BSA B50 -500 APG Build

[wobblywalrus]

The air is thick on this side of the border during years divisible by four.  It increased your aero drag.  You will have better luck in 2013.

[Koncretekid]

I made an air box which is chronicled on the tech site under "helmholtz resonator".  Here is a picture of the finished box with 2 - 2" elbows connected to 1-1/2" pipes to the front of the bike. It's a little crude, being thin aluminum with lots of Wobbly's rivets, and reinforced with a mat of fiberglass and resin.  I dynoed (apparently not an actual word) it last Saturday at NRHS Performance in Longmont with little success.  First we ran it several pulls with the top of the airbox off and got 42.5 hp, down about a 1/2 hp from last year.  Then we cut the exhaust off from about 29" to 24" because I had lengthened it to get thru my new fairing.  We immediately gained 1-1/2 hp to just over 44 hp, which means I'll have to re-route the pipe and modify the exit thru the fairing, but that's doable.   Funny thing is that the power curve moved down about 500 rpm from last year.  Possibly thru a couple of rebuilds I have changed the lobe centers, which is easy to do with 5 different keyways and three different offset keys for the crank pinion which drives the cam gear.  Unfortunately, by this time the entrance spigot to the air box broke loose (but not off) from the airbox.  We then put the cover on the airbox and ran another pull.  We lost about 5 hp.  I then removed the 1-1/2" pipes to the front of the fairing leaving only the 2" elbows and tried again.  We only gained back about one hp, so I concluded the airbox was not going to work.  Perhaps too small (approx. 5" cubed.)  But the good news is that I gained 1-1/2 hp from how I ran at BUB this year.  I hope to get more dyno time before next August to try some different intake airhorns and possibly different exhaust combos. Other suggestions are welcome.
Tom

[Grandpa Jones]

Hi Tom,

Curious, are you running a megaphone or straight pipe exhaust? I've goofed
around with SR 500's but never had one on a dyno. Interested to see the
results of your testing.

Cheers,

Dave

[Cereal KLR]

In our youth while trying to make a megaphone "work" without dyno benefit, we were approached by an older gentleman that said it was simple. Paint the pipe inside and out with flat black and run it hard, wherever the white ring was, that is the optimum pipe length.

Can`t remember if we tried it or thought it was hooey, would be interesting to hear if it was tried.  

[wobblywalrus]

Tom, this is intake tuning made easy.  There are various intake harmonic lengths.  Some are better than others.  Use Pipemax to figure out a good length that will fit in the available space.  Make some intake manifolds this length, shorter, and longer in 1/2 inch increments.  Try them on the dyno to arrive at the optimum length.  Once this is figured, try different inlet bell edge configurations, such as sharp edged, 1/4 inch radius and 3/4 inch radius.  Recheck the tuned length.  It may change slightly if a different bell edge is used.  Once the intake length and bell shape are optimized you can connect an air box, your resonator, or a larger pipe to the bell.

[Old Scrambler]

Tom.....what Wobbly said....before you install the air-filter and plenum to the bell.  Your forced air induction may blow the lid off at 130 mph......and maybe something else close to your seat

Assuming you have fans in the dyno.....are the fans directing 130mph air directly at intake ducts?  Could you cover the box with an air-filter material?  Personally, I would just install that big K&N on the end of the intake duct (plenum) and not worry about more 'stuff' getting in the way of a good run.

I was told that the lenth of the exhaust pipe should be determined and then add the mega.  Also, the internal diameter of the pipe....especially the first few inches from the port....is most important.  Very interesting to see the increased HP with the shorter pipe.

[Koncretekid]

Dennis,
We blew the air sideways across the motor to keep it cool.  We didn't even attempt to force feed the intake ducts, because that would be a pretty uncontrollable variable.  I'm still toying with the idea of a much larger plenum with 2" ducts to the front with an enlargement near the front to incorporate filters.  Hopefully I'll get some more dyno time to try some longer and shorter exhausts and intake lengths. 

I'll try to post some jpegs of dyno runs but I don't know if they will post.  The latest one is somewhat confusing to me compared to last year because power drops off so much after 8000 rpm.  The lower line on this year's run is with the airbox covered, but with just the 2" silicone rubber elbows in place.

Finally, I have a new mechanic this year!

Tom

[Koncretekid]

Dyno runs

Sorry about the orientation.

[Koncretekid]

Whoops! I posted the wrong photo of my new helper, and I can't resize it small enough to add it to the last post, so here it is.

[Peter Jack]

Tom, you never know which one might take to being the helper. My daughter was always big on racing and motorcycles. She did a fair bit of riding herself until the three kids came along. You never know............. after the kids get a little older.

Pete

[hotrod]

I took the liberty of rotating the dyno plots for you.

Larry

[JustaRacer]

1.20 SAE correction?  Dang.  Well at least the jetting will good at 7500' DA.

[Koncretekid]

The elevation here is 5300 feet.

And Peter, they are grandchildren, of course!

And thanks, Larry.  Someday, maybe I'll figure that out too.

[hotrod]

1.20 SAE correction?  Dang.  Well at least the jetting will good at 7500' DA.

That is a typical correction for the Denver Metro area. SAE corrections here usually range from about 1.15 - 1.25 depending on temperature and barometer.

A 50 deg F day here has about the same real air density as Bonneville at about 85 deg F.

The one problem people run into is the SAE correction is fairly accurate for NA engines here, but turbocharged/blown engines the correction is about 2x too much. For turbocharged cars at this altitude you should cut the SAE correction in half (ie if the dyno wants to use a correction of 1.18, on a turbocharged setup the proper correction is closer to 1.09 at typical street car boost levels)

Larry

[DND]

Hi

Do you run the BFS a little richer on a air cooled engine so as not to hole a piston from being too lean, does the air cooled engine get hotter as you get down the course so i bit richer would be a safety feature to keep it in one piece.

Lots of dyno time in the past with water cooled engines. Just tuned my 4 stroke dirt bikes out on the fire roads

Thanks, Don