What you are failing to realize time and again is that this dividing number is a guess at best. It does not mean the manufacturer was right.

You can test 3 identical cars, with 3 different WHP outputs and then use a different loss coefficient and still come up with the same flywheel hp and I guarantee you that it will all be magic. What I am saying is that I can make ANY car spit out ANY flywheel hp by simply adjusting the loss factor.

I am done trying to explain this to you. Please read the articles and do some research on the topic.

Tom's right. I was just giving Sound8 something to use, since he was desperately seeking a conversion number. It seems, the MB community has agreed upon the arbitrary number of 18% drive train loss. It's not exact, but it's probably close to ~2%.

As stated, it so hard to calculate gains if you only have the 'after mods' horsepower. But, 1/4 mile trap speed is probably a better calculating factor. We can dig up umpteen stock SL63 trap speeds and see if yours is any different. Even that's not going to be 100% due to different D.A. at different tracks.

To put this to bed, you really needed to do a baseline on the same dyno that you're going to use for 'after mod' testing.

Since your friend is a tuner, he should be able to flash you back to stock in 10 minutes. You can dyno, then put your tune back on in another 10 minutes.

That will give you the data you seek.

Let's get one thing straight, I am not interested in learning about dyno's, this discussion is all about how a figure is arrived at when using a rolling road dyno. I have explained how it is done in the UK and other members have said how it's done in the States. I have been told by Benz-O-Rama that you simply divide by a number, and as much as other members disagree with the method of running down to achieve a flywheel figure I would rather believe that a computer measuring the run down instead of using a one fit's all number to divide by to be the best. I have said on numerous occasions that the flywheel figures I have obtained so far on various cars have been pretty accurate compared with tuners and manufacturers figures.
The problem I have now is whether to put my SL63 on a rolling road, will anybody believe the figures!

sound 8:

Any comment on this article?

Tom

You should very much be interested in learning how dynos work - otherwise how can you expect to have an intelligent conversation on the subject?

I will second the question, did you read this article: http://www.pumaracing.co.uk/coastdwn.htm ?

I commend you for trying, Bvldari, but you may as well do this...

-Rob

His silence is deafening...

Tom

Hi, glad you missed me
It would appear that I made a mistake on post 32, at the time I was answering a question regarding my re mapped SL63 and how to measure 560+ and should have been on thread SL63 vs SL65 which dragged us into an argument about dyno's, so I am sorry, I started it.
Next, yes I have read it, but one thing I disagree with.
Quote: To run the test , the car was warmed up and given a couple of runs on the rollers to stabilize the temp etc..
I would never do a run unless my car had reached optimum temperature which in my car takes around 20 minutes this time of year. Giving a car full power on a cold or warm engine could seriously damage it. You should drive a car first until it reaches full temp before putting it on a rolling road, plus it sounds amateurish. Also every time you do a run, heat build up, especially in inter coolers will increase and lower your horse power, fans are inadequate.
However I have made the decision that a flywheel figure cannot be achieved on a rolling road. Sure measure a stock car's whp and again after tuning to see the gains, however it still wont give you a flywheel figure!
I started this thread and it was going great guns until my gaff on post 32, so
perhaps we can return to the op. Thanks Paul.

sound 8:

I commend you on your admission. It isn't always the easiest thing to do.

I agree with your point on warming the car up before running. However, I think most people don't have a problem getting a car back to normal operating temps at the dyno. In reality people need to drive a certain distance to get to the dyno place. Letting the car sit for 1/2 hour while waiting to do a few runs isn't going to require a lot of time to get the operating temp back up.

What was great was on my E39 M5 would have the tach LED lights have an extended "yellow" line until oil temps reached normal. The car would need to be shut down a few hours for the yellow lights to come back.

Tom

Whilst we are on the subject, how accurate are engine dyno's. I presume the
DynoJet you mention is only a rolling road!

A DynoJet is indeed a rolling road. Most DynoJet's are configured the same so it is pretty accurate depiction of hp to the wheels (within the context of comparing to other Dynojets). As I mentioned before, I have dynoed on two DynoJets and the results were within 3 hp...which on my car represents a deviation of about .5%.

I asked previously a question about your tune but never received an answer. Did the tune change your shift points? I am asking just out of curiosity.

Tom

To be quite honest, I left him to it. These guys don't like people leaning over their shoulders, but next time I talk to him I will ask. I can't feel any difference gearbox wise, the car just feels more torquee, if there is such a word. When a manufacturer prints the spec I presume the power figures are taken from an engine dyno not a rolling road. Do you know what whp my 63 has stock,how much extra whp would roughly translate to 560 hp.I realize these figures are ball park!

A stock S63 did 415rwhp:

http://www.dragtimes.com/2009-Merced...phs-16625.html

The S63 and the SL63 have the same engine hp rating from the factory. However, the SL63 has the MCT transmission and a shorter (lighter) drive shaft. I would imagine that even though the engine is rated the same, the SL63 has a greater efficiency (less parasitic loss). So in theory the SL63 should produce more rwhp on a Dynojet. So if you look at it mathematically, the S63 (using SAE rated hp) is rated at 518hp at the flywheel and 415rwhp on a DynoJet...parasitic loss of around 20%. An SL63 may have only 18% parasitic loss which would translate to 425rwhp (518hp X (100%-18%)).

Also, the S63 was dynoed at DC Performance which is in CA. Here on the East Coast we have 93 octane readily available. I am not sure if the ECU would pull timing if it sensed knocking with weak CA 91 octane gas (99% of CA gas stations have a maximum 91 octane available). Just an FYI, 91 octane (AKI) is equivalent to 95 RON. 93 octane (AKI) is equivalent to about 98 RON.

So an SL63 may also pick up hp with better octane gas. So I would throw a range of 420rwhp to 430rwhp for an SL63 on a DynoJet.

I would say that an SL63 would have to make about 450-460rwhp to hit the theoretical 553hp SAE or 560PS mark.

Tom

You certainly know your stuff!
We have 99 octane at the pumps here, so if I take my 63 to a rolling road to measure whp then 460 would be quite good, but I seem not to trust them anymore so how do I know if it's over or under inflated
Believe me, and I have always said it as it is, if it was under I would still publish it, and no doubt upset all the 63 owners, as I did many moons ago with my 65. It turned out to be an oddball with no exclusive nappa leather and a S600 instrument cluster, I also found out it was a year at a dealers
before I purchased it.
I will certainly still take it.

Interesting. I'm glad this thread was on the first page... a friend took a ride in my E55 and became obsessed with it, and now he wants to buy it for his wife. I've been eyeing the SL600 for quite some time now, and I told him if I could find an SL600 w/ extended warranty (or buy an EW), that I'd sell him my E55.

Stock for stock (since it may be a while before I get a tune), how would you compare the SL600 to the E55?

After talking to my tuning guy, he also says a flywheel figure will be mostly inacurate, however he says some tuners do re mapping and other mods on an engine dyno, these will give accurate figures when transfered to a car.