Been a few years! Back somewhat but with an SL65 (6.2)

[supermono]

Was a GT2 man for a long long time, now I've got an SL63 -- different car obvs.

Hi!

I have a question... I bought this SL a few weeks back -- 24k miles and a new engine 1000 miles ago (head bolt failure). It's great but just doesn't quite seem to have as much power as I'd expected. Put it on the dyno today and after going into dyno mode (sigh) it ran into speed limiter in 5th at 6200rpm so only made 460bhp. Then we tried it in 4th and for some reason the power curve tracked below the 5th gear one consistently although reached nearly 7k rpm at the same power 460.

Obvs I was expecting over 500, but this lower power in 4th gear looked like some sort of a restriction in the lower gear -- is that for real? Limiting power in 4th?

Edited by supermono on Sunday 22 September 08:24

Edited by supermono on Sunday 22 September 08:24

[Venisonpie]

Your title says SL65 but with a 6.2 engine and in the post you quote 560 and then 460 bhp.

Assuming its a 63 with a 6.2 I think they made 525bhp stock. If its only 1000 miles old I imagine carefully running it in might produce the best results..

[supermono]

Yes it's a 63 -- typo... 2008 naturally aspirated 6208 V8 rated at 520ish bhp from the factory.

Thanks and yes it was run in by the previous owner, the sticker on the windscreen says no hard revving for 1k and it's a few hundred over that.

However, there was a very specific question beyond the typos although thanks for the generic running in advice.

Question: Does it limit power in 4th gear? I'm looking for an explanation as to why the chart ran beneath the 5th gear figure. Has anyone else perhaps got a dyno chart from an SL63 speficically (we compared with a C63 chart which didn't do the same thing)

[Venisonpie]

supermono said:

Yes it's a 63 -- typo... 2008 naturally aspirated 6208 V8 rated at 520ish bhp from the factory.

Thanks and yes it was run in by the previous owner, the sticker on the windscreen says no hard revving for 1k and it's a few hundred over that.

However, there was a very specific question beyond the typos although thanks for the generic running in advice.

Question: Does it limit power in 4th gear? I'm looking for an explanation as to why the chart ran beneath the 5th gear figure. Has anyone else perhaps got a dyno chart from an SL63 speficically (we compared with a C63 chart which didn't do the same thing)

Does your car have the 5 speed or 7 speed unit? Either way I'd be surprised (but don't know) if there was any limitation in the higher gears.

I have an R230 500 with the 7 speed box and by the time you're in 4th its quite a tall gear so doubt there would be a need to reduce power/ torque.

[supermono]

It's the seven speed wet clutch AMG set up.

Indeed there wouldn't be any need to limit power in 4th as it's tall like you say -- does about 130 at the redline. But some bikes have power limiters on 1st/2nd as you can't use all the power usually due to wheelying. I was purely guessing maybe it would limit power in lower gears for this reason (though it would be stupid) although in 4th as you say, it's well past power causing issues other than in the wet and really when hooning you'd probably not get into 5th anyway as speed would be an issue then.

[Venisonpie]

Aside from potential dyno error or the engine being a bit tight still, another thought.

I think the 6.2 engine was offered in 3 different outputs, in the E, S and SL models it was 525bhp but in the C class was circa 460bhp and limited model editions with 480 and 525 bhp. I don't know what differentiated them but I wonder if the fresh engine is actually the right spec? Might be worth speaking to a Merc main dealer or specialist to eliminate that possibility.

[supermono]

Very good information, thanks. Actually it was changed at Mercedes Watford who apparently are an AMG specialist dealership. I'll definitely ask them. The two different dyno outputs were pretty much parallel just a bit lower in 4th gear compared to 5th.

I have the engine number etc, and yes it could be tight so down on power a little bit, but I didn't really think new engines these days especially after I think actually 1500 miles would be tight.

[Faszination76]

I’d be surprised if a stock M156 6.2 makes much more than 500hp. The only way you’re going to get significant gains is with a supercharger in my opinion.

[supermono]

Ah, I'm not looking for gains, you misunderstood my post. I'm specifically asking if anyone knows of a reason why a pull in 4th 10 minutes after a pull in 5th made exactly, say, 10% less torque the whole way to the redline. Peaking at the same number of BHP as 5th gear around 1000rpm less when the speed limiter came in.

That's what I'm looking for specifically. I'm very happy to leave it entirely stock. Anyway it has a mercedes warranty so I'm not going to dick around with it.

Edited by supermono on Monday 23 September 09:22

[MustangGT]

supermono said:

Ah, I'm not looking for gains, you misunderstood my post. I'm specifically asking if anyone knows of a reason why a pull in 4th 10 minutes after a pull in 5th made exactly, say, 10% less torque the whole way to the redline. Peaking at the same number of BHP as 5th gear around 1000rpm less when the speed limiter came in.

That's what I'm looking for specifically. I'm very happy to leave it entirely stock. Anyway it has a mercedes warranty so I'm not going to dick around with it.

Edited by supermono on Monday 23 September 09:22

Did the dyno show power at the wheels, or an estimated engine power using residual losses at the end of the run? It may be there is a different drag factor in different gears.

Also, different dynos give different power values when compared to each other, weather is also a factor.

Equally the engine setup may limit torque in lower gears, could even be differing amounts.

[supermono]

MustangGT said:

Did the dyno show power at the wheels, or an estimated engine power using residual losses at the end of the run? It may be there is a different drag factor in different gears.

Also, different dynos give different power values when compared to each other, weather is also a factor.

Equally the engine setup may limit torque in lower gears, could even be differing amounts.

Thanks for the reply. Yes calculated engine power from run down losses both runs same dyno and same weather so the only difference was gear and calculated torque was less in 4th. Of course torque at the wheels would be a fair amount higher in 4th compared to 5th so this is all calculated engine power.