Member Contributer Rush2112 Posted August 6, 2014 Member Contributer Share Posted August 6, 2014 I am targeting a 76mm bore and I guess (based on the above info from Mohawk and Rush - hey, that sounds like a wild west saloon?-) that I am looking for some stock Honda con-rods with a length of 99-99.5mm with a 36mm big end and a 17mm small end diameter. Am I missing anything else? What would that put the displacement at? 76mm x 52mm would give you a 944cc engine with 13.8:1 static compression ratio (I have a spreadsheet :)) That's based on the 99.5mm con-rod... I'd have to recalculate combustion chamber volume for a 4mm stroke and 99mm con-rod. Displacement would be the same but your CR would drop... BTW, the Rod/Stroke ratio would be 1.91 or 1.90 if your interested in those things... Link to comment Share on other sites More sharing options...
Member Contributer CornerCarver Posted August 6, 2014 Member Contributer Share Posted August 6, 2014 While the 944 wasn't the best Porsche ever released (far from it) I think this would be a perfect compromise for me. Link to comment Share on other sites More sharing options...
Member Contributer CornerCarver Posted August 7, 2014 Member Contributer Share Posted August 7, 2014 Thanks Rush.... was that 1.90 a good ratio from your earlier discussion? I cant find it at the moment. Link to comment Share on other sites More sharing options...
Member Contributer Rush2112 Posted August 7, 2014 Member Contributer Share Posted August 7, 2014 Thanks Rush.... was that 1.90 a good ratio from your earlier discussion? I cant find it at the moment. Stock VFR800 R/S ratio is 2.11... most modern Honda motorcycle multi-cylinder stock Rod/Stroke ratios I've calculated are around 2.0 +/- 0.1 The stock CBR929 is 1.94 Not going too low with the R/S ratio will keep us from causing too much lateral force and friction/wear on the cylinder wall. Another concern is the increased acceleration forces from the shorter rods and higher max piston speeds that will result from stroking this engine... The shorter the rods the faster the piston reaches max velocity. We'll need lighter pistons and rods to reduce inertial mass... maybe even Ti wrist pins (those can be bought off the shelf because of generic Honda parts bin sizes :). I'm making some spreadsheets to calculate max piston speeds and comparative forces involved for the different rod lengths and strokes and max rpms... I want to see if getting to 54mm stroke is doable in our motor... at 54mm stroke the R/S ratio is 1.82... John Britten was quoted at Daytona as saying "If Cosworth can use a rod ratio of 1.8, so can I"... and he proceeded to pull a custom rod out of his pocket... Most sources I've read don't go below R/S 1.8 for high rpm multi-cylinder motorcycle engines... car hot rodders go to 1.5 or even lower but they have different dynamics with larger bores and different Bore/Stroke ratios. That large 76mm bore will need some investigation to ensure the wider piston will have the stability with the increased stroke and shorter rod. The CBR954 goes with a 75mm bore and 54mm stroke but it has a 105mm con-rod... Link to comment Share on other sites More sharing options...
Member Contributer HighSideNZ Posted August 7, 2014 Member Contributer Share Posted August 7, 2014 Stroke to rod length ratio is pretty critical for engine life. When I built my VF750F based Superbike back in the '80s I was carefull to maintain the largest ratio possible and just measuring my spare Ti rod that I still have, the ratio was 2.32:1 This is based on a stroke length of 48.6mm and an eye to eye length for the rod of 113mm Now a standard VFR800 has a stroke of 48mm and a rod length of 102mm (rough measure with a rule) would give a ratio of 2.125:1 I get your feelings about shorter ratios, but the question I'd ask is, how often do you want to rebuild it. Shorter ratios are going to give the piston skirts hell, as well as increase the overall acceleration of the recipro parts. Just my 2 cents worth. Link to comment Share on other sites More sharing options...
