Optimizing 8v71 High Altitude Performance

[technomadia]

Hey Cris, just tell the shop what you want, the most power you can get safely and reliable. If they are Detroit 2 stroke guys they should have a solution for you. 

The shop here thinks that both N65's and N70's are good options.

The old 2-stroke expert here thinks N70's - but he admits he doesn't care much about making smoke or fuel economy.
The younger 2-stroke guy thinks N65's - should still be plenty of power, and potentially less smoke and a bit better economy.

In the end - they suggest comparing notes with other bus guys and letting them know which way we want to go...

  - Chris

[Lin]

When we replaced my old C60 injectors, Don went with the N65's.  I do not remember discussing N70's but I believe he wanted to give me the safest upgrade.  I think that my engine having the older dry block my have been part of the decision.

Now with regard to getting more air to the engine, would a toggled booster fan at the air intake make any difference?  I have sometimes thought of spraying propane in the intake also, but wonder whether, since lack of air is the issue, it would make any difference for this problem.

[muldoonman]

I have the 8V92TA in my 40,000 lb. coach and have all the power we need  but have heard of the propane addition on Detriots but does it start affecting reliability? More heat and pressure in engine? Wondering if it was like my old drag car days when we first tried nitrous. Blew a engine or two up before we figured it out. Just curious.

[Barn Owl]

The difference between the injectors is one allows you to put more fuel into the engine if you choose. The 65 will take that choice away. BTW, you can still make both of them smoke at altitude.

[Ed Hackenbruch]

Can't remember for sure, its been awhile since i looked, but i think that i have N60s in my 8v71. Get some smoke at altitude even with those, i just let up on the pedal and or gear down as needed.

[technomadia]

The difference between the injectors is one allows you to put more fuel into the engine if you choose. The 65 will take that choice away.

This is what I have been trying to understand - will the N70's with a light foot on the throttle end up with the economy and smoke characteristics of an N65? But if I punch it (and there is enough air), the N70's will give me a little more oomph?

That seems like a good plan.

 - Chris

[luvrbus]

You guys are out to lunch on the injectors the 65 will produce more smoke it has 8 holes (brown tag) on a angle, the 70's have 7 holes straight same size holes in tip 006 only major difference is the plunger the N65 uses a N65 plunger the 70's use the 7N plunger now the white tag N65 is a totally different animal 

Go with old guy he can set the 70's where there is not much smoke if he sets those at a 304 hp which is the max for a N65 the 70's you can go to the full 318 hp and then they do smoke 

[bevans6]

That is my theory too - my N80's can smoke with the best of them at full throttle, full load, but are clean clean clean at part throttle part load.  Don't forget that the throttle control (actually sometimes called the speed control in the manual, since there is no throttle) only has a tangential impact on where the governor sets the injector racks and hence the amount of fuel injected.  If you set the speed control lever to let you run at 60 mph on the flat and you start to climb a hill the governor will try to maintain that speed and will increase fuel to do so.  It will eventually have the racks full open while you haven't changed your foot position at all.  I never felt this with the 8V-71N but it is quite apparent with the 8V-71T, I could really hear the engine note change when I got to a hill and the feeling of power being added was tremendous.  What I do is adjust the mirror so I can see the smoke.  If I want the power I ignore it, if I am being polite I vary my foot to adjust.  Don't forget that where you set the injector timing can have an impact on power and smoke.  If you advance the timing you can inject the fuel earlier, which has the effect of starting the combustion event earlier, increases cylinder pressure and heat, makes more power and burns more of the fuel reducing smoke and some other pollutants.  The downside is you can burn up the engine.  It's all a balance.  I have no clue which injectors you should have, btw.  If it was me I'd just keep what I had if they were good, and use the N70's.  If not, I'd install the set of brown tag N65's I have on my shelf, left over from my engine swap which need a good home...  

