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Honda VFR 750 or 800 Long Throw Crankshaft Is It Possible?

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crazymonk
L Plate Warrior



Joined: 02 Apr 2009
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PostPosted: 10:40 - 02 Apr 2009    Post subject: Honda VFR 750 or 800 Long Throw Crankshaft Is It Possible? Reply with quote
Hi, has anyone increased the capacity of their vfr? and I don't mean by the tiny amount that the big bore kits offer. I was wondering if the crankshaft from another honda v4 could be fitted, with oversized pistons of a couple of mm to create an engine with a bigger capacity. I was looking at a VF1100 crank earlier, but it looks slightly different, although the stroke would be just right. With a spacer for the cylinder casing and custom cylinders it would make for a pretty cool engine.
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MarJay
But it's British!



Joined: 15 Sep 2003
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PostPosted: 15:07 - 02 Apr 2009    Post subject: Re: Honda VFR 750 or 800 Long Throw Crankshaft Is It Possibl Reply with quote
crazymonk wrote:
Hi, has anyone increased the capacity of their vfr? and I don't mean by the tiny amount that the big bore kits offer. I was wondering if the crankshaft from another honda v4 could be fitted, with oversized pistons of a couple of mm to create an engine with a bigger capacity. I was looking at a VF1100 crank earlier, but it looks slightly different, although the stroke would be just right. With a spacer for the cylinder casing and custom cylinders it would make for a pretty cool engine.


I think the VF1100 has chain driven cams whereas the VFR750/800 is gear driven.

Its not really the kind of engine where you are likely to be able to fit a longer throw crank TBH. You'd have to find shorter connecting rods and the piston speed would go through the roof so you may even lower your rev limit doing that. There is no space in the barrels for the pistons to be closer to the head (which cannot be moved easily due to the gear driven cams) and I'd be surprised if there was any excess barrel underneath the BDC position of the piston...

This isn't an old Pinto or Cosworth engine, there isn't much room for the kind of tuning you're talking about in a microscopic Honda V four engine. That isn't to say that its not possible, but if it is possible I would be very very very surprised and in a way slightly dismayed at Hondas inefficient engineering.
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British beauty: Triumph Street Triple R; Loony stroker: KR1S; Track fun: GSXR750 L1; Commuter Missile: GSX-S1000F; Cheap project: CBR900RR FireBlade
Remember kids, bikes aren't like lego. You can't easily take a part from one bike and then fit it to another.
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stinkwheel
Bovine Proctologist



Joined: 12 Jul 2004
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PostPosted: 15:19 - 02 Apr 2009    Post subject: Reply with quote
It barely fits in the frame as it is.
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I did the 2010 Round Britain Rally on my 350 Bullet. 89 landmarks, 3 months, 9,500 miles.
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Kickstart
The Oracle



Joined: 04 Feb 2002
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PostPosted: 15:35 - 02 Apr 2009    Post subject: Re: Honda VFR 750 or 800 Long Throw Crankshaft Is It Possibl Reply with quote
crazymonk wrote:
With a spacer for the cylinder casing and custom cylinders it would make for a pretty cool engine.


Thought the V4s used a combined casting for both the barrels and upper crankcase, so no real way to space the barrels up.

All the best

Keith
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duhawkz
World Chat Champion



Joined: 03 Dec 2006
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PostPosted: 06:28 - 03 Apr 2009    Post subject: Reply with quote
you could always stick a supercharger on it

https://www.vfrdiscussion.com/forum/index.php?showtopic=31492&start=100
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Coxyzxr
Brolly Dolly



Joined: 22 May 2008
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PostPosted: 07:53 - 03 Apr 2009    Post subject: Re: Honda VFR 750 or 800 Long Throw Crankshaft Is It Possibl Reply with quote
crazymonk wrote:

This isn't an old Pinto or Cosworth engine, there isn't much room for the kind of tuning you're talking about in a microscopic Honda V four engine. That isn't to say that its not possible, but if it is possible I would be very very very surprised and in a way slightly dismayed at Hondas inefficient engineering.


I like this.

You can't get much past the Jap stuff when it comes to engineering quality.

I starting to rebuild one of my zxr engines, die grinder out ready to flut the oil holes on the crank journels and such... oh they've already been done... from the factory.

This is fundamental stuff listed in my 'Engine builders handbook' I'd thought I'd be able to tackle confidently on my own.

If it was worth doing, the Jap big 4 would of done it already. (As my old man says)
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