Member Contributer Madsen Posted January 10, 2016 Member Contributer Share Posted January 10, 2016 Hi. How is the best way to raising compression ratio a littel bit on my 5´th gen. VFR800? I am getting the cyllinderhead ported and the camshaft retimed, and I would like to raise the compression ratio to maybe 12:1 Link to comment Share on other sites More sharing options...
Member Contributer CornerCarver Posted January 10, 2016 Member Contributer Share Posted January 10, 2016 Not easy to do with the gear driven cams. Possibly finding a replacement piston with a dome that increases compression would be easier than messing with the GDC carriers. If you do it yourself pay attention to valve interference. Link to comment Share on other sites More sharing options...
Member Contributer Rush2112 Posted January 10, 2016 Member Contributer Share Posted January 10, 2016 If you have engine apart you could bore out the cylinders and the increased sweep area will increase your compression... this would also require new pistons. Increasing the bore to 73.5 mm will give you 815 cc and 12.05:1 compression according to my calculations. So you'll get increased displacement and increased compression... best of both worlds! Link to comment Share on other sites More sharing options...
Member Contributer Ultimatevfr Posted January 10, 2016 Member Contributer Share Posted January 10, 2016 So you'll get increased displacement and increased compression... best of both worlds! I have heard that sometimes the first one , leads to the second one........;) Link to comment Share on other sites More sharing options...
Member Contributer Switchblade Posted January 11, 2016 Member Contributer Share Posted January 11, 2016 So you'll get increased displacement and increased compression... best of both worlds! I have heard that sometimes the first one , leads to the second one........;) Link to comment Share on other sites More sharing options...
Member Contributer Madsen Posted January 11, 2016 Author Member Contributer Share Posted January 11, 2016 I was looking for a way to do this whiteout have to bore out the cyllinders, but maybe it can´t be done whiteout boring the cyllinders. Link to comment Share on other sites More sharing options...
Member Contributer Rush2112 Posted January 11, 2016 Member Contributer Share Posted January 11, 2016 I was looking for a way to do this whiteout have to bore out the cyllinders, but maybe it can´t be done whiteout boring the cyllinders. What CornerCarver recommended does not require boring the cylinders. See if higher domed pistons are available or ones with ~0.25 mm - 0.5 mm more distance between the piston wrist pin and the piston deck height. Valve clearance will have to be taken into consideration to make sure no serious engine damage occurs. Link to comment Share on other sites More sharing options...
CandyRedRC46 Posted January 11, 2016 Share Posted January 11, 2016 This is the one time where us 6th geners get to sit back and laugh at you fifth gen guys :P Anyways to the op, its not going to happen. You are looking for a simple head mill bump, but your gear driven cams aren't going to let that happen. You could weld up your heads, but I doubt you're going to do that either. The real way to bump up the 5th gen compression ratio is boring out the cylinders for cbr929 pistons but thats not going to happen either. Moral of the story, try again with a sixth gen engine. For anyone that feels like doing some research, the 8th gen vfr800 supposedly has 11.8:1 compression. Whether that extra 0.2:1 comes from different piston, head, head gasket, rods etc is anyones guess, but if the 8th gens have a redesigned piston, one may be able to run 0.50 over 8th gen pistons, take a couple thousands off of the heads and deck and get to 12:1 pretty easily.... Link to comment Share on other sites More sharing options...
Member Contributer CornerCarver Posted January 11, 2016 Member Contributer Share Posted January 11, 2016 This is the one time where us 6th geners get to sit back and laugh at you fifth gen guys :P Anyways to the op, its not going to happen. You are looking for a simple head mill bump, but your gear driven cams aren't going to let that happen. You could weld up your heads, but I doubt you're going to do that either. The real way to bump up the 5th gen compression ratio is boring out the cylinders for cbr929 pistons but thats not going to happen either. Moral of the story, try again with a sixth gen engine. For anyone that feels like doing some research, the 8th gen vfr800 supposedly has 11.8:1 compression. Whether that extra 0.2:1 comes from different piston, head, head gasket, rods etc is anyones guess, but if the 8th gens have a redesigned piston, one may be able to run 0.50 over 8th gen pistons, take a couple thousands off of the heads and deck and get to 12:1 pretty easily.... If anyone wants to swap a 5g engine for a 6g unit in the interest of having an easier to mod engine I have a pair of 6g units sitting on the floor of my garage. They were removed from 6g frames to accomdate an older, more difficult to modify 5g engine. Yours for the asking (and your old running 5g lump). Link to comment Share on other sites More sharing options...
