Exotic/Rare Bikes

[Le_Fromage_Grande]

Somewhere along the line didnt Yamaha admit the gains from extra valves were marginal or have I imagined that?

What engines were the 7 & 9 in? I'm only aware of 5 in bikes and race cars (but I haven't kept up with engine development since the end of the 90s)

Development engines before they settled on 5 valves per cylinder

[Le_Fromage_Grande]

Somewhere along the line didnt Yamaha admit the gains from extra valves were marginal or have I imagined that?

What engines were the 7 & 9 in? I'm only aware of 5 in bikes and race cars (but I haven't kept up with engine development since the end of the 90s)

I think Yamaha persevered with 5v heads for rather longer than they should have. For a while they ran 5V heads in the F1 engines they built for various teams but quietly went back to 4V heads later in the program while still publicly maintaining they were 5V units.

Never really saw the point of 5V heads meself. A marginal increase in valve area offset by significantly more complexity. Pretty sure that most high performance motors these days are 4V.

The 5 valve Yamaha head isn't complicated, it's bucket and shim and the intake cam has an extra lobe and there's an extra intake valve, it's less complicated than the early Suzuki 16 valve heads.

[Mr. Dazzle]

Its like they say though, the most reliable part is "no part" so 5v heads are always (on average) gonna be more expensive and less reliable than 4v. Therefore the benefits have to be worth it.

The benefit of 4v over 2v is demonstrably worth it cause 4v heads are absolutely dominant in performance engines. 5v heads have had a few outings but they've never really displaced 4v and everyone who's dabbled in them has quietly returned to 4v pretty much?

[Le_Fromage_Grande]

I think that improved metallurgy has done away with the reasons to have a lot of small valves, as the slightly larger can now rev as hard as the smaller valves without the heads dropping off.

When the FZ750 came out in 1985 the GSXR750 had larger valve area, but Yamaha claimed the greater circumference of 5 valves gave better flow, the FZ750 engine was very popular and successful in racing from 1985 to 1989, but whether this was thanks to the 5 valve head or just a well made engine I don't know.

[mangocrazy]

I think the simple question is - who is using 5V heads now? I can't think of a single manufacturer, car or bike. That tells you all you need to know about the benefits (or otherwise) of 5V heads.

[Mr. Dazzle]

I think the simple question is - who is using 5V heads now? I can't think of a single manufacturer, car or bike. That tells you all you need to know about the benefits (or otherwise) of 5V heads.

'tis the true test of a good idea. Do people actually use it?

That said, I do think the NR is a good idea, but only 'cause it's addressing an incredibly specific set of circumstances. I suppose the irony is, loads of the bits on it are actually way more common now whereas the flagship pistons are long gone.