Multis vs V-twins

**dipshit** · 28th October 2008, 20:34

Originally Posted by johan

What is linear piston speed?

It's the speed of the piston and rings travelling up and down the bore. Usually measured in metres per sec.

Bigger pistons with longer stroke, travel greater distance for the same given rpm.

**pritch** · 28th October 2008, 20:48

Originally Posted by discotex

RSV/1098/848/etc are all way pricey but if I could afford one I'd be in in a heartbeat.

You missed the pick of the bunch: the RC8

**BMWST?** · 28th October 2008, 20:54

ahhh s2 Ductai eh...yes.I had one after a long line of UJM(one of which was a triple...) And after that i had a longitudinal flat four.....I liked em all..and you cant get any different than a s2 ducati and a BMW k 100 rs...the thing about the ducati was it ALWAYS hooked up,..the beemer had much much much more tourque,and it had amazing rear grip too..

**discotex** · 28th October 2008, 21:08

Originally Posted by pritch008

You missed the pick of the bunch: the RC8

Oh yeah there's a bunch more brilliant exotic sports twins that I didn't think of at the time. Should really take the RC8 out for a spin sometime.

**Boob Johnson** · 29th October 2008, 00:09

Originally Posted by Sensei

This coming from someone that went on how fast they went in a straightline on ya RF900 ?? No worrys Boob have heard it all before . People that have natural talent & like show it off will always be criticized don't feel bad & buying a fast bike want help either !!

lol sorry Scotty as I said I don't do pissing competitions mate

You remind me of my dog I had growing up, very intelligent, well liked by the majority of other dogs in the neighbourhood, highly skilled & when he would get together with his buddies he would go around the lot of them nipping them all on the butts with his tail straight up in the air, once the alpha male had established himself off they went and all was well

You're a good bugger Sensai, spoken with you plenty of times out and about on rides & you seem like a decent bloke, I know a few others that know you & they speak well of you also, you're a very highly skilled rider of many many years as most know im sure (just one bin, last year wasn't it?). I never forget that ride down to the Cemetary curcuit last boxing day, you came across the pack & exactly like my dog above you rode through us very closely as if to nip us on the butts metaphorically speaking, at light pace not much quicker than ours but with a certain attitude, had ya left hand wresting on ya thigh while you went through by us, clutchless up shifting & gassing it on to make sure we heard you lol (does sound farkin sweet too), was funny as hell from where I was sitting, on the USS Nimitz . Im not havin a go at ya Scotty, you're a good bugger, im sayin lighten up mate, I will never be ashamed or feel embarrassed to say in public I enjoyed taking my (at the time) new bike up to close to it's top speed on the first day of ownership, mate I farkin love speed, have done since....for ever, couldn't give two hoots what you or anyone else thinks if ive expressed I LOVE motorcycling, on any road be it straight or bent

**Boob Johnson** · 29th October 2008, 00:11

Originally Posted by pritch008

You missed the pick of the bunch: the RC8

Hell yes, had a good look at one for the first time in the flesh in Palmerston North two weeks ago, to say its an amazing piece of machinery would be an understatement.

**BarBender** · 29th October 2008, 07:01

Originally Posted by DMNTD

Fishing with the wrong rod brother?

LOL
Rods alright.
Using the wrong bait.

**dipshit** · 29th October 2008, 07:45

Originally Posted by Boob Johnson

had ya left hand wresting on ya high while you went through by us, clutchless up shifting & gassing it on to make sure we heard you lol ....

Do you need any tissues to wipe the cum off your monitor..?

**Boob Johnson** · 29th October 2008, 08:10

Originally Posted by dipshit

Do you need any tissues to wipe the cum off your monitor..?

Sorry if I offended you with the "SV thou's are the diet coke of v twins"

Won't happen again

**Dazza** · 29th October 2008, 08:51

Originally Posted by pritch008

You missed the pick of the bunch: the RC8

Ahmen to that Pritch, I'm going to take it for another spin in December, this time she's got the full Akrapovic,nice & fruity

**Forest** · 29th October 2008, 09:07

Originally Posted by johan

What is linear piston speed?

The answer was given earlier, but basically in a large-capacity v-twin engine the pistons have to move further than in other multi-cylinder engine configurations.

Unfortunately there are physical engineering limits on the maximum linear speed that a piston can travel. If you exceed these limits, the oil isn't able to keep the engine lubricated and the cylinder bores start to wear out.

In a race engine this isn't really a problem since the mechanics rebuild the engines regularly. However it is a problem on road bikes since the repair work is complex and costly.

The high-performance large-capacity v-twins used in modern sports bikes like Ducatis, Aprilias, and KTMs are running very close to the engineering limits for linear piston speed. This is what prompted my earlier comment.

**johan** · 29th October 2008, 10:59

Originally Posted by Forest

The answer was given earlier, but basically in a large-capacity v-twin engine the pistons have to move further than in other multi-cylinder engine configurations.

Unfortunately there are physical engineering limits on the maximum linear speed that a piston can travel. If you exceed these limits, the oil isn't able to keep the engine lubricated and the cylinder bores start to wear out.

In a race engine this isn't really a problem since the mechanics rebuild the engines regularly. However it is a problem on road bikes since the repair work is complex and costly.

The high-performance large-capacity v-twins used in modern sports bikes like Ducatis, Aprilias, and KTMs are running very close to the engineering limits for linear piston speed. This is what prompted my earlier comment.

Thanks for that explanation. I do understand piston speed, but I haven't seen 'linear' piston speed before.

I thought the higher RPMs in the il4 made the piston speed pretty much the same as a twin with longer stroke but lower revs?

I would imagine a 16,000 rpm 600cc falling apart a lot quicker then a 9000 rpm twin?

But as you said, on a road bike, I doubt the engine spend much time at the redline/maximum piston speed and if it is a race bike, then that's a part of the game.

**Forest** · 29th October 2008, 11:32

Originally Posted by johan

Thanks for that explanation. I do understand piston speed, but I haven't seen 'linear' piston speed before.

I thought the higher RPMs in the il4 made the piston speed pretty much the same as a twin with longer stroke but lower revs?

I would imagine a 16,000 rpm 600cc falling apart a lot quicker then a 9000 rpm twin?

But as you said, on a road bike, I doubt the engine spend much time at the redline/maximum piston speed and if it is a race bike, then that's a part of the game.

You are right. Given that pistons only travel in straight lines, the 'linear' is probably redundant

For a real world example, consider the Honda CBR600 and the Ducati 1098. I'm probably being unfair in comparing these at the engine red-line (but that's when the greatest engine damage will occur).

Honda CBR600:
42.5mm stroke
15,000 rpm redline
average piston speed = 2 x 15,000 x 42.5mm / 60 seconds = 21.25 metres per second

Ducati 1098:
64.7mm stroke
10,700 rpm redline
average piston speed = 2 x 10,700 x 64.7mm / 60 seconds = 23.08 metres per second

Note: Got the stroke and redline numbers through google. Please correct me if they're wrong.

**Forest** · 29th October 2008, 11:54

If anybody knows the conrod length (between centres) for the CBR600 and 1098 then I'll do some trigonometry and calculate the peak piston speeds as well.