dsb

I know the topic may have got you interested, but this thread is more questions than answers.

I curretnly have a slk55 with NO performance mods. I keep seeing more and more people getting performance upgrades including a supercharger, LSD, exhaust, headers, ECU, etc.

I am getting more involved in racing. I have already attended some AutoX. I plan on attending some track experiences which means I will be very aggressive on the car for much longer periods of time (ie 20min or more).

My question is this: The SLK already runs a high compression, what type of reliability issues do you cause by running these performance mods, especially the supercharger? I'd imagine that getting headers and exhaust would be less taxing on the car and possibly help its longevity?!

I don't know. What are your thoughts? If you plan to track this vehicle, should you not perform some of these mods?

ClayJ

If I were planning on AutoX with an SLK I would be far more concerned about the difference that track tires (and plus 1 lightweight wheels) would make in my times....

AMG_55

i would keep the 18in diameter but get much lighter wheels and semi slick tires, s/c will most likely hurt ur times

RSBSLK55

I put upgraded headers and CF airbox on mine. Gonna let the N/A engine breath. I respectively disagree with AMG_55. I think you would do better handling with 19's and light competition wheels.

Rob

slk55er

IMHO you are on the right track if your first priority is to attend a few autocross or high-performance driving schools. I get a chuckle with all the $$$ wasted on superchargers, stress bars, headers and even low-restriction air filters when the drivers are clueless WRT theory, techniques and implementation of such.

Here is a link to some basic charts that I've assembled in my 20 years of instructing:

http://home.earthlink.net/~hainesinutah/drschool/

but this is just a start. First spend your $$$ on yourself rather than on your current vehicle. Your training will last a lifetime, long after the supercharger is rusting in a junk yard.

To make your car go fast, spend it's driver to school.

dsb

Slk55er, I do plan to attend some classes in the future. However, it may be a little difficult because most tracks seem to require a rollbar for any convertible. I hope to find a place that only requires that I run with the top up and added safety like helmets, etc.

My main question in this thread was the stress placed on the engine with these performance modifications. Are you better off NOT getting a supercharger? Should you get headers? Those are the sort of questions I was trying to find answers to.

ClayJ

I have not yet in my life found a track that did not treat a MBZ folding hardtop as a hardtop. I think that the only time you might run into a rollbar/safety cage requirement would be in the higher speed classes in a sanctioned public road race or high speed run, or in an actual sanctioned racing activity (like SCCA for example).

RSBSLK55

SLK55er is absolutely correct. I've been to several driving school programs, including a three day racing school.What you learn is invaluable. The headers and airbox do help though.

Rob

AMG_55

i know that 18in wheels r better for grip, response etc... u think
i respectfully disagree w/ u.
there have been numerous tests performed by many publications and 18in wheels prove 2 b faster, and have better characteristics

vraa

Now you're being too vauge.

You can't just say 18's are better than 19's. There are a billion different variables that come into play.

If you're going to compare my BMW's 18's versus Vic55's 19" HRE C's, then obviously his 19's will prove to be a better rim depending on the car they are put on.

Some of the things you have to look for when you are buying a rim are the following things

1) Does the rim fit bolt pattern wise?
2) Does the rim fit with the tires I want? No rubbing?
3) How off will I be in the overall rolling diameter as compared to stock setup?
4) What is the weight of the wheel?
5) How strong is the wheel? What is it rated for?

There are plenty more things you should look for, but those are key points.

Questions 1 and 2 are no brainer. Question 3 is needed because you don't want to throw off your speedometer too much. Question 4 is needed to calculate rotational intertia, which affects acceleration and braking (to a very large extent). Wheels, tires, and braking components (and I think suspension) parts are considered unsprung weight. Unsprung weight taxes the abilities of the car I believe 4x more than regular weight. That is, for every 10lb's you can reduce unsprung, that's about 1-2hp you 'free' up.

Question 5 is needed because you need to know if the wheel was designed with the constraints of your car in mind. I can't put on HRE C series rims on my X5 because my car weighs too much and falls outside of the technical parameters of the HRE C Series.

AMG_55

i dont c where ur coming from

what im saying is that:
given same wheel same tire brand, a 18in wheel will perform better than a 19in.

the points u state r obvious, u need the right wheels for the car.

vraa

See once again there are many variables you fail to consider.
An 18 inch rim will have a larger sidewall to compensate for the lost rolling diameter which may decrease handling because the sidewall flexes. Rims don't flex.

I'm just saying that you can't establish the fact that 18's are better than 19's. It always depends.

AMG_55

of course u would need more tire on the 18, thats why its better purely from a performance perspective. the tire (little) flex helps the tire grip and the breakaway is a lot more predictable.

this has been established by numerous publications... i dunno what else to tell u.

on a larger car where u can run a 20 or a 19 the 19 will (much) more than likely be the better choice for performance.

trompazo

If you actually want to autocross this car, consider the following:

In stock class you can't change the diameter or width of the wheels. Lighttweight wheels would be very beneficial, but you would have to get them in the exact stock size.

If you want wider wheels, this would put you into ASP class, which will include modded 2006 Corvette Z06s, Vipers, porsche GT3s, 911 turbos, etc. In other words, you will get anihilated.

19" wheels are not even an option for autocross as Hoosier or Kumho don't make any R-Compound tires in 19" yet. If you are not running R compound tires, you will have no chance of being competitive

trompazo

I will likely take the SLK to a few autocross events this year just to see how it does. Autocross is all about handling and driver skill, although power is somewhat important.

