Need power or torque data for Detroit Diesel 8V71 !!

[JimGnitecki]

Hi, I'm a new member with a 1979 Eagle conversion bus and a lot of plans!

But, first things first.

My bus has a Detroit Diesel 8V71 (2-stroke) engine, with Roots blower but NOT turbocharging. The bus dealer from whom I bought it recently said it is the "318" version, which means 318 crank horsepower (maybe a little optimistic ).

But, I need way more dtaa than that in order to do some engineering analysis. Its eems that this bus was originally a manual transmission model, into which an Allison 740 automatic was installed. I suspect the rear axle ratio was never changed, and it may not NEED changing, but I won't know until I get a power or torque curve for the engine, that shows either power or torque versus engine rpm.

I have looked in a lot of places for that graph or table, without success. I googled. I called Detroit Diesel, and I asked a few mechanics. Detorit Diesel was uninterested in looking for the data in their files, and no one else has the data readily available for an engine this old.

Anyone out there know where I can get the data, in either graph or tabular form?

I ahve found the gear ratio data for the Allison 740, have road and wind resistance data from a Caterpillar publication, and am seeking the rear axle ratio in a separate thread, but am sort of stuck on the power or torque data. Anyone out there have the right "connecitons" with Detroit Deisel or a dynamometer-equipped diesel shop to get the data?

Once I get the data, you will be amazed what I can do with it, and I promise to post the analysis results!

Jim Gnitecki

[luvrbus]

Jim, look under old 2 cycle brochures at www.powerlinecomponents.com they have some graphs also your Eagle will probably have a 3.73 rear gear and 272 hp    good luck with your Eagle just so you know Eagle owners have a board also www.eaglesinternational.net

[Dreamscape]

Jim,

Don Fairchild in Bakersfield CA is quite adapt with 8v71's. I'm sure he will see this and respond.

If not, I'll let him know you posed the question here, or ask him get in touch with you.

~Paul~

[cody]

Welcome to the insanity, it's always good to see another iggle owner that speels like me lol.

[HighTechRedneck]

Not a chart showing the curves, but a little info.

http://en.wikipedia.org/wiki/Series_71#Popular_Horsepower_Ratings_.288V-71.29

Popular Horsepower Ratings (8V-71)
866 ft·lbf @ 1400 rpm 318 hp (237 kW) governed at 2100 rpm
990 ft·lbf @ 1400 rpm 305-350 hp governed at 2100 rpm (turbocharged)
1064 ft·lbf @ 1200 rpm 305-370 hp governed at 1800-2100 rpm (turbocharged/aftercooled)

[luvrbus]

Jim, if you know the injector size we can give you a answer the 318 hp is actually a 302 HP.If you buy a series 71 manual it will have the HP and torque rating for the injector size and timing has graphs and charts     good luck

[Jerry Liebler]

Jim,
    The  torque peak for the "318" is at 1400 Rpm.  The "318" uses "advanced? injector timing to allow the use of larger injectors  (N65 s) while the typical bus engine uses " standard" injector timing which limits injector choices to the N60 or smaller (going larger makes lots of smoke).  The standard timed engines have a lower torque peak, 1200 RPM and a flatter torque curve which gives better performance with 3 and 4 speed transmissions typically found in buses.   You'd have to pull a valve cover and look for markings on injectors to verify that you do really have a 318.   With a 4 speed manual or automatic you are best off with the standard timed engines.  The 318 setup is best for trucks & a few buses with 10 or more gears.
Regards
Jerry 4107 1120

[JimGnitecki]

Wow!!

You guys are GREAT!

That Powerline Components website has not only all the variaitons of power curves for all versions of the 8V71 AND 8v92, but also has power and torque curves  for the 8V71 with attached torque converter (the "fan to flywheel" versions of the engines)! Furthermore, it actually includes the fuel consumption per brake horsepower produced (pretty dramatic differences between the early 8V71s and the "fuel squeezer" 8V71 versions and the 8v92s on fuel consumption!)

All this data, coupled with the rear axle ratio information I have posted about separately on this forum, and coupled also with the Caterpillar "Understanding Coach / RV performance" booklet I already have, equips me to do stuff like:

- Model the acceleration and cruising performance of the bus in my computer modleing software
- Predict the best speeds under different road and wind conditions for best fuel mileage
- Predict the top speeds with different gearing and tire sizes
- etc, etc

and share that here over the next few weeks.

What a treasure trove of data!

THANK-YOU ALL!!

Jim G

[RJ]

Jim -

You've got to pull one of the valve covers on your 8V71 to find out what injectors are in there.  Without that info, well, you're just guessing.  Or playing!

If it's a stock coach engine, there's a 99% chance it has either N60 or C60 injectors.

Below is the original power & torque graph for the 8V71 coach engine equipped with N60 injectors as installed in the PD4106.   This was the FIRST bus application, in 1961, back when Detroit Diesel was still known as GM Diesel.  Peak HP is 272 at 2000 rpm, and peak torque is 770 ft lbs at 1200 rpm.  Peak efficiency is in the 1500 rpm range.

Originally, GM governed coach engines at 1650 rpm, but that was quickly bumped up to 2100, which has been the recommend max right up until today.  "Fire Apparatus" was one of the rare applications where 2500 rpm was allowed.  The more you tweak the 2-stroke over the 2100 recommended max, the shorter the overall engine life, which is sort of a moot point in an RV.

