revtothelimit - motorbike forum

Yeah they just wouldn't work if they weren't. Unlike a bike the inlet port is above the piston so there's no "suck" in the suck-squeeze-bang-blow cycle. So you have to force the air in with a turbo. So its kind "push in - squeeze - bang - blow".

Edit: Ship engines are generally both super and turbo charged. They often have a crank driven compressor to get it going at low speed - it just won't run without one - which then gets disconnected at higher speeds and is driven by the exhaust instead.

Nice bike find, I like.

Quite like that, it looks like a proper production bike, got mudguards, mirrors and so on.

One thing that always gets me is the shite people talk about two strokes revving high, they sound like they're reving hard but thas cos they fire twice as often. Anyone with eyes can see on the revcounter that they're not doing 13000. Journalistic hyperbole.
This one makes 88 bhp @ 9885 rpm and I don't know what it revs to but most twostrokes Ive been on sign off fairly quick and you better change gear fairly sharp to make decent progress.

Radial calipers on axial mounts, I’m out

This pic is by far the most interesting one to me.
Hell, its even got an airbox.

Looks like the put the reg/rect in a typically Honda position though eh? Nice and warm next to the spannie.

demographic wrote: Tue Mar 16, 2021 8:00 pm Quite like that, it looks like a proper production bike, got mudguards, mirrors and so on.

One thing that always gets me is the shite people talk about two strokes revving high, they sound like they're reving hard but thas cos they fire twice as often. Anyone with eyes can see on the revcounter that they're not doing 13000. Journalistic hyperbole.
This one makes 88 bhp @ 9885 rpm and I don't know what it revs to but most twostrokes Ive been on sign off fairly quick and you better change gear fairly sharp to make decent progress.

I suspect most of that goes back to the 70s when 4 strokes hand grenaded if you revved them beyond 8000 rpm, I think the red line on my 350 YPVS is 9000rpm, my 1983 GPZ1100 redlines at 8500rpm, my 1990 FZR400 redlines at 14000, and makes power to 15000

Le_Fromage_Grande wrote: Tue Mar 16, 2021 8:40 pm

demographic wrote: Tue Mar 16, 2021 8:00 pm Quite like that, it looks like a proper production bike, got mudguards, mirrors and so on.

One thing that always gets me is the shite people talk about two strokes revving high, they sound like they're reving hard but thas cos they fire twice as often. Anyone with eyes can see on the revcounter that they're not doing 13000. Journalistic hyperbole.
This one makes 88 bhp @ 9885 rpm and I don't know what it revs to but most twostrokes Ive been on sign off fairly quick and you better change gear fairly sharp to make decent progress.

I suspect most of that goes back to the 70s when 4 strokes hand grenaded if you revved them beyond 8000 rpm, I think the red line on my 350 YPVS is 9000rpm, my 1983 GPZ1100 redlines at 8500rpm, my 1990 FZR400 redlines at 14000, and makes power to 15000

Pah, me GIXER revs to 14,500

Couchy wrote: Tue Mar 16, 2021 8:06 pm Radial calipers on axial mounts, I’m out

That's so weird. Good spot.

Yorick wrote: Tue Mar 16, 2021 8:47 pm

Le_Fromage_Grande wrote: Tue Mar 16, 2021 8:40 pm

demographic wrote: Tue Mar 16, 2021 8:00 pm Quite like that, it looks like a proper production bike, got mudguards, mirrors and so on.

One thing that always gets me is the shite people talk about two strokes revving high, they sound like they're reving hard but thas cos they fire twice as often. Anyone with eyes can see on the revcounter that they're not doing 13000. Journalistic hyperbole.
This one makes 88 bhp @ 9885 rpm and I don't know what it revs to but most twostrokes Ive been on sign off fairly quick and you better change gear fairly sharp to make decent progress.

