450 Catalytic converter question
 

I have a couple questions about my 1975 450 SL, I wanted to know if you can remove the catalytic converter and retrofit one further down the line in the exhaust to where it is on the later years? This would eliminate the excess heat generated by it being under the hood but still have the car pass emissions tests. Also, my battery is in my trunk and I thought the battery was not move to the trunk until 1978? Thanks for any advice you have.

You may have missed the Happy Birthday e-mail I sent you a few days ago, but I hope it was a happy one.

I think that you should go to www.timevalve.com, get their phone number and talk to them about this. They know everything about MB exhaust systems.

BTW - did you ever get your engine noise figured out?

The thought now is that the noise is from the catalytic converters going bad. On the 1975 450 SL, the catalytic converters are in the engine, mounted to the exhaust manifold. From this forum, I learned how to test them so that is the next step. Diagnosis! Wow! What a concept! If anyone has some insight on these catalytic converters, please post! They were only made like this for two years so there is not a lot of info about them. Thanks for the birthday wish! My car was supposed to be ready in time to celebrate but no such luck. I will be celebrating late this year.

Try contacting your states version of Bureau of Automotive repair. They will know what is legal. In California sometimes you can get a variance if parts are unavailable etc...

I got to drive my car today for the first time since April!!!! It is amazing what a difference a competent mechanic makes. It is not completely finished, but it is finally running and sounds better than it has since I've owned it. The cats have a hole in them so the engine is loud, but it is a deep throaty chuga-chuga-chuga sound. There is still a tick but not nearly as loud as it was and the engine still idles rough but does not have the violent shudders it used to. Tomorrow he is going to DIAGNOSE whether the tick is due to an oiling problem or an adjustment problem and figure out what part of the fuel system is making the engine idle rough. My car does not have to pass an emissions test since it is so old, will I cause any damage to the engine if I do not get the cats replaced right away? He said that the engine ran rich for so long it clogged up the cats and the built up pressure fron the engine exhaust eventually busted a hole in each one. I can also just take the cats off and have a straight pipe put in. That would also reduce the heat and therefore reduce the wear and tear on my enige. Does anyone have any experience with this? How would it affect my engine performance (power, gas milage, etc.)? thanks!

As I recall 1975 was the only year MB hung the cats right on the engine. Big disaster. Any slight richness in mixture and they would attempt to super nova. In 76 they went under the car. Since you car is no longer required to meet any requirements in Texas, I would suggest converting to a 1972 or 1973 exhaust system. You should be able to pick up manifolds and whatever you need at a wrecking yard. The prices should be reasonable, because there shouldn't be much demand for those items. The only demand for any parts from an SL of that vintage would be for sheetmetel parts for 380s and 560s and the doors can't even be used on 560s. You should be able to get engine and exhaust parts for cheap.

Good luck,
Peter

Will the exhaust manifolds from a '73 fit right on my engine or will they have to be retrofitted? What about just taking the catalytic converters out and putting in straight pipe?

Re: Cats
 

Hi princess

i seem to remember an old post one of the techs wrote that 1979 cats will work on this car.

I also have a 75 with the same problem.
If i can find the post i will forward it to you.

Razorman

An earlier exhaust system should just bolt up since the chassis is the same and the engine is the same M117. It would be more difficult to manufacture straight pipes since you would have to make them fit the manifolds somehow.

Peter

I did it!!
 

I have a '76 450SL... I had my cats removed and had bad manifolds too, so they were replaced and the appropriate piping was installed... so now I just have the rear muffler. Both 75 and 76 models had the cats under the hood... in 77 they moved to a single cat under the chassis. Go ahead and rip 'em off... they're far too expensive to consider replacing especially if you don't have to worry about passing emmissions... besides from what I hear, the jury is still out as far as wether or not they actually do much of anything.

Best of luck!!

I agree.

Why put catalytic converters back on the car when you don't need them anymore?

They restrict flow out of the tailpipe and lower power.

I'd pull them out and put on new exhaust manifolds and tail pipe without a cat.

CATs out, Pipes in
 

I live in a state not requiring CATs. I had them removed and straight pipes to the muffler installed. The mechanic that made them is an artist with pipes. Hooked them directly to the existing exhaust manifold. I definatly picked up some additional performance.
79 450 SLC (with 450 SEL engine)

Update
 

Thank you all for your advice! I am just going to take out the cats. This happened because I have a leak in the intake manifold gasket and the engine was running rich. Blew out both cats! Other than that, my car is running great finally! It is still loud with the cats the way they are but I can't wait until the weather clears up and I finally get to drive my car (after only a year and a half in the shop! Amazing what a difference a good mechanic makes!).:)