R171 - R172 power change - Mercedes Benz SLK Forum

AMGs For those high performance Mercedes-Benz R170/R171/R172 cars tuned by AMG

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#1 Old 08-22-2016
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R171 - R172 power change

Using the same power plant, without the aid of a blower they went from 360 to 415 hp.

Has anyone retro fitted whatever they have done to the R172 V8 Amg to the R171 to bump the power to the 400 range?

I'd like to breathe a bit more into the R171 without going to extreme measures.
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#2 Old 08-22-2016
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Originally Posted by nimbusgb View Post
Using the same power plant, without the aid of a blower they went from 360 to 415 hp.

Has anyone retro fitted whatever they have done to the R172 V8 Amg to the R171 to bump the power to the 400 range?

I'd like to breathe a bit more into the R171 without going to extreme measures.

They're not the same engines unfortunately - although both notionally 5.5l V8s, the R171 is 5439cc and the R172 5461cc. The latter has a higher CR (12.6:1 for the M152 engine in the R172, which is huge for a road petrol engine), cylinder shutdown tech and a whole heap of other differences. The M152 engine can be considered nearer to a sleeved-down M156 6.2l and nearer in design efficiency to that than its forbearer in the R171.


So bottom line is no, you can't retrofit the mods to make the older engine faster unfortunately.
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#3 Old 08-22-2016
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Originally Posted by R1NGA View Post
They're not the same engines unfortunately - although both notionally 5.5l V8s, the R171 is 5439cc and the R172 5461cc. The latter has a higher CR (12.6:1 for the M152 engine in the R172, which is huge for a road petrol engine), cylinder shutdown tech and a whole heap of other differences. The M152 engine can be considered nearer to a sleeved-down M156 6.2l and nearer in design efficiency to that than its forbearer in the R171.


So bottom line is no, you can't retrofit the mods to make the older engine faster unfortunately.
So it's a supercharger upgrade then !
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#4 Old 08-22-2016
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add ecu tune. 25 hp and headers, 25 hp to your 55 like i did...= 415 hp
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#5 Old 08-22-2016
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They did a huge amount to the new engine. Very impressive. I wonder if anyone has modded the R172? So much power already.
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#6 Old 08-23-2016
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They did a huge amount to the new engine. Very impressive. I wonder if anyone has modded the R172? So much power already.

Suspect a similar ECU tune, headers and 2ndery CAT removal might realise 460-470bhp, which is not to be sniffed at!?
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#7 Old 08-23-2016
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Suspect a similar ECU tune, headers and 2ndery CAT removal might realise 460-470bhp, which is not to be sniffed at!?
Headers tend to make power at the top end of the RPM curve, and usually you lose a bit of low-end torque due to valve overlap and fuel blowby. Similar results with secondary cat removal, less exhaust restriction usually results in loss of low-end torque. To get the full benefit of the mods, you have to be in the habit of winding 'er out to the top end...which you may be!
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#8 Old 08-23-2016
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Is the sky-high compression ratio why there don't seem to be supercharger kits for the R172 55s?
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#9 Old 08-23-2016
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That would be my guess.
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#10 Old 08-24-2016
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Originally Posted by sleebus View Post
Headers tend to make power at the top end of the RPM curve, and usually you lose a bit of low-end torque due to valve overlap and fuel blowby. Similar results with secondary cat removal, less exhaust restriction usually results in loss of low-end torque. To get the full benefit of the mods, you have to be in the habit of winding 'er out to the top end...which you may be!
That's a very good observation and in truth 400lbs/ft of torque (or thereabouts) is plenty and is what makes the car so useable. Torque is more useful on todays' roads than outright power, so I guess there's little need to chase 500bhp at its expense really.


I would imagine that fitting a supercharger to the M152 would be a technological step too far and a real headache in terms of setup and integration with all the high-tech engine control features. No, I think I'll leave mine well alone for now thanks....!


I do hear that a well engineered remap releases about 5-6% increase (to about 440-450bhp) and if combined with a TCU tweak as well, makes the shifts very quick in Sport/Manual when pushing on with large throttles. DMS have such a package which is interesting.
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#11 Old 08-24-2016
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Yeah, when I went through all of this waaaaay back in 1996 with my 1995 Z28 Camaro (5.7L) it was definitely noticeable how the bottom end went away with headers and low restriction exhaust. Did good on the top end, but never pulled like the 55 does now. I had a Borla exhaust with an exhaust bypass, I kept it on the mid plate, but always put the complete block plate back in when I went to do my yearly state inspection. I was always surprised how much low-end torque came back with the bypass blocked out. Made the car easier to drive (6 speed manual) for sure. I did a remap on mine too, really didn't notice anything as a result. I would be very surprised if a ECU remap could get you 36 HP, and more importantly where would that HP land on the RPM curve? Getting gains way up high is great, but my problem is that to get to them, you've got to be going warp 10, and the local boys in blue don't take kindly to that. Where the gains are is as important as how much gain there is.

