questions on a big bore kit??

[11Rider]

Funny, I was just thinking about that the other day. I've heard chain looses about 2%, shaft 10-15% efficiency. If these figures are in the ballpark, one should gain close to 10 hp at the rear wheel converting to chain.

[Rasputin]

Hey TC did your pistons look like these?

[WMarshy]

So I'm looking through the catalog from Megacycle and it says some of their cams require shim under tappet... Does anyone know if our stock valves are compatible with the shim under tappet setup? Would you still have to use a shim on top of the bucket as well?

[crazy steve]

...Dan Hodges has done a lot of work on trying to squeeze as much HP from the XS11 engine, multiple types of cam swaps, etc..

Yeah, for anybody looking for more power, find and read Dan's posts. He spent more money on dyno time than most have in their whole bike, and the end result is he found there ain't no magic bullet for these motors....

A good condition, very-well-tuned '78 can deliver between 85 and 90 HP to the rear wheel, about 5 less for the later motors. Step up to one of the better (but no longer made) 4-1 exhausts, pods, big bore, and you can see 100 HP (at about $150 per HP). More than that, figure about $200+ per HP once you go above that number, not including dyno time. IIRC Dan finally managed to get 120 reasonably streetable HP, but he had about $5K into it.... You may not even be able to duplicate what he did now, as a lot of this stuff has gone obsolete as the bikes have aged.

For big power, look at a nitrous kit or a turbo....

[crazy steve]

Funny, I was just thinking about that the other day. I've heard chain looses about 2%, shaft 10-15% efficiency. If these figures are in the ballpark, one should gain close to 10 hp at the rear wheel converting to chain.

That's reasonably accurate. But currently available conversion kits are at $1600 (not including chain, sprockets, swingarm, wheel) so that's not a low-buck choice either.

[jetmechmarty]

A used FZ1 might be the answer!

[11Rider]

That's reasonably accurate. But currently available conversion kits are at $1600 (not including chain, sprockets, swingarm, wheel) to that's not a low-buck choice either.

http://www.ebay.com/itm/YAMAHA-CHAIN...r#ht_1928wt_73

This is the one I was looking at. I don't know if this one is of good quality though. And you're right that there are more parts to get such as swingarm. All in all though it might be one of the best bangs for the buck if you don't mind chain mantenence.

[crazy steve]

http://www.ebay.com/itm/YAMAHA-CHAIN...r#ht_1928wt_73

If you're planning on fitting a super-wide tire as shown, then that conversion is for you. But if you want a 'conventional' set-up, then that one locates the front sprocket too far out; it ends up outside the frame. This is the one you need for a 'normal' chain conversion... http://www.xs11.com/forum/showthread.php?t=36250

[11Rider]

Makes sense!

[airborneXS]

so a turbo setup versus a big bore kit? im intrigued....

[crazy steve]

So I'm looking through the catalog from Megacycle and it says some of their cams require shim under tappet... Does anyone know if our stock valves are compatible with the shim under tappet setup? Would you still have to use a shim on top of the bucket as well?

Yes, you would need shims both places. Those cams (shim under bucket) are too radical for a street bike; all the power is in the upper part of the RPM range and it won't be much fun at slower 'normal' cruising speeds. The other thing to be leary of is these are welded cams; note they require a 'core'. They weld extra metal onto the lobes, then regrind them to get the desired profile. Longevity is compromised, and lobe failure isn't unknown. The 'shim under bucket' cams also have a reduced base circle, which increases side loads and bucket/shim wear. If racing is what you're doing and constant checking of your valve train isn't a problem, then by all means. But for a reliable, long-running street bike not something I'd use...

[WMarshy]

Yes, you would need shims both places. Those cams (shim under bucket) are too radical for a street bike; all the power is in the upper part of the RPM range and it won't be much fun at slower 'normal' cruising speeds. The other thing to be leary of is these are welded cams; note they require a 'core'. They weld extra metal onto the lobes, then regrind them to get the desired profile. Longevity is compromised, and lobe failure isn't unknown. The 'shim under bucket' cams also have a reduced base circle, which increases side loads and bucket/shim wear. If racing is what you're doing and constant checking of your valve train isn't a problem, then by all means. But for a reliable, long-running street bike not something I'd use...

Thanks Steve, if I ever got enough money to embark on such an endeavor I would want to keep some street manners. I wonder what kind of power one could expect with their street cam in a stock engine...

[crazy steve]

Everything they sell is a welded-lobe type, so for me that would be just a bit too spooky. Their 'street cam' is basically a higher-lift version of the '78-79 cams (about the same duration numbers) so with the higher lift and same duration you'll see faster 'ramps' (rate of opening/closing) so there's still increased lobe/side loads. Should be worth about 5-10 HP depending on the rest of the tune.

This is a inherent problem on lobe-on-bucket valvetrain, the difficulty in getting higher lifts without compromising durability. Usually solved by going to more valves (3, 4 or even 5 valves per cylinder) to get flow. This is why you still see SOHC and pushrod designs with rocker arms; you can keep lobe lift low but mess with the rocker ratio to gain lift.

[WMarshy]

Everything they sell is a welded-lobe type, so for me that would be just a bit too spooky. Their 'street cam' is basically a higher-lift version of the '78-79 cams (about the same duration numbers) so with the higher lift and same duration you'll see faster 'ramps' (rate of opening/closing) so there's still increased lobe/side loads. Should be worth about 5-10 HP depending on the rest of the tune.

This is a inherent problem on lobe-on-bucket valvetrain, the difficulty in getting higher lifts without compromising durability. Usually solved by going to more valves (3, 4 or even 5 valves per cylinder) to get flow. This is why you still see SOHC and pushrod designs with rocker arms; you can keep lobe lift low but mess with the rocker ratio to gain lift.

I got to believe the durability of the cam isn't compromised and awful lot. I understand it places more stress/strain and wear on the components but the street cam probably would drastically decrease the overall life of the engine...would it? I would be more concerned about the longevity of the bearing surface on the head and bearing caps. It would have been nice if they originally designed the head with with removable bearing sleeves.

Everyone always seems to be looking for a little extra cheap performance, why wouldn't cams fall into that category? Does anyone know what the cost is? Seems like it would be plug and play in addition to some carb tuning...

Great discussion, thanks for the info.

[trbig]

My understanding is that cams don't make any more HP, they just move around the HP the motor already makes?