Back into Sprees and looking to build.....

Mattedroom · Post by **Mattedroom** » Thu Jul 17, 2008 9:35 am

I am not sure where the 5mm thing came from. I didn't really have any plans on making a big bore kit.

I would buy one of those mufflers too. For $100, that would save me lots of time.

Post by **noiseguy** » Thu Jul 17, 2008 10:40 am

Those suggestions are in that order for a reason... it's the order that I'd suggest in terms of ease and effectiveness.

I've done 1,2,3,5 myself. I have parts for 4 and 6 on the shelf, but I've been so busy over the past 2 years that I haven't had time to do much more than collect parts and information.

Post by **noiseguy** » Thu Jul 17, 2008 10:48 am

A lot of good points in here. How did you get the tight bends in the EMT? I hadn't though of using that material but it makes sense. I get worried about welding galvanized material though; fumes are toxic.

The EMT + the flanges would make the muffler less dependent on other parts. I got around this problem by using stock muffler downtubes.

I also agree with what you found on aftermarket pipes. At GM we used to dyno test some of the aftermarket exhaust systems to see what they were doing in terms of performance. Let's just say I have a lot less respect for aftermarket parts than I did b/f I worked there... a lot of bling and noise with no performance benefit to the buyer. Some actually made less power than stock.

keithw wrote: I went with making my own pipe from scratch to make sure it was correct for my engine. Taking one for another engine and adapting it should be better than stock but not necessarily the best. For head pipes I'm using 3/4" electrical emt. It's a pain to get the bent tight enough but the diameter is bigger than the stock pipe and matches the port fairly well. If I was going to adapt a pipe I would run the calculator to see what it thinks a good pipe would be then try to match it as closely as possible. Total length is critical. The tuned length varies about 500 rpm per inch. A couple of inches can make a big differance.

For those of us that want to make pipes, having prefabed flanges that bolt to the head would be great. Make the hole in the center stock size so you could either go with the stock size or open it up for larger pipe. Should be pretty simple to copy a stock one from the original pipe. If the price was reasonable I'd buy half a dozen. Cutting my own by hand is getting real old real fast.

Back when my friend was riding a dyno and designing tuned pipes they would get pipes from all the other makers for test. Some of the high dollar, nice looking pipes actually made less power than stock.

keithw

keithw · Post by **keithw** » Thu Jul 17, 2008 12:00 pm

Welding galvanized is an issue. I am very carefull to either sand it off or make darn sure to stay down wind. The head pipe length for a Spree is about 4 to 6 inches. Normally I go with about 4". I start with bending the emt with a conduit bender. This gets it almost tight enough. Then I make three cuts with a hack saw about half way through on the inside of the curve. Then bend it till the cuts close and cut them again. The cuts end up being two blade thicknesses wide. Bend till they close and weld together. Use a round file and smooth the welds on the inside for good flow. If you can find a shop that fabs hydraulic tubing for construction equipment and such they should be able to make about any bend you need. Most of the head pipes I've seen on aftermarket pipes are way too long for best performance. They end up being more of a low restriction muffler than a true tuned exhaust. Not that that is all bad. They do increase performance over stock but not as much as they could.

keithw

Post by **noiseguy** » Thu Jul 17, 2008 5:10 pm

I'll have to measure mine, I think the head tube was about 9", and I don't recall the effective length. I should probably measure all that stuff and post it up for reference.

I wonder if conduit-thickness mild steel pipe is available... this would save welding around galvanization. What's the wall thickness on that stuff?

I built a pipe with a "too long" runner (3-4" too long); the performance was better at low end but it didn't help get the engine up to 11K, like you said more of a noisy muffler.

Another option to cutting/bending cones is hydro-forming a pipe... have you seen the pics of guys that do this? They figure out what the cross-section should look like, then make 2 pieces that are 1/2 the diameter as you go along the cross-section. They then weld the edges. At one end they put in a closeable tap, the other gets a water hookup. They attach this to a 600 PSI water pump to it (plumbers use these), fill it with water and let out the air. The high-pressure water blows it up like a balloon. You weld on flanges and a silencer and you're ready to go. There are a couple of websites that talk through this procedure.

Since water's incompressible, there's no danger of an explosion (unlike air.) Water will just leak out if there's a gap.

keithw · Post by **keithw** » Thu Jul 17, 2008 6:12 pm

I'm sure that conduit size mild steel tube is available. The wall thickness is about .030" or so. I just grabbed a stick of conduit I had laying around. What the longer head pipe does is widens the power band and makes the peak hp lower. If you make the head pipe too short it gets really peaky and gets hard to ride because you are in and out of the power band in a narrow speed range. This isn't so bad when you have a number of gears like a motorcycle but with the Sprees single speed it's not so good. A little longer is better than too short.

Hydro forming is the ticket for production work. You just need to make and sell enough to pay for the tooling and setup.

keithw

re previous post, I stay upwind of welding galvanized.
kw

Post by **noiseguy** » Fri Jul 18, 2008 9:19 am

On my '84 Spree, the pipe would hit at about 15 MPH and stay strong up to 35 MPH. Takeoff wasn't great though, which is the downside to a single-speed transmission. With a regular muffler this bike struggles to maintain 28 MPH.

Equipment costs could probably be avoided if you knew where to borrow the stuff. Here's a vid of a guy forming an expansion chamber using a pressure washer. Not sure how he's getting the air out of the chamber beforehand... setups I've seen have a valve on the end to let out the air.

http://www.youtube.com/watch?v=I_Z3AIFSd60

keithw · Post by **keithw** » Fri Jul 18, 2008 11:14 am

He fabed it flat then blew it up. Pretty neat idea and saves on the tooling. Being flat there wouldn't be enough air inside to bother with. It would take a couple tries to get the bends right but once you had the pattern done it should go pretty quick.

keithw

Post by **noiseguy** » Fri Jul 18, 2008 12:34 pm

Exactly. There's no tooling per se, the exterior volume just forms up.

There are a couple of websites that talk about this in more detail in terms of how the design works. You can essentially lay out the pipe in cardboard, with widths equal 1/2 the circumference. Then you can cut the form at an angle and tape it back together to design the bends. I believe the tendency is for the inside curves to pull together further.

One nice thing is that your downtube can be automatically formed. You just need that flange.