Intake Manifold: MPG increase?? - Page 2 - PeachParts Mercedes-Benz Forum

t walgamuth · #16 11-13-2012, 09:05 AM

A taller tire will increase the effective gear ratio, but if its heaver it will also raise center of gravity and make the car ride rougher.

I'll have to study to answer the question about what models had what gear ratios on your car. I know all the 123 gear ratios but not other models so much.

Silber Adler · #17 11-13-2012, 10:28 AM

I would agree that the K&N doesn't filter very well. I ran one on a motorcycle for some time and noticed the dust on the inside of the carburetor and on the clean side of the airbox.

For mileage, one thing I have found was to run the tire pressures high. How high? I run mine at the max rated pressure and still get even wear. Actually I would generally wear front tires out on the edges on all of my vehicles before I started bumping them up. I still have excellent control. They respond faster with less side wall flex.

The tires that came on my Merc are rated at 35 psi. They are some sort of bf good rich touring tires. I plan on putting on some tires rated at 51 psi before too much longer.

The down side is that you will have a rougher ride.

Gregory · #18 11-22-2012, 10:32 AM

Yesterday I got 3/4 the way to Reno and the car lost power at high speed. The change is instant. Wes going 85 mph, and suddenly it slowed to 65 at full throttle. I pulled over and had a look, seems like the whole top of the engine is oily, I had recently cleaned it at the spray wash.

After reading through a lot of threads here, my guess is the intake manifold gasket has blown and the boost is leaking. The car drives ok, but with no power at speed or going up hills.

Are new intake manifod bolts required to do the job right?

Gregory · #19 11-22-2012, 11:09 AM

Well I posted my theory too soon. I just went out and popped the hood, with the engine running to look for bubbles at the intake manifold. No bubbles. However I did notice a vacuum line that was partially off.

It goes to the middle of the intake manifold, on the drivers side. The line was slipped out of the rubber boot slightly, but still hanging on. I missed that when I inspected it by the side of the road yesterday.

The car is up to par for its name again, Zippy.

ngarover · #20 11-22-2012, 11:38 AM

I got 32 with my 85 sedan, new engine. I get 28-29 with the 85 TD and it's running perfect. I just don't see how you could mod it to gain 10+ more mpg per gallon. These are Highway miles, as I have a 1-1.5 hour commute to work in the car every day. I have thought about putting the 2.24 rear end in it since It's a flat trip to and fro, but worried about the effect it would have on the aging clutch due to it's lack of lockup.

Gregory · #21 11-22-2012, 12:08 PM

Since to odo is broken, I used an app on the smartphone to track distance travelled yesterday.

At 80 to 85 mph, into a 30 mph headwind the 190D turbo got 24.6 mpg. I filled the car in Winnemucca, NV, then about 10 miles later the problem happened, which ended up being a loose vac line.

Silber Adler · #22 11-22-2012, 12:59 PM

Here is a chart that shows what a 300sd might do. The 300D is a bit smaller but not as smooth aero wise. It might be similar.

According to an engineer friend of mine it means that it takes 20 kw of power at 2500 rpm and it is burning 300 grams of fuel per kw. or 6000 grams of fuel when running 2500 rpm. Say that is 55 mph (It is on my car.).

That means you can go 55 miles on 6kg of fuel. He told me that diesel weighs about .8kg per liter. In other words your are using 7.5liters of fuel to run 55 mph. Or about 27 mpg. If you go 3000 rpm you get about the same efficiency but you are needing 30kw of power.

He went on to say that by looking at the graph the car is geared too low for economy. I understand fairly well what he was saying but I looked at the graph for some time.

I am one of those who generally likes to conserve fuel.