Performance Modifications for SL600 - Benzworld.org - Mercedes-Benz Discussion Forum

Michael A. Comisky · 05-03-2007, 08:59 PM

I'm fishing for ideas concerning perfomance modifications of the SL600 with the only current restriction being that the motor is not opened. As you may be aware, perfomance parts are not readily obtainable, short of a major stroker engine package for $20,000+ The goal is to have an overall mix of handling and perfomance. I want the car to run to full potential, not emission bogged potential.
My car is a 1994, and has 87,000 miles with questionable plug wires, 02 sensors; and spark plugs. (I've not replaced these items yet, and some parts look really original) I intentionally looked for a 1994 or 1995 car because the value was less, emissions were pre-OBDII, and I was convinced that the car could be made to run better than all the literature I had read after driving three or four candidates.
I picked my car up in Beverly Hills from a heart surgeon last year -- then immediately drove it 1550 miles home. I was not satisified with the performance of the stock car, it seemed lethargic in responsiveness. I could sense and hear the car loafing -- at least it was not sharp in response. In particular, the transmission and gearing were too efficient. The engine began moving the car right off idle (ie. 600 rpm), so there was no snap when floored, even in first gear. Don't get me wrong, the car ran well, but did not have the right tone or responsiveness from the engine or driveline.
I've done the following to my 1994: 1) Split the airboxes open at the seams and removed the foam deadening material and ground out the reinforcing ribs to gain better added cfm and airflow, then reassembled them; 2) K&N airfilters; 3) eliminated the 1/4 inch honeycomb MAF screens on the intake side and replaced with regular thin screens like on the back of the MAF; 5) Removed the rear muffler and fabricated a stainless race muffler replacement with a three inch diameter outlet; 6) Modified the cats; 7) ECU perfomance chips; 8) New caps and rotors; 9) and a much bigger and wider set of tires and rims off a new CLS series. Best measured performance by G-Timer is: 4.95 0-60; 13.35 1/4 mile; 106mph trap speed. The car will not spin the tires unless power braked.
Future modifications include: plugs, wires, O2 sensors, stall converter (about 2000 rpm), elimination of the middle muffler, first gear enabled starts in drive, stiffer front springs, new front struts and new a-arm bushings. Every modification so far is reversible, and the original parts have been saved, and can be can be reinstalled.
Is there anything else other than possibly altering timing with off-set keys in the rotor assemblies to gain static advance (not sure if this will work with the computer controlled ignition), raising the compression to 11/1 with head milling and some porting; installing a device to quicken throttle response, and installing some type of limited slip parts in the rear differential for traction with the stall converter effectively lowering the gear ratio?
Any suggestions would be appreciated.
-- Thanks - Mike.

Jomzo · 05-04-2007, 05:36 AM

The sl is not a pure racecar. The 600 is made for people who want lot's of 'smooth' power & still have a lot of comfort. It is normal for an automatic transmission that it will move the car on idle, this is exactly done to make it smooth, it is meant not to snap when floored.

If U want to make it a racer then U should modify a lot about it, strip it completely down, only use components that a race car needs, remove electronics, replace/remove heavy stuff, add wings, lighter manual transmission and so on...

IMHO this is a bad idea, all the adbove will help but U will never get the real race performance out of it because of aerodynamics and weight.
Sure it'll be fast in straights but it's just too heavy to take fast corners like a real racecar.

Also most people will find it difficult to drive cause of the bumpy behaviour which is very tiresome so it will be very difficult to re-sell it later on. By adding all this modifications u will decrease the car's re-sell value while U have pumped a lot of money into it. Unless U are absolutely sure U are going to keep the car untill it dies I wouldn't do it.

If I had the money i'd buy a porsche to race and a sl for everyday use...

It all depends how for U wanna go, it's do-able but not an easy job.

I'd like to be proven wrong though ;-)

Good luck!

Michael A. Comisky · 05-04-2007, 09:49 AM

I appreciate your imput. A 911 Turbo is already in the future. I am not trying to make the SL600 a racer, but there are improvements that can be made. Also, I don't think resale value on my year will ever be that good, and I can convert back to original parts. In my part of the country, the roads are fairly straight so acceleration is king. I will post results as modifications are made.

Tech-Tune · 05-04-2007, 01:58 PM

Im rooting for you Michael. I know you can, and will find ways to make that beauty accelerate like a bat outa hell.

If I come across anything durring my hunt, I'll be sure to post it here for you.

In the meantime, Good Luck

tjobeid · 05-04-2007, 07:37 PM

Quote:

Originally Posted by Tech-Tune

Im rooting for you Michael. I know you can, and will find ways to make that beauty accelerate like a bat outa hell.

If I come across anything durring my hunt, I'll be sure to post it here for you.

In the meantime, Good Luck

i really would like to see more pis of your car man ,....

Tech-Tune · 05-04-2007, 08:11 PM

My next thread is going to be a picture thread.
Just as soon as I'm done doing some custom paint work under the hood.

SL600 V12 · 05-04-2007, 08:49 PM

Do yourself a favor and just get yourself the 911 Turbo now. I drove a genuine SL73, and even after that, I went with the 911 Turbo. If you want true high performance, there is just no place for all of that weight.

Also, you should NOT have removed those honeycombs. Thos honeycombs are aerodynamic devices that smooth out the airflow and form it into a specific pattern so that the MAF can accurately process it. If you end up with a tuning issue or check engine light in the future, I guarantee you that is where it will come from.

Good results otherwise. Take it to the track and see if your Gtech results are accurate.

D!CK's V12 · 06-20-2009, 10:53 PM

YouTube - SL600 vs 911 Carrera

Dont listen. 911 Carrera's are slow. Even when they are 1000lbs lighter. LOL

o_Anapodos... · 06-21-2009, 07:36 AM

post some pics of the mods you have done please (if taken)

chriswufgator · 06-21-2009, 07:50 AM

I had a stock 911 (996), and also a supercharged boxster. Both were slower than my stock SL600. Much slower. Which is why it boggles my mind that the "official" 0-60 figures are so much quicker for the 911, but in the real world it's really a noticeably slower car.

And compared to the nice cushy ride and interior of the Benz, both my Porsches were like driving a go-cart. Wind noise, rattly, very high levels of engine noise in the cabin. Honestly, totally disregard the advice about "if you want a performance car, then get a porsche". Been there, done that, and am far happier with my Benz.

And I wish we had found this thread earlier, because we could've saved the OP tons of money! All he needed was a 1st-gear start module, his problem wasn't lack of adequate power, it was that silly 2nd-gear start that the pre-1995's have. That was his performance problem.