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Message |
Lee Dove (148.78.255.44)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Saturday, September 15, 2001 - 1:32 pm: | |
I have a 1973 MC7 with an 8V71 DD. I know they are called 318 hp.
Is this with a 871 blower/supercharger? Or without the blower?
If this is without the blower, What is the HP rating with the blower? Thanks |
RJ Long (66.74.169.186)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Saturday, September 15, 2001 - 3:17 pm: | |
Lee -
A quick lesson on Detroit Diesel engines:
All 53, 71 and 92 series Detroits are two-cycle engines, and all require the stock Rootes-type blower in order to run properly. This blower is designed to blow 25% more air thru the cylinders than they are capable of holding (at sea level), this provides good exhaust gas scavaging and some cooling effect. They will run without this blower, but not very well.
This blower is different than a turbocharger, as it is gear-driven, whereas a turbo is exhaust gas driven.
The nomenclature tells you what type of engine it is, for example, a 6V92TA:
6 = Six cylinders
V = "V" style block, as opposed to an inline.
92 = # of cubic inches per cylinder
T = Turbocharged
A = Aftercooled
Most 8V71s used in the bus industry came from the factory with somewhat conservative HP output. The two most common setups were with N55 injectors, yeilding about 250 hp, or about 275 hp with N60 injectors. Both using "standard" camshaft timing.
The next HP jump required the camshaft timing to be changed from standard to advanced (or "A-timed", as it was/is commonly called). This requires tearing down the bell-housing end of the engine, making the change, then reinstalling - a lot of work that most bus companies won't do, unless it's overhaul time. The injectors are also changed to N65s. This configuration yeilds about 305 hp. It also increases the amount of black smoke visible out the exhaust, and lowers the fuel economy. . .
There seems to be some "mystery" about where the "318 Detroit" came from. It is originally a trucking industry term, so it probably came from somebody who pulled the N65s out and popped in a set of N70s, then ran the truck on a dyno and came up with that figure.
N70s in an 8V71 will not make friends with your neighbors - and will get all the environmental wackos after you, too!
Except:
The 8V71TA uses N70 injectors, standard timing and a turbocharger to boost the HP to 370. But until the boost from the turbo comes in, you'll still leave a smokescreen with anything more than a very gentle initial throttle.
The way the turbo is plumbed on these engines is rather simple. The regular blower handles operations from idle up to about 1000 rpm or so. Above that, a by-pass valve opens, and the turbo provides the boost that the engine needs.
You can't just throw a turbo on top of your stock 8V71, however. There are several internal engine changes that must be made, as well as sizing the turbo correctly.
You might want to climb into your MC-7's engine compartment, pull one of the valve covers and check the injectors to see what size you've got. Looking at the injector, you'll find a colored tag with a number on the side.
Hope this helps, or have I "corn-fuzzled" you??
RJ
PD4106-2784
The Giant Greenbrier
Fresno CA |
Mallie (208.165.105.109)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Sunday, September 16, 2001 - 12:02 pm: | |
Hello Lee: I think RJ pretty well answered you question. I will add a couple of thing.
The 318 is the Maximum rated HP of the engine with advanced timing/ 65 injector, @ 2100. Detroit has two ways of measuring HP. One is the Max Rated, measured at 60F and (29.92 in Hg) Sea Level, and the SAE, which is measured at 85F and (29.00Hg) 500Ft Elev. The SAE is the standards by which the HP is federally certified. It is also the HP you will find in DD Tune up manuals. Almost all of the HP ratings for the 71 & 92 are given at 2100RPMs.
The 8v71 max rating under SAE condition is 304.
You can turbo an 8v71 and get 370 SAE HP @2100 with N75 Injectors. The pistons must be changed to lower compression from 18.7:1 to 17:1, The liners changed from 1.05 port height to .95, and the blower ratio changed from 2.05:1 to 1.95:1.
The blower seals have to be changed too. An oil port would have to be drilled and taped for the Turbo supply oil. And if you want to get the last 20 Hp, you will have to install an after cooler, if your block is designed to accept one. And of course install the Turbo, and the connecting exhaust and intake pipe.
You will find a few turboed 71s in buses, not many are original.
As RJ said, the engine may technically run, but will not function with out the roots blower.
Mallie |
Lee Dove (148.78.255.45)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Sunday, September 16, 2001 - 1:37 pm: | |
Thanks for the lessons.......
Still green to this bus thing but, learning. |
Tom Caffrey (Pvcces) (12.146.32.12)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Saturday, October 06, 2001 - 12:28 am: | |
These engines, when in trucks in the last 30 years were referred to as 318 Detroits, and they used 70 injectors. The bus companies seemed to be very concious of smoke, and they used a number of ways to make it less obvious. The 60 injectors and the hybrid governor made it easy to run them with four speeds without overlap and the exhaust is restricted enough to accelerate in the tailpipe. It is then discharged at high speed and at an angle to the direction of travel. Very effective dispersion.
I can't help believing they were trying to make it less conspicuous if there was any visible smoke.
Tom Caffrey PD4106-2576 |
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