82mm Big Bore for the GS500?

[idgs500e]

So a friend of mine and I were having a beer in the shop and got to talking about a GS500 engine I have laying around and various ways to improve it. The topic of increasing the bore came up, first as a joke, then as a thought exercise, then finally as a full blown engineering project. The only big bore option that I am aware of is the V&H/Wiseco 555 kit, which uses the factory liners bored to 79mm. This results in a really thin liner, particularly at the bottom. This kit is also NLA as far as I know.  Based on our measurements (and preserving close to factory wall thickness), the factory cases can fit a maximum bore size of 81-82mm without case clearancing if the liner is properly clearanced and a modern piston design with no bottom band is used. 82mm works out to be 598cc, a hefty bump in displacement!  The old liners would have to be removed and the cylinder block opened up for the larger liners of course, but this is something any machine shop could do. It's actually easier than boring cylinders since no honing is required.

We fleshed out the technical details, made some drawings, etc. before the beverage impeded any further progress. In fact, the whole project seemed remarkably doable/affordable based on my previous experiences ordering custom pistons and liners. And it got me thinking maybe I'm not the only one questing for increased displacement?...........

So that's the question I'm posting to the GS500 masses now. Is there any need for an 82mm big bore kit on our beloved GS's? My thought was to have the kit include the pistons, larger liners and headgasket. The buyer would heat their cylinder block, knock out the liners, and have a machine shop cut it for the larger (and clearanced) kit liners. Then, they install the liners and reassemble. Not quite bolt on, but close. Price point would be in the $500-600 range.

What say you?

[CrispThat]

This is something I would be interested in with a little more info. Having some solid data on predicted power/torque gains would be the deciding factor for myself. If reasonable gains are achievable, I'd do it. Especially for $500-600.

If you move ahead on the kits, let me know.

[idgs500e]

Yeah, the GS presents a pretty hard price point. Folks are willing to pay $250-300 for modifications that only net a few HP, but much more $ than that and it's a hard sale. A turbo kit is a prime example. Even if it makes 70% more power, not many people will spend $1-2k on a GS.

[NikonAndy]

$500-$600 without machine shop costs right? So closer to $1k if you're lucky. Sounds really cool though. Definitely hard putting $ like that into a bike that's not worth much more. Atleast in the US, apparently AUS is hard up for em.

I'd love to hear performance specs when you're done, also be interested in how cool it stays with the thinner walls. Also, oil delivery for the greater displacement might be difficult, but I'm not sure.

[Joolstacho]

Then you'd just need an 8-valve head to feed the weapon.

[idgs500e]

$500-$600 without machine shop costs right? So closer to $1k if you're lucky. Sounds really cool though. Definitely hard putting $ like that into a bike that's not worth much more. Atleast in the US, apparently AUS is hard up for em.

I'd love to hear performance specs when you're done, also be interested in how cool it stays with the thinner walls. Also, oil delivery for the greater displacement might be difficult, but I'm not sure.

$1k? Yikes, remind me not to go to that machine shop. A local place here quoted me $40 per cylinder to fit new liners.........

[TheOzTurkish]

this sounds really interesting, logically it all makes sense, definitely an 8v head and bigger carb jets? or shoe-horn in a completely new carburetor?

[idgs500e]

Then you'd just need an 8-valve head to feed the weapon.

This is an excellent point. I would expect the maximum torque to increase proportionally with the displacement bump (let's say ~20%), but peak horsepower would likely not due to the flow limitations of the stock ports/valves/cams. That being said, increased displacement coupled with wilder cams would help compensate for that.

Note to self....... piston valve cutouts must be deep enough for Megacycle 384-20 cams 

[yamahonkawazuki]

So a friend of mine and I were having a beer in the shop and got to talking about a GS500 engine I have laying around and various ways to improve it. The topic of increasing the bore came up, first as a joke, then as a thought exercise, then finally as a full blown engineering project. The only big bore option that I am aware of is the V&H/Wiseco 555 kit, which uses the factory liners bored to 79mm. This results in a really thin liner, particularly at the bottom. This kit is also NLA as far as I know.  Based on our measurements (and preserving close to factory wall thickness), the factory cases can fit a maximum bore size of 81-82mm without case clearancing if the liner is properly clearanced and a modern piston design with no bottom band is used. 82mm works out to be 598cc, a hefty bump in displacement!  The old liners would have to be removed and the cylinder block opened up for the larger liners of course, but this is something any machine shop could do. It's actually easier than boring cylinders since no honing is required.

We fleshed out the technical details, made some drawings, etc. before the beverage impeded any further progress. In fact, the whole project seemed remarkably doable/affordable based on my previous experiences ordering custom pistons and liners. And it got me thinking maybe I'm not the only one questing for increased displacement?...........

So that's the question I'm posting to the GS500 masses now. Is there any need for an 82mm big bore kit on our beloved GS's? My thought was to have the kit include the pistons, larger liners and headgasket. The buyer would heat their cylinder block, knock out the liners, and have a machine shop cut it for the larger (and clearanced) kit liners. Then, they install the liners and reassemble. Not quite bolt on, but close. Price point would be in the $500-600 range.

What say you?

always the option of taking the cylinders to a reputable engine builder and having them re-sleeved? consider that as well. not sure on price though.

[gsJack]

Test on the GS that V&H built up with the 555 Wiseco pistons back in 89 is on my list of GS published tests. Note stock GS in the first 89 test was quicker than they were later on.  V&H used jetting and intake mods with their exhaust and with stock 2 valve head that had some porting work done on it.

http://www.gs500.net/gallery/data/500/GS500tests.jpg

[xunedeinx]

Would love to overbore and destroke it back to 500cc... Over-square it to Panigale levels...

Higher rpms, same tq as stock, and a good hp boost. Less Street friendly, but should be less stressful to the crank and rods due to lower piston speeds.

[Joolstacho]

At least with a bigger bore you might be able to squeeze in bigger valves. I wonder about those cams too, maybe they could do with a little more duration?

[Wagoneer]

Like you said, it probably wouldn't net much of a peak bhp bump. It would definitely improve torque. But I already find the GS to be pretty torquey, the top-end is what needs help. I think a head-flow improvement would be time/money better spent.

Not to mention a bore that large would put TONS more pressure on the crank and we don't really know the torque limitations of the internals.

But considering the V&H 555 bike picked up 10mph in the 1/4 mile, there has to be some sort of power picked in the top-end for sure.