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103" to 107"

22K views 71 replies 23 participants last post by  dozer23 
#1 ·
Can you bore a 103" to 107" or are you best to buy 107" cylinders? it seems to me there are a lot of venders selling 107" cylinders with piston kit. Is there any differences between the kits?
 
#51 ·
110 is the most you can go without case boring. I went 113 and make 125/131 effortless power 10.2:1 and my mileage (cruising) is about 1/8 tank more than my wife's 103 per fill up. I agree 103 to 107 isn't much. Big valves, jacked compression and big cams make power but big inchers IMO make more reliable power.
 
#4 ·
4 cubic inches isn't really much of a big deal. With the proper cams, compression, heads, exhaust, and tuning, you'll see somewhere around 120/120 and you'll have several thousand dollars invested in your engine. You'll have a dyno sheet you can be proud of, and you'll have a Road Glide that's somewhat faster than stock Road Glides. But it's still a 900 pound bike with lousy aerodynamics, and it's still comparatively slow when comparing to other motorcycles.

You can do a good Stage 1 for about a grand; less if you troll the Classifieds. The performance increase from that to a built-out 107 will be noticeable, but just ain't worth it to me.
 
#14 ·
No sour apples here, just a shot of reality. 120/120 from a 107 is going to mean that it's making more power to the right hand side of the graph, which means you're going to have to work it to see that. No big deal, but it's something to be aware of. And while it may be "fun-er", you need to decide if that little bit more fun is worth several thousand dollars. Especially knowing that even with that money spent, you're still going to be slower than most other non-Harley motorcycles.

I'm not saying this to be a downer. I've spent a fortune on motor work with one of the best engine builders in the country. My Night Train rips......For a 600 pound bike. And it gets embarrassed by any decent rider on a 600cc crotch rocket. I did the whole "compression and cam" thing on a CVO 110 (.30 Cometic and Andrews 57 with a big TB and a great tune). Yes, I could tell it wasn't stock anymore, and yes, I could see the benefit on the dyno sheet (and this wasn't a happy dyno like some others use), but it wasn't eye-opening by any stretch.

You want to have your Harley be more fun? Get a good Stage 1. Get yourself a pair of Ohlins shocks, throw a pair of Intiminators in the forks, and get some good EBC HH brake pads.
 
#6 ·
We were on of the first shops in the country to start boring the OEM cylinder to the 3.937" bore size in 2006.
Our proprietary kits come with a complete Cometic gasket set, cylinders are bored/torque honed/plateau honed, ring end gaps are set, and installed on the pistons, in either flatop or 4cc domes.
Still only $600.00
We also have 107" combos with cams, w/o head work starting at $998.00.
BTW, ALL machine work stays in house, here. :)
Scott
 
#8 ·
Just stick with the 103 and install a good cam. The cam will wake up the bike and you can run it like that for a long time if you want. The 106 or 107 will be a good upgrade when you decide to freshen the engine but it's not worth doing it until that time comes.
 
#18 ·
Have you guys not seen the hp/tq dyno graphs from fuel moto's 107 kit? They are impressive. My 103 with exhaust/breather/cams/fuel pump/dyno tune put down 84 hp 101 tq at 5k feet elevation. 107 kit is doing 115 hp 120 tq. That is pretty substantial for the 2k. Sure you can do stage 1 for 1k used but i wanted specific headers/mufflers/breather, my stage 2 was almost 3k. The 107 kit from fuel moto is nothing to sneeze at, it puts down more power than CVO 110 motors with cams. 117/120/124 motors can be built to be crazy high hp but they are substantially more money. 107 is good bang for buck.
 
