Author Topic: 100 C.I. Displacement  (Read 912 times)

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Offline WhipLash96

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100 C.I. Displacement
« on: October 29, 2019, 12:25:30 AM »
What is available out there to make my Sportster a 100 C.I. fire breathing monster? I did a soft search and it doesn't look like there's much available. It looks like I will have to bore the case to accept the 4" stroke and cylinders. What do you all got? :pop:
Thanks,
Whip

Offline Johnwesley

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Re: 100 C.I. Displacement
« Reply #1 on: October 29, 2019, 07:02:11 AM »

Offline aswracing

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Re: 100 C.I. Displacement
« Reply #2 on: October 29, 2019, 07:50:27 AM »
What is available out there to make my Sportster a 100 C.I. fire breathing monster? I did a soft search and it doesn't look like there's much available. It looks like I will have to bore the case to accept the 4" stroke and cylinders. What do you all got? :pop:

From a practical point of view, a 3.875" bore is the biggest that can be supported by a stock crankcase. That's 90ci when combined with the stock 3.813 stroke and stock 6.926 rods. The combination comes out stock height with an acceptable piston skirt.

You can certainly stroke it as well, if you're willing to deal with the issues of a taller motor (frame mods, custom exhaust, wider intake manifold, etc). S&S offers a 4-5/16 stroke crank and 7.113 rods to match. That combination comes out 5/16" taller than stock, and Axtell can make the cylinders you'd need. At 3.813 bore it comes out to 98ci and at 3.875 bore it comes out to 102ci. But you don't have much skirt left. That crank and rod combo is really made for their 3.625 bore 89ci kit.

You can of course go with even longer rods and taller cylinders to get some skirt, but now the motor height problem just keeps getting worse.

Also keep in mind that the stock crankcase is really weakened by boring to the limit like this. They like to crack on the right hand side, from the inner cylinder studs down to the timing plug hole. Cylinder construction has an effect on their strength, though. If you go with an aluminum cylinder, I wouldn't push it past about 120hp. With a cast iron cylinder, we don't typically see issues with them cracking until we're north of about 140hp. But no guarantees.

The SB100 uses the "Special Application" (SA) crankcase, which relocates the cam box outboard 1/2" to allow a bigger bolt pattern for the cylinders. There's a longer pinion shaft to match. The standard 4" bore/4" stroke/7.113 rod combination comes out a little taller than stock. It'll still fit in the stock frame, but you have to pull the motor to get the rocker boxes off. And the pistons don't have much skirt. It's not a long-life motor by any means.
« Last Edit: October 29, 2019, 07:54:51 AM by aswracing »

Offline WhipLash96

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Re: 100 C.I. Displacement
« Reply #3 on: November 02, 2019, 05:18:33 AM »
What is available out there to make my Sportster a 100 C.I. fire breathing monster? I did a soft search and it doesn't look like there's much available. It looks like I will have to bore the case to accept the 4" stroke and cylinders. What do you all got? :pop:

From a practical point of view, a 3.875" bore is the biggest that can be supported by a stock crankcase. That's 90ci when combined with the stock 3.813 stroke and stock 6.926 rods. The combination comes out stock height with an acceptable piston skirt.

You can certainly stroke it as well, if you're willing to deal with the issues of a taller motor (frame mods, custom exhaust, wider intake manifold, etc). S&S offers a 4-5/16 stroke crank and 7.113 rods to match. That combination comes out 5/16" taller than stock, and Axtell can make the cylinders you'd need. At 3.813 bore it comes out to 98ci and at 3.875 bore it comes out to 102ci. But you don't have much skirt left. That crank and rod combo is really made for their 3.625 bore 89ci kit.

You can of course go with even longer rods and taller cylinders to get some skirt, but now the motor height problem just keeps getting worse.

Also keep in mind that the stock crankcase is really weakened by boring to the limit like this. They like to crack on the right hand side, from the inner cylinder studs down to the timing plug hole. Cylinder construction has an effect on their strength, though. If you go with an aluminum cylinder, I wouldn't push it past about 120hp. With a cast iron cylinder, we don't typically see issues with them cracking until we're north of about 140hp. But no guarantees.

The SB100 uses the "Special Application" (SA) crankcase, which relocates the cam box outboard 1/2" to allow a bigger bolt pattern for the cylinders. There's a longer pinion shaft to match. The standard 4" bore/4" stroke/7.113 rod combination comes out a little taller than stock. It'll still fit in the stock frame, but you have to pull the motor to get the rocker boxes off. And the pistons don't have much skirt. It's not a long-life motor by any means.

Yeah I'm not interested in altering the frame. Lots to think about. Thank You Aaron.
Thanks,
Whip

Offline sfmichael

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Re: 100 C.I. Displacement
« Reply #4 on: March 12, 2020, 08:09:56 PM »
Here she is ready to bolt in with much better cases that stock.

https://www.sscycle.com/products/sb100-complete-assembled-engine-for-1986-03-hd-sportster-models/

I clicked the link to check it out and peed a lil bit...$$$$$$$$  :dgust:
   :hyst:
Colorado Springs, CO.

Offline Panzer

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Re: 100 C.I. Displacement
« Reply #5 on: March 13, 2020, 06:57:16 PM »

10K................ouch, like BIG OUCH!!
You'll always be my best friend because you know to much.

Offline Hillside Motorcycle

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Re: 100 C.I. Displacement
« Reply #6 on: March 19, 2020, 04:16:36 AM »
A 107" can be had also.
Freinds of ours had the #1 AHDRA plate years ago with one of our dual-B Cross Ram set ups.
That engine produced 182 hp, 144 ft/lbs....in a 525 bike/rider total class weight.
Ran 8.61/152.
Larger cubes can be had also.
Otto Knowbetter's business rules;
1) Mind yours, 2) Stay out of mine.