flyguyeddy Posted April 21, 2012 Share Posted April 21, 2012 ok i have one modified. it was kind of a pain in the ass to do so i will probably take a while till i get the other 7 done, or another 3 for that matter lol this is the finished result, minus the swaintech coatings i plan to have put on it. Link to comment Share on other sites More sharing options...
Member Contributer karhawk Posted April 22, 2012 Member Contributer Share Posted April 22, 2012 and you can do a valve job at home, leave stock cams in, You can also have the cams reground for some more lift or fit VFR800 valves (and seats) which I think are about 1mm larger in diameter. The larger displacement engine has to be able to breath after all. Interesting, does an 800 head fit on a 4th gen lower Chris Oakland, ca. Link to comment Share on other sites More sharing options...
Member Contributer YoshiHNS Posted April 22, 2012 Member Contributer Share Posted April 22, 2012 Did you lose the chamfer on the outside when you cut the top down or can I just not see it in that pic? Link to comment Share on other sites More sharing options...
The Phantom Posted April 22, 2012 Share Posted April 22, 2012 Interesting, does an 800 head fit on a 4th gen lower No, totally different motors. The 4th Gen has the gear drives for the cams between the pistons, whereas the 5th Gen has it on one side of the motor. The 5th Gen motor is actually the RC45 motor, with a 180 degree crank rather than the RC45s 360 degree crank. Nice work FGE, looking forward to seeing more. Link to comment Share on other sites More sharing options...
flyguyeddy Posted April 22, 2012 Share Posted April 22, 2012 Yoshi: There is a chamfer, its not very big. Does it need to be substantial? Link to comment Share on other sites More sharing options...
Member Contributer YoshiHNS Posted April 22, 2012 Member Contributer Share Posted April 22, 2012 Yoshi: There is a chamfer, its not very big. Does it need to be substantial? No professional opinion. Though re-reading the first machining post, I misunderstood what you did. Ignore me. Carry on! Link to comment Share on other sites More sharing options...
Guest Posted April 24, 2012 Share Posted April 24, 2012 I think my question would be "why bother?" I have a 1997 VFR750 with 160,000klm on it and I have NEVER found the power output to be inadequate, unless you think 200kph into turn 1 at Phillip Island is far too slow. It was quite fast enough for me! Although I am Californian Superbike School trained I do admit I am not 'quick'. It might be that I am now 66, but I never was 'quick. I do love my VFR though, all 750cc of it! Link to comment Share on other sites More sharing options...
Member Contributer Dutchy Posted April 24, 2012 Member Contributer Share Posted April 24, 2012 Why do people climb mountains? Because they CAN!!!! Link to comment Share on other sites More sharing options...
flyguyeddy Posted April 24, 2012 Share Posted April 24, 2012 Lets keep the "why bother" comments out of this thread. Thats a good way to derail the progress that comes from these threads. Link to comment Share on other sites More sharing options...
Guest Posted April 28, 2012 Share Posted April 28, 2012 Just bought my 96 vfr with 2700 miles 2 days ago and this already sounds good lol Link to comment Share on other sites More sharing options...
Veefer800Canuck Posted April 28, 2012 Share Posted April 28, 2012 Just bought my 96 vfr with 2700 miles 2 days ago and this already sounds good lol Two thousand, seven hundred? NEED PICS!!!!! Start new thread stat! (and welcome to the site BTW) Link to comment Share on other sites More sharing options...
Member Contributer JZH Posted April 29, 2012 Member Contributer Share Posted April 29, 2012 836cc. Im hoping to not lose too much compression with the smaller dome. So you're effectively making your own TTS Big Bore kit? If that is the case, then the main issue will be with boring the cylinders. Back in the day, when Brian Law at Dynamo Humm sold the TTS kits and built the engines, there were a few stories of ruined engine cases, incorrectly bored by engine shops that had no experience with VFR-type v4 engines. Brian used OEM head gaskets, hand-reamed using an air grinder. If my 837cc 3rd-gen is anything to go by, there isn't a huge difference from the extra 89cc, though it does feel stronger. Ciao, Link to comment Share on other sites More sharing options...
flyguyeddy Posted May 8, 2012 Share Posted May 8, 2012 Basically thats what im doing. I have a place to send my engine block that another forum member has sent his to in the past so i think im good there. Link to comment Share on other sites More sharing options...
Member Contributer karhawk Posted May 8, 2012 Member Contributer Share Posted May 8, 2012 836cc. Im hoping to not lose too much compression with the smaller dome. The dome looks smaller, how will you determine the compression rating of the new pistons? I'm not sure I would just stuff them in there and hope the compression will be OK. I would measure to see where you're at. Chris Oakland, C.a Link to comment Share on other sites More sharing options...
woody77 Posted June 4, 2012 Share Posted June 4, 2012 flyguyeddy - glad to see that you're still making progress on this. I'm surprised at the lower dome, though. I had been expecting (from the reading on this), that the need to cut into the pistons was also going to be increasing the compression ratio. Anyway, definitely glad it's still progressing, and I'm very curious how it turns out. Link to comment Share on other sites More sharing options...
93 VFR750 RC36 Posted June 11, 2012 Share Posted June 11, 2012 Keep it coming, this is a great thread. If the heads and valves are done to flow better (I think 800 valve stems are longer so need to be shortened) then up to 118ish flywheel hp has been obtained. A couple of guys in Europe have added cams, carbs and lots of fettling to that and managed somewhere in the region of 125-130 at the rear wheel. Just gotta get my other projects done and I'll be on this. Link to comment Share on other sites More sharing options...