Brian

[pvcces]

Chris, I didn't see where you said which cam timing your coach has. As I understood it, standard timing used N60 injectors and advanced timing used N65s. The best fuel economy that I know about occurs with standard timed engines. With advanced timing, RPM has to be kept higher and more heat is generated. It seems like the power band is wider with standard timed engines.

Our coach uses standard timing and N60s, and it will smoke plenty at 6,000 feet. It's quite noticeable at 3,000 feet. I would not consider going to larger injectors without a very good reason. I do understand that adjustment of the rack can make a big difference.

I figure that the hydrogen in the fuel is stripped off first and then the carbon is burned only if there is enough oxygen left. When you're at high elevation, there is a bunch of leftover carbon, hence the soot in the exhaust. Since we get no work out of the carbon in the exhaust, it stands to reason that power output is reduced accordingly at high elevation.

Imagine what the effect might be if oxygen was added to the air intake at high elevation. Since no one that we know of is using that setup, there may be some unwanted effects that go with it.

I did see that propane injection seemed to be well tolerated by the people that tried it.

Tom Caffrey

[TomC]

If you do alot of altitude driving, DON'T go with the N70's-you'll be smoking like a locomotive. Mine had N65's that I had to pull up on the accelerator about an inch to keep it from smoking at altitude. But then you don't have much power. Once again-turbocharge the engine and you don't have to worry about smoking at altitude plus you'll get better fuel mileage. If you're going to keep the bus for a while, you'll be very pleased with turbocharging. Good Luck, TomC

[luvrbus]

Their engine had 70's it's well documented by the 2 they had no smoke I setting up a 8v71 NA now with the 70's it had no prior smoke either just don't use A timing

A timing You don't A time a 92 series N/A or turbo it can all be done through the injectors

[technomadia]

Their engine had 70's it's well documented by the 2 they had no smoke I setting up a 8v71 NA now with the 70's it had no prior smoke either just don't use A timing

Very good point - we hardly had any smoke with our old engine setup and N70's when we first bought the bus, and took it up to Flagstaff, AZ to escape the heat. That was near 7,000ft elevation.

As for A-timing though...  The shop here seems to think that A-timing is a must for N65's and N70's.

What is the reasoning not to go A-timing?  Is there some documentation I should point them to in order to convince them that standard timed N70's are a good idea?

  - Chris

[bevans6]

Chris, I will email you directly a PDF file that shows the recommended timing settings for the two injectors, and has a great description of how they work.  The N65 brown tag non-turbo has a recommended setting of 1.484 with advanced cam timing and 1.460 with standard cam timing.  The N70 non turbohas only one recommended setting, that is 1.460 with advanced cam timing.  You can see that 1.460 is more advanced than 1.484, so the N70 is, compared to the N65, getting advance from both the timing setting and from the cam gear setting.  This is in line with my earlier comment that a more advanced setting allows more fuel more time to combust, increases power and reduces smoke.  Also recall that the advanced cam setting also advances the exhaust valve timing so the exhaust valve opens and closes sooner, starting the compression event earlier and ending it earlier.  This should have the effect of increasing dynamic compression but reducing the length of the power stroke interval.  I honestly have no idea what effect that would have, probably reduces efficiency and increases fuel consumption.  But it's clear that the recommended cam wheel timing is advanced for both injectors.  I think standard timed N70's are a quite bad idea, and it might be a good idea to let the experts you have hired do their thing.  If you don't believe they know their craft, why are you letting them work on your engine?

You are far better with computers than I, maybe you can post the PDF file in a manner that all can access it who care to.  I think the server I took it from it gone now, it was on George Brown College in Toronto.

Brian

[luvrbus]

N70's are 1.496 for standard timing for no smoke some old timers use 1.500  for coaches it's in da book

[bevans6]

Chris, I sent the file to the email in your profile.. I guess, like a lot of things in life, you have a lot of choices on how to time your injectors!    FWIW, the numbers I quoted match those in my 1980 Detroit Diesel manual for 1970/71 engines with N65 and N70 in natural engines.  Clifford rightly points out that there is more than one way to skin a cat, and you can get different results with different settings.

Brian