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Detroit Engines

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Detroit Engines
Tue Dec 12, 2017 6:47 pm


I'm curious if someone could answer a few questions for me that might be a little controversial? I wanted to ask you fellows who have driven more than one model of Detroit engine which one you would recommend for a 40 foot eagle? Ive looked at the specs and think I know what I have read but Id like a little more from you with experience.

I like power and am sure most of you do also. At the moment I am looking at a 1983 model with a 6v92 with turbo and am wondering how it does if running properly in mountain areas. I don't know the exact weight but would guess around 35kish? This particular bus has an Allison automatic transmission so I have no idea what that's like. I hope you guys can be honest at the risk of insulting someone who has this engine if its a weak engine. I had a 1987 chevy with a 6.2 diesel when i was younger and I had to set up every pass I made as it had no power and i promised I would never own something else like that again if I could help it.

Thanks for any information you can give me from your experience or knowledge of these engines to someone who's never mashed the throttle on one.
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Re: Detroit Engines
Wed Dec 13, 2017 6:14 am


If not an answer specifically to what I asked could some of you just say what your bus weighs, what engine and what mpg you get? How it does it mountains?
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Re: Detroit Engines
Wed Dec 13, 2017 8:08 am


If you are into power the 6-92 will disappoint you and if you tow something it gets worse. I have traveled with busses that have 6-92's and on the flat they are fine but come to a hill and they fall off fast. I do know of a 35 foot eagle that has a 6-92 that does fine but it has to be lighter than a 40 footer. My 05 has an 855 big cam 3 cummins set at 400 horse. I am 40K and tow a jeep. It is fine but I could use a little more power ( I like power to ) Guys that have 8-92's seem to be smiling most of the time.
P.S. an 8-71 turbo makes some good power also.

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Re: Detroit Engines
Wed Dec 13, 2017 10:46 am


Thanks for reply. Do you have any idea what kind of fuel mileage the 6v92 averages? What does you Cummins do on long trips?
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Re: Detroit Engines
Wed Dec 13, 2017 12:43 pm


I don't know for sure but between 5 and 6 would be my wag. I get just under 7 with my setup
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Re: Detroit Engines
Thu Dec 14, 2017 10:07 am


Barry the response to your question could fill many pages. Indeed it did when I wrote my engine conversion series for Bus Conversion Magazine: http://eaglesinternational.net/engine-c ... -for-buses . That series was written in 2009 when engine conversions often took place in all kinds of buses. Now you don't hear much about these conversions with the possible exception of Eagles. You can now buy other makes of buses with modern 4 stroke engines for a very attractive price.

But with our Eagles (with some very minor exceptions), we don't have much choice of engines (unless someone has done a conversion). Mostly the early models came with 8V71 non-turbo engines and then later 6V92 turbo engines (both mechanical and DDEC). Many folks point out that these combinations plied the highways with no problems for decades. That is true, but trucks and buses have a lot more power today and the expectation is "decent" performance on the big hills. At altitude, the 8V71 will be very slow. We live at 7500 feet and had a friend visit a few years ago. I led him up the our somewhat steep 4 lane highway to our house and at times he was down to probably 10 mph (maybe less).

Mechanical 6V92 engines in Eagles were set at something like 270 HP from the factory. With turbo and injector changes you can get that up to 350 HP pretty safely (many 6V92 are set to put out a lot more power but their life suffers and we don't have a way to cool them).

My bus came with a mechanical 6V92 that was probably set at 270. It was pretty slow even in the empty condition. I changed it over 350 HP and that was better, but I really never got a chance to drive it much at the setting. I am pretty sure that a local emission company overheated the engine and it split a head on the way home.

That forced me to do a lot of thinking about repair/replace/convert. I finally chose the Series 60 conversion and have enjoyed the results. I get between 7 and 9 MPG and with the 10 speed, I can climb any hill at reasonable speeds. Many of those miles we were towing a service truck that weighed close to 9,000 pounds loaded which put us well into the 40,000 range (total).

There are a ton of Eagles out there with some sort of engine conversion. Several folks have installed 8V92 - a pretty straight forward conversion (but must deal with heat) and even more have updated to some sort of 4 stroke engine.

Not sure that I even approached answering your question, but maybe it is a start.

Jim
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Re: Detroit Engines
Thu Dec 14, 2017 12:11 pm


For starters...

8 X 71 = 568 cubic inches

6 X 92 = 552 cubic inches

Difference = 16 cubic inches in favor of the 8V-71.

That kind of makes you wonder why Detroit did't make it a series 96 engine with 576 cubic inches to make the 6V-92 just a little bigger than the 8V-71. The 92 series had a larger bore 4.84" compared to 4.25" for the 71 series but both had the same 5 inch stroke. That let the 92 run at the same 2100 RPM speed of the smaller 71 engine.

OK, the 6V-92T had a turbo but it also normally had an automatic transmission to absorb part of the engine's power. I think Eagle's goal was more torque and better fuel economy rather than more horsepower. The 1960-61 NEW Silver Eagles had Cummins inline NRTO 300 HP engines until the 8V-71 finally became available. The power was appreciated but the noise level and fuel consumption were not so the NRTO's did not last very long.

Continental normally rated it's 8V-71's at 285 HP but I've heard that early Eagles (early 60's) had 265 HP. Continental must not have been happy with that and went to larger injectors to get the performance they wanted..

8V-71 Eagles with the Spicer four speed seemed to be a little more lively than the 6V-92 Eagles with four speed Allisons. I do not know what the weight difference was between the two different engine and transmission combinations. And of course the 8V-71 did not have turbo lag and converter lag to hold them back when starting from a standstill.

