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Old 02-15-2021, 03:10 PM   #1
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6 cylinder or 8 cylinder?

Hi there, I am looking to buy my bus and convert. I currently live in a 40 ft D444T 8 cylinder international. I am having a hard time finding buses for sale with 8 cylinders. Most I find have 6. More cylinders = more power right ?

Iím concerned that if I get a full sized (40 ft) 6 cylinder bus Iíll have issues driving mountainous terrain, ie not enough power.

What are your thoughts on this? Anyone built out a 40 footer with 6 cylinders and have experience driving around in the west ? Help please !
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Old 02-15-2021, 03:20 PM   #2
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Cylinders dont equal power my 1999 ford f350 with a t444 8 cylinder engine makes 250 horsepower and 525 lb/ft of torque. My 2016 6 cylinder ram 3500 with the cummins makes 385 horsepower and 935 ft/lbs of torque.
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Old 02-15-2021, 04:13 PM   #3
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6 cylinder motors generally produce more torque. Torque is your friend. horse-power is (very simply put, but in reality a bit more complicated) torque ◊ engine speed. In other words, HP can be deceiving.


A motor that can deliver higher torque at a lower engine speed will pull from a start up a hill without having to rev the motor and stress the tranny.
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Old 02-15-2021, 05:01 PM   #4
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Be concerned...A 40ft school bus is freekin heavy and none of them go fast no matter what engine it has, not meant to, not to say it can't go 100 mph going downhill, but not a chance uphill, more like 10mph. Without enough torque, it will go 0mph uphill.
Don't get one if speed/acceleration is your desire.
Get a smaller lighter vehicle.
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Old 02-15-2021, 06:03 PM   #5
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So the DT466 , do you know much about the torque ? I’m not looking for anything fancy, I just want to get uphill at a low speed that doesn’t stress the engine too much.
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Old 02-15-2021, 06:16 PM   #6
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Mine is 30,000 pounds plus the weight of the toad on the rear. I don't go to California. Came from there, not going back. We do have hills here in NM. Up hills I am in the slow lane with the trucks. Mine is 250 hp 8.3 with about 800 ft lbs. Power to weight ratio I am about the same as a large 80,000 pound truck. If I had 100 more hp and the torque to go with it I might be able to pass them if I had enough passing lane. No you won't go fast. You should be more concerned with coming down the hills safely. Learn to live in the slow lane or buy something smaller.
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Old 02-15-2021, 06:27 PM   #7
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Our MCI MC-7 is a big, heavy old Greyhound coach bus...bigger and heavier than almost any school bus. And she's now got a 6-cylinder diesel to replace the 8-cylinder one she had before, with the result that she drives much better now.

Heck, two of our buses have 4-cylinder engines! And they're a pleasure to drive.

So...no...more cylinders don't necessarily mean more power or better drivability.
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Old 02-15-2021, 07:39 PM   #8
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I like the t444 because of cheap parts and good aftermarket support.
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Old 02-15-2021, 11:39 PM   #9
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The I6 configuration will always have more torque than a V8 of the same displacement at lower RPM. The larger area of the I6 piston will produce more force than the smaller area of a V8 piston. V8s often have a higher hp rating as they can spin at a higher max RPM than an I6 due to the lower reciprating mass of the smaller pistons.

There is no replacement for displacement.

Ted
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Old 02-15-2021, 11:58 PM   #10
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HP = speed, it's for cruising.
Torque = push up hills, pull loads

6 & 8 cylinders each have their pros and cons.

More importantly, IMHO, is gearing ratio and number of gears.

I'd rather have a 6 gear, 5 at least, tranny with lower HP and torque than a high HP and high torque with 4 gears. Why, because guess who has 230hp, 620ftlbs of torque but only 4 gears?

Plus, my tranny is mechanical, and while it locks up in 3rd and 4th for 1:1 for cruising, it has difficulty downshifting in a timely manner, causing me to loose my power range when climbing. In addition, I had to change out the differential to lower my RPMs from 2400 to 2050 at 60mph. So, now, my gearing is even more challenged.

Yes, you need HP to push those higher gears and speeds, and you need that torque to push/pull, but when your gears are far apart, even high torque won't keep you from downshifting.

Plus, the tighter your gears, the less your entire drive train has to work.

If I were to buy again, I'd:
Look for a 6 speed
Probably front engine (it's a long way from the RE and the dash for running gauges, heater hoses, etc.)
Assure it can already cruise at 65 at about 2k rpm
Has cruise control

Love my bus, yet we all have a wish list for the next time around.
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Old 02-16-2021, 02:05 AM   #11
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Quote:
Originally Posted by TJones View Post
The I6 configuration will always have more torque than a V8 of the same displacement at lower RPM. The larger area of the I6 piston will produce more force than the smaller area of a V8 piston. V8s often have a higher hp rating as they can spin at a higher max RPM than an I6 due to the lower reciprating mass of the smaller pistons.

There is no replacement for displacement.

Ted
Except that v8ís are winning the torque wars between the big 3 right now. Itís not lower reciprocating mass In the pistons and the rods that limits inline engines, the engines that rev the highest in common circulation are exclusively inline 4 cylinders in motorcycles. Were talking 14k+ rpm.

Motorcycles make their power with revs, there is a reason why the big power motorcycles are all inline engines.

The problem with big inline six cylinder diesels is the massive crankshaft that is needed to take the strain of the diesel combustion process over a really long crank that is often less supported than V8 cranks.