In stock class, you will be up against the class dominating Honda S2000. Although we kill them in power, i think the Honda will have a significant edge in tight corners/slaloms/transistions and I don't think the SLK will be very competitive. But I may be proved wrong.

Hoosier does make some autocross tires that would fit the stock size wheels. I don't know of any company that sells a lightweight forged wheel in the stock size. CCW won't make one. Fiske might but I haven't checked. I'd just run some R compound tores on the stock rims and see how well the car does before you spend cash on expensive stock sized wheels on a car which may not be competitive.

dsb

I agree with you regarding the wheels/tires. To your point, there's not alot of options for lightweight 19" wheels. Also, since I'm just getting my 'show' wheels this week, I'd rather not buy another set. I am new to the track so my skills need to be improved before my car (the shoes don't make Jordan). If anything, I will get some competition tires for my stock wheels. I may go from 245/35 to 255/35 in the rear for just a bit more grip as well.

Back to the original question...

Is there really any adverse effects of taking a power mod'ed car (supercharger, headers, etc) and driving aggressively for extended periods of time?

trompazo

Of course, but it mainly depends on the tune.

I would never add forced induction without having a wideband 02 to monitor your Air/fuel ratio at all times, and have the ability to change fuel and timing curves on my own.

But I suspect most people who add SC to mercedes don't do this.

Then again, my power goals would probably be higher than most.

Bottomline is that the more power an engine makes, the more probe to failure it will be. COuld it last for a very long time? Yes, if it was tuned correctly it should be durable. Your tune has to be even more spot on as you make more power.

Yellow R1

Adding headers, exhaust, or an LSD does nothing to reliability. In fact, it will likely enhance it via lowering of underhood temps & allowing your engine to exhale better (not as much backpressure).

People may say (as one has) that adding power always decreases reliability. I disagree. Each case/car/modification is different. In some cases, reliability can be increased over stock via lighter weight components, more durable parts/hoses/clamps, better cooling, etc. Reducing weight, increasing cooling, & using higher performing parts can increase longetivity in many cases.

If you opt for a blower, I'd recommend Kleemann's due to the following:
1) light weight (replaces stock manifold & weight is not noticibly increased)
2) more efficient IC pump than the AMG unit used to support its blown 5.5L
3) 1 year warranty

As mentioned above, I'd also opt for the headers & exhaust as it reduces backpressure on the blower (although Kleemann's patented design mitigates this hot air coming back into the unit - its just another thing you can do if you are overly concerned).

The biggest reliability mod you can do if you run your car hard is to change the oil at least every 3k miles. You can also run a higher ratio of water (recomend distilled) to coolant as H2o has a higher thermal loading capability than coolant.

If you are still concerned about damaging the car, maybe get a dedicated track car & leave your SLK to more routine activities? Just my 2 cents.

See ya,
-Matt

trompazo

I agree headers/exhaust/LSD will have almost no effect on reliability.

My statement about adding power was more in line with the original question about adding a supercharger. Without supporting mods this will unquestionablly potentially lead to engine failure sooner.

If mods are taken to make the components stronger, then reliability can be enhanced. But hoses and clamps aint gonna cut it.

For a couple of my cars, the power output is 300% more than the stock engine. But to build something like this requires alot of other things than increased cooling.

CP forged pistons, pauter rods, Clevite bearings, balanced forged crank to 10,000rpm, Ductile Iron piston sleaves, much bigger fuel lines, injectors, an ECU that can read AFR and cut timing when it senses knock, ARP head studs, iron head gasket, boost activated alchohol injection, much bigger rad, getting your pistons custom made to your application to adjust the compression to your specs, etc. will increase reliability.

But I doubt the average guy slapping on a blower to a 11:1 compression mercedes with some generic ECU that is not tuneble will not increase reliability.

Yellow R1

Bingo - exactly my point. If supporting modifications accompany the "right" blower (ie Kleemann), I seriously doubt reliability will be adversly impacted. If it were, AMG would not be producing blown versions of the MBs powerplants.

BTW, I don't think "DSB" is an avg guy slapping on a blower with no tunable ECU. He is driving a $70k Mercedes, appears very educated, and is interested in obtaining some feedback on correct mods & associated impact on reliability whilst tracking his car. I think he is being proactive to ensure he does nothing to ruin his SLK under heavier driving conditions.

See ya,
-Matt

dsb

Thanks for the love, Matt.

trompazo

By tuneable ECU, I mean one that I can tune myself with my laptop in the car and datalogging.

I don't believe this exists for a mercedes.

Running someones generic program is substandard when adding forced induction. I've blown up too many engines to know that to be true.


Then again, In my forced induction cars I run crazy boost (over 30psi).

Running light boost (7psi) that these kits offermay be OK. But your power will be low (to my standards).

dsb

Thanks for all the feedback.

Although I won't be getting engine upgrades immediately, this info does really help. When the time is right, I'll start with the basics (exhaust, headers, ecu) then later into the superchager and lsd. I'll stick with Kleeman. 550-600 hp is good enough for me as is 7psi.

Trompazo, I appreciate your info but I'll never have the need to run 30psi nor 1100hp. This is my weekend/sun's out/occasional trackday car. Note, track day car is listed last. In that respect, maybe I am "the average guy." Nonetheless, I do appreciate your info as well.

Dan

trompazo

If thats the case, I's say get the LSD, headers, ECU and leave it at that.

The car will be more enjoyable on those occaissonaly track days without the supercharger. The more you can have the foot on the gas, the more fun it is. If you foot is on the brake most of the time, it's less enjoyable.