JES_VFR

I'm 6 ft and have the MRA vario as well. I'll put just the touring on my second 5th gen as Its not going to be the big touring machine, Instead its going to be the commuter.

Okay, Did you cc the head to see how much your blending back the chamber periphery might have added? It wouldn't take much to add a couple of cc's and they will drop the CR pretty fast. I'd even bet a good de-shrouding and matching to the new bore would keep some of the bigger bore jobs from breaking 12:1.

Phil, I'm try to vet my calculations, how thick was the head gasket after compression?? I'm coming up with .799 mm and a negligible cc gain in the Head's chamber...

That's a great shot. It does beg the question. Since the heads are off the cases, so that they cylinders can be enlarged, why not have the edges of the combustion chamber "laid back" to meet the new cylinder bore? It would help the head's flow characteristics and add a few cc's to the chambers volume to help with the compression ratio... Just some rough calculations.. Using the stock bore & stroke, the stock CR and calculating the compression volume. Removing 1cc worth of metal from the chamber would drop the CR to 11.1 Does anyone know how the head gasket is?? Another thought, While the heads are off, has anyone considered o-ringing the cylinders? Or are we all thinking of using the MLS gaskets from Cometic?

Sorry if I'm asking questions that have been answered in this or the other threads, but I'm just getting back to this after last years crash. Finally got the '01 back and the autotune module is dead, so I have to do something about the tuning. Now I can't say I'm not shocked and surprised that the RB units can not do gear by gear on the VFR. The PCV can do it without the gear position sensor, they just tap into the Tach signal and the speed sensor and compare to some stored gear ranges and know the gear your in. Why can't the RB units do the same?? Also is the issue with the 5th gen's narrow band sensors not trimming fuel related to how seldom the 5th gen ECM is in closed loop mode? The 6th gens go into closed loop mode a lot more often to meet the later emissions standards.

Okay Sorry for the thread hijack, now that I've the correct info from the correct dealer in the US and will be visiting them in a couple of weeks back to the bore and stroke discussion... Wait, a 75 or 76 mm big bore just means you are boring the MMC liner out and then pressing in a sleeve against the MMC (not the aluminum block). That's what Dynamo Humm did for the 76mm bore of 870cc kit. If you want to go bigger than that just with a big bore, then you need to bore out all the MMC liner, right to the aluminum block and then sleeve the bores against that. iirc - someone here cut up a block and found the total thickness of MMC liners to be 4mm thickness,.. with 1mm steel sleeve, that takes us to 78mm and with a stock stroke would yield the 917cc. The next question is if you are using a Steel sleeve instead of the composite material in the liners, Can you safely bore more than 80mm removing aluminum from the actual block? I don't know that you would need adjustable cam sprocket carriers, just to get the cams to time properly. I do think it would put a strain on the chain tensioners and perhaps the guide's would need to be altered. But, since none of that is an option on the 5th gen engines, I would look to milling the chamber out to match the larger bore and head gasket opening, as well as starting with a dished piston. The dish in the piston will contribute to complete combustion and making torque, as well as managing the CR. I would put in a steel alloy sleeve with a ceramic coating all round to keep the heat in the cylinder. I'd also coat the chamber of the head and the exhaust ports

RapidBike only lists a #1 module for the 5th gen. Now Power Commander doesn't list a PC5 for the 5th gen either, but one for a Vtec bike works. I guess I need to contact RapidBike and see what they really have for the 5th gen... I'd love to have a tuner that will hold 2 maps per gear (maybe even front bank versus rear bank), including timing and a wide band tuner. That way I could run maps for two different fuels..

That's interesting, I have a pc5 on my 5th gen because it allows me to have fuel maps based on what gear I'm in. I'd love to be able to work with the timing, but I really don't want to give up the Gear by Gear. Maybe Rapid will release a unit that handled gear by gear soon

That's as big as you can go in the 782 block without sleeving the bores. If they also had the 870 kit if you were willing to do sleeves to support the Honda composite liners. Frankly I cant wait to see what can be done by boring out the entire liner and using a full thickness sleeve, that's the 916 territory.

