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Open Roads Forum  >  Class B - Camping Van Conversions

 > Chevy engine power curves

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booster

Minnesota

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Posted: 08/28/09 08:39am Link  |  Print  |  Notify Moderator

I finally came across the full range of Chevy power curves, for all the years and all the engines. There has been a bunch of discussion here on the merits, or not, of the different engines, but with only the peak hp and torque given, they are very hard to evaluate.

Here are the 3 engines that are probably of most interest at this time.

First, the old standard 6.0 liter, before the VVT was added:



This looks just like you would expect a relatively old school pushrod V8 truck engine to look. Good torque down low, relatively flat torque curve, falling off after 4000 rpm, and all done by 5000 rpm.


Now the new 6.0 with VVT:



This is pretty surprising, considering it is a supposed improvement. They have definitely gone away from the heavy truck style engine with this one. They have lost torque below 3000 rpm compared to the non VVT engine, which really isn't what you want with a near 10K pound vehicle. It is also very interesting that the tested hp curve continues to climb after the "rated" max hp level at 4600rpm. This would normally mean that the engine could make the power at that level, but they don't want it to, probably because they can't get the heat out of it at that level. It is fairly common for this to happen as vehicles get heavier and could actually use that much power continuously. In a car, they could have all that power available for accelleration bursts because there is no way it could ever be needed continuously. My guess is that they added a bigger intake setup, and maybe more cam, and lost the bottom end torque. Since the old engine was already tuned for low end, the VVT only gave them benefit up top, but they aren't able to use it. Not a very good choice, I think. The engine is probably just a hp limited light pickup engine, as they have be available for quite a while, and have the higher hp numbers. It would be a cheap and easy way to put in an "update" and eliminate making both engines.


And now the one that I was wondering the most about, the 4.8 VVT that is going into the base Roadtreks.



This is obviously a newer, and quite good design. It has the extremely flat torque curve typical of the new, ground up, designs. It is down from the low end torque of the old 6.0, but at 1500 rpm is almost equal to the VVT 6.0. Above that, however, it loses ground quickly to both of them. By the time you get to cruise rpm range (2-3000 rpm), the 4.8 is down 50-60 foot pounds of torque to the 6.0. This will make for a lot more downshifting, and the need for the 6 speed transmission. Based on how much throttle our 6.0 takes in various driving, I would say the 4.8 would be pretty good in normal driving, although it will need more throttle and use a higher percent of its max power. I think it will be in a bit of trouble in the mountains, however. With big climbs, you are in a lower gear, at higher rpms, and the 6.0 gains much more torque at the higher rpms than the 4.8 does, and is down over 20% on torque compared to the 6.0 at max. Personally, I think it is a bit small for a class B.


I know this will cause a stir, but one more thing to condsider. The old I5 Sprinter diesel had max torque of 243 foot pounds at 1600 rpm, and is considered a torque monster. All of these gas engines match, or beat that number at 1600 rpm. I was very surprised at that. The new V6 Sprinter engine is rated 280 foot pounds at 1200 rpm (really low), and the old 6.0 matches that. Looking at this, I would have to give the gas engines (6.0) a large pulling power advantage, as they match the diesels on the bottom, and beat them handily as rpm increases. As I said, this was a large surprise to me, as I though the diesels would be way better than gas below 2000 rpm.

topless

Wichita, KS

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Posted: 08/28/09 09:42am Link  |  Print  |  Notify Moderator

I haven't found many actual dyno charts for a stock 2.7 I-5 Sprinter. This one shows mph ,not rpm (unfortunately). But, as you can see, the torque at the wheels-stock is higher than published and that is because this chart was done on a chassis dyno where there is a load. http://bullydogdieselperformance.biz/rapidpwr.pdf

I will also add, the temperature, humidity, and barometric pressure will affect every dyno run. There are correction factors needed to do a fair comparison and even then the results are only relative to the same dyno.

The peak numbers you see on the chart for a stock Sprinter are 155 hp and 269 ft lbs. Add about 20% to those for the power at the flywheel making the peak torque over 320 lb ft.

You will see a 18-25% drop in engine power as it goes through the drive train. These are parasitic loses due to power it takes to turn the transmission, driveshaft, differential and rolling resistance of the tires. A drive roller type dyno (like the one used to get this chart) will actually increase rolling resistance of the dyno roller based on the vehicles, frontal area and weight.

