drummerdimitri

If a CLA 250 makes 350 NM at 1200 rpm with a tiny 2L engine with a tiny turbocharger on it, then I really can't see why a 6.2 L NA monster can't produce 50 more NM of torque at 200 rpm's less.

Ingenieur

Exactly

Our engine is 3 times larger with a higher comp ratio
Even if the cla runs 1.5 atm of boost 22 psi
It is effectively a 5 liter with lower comp ratio
So our engine should make at least 20% more or 420 Nm at 1200 310 lb ft
This does not account for higher comp ratio and assumes 22 psi boost, inlikely

Cla
Boost 26 psi higher than I thought
Cr 8.6:1 lower than I thought

Eff V = 8.6/11.3 x (1 + 26/14.7) x 2 = 4.2 l referenced against C63 6.2
Our engine should have 45% more torque
380 lb ft at 1200
Our vol eff is lower vs turbo but at least 340 lb ft at 1200

Ingenieur

Side note
Our cars won't engage a higher gear below ~1300 rpm
Even in manual

I don't understand why folks don't believe the same physics apply at 1000 or 2000 or any rpm

Much torque can be made at low rpm
100 hp electric motor 900 rpm (slip loaded 860)
T = 5252/860 x 100 = 610 lb ft

whoover

Our engine produces max torque through 5,000 RPM, a full 1,000 RPM higher than the CLA250. Modern engines have wondrously flat torque curves thanks to variable valve timing and other tricks, but engine design still involves tradeoffs.

So many things affect a real torque curve that extrapolating from 2,000 or even 1,500 RPM is just speculation. Yes, our engine has considerable torque off idle. But attempting to quantify it from the torque at 1,000 RPM is not likely to be accurate.

I have observed that the throttle needs some feathering at 1,000 to avoid lugging that it doesn't need at 1,500. That leads me to believe there is a big falloff in torque between those engine speeds. Given that wonderful burst of power at high revs, that only seems reasonable.

whoover

Under part throttle, mine regularly drops to 1,000 when cruising. Giving it much throttle then, without a gear change, clearly causes lugging.

Ingenieur

Torque can be estimated for all the reasons above
A dyno curve that goes down to 1500 gives a good starting point
T only depends on displacement and pressure (cr or boost)
A diesel can make a lot at 600 rpm due to set-up and cr
And a healthy displacement

Ingenieur

I just drove mine
In manual
Level road
Let rpm drop from 1500 in 5th
Would not shift up
When it hit 1300 downshifted automatically in manual

whoover

I'm talking about C. Mine definitely doesn't downshift at 1,300 under light load. Does yours?

What does a diesel's torque at 1,000 RPM have to do with the M156?

Ingenieur

The torque of a diesel and gas engine use the exact same torque equation based on displacement and comp ratio
Exactly
The m156 makes 90% t from 2300 to 6000
A very wide band
The engine is extremely flexible/elastic

I dont know about auto only tried it in manual
In sport it shifts at 1300
I 'll have to try comfort

whoover

One last try. There's a reason that factory torque/power curves don't go down to 1,000 RPM. Engines made from metal, and not paper, have design tradeoffs because they don't have perfect, flat torque curves. A diesel has great low end torque because it has high compression (and it uses more energetic fuel, which you omitted from your calculations) but it won't spin at 7,000 RPM. The kind of induction hardware our engines have (to allow 7,000 RPM breathing) would be counter-productive on that diesel. Our cars have tricky intakes that allow high-RPM and low-RPM airflow with velocity, but the low-RPM path will become very subobptimal below a certain flow. Engines have torque peaks.

There are so many ways that designers can tailor those torque curves that it's not possible to predict what they look like below the published portion. Here's an amazing tri-turbo BMW diesel six. If the torque curve started at 2,000 would you have predicted its 1,000 RPM torque?:
http://www.gizmag.com/bmw-adds-four-...27/pictures#32

Or here's a BMW gas V8. It has very healthy torque, but 2,000 RPM doesn't predict 1,000:
http://img826.imageshack.us/img826/475/dynobmwm3.jpg

And these are engines where the manufacture published the 1,000 numbers. If they don't, you can assume they're even less pretty.

