Bonneville Salt Flats Discussion > Build Diaries
100" alky Sportster
delcrossv:
At Stainless' suggestion, I'm going to keep a build diary for this.
Oldest son has an '08 XL that had a lay down with some front end damage so we figured it would be a good time to do an engine build and associated frame mods with the idea of running the bike at Speed Week / USFRA in what is looking like 2025.
New engine started life as a "kinda" SB100 which we picked up as parts. We're keeping the square 4" x 4" bore and stroke.
Came with STD dual carb heads, but testing showed they wouldn't flow more than 250cfm even at .700 lift.
Note the pocketing and lack of squish
The rear cylinder was scored due to a button failure and I wanted longer skirts than stock SB100 pistons so I called Dan at Axtell for taller ductile cylinders.
Since the bolt pattern was open, we decided to modify Milwaukee 8 heads to match Sporty cam geometry. Also since we're designing the engine for 8000 rpm WOT it's a lot easier to move 4 little valves .570 than 2 big valves .700+
Flywheel spread is an issue so when I ordered the rods from Carrillo, I went longer (7.440) and a 1.500 big end- like an XR. But XR rods are narrower so I was able to find a XL width 1.500 crankpin
Stock sportster pin
XR pin
The S&S pin we're using. Drive side is welded
delcrossv:
Decided to keep ignition simple so we're going with Morris Magneto. Picked up a older ironhead cam cover off the bay which we're machining to get the oilways to line up.
Case is machined for an alternator which is good as a generator would simply explode at that rpm.
I'm drawing a reed valve that will go where the generator shaft would to help evacuate the cam box. Cases already have a reed between the crankcase and sump so between the two it should be well ventilated. Hope I won't need a catch can.
I have a gas Super D carb and an extended bowl but will need to convert it to ethanol. Planning on about 14:1 static compression which should be fine with E98 (or "good" E85)
sabat:
Best of luck with the build. It looks like the record is 180mph in M-PF 1650, is that your target? How much power do you think you can make? -Dean
delcrossv:
Hi Dean-
That's the hope.
Here's how I'm figuring it from first principles as I have no good models to work from :
At 8000 rpm the engine will draw about 238 cfm of air. At STP, that's 19.21 lbs/min. Running e98 at 8:1 ( little rich) means the engine will take 2.40 lbs/min of ETOH. that's .36 gal/min. Dividing by 60 gives gal/sec. Multiply by energy density of ETOH (~76000 Btu/gal) gives 462.76 Btu/sec. Convert Btu/sec to HP gives 655 hp @ 100% efficiency. If only! :-D :-D :-D
Figure 45% thermal efficiency (gets a little something from charge cooling) gives about 294 hp- less friction (WAG) losses puts it around 250 or so.. Like an alky drag bike.
So going conservative, better than 200 hp back of the envelope or thereabouts.
Make sense?
We lose 2 psia due to altitude so if a forward facing air scoop is allowed under Nat. Asp.,I can get back toward those sea level numbers.
Rex Schimmer:
Wow! what an engine project. I know absolutely nothing about Harleys but any two cylinder, vee configured engine that turns 8000 has got to be interesting. I like your method to estimating the hp. Why not just run methanol instead of E98?Are you planning to run a carb or injection?
Rex
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