Member Contributer Rush2112 Posted August 7, 2014 Member Contributer Share Posted August 7, 2014 Stroke to rod length ratio is pretty critical for engine life. When I built my VF750F based Superbike back in the '80s I was carefull to maintain the largest ratio possible and just measuring my spare Ti rod that I still have, the ratio was 2.32:1 This is based on a stroke length of 48.6mm and an eye to eye length for the rod of 113mm Now a standard VFR800 has a stroke of 48mm and a rod length of 102mm (rough measure with a rule) would give a ratio of 2.125:1 I get your feelings about shorter ratios, but the question I'd ask is, how often do you want to rebuild it. Shorter ratios are going to give the piston skirts hell, as well as increase the overall acceleration of the recipro parts. Just my 2 cents worth. I agree 100%... I'm trying to figure out what combinations would give similar forces to existing setups. I don't know how much higher we can move the wrist pin on the piston to maintain the rod length and keep a decent ratio... and the piston speeds will likely reduce the redline without lightweight parts so more $$$... I don't think 54mm stroke is doable... 52mmm might be a stretch... I'll have to see what the calcs show. Anyone have a 5th gen piston that they could accurately measure the distance from the wrist pin to the top edge of the piston? I don't have one handy that is not in an engine... Link to comment Share on other sites More sharing options...
Member Contributer Mohawk Posted August 7, 2014 Author Member Contributer Share Posted August 7, 2014 I got one, when you say top edge, do you above the top ring the "deck height" or the underside. Remember with your strokers you will need under piston clearance too & short rods do not make that any easier ! I'll do some measuring in a bit. Link to comment Share on other sites More sharing options...
Member Contributer Rush2112 Posted August 7, 2014 Member Contributer Share Posted August 7, 2014 I got one, when you say top edge, do you above the top ring the "deck height" or the underside. Remember with your strokers you will need under piston clearance too & short rods do not make that any easier ! I'll do some measuring in a bit. I was looking for above the top ring deck height... you are totally correct on the under piston clearance too. I'm looking to see how many mm we can move the wrist pin up and still have room for the rings and under piston clearance... will ask CP-Carillo or JE what they can make... Thanks for the info Link to comment Share on other sites More sharing options...
Member Contributer Mohawk Posted August 7, 2014 Author Member Contributer Share Posted August 7, 2014 OK here's the numbers. VFR800 std piston top of wrist pin to deck height = 14.00mm top of wrist pin to crown of piston = 14.80mm top of crown to bottom of skirt = 42.30mm CBR954 std piston top of wrist pin to deck height = 15.00mm top of wrist pin to crown of piston = NO CROWN deck is full height top of crown to bottom of skirt = 38.50mm Hope that helps Link to comment Share on other sites More sharing options...
Member Contributer Rush2112 Posted August 7, 2014 Member Contributer Share Posted August 7, 2014 OK here's the numbers. VFR800 std piston top of wrist pin to deck height = 14.00mm top of wrist pin to crown of piston = 14.80mm top of crown to bottom of skirt = 42.30mm CBR954 std piston top of wrist pin to deck height = 15.00mm top of wrist pin to crown of piston = NO CROWN deck is full height top of crown to bottom of skirt = 38.50mm Hope that helps It does... Thank you Mohawk! Link to comment Share on other sites More sharing options...
Member Contributer HighSideNZ Posted August 7, 2014 Member Contributer Share Posted August 7, 2014 You need to be careful moving the pin higher as the rocking moment on the piston will increase and the skirt will take a beating. Also, the between ring lands are pretty narrow now. I still come back to my earlier statement "How often do you want to rebuild" Link to comment Share on other sites More sharing options...
Member Contributer Rush2112 Posted August 7, 2014 Member Contributer Share Posted August 7, 2014 You need to be careful moving the pin higher as the rocking moment on the piston will increase and the skirt will take a beating. Also, the between ring lands are pretty narrow now. I still come back to my earlier statement "How often do you want to rebuild" I hear ya... My motor build is going in a track bike so... do i want it to grenade, no... if it doesn't last forever and it's fun while it lasted, I'm ok if the fun outweighs the effort... Do you think FSR forgings with the shorter wrist pin would allow tucking the pin a little higher (~2mm) without bothering the rings? Link to comment Share on other sites More sharing options...
Member Contributer HighSideNZ Posted August 7, 2014 Member Contributer Share Posted August 7, 2014 I suppose it is completely over to spend versus outcome. A forged piston would be the only way to go but you still need to try and keep the mass down. Short rods and high mass normally do not mix. Back to the acceleration issue. I really am not up with the play these days with what can be done with pistons as new materials and processes have made big differences in the last 15/20 years. Talk to some of the experts as you mentioned above. Link to comment Share on other sites More sharing options...
