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!

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

[delcrossv]

Hi Rex,

We're going with a carb.

We're going ethanol  for a number of reasons- we're in Illinois so it's available everywhere, it's easier on the parts, and e98 is pretty cheap. You get a little stoich advantage with methanol, but charge cooling (really important for an air cooled V engine)is better with corn squeeze so it's a wash IMO.

[Stan Back]

I was wondering the same thing.  But I don't even know enuf of what you're saying to doubt it.

So, I'll go along with your explanation.  Keep us informed and after a month (year?) or two, I may be able to understand it.

I'm not being sarcastic.  I know when someone knows a lot more than I do on a certain subject -- and after a while I get to know something I didn't know (or thought of) before.  Keep us informed on your quest, please. 

[delcrossv]

No worries Stan. 

Just to make sure I checked using the calculators on Wallace's and got 239, So close enough. 

I'll keep everyone apprised as things get done . '24 is probably too aggressive a target especially figuring out a new fuel. 2025  definitely.

I'm sort of worried about what class this will fit in as the engine will not fit into an un-modified Sportster frame (too tall) so I have to raise the backbone. I'd also would really like a longer swingarm. I can keep the rest of it "stock".

[sabat]

You can change the steering head angle, but you can't change the frame perimeter within the Modified class. The A-PF record is 195, so maybe try to cram it in there, or find a stock Harley frame it will fit into.

For power estimation, is there a drag class that is close to your specs? I'm not a Harley guy, but I think AHDRA has a 100" normally aspirated alcohol class. You could check their 1/4 mile trap speeds to see what's possible. 

[salt27]

I'm sort of worried about what class this will fit in as the engine will not fit into an un-modified Sportster frame (too tall) so I have to raise the backbone. I'd also would really like a longer swingarm. I can keep the rest of it "stock".

In modified you are allowed a 10% increase in wheelbase, so you can do a longer swingarm.
Make sure you have documentation listing the factory wheelbase.

As Sabat stated, if you raise the backbone you will be in "A" class, the good news to that is you would no longer be restrained on wheelbase.

  Don

[Stainless1]

I know there might have been discussion on this before.... but does the S&S engine meet the requirements of frame and engine from the same manufacturer...
You might want to get a written answer from the motorcycle chair for your log book. 

[delcrossv]

You can change the steering head angle, but you can't change the frame perimeter within the Modified class. The A-PF record is 195, so maybe try to cram it in there, or find a stock Harley frame it will fit into.

For power estimation, is there a drag class that is close to your specs? I'm not a Harley guy, but I think AHDRA has a 100" normally aspirated alcohol class. You could check their 1/4 mile trap speeds to see what's possible.

Good to know. Yes AHDRA has the "Super Modified" Class 104 cid max, gas or alcohol. Talked to the sponsor so around 200 hp on alcohol, 160+mph in the 1/4 so with different gearing it's believable.

So, it does not have to be a Sportster frame? Just any stock Harley frame?

[delcrossv]

I know there might have been discussion on this before.... but does the S&S engine meet the requirements of frame and engine from the same manufacturer...
You might want to get a written answer from the motorcycle chair for your log book. 

Motorcycle Chair? SCTA?

[Stainless1]

The best start for building for Bonneville is get a rulebook and read it over and over. 
PM sent...

[delcrossv]

The best start for building for Bonneville is get a rulebook and read it over and over. 
PM sent...

Awesome! Thank you!