CandyRedRC46 Posted January 11, 2016 Share Posted January 11, 2016 Bro just mill the cam gears!!! Lol Sent from my A0001 using Tapatalk Link to comment Share on other sites More sharing options...
Member Contributer Rush2112 Posted January 11, 2016 Member Contributer Share Posted January 11, 2016 Bro just mill the cam gears!!! Lol Sent from my A0001 using Tapatalk Wow... that sounds so simple... sweet Link to comment Share on other sites More sharing options...
Member Contributer Switchblade Posted January 11, 2016 Member Contributer Share Posted January 11, 2016 Bro just mill the cam gears!!! Lol Sent from my A0001 using Tapatalk Wow... that sounds so simple... sweet Dont grind, that way you will get more of the gear whine, for a little while . Link to comment Share on other sites More sharing options...
Shinigami Posted January 11, 2016 Share Posted January 11, 2016 Genuinely curious, how much power could one add from this type of mod (presuming the need for premium fuel) and what's the downside (besides the lack of a knock sensor) Link to comment Share on other sites More sharing options...
CandyRedRC46 Posted January 11, 2016 Share Posted January 11, 2016 Highsidenz is at about 140 whp on his fifth gen and Mohawk is right behind him at around 125whp. Both fifth gen motors.... Do some research man. They are both avid members with a lot of educational posts/threads.... Sent from my A0001 using Tapatalk Link to comment Share on other sites More sharing options...
squirrelman Posted January 11, 2016 Share Posted January 11, 2016 Downside is increased engine heat that needs to be got rid of. Link to comment Share on other sites More sharing options...
Shinigami Posted January 11, 2016 Share Posted January 11, 2016 Highsidenz is at about 140 whp on his fifth gen and Mohawk is right behind him at around 125whp. Both fifth gen motors.... Do some research man. They are both avid members with a lot of educational posts/threads.... Sent from my A0001 using Tapatalk Zounds, I used to follow NZ's build thread, but somewhere I stopped following - perhaps around the third time he had trouble getting his cams profiled properly. Thanks for the reminder! Link to comment Share on other sites More sharing options...
CandyRedRC46 Posted January 11, 2016 Share Posted January 11, 2016 Downside is increased engine heat that needs to be got rid of. Yeah he wound up fitting a third radiator lol Link to comment Share on other sites More sharing options...
Member Contributer MaxSwell Posted January 12, 2016 Member Contributer Share Posted January 12, 2016 This is the one time where us 6th geners get to sit back and laugh at you fifth gen guys :P Anyways to the op, its not going to happen. You are looking for a simple head mill bump, but your gear driven cams aren't going to let that happen. You could weld up your heads, but I doubt you're going to do that either. The real way to bump up the 5th gen compression ratio is boring out the cylinders for cbr929 pistons but thats not going to happen either. Moral of the story, try again with a sixth gen engine. For anyone that feels like doing some research, the 8th gen vfr800 supposedly has 11.8:1 compression. Whether that extra 0.2:1 comes from different piston, head, head gasket, rods etc is anyones guess, but if the 8th gens have a redesigned piston, one may be able to run 0.50 over 8th gen pistons, take a couple thousands off of the heads and deck and get to 12:1 pretty easily.... If anyone wants to swap a 5g engine for a 6g unit in the interest of having an easier to mod engine I have a pair of 6g units sitting on the floor of my garage. They were removed from 6g frames to accomdate an older, more difficult to modify 5g engine. Yours for the asking (and your old running 5g lump). Now here is a man who knows a great engine when he sees one, or hears one, our feels one. Or all three. Link to comment Share on other sites More sharing options...