Member Contributer belovian Posted July 17, 2012 Member Contributer Share Posted July 17, 2012 836cc. Im hoping to not lose too much compression with the smaller dome. So you're effectively making your own TTS Big Bore kit? If that is the case, then the main issue will be with boring the cylinders. Back in the day, when Brian Law at Dynamo Humm sold the TTS kits and built the engines, there were a few stories of ruined engine cases, incorrectly bored by engine shops that had no experience with VFR-type v4 engines. Brian used OEM head gaskets, hand-reamed using an air grinder. If my 837cc 3rd-gen is anything to go by, there isn't a huge difference from the extra 89cc, though it does feel stronger. Ciao, I know Brian Law quite well, grew up with his kids. I also know Bruce Allnut, the main mechanic involved in dynamo humm. Bruce and another friend are starting a new custom shop twenty minutes from me, focusing on older bikes, mainly seventies goldwings. They just bought the shop and aren't all set up yet but it's coming together. Jess Link to comment Share on other sites More sharing options...
Member Contributer Mohawk Posted July 30, 2012 Member Contributer Share Posted July 30, 2012 i'm looking at this now for a VFR800, the 929 has the same style pistons as the 800, i.e. NO dome. These pistons may not make the compression you expect in the 750, due to the wider valve angle of the 750 head. The 800 & 929 are next generation combustion chambers with flat top pistons. Honda & Suzuki experimented for years with domed, hemispherical & pentroof combustion chamber designs, when what they were lacking was metalergy & water cooling ! Most bikes & cars now use close angle valve trains & that in turn allows for flat topped combustion chambers with great squish area to improve combustion. I've just had some 929 pistons delivered & will be pulling a rod & piston from my spare engine in a couple of weeks to measure everything. before making a decision on whether to pull the engine apart to get it bored ! Link to comment Share on other sites More sharing options...
flyguyeddy Posted July 30, 2012 Share Posted July 30, 2012 yea i know there is less dome on the 929 piston, but i was told by a speed shop that the loss of the dome might be made up with the size increase. and really, there is a little bit of a dome once the pistons are cut down to the proper height. Link to comment Share on other sites More sharing options...
NakedViffer Posted July 30, 2012 Share Posted July 30, 2012 yea i know there is less dome on the 929 piston, but i was told by a speed shop that the loss of the dome might be made up with the size increase. and really, there is a little bit of a dome once the pistons are cut down to the proper height. Guy at the speedshop was ill informed, bore size does not affect static compression ratio. The compression ratio is dictated by combustion chamber volume with piston at TDC. Link to comment Share on other sites More sharing options...
Member Contributer Mohawk Posted July 30, 2012 Member Contributer Share Posted July 30, 2012 Guy at the speedshop was ill informed, bore size does not affect static compression ratio. The compression ratio is dictated by combustion chamber volume with piston at TDC. Bore size most definately affects static compression, as does stroke. If you change either of those then you increase the swept volume (which is what CC or CU really mean) then more air/fuel has to fit into the same sized combustion chamber, the only way this can be done is if the compression is increased. Assuming that the bore is increased 4mm on the VFR750, then 37x37x3.14x48.6x4/1000=835cc or plus 86cc swept volume. So 835/749=1.1148 or 11.48% increase in swept volume. So a very basic estimate based on 4th gen standard CR of 11:1 gives approx 12.2:1 with the big bore. That CR increase is worth 2-3% more power even without the CC increase, so 92hp becomes 94hp, plus 11% makes for roughly 104hp. There was a Dynamo Humm built 4th gen that with a TB pipe & K&N & jetting kit plus the 837 big bore, went from 92hp to 117hp. A German took his big bore with cams, FCR39mm carbs & RC30 exhaust system to 123hp. Both showed masses of extra torque & more power everywhere. So it is a worth while exercise. Link to comment Share on other sites More sharing options...
NakedViffer Posted July 30, 2012 Share Posted July 30, 2012 Guy at the speedshop was ill informed, bore size does not affect static compression ratio. The compression ratio is dictated by combustion chamber volume with piston at TDC. Bore size most definately affects static compression, as does stroke. If you change either of those then you increase the swept volume (which is what CC or CU really mean) then more air/fuel has to fit into the same sized combustion chamber, the only way this can be done is if the compression is increased. You, sir, are absolutely right. Been building engines for some time, but I haven't dealt with measuring compression ratios in 10-12 years. I wasn't thinking about the increase in cylinder volume. I was just thinking about the piston being at deck height, and enlarging it wouldn't change anything from that aspect. Thanks for the correction. Engines are such a second nature to me, I sometimes feel like I don't have to think about questions before I answer them.. Link to comment Share on other sites More sharing options...
Veefer800Canuck Posted July 30, 2012 Share Posted July 30, 2012 i'm looking at this now for a VFR800, the 929 has the same style pistons as the 800, i.e. NO dome. Link to comment Share on other sites More sharing options...
Veefer800Canuck Posted September 23, 2012 Share Posted September 23, 2012 Mohawk: Any new information??? Link to comment Share on other sites More sharing options...
flyguyeddy Posted October 4, 2012 Share Posted October 4, 2012 i need to get off my ass and finish modifying the pistons. ive been slackin' Link to comment Share on other sites More sharing options...
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