far as power/torque output and rpm range or "sweet spot"?

[luvrbus]

A timing in a bus with a 4 speed auto or manual does very little that was a set up for trucks with a close rpm split going through gears most were 10 speeds the N65 works ok without A timing just more smoke 90% of the bus engines won't be A timed,have any of you A timers ever noticed nothing is ever said about A timing on a 92 series it never happens 92 series are standard timed because they don't use the needle valve injectors 

good luck

[bevans6]

N65 with advanced timing is what I had in my 8V71N, which was a Navajo Nation MC-5C.  The combination shifts the peak torque from 1200 rpm to 1600 rpm, but you don't lose anything - the torque at 1200 rpm is still greater than N60's and standard timing.  Mine smoke a bit on take off, never noticed anything climbing a hill.

Brian

[luvrbus]

You guys with A timing and N65 get up around 7500 ft then see what you have lol plenty of heat and smoke that is what you have

good luck

[artvonne]

  Whats the simplest way to check cam timing?

[bevans6]

If the bell housing is on, there is no simple way to check but it's not rocket science.  The method is to remove an injector, use a dial indicator to find top dead center on that piston, then re-install and time the injector and use the dial indicator to measure the amount of injector stroke at TDC for that piston (doesn't have to be true TDC, just for the piston you are checking).  Standard timing is .230", while advanced timing is .262".  If you've ever timed a cam, it's wouldn't be an unfamiliar task.  The difference in injector stroke is substantial at .032", and if you had a way of telling where TDC was you wouldn't even need to pull an injector out.  If the bell housing is off, you just look at the gears with the engine rotated so the marks line up.  The trick is arranging for the bellhousing to be off...

The highest pass I ever took the bus over was I-26 at 4,000 feet.  That was 45 minutes to an hour of 2nd gear on the governor and 30 mph, but it was a nice day, the scenery was pretty, and I was in a long line of trucks doing exactly the same speed.  The highest pass I do normally is 2700 feet.  Plus my new engine has a turbo...

I may well take the time to put a TDC indicator on the front pulley of my new engine, it could come in handy some day for something or other.

Brian

[artvonne]

  Thanks Brian. I have a dial indicator and degree wheel and all that stuff and know how to degree an engine. I was hoping there was an easier way, a cover you could pull or something. No banana there I guess.

  Is the general consensus that an 8V71 with "A" timing and 55 injectors would have the highest low end torque at low rpm, and the best fuel economy?

[bevans6]

No, I think the N55 injectors will not supply sufficient fuel to allow advanced timing to work to any advantage.  The reason for the advanced timing is to allow more time for amount of fuel delivered by the N65 to fully combust.  Don't forget that it also advances the timing elements for the exhaust valves, opening them sooner and reducing the time for the combustion to deliver power, and closing them sooner reducing the time for the intake charge air to enter the combustion chamber.  It's all a balance.  Turbo charged engines mostly run standard timing, all the ones I've found anyway.

Brian

[luvrbus]

Not all 6v92 or the 8v92 are turbo engines and they still have standard timing