Putting a supercharger in a high performance naturally aspirated engine is not a matter of if you're going to blow it up, it's when. The high compression ratio is roadblock #1 . #2 is that i'd gamble that the engine has hypereutectic pistons in it, and they don't withstand detonation very well. Hypereutectic alloys are used because of their low coefficient of expansion, which means less exhaust blowby (can make the cylinders to tighter tolerance) and better emissions as a result -- but they are more fragile. Anyway, usually what happens is that people blow the ring lands off. If you do that in a SB chevy 350, it's a problem but not a big one because there's zillions out there, and there's a ton of aftermarket support. A bit more of a problem with a MB motor. Factory Turbo'ed and supercharged motors have forged pistons, and they can handle detonation with no problems.

So as you can see, I've played with this a bit before, haha. Now I've got a car that runs low 12's completely stock, no mods for me, thanks!

Just noticed you're in Guildford. I was living in West Byfleet and working in Farnborough up until the middle of July.
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#12 Old 08-25-2016
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I didn't notice any low-end torque loss when adding headers to my SLK55. How low of rpms are you talking about?
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#13 Old 08-25-2016
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Originally Posted by sleebus View Post
Yeah, when I went through all of this waaaaay back in 1996 with my 1995 Z28 Camaro (5.7L) it was definitely noticeable how the bottom end went away with headers and low restriction exhaust. Did good on the top end, but never pulled like the 55 does now. I had a Borla exhaust with an exhaust bypass, I kept it on the mid plate, but always put the complete block plate back in when I went to do my yearly state inspection. I was always surprised how much low-end torque came back with the bypass blocked out. Made the car easier to drive (6 speed manual) for sure. I did a remap on mine too, really didn't notice anything as a result. I would be very surprised if a ECU remap could get you 36 HP, and more importantly where would that HP land on the RPM curve? Getting gains way up high is great, but my problem is that to get to them, you've got to be going warp 10, and the local boys in blue don't take kindly to that. Where the gains are is as important as how much gain there is.

Putting a supercharger in a high performance naturally aspirated engine is not a matter of if you're going to blow it up, it's when. The high compression ratio is roadblock #1 . #2 is that i'd gamble that the engine has hypereutectic pistons in it, and they don't withstand detonation very well. Hypereutectic alloys are used because of their low coefficient of expansion, which means less exhaust blowby (can make the cylinders to tighter tolerance) and better emissions as a result -- but they are more fragile. Anyway, usually what happens is that people blow the ring lands off. If you do that in a SB chevy 350, it's a problem but not a big one because there's zillions out there, and there's a ton of aftermarket support. A bit more of a problem with a MB motor. Factory Turbo'ed and supercharged motors have forged pistons, and they can handle detonation with no problems.

So as you can see, I've played with this a bit before, haha. Now I've got a car that runs low 12's completely stock, no mods for me, thanks!

Just noticed you're in Guildford. I was living in West Byfleet and working in Farnborough up until the middle of July.

Interesting history and experiences Sleebus and I completely get your take on things. Although on a MUCH smaller scale, I fitted an HRC kit to a Honda XR650 Supermoto that I built and found a 20% increase in power (from 51 to 61bhp), which although doesn't sound much, sure does feel a lot when it only had me and a 115kg bike to move....! All very good, but the free flowing exhaust, flowed head and perkier cam lost bottom end torque and it was less fun to ride day-to-day and needed at least one cog less before it decided to fly. Quite simply it was better stock.


I also agree with the comment about needing to be at Mach2 with pants on fire to enjoy the additional top end, which is why I'm not interested in things like McLaren 12C's and the like (not that I could afford them, but I have driven a couple) as they don't talk to you at road speeds any more.


I have tried an R172 55 with a DMS map and it was definitely better overall with gains over ours from low down and the noise was sharper too - they apparently are able to do quite a lot with timing to optimise things and that's how it felt. TCU map made the shifts in Sport/Manual on high load (and downshift blips) much more aggressive, which was good. Pricey at the neck end of Ł1000 for both ECU and TCU, but fun all the same.


Still tempted by a secondary CAT and Resonator removal, but worried about the noise on the R172, as the active flaps already do a pretty good job. Suspect I too will leave alone however. Which will probably be a first for me, as nothing has ever stayed standard in my garage - maybe till now....
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#14 Old 08-25-2016
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Yep. I agree 100% with your supermoto experience. With my Z28, even with putting 4.10 gears in the rear, which helped with the loss of torque, the car was a b*tch to launch right. I'd probably hit it once out of ten tries...which doesn't say much for my driving skill now does it? haha. Anyway, it was easier if you had a automatic. I think in the auto, 3.73 gears were equivalent to the 4.10 in the manual. Match that with a high-stall torque converter (like around 3,000 rpm) and you'd have quite the rocket on your hands. However with the manual, it was not quite as fun.

With any kind of tweaks, everything is a compromise. It just depends what ya want, and what you're willing to give up!
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