Saturday, December 23, 2017

Biodiesel Sportster Land Speed Racer - Supercharger!

It's been three months since the last update...but you didn't think I was sitting around, did you? I've been welding, fabricating, and testing, all in the pursuit of straight-line speed. Here, just in time for Christmas, is the latest incarnation of the Biodiesel Sportster!

At Loring this past September, the Sportster maxed out at 86.5mph in the final pass. I'm confidant that we finally ironed out all the bugs, and any further improvements need to focus on the limitations of the stock naturally-aspirated engine. The engine is a 836cc v-twin by Kipor, rated for 20hp at 3600 rpm.

When dealing with a diesel engine, most upgrades for horsepower are pointless unless you correspondingly increase the air flow, either by super- or turbocharging. Fuel can only combust and produce horsepower in the presence of enough air. Once the intake air is used up, any extra fuel will just become smoke.

At first, I wasn't sure which method to use. There are numerous small turbo kits available, most with questionable quality and reliability. Regardless, I wasn't confidant that the engine's oil pump had spare capacity to feed a turbo as well as the crank. Alternatively, a supercharger builds lower boost pressure and consumes a bit more horsepower with the pulley system, but ultimately runs cooler and has a self-contained lubrication system. Eventually, I decided to use an AMR500 supercharger from a Japanese kei car.

I fabricated two brackets to suspend the supercharger on the left side of the bike, directly in front of the transmission primary. Then, I re-machined a pair of 4-inch V-belt pulleys from the hardware store to drive it.

The supercharger is rated at 500cc per 1 revolution (1000cc per 2 revs), and the engine displaces 836cc per 2 revolutions. Therefore, by using a 1:1 pulley ratio, the supercharger is providing 19.6% more air to the engine. Ignoring pumping and friction losses, this will allow the engine to produce about 4 more horsepower. In practice, it would probably be closer to 2.5-3hp. I will likely increase this later, but this is enough for testing purposes.

Next was the intake plenum, which I fabricated from 2inch steel piping.

The placement of the supercharge interfered with the original exhaust, so I welded a set of scrambler-style high pipes.


Finally, I had to increase the fueling to take advantage of the extra air. Information is limited for this engine, so I decided to open the governor housing to document the design and look for improvements. It's difficult to see through the small access hole, but after a few hours of tinkering, I drew this diagram:

- Lever "A" is the main pivot in the assembly. The governor pushes against it on the upper left, and it adjusts fuel on the bottom right.

- The throttle cable is attached to lever "B". Both pivot on the same shaft, and are connected by springs and direct contact as they rotate.

- The main spring to fight against the governor is attached to lever "B". There is a tiny spring attached between "A"and "B" that is too weak to have a anything to do with governing. I think it's just there to keep things held in place and prevent slapping.

- I noticed during examination that, when lever "B" is held at full throttle, lever "A" isn't held tight against it. The governor can push it back a bit before it comes to a rest against lever "B". This basically disables the upper 10-15% of throttle position at the injection pump, because there is nothing to hold it there against the governor.

- Lever "B" has a threaded hole that is missing some type of set screw. When at full throttle, without that set screw, the only spring fighting the governor for the top 15% is the tiny spring. Once lever "A" makes contact with lever "B", the main spring takes over.

To increase pump position and horsepower, I needed to purchase or fabricate a new set screw, then adjust it until there is no slop between the levers. Factory replacements are impossible to find, so I decided to make one. Unfortunately, it is a very unusual, and unavailable, thread (M14x1.0), so I had to special order threaded rod from China. Once it finally arrived (2.5 weeks of shipping!!), I made the screw.

Wednesday, September 13, 2017

Biodiesel Sportster Land Speed Racer - Loring Timing Association Sunday Pass (Video Post)

Onboard footage from one of the passes I made on Sunday. The weather was perfect and winds were favorable, and the bike managed an 86.5 mph pass.

Monday, September 11, 2017

Biodiesel Sportster Land Speed Racer - Loring Timing Association 2017

On Labor Day Weekend 2017, we once again drove to the great white north (almost) for the yearly pilgrimage of speed, cramped legs, road food, hotel beds, and surprisingly cold weather!

Joining this year was my extremely patient and understanding girlfriend Hannah, as well as great (and slightly crazy) friends Drew and Maggie.

Side note: Drew and Maggie rode 650 miles two-up on a Honda VFR800 to be there. They are the true heroes of the weekend, and I bravely salute them from  my heated truck cab.

Photos courtesy Maggie Rusch, Hannah Knight, and Myself.

After work on Wednesday, I picked Hannah up from the train station and drove directly to the Port Jefferson ferry. We were first on and off, and got the best seat in the house!

After spending the night with a friend outside of Boston, we headed north.

Mount Katahdin!

Haystack Mountain

We arrived in Presque Isle on Thursday night, and spent Friday going through registration and tech inspection at the track, settling into our hotel, and purchasing wool socks and gloves because of the "unseasonably cold" high-40's weather.  

By that evening, Drew and Maggie had arrived and we warmed our bones at a nearby pub.


By Saturday morning the weather had improved, and we arrived at the track and set up. We were able to make 5 runs during the day, and the bike got progressively faster with each pass as we worked out the bugs. We made several tuning changes to the transmission, but in reality most of the improvements were made by properly inflating the tires....

The final pass on Sunday morning was 86.5mph flat out, the class record, so we packed it in and began the long trek home.

My other favorite Maine tradition!!!

Wednesday, September 6, 2017

Honda CB500F Rebuild Part 8 - Carburetors And Exhaust

The final parts of the rebuild were the intake and exhaust systems. I prefer round slide carburetors to vacuum carburetors, so I purchased an incomplete set from eBay. I completely rebuilt them only to discover that Honda had they have a different center-to-center spacing then the engine I had installed.

Apparently, when Honda switched the CB650 from slides to vacuums, they changed the spacing of the cylinder head intake runners, rather than modify the carbs. I decided to disassemble my set, fabricate custom piping and brackets, modify the throttle and choke linkages, and respace them to match the head.

Disassembly Begins

Grinding clearance into the carb bodies

Custom crossover piping

Narrowing a factory fuel fitting

Drilling new holes in the throttle linkage

I modified a set of spacers from the later vacuum carbs to lock the rack together.

Finally, I fabricated a new exhaust system. An aftermarket 4 into 2 CB650 exhaust will not clear the footpegs on a CB500 frame, so I purchased several rotten sets of original CB650 pipes. A few weeks with a hacksaw and hand file, as well as a pair of stainless 2 to 1 pipe fittings, and the bike was complete!