CandyRedRC46 Posted January 12, 2016 Share Posted January 12, 2016 vtec shmeetec Link to comment Share on other sites More sharing options...
Andy Griff Posted November 15, 2016 Share Posted November 15, 2016 Got his issue with my 837cc RC36. I want to get the heads optimised, but chamber grinding will reduce the 11.5:1 CR I have with the JE pistons. If I get time this winter I'm going to remove the backlash gears from a cam drive cassette and calculate the difference in gear train backlash between a cold vs hot engine. Providing the clearance increases due to thermal expansion of the block and head I'll get a spare head milled a few thou and attempt to calculate the relationship between head skim, gear backlash and engine temp. The idea being I can run minimal backlash when cold, increasing to a safe running clearance when hot, following a modest head skim. I'm looking for around 12.5:1 CR if possible after cylinder head work. Link to comment Share on other sites More sharing options...
CandyRedRC46 Posted November 16, 2016 Share Posted November 16, 2016 15 hours ago, Andy Griff said: Got his issue with my 837cc RC36. I want to get the heads optimised, but chamber grinding will reduce the 11.5:1 CR I have with the JE pistons. If I get time this winter I'm going to remove the backlash gears from a cam drive cassette and calculate the difference in gear train backlash between a cold vs hot engine. Providing the clearance increases due to thermal expansion of the block and head I'll get a spare head milled a few thou and attempt to calculate the relationship between head skim, gear backlash and engine temp. The idea being I can run minimal backlash when cold, increasing to a safe running clearance when hot, following a modest head skim. I'm looking for around 12.5:1 CR if possible after cylinder head work. A ten month thread resurrection of epic proportions :) Look into flat faced valves if you don't already have them. (this could possibly get you back to the same volume as before headwork) Also look into ceramic coating the piston tops and combustion chambers. (great way to reduce hot spots and add a possible 0.1 or so of compression) You could always go into more advanced head optimization, that involves welding, to further optimize the cc shape and reduce volume. Link to comment Share on other sites More sharing options...
CandyRedRC46 Posted November 16, 2016 Share Posted November 16, 2016 Looking at vfr750 cylinder heads, you can definitely benefit from flat faced valves. Link to comment Share on other sites More sharing options...
Andy Griff Posted November 16, 2016 Share Posted November 16, 2016 Sorry to resurrect this thread, interesting subject though:-) Re flat faced valves, any recommendation on a quality manufacturer of such items ? Would like to slightly increase intake valve diameter anyway due to severe valve seat overhang on OEM heads so a valid consideration. Link to comment Share on other sites More sharing options...
The Phantom Posted November 17, 2016 Share Posted November 17, 2016 Hi Andy Aussie VFR400 racers routinely remove the scissor gears from their cams in the chase for power - they are getting up to 75hp out of them. Sounds like there's a bag of nails in the heads at idle, but no different to stock when under load. Link to comment Share on other sites More sharing options...
CandyRedRC46 Posted November 17, 2016 Share Posted November 17, 2016 15 hours ago, Andy Griff said: Sorry to resurrect this thread, interesting subject though:-) Re flat faced valves, any recommendation on a quality manufacturer of such items ? Would like to slightly increase intake valve diameter anyway due to severe valve seat overhang on OEM heads so a valid consideration. Thats a good question. Maybe https://www.ferrea.com/ or https://www.supertechperformance.com/racing-engine-valves-p121 And since you have overbored so much, you might have room to go up a mm or two. Link to comment Share on other sites More sharing options...
Member Contributer HighSideNZ Posted December 1, 2016 Member Contributer Share Posted December 1, 2016 HRC did try larger valves in the RC45s at one stage but went back to the stock sizes. There is not much to gain from valve size on these. The other thing to keep in mind going to flat faced valves is valve head mass. The flat faced vale will weigh more in the wrong place for a steel valve. If you are going to rev the ring out of the thing you want less mass not more. Phil Link to comment Share on other sites More sharing options...
Question
Madsen
Hi.
How is the best way to raising compression ratio a littel bit on my 5´th gen. VFR800? I am getting the cyllinderhead ported and the camshaft retimed, and I would like to raise the compression ratio
to maybe 12:1
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