FYI, the V-drive manual gearbox PD4106 was geared to run 60 mph at 1650 rpm with tires that turn 495 revs/mile.  The overall final drive ratio is 3.333, factoring the rear axle ratio (4.125:1) times the bevel gear ratio (0.808).  Transmission ratios are First 4.32:1, Second 2.50:1, Third 1.50:1, and Fourth 1.00:1. 

I think if you look at the HT-740's ratios, you'll find them very similar to the manual box above.

Since a lot of what you want to do with your computer modeling software has been hashed over and over again on this forum and on BNO, some searching thru the archives will yield lots more data to play with.

And FYI, a stock 8V71 in a Model 5 Eagle equipped with an HT-740 and the OEM 3.73 axle will give you 5.5 - 6.5 mph consistently, uphill & down, w/ or w/o headwinds.  Sometimes seven mpg downhill with a tailwind.  Just like the MCI & Prevost guys. 

Remember that wind resistance goes up by the cube of the speed, and you're basically pushing a vehicle with the aerodynamics of a brick thru that wall of air. . .

As for acceleration, well, let's just say pray for downhill freeway on-ramps!  Especially if your  8V's got a few hundred thousand on it.  Transit buses will clean your clock 0-30, btw, but you'll pull away once they run out of rpm at 57 mph.

One more thing, or rather, two more things.  So you don't have to re-invent the wheel, here are a couple of calculators to play with:

Mallie's: http://www.cwis.net/~mallie/page12.html

Daris: http://www.thebouthilliers.com/4106    Click on the "MPH Calculator" in the LH menu.

That said, here's the "original" 8V71 coach power & torque graph for you.

FWIW & HTH. . .

[quantum500]

What are they rated at in the fire trucks that govern at 2500?

[RJ]

What are they rated at in the fire trucks that govern at 2500?

Never seen a graph for fire apparatus settings.  Most hush-hush, just like the military 8Vs. . .

 

[buswarrior]

The HP line is beginning to flatten in RJ's graph, I expect that it will flatten more quickly above 2100.

At 2500, I'd guess it will be flattening still somewhere below the top line.

Also note that the torque will keep dropping, the higher the rpm, so more spin just gives you a longer run at the hill?

happy coaching!
buswarrior

[JimGnitecki]

Jim -

Transmission ratios are First 4.32:1, Second 2.50:1, Third 1.50:1, and Fourth 1.00:1. 

I think if you look at the HT-740's ratios, you'll find them very similar to the manual box above.

. . .

And FYI, a stock 8V71 in a Model 5 Eagle equipped with an HT-740 and the OEM 3.73 axle will give you 5.5 - 6.5 mph consistently, uphill & down, w/ or w/o headwinds.  Sometimes seven mpg downhill with a tailwind.  Just like the MCI & Prevost guys. 

Remember that wind resistance goes up by the cube of the speed, and you're basically pushing a vehicle with the aerodynamics of a brick thru that wall of air. . .

The HT740 ratios are indeed close, but different enough to take into account:
1st   3.69 versus 4.32
2nd   2.02 versus 2.50
3rd   1.38 versus 1.50
4th   1.00 same

Your 5.5 to 6.5 mpg prediction is excellent as it turns out. On the maiden 1200 mile trip from where I bought the bus (Lakeland, FL) to my home in Austin, Texas, I checked the fuel mileage at EVERY fuel stop, and it was EXACTLY 5.0 mpg EVERY time, regardless of wind and terrain, and even after the air filter began to exhibit severe air restriction symptomns the last 75 miles or so. That sounds at first lower than your 5.5 to 6.5 mpg prediciton, BUT that is because:

1. I ran the generator the whole time (no bus air, so ran the basement air), plus overnight both nights, and
2. I averaged 73 mph on the interstate, which certainly uses more fuel than I would at 60 mph!

Jim Gnitecki

[TomC]

If you're looking at the automotive brochures, you have to give some latitude to advertising.  For instance, the torque and rpm on the N65 8V-71N is listed as 866lb/ft @ 1400rpm.  Yet the industrial version with the same injectors is 800 @ 1600rpm-personally will go with the industrial ratings.

On an up dating issue-it's amazing what technology will do.  Detroit Diesel's new DD16 that will be coming out only as a 2010 engine equipped with Urea injection in the exhaust will be rated up to 600hp and 2050lb/ft torque weighing around 2950lbs.  As compared to Detroits last 12V-71TA with 80 injectors at 600hp with 1800lb/ft torque weighing around 3550lbs!  What's amazing is the new DD16 will do this getting close to twice the fuel mileage and be as close to a green clean engine as technology will allow today.

The new ratings for Detroit Diesels new engines will be DD13 up to 500hp and 1650lb/ft torque, DD15 up to 560hp and 1850lb/ft torque, and the for mentioned DD16.  These are all 2010 ratings for clean Diesel engines.  Good Luck, TomC

[HB of CJ]

If memory serves, (always suspect!)  the fire service N versions had advanced timing, N90 injectors and the 8V71N was rated @ 350 hp @ 2300 and 900 torque @1600 and the 671N was rated at 262 hp and 676 ft lbs.

The American LaFrance ladder truck I drove had the governor set at a whopping 2550 rpm, giving the short geared vehicle a top speed of about 65 mph.  They sounded sooss cool winding thru the T905M tranny.  HB of CJ