Ducati.ms - The Ultimate Ducati Forum banner

1 - 20 of 36 Posts

·
Registered
Joined
·
3,623 Posts
Discussion Starter #1
Forget about the logic for this post.

1) I have a 999S crank and ti-rods as well as 996 pistons that I reduced a few gram to weight less than the original 100mm pistons that were on the 999S crank
2) I have a pair of 996 cylinders with 2mm shaved off the top and the crown of the piston is flush with the top of the cyinder
3) I can run the 999S crank on the 996 to make a 955. I will purchase or fabricate oversized pulleys later

A) I can pickup a 1100 crank, pick up some 4mm or 5mm base gaskets and have a 1080 with the drop in crank
B) Timing shaft will probably need to be machined to clear the con-rod bolts

  • I have a lightened flywheel that is installed
  • I have all the other gears that have been lightened but not installed
1080 is more power. The 955 is is a lighter crank. I have run bikes with more power than the 996, but I've not run the older desmos with lightened internals. a few CCs down from 996 to 955 doesn't matter to me and as is The Time Machine is still quick enough everywhere but the straits.

Thoughts one way or another.
 

·
Premium Member
Joined
·
598 Posts
I would do a lightened 955 motor. I bet it produces a good amount of power (135 RWHP) but spins up nicely, has a nice power band and is a real joy to ride at the track.
 

·
Registered
Joined
·
1,905 Posts
i'd use a 900 crank and 1 extra base gasket.

the problem you may have with the 1000/1100 crank, especially if you lift the cylinders 2.5mm to compensate for the extra stroke, is how far the piston pulls out of the cylinder at bdc. that would be my first concern to check

i like the 900 crank idea. 12.7 comp, nice squish, no belt issues.
 

·
Premium Member
Joined
·
598 Posts
i'd use a 900 crank and 1 extra base gasket.

the problem you may have with the 1000/1100 crank, especially if you lift the cylinders 2.5mm to compensate for the extra stroke, is how far the piston pulls out of the cylinder at bdc. that would be my first concern to check

i like the 900 crank idea. 12.7 comp, nice squish, no belt issues.
That puts it at 984cc, yes?
 

·
Premium Member
Joined
·
4,938 Posts
Shorter stroke, less power everywhere. Valves, cam and rpm dictate top end. It’ll only pull only so much air at 10-11,000, depending on cams etc. Big bore will reach that limit early but the bottom and mid gains a great. Top end won’t be much different to the short stroke so I’d be making it big. Just my opinion. Because you asked. 😃
Nothing beats cubes. Except a turbo. 🤠
 

·
Registered
Joined
·
3,623 Posts
Discussion Starter #8
Thanks guys. Perhaps I'll do both. I'll wait around for a 996 short block for the 955 plan. In the meantime, I am looking forward to having some fun on The Time Machine if/when we are told to do as we are told and stay home.
 

·
Registered
Joined
·
274 Posts
whats the use case? Just for fun trackday kinda thing or purely street machine? I generally prefer on the track lighter, smaller feeling on the track provided I'm not ruining the torque curve. On the street I'd happily give up revs (as I'd suspect you'd have to with a 71.5mm stroke) to have the grunt and pull down low.

If the cylinder heads/cams etc is a decent match for the 999 stroke and can make more power revving higher, I'd go that route for track use. I bet it'd be just as fast as the 1080 bike and easier to ride at speed.
 

·
Premium Member
Joined
·
5,019 Posts
Shorter stroke, less power everywhere. Valves, cam and rpm dictate top end. It’ll only pull only so much air at 10-11,000, depending on cams etc. Big bore will reach that limit early but the bottom and mid gains a great. Top end won’t be much different to the short stroke so I’d be making it big. Just my opinion. Because you asked. 😃
Nothing beats cubes. Except a turbo. 🤠
You can however keep the cubes exactly the same but configure them differently, e.g., exactly what we had Mountune do for us with the MonoR. Reduced stroke, increased bore... same displacement, 1000 Rpm higher ceiling, 35 more HP.
 

