Stock Exhaust

This is turning out to be something of a reverse order listing of what I've done but I found the pics from when I originally discovered the stock double wall exhaust configuration. I believe the inside pipe was 1.33" ID so the 1" I've replaced it with should lower the efficient range of exhaust tuning/ engine operating RPM. I believe that if the entire engine's intake and exhaust passage ways could be resized for below 4,000 RPM operation it would yield significant FE gains. Unfortunately this would be quite difficult to do so maybe the next best idea would be to take an engine that was made in different displacements and swap the heads with the smallest ports onto a larger displacement block, this isn't possible with the 1.0 metro engine though. Most engines made today can rev to and produce peak power at 6,000 plus RPMs which means all the ports/ intake/ exhaust passages and cam profiles are sized much too large for low RPM operation, which is where the motor operates for the vast majority of the time. I'm rambling now...

Exhaust size

I used the calculator here to evaluate not only what the engine might need but what the pipe I had would like. The first box is optimized for engine size and RPM while the second box is more generalized and considers engine HP.

First is what the engine would like @3600 RPMs which is 60MPH in the car and the upper end of speeds I routinely travel. As you can see the 1" ID conduit I chose is still over sized because it recommends 1" OD with 0.0625 wall thickness (16 Ga), which would be 7/8" ID.

Second is what RPM level the 1.75" ID pipe would support with the same size engine. This is about 10,000 RPMs higher than I ever get to.

Third is the HP level that the 1.75" ID pipe would support. This is about 100 HP more than I have.

Finally the engine displacement that the 1.75" pipe would be optimized for at 3600 RPMs. The engine is a 1.0 liter 3 cylinder, I could run 4 of them through that size pipe for what I am doing.

So you can see I've been running a pipe that was 3 to 4+ times too large for my engine and operating conditions. I don't have any numbers yet but the Instantaneous FE reading on my MPGuino are at least as good as or slightly better with the smaller pipe, so I certainly haven't lost anything.

Smaller Exhaust Tubing

One of the first modifications I made to the metro was removing the inner part of its stock double wall exhaust pipe that was stock from the manifold to the catalytic converter (about 13" long). I wasn't really intending to focus on MPGs at the time so I thought it would be good to have a very low restriction exhaust for better power. In hindsight it was a mistake, a 1.0 liter engine just doesn't need a 1-3/4" exhaust pipe (that's the size the remaining stock outer tubing was). Driving the car with the large exhaust I could feel how the sweet spot (when the motor really ran best) was way above the normal operating RPM range so I decided to put some smaller tubing back in place. After a doing some research on several websites I settled on 1" ID tubing which worked out well since I had some 1" EMT (conduit) laying around and a bender to bend it with too. Here are some pics comparing the difference between the old and new pipes.

Kammback progress

Didn't get it quite done but made a lot of progress. Somehow the angle is now 17 degrees, not sure what happened but I think it will be OK since the roof in front of the hatch is 10 degrees already. Still have the trickiest part left, the corners, should be able to finish it up tomorrow. The sides were left long until the corners are completed then they will be trimmed. The sides are aluminum so I think I'm going to polish them instead of painting, I'll paint all the steel parts though.

Updated pics of front airdam

It scraped too much and since I lowered the car it was going to be even worse so I had to shorten it up some. Paint doesn't stick well to galvanized metal so I just took it off, I'll get some self etching primer and re paint it eventually...if I don't make a complete new front for it before then.

Kammback begins

The beginnings of a Kamm back extension for my Metro, this is going to be a (hopefully) bigger and better permanent version of the cardboard prototype. The angle is 15 degrees and as shown here it's 36" wide. It will have smoked plexiglass for the flat sections seen here and sheet-metal will enclose the rest. The original glass will be removed before construction progresses much further. It's been raining for the last 2 days so hopefully tomorrow I can get this finished.

The scrap masonite panel on the bottom is just for mock-up, it will be plexiglass when finished.