I assume you know all this anyway so I'm done. As long as you're happy with your 1,000 RPM torque estimate, we're good.

Ingenieur

You can use a lot of words but numbers describe it better
Lack of comprehension does not void them

It makes 340 at 1500
300 to 340 at 1000

Not sure what you think happens since t is independent of speed
It goes to 200 at 1400?!?
Lol

Designers want torque as constant as possible or at least almost constant and linear with rpm
It make the delivery more predictable and controllable
You don't want a steep or step curve
If t went from 200 at 1000 to 340 at 1500 it would be jerky
500 is a small change
A very small change in throttle would result in disproportionate power/t increase
Like the old turbo systems

I deal with combustion power units almost daily
I have a basic understanding of how they work

roadtalontsi

Where is this dyno? You'd never be able to measure this. Giving the engine enough throttle to cause the turbo to spool would induce a down shift. Ya'll are crazy to think it's making anywhere near that much torque. Go drive a blown car or a v12 that actually makes REAL torque numbers. The m156 doesnt make crap for torque. The m159 makes even less torque from the massive intake manifold - compared to a tuned 63.

If my car is put back together in 2wks at the dyno day I'll be at. I will try and see if i can get the car to dyno that low just to settle this. Ofcourse my car will only be good for a blown 63 comparison. Someone with an N/A will have to step up. not to mention i doubt the converter truly locks until maybe 1800rpm



based on this REAL dyno we are looking at 240wtq at 2500rpms. It will only dive off worse.
Id also like to see some dyno's without smoothing set to 5. Smoothing at 0 would be way more interesting. I did a google search for c63 dyno, wow lots of b.s. floating around those parts of the woods.

whoover

Nothing spoils you for off-idle torque like an S65. 450 ft-lbs. at 1,500 RPM (which AMG does publish ) on the way to 738 by 2,300 RPM. That torque curve looks like a mesa because it's limited to 738 to save the trans. It would peak over 1,000 if the ECU allowed it. It's 738 from 2,300 to 4,300 RPM and stays above 500 ft-lbs. past 6,000 RPM.

I assure you I never felt that engine lug at any RPM.

drummerdimitri

I found that output graph on the official MB CLA brochure. They always give you the power output of some of their engines in those.

drummerdimitri

I absolutely love the 65 engine. My next car should be one with either the 600 or the 65 engine or maybe even the latest bi-turbo 63 engine. I enjoy the effortless low end power those engines have. I love the feeling of looking at the speedometer and seeing the numbers increase as you are climbing a mountain with the engine turning below 2000 rpm. I would only enjoy revving the engine if I wanted to go FAST no cruise around comfortably.

whoover

Yeah, that TT 5.5 torque curve looks similar. It's a flat line at 900 Nm from 2,200 to 3,700 RPM, as opposed to the V-12 which is 1,000 Nm from 2,300 to 4,300. They both still deliver 650 Nm at 6,000 RPM. I bet they'll get it to 1,000 Nm (738 ft-lbs.) at some point. There's nothing like the turbine-like smoothness of the V-12, but the V-8 delivering the same performance will be very attractive. That V-12 is so damned heavy that no amount of suspension magic can do away with the understeer. At the end of the day, a C63 is a lot more fun to drive. The S65 is the way to get from SF to LA with very little fatigue, though. And a fair amount of fun, too.

Ingenieur

The official curves as shown in the 944 turbo manual go down to 1000 rpm
Makes 25 hp and 125 lb ft
2.5 liter low compression no boost yet
Not hard to expect an engine with higher compression, 2,5 times larger and with better controls to make 2.5 times as much or 65 hp 320 lb ft
I was looking for the climbing performance chart
In 1st it will climb a 62 % grade

MB is probably lying
Or using an engine dyno vs chassis type