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TOPICS => THE BOARD => Topic started by: billmoocow on June 30, 2012, 11:17:37 PM
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Trying to figure out how much the 8v71 uses at high idle? :o I have not had a chance to work my advanced technology stick to dip in tank.
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At a 1000 rpm and a average 145 hp on high idle .482 lbs x 145= 69.89 divide by 8 the weight per gal of diesel = 8.74 gals per hr and that should be pretty close for a 8v71N/A with 60 or 65 injectors same engine @ 296 hp at 2000 rpm will be 15 gals per hour @ .403 usage hope this helps
good luck
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Oh boy. That looked like Greek to me. :o Fuel here is $3.70 gal X 15 in an hour? Not that i would sit there and idle for that long but i do occasionally go out and rev the @^#T@@ out of it for about twenty minutes.
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Oh boy. That looked like Greek to me. :o Fuel here is $3.70 gal X 15 in an hour? Not that i would sit there and idle for that long but i do occasionally go out and rev the @^#T@@ out of it for about twenty minutes.
Bill -
Far better to drive the coach (i.e. put the engine under load) than to go out and rev the @^#T@@ out of it for about twenty minutes.
A half-hour to an hour drive does wonders for all involved. ;D
FWIW & HTH. . .
;)
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Any engines fuel use depends on the LOAD the engine is under.
High idle , not humping the ancient air cond (40-80 hp), is almost zero load .
A smart marine 3 or 4 stage regulator working with your alt is also minor.
Figure 1 GPH per hour of idleing .
However idleing is not good for your engine , tho it may be required for a couple of min to air up , it should never be used instead of a road run.
100mi , 2 hours every month, will keep your engine , and all the rest of the systems happy , and help not loose your road skills.
FF
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A gal of fuel a hr at 900 to 1000 rpm with a 8v71 dream on the cooling fan,alternator and air compressor take close to 50 hp alone
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I have no idea where Clifford came up with 15 gallons an hour at 2000 RPM to just idle. Perhaps he meant 1.5 gallons. It would usually take less than 15 gallons to drive an hour at 60 MPH! 2000 RPM seems like an awfully fast idle RPM to me.
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Fred, you are right about i should not let it idle but need to air up once in a while to move bus. Still got crap all over the place in there and need to tidy up before i take it on a good run. The factory air has been taken out so no load there. Was just trying to get an idea of what the fuel consumption was whenever i did have it on high idle. Actually higher than high idle since i hold my foot on gas pedal. The high idle solenoid needs to be replaced so my foot is the high idle LOL. Luvrbus, thanks for the math.
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I get it straight from the DD fuel chart I wasn't talking about idle at 2000 rpm but producing 296 hp at 2000 rpm it is in the manual in black and white if the 8v71 was in a boat producing 296 hp could you cover 60 miles in a hr ? and fast idle on a stroke is 900 to 1000 rpm some go as high as 1200 rpm where your series 60 are usually set at 750 rpm
When I test run the 8V71 series and 8v92 a 1.5 gals won't hardly prime one lol
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I have yet to see a graph from Detroit that takes into consideration the load at any given RPM other than at full load. This makes it very hard to figure out how to set them up for best fuel economy. I do agree that Detroit does provide fuel curves, just not for partial loads.
That has led me to try to figure fuel use by experimenting. I've had a few successes, but it's time consuming.
Tom Caffrey PD4106-2576
Suncatcher
Ketchikan, Alaska
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A simple rule of thumb is operating at 60% power or above a 2 stroke DD will create 16 HP for each gallon of fuel burned.
Spinning an engine is cheap with no external loads (an alt will take few HP for 50-100A@12v ) AND MANY FANS ARE oil temp thermostated , so will not even come on at idle.
Go on one of the truckers boards , there may still be enough old folks that will remember ideling all night , to assure you of the burn.
Yes it waisted fuel, and caused the early death of the engine , but for most it was the companies truck, so "what me worry?".
FF
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Tom it is done by hp and rpm the engine produces hp at any speed loaded or unloaded the next time you stop by I will give you a copy of the chart they use for marine and industrial engines
A simple test use a 1 gal jug turn the 8v71 at 1000 rpm and see how long it last it won't be anywhere close to a hr or find someone with a DDEC 6v92 and DD software it will tell you no guessing there and FF the fan on a MCI turns all the time it takes hp
good luck
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Others can chime in on the physics involved, but those of us with functioning shutters and damper doors enjoy a reduced fan load when the cooling fans are choked off when engine temps are cool enough.
