Series 60 HP

[JIM CHALOUPKA]

I have seen adds for busses with DD engines and claimed HP 475, 500, and 515.
475 seems ro be early version.
500 most others.
515 occasionally.
Where is the increase derived? Is it in the computer program, or what?
JIM

[Ray Davis]

The horsepower can be changed somewhat without hardware change by computer programming the DDEC. My bus was originally a 475, and the previous owner had it changed to 500.

I had a good friend who is a DD specialist, and at his suggestion, I put it back down to 450. His suggestion was that it would run cooler, last longer, get better mileage, and hopefully not notice any effect of lost horsepower.

So far I'm leaving it that way. I outran a couple of other coaches going up the El Cajon pass last POG trip.

But, point being within some margin the horsepower can be changed. beyond that they said that you'd need changes in injectors and/or other motor changes.

[Jon Wehrenberg]

Anyone can increase their HP. But the problem that is encountered after spending the bucks to get the increase is that you do not get to use your new HP.

For the brief period before the engine starts to get hot the HP is available to use. But to produce HP your engine also generates a lot of heat. Before Prevost can install DD engines with more HP they must also install cooling systems capable of getting rid of that extra heat and the installation must be approved or certified by DD.

Unless you have increased the cooling capacity the DDEC will allow whatever HP has been programmed, until the cooling system is incapable of keeping the temperature below a certain point. Then the DDEC will start cutting back on the HP available until the coolant temperature drops to within acceptable limits.

When Ray goes up a long hill fast, it is because the engine HP output is not overwhelming his cooling system so his DDEC is allowing him to have all the power available. Someone else with 500 HP, but 470 HP of cooling capacity will start losing power, and that reduction in power may be below what Ray has available to him.

[Ray Davis]

Someone else with 500 HP, but 470 HP of cooling capacity will start losing power, and that reduction in power may be below what Ray has available to him.

And here I thought I had this super strong, killer 8v92 engine!!!

[matsprt]

Ray,

I think Jon is funnin with you somewhat. It's a whole lot more complicated that what he wrote....

Michael

And here I thought I had this super strong, killer 8v92 engine!!!

[JIM CHALOUPKA]

Thanks Jon & Ray, that's very interesting.

When I typed that I thought about Bob & Ray, but I won't go there.

Jon, a little more on the topic. Do you think the busses with 515HP have a better cooling system if it comes from Prevost with that rating or is this HP thing sales hype?

[Jon Wehrenberg]

If the HP was delivered by Prevost the cooling system is designed for it.

At one of the early Prevost seminars they explained in great detail about what hoops they must jump through to install a DD engine. Detroit has to stand behind the engines so they must certify or approve the installation and it is a very comprehensive engineering task to get to that point.

Our engines generate a lot of heat and that heat must be removed. The engines are very sensitive to heat to the extent that certain of the DDEC faults will bring about a shut down such as the low coolant sensor. The Detroit position on this is that if a hose fails and the coolant drops for example, the engine could be destroyed very quickly as a result of the loss of coolant. So even if the engine temperatures are well within the acceptable range DDEC is set up so that the engine is shut down before that low coolant level can result in an overheated engine.

I don't know the specifics as to temperature or percent of power removed, but if the engine coolant temperatures exceed a certain value, such as pulling a long hill on a hot day, the DDEC will begin limiting HP to limit engine temperatures.

[Jon Wehrenberg]

Ray,

I think Jon is funnin with you somewhat. It's a whole lot more complicated that what he wrote....

Michael

I'm not sure what Michael is referring to, but unless you are comparing apples and apples (2 coaches with an 8V92, and similar rear end ratios) it is possible for a coach with a seemingly lower HP engine to outperform another.

My 8V92 had 3.73 gearing (going by memory) so combine that with the old five speed transmission and I could go up almost any hill at almost any speed I wanted. First the gearing was so low I was fully wound out at 72 mph. But like a low geared dragster I had the ability to pull strongly.

My coach now has the six speed transmission, and higher gearing. So unless I hit the mode button on the transmission, and downshift the engine will be lugging and it will be upshifting or downshifting for economy, and not for power. Where the old five speed would wind up to 2100 RPM before shifting as long as I had my foot to the floor, I can only do that if I either manually shift my six speed or I was in the performance mode and my foot is on the floor.

[matsprt]

Jon,
In its simplest terms, it's a power to weight ratio (going up the hill comparisons). Reference cooling, a 5% increase in HP will not tax the existing cooling capacity enough to be the sole cause of overheating...but add in a cooling system in need of attention, or clogged radiator, or...etc and you could have just enough to get into trouble.

On the flip side I doubt anyone will see any difference in performance with an increase of 25 HP except in a very limited number of situations. I think Ray did it right going back to original spec's. Put it this way...going uphill at 30 MPH = one mile every 2 minutes. Doing it at 60 MPH = one mile every minute....a 5 mile grade ?? 5 minutes, not really a big deal now is it ?? AND the more HP you pour through the drive train the quicker it dies...and rips off the rubber. I just bought 176 tires...I would like them to last as long as possible.


Michael

I'm not sure what Michael is referring to, but unless you are comparing apples and apples (2 coaches with an 8V92, and similar rear end ratios) it is possible for a coach with a seemingly lower HP engine to outperform another.

My 8V92 had 3.73 gearing (going by memory) so combine that with the old five speed transmission and I could go up almost any hill at almost any speed I wanted. First the gearing was so low I was fully wound out at 72 mph. But like a low geared dragster I had the ability to pull strongly.

My coach now has the six speed transmission, and higher gearing. So unless I hit the mode button on the transmission, and downshift the engine will be lugging and it will be upshifting or downshifting for economy, and not for power. Where the old five speed would wind up to 2100 RPM before shifting as long as I had my foot to the floor, I can only do that if I either manually shift my six speed or I was in the performance mode and my foot is on the floor.

[Jon Wehrenberg]

Michael,

Couldn't agree more. We have a very long grade north of Knoxville that we have to take often. I have noticed that on both the coaches that after about 4 miles the engine and transmission temps are not cycling up and down as much as I can determine from the small gauge when it is 90 degrees out. That tells me that the cooling system is maxed out or at least very close to being at its peak.

The last two miles before the peak the bus is running fine, the temps are not climbing, but they aren't going down, even the slightest. I think with a bus we lack the benefits of natural airflow that a truck gets, and everything under those hill climbing conditions has to be working correctly.

When I reach the peak of the hill and the turbo boost drops off even slightly, indicating the cruise control is backing off on the throttle a little, the temperatures drop almost instantly, something I find amazing, considering the mass that has been heated.