Sportbike World banner

1 - 7 of 7 Posts

·
Registered
Joined
·
90 Posts
Discussion Starter #1
I've posted this in one or two other locations with little response so please forgive me if your reading this twice. Is there any good information available, or can someone explain, how/why similar displacement V-twins and Inline 4s produce power differently? Surely the Ducatisti know?!
 

·
Registered
Joined
·
148 Posts
Wow... that thread is certainly interesting but some of it went over my head!!

Particularly:

"The liter inline fours (GSXR-1K, R1 & 929) have become increasingly less 'over square', whereas the 'opposite' trend has become prevalent in the liter twins (998, TL, RC-51 & Prillers). This trend attempts to make the four's more like twins and twins more like fours, in terms of bore vs effective valve area."

Anyone got any idea what this means?

And does moving intertia of the larger piston mass have no effect - is it just the valve/exhaust area issue?
 

·
Registered
Joined
·
6 Posts
It means that the bore to stroke ratio of v-twins are increasing (bore is increasing while stroke decreases) in order to rev higher to get more horse power.

While on the inline fours, the ratio is decreasing (smaller bores with longer stroke) so that the engines can breathe better at slow speed, this making more torque at lower rpms.

Case in point, the new Ducati 998/999 testastretta engine has bore and stroke of 100x63.5xmm compared to 98x66mm from the 996. And the 2002 Yamaha R1 is 74x58mm compared to old YZF1000 at 75.5x56mm. The mighty Suzuki GSXR1000 has an even smaller ratio at 73x59mm (the GSXR1000 shares the same head as the GSXR750).

Advances in material sciences and manufacturing methods have lead to stronger and lighter parts that are up to the task. It's fascinating stuff. Check out the references below.

The New Testastretta
YZF-R1 Engine Article
 
1 - 7 of 7 Posts
Top