revtothelimit - motorbike forum

Mr. Dazzle wrote: Sun Jan 24, 2021 8:08 am More valves generally also means more valve area, which is one of the big reasons they do it. The valves are circular, so if you imagine fitting circular valves into a circular cylinder head you can 'cover' more of the bore with a greater number of smaller valves.

That in turn means you have less restriction on gas getting jn/out of the cylinders. One of the limitations on engine power is how quickly and easily you can get the fuel in and the exhaust out. More valve area means you can shove it in/out more quickly so you push the revs higher and the peak power up.

5v doesn't intrinsically make an engine peaky, bit it does facilitate tuning for high peak power at peak revs, which has the effect of making the engine revvy. Chicken and egg kinda thing.

The Spin Doctor wrote: Wed Apr 21, 2021 12:21 pm

Mr. Dazzle wrote: Sun Jan 24, 2021 8:08 am More valves generally also means more valve area, which is one of the big reasons they do it. The valves are circular, so if you imagine fitting circular valves into a circular cylinder head you can 'cover' more of the bore with a greater number of smaller valves.

That in turn means you have less restriction on gas getting jn/out of the cylinders. One of the limitations on engine power is how quickly and easily you can get the fuel in and the exhaust out. More valve area means you can shove it in/out more quickly so you push the revs higher and the peak power up.

5v doesn't intrinsically make an engine peaky, bit it does facilitate tuning for high peak power at peak revs, which has the effect of making the engine revvy. Chicken and egg kinda thing.

You can also close the exhaust valves sooner, which means less fresh charge chasing the burnt gases out the exhaust ports.

That's why the FZ was so frugal. My 1990 version averaged 55 mpg, would hit 60 mpg without too much trouble and got close to 70 mpg on one Bank Holiday Monday run back across France when I couldn't find an open filling station for 200 miles. Nicest engine on anything I've owned.

My 92 WN GSX-R750 was more powerful (according to the spec sheet) and was far more peaky, but struggled to top 40 mpg. One German autobahn run got it down to just under 30 mpg.

Yorick wrote: Wed Apr 21, 2021 12:23 pm
You must ride like a gurl. I used to get my GSXR1000 down to 17 mpg

The Spin Doctor wrote: Wed Apr 21, 2021 12:21 pm

Mr. Dazzle wrote: Sun Jan 24, 2021 8:08 am More valves generally also means more valve area, which is one of the big reasons they do it. The valves are circular, so if you imagine fitting circular valves into a circular cylinder head you can 'cover' more of the bore with a greater number of smaller valves.

That in turn means you have less restriction on gas getting jn/out of the cylinders. One of the limitations on engine power is how quickly and easily you can get the fuel in and the exhaust out. More valve area means you can shove it in/out more quickly so you push the revs higher and the peak power up.

5v doesn't intrinsically make an engine peaky, bit it does facilitate tuning for high peak power at peak revs, which has the effect of making the engine revvy. Chicken and egg kinda thing.

You can also close the exhaust valves sooner, which means less fresh charge chasing the burnt gases out the exhaust ports.

That's why the FZ was so frugal. My 1990 version averaged 55 mpg, would hit 60 mpg without too much trouble and got close to 70 mpg on one Bank Holiday Monday run back across France when I couldn't find an open filling station for 200 miles. Nicest engine on anything I've owned.

My 92 WN GSX-R750 was more powerful (according to the spec sheet) and was far more peaky, but struggled to top 40 mpg. One German autobahn run got it down to just under 30 mpg.

The Spin Doctor wrote: Wed Apr 21, 2021 12:25 pm

Yorick wrote: Wed Apr 21, 2021 12:23 pm
You must ride like a gurl. I used to get my GSXR1000 down to 17 mpg

Yeah, but you have bigger bores than me

Le_Fromage_Grande wrote: Thu Apr 22, 2021 7:46 am

The Spin Doctor wrote: Wed Apr 21, 2021 12:25 pm

Yorick wrote: Wed Apr 21, 2021 12:23 pm
You must ride like a gurl. I used to get my GSXR1000 down to 17 mpg

Yeah, but you have bigger bores than me

Nah, you ride like a gurl, I've never got 50mpg out of an FZ, and my early R1 used to do about 20mpg, I ride like a twat.

Bigjawa wrote: Wed Apr 21, 2021 9:54 pm

Most of the Slingshot and WN on GSXRs had carbs that were far too big, same with the 1100.