M272 vs M273 Hp/Torque output

[HWW212]

Litre for litre, the M272 is a more powerful engine than its bigger M273 brother.

Seeing that the 2 engines are very similar in architecture and construction, does anyone know exactly why the M273 is not as powerful, litre for litre, to its smaller brother ?

By my calculations, the M273 should be making 418-421 Hp and 402 ft lb.

Thats a whopping +36 hp above what a stock M273 makes.

(ps. I'm referring to the M272 which makes 268 hp)

 

[PobodY]

Is the answer that it's tuned to produce more torque (via the constantly variable cam timing), so maximum power is compromised?

There might be something similar if you compare the M272 with the M112. - The M272 hits maximum torque by ~2500 RPM and then holds that until ~5000 RPM (whereas the M112 reaches it at ~3000 RPM and is done by ~4500 RPM).

What the M273 definitely does better is not eat balancer sprockets!

 

[HWW212]

Is the answer that it's tuned to produce more torque (via the constantly variable cam timing), so maximum power is compromised?

There might be something similar if you compare the M272 with the M112. - The M272 hits maximum torque by ~2500 RPM and then holds that until ~5000 RPM (whereas the M112 reaches it at ~3000 RPM and is done by ~4500 RPM).

I thought of that (variable valve timing) however the range that the M272 and M273 camshafts can be adjusted is the same as far as I know. At full throttle, they should be adjusted to make maximum amount of power irregardless of where you are in the rev range.

Even so, litre for litre, the M272 is still making more torque (although not by much) compared to the M273

There has to be something holding the M273 back from making that extra +36 hp at the higher end of the rev range.

 

[clk208]

The M272 350 CGI direct injection does 292bhp so even more of a disparity.

Did they offer a CGI on the M273?

 

[HWW212]

The M272 350 CGI direct injection does 292bhp so even more of a disparity.

Did they offer a CGI on the M273?

Not the M273.
The successor to the M273 was the M278 which is turbo charged and has direct injection.

I have a small mp4 which shows how the ECU adjusts the cams on a 3rd gear run to redline, however, I'm unable to attach it to this post (mp4s not allowed)

 

[SW18]

Could it be that the M273 is set up to be less stressed for longer endurance? It’s a big seller in the US where cars often last for hundreds of thousands of miles.

Another thought is that the M273 is surprisingly efficient; again, could the set-up be to optimise economy?

 

[PobodY]

This has me intrigued now.

If it's a detuning thing it's usually the other way around; take power from the V6 so that it doesn't out-perform the flagship V8.
Holden used to do this with the supercharged (Buick) V6 when it first came out in Australia so that it didn't make more power than the 5L V8 (Chevy LS1).

 

[HWW212]

Could it be that the M273 is set up to be less stressed for longer endurance? It’s a big seller in the US where cars often last for hundreds of thousands of miles.

Another thought is that the M273 is surprisingly efficient; again, could the set-up be to optimise economy?

I haven't been able to find any camshaft specifications to compare the M272 to the M273. I'd like to see what Mercedes had in mind with regards to state of tune. Seeing that both engines peak power is at 6000 rpm, I can't image the specs being that much different (duration wise).

I have come across very few tuners (Shrick, Kleemann) that do offer upgrades, however, they don't supply their camshaft specs either. As far as remapping, I'm kind of skeptical of the gains claimed (405 hp, 425 ft lb) on just an ECU tune alone. I've had a previous German car (V8 naturally aspirated) remapped and didn't see gains near 30+ hp or torque with a ECU tune alone.

 

[HWW212]

This has me intrigued now.

If it's a detuning thing it's usually the other way around; take power from the V6 so that it doesn't out-perform the flagship V8.
Holden used to do this with the supercharged (Buick) V6 when it first came out in Australia so that it didn't make more power than the 5L V8 (Chevy LS1).

Yes, this is what I would expect.

 

[SW18]

Perhaps the rationale for detuning the V8 was that otherwise it would start to tread on the toes of the AMG V8?

 

[HWW212]

Perhaps the rationale for detuning the V8 was that otherwise it would start to tread on the toes of the AMG V8?

Possibly. The M273 is only 0.7 litres smaller than AMG's V8 where as its a full 2 litres bigger than the M272.

It has great compression at 10.7 to 1 (slightly down to AMG's V8) and all the other right pieces to make it a good performance motor but its still down on power in my opinion.

With 5.5 litres available, I'm somewhat surprised aftermarket tuners didn't jump on this motor extracting its full potential.

Still, there has to be something holding the M273 back from making that extra +36 hp (and more) at the higher end of the rev range.

 

[HWW212]

Thought I'd post a cam catalog showing what camshafts are available. My guess would be that the M273's are probably similar to the M272's although, again, they're not listed for some reason.