Per 4 cycle combustion process Each cylinder is responsible for 90 degrees of crank throw where as in a 6 cylinder engine it is responsible for 120 degrees.
This means the crank is taking quite a pounding in an inline six so the cranks are massively built.

People often look at engine internals of inline sixes and view those engines are more durable because of their massive size. The truth is that they need to be overbuilt or they wont last.

Big inline 6 diesels are dinosaurs and though I love them they simply produce less torque and a lot less horsepower than their V engine counterparts these days. They rev up and redline slower giving you slower access to the power they do have and the crazy pressures that you have to achieve to overcome that batter them. Diesel technology has seemingly left the big sixes behind. For now...
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Old 02-16-2021, 08:16 AM   #12
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Quote:
Originally Posted by TJones View Post
The I6 configuration will always have more torque than a V8 of the same displacement at lower RPM. The larger area of the I6 piston will produce more force than the smaller area of a V8 piston. V8s often have a higher hp rating as they can spin at a higher max RPM than an I6 due to the lower reciprating mass of the smaller pistons.

There is no replacement for displacement.

Ted
Couldn't have said it better myself.

Read the last bit a few more times if you're at all confused as to how to get a bus around in a mountainous area.
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Old 02-16-2021, 08:35 AM   #13
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Power (kW) = Torque (N.m) x Speed (RPM) / 9.5488









By the above formula's ( wiki).. for moving weight up the hill torque is not interesting. Only power is.. Gears do the rest. I know science is annoying but it is what it is.



The V8 can in general run faster and as a result can develop more HP. The shorter crankshaft and less torque fluctuation make it a better setup. You just need gears to get to the torque. The V8 has more moving parts so more energy is lost in friction.



Nice proof of torque versus HP is the gas turbine in military tanks.. Lots of rpm and lots of gearing.




Johan
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Old 02-16-2021, 09:08 AM   #14
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Except that v8ís are winning the torque wars between the big 3 right now. Itís not lower reciprocating mass In the pistons and the rods that limits inline engines, the engines that rev the highest in common circulation are exclusively inline 4 cylinders in motorcycles. Were talking 14k+ rpm.

Motorcycles make their power with revs, there is a reason why the big power motorcycles are all inline engines.

The problem with big inline six cylinder diesels is the massive crankshaft that is needed to take the strain of the diesel combustion process over a really long crank that is often less supported than V8 cranks.

Per 4 cycle combustion process Each cylinder is responsible for 90 degrees of crank throw where as in a 6 cylinder engine it is responsible for 120 degrees.
This means the crank is taking quite a pounding in an inline six so the cranks are massively built.

People often look at engine internals of inline sixes and view those engines are more durable because of their massive size. The truth is that they need to be overbuilt or they wont last.

Big inline 6 diesels are dinosaurs and though I love them they simply produce less torque and a lot less horsepower than their V engine counterparts these days. They rev up and redline slower giving you slower access to the power they do have and the crazy pressures that you have to achieve to overcome that batter them. Diesel technology has seemingly left the big sixes behind. For now...

In the light truck market the v6 and v8 make sense with the faster reving, higher red line and higher advertised hp offering more car like performance. Keeping in mind the higher rpm and horse power ratings equate to a shorter service life. That is why many engines that see service in both the light duty and medium duty market have max rpm and horse power derated for medium duty use.


Is there a commonly produced class 8 truck engine that is not an I6 configuration?

Ted
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Old 02-16-2021, 09:43 AM   #15
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Yes, in europe and australia. Built by Scania.

Not sure why they haven't caught on or aren't sold here.
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Old 02-16-2021, 11:52 AM   #16
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Yes, in europe and australia. Built by Scania.

Not sure why they haven't caught on or aren't sold here.
That is a rockin motor.
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Old 02-16-2021, 12:01 PM   #17
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Is there a commonly produced class 8 truck engine that is not an I6 configuration?

Ted[/QUOTE]

Is there a class 8 engine that makes Anywhere near the torque and horsepower per cubic inch of a medium duty diesel v8?
So power isn't their only consideration. Power is what we were discussing in this thread. There is no replacement for displacement but people think that means means bigger motors are more powerful but they aren’t. an internal combustion engine is a hell of a lot less efficient of an air pump than a turbocharger. 2 litre small diesels running 35-40 pounds of boost are putting down numbers that kick the snot out of my 7.3 powerstroke. The reason why there aren’t more v8’s is that american class 8 diesel engine manufacturers are stuck in the stone age because nostalgic customers want big in efficient inline sixes with perceived lower maintenance costs and more perceived torque.
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Old 02-16-2021, 03:18 PM   #18
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That scania beats the hell out of the dd16 and the x15 by at least 25% in torque.
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Old 02-16-2021, 03:22 PM   #19
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https://demanddetroit.com/engines/dd16/
https://www.scania.com/content/dam/s...686A_566kW.pdf
https://www.cummins.com/engines/x15-...ce-series-2021

Ouch inline 6...
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Old 02-16-2021, 04:08 PM   #20
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DD 16 - 15.6 L - 600 HP - 2050 lb ft
X15 - 14.9 L 675 HP 2050 lb ft
Scania DC16 16.4 L - 770 HP - 2347 lb ft

No replacement for displacement. Of more interest look at the torque curves in the links I posted. The I6s much flatter than the v8.

The V8 would lend itself to the cab over being the engine is probly shorter.

Ted

https://demanddetroit.com/engines/dd16/

https://mart.cummins.com/imagelibrar...es/0042772.pdf

https://www.scania.com/content/dam/s..._566kW_SCR.pdf
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