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  #1  
Old 01-21-2015, 12:29 PM
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Squeezing a little more power?

Hello people I own a 1975 mercedes w115 230.4, I know it's not built to be a power house but is there any cheap and cheerful performance mods I can do to help the engine run better and/or even squeeze abit more power out?

Thanks

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Old 01-21-2015, 01:25 PM
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First, I would try to bring it back to factory spec. It's amazing how time and miles shave off performance, and at such a slow rate the owners aren't aware. Consider getting a baseline dyno done.

If the expense of that step doesn't drain the bank account, then you may want to consider subtle changes to the exhaust system to improve exhaust flow.

However, I have found that in 20+ year old cars, a suspension refresh results in the perception of increased performance. Not from "stoplight to stoplight" but having the confidence and feedback that allows you to corner faster.
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Old 01-21-2015, 01:48 PM
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Those stromberg carbs are great when they are working, and awful when they aren't. Make sure your carb is doing everything it should.

If you're in the US, your car will have some annoying solenoids and emissions related stuff attached to the carb. Make sure all of those relays and solenoids are working as they should.

Make sure you've got proper non-resistor plugs in it, and quality set of wires.

Make sure you've got all the power you started with before you go looking for more.

The way the M115 intake and exhaust manifolds bolt together, I think it would be tough to improve on the exhaust without extensive work. I have a spare 190SL header and it will bolt up to the M115, but it will not clear the frame rail in a W115.
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Old 01-21-2015, 01:57 PM
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Mercedes did not leave a lot of hp "on the table" for owner to unleash, certainly not inexpensively. I have often told owners . . . want to go fast? Okay, but it's going to be cheaper to buy a newer used car than it will be to make the older one a full second faster to 60 mph.
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Old 01-23-2015, 06:38 PM
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thanks for the reply lads, I'm not after huge power just to free up Abit of power really or in fact bring back lost power! The carb apparently was cleaned and reset just before I purchased the car. Is there any direct replacement exhaust/intake manifold that would fit and be a decent upgrade? Or air filters or anything like that? Also to answer the question above I have no idea what plugs are in there but should I get some specific ones? Thanks
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Old 01-25-2015, 12:43 PM
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The easiest way to improve performance on almost any engine is to develop a more aggressive spark advance map. OE maps are "lazy", i.e. the spark advances slowly with increasing revs. This is to keep the engine out of detonation in worst cast conditions. Emission controlled engines are even more lazy to generate high EGT, which promotes oxidation reactions in the exhaust system.

I don't know the architecture of your spark advance system, but typically on pre-'80 engines the centrifugal advance is just a set of flyweights and springs inside the distributor, and installing lighter springs will bring full centrifugal advance in earlier.

On the M103 engine family there is a resistor that plugs into a wiring harness pigtail that determines the rate of advance with engine revs. Simply removing the resistor will provide the most aggressive map. Most of the benefit is in the lower rev range where you spend most of your time, and you can experiement around with different initial timing settings to increase the total WOT advance.

Start by finding the OE spec for your spark advance map, then use a dial back timing light to measure it on the car.

On my 190E 2.6 five-speed removing the resistor considerably increased low end torque. Prior to the change fifth was unuseable below 45 MPH. Now I can drop it into fifth at 35. Around town fuel mileage increased by well over ten percent, but highway mileage is about the same. IIRC total WOT advance is 32 at 3200, but it comes in quicker in the 1200-2500 range. Initial advance on M103s is not adjustabable.

If you search R16/1 under my handle there is a lot more information on the benefits of a more aggressive spark advance map.

Don't waste your money on air filters or other bolt-on aftermarket pieces that claim "more power". Most of it is just unsubstantiated marketing hype. Lower restriction exhaust systems can improve top end power assuming the OE system is restrcitive, but I think most OE MB exhaust systems are relatively low restriction, even though they are very quiet, and many aftermarket systems can be unpleasantly loud inside the car.

The mid-seventies saw some of the lowest power ratings of the post war era due to manufacturers struggling to meet rapidly tightening emission standards. The 1975 Corvette base 350 CID engine was strangled down to 165 net HP due to the use of a single restrictive catalytic converter. The same basic internal engine configuration in '74 was rated at 195 with the full dual exhaust system and no catalyst. That's a 15 percent loss due to increased exhaust parasitic pumping power. My 1975 Cosworth Vega was strangled down to 110 net HP due to both the restrictive catalyst and a poorly designed exhaust system. With a modern low restriction catalyst and better design exhaust system they make about 140 net with the meager 8.2:1 compression ratio on regular unleaded fuel. That's a 27 percent increase with a proper exhaust system.

The most effective way to increase top end power on most engines (assuming a low restriction exhaust system) is to massage the head ports for better flow efficiency, but that's a pretty big job. The best time to do this is when the engine needs an overhaul.

Last edited by Duke2.6; 01-25-2015 at 01:06 PM.
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Old 01-25-2015, 04:03 PM
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Ali:

Do you have a silk purse factory near you? Ask those folks about a rework of your M115 ear.
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  #8  
Old 01-26-2015, 07:45 AM
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Quote:
Originally Posted by Frank Reiner View Post
Ali:

Do you have a silk purse factory near you? Ask those folks about a rework of your M115 ear.
Now now Frank!

(sell him a K&N filter and the magpie effect will take over => shiny after market always makes it feel faster!)

@OP see post #3
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  #9  
Old 01-26-2015, 12:31 PM
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Quote:
Originally Posted by Stretch View Post

(sell him a K&N filter and the magpie effect will take over => shiny after market always makes it feel faster!)


MG Triumph Saab Volvo Zenith Stromberg CD150 150CD Carb K N Air Filter New | eBay

It's even a bolt on kit! That's got to unleash many, many horsepowers. As it sucks in flaming hot air off your exhaust manifold.
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  #10  
Old 01-26-2015, 04:27 PM
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Thank you for your genuine posts lads been a big help


Quote:
Originally Posted by Frank Reiner View Post
Ali:

Do you have a silk purse factory near you? Ask those folks about a rework of your M115 ear.
Haha just because I don't about these particular cars doesn't mean I don't know about cars mate, I'm not asking how to add 6000000bhp just asked what's the best way to free power or add a few. I've had plenty of cars and built Afew of my own track cars. Not boasting just tryna show you I'm not a noob so please don't talk to me like I'm one

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