#19 ·
Black Hills Ken, in Rockaway, NJ, just finished a tune on a 107" we built for a client in Albertson, NY.
119 hp, 118 ft/lbs, sae, on a "honest", repeat "honest" dyno, with lower gearing, in not the best air quality.
That was with our Stage III Super-Tour Cylinder Heads.
Hits 100 ft/lbs at just about 2500 rpms, and finally "curls" at about 6300 rpms.
Mid 120's square with our Stage IV Heads with several different cams is not a problem.
Not a big hurdle tp establish this power here, as we've had 107" engines over 20 years ago, making those numbers.
All depends on what the client wants.
Scott
 
#20 ·
Really the head work isn't going to produce much more torque and it would be a waste of good money. Head work will give you 3 to 5 ft lbs of torque and for the cost it isn't that much bang for the buck.
Just do a good cam which will get you around 110+ ft lbs of torque and pocket the rest of your money until you want to go with a 120 or 124 engine.
A 103 with 110+ ft lbs of torque is a good dependable touring bike and will give you miles of smiles.
 
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#22 ·
If you look at dyno sheets of similar 103 builds you will see that head work will only give your bike 3 to 5 ft lbs of rear wheel torque and for the cost of doing the heads it isn't that much of a gain for the money spent. You won't even feel the difference when riding the bike.
 
#23 ·
Agreed. If everything's apart and you're making massive changes, that's one thing. Otherwise....

From both an absolute power standpoint and a seat-of-the-pants, bang-for-the-buck standpoint, the best thing you can do to a Harley motor is a good Stage 1. Anything you do afterwards will cost more money and give you less of a return. Sure, you might get an additional 10 horsepower from cam "X", but how much difference is that going to make when you're surrounding it with at least 1,100 pounds of bike and rider? And are you willing to spin the motor above 5,000rpm to feel it?

Your money, your bike. Just saying that you're talking about dumping thousands of dollars into trying to make more power in an engine that traces its design roots back to WWII, that's in a motorcycle that weighs nearly a half ton.
 
#24 ·
I say this all the time. I have built bikes to the max and borderline worrying about long rides. On my latest bike, 16 RGS, I did the D&D Fatcat, Andrews 57H cam ($203) and a dyno tune with direct link, $400. It now runs with about 100 hp and 110-113 tq., gets 42 mpg and runs close to my 98" that has had everything done to it $5000 in the engine along. This bike runs better than any bike I have built seat of the pants versus dollar spent of any of them. I love it.
 
#25 ·
103" to 107"

It all depends in the end as what it takes to trip your trigger or float your boat. My 2008 RG I dumped a good chunk of change into it because I had to have a hotrod. Seeing how I also like do long trips I was reminded that with all that I did to the motor I would also end up sacrificing reliability on those trips.

So ended up buying 2009 RG CVO and just added comfort mods like apes, road zeppelin seat, Madstad & Avon grips. Promised the wife I would leave the motor alone at least until it needs to be replaced. So far two trips and the damn thing goes into limp mode twice on each one. So not sure I'm happy with that promise now. lol
 
#26 ·
Just sayin' that 10hp and 10b-ft at the peak is about the best you're going to get from a cam (over a Stage 1). And sure, the area below the peak will probably look better too. Assuming equal talent behind the bars, that's about a bike length, maybe two, at the end of a 1/4 mile. If that 20 feet or so is worth your money, then have at it.

I ride with a guy who's spent a fortune on his CVO engine. I had no problem at all keeping up with him in the mountains with my Stage 1 103 in my '10 FLHTK. I couldn't pass him, but he couldn't shake me. I rode with another guy in Arkansas that went nuts with his build, and given a long enough straightaway, he could inch past my Stage 1 CVO, but we were both over 100mph.

Oddly, both of their motors are broken.

Just sayin'.....
 
#29 ·
Nice #'s Frank but your talking about a big bore kit that has more compression and with the cams and headwork that cost $2500.
Just using stock pistons and compression with a good cam and mild head work the engine will not produce those #'s.
Wouldn't it be better to save the $2500 and put it towards a Drago's 124 if the OP wanted a real HP/torque increase?
 
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