Eagle had different transmission gearing than the GMC Scenicrusier even though both had Spicer transmissions and it made a big difference in acceleration between them. The shift points were as follows...

Eagle First to Second: 20-MPH---Second to Third: 35 MPH---Third to Fourth : 55 MPH. Engine speed after shifting to second: 1200, to third: 1650, to fourth: 1700 RPM. .

GMC First to Second: 15 MPH---Second to Third: 30 MPH---Third to Fourth: 45 MPH. Engine speed after shifting to second: 1100, to third: 1400, to fourth: 1500 RPM.

Both had a 1:1 (direct) fourth gear and very likely had the same 3.70 or 3.73 drive axle ratio and tires with the same rolling radius. Unless Eagle speedometers were blatant liars, that gave a road speed just short of 80 MPH, something I saw quite a few times over the years.

The GMC had more grunt off the line with lower gearing but the race was lost when it was shifted into third By the time the engine came up to speed in third, the Eagle was in fourth and the Greyhound driver ended up with a nice view of the Eagle's rear lighting assemblies. And I believe the 8V-71 'Cruisers were also heavier than the Eagles were.

What this means is the Eagle had a closer ratio transmission and was geared a little longer than the GMC in the lower gears. That means the drop in engine speed after shifting up was less on the Eagle. Staying in third gear for an extra 10 MPH reduced the RPM drop upon shifting to fourth and thereby improved acceleration. And getting into third gear at a road speed 10 MPH faster improved hill climbing. Another thing here is that Greyhound normally used 55 injectors so they were getting less power. Add that to the shorter gear ratios meant that 'Crusiers couldn't keep up with the competition even if they used less fuel along the way. I think that MC-5, MC-7, MC-8 and MC-9 buses with manual transmissions used the same ratios as the Scenicrusier did.

In other words, The 6V-92T was not a performance improvement. If you have one and want to keep it., go to the biggest possible injectors and hope for the best.

Then again, you could always try repowering with a DD 12V-71, 71N, or 71T. It should fit because the first Eagles had inline six cylinder engines from MAN and Cummins. Greyhound tried the 12V-71 with about 450 HP in the MC-6 with four speed manual transmissions. Later most were converted to 8V-71 T engines with a resulting loss of power and performance. Another choice would be the 8V-53T engine. It has 424 cubic inches, nearly identical to the 426 of the 6 or 6V-71. The attraction here is the Series 53 runs at 2600 RPM (500 RPM and 24% higher) so it can make more horsepower per cubic inch than 71 and 92 engines. With the turbo and 90 injectors you should be able to get up to about 330 HP or maybe a little more with an inter or after cooler. Another advantage is the faster 53 can be used with a lower axle ratio, which is numerically higher. This gives you better torque multiplication (lugging ability) plus faster acceleration and makes hill climbing easier.
Last edited by Bus & Car on Fri Dec 15, 2017 10:13 am, edited 1 time in total.
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Re: Detroit Engines
Thu Dec 14, 2017 7:54 pm


Thank you fellows very much for the replies. At the moment I'm not in a position financially to do much as far as a conversion. I've found a bus I'm interested in but that engine (6v92) worries me. I spoke with the owner (now) and the builder(converter) and both said "no power on hills, it will do it but SLOW. Sounds like on mostly flat ground it runs well and gets pretty good mpg. Represented as no leaks/clean engine. I wish I knew what you fellows know . :?:


Can/should an exhaust brake be used with this engine?


More than anything I don't want to impede traffic and become a nuisance for traffic.
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Re: Detroit Engines
Fri Dec 15, 2017 9:37 am


The 6v92 is not a power house but they do alright at 350 to 400 hp with 1100 ft lbs of torque,no you you can use Jake brakes on a 6v92 but not the PacBrake exhaust brake
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Re: Detroit Engines
Fri Dec 15, 2017 10:11 am


Ok, lets talk supplemental brakes.

First, why could there be a need for something besides our service/toad brakes? In my mind there are two reasons. First, our service brakes are considered marginal by some - especially the 01 and 05 models. Secondly, in general, diesel engines do not have good "compression braking" like gas engines do.

There are several "auxiliary" brake systems out there, including: transmission retarders, auxiliary drive shaft dynamic systems such as Telma, exhaust brakes (like a valve in the exhaust pipe), and what we know as Jake brakes. Because of our drive train layout (at least on the 05,10,15), we can only take advantage of the transmission retarder and Jake brake options. Some of our buses came with transmission retarders (my bus had a Voith transmission with a retarder). I never did get to drive mine much with that transmission. Folks who have them say they do a good job, but the heat buildup only allows short application periods.

By far, the best aux. brake system for our Eagles is the Jake system. When set properly, it does a pretty darn good job. Some say they are not as effective on two stroke engines - I don't have experience with that combination. On my Series 60 with the 10 speed and Jakes, there is hardly ever a situation where I have to do anything beyond a quick stab of the brakes on very steep roads.

Do we need them? Again, lots of folks point out that trucks and buses drove all over the US without them years ago. That said, I would not drive my bus in our area (steep mountains) without my Jakes. Indeed, I have driven all over the country and encountered some downgrades that would have been downright scary without the Jakes.

Jim
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'85 Eagle 10 with Series 60 & Eaton AutoShift 10 speed transmission - not at all fancy, but fully functional
Bus Project pages: http://beltguy.com/Bus_Project/busproject.htm
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