Why are those numbers higher than the ones published? Easy, a turbocharger has to have a load to make boost. With no load, the boost levels will only be the amount of resistance of the air moving through the intake system. Bog the motor down and then the turbo will continue to push the same amount of air into a slowed motor, thus increasing the pressure in the intake track, increasing the pressure in the cylinder and making more power.

That's why turbochargers are more efficient than other types of intake systems. It's power is on demand, not wasted by being there all the time, consuming fuel. Turbo's use fuel under boost, when there's no boost, it turns into a small motor.

There is a reason all big trucks use turbo diesels. More load = more power, and diesels will not pre-detonate (ping) under load. Engine speed is controlled by fuel, not air like a gasoline engine.

* This post was edited 08/28/09 09:57am by topless *





booster

Minnesota

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Posted: 08/28/09 10:06am Link  |  Print  |  Notify Moderator

There is no question that there is a huge difference between dyno. 20% difference between dynos with the same engine isn't really unusual. It is also very common for vehicles to show better than rated numbers. Hopefully, all the manufactureres are publishing minimum numbers, not maximum, within the build of engines. Back in the day, I saw a 425hp rated stock hemi pull almost 500 on the dyno. It is much better now than in the past, because of better quality control. As far as the turbo making the difference between the rated and actual, I would have to disagree. The original factory rating was also done with the turbo in place and loaded to full capacity. That is what a dyno pull is, you set the rpm of the dyno, go to full throttle on the engine, and the dyno will put on as much load as the engine can take without slowing down. Loading it more won't change anything, as the turbo is already working to max capacity, it will just slow down. Don't get me wrong, turbos are a great thing. I have a 600hp twin turbo '70 Challenger that I built from the ground up. 600hp and 20mpg, I love turbos.

As far as I know, trucks engines are rated like car engines, and are required to have all accessories and drivetrain in place, so it should be an apples to apples comparison between rated engines.

topless

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Posted: 08/28/09 10:54am Link  |  Print  |  Notify Moderator

You may be right. But I still have my doubts that the hp & torque rating for the Sprinter engines are done fully loaded. It doesn't add up when you consider the size and weight of a converted Sprinter to it's performance and fuel economy, especially in the mountains.

All the domestic mfgr's fudged in the old days. GM's Z-28 was rated at 290hp and the ZL-1 at 435hp, LS6 at 450hp were all a joke. Ford did the same with their motors. Thank the insurance industry for that and the decline that followed.

Atlee

Mechanicsville, VA

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Posted: 08/28/09 11:28am Link  |  Print  |  Notify Moderator

booster wrote:

I finally came across the full range of Chevy power curves, for all the years and all the engines. There has been a bunch of discussion here on the merits, or not, of the different engines, but with only the peak hp and torque given, they are very hard to evaluate.



Where is that full range of Chevy power curves located? A link, perhaps?

I'd like to see what the dinosaur motor in my 1995 Chevy Chassis, 1996 RT is like.


Erroll, Mary, Duffy the Badger Dog plus "Ollie"
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booster

Minnesota

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Posted: 08/28/09 12:31pm Link  |  Print  |  Notify Moderator

Atlee wrote:

Where is that full range of Chevy power curves located? A link, perhaps?

I'd like to see what the dinosaur motor in my 1995 Chevy Chassis, 1996 RT is like.


Here is a link to the 2007 info listing. I just tried going older than that without success. I have not been able to find a way in to the index on this GM site. I was only able to get the different years by changing the address in the address bar. eg changing the 2007 and 07 to 2008 and 08. The information you are looking for is probably there if you can find a way in.

link to GM engine specs

loving retirement

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Posted: 08/29/09 02:31pm Link  |  Print  |  Notify Moderator

I could not find any plots for the old 5.7L in my 2002 Chevy. Anyone found a way to locate the power curve info at the web site? I would really like to see how that old 5.7L which many of us have matches up to 6.0L and the new 4.8L.

Atlee

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Posted: 08/29/09 08:25pm Link  |  Print  |  Notify Moderator

loving retirement wrote:

I could not find any plots for the old 5.7L in my 2002 Chevy. Anyone found a way to locate the power curve info at the web site? I would really like to see how that old 5.7L which many of us have matches up to 6.0L and the new 4.8L.


When I checked that site, I noticed it didn't include the old 5.7 engine. I'd like to know what my '95 5.7L engine is about. I know your '02 5.7L is a lot stronger than my '95 5.7L is.

I bet that modern 4.8L's numbers are superior to the 5.7L in my old '95.

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