I heard, and this maybe B.S., that someone at Harley let the patent on the Evo design expire. That's why S&S, and all the other engine companies came out with their own Evo clones. Now until that event, companies could make replacement parts, but not complete engines. So the MOCO decided to change it up so to keep the money rolling in.

 

Sorry, but that's truly an absurd supposition. You don't "let" a patent expire, it expires after a number of years.

The main force behind the twin cam development were pending government regulations: specifically noise and emissions. The majority of the design differences are to allow an air cooled engine to go as far as possible in meeting regulations while maintaining HD traditions.

 

Yes and no:

1. Patent protection for an engine would be in the form of a Utility Patent that lasts 20 yrs.
2. During that 20yr period, if the patent holder fails to pay maintenance fees, the patent expires.
3. Patents cannot be renewed after the 20 yrs.

But you are right: the Evo engine has been in production since 1984; it is reasonable to assume that the MoCo obtained a patent then, and the said patent would've expired in 2004 or the whereabouts.

 

Come on now vdop, you're being pretty modest here. Any Harley twinkie that is putting out 145HP/130 torque is a whole lot more than just a "little above average." That's at least double the HP of a stock 103" engine.

Mind if I ask you a few questions about your build? I know you had to bore your stock Harley cases in order to accommodate your build...just wondering if you used the stock crank, and if so, did you plug, weld, and true it? I imagine with all that HP, you really had to beef up the bottom end. Do you have any concerns about the stock Harley cases holding up to your build, after being bored?

Lastly, just curious if you put some kind of compression releases on the bike. My FXR has 10:1 compression, and I have a twin cam bagger with 10.5:1 compression, and I have manual compression releases on both of them, otherwise I'd be eating up batteries and starters left and right. I can't imagine yours being without them at 12:1 compression. No pinging on 89 octane...really?

 

S&S flywheels, welded and timken conversion. Cases are bored but not to the max. Not worried about the bottom end.

I'm using automatic compression releases. The static compression is high but the corrected compression with these cams isn't too crazy, 210psi on a gauge, it's all set up to work well together. It's got a very good tune. I keep the timing conservative in cruise range and it's nice and fat to keep it cool. Never pings and still has tons of part throttle power, very touchy at slow speeds. I pour the timing to it at wot and it loves it. It's strong at any rpm but over 4k it's serious business. Better know wtf you're doing if you're gonna grab a handful.

 

I prefer the evo.

 

I LOVE the Evo motor! I also love the power and speed of a twin cam! I tend to travel distances at times and do a bit of high speed touring. A simple Evo with a cam couldn't take what I dish out for extended periods of time. Yes,six speed transmission and all that. My twin cam ROCKS with a five speed and 95 kit and cams. Just my opinion.

 

I much rather have a petcock and choke than sit on the side of the road when the fuel pump quits. Only use the petcock when I hit reserve or store it longer than a month. Owned three twinkies and won't own a fourth. I'll ride my 98 WG until I can not longer lift it off the sidestand.

 

Love that...with you brother....

 

On any motor, the cylinder heads are the key to power, and I have to believe the Twin Cams are a superior design to the Evo heads.

I also think the Twin Cam is a lot better looking motor than the Evo, especially the rocker covers. Not that that should matter, but it kinda does.

Seems to me that the Twin Cam is a better design than the Evo, but built to a lower standard of quality.