Hello. This is the first time joining a forum. I am getting ready to build an engine for a 2003 RC. I am trying to nfind out if any one out there knows what materials the internals are made of. For example, are the rods, pistons and crank cast or forged? I'm also trying to find out if the exhaust valves are made of stainless. And also, does anyone make good hardcore rods for this bike. Thanks to all that can help me with these questions. Thanks a million and ride safe.

Dan Kyle racing could prob get you all the internals for this engine.
One of the members " Subsailor" could tell you what things are made from.

Thanks a lot. That should help. i appreciate your time.

The pistons are cast, the crank is forged, the rods are forged and carburized.
Both intake and exhaust are typical steel valve material, not stainless or titanium.

The HRC WSBK spec bike used titanium valves, forged pistons, but used the stock rods.
Carrillo makes rods for the RC51, and are works of art, but way pricey.

Thanks again guys. you have been very helpful. It looks like the only thing I have to get would be forged pistons. I called Ross Pistons and they said they could make me a set of 8.5:1 for $101 apiece. Pretty cheap for a custom forged piston. Figured I would throw that out there if anyone on here is ever looking for custom pistons. Is there any companies that make stainless valves for this bike? Once again, thanks for the time taken to help out the RC newbie. These things are 100% wicked.

Not too many companies made parts for RC51 as it wasn't sold in such large numbers as their I-4 bikes to warrant tooling.
You might be able to find someone who's willing, like Manley.

Why wound't you go with hi compression pistons in the order of 10:1 or 11.5:1? Most current Hi power vee engines are running those pressure levels.
Can't these engines take the extra pressure and heat?

Do these engine typically run hot?
I see where people are doing radiator mods to extra cooling.

I would think that Honda chose 10.8:1 as a compromise that could operate with 91 octane non-leaded fuel.
The reason that today's v-twins such as Ducati 1098/1198, or KTM RC8/R can run fine on non-leaded fuel with higher compression ratios is due to extremely careful cylinder head/piston design coupled with more advanced ignition and fuel injection systems.
Could Honda do likewise with today's technology? Absolutely.
Their RC51 race bikes ran 12.8:1 compression.

I don't think these engines run any hotter than others on average. The use of two radiators mounted on the sides rather than a large slab in front may make then a bit inefficient in traffic, but once rolling they flow air with no problem.
This summer, the warmest my engine got to was 220 deg. F, and it quickly cooled down to 209 once the fans ran a short while.

Someone told me that removing the right radiator fan actual made the bike run cooler because that side pulls hot air from across the engine to blow through the radiator. That doesn't make any sense to me. Even hot ambient air drawn across the engine is cooler than 220 degree water so there should still be some benificial cooling. He said it was a common modification on the RC51's.
Ever heard of that?

I've seen after market carbon fiber fan shrouds for these bikes and sometimes they remove the side radiators and install a large front radiator. I get the impression they run hot and I'm worried about buying one. I don't know anything about the Rc51's.

i don't know if anyone here has used this builder --- but this is where i'm going to get my porting done --- he has all the numbers to back him up --- if U check out his full mods for his motors --- he can build U a 160hp rc51


http://www.hordpower.com/index.php?main_page=product_info&cPath=3_31&products_id=209

The important question to ask is, how reliable is that 160 HP engine?
The WSBK RC51's put out 185 HP, but had to be rebuilt every 3300 Kms (that was from Colin Edwards).
Also a critical component of the engine is the cams.
The cast cams don't last long if they've been modified by welding and regrinding.
Hord's site shows several pieces of that successful but brief test.
Why Honda chose this I'll never know. The RC30 and RC45 used steel rather than cast iron for their cams.
On the plus side, I read and old article where they tore down Nicki Haydens RC51 engine after running the Daytona 200 and there was virtually no wear. So she's a tough old war pony.

yea SubSailor --- a 160HP motor is a handgranade --- that's why i'm just going for a port job

A good port job (and Hord does a good job) will add a few more ponies.
The JE 12.8:1 pistons combined with stock cylinder heads average out to 11.5:1 compression.
That should be good for 93 octane gas. The torque and therefore HP should increase a bit.

Hord is a great builder and will rework your heads nice. From the dyno sheets I've seen a port & polish is worth about as much as a tuned snorkel & airbox. If you got the cash do it. I agree that the cams are definitely the weak spot. If you could score some billets then you'd be good to go.

What's wrong with the OEM cams? What is the weak spot?

How much HP does the airbox and snorkel add?



Horde is a great builder and will rework your heads nice. From the dyno sheets I've seen a port & polish is worth about as much as a tuned snorkel & airbox. If you got the cash do it. I agree that the cams are definitely the week spot. If you could score some billets then you'd be good to go.

What's wrong with the OEM cams? What is the weak spot?

How much HP does the airbox and snorkel add?

As sub said they're cast iron. Meaning they're not very strong. You can upgrade the cams to billet steel ones by Moriwaki and I think they're might be 1 or 2 other manufacturers of them. Actually I don't know if Mori even makes them anymore. You can still find them around though just gotta look hard.

The box and snorkel by itself won't do much. You have to get a custom tune to benefit from those. I've seen gains of 8+ hp it just depends on your supporting mods. After adding mine I gained alittle over 4hp. Another guy on here that goes by Defender he gained over 5hp I believe and posted his dyno sheet.

There's one dude in NZ that makes billet cams for the RC51, but they're like over $1800 for a complete set, plus he needs the OEM gears to mate with the shafts.
You would think that the cam companies that make cams for dirt bikes and street bikes would be onto this since they already have the machinery in place, but the RC51 is no longer in the spotlight.
Too bad, as this would be a great mod to go with a great engine (along with springs, retainers, etc).

I have a buddy that will port my heads. Anyone have experience with porting without cams? Maybe shaving the heads a little to bump up compression.

I have a buddy that will port my heads. Anyone have experience with porting without cams? Maybe shaving the heads a little to bump up compression.

No can do milling the heads.
Remember the RC51 uses gear driven cams.
Milling the heads would cause incorrect gear tooth mesh and wear out or damage the gears.