Removed, the fan consumes HP all the time.
happy coaching!
buswarrior
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BW, I can picture the fans trying to suck air against the closed shutters like a vacuum cleaner working harder with the curtain stuck in the nozzle. Would those squirrel cages work harder, or are they just spinning air without strain? Has the HP draw of those rad fans with shutters open and closed actually been measured? Just curious.
JC
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This could get interesting! ;D
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acually - fans with curtains stuck to them - work less / use less power
that's why they speed up a little
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A simple test use a 1 gal jug turn the 8v71 at 1000 rpm and see how long it last it won't be anywhere close to a hr .
Wont work!
It would require 2 jugs as a DD will pull loads of fuel from the tank and return most of it depending on load.
At idle , or 1000RPM the actual fuel BURN , will be about 1 gph.
There hard to come by but most engine MFG will have a NMEP chart , or fuel map .
These look like a kids drawing of a cloud , one outside the next.
The inner circle is the lowest fuel area , HP /load at a RPM.
Any loading inside that area is optimum.
For MFG folks designing a gen set or pump these values are key .
For boaters they show where long range cruise should be done for best efficiency.
For bus campers they are fun , but useless as a builder can select a Gen head size , or a boat tranny prop combo, but we can not select the size hill or headwind.
FF
FF
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Lost and Pete are on the way...
Ok, I'll try to replicate the explanations of the long gone masters...
A vacuum cleaner is just a fan sucking air up the hose. For the purposes of this simple explanation, the same as our cooling fans on the engine.
If your vacuum cleaner was straining when you plug the nozzle, which we might think of as more work to do, and with their small electric motors and simple on/off controls, if it was loaded, wouldn't we expect the motor to slow down... ?
But, the scream we hear is the motor speeding up, which indicates the physics at play, there is less load on the vacuum cleaner when you plug the hose.
It gets hot under these conditions because of a lack of air flow to cool it, not because it is straining.
It has to do with the air pressure at the fan blades dropping. Thinner air, less resistance for the fan to spin, less work for the driving force turning the fan.
The shutters and dampers on an MCI do the same as plugging the intake on the vacuum, the air pressure in the fan enclosure drops, by way of thew fan chopping away in there and not having sufficient make up air passing into the fan enclosure, and the fans are able to spin in there more easily, using less engine power to turn them.
Pretty neat idea from a time before the compact fan clutches were available, to just stop the fan from turning when it isn't needed.
I can't remember what the physics terms involved are called, but there you go.
happy coaching!
buswarrior
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I love it when someone explains something like a great teacher. Good job warrior!
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I have been told that running at high idle for a few minutes to allow engine to cool after a road run is a good idea before shutting off...
comments invited ???
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I have been told that running at high idle for a few minutes to allow engine to cool after a road run is a good idea before shutting off...
comments invited ???
Hound -
Generally speaking, by the time you come off the freeway and meander around town or rural area to where you're going to park for the night, the engine's cooled down to a fast idle temp. Even if you just go a couple of blocks to the truck stop to get fuel, the temps come down quite quickly.
Is it worth it? Your engine, your fuel, you decide.
BTW, your fast idle should be tied into the "Johnson bar" handbrake: If the fast idle switch is on, and handbrake is on, fast idle should work. Fast idle switch on, handbrake off = no fast idle. If your handbrake has been disabled/removed because somebody installed spring brakes, then whoever did the conversion should have also integrated FI into the spring brake button.
FWIW & HTH. . .
;)
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"I have been told that running at high idle for a few minutes to allow engine to cool after a road run is a good idea before shutting off..."
IF needed at all it will mostly be a turboed engine that can use a min or two to cool.
Driving in a campground at 5mph , after checking in , is far more cooling than even a turbo would require.
Drive to the Top of Rockey Top , at 35psi boost , then pull into the view area , a bit of cooling would keep the oil in the turbo from cokeing.
FF
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Actually it is pretty easy to explain, and it is the reason bus and truck builders put shutters on sideways radiators. Shutters need to be on front radiators to reduce forced airflow on cold days. Shutters are put on sideways radiators for greater fuel economy.
A fan takes LESS horsepower to run in LESS DENSE air, so when a fan has emptied the the fan shroud of of the ambient pressured air, it runs much easier in thin air.
You hear a vacuum cleaner speed up when you block the suction hose, not because it is "trying harder," but because the motor speeds up because there is less load on the fan. This can be easily proven with a clamp-on ammeter. Get one wire separate from the two wires in the cord somehow, and read the amperage with a nice new filter and no hose. When you connect the hose, the amp draw will go down slightly, and when you block the hose completely, the motor will speed way up, and the amps will go down by at least a third.
I wrote this before I got into the topic summary, and its already there, and BW is right.
G