·
Premium Member
Joined
·
4,938 Posts
Morning Proph. Of course it can but duke heads and cams don’t flow well after 10 without lots of work. Then there’s the crank case killing rpm problems. Even the Pani suffers this though not as common. It would be interesting to see what a short stroke 600 would do but I suspect not much as Ducati haven’t shown any interest. And there’s the fact that regardless of bore /stroke ratio, it’s still a twin and there’s a lot of weight thrashing around in those cases at elevated rpm. AND valve time area just isn’t there in a twin compared to a 4 so a twin is just dead in the water if it was a head to head race. This is why Ducati always had to have extra capacity for parity and the L4 had an rpm ceiling.
 

·
Premium Member
Joined
·
5,019 Posts
Morning Proph. Of course it can but duke heads and cams don’t flow well after 10 without lots of work. Then there’s the crank case killing rpm problems. Even the Pani suffers this though not as common. It would be interesting to see what a short stroke 600 would do but I suspect not much as Ducati haven’t shown any interest. And there’s the fact that regardless of bore /stroke ratio, it’s still a twin and there’s a lot of weight thrashing around in those cases at elevated rpm. AND valve time area just isn’t there in a twin compared to a 4 so a twin is just dead in the water if it was a head to head race. This is why Ducati always had to have extra capacity for parity and the L4 had an rpm ceiling.
All extremely good points my friend...
 

·
Registered
Joined
·
3,623 Posts
Discussion Starter #14
You mean that running around 7k rpm in 5th WOT then slamming it down to 4th b/c you haven't decided if you want your rpms in the mid or high range as you roll on the throttle after the apex is a bad idea? I've never spun a rod bearing doing that. The answer is mid-range for a Ducati (where is davy.j, I haven't seen him on here for a while)

The idea behind the 955(958) is to have a power band similar to a 748 kitted to an 853, and not copy the true 955 which is 96mm x 66mm. I love the 853, and think 100cc more will be more fun, and that 98mm x 63.5mm will do that for me. I know what increasing the stroke will do, it will make a more powerful tractor.

Belter, I am always a tighter on money when it comes to bikes, but I don't mind ruining an engine or working on them.
 

·
Registered
Joined
·
1,905 Posts
the rpm concerns are around heads, in particular collets, and cases, although by 996 and certainly 2001 the cases were much better. i'd have no concern for big ends. how much further it's worth revving it depends on head work and cams. if it's std heads and cams there's no point trying to make it rev. plus the smaller you go the more you need to work to get the comp back. the 999 crank will cost about half a point in comp, everything else being equal.

imo the close ratio gearbox is far more responsible for the 853 "feel" people go on about than the bore and stroke. plus the 748 head seems to work particularly well at 850cc, certainly as well or better than any other 33/29 heads with larger ports do. and if you put one together with normal kit flat top pistons and std heads it'll have more than 13:1 comp. if the cams aren't advanced it'll certainly be top endy too.

conversely, i think the tractor comments with regard to an increase in stroke of 3% are just silly.

i think what most people feel is the shape of the torque curve. if it's flat it's boring.
 

·
Registered
Joined
·
3,623 Posts
Discussion Starter #16
I don't understand the "conversely... 3% are just a silly.." comment. The 996 pulls like a tractor stock. Making it a 1080 based on a longer stroke will maket it more tractor-bee-like. A very similar torque and power curve as the 996, with more torque and power all around. More tractor is more tractor.
 

·
Registered
Joined
·
3,623 Posts
Discussion Starter #18
I've played with that in the past. Just admit the 996 is a tractor and I'll be able to hear you. Come on, say it.
 

·
Registered
Joined
·
1,905 Posts
i'm not that kind of parrot. why is it a tractor? i don't understand the comment, never really have. maybe you've just never ridden a good one?

is a 996sps also a tractor?
 
1 - 20 of 36 Posts
Top