tuning vfr750

[kaighn80]

does anyone know what needs to be done to the viffer to extract some more ponies?

im doing the zorst and filter and will set the fueling to suit but what else can be done on the cheap? is there a different cam set or can i increase compression? its a bogo 86 model but im doing everything else so it would be a shame not to do the lump whilst its out for detailing.

[Egg on Leggs]

Big bore to 836cc I think.

[kaighn80]

ok so who does what then?

[lorenzo]

You're going to struggle to get the heads skimmed: the gear driven cams prevent much being done on that score. Speaking to kent about a regrind on your cams may not be a bad way to go, but bear in mind that to get any really decent gains you'll want to be modifying the cam gears so they can be adjusted, then spend some time dialling them in. Then a whole load of dyno time too. You'll get benefits, but don't be fooled into thinking it's a cheap mod because the regrind only costs a couple of hundred quid, that's only a section of the work done. See if somebody like TTS does a big bore or whatnot, that's going to be a decent hike in power, but being an older engine, I wonder if you'll be able to get high comp pistons etc for it?

[madmike]

In a fair few years when I have the money (and not a student) I'm going to buy a shitter of a VFR800Fi... extract that lovely 800cc V4! Then not rush and make a proper awesome RC212V Replica!

Don't know how like... But its something I dream about far too often!

[ssray]

The cam drive gears have anti rattle/backlash gears-remove them, rc30 carbs?

ray

[madmike]

Hmm...that engine in a CBR400 frame, tyga bodywork...?

Cibbersix's MotoGP style exhaust off his trackbike to thank you very much!

[lorenzo]

In a fair few years when I have the money (and not a student) I'm going to buy a shitter of a VFR800Fi... extract that lovely 800cc V4! Then not rush and make a proper awesome RC212V Replica!

Don't know how like... But its something I dream about far too often!

I sound like such a grumpy bastard, ruingin peoples ideas, but first of all, a VFR800 isn't, despite the name, 800cc, it's just about 780 or so. You don't want to give up your extra few cc over those motogp boys, do you? The biggest problem with putting the 800 engine in anything is the fact that the engine is also the swingarm mount, rather than the frame like on 99% of bikes. This means it's a bit bigger and longer than most.

Anyway, what you want is a supercharger...

[madmike]

I sound like such a grumpy bastard, ruingin peoples ideas, but first of all, a VFR800 isn't, despite the name, 800cc, it's just about 780 or so. You don't want to give up your extra few cc over those motogp boys, do you? The biggest problem with putting the 800 engine in anything is the fact that the engine is also the swingarm mount, rather than the frame like on 99% of bikes. This means it's a bit bigger and longer than most.

could you not get a normal swing arm off another bike and just chop the right mount off so it only mounts on the left?

[lorenzo]

The swingarm mounts onto the cases. You could make new cases etc, but why would you want to make new cases for an overweight engine that produces less than 110hp on a good day? Stick to an earlier 750 engine, they're just as powerful and less awkward. And supercharge it.

[madmike]

Well if couldn't make my RC212V I'd wait until I could afford a smashed 09 R1 and turn it into a M1 then! Get the fairings done propa' n all that init'

[timbrell]

I'm a big fan of viffers, my first big bike was a 91 VFR750 and I raced a 96 VFR 750 in the no budget cup race in September. The story goes that the VFR Haslam raced in the transatlantic challenge was completely stock and fresh out of the crate, there is a really tasty VFR 750 that races at the front in thunderbikes that was featured in PB's Obsession feature. I have the engine from the 91 sat in the garage and I'm going to do some work on it but getting BIG power is not really possible without spending totally unreasonable money.

The gear driven cams make things awkward as has been mentioned. There is a 837cc big bore kit for them, I think it's TTS that do it (a quick google will tell you), and some RC30 parts would fit but not all the internals will. Supercharger is the best way for big numbers, but you'll probably need some custom made forged pistons to handle any real boost pressures unless someone still makes forged low compression pistons for them, but they're not a common choice for tuning.

I'd recommend spending some time on some light head work as it's cheap and you can do it yourself, remove the quietening gears, get the carbs set up right or get hold of some RC30 carbs which should fit if you can find/afford them. The HRC slipper clutch setup from an RC30 fits (I've been told) which would make more difference to fast riding than any engine mod. Don't mean to piss on your chips but getting the thing to handle and brake properly, lowering the gearing and losing some weight would be much more worthwhile. The best thing about the V4 is it's bomb proof and the power delivery lets you get on the throttle nice and early and has a flat linear torque curve. The slipper clutch would make a huge difference as they can be a bit of a handful in really fast corner entries.

I beat R1's, SRAD's, Blades, ZX7R's, dukes and aprilias in the race and my engine was completely standard except for some colder plugs, so make the most of the ponies you have and spend more on riding it hard! Ramble over.

