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Old 01-16-2018, 02:59 PM   #1
Mini-Skoolie
 
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Engine spec ratings... comparing apples to apples

There are several engine manufactures that are used in these buses. Each engine has its own HP and torque ratings. So to compare "apples to apples", would it be wise to compare hp ratings not just then engine itself in raw form? For example, engine A is a 5.9L 250hp, engine B is a 7.3L 200hp (numbers are for example only).Would the larger HP be a better choice, all other things being considered equal? The heart of this question is it better to look at HP ratings for each bus engine or displacement?
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Old 01-16-2018, 03:24 PM   #2
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A thing to remember is that horsepower is a math function of multiplying torque and rpm and dividing by a constant (5252). Torque is the actual amount of force the engine can produce. With this said, horsepower numbers for engines that don't turn high rpm can seem really low, even though you may have gobs and gobs of torque.

A lot of these engines are limited to 2500-ish rpm. Engines that have a medium duty truck version in adition to a passenger vehicle version, you will see that the passenger vehicle version can rev much higher, and as such has a much higher horsepower rating. As an example, the lowest rated T444E (175hp) had a maximum torque of 460 (at 1400rpm) and a 2600rpm redline. The Ford version (Powerstroke 7.3) includes a model making 450 lb/ft of torque with a rating of 220hp (at 3000rpm). Which is the engine you would want for your bus? Horsepower rating only tells part of the story.

It isn't hard to find a low tuned T444E, or a high tuned 5.9 Cummins. Unlike cars, the higher horsepower versions weren't sold as luxury upgrades, they're means to an end... But there are big differences between them, the CUmmins is a 359 cubic inch inline 6, the T444E is a 444 cubic inch V8. They ultimately play in the same playground, and the bigger brothers (T466E, cummins 8.3) are the next step up in performance.

Clear as mud?
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Old 01-16-2018, 03:30 PM   #3
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Clear as mud?
This made me laugh because it is so true.

So really ,if comparing specs ,then HP "could" be tossed out while looking at torque specs alone?
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Old 01-16-2018, 03:34 PM   #4
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Yeah and no. If you're looking at it from strictly a hp perspective then yes, engine A would be better. However, you also have to look at it from torque standpoint, RPM operating range , maintenance costs, commonality of parts, and age/wear on the engine.

Case in point is that there could be a huge difference between two competing engines that both have the same HP. An example of that coming from Cummins is the ISX385 and ISB6.7. Both are available with 385 hp, however the ISX delivers 1450 lbft of torque while the ISB gives 900. Huge difference there that hp rating alone won't tell.

It's not as simple as saying cummins is the best bar none, or the higher hp engine is always better. But sadly, that's what a lot of people want to hear and numerous people will say something to that effect.

Each engine has to be looked at on a case by case basis. Much in the same way a bus has to be compared.
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Old 01-16-2018, 03:46 PM   #5
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Quote:
Originally Posted by kenfoozed View Post
This made me laugh because it is so true.

So really ,if comparing specs ,then HP "could" be tossed out while looking at torque specs alone?
Even with that in mind, transmission type, number of gears, final drive ratio, and ecm programming mean just as much if not more. You need to know all the pieces to make an informed decision.

Example: ECCB got a short bus with a DT466 and a 6 speed transmission, and it's electronically limited to 55mph. I have a much less powerful T444E and a 4 speed transmission and my limiter is set at 65mph. Not knowing the whole picture, you wouldn't expect me to win any races.
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Old 01-16-2018, 03:53 PM   #6
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Originally Posted by brokedown View Post
Even with that in mind, transmission type, number of gears, final drive ratio, and ecm programming mean just as much if not more. You need to know all the pieces to make an informed decision.

Example: ECCB got a short bus with a DT466 and a 6 speed transmission, and it's electronically limited to 55mph. I have a much less powerful T444E and a 4 speed transmission and my limiter is set at 65mph. Not knowing the whole picture, you wouldn't expect me to win any races.
As an example of flexibility ...

I have a Cummins 8.3-250 hp, MD3060 trans and 5.38 Final drive. Engine is governed to 2200 rpm.

My current top speed is 67 mph @ 2200 rpm.

There are a bunch of ways I can change this.

1. Get Allison to unlock 6th
2. Change the governor springs, or shim the springs to give more rpm
3. Change the FD ratio

If I want more power, which would also improve fuel economy:

1. Slide fuel plate forwards
2. Advance timing
3. Change fuel plate
Change injectors and/or turbo and increase fueling.

I can probably release another 50 hp just by sliding the fuel plate forwards and advancing the timing.

Engine can go to 3400 rpm without changing valve springs. 3000 rpm with current set up would give a top speed of 88 mph.

The extra 50 hp would cause no trouble, the same engine leaves the factory with 300 hp when destined for RVs.

There are a myriad of possibilities
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Old 01-16-2018, 05:36 PM   #7
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I can probably release another 50 hp just by sliding the fuel plate forwards and advancing the timing.
Can't wait to see you roll coal. I've done it with my 6CTA's and is a hoot.

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Old 01-16-2018, 05:44 PM   #8
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Quote:
Originally Posted by kenfoozed View Post
This made me laugh because it is so true.

So really ,if comparing specs ,then HP "could" be tossed out while looking at torque specs alone?
I'm more worried about what transmission a bus has than how much HP.
That said, having high hp is nice.
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Old 01-16-2018, 05:48 PM   #9
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Even with that in mind, transmission type, number of gears, final drive ratio, and ecm programming mean just as much if not more. You need to know all the pieces to make an informed decision.

Example: ECCB got a short bus with a DT466 and a 6 speed transmission, and it's electronically limited to 55mph. I have a much less powerful T444E and a 4 speed transmission and my limiter is set at 65mph. Not knowing the whole picture, you wouldn't expect me to win any races.
I got a 5 speed auto with lockup and OD.
As soon as Chris comes over and raises my top speed my bus will be pretty darn fast for a school bus.
My last shorty weighed more and only had a 175hp 444e and allison 545 and I got it up to 75 a few times. The 4.10 rear end made that possible.
With 10R's on my bus and the computer limit raised, my bus would be capable of 80+.
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Old 01-16-2018, 05:51 PM   #10
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I got a 5 speed auto with lockup and OD.
As soon as Chris comes over and raises my top speed my bus will be pretty darn fast for a school bus.
My last shorty weighed more and only had a 175hp 444e and allison 545 and I got it up to 75 a few times. The 4.10 rear end made that possible.
With 10R's on my bus and the computer limit raised, my bus would be capable of 80+.
I thought your transmission was a 6 speed with 6th gear disabled?

Wouldn't take much to get your bus rolling faster down the highway than mine, I"m just pointing out that horsepower ratings only tell part of the story!
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