That would be very interesting.. If you do buy him out, you will need move several of the parts from multi part fabrications to single construction pieces, maybe make them from different materials. But that is a different thread, unless you intend to sell it as part of a big bore kit....

Well I don't think it just applies to VFR's, I've always been that way, With cars, sportbikes and even things like lawnmowers. But I will say I don't just go for power, I start with suspension, brakes, weight, tuning and then end up really modifying the engine. I'm all in for the 916 with a complete spare engine to work with. In the mean time I've got plans for the brakes and suspension on both my 5th gen's

First Mohawk thanks for sending the Email to Brian. I thought I remembered him saying it would need sleeves, but it was so long ago and many hard drives in the past. So, I was right, bore out the MMC liners to their bottoms and install a steel sleeves. That along with the Cam gear drive means that there is a hard limit to the total range of piston travel, and any stroker will have to be created using shorter pistons. Now as you pointed out the 954 pistons are approximately 6mm shorter than the VFR pistons. 1mm oversize 954 pistons are out there so the 76mm is not impossible to come up with. Still adding 6mm of stroke?? That would be a lot of material to take off the rod journals of the crank in offset grinding, far too much in my opinion. But,... What about adding a little more stroke? Say 1.5mm more... That bumps your 848, to an 875 and the 870 to 898, heck even the stock 781 finally checks into the 800cc range at 806. 2mm more stroke the numbers are great, 848 to 884, 870 to 907. or better yet push it to 3mm. Now the 848 goes over the 900 mark and the 870 jumps to 925. Still you've got almost 3mm more clearance up from the bearing webs than you did with the stock VFR piston. Sure then the piston has to be dished to keep the compression ratio under control, but I'm sure between a bit a dish in the piston and bit of very light porting (basically just matching the perimeter of the chamber to new bore size) the CR can be kept street gas friendly.. So I guess the big question(s) for the folks at Falicon are What is the smallest you can 'safely' offest grind VFR rod journals and still use a standard VFR rod with an undersize bearing? What is the limit for welding on new new metal on the outside of the journals to offset grind the crank and use standard honda bearing sizes? Well you don't have the limitation of the cam gears, but you still have the limitations of the VFR block. You could run a thick head gasket to help a smidge with compression, but you would still have to use shorter pistons and you still have to deal with the stroking the crank.

Oh, Oh I know this one.... As a former RC51 owner I know this trick. The gears Bruce is referring to are called quieting gears (or silenceing gears) and maintain what is called a zero backlash drive in the cam gear drive. What they are is a spring loaded second gear that keeps pressure on the back side of the gear faces. That keep them quiet and relatively rattle free as well, but adds a bit more friction to cam gear drive. Removing it frees up the gears and they all spin much easier as well as removing a bit of weight ( 15 ounces of rotating weight on each cylinder of the RC51). Sure it allows a tiny bit of backlash (.015 degrees of play at the camshaft on the RC51) to occur any time you violently decelerate the engine, but how often does that really happen??? About the only downside on a Street bike is that the gear driven cams will now clatter quite a bit. On the already loud RC51, it sounds a lot like you somehow added a vented dry clutch. I don't now how much louder it would make the VFR sound, but I'm not rushing to remove them on my street bikes. But those that are thinking of racing, might want to do this "free" mod.

Yeah I want to know the cylinder to cylinder measurement, as well as the total depth to the cylinder liner. 870cc big bores have been done, I just don't know how to get in touch with the true source Brian Law.. I would think that either Brian worked out that 6mm MMC sleeve walls were still thick enough or He replaced them with them with tougher steel sleeves 6mm thick. What I'm thinking is what if someone was willing to bore the cases for sleeve larger than 88mm in diameter, say 92 mm? Even if you stay with 7mm walls (the allowed overbore thickness of the mmc liners) your talking about being able to fit 78mm pistons. That puts you over 917cc's. That's getting into a very over square engine. In fact it is so far oversquare, that I'm starting to think about the rods and a stroke increase again. Now with the information about length of the rods, and total length of the cylinders, a stroker kit could be put together with a crank and alternate length rods.