[kaighn80]

yeah i was sorting chassis and suzzy first, im negotiating the release of a tl/sv1000 rolling chassis, has usd front end with hagon internals, was thinking of selling the rest to help fund the build. i'm lining up carbon bodywork and putting my girl on a diet (along with myself cos im 12stone now!) the book says 220kg dry i want to get it down to 180ish wet, i think i might be able to do it if i get rid of pretty much everything that i dont need i.e. massive seat unit and all the iron work under it, massive lights (replacing with modern lighter weight items where i cant get away with leaving off) and new miniscule dash to replace the one that honda obviously robbed from a hgv somewhere. so im learning how to ally weld so i can make light weight components for myself. im changing the rear end asap, might have to use the thou rear wheel with a slightly slimmer tyre unless i can lay my hands on an offset sprocket that will let the chain clear the tyre (its a 180 at the mo) have been offered a spare engine for a nifty has done more miles than mine so if/when i do the engine work it will probably be to that one so i know if it all goes tits up i have the original low mileage one to put back in.

as for the anti backlash bits are they not doing a fairly important job?

[Evilchicken0]

Best thing to do is the air filter and pipe, make sure the engine has good comperssion and the valve clearances are ok then ...

Fit lightweight wheels and lower the gearing a touch.

[lorenzo]

On my 800 I had, I managed to get 108 at the wheel and a fully wet weight of 202KG's. Aluminium subframe at the back and front, tiny weeny little plastic headlights from a scooter, part carbon part fibreglass RC45 bodywork, stainless exhaust with titanium cans (twin shotgun style 'cause they is cool, innit), K&N, power commander, flapper valve removed from the airbox, SP1 front wheel, cycle speedo as clocks. I should've done a better job of getting the suspension revalved (hyperpro rear shock was a bit too firm as it was for a stock bike, front from a 929 blade needed more damping, even after being resprung) but all the same, after all of the work I did on it, it didn't feel like a really sharp sports bike, as much fun as it was.

[Rompy McPoot]

I loved that bike. I was too poor to buy it when you sold it, else I'd have had it like *that*

[ssray]

The anti backlash are just there for noise reduction, supposed to sound like a bag of spanners when you remove them.

when I had mine there was talk og a gsxr1000 flywheel and generator fitting, std one a bit large.

Ray

[timbrell]

Sounds like you're doing a pretty thorough job on it, make sure you get some tasty pics up when it's done! Taking the quetening gears off depends on what you're gonna use it for and how often, if it's gonna be a track bike mainly and get lots of TLC and maintenance then get rid of them and it'll help the engine spin up quicker. It's a very common mod on 400 V4's for racing and I haven't heard any horror stories yet. It's a personal choice thing, pay your money take your choice.

Good luck with it

[kaighn80]

thats decided that then, its for mostly road use and if i can be bothered i'll throw in a couple of trackdays, but i plan on keeping this one for quite a while. i would love a supercharger but the price is just a little too much, although im doing the carbon and lightweight stuff im doing all the work too so that this don't end up being a money pit. had a good look round the web last night and found a few interesting things, like they all had 70mm pistons and a 48.6mm stroke which gives a fraction over 187cc per cylinder, so if i get pistons that are 2mm over sized i end up with 836cc, which is a good start, might see if i can find some with a slightly bigger crown, not like mms bigger but a fraction just to increase the compression a bit. then its head work and balancing things like pistons and conrods, it all helps.

[kaighn80]

justa thought, whats the dia of the 800's pistons? wonder if there is a cheap swap on the horizon? (yes i know i need to know crown height too!)

[redmarque]

I heard from someone on the forum that Tony Scott once built a 900cc V4 from an 800 using Fireblade pistons.

[kaighn80]

I heard from someone on the forum that Tony Scott once built a 900cc V4 from an 800 using Fireblade pistons.

details man i need details!! have procured a spare engine from a more recent bike for the trade of labour! happy days.

[redmarque]

Only know from hear say that it happend

From what I gather it's the inbetween cylinder wall thinkness that restricts the VFR motor being overbored bigger.

Only other possibly useful info I have is the details on a TTS spec 837cc JE Pistons.

TTS PERFORMANCE ENGR LTD

HONDA M/C 750cc VFR750

Bore 2.913

Comp Height .900

Forging 75M

Pin Dia .669

Pin Length 2.050

JE .050 Wire Locks

Dome .155

Top Ring .8mm

2nd Ring .8mm

Oil Ring 1.5mm

Piston weight 176

PART 150871

[kaighn80]

ive had a look at the fireblade range of pistons, and ive found that the 954 2mm oversized pistons would give 905cc, now looking for a piston

[redmarque]

Might be worth taking your spare engine to a re-boring outfit to get an opinion on the min thickness between bores.

interesting to know if the fireblade dimensions are workable without too much modification.