I'm going to replace the four speed spicer with an Allison MT644 this month. While I have the 871 out of the MC-5 I'm wondering if I should put bigger injectors in it to compensate for any power loss through the automatic transmission? (I don't remember but I think it has N65 and whatever they are I seem to recall deciding that it should be putting out about 290 HP.
My 871 is still in pretty good shape; no smoke; average oil consumption.
Fred
Fred -
"If it ain't broke, don't fix it!"
Even the way it's set up now, the coach is going to feel faster with the automatic.
That being said, N65s are about as big as you can go w/o creating a smokescreen.
OTOH, adding a turbocharger will "wake up" the 8V, especially at altitude.
Then you'd have to figure out a way to keep it cool, in addition to the transmission's heat load.
Isn't hod rodding fun?
FWIW & HTH. . .
;)
Leave it be until you drive it again. With the automatic, it will be faster. Maybe a bit slower on the hills though. 290hp sounds like N60 injectors-which have the torque rated at 1,200rpm-which is much better for the automatic. You've got to remember the MT644 has a limit of 300hp and 850lb/ft torque (if I remember correctly). Turbocharging but keeping the same injectors will assure you that no power loss will occur at altitude. Good Luck, TomC
I have N60's in my 8v71 and go as fast as i want on flat or slightly sloping ground. Going up hills/passes a lot of times i am in 2nd or even 1st gear.....but unless it is really hot out i don't have a problem with overheating.
Hi Fred, I have an MC9 with an 8v71 with N65 injectors, Advanced timing and an Allison HT740 and seem to have enough power for me. I have NO smoke. I only have about 10,000 miles on an inframe rebuild and seem to be gaining power as I get more miles on it.
As has been said, if it aint broke don`t mess with it!
FWIW I had some Detroit Diesel graphs that showed that while the 8V-71 with N60's and standard cam timing had a torque peak at 1200 rpm, the 8V-71 with N65's and advanced timing had more torque at 1200 rpm even though it kept going and peaked at 1600 rpm. Not much more, but more. No reason to think an engine with N60's is better matched. Also, an engine only develops peak torque when it's at full power at that RPM and not accelerating. In other words, load perfectly balances power. If you are at full power at 1600 rpm and not able to accelerate, as would be the case on a hill, you can downshift to a lower gear to raise the rpm which both reduces the torque through the transmission and increases the power available from the engine. It's power that does work, so your performance on the hill will be improved.
Brian
The 8v71 N/A fire truck engine was the only true 318 hp it used N 70 injectors on the low calibration setting peak torque was 1400 rpm I like 1400 better than 1200 rpm myself
Now most of the injector re builders set all the N injectors on the high calibration and let you worry about the smoke
Long ago and far away. The pretty city of Bakersfield California. 350 hp at 2300 RPM and 900 torque at 1400 RPM. Fire service ratings. The problem was that if the Engineer, (apparatus operator) applied too much foot at too low of RPM, the set up resulted in literally clouds of black smoke. Usually Fuller T905M straight five speeds. As early as around 1974, "the shops" set the Detroits back with, I believe, N65 injectors, but kept the 2500 RPM full load governor setting.
This fixed the black smoke for the most part, but we still had to learn to keep our foot out of it until we had built up some RPM. The apparatus was considered fast for the era of time, but all of the modern stuff with the big DD Series 60 500hp rigs would literally runs circles around the old stuff. The old stuff had a whopping 50 mph road speed at 2100, thus the high governor settings. The new stuff will go 90+. Long ago and far away. They sounded so cool also. HB of CJ (old coot) :)
Tom,
Now that you say that, I'm sure it has N60s. I know I determined it must be about 290 HP when we ran the rack. I just forgot to write down which injectors it has.
I just figured when the engine is out of the bus, that's the time to put injectors in because it's easy.
Can I have them tested to be sure they are all working to spec? It sort of lumbers to a start whenever I start it and it seems like its either got a weak cylinder (or two) or a misfiring injector (or a few?)
If the engine has not been overhauled recently, then installing new rings, bearings, having the blower rebuilt, having new injector tips installed, and checking the heads for cracks is a good time to do it. You'll like the freshened up engine. Good Luck, TomC
Have played with the injector timing on many 71 & 92 series, yes have burnt pistons with too much advance etc, however did wind up with a great in between setting with 70 series injectors that did not burn piston/rings and did not smoke, seem to recall 1.754 with advanced setting on 71 series. That was years ago and may be bad memory. seem to recall the 1.460 advanced with the 70 injector did burn the piston & top ring. Hell memory recall seems to be escaping me, but did have a lot of fun playing the V71 games.
Dave M