Member Contributer Rush2112 Posted August 7, 2014 Member Contributer Share Posted August 7, 2014 I suppose it is completely over to spend versus outcome. A forged piston would be the only way to go but you still need to try and keep the mass down. Short rods and high mass normally do not mix. Back to the acceleration issue. I really am not up with the play these days with what can be done with pistons as new materials and processes have made big differences in the last 15/20 years. Talk to some of the experts as you mentioned above. Thank you, Sir... I value and appreciate your input!!! Good luck with your build... I'm on the edge of my seat waiting to hear progress & results Link to comment Share on other sites More sharing options...
Member Contributer Rush2112 Posted August 14, 2014 Member Contributer Share Posted August 14, 2014 Thanks Rush.... was that 1.90 a good ratio from your earlier discussion? I cant find it at the moment. Stock VFR800 R/S ratio is 2.11... most modern Honda motorcycle multi-cylinder stock Rod/Stroke ratios I've calculated are around 2.0 +/- 0.1 The stock CBR929 is 1.94 Not going too low with the R/S ratio will keep us from causing too much lateral force and friction/wear on the cylinder wall. Another concern is the increased acceleration forces from the shorter rods and higher max piston speeds that will result from stroking this engine... The shorter the rods the faster the piston reaches max velocity. We'll need lighter pistons and rods to reduce inertial mass... maybe even Ti wrist pins (those can be bought off the shelf because of generic Honda parts bin sizes :). I'm making some spreadsheets to calculate max piston speeds and comparative forces involved for the different rod lengths and strokes and max rpms... I want to see if getting to 54mm stroke is doable in our motor... at 54mm stroke the R/S ratio is 1.82... John Britten was quoted at Daytona as saying "If Cosworth can use a rod ratio of 1.8, so can I"... and he proceeded to pull a custom rod out of his pocket... Most sources I've read don't go below R/S 1.8 for high rpm multi-cylinder motorcycle engines... car hot rodders go to 1.5 or even lower but they have different dynamics with larger bores and different Bore/Stroke ratios. That large 76mm bore will need some investigation to ensure the wider piston will have the stability with the increased stroke and shorter rod. The CBR954 goes with a 75mm bore and 54mm stroke but it has a 105mm con-rod... I found the trigonometry and calculus equations to do the calculations and made a spread sheet and table comparing piston velocities, acceleration, and max forces. The forces calculated are only for the acceleration of the piston and wrist pin and do not include the mass of the reciprocating portion of the connecting rod (I don't have that info).... At 11,750 rpms a stock (48mm stroke, 101.5mm con-rod) VFR800 engine piston has a mean piston speed of 18.8 m/sec and reaches a max velocity of 30.31 m/sec at ~77.6° BTDC & ~77.6° ATDC; max acceleration (change in speed) of 44,928.5 m/sec2 occurs at TDC created by a force of 10692.98 N (kg*m/sec2). At 11,750 rpms a stroked (52mm stroke, 99.5mm con-rod) VFR800 engine piston has a mean piston speed of 20.37 m/sec and reaches a max velocity of 33.01 m/sec at ~76.5° BTDC & ~76.5° ATDC; max acceleration (change in speed) of 49,650.88 m/sec2 occurs at TDC created by a force of 11816.91 N (kg*m/sec2). Stroking the engine to 52mm increases max piston velocity by 8.9% and max acceleration and force by 10.5%. The increased piston speed does not exceed those capable with good crank, rods, bolts, and forged pistons1. Reducing the piston+wrist pin weight from 238g to 215g would balance the forces associated with the piston acceleration so the stroked motor would match the stock motor. The reciprocating portion of a -2mm shorter connecting rod would also weigh less further reducing its contributions to the force. The physics work to be able to stroke this motor to 52mm. 1) 4009.8 feet/sec max mean piston speed for a 52mm stroked VFR800 engine at 11,750 rpm; reference max mean piston speeds are from the book, Performance Tuning in Theory and Practice, by A.G.Bell Link to comment Share on other sites More sharing options...
Member Contributer Rush2112 Posted August 17, 2014 Member Contributer Share Posted August 17, 2014 BTW... the 52mm stroked motor with stock 72mm cylinder produces a 847cc displacement with 12.48:1 static compression ratio and a 1.91 Rod/Stroke ratio... Link to comment Share on other sites More sharing options...
