You are absolutely right, I corrected my post above showing the correct placement of the O-Rings.

GRP now has their user manual posted on their site. Here is the link in case you haven't seen it.

GRP User Manual

Picked up a .21 GRP tonight, looks good. I want to pop a Ceramic rear bearing in it but cant find the bearing size anywhere.. Anyone know what the size is?

Also the porting isn't so hot, so I'll probably port, smooth, and taper the sleeve. The back of the crank could use a knife edge job too, its a bit blocky and heavy. Once thats done this baby should sing for about 11 minutes!


Rear Bearing Size....?

I've not had mine apart yet, but I'll bet the rear bearing is the same as the Ninja engine. Which is the same size as what goes in the V-Spec. Can't remember the size off the top of my head though...

Just remember once you start taking some weight off the crank, you're going to lose some torque...

smoothing the sleeve will not help the motor...exterior sleeve work adds zero power to these motors........... I would not touch the crank either........ my bet is you would lose HP not gain HP with the mods your propose.........Do not cut the sleeve, its a urban myth that sleeve mods add power !!!!

I always thought GRP where a bit rough on the cuts and machining.

they are somewhat rough the way they are cut... Very similar, if not identical to how my newest Sirio's are cut... The GRP sleeve and the Sirio sleeve look as if they were cut using the same machinery.....

The thing is where they are rough will not really affect performance, the key areas of the motor are machined just fine.... Most poeple look at the bottom of the ports and thing smoothing there will create better power, but the top of the port is much more critical, as when the piston first unshrouds the ports its the top of the port that gets opened first, by the time the piston hits BDC the crankcase has lost all its pressure and gas transfer has mostly stopped, most of the intake charge entered the chamber when the port was first opened and crankcase pressure at its highest......... GRP engines do look sloppy at the bottom of the port, but are well designed where it counts...the ports are nicely cut and well directioned, as well they have very good port timing............. Look into the exhaust port of a GRP mill and look how the ports are shaped and directioned, then you will see the real magic of these engines.......

I'm not going to argue with your advise, as I've only been modifying my own motors for about 3 years. I'm sure you know whats up more than I. However I'd like to run something by you guys on the porting.
Its my understanding that when a sleeve is ported, tapered, smoothed and such.. that this increases flow at higher RMP. Also when the fuel charge is thrown from the crank upwards onto the sleeve, that their is a certain amount deflection off the bottom of an un-tapered sleeve. That being said, doesn't the deflection cause an inefficiency? If that deflection of fuel-air was reduced and the ports had a smooth clear path up into the sleeve, wouldn't that increase efficiency?! If you remove the inefficiency's of the motor however minor, you should be able to slightly lean the motor and keep the same performance, thus increasing fuel mileage. Fuel efficiency is the only reason to port a motor in my opinion, as power really isn't increased much at all. Is that an urban legend? Also I get 9-10 minute runs on my RB's at 230 after my mods. Before the mods its 8-9min I've proven this over and over and over again.

One more thing... how does a lighter crank = less power? In every kind of racing, drag racing through motocross, kart, F1, Nascar...ect etc... a lighter crank increases throttle response and efficiency, as it takes less fuel to turn a lighter crank. I do know from my own experience that too light of a crank can effect how an engine idles. Not enough mass to keep it turning... Timing, I rarely mess with except on the WS73 as it needs a bit of a closing side increase because the duration is a bit off on those motors and graet power increases can be made.

I don't know... could all this be BS... maybe
Anyways, this GRP will probably be done as do my others, and I guarantee I'll smoke the stock guys out their.

Peace...

If you got it under control props to you, i had no idea you knew anything about modding..............my only to respond is because i see people mistakenly judge a motor by the fancy cuts on the sleeve, or in a Ninja's case lack of fancy cuts...... The Ninja is very advanced, you just got to know what to look for.....

Same thing here. I know from actual engine building, the weight of crank changes how fast it revs or makes power, but almost does nothing on the dyno as far as HP rating. Balancing is another aspect of the engine as it will climb RPM faster since it spends less effort wasted in drag or centrifical force to climb the power band. What you will see on a dyno is the power band smooth out compared to a jagged power band from a not so balanced engine that has certain orders of vibrations aligning at certain RPM's. Plus the throttle response feels more accurate when it balanced better. Add better fuel economy also. Right now, I know driver's who are after fuel economy, smooth power and accuracy. The engines are making enough power now, we just need to make use of it efficiently. Then again, we mostly run blue groove, dusty or loamy.

Cool, thanks guys.

Ok, since we are on this topic.. you guys have to see this crank mod I did on a C6BB. It was code named (Starfish) for the quad turbo cuts. Oh man I laugh so hard when I see this thing. I ran it until the crank pin was worn out, it was done after abut 16 gallons. Fastest motor I ever ran, but I wont be doing this to my GRP!!



Oh ya anyone know for sure about the rear bearing size on the GRP?

I think its like the older Ninja. 14x25.4x6mm. Very common, unless they've changed it like Novarossi likes to every year or so.

Thanks.

One other quick question... Turbo plugs??? $11.50-$12.00 a pop for GRP's! Anyone know of another brand that will fit properly at a better price? I held a Novarossi plug up to the GRP, and thats a no-go as the conical is different shape and length. I know turbo plugs last long but come on! Help! Where do you guys stock up on plugs for this engine?

Well if the GRP's are the same as the Ninja, I've always ran OD97T with great results...

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