Looking at buying a 2009 C63 with a stage 3 Renntech kit installed. The car has 12k on the odometer and the upgrade was done at 8k. I think parts and labor came to over $13k. I see stock cars going for $48-50 with this mileage. I got the dealer down to $53k, sound fair?

What does the RT stage 3 kit consist of?

The kit consist of Carbon fiber airbox, ECU flash, Short tube headers and something they call a Sound pipe. I believe its a special pipe that takes place of
the resonators. The upgrade boosts the horsepower to 550.

The renntech mods are worth zero $$ especially if bought from a dealer. Should have nothing to do with the price of the car.

53K sounds reasonable.
Ask them if the car still has warranty, even with the Renntech mods.

With Renntech you only pay for the name. Sound pipes alone are around $2,400!
They do make some great products though, just overpriced.

That statement has no logic. Mods may have no value to you, but they may have value to someone. Typically, expect to pay 50 cents on the dollar for modifications if you really want them.

If anything a modded car is worth less than a non modded car.

Being that Renntech is a highly reputable company I would think that their products would have significant value to the right buyer.

Key word is right buyer. If a Mercedes dealer has this they just want to sell it mods don't matter. You'd expect to see modded cars for sale on forums as 99% of buyers would want stock. The only thing the renntech name carries is a high price tag.

Other than the tune, I think the only thing worthy is the airbox. The Renntech shorties, IIRC, only adds a few HP (less than Kleemann K2) since they are more like PLM manifolds and they retain the same choke point (opening to stock primary cats). The soundpipe is an H-pipe that replaces the secondary cats. You are better off getting MBH's X-pipe for a lot less $$.

I see. Sounds like some cool mods. I'm sure the car would be fast.

I do find it ironic that a dealer may be charging a bit more for the car because it is modded considering if you were trading it in, they would most likely not pay you more for the mods.

I agree for the most part. Some mods can add some value. But, not these RT mods; at least not for the majority of buyers.

I would think some very expensive wheels could add some value. Maybe KW coilovers. Perhaps a C/F hood if the stock hood is also available. But, generally, as it sounds like you know, power making mods do not typically add any value.

Mods like these might be the perfect reason for a buyer to want to pay a bit more for this car; that is, if the buyer was planning on installing mods like these at some point. In that case, this is a great deal. I mean, RT airboxes work (as has been proven) and they cost a pretty penny, so that alone could warrant a slight premium for the car's purchase price.

I believe you are correct. I've spoken with some car dealers about this; some have even shown me a list of recent auction prices and the more stock the car is, the better (for auction prices).

Since you mentioned other mods it does have a set of mesh 3 piece 19" Modulare Forged wheels. The problem I saw with these is the clearcoat is peeling and looks like the wheels would need refinishing. Other than that the car is a 10.

Good point. I know that some northeast US MB dealers install Renntech and one told me that it was factory authorized and thus the MB warranty stayed in force. Who did the install?

Don't know about used cars with the new car warranty based on time mileage.

I'd subtract for the dodgy wheels. Wheel and tire problems suck and are time sinks, possibly dangerous.

On a used car the dealer will not pay you extra for your trade in with mods, but the dealer will talk you into paying more for a modded vehicle. Ask for a warranty contract with the mods, even if you like the mods act like you dont, if it has rims say that the rid is harsh and will return it to stock. Then tell him the cost it will run you to return it to stock, use that amount toward a discounted price. Have him tell the manager that you like the car but not the mods. That is how I handle business.

Mods are typically "for the owner" and any future resale will only result in pennies on the dollar (much better to return to stock and sell parts separately). I believe in making the car "yours", but don't expect to see a return upon selling the car. However, the mods sure can be fun......