Member Contributer zupatun Posted August 17, 2014 Member Contributer Share Posted August 17, 2014 the displacement of the dynamo Humm kit was 837cc...slightly better! Link to comment Share on other sites More sharing options...
Member Contributer vfrcapn Posted August 17, 2014 Member Contributer Share Posted August 17, 2014 There were some comments a few months back about adjusting timing, for the 5G doesn't the old PC2 allow some timing adjustments out of the box? From the manual, never played with mine as the motor is stock. From what I read the later PCs eliminated this adjustment. Table 4 Ignition Adjustment for ignition timing is +4/-11 degrees. Timing is adjustable from 2,000 rpm to redline at all throttle positions. On street bikes with normal fuel, advancing the timing does little to improve power. It is possible on some models to achieve small gains as long as the highest octane fuel available is used. Great read though, nice to see all the engineering going in to this. Link to comment Share on other sites More sharing options...
JES_VFR Posted August 17, 2014 Share Posted August 17, 2014 the displacement of the dynamo Humm kit was 837cc...slightly better! 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. Link to comment Share on other sites More sharing options...
CandyRedRC46 Posted August 17, 2014 Share Posted August 17, 2014 There were some comments a few months back about adjusting timing, for the 5G doesn't the old PC2 allow some timing adjustments out of the box? From the manual, never played with mine as the motor is stock. From what I read the later PCs eliminated this adjustment. Table 4 Ignition Adjustment for ignition timing is +4/-11 degrees. Timing is adjustable from 2,000 rpm to redline at all throttle positions. On street bikes with normal fuel, advancing the timing does little to improve power. It is possible on some models to achieve small gains as long as the highest octane fuel available is used. Great read though, nice to see all the engineering going in to this. The 3.5 degree advanced ignition map that came with my rapid bike 2 was worth 8% more hp/tq in the midrange. It was fine on 90 octane, though I normally run 93. Link to comment Share on other sites More sharing options...
Member Contributer Rush2112 Posted August 17, 2014 Member Contributer Share Posted August 17, 2014 the displacement of the dynamo Humm kit was 837cc...slightly better! 837cc is a stock stroke with 74.5mm bore... 2.5mm overbored from the stock 72mm There were some comments a few months back about adjusting timing, for the 5G doesn't the old PC2 allow some timing adjustments out of the box? From the manual, never played with mine as the motor is stock. From what I read the later PCs eliminated this adjustment. Table 4 Ignition Adjustment for ignition timing is +4/-11 degrees. Timing is adjustable from 2,000 rpm to redline at all throttle positions. On street bikes with normal fuel, advancing the timing does little to improve power. It is possible on some models to achieve small gains as long as the highest octane fuel available is used. Great read though, nice to see all the engineering going in to this. The 3.5 degree advanced ignition map that came with my rapid bike 2 was worth 8% more hp/tq in the midrange. It was fine on 90 octane, though I normally run 93. What rpm range and throttle position did you add that ignition advance? I've looked at the pic of your 3D graph but I would like reference data points if possible. Thanks... Link to comment Share on other sites More sharing options...
CandyRedRC46 Posted August 17, 2014 Share Posted August 17, 2014 Post up the pic and I'll explain. I'm on mobile for a while. Link to comment Share on other sites More sharing options...
JES_VFR Posted August 17, 2014 Share Posted August 17, 2014 The 3.5 degree advanced ignition map that came with my rapid bike 2 was worth 8% more hp/tq in the midrange. It was fine on 90 octane, though I normally run 93. 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 Link to comment Share on other sites More sharing options...
Member Contributer Rush2112 Posted August 18, 2014 Member Contributer Share Posted August 18, 2014 The 3.5 degree advanced ignition map that came with my rapid bike 2 was worth 8% more hp/tq in the midrange. It was fine on 90 octane, though I normally run 93. 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 RapidBike Race allows 2 maps per cylinder per gear ... 48 maps total! You can switch between two settings with a switch, each setting allows map by cylinder and by gear with ignition adjustability... pretty sweet set-up!!! I can't wait to get my hands on mine!!!!!! Link to comment Share on other sites More sharing options...
CandyRedRC46 Posted August 18, 2014 Share Posted August 18, 2014 Plus one, even the lower end Rapid Bike Evo has map by gear ;) Link to comment Share on other sites More sharing options...
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