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Old 09-11-2008, 04:54 AM   #1 (permalink)
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SL600 Mild Tuning

For anybody that's interested. I replaced my 95 SL500 in March this year with a 96 SL600. I was planning to do a bit of tuning on the 500 but when I drove the 600 I was completely smitten - so change of plans. Anyway I decided that I needed to hear the engine, so the first thing to go was the standard exhaust. I had a custom system made here in Johannesburg by a specialist company (TNT Performance Exhausts), but nothing too extreme as I still wanted to be able to drive on the highways in relative peace. Then I added a set of K&N air filters, and finally had the ECU upgraded using a pair of Unichips with custom mappings by RG Motorsport. I am a very happy person with the results. I think MB was very conservative with their SL600 mappings as they needed to differentiate between it and the SL60. My wheel HP went from 268 to 311 - equating to about 450hp at the flywheel at sea level. Before I get flamed for my calculations, we are at an altitude of around 5500ft here in Johannesburg, resulting in an approx 18% power loss for normally aspirated engines.

Anyway the results on the road are better than I hoped for. The car sounds great and feels so much faster. I not going to say it has been transformed because I thought it was brilliant before, but now it's just so much better.
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Old 09-11-2008, 05:37 AM   #2 (permalink)
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Originally Posted by bflannigan View Post
For anybody that's interested. I replaced my 95 SL500 in March this year with a 96 SL600. I was planning to do a bit of tuning on the 500 but when I drove the 600 I was completely smitten - so change of plans. Anyway I decided that I needed to hear the engine, so the first thing to go was the standard exhaust. I had a custom system made here in Johannesburg by a specialist company (TNT Performance Exhausts), but nothing too extreme as I still wanted to be able to drive on the highways in relative peace. Then I added a set of K&N air filters, and finally had the ECU upgraded using a pair of Unichips with custom mappings by RG Motorsport. I am a very happy person with the results. I think MB was very conservative with their SL600 mappings as they needed to differentiate between it and the SL60. My wheel HP went from 268 to 311 - equating to about 450hp at the flywheel at sea level. Before I get flamed for my calculations, we are at an altitude of around 5500ft here in Johannesburg, resulting in an approx 18% power loss for normally aspirated engines.

Anyway the results on the road are better than I hoped for. The car sounds great and feels so much faster. I not going to say it has been transformed because I thought it was brilliant before, but now it's just so much better.
Nice, what did you do with the exhaust specifically? Got any pics?

Also, I completely agree with you that the stock tune on the SL600 leaves a lot to be desired. The a/f ratios can be richened by almost a full point at WOT, and can be leaned out half a point or so during most of the rest of the range, without causing any problems. The timing is also very retarded, and you can advance it significantly with no issues as long as you use premium fuel.

Stuartknight gained 40hp just from an ECU tune, which sounds to be about what you gained as well. You have to remember, in German-market trim, the factory power rating for the M120 was 410hp, and the actual real-world number was closer to 440hp. And that's stock. Beginning in 1994, and for all US models from inception forward, they de-tuned it to 389hp to comply with emissions regulations.

So yeah, getting it back to where it was supposed to be is a good thing.
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Old 09-11-2008, 07:24 AM   #3 (permalink)
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It's going for tyres & wheel alignment at the weekend so might try and take some pics of the exhaust then & post them. I haven't had a good look at it myself. I just ask the guys to make it less restrictive and sound better. I think the fitting of cats took the power down to 390 everywhere. I was working back from the dyno - allowing 18% for altitude and 20% for drivetrain sort of worked back to the book numbers at the flywheel. I suppose the only thing that matters really is the comparative real wheel hp. Either way it was a pretty cheap way of adding +15% power (just over USD2100 in total).
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Old 09-11-2008, 07:47 AM   #4 (permalink)
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Originally Posted by bflannigan View Post
It's going for tyres & wheel alignment at the weekend so might try and take some pics of the exhaust then & post them. I haven't had a good look at it myself. I just ask the guys to make it less restrictive and sound better. I think the fitting of cats took the power down to 390 everywhere. I was working back from the dyno - allowing 18% for altitude and 20% for drivetrain sort of worked back to the book numbers at the flywheel. I suppose the only thing that matters really is the comparative real wheel hp. Either way it was a pretty cheap way of adding +15% power (just over USD2100 in total).
I'm pretty sure they always had cats. I think there were other changes that bumped down the power, mostly via programming, but I could be wrong.
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Old 09-11-2008, 07:53 AM   #5 (permalink)
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Quote:
Originally Posted by chriswufgator View Post
Nice, what did you do with the exhaust specifically? Got any pics?

Also, I completely agree with you that the stock tune on the SL600 leaves a lot to be desired. The a/f ratios can be richened by almost a full point at WOT, and can be leaned out half a point or so during most of the rest of the range, without causing any problems. The timing is also very retarded, and you can advance it significantly with no issues as long as you use premium fuel.

Stuartknight gained 40hp just from an ECU tune, which sounds to be about what you gained as well. You have to remember, in German-market trim, the factory power rating for the M120 was 410hp, and the actual real-world number was closer to 440hp. And that's stock. Beginning in 1994, and for all US models from inception forward, they de-tuned it to 389hp to comply with emissions regulations.

So yeah, getting it back to where it was supposed to be is a good thing.
chriswufgator the M120 started it's life in Euro spec with 408 BHPs and after a few years they tuned it down to 394 BHPs because (it's a rumor) in 408 spec it was said to blow or spoil the cats after 62,000 miles.
Also rumored is that the figures were higher but no one knows for sure unless they dyoned their cars.

Cheers.
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Old 09-11-2008, 08:01 AM   #6 (permalink)
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chriswufgator the M120 started it's life in Euro spec with 408 BHPs and after a few years they tuned it down to 394 BHPs because (it's a rumor) in 408 spec it was said to blow or spoil the cats after 62,000 miles.
Also rumored is that the figures were higher but no one knows for sure unless they dyoned their cars.

Cheers.
I think they were a little stronger than the factory figures, based on the few dynos I've seen of M120s. Mine pushed 316rwhp on a 100-degree day with a bad radiator and 100c operating temps.
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Old 09-11-2008, 08:13 AM   #7 (permalink)
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Looking over the numbers and compensating for altitude (~18%). Mine was producing around 325rwhp before the mods. That would mean either drivetrain losses were under 20%, or, more likely and as hinted at, MB understated the numbers. Have also heard that their quoted 0-60 times for both the SL60 & SL600 were also very conservative.
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Old 09-11-2008, 08:17 AM   #8 (permalink)
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Here in South Africa, I think the pre 96 models didn't have cats as unleaded wasn't available until then. Certainly my 95 SL500 had no cats (and about 10hp more than the 96 model which did).
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Old 09-11-2008, 08:50 AM   #9 (permalink)
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Quote:
Originally Posted by bflannigan View Post
Looking over the numbers and compensating for altitude (~18%). Mine was producing around 325rwhp before the mods. That would mean either drivetrain losses were under 20%, or, more likely and as hinted at, MB understated the numbers. Have also heard that their quoted 0-60 times for both the SL60 & SL600 were also very conservative.
Driveline losses are normally 18%-20% for an automatic transmission, so if you ran 325rwhp then that translates to a little over 400hp, which is in line with my car and the few other M120 dynos I've seen.

The official numbers are low.
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Old 09-11-2008, 06:21 PM   #10 (permalink)
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bflannigan, do you happen to know where your current air/fuel is?
Also, do you have any dyno's you can post for us?

I'm asking because I'm curious to see if your tuner richened or leaned your stock mappings.

Thanks
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