I suspect most of that goes back to the 70s when 4 strokes hand grenaded if you revved them beyond 8000 rpm, I think the red line on my 350 YPVS is 9000rpm, my 1983 GPZ1100 redlines at 8500rpm, my 1990 FZR400 redlines at 14000, and makes power to 15000

Pah, me GIXER revs to 14,500

It's not 30 years old though, I'm expecting the 400 to throw a rod before too long.

Le_Fromage_Grande wrote: Tue Mar 16, 2021 8:40 pm

demographic wrote: Tue Mar 16, 2021 8:00 pm Quite like that, it looks like a proper production bike, got mudguards, mirrors and so on.

One thing that always gets me is the shite people talk about two strokes revving high, they sound like they're reving hard but thas cos they fire twice as often. Anyone with eyes can see on the revcounter that they're not doing 13000. Journalistic hyperbole.
This one makes 88 bhp @ 9885 rpm and I don't know what it revs to but most twostrokes Ive been on sign off fairly quick and you better change gear fairly sharp to make decent progress.

I suspect most of that goes back to the 70s when 4 strokes hand grenaded if you revved them beyond 8000 rpm, I think the red line on my 350 YPVS is 9000rpm, my 1983 GPZ1100 redlines at 8500rpm, my 1990 FZR400 redlines at 14000, and makes power to 15000

Its port time area innit.
Four strokes go oversquare to increase valve area and rev harder, twostrokes have the ports in the cylinder wall and can only go so big on the ports without breaking rings so have longer strokes to increase port time area. Longstroke isn't really helping with the high revs but does help with crankcase compression to get that air fuel mix into the cylinder from the crankcase.
Hell, even my old GSXR has its redline at 13,000 and as far as I remember the Honda RS125 a mate owned had the highest number on the revcounter at 14,000 and that was a full on Honda twostroke racebike.

Plus the fact reving higher means better bearings, lighter pistons, stronger rods, better bore finishes and so on, none of which mates very well with having no oil supply to your rod ends and holes in your cylinder walls.

Itd be interesting to see how fast a supercharged poppet valve stroker went.

That SRC logo on the seat unit will guys in the Honda copyright dept itching, its very HRC

Nice looking bit of kit though.

Mr. Dazzle wrote: Wed Mar 17, 2021 9:13 am Plus the fact reving higher means better bearings, lighter pistons, stronger rods, better bore finishes and so on, none of which mates very well with having no oil supply to your rod ends and holes in your cylinder walls.

Itd be interesting to see how fast a supercharged poppet valve stroker went.

People seem to think two strokes are high revving, narrow power banded buzz bombs, whilst this is true of 1970s race bikes, there are loads of two strokes that are torque monsters, RD400s and CR500s spring to mind, one of the great things about a two stroke is that it's relatively easy to get the power where you want it, for instance my RD350 and FZR400 make roughly the same amount of power from similar engine sizes, the RD has loads more mid range than the FZR and is easier to ride.

Le_Fromage_Grande wrote: Wed Mar 17, 2021 3:46 pm

Mr. Dazzle wrote: Wed Mar 17, 2021 9:13 am Plus the fact reving higher means better bearings, lighter pistons, stronger rods, better bore finishes and so on, none of which mates very well with having no oil supply to your rod ends and holes in your cylinder walls.

Itd be interesting to see how fast a supercharged poppet valve stroker went.

People seem to think two strokes are high revving, narrow power banded buzz bombs, whilst this is true of 1970s race bikes, there are loads of two strokes that are torque monsters, RD400s and CR500s spring to mind, one of the great things about a two stroke is that it's relatively easy to get the power where you want it, for instance my RD350 and FZR400 make roughly the same amount of power from similar engine sizes, the RD has loads more mid range than the FZR and is easier to ride.

Nearly all trials bikes were 2 strokes for awesome torque from zero revs.

They're really good when they're in their 'zone' which is why you see them so much in applications where they can run at a set condition constantly.

Edit...the FZR400 vs. RD350 thing is an interesting point, they're similar power but in different states of tune. If you accept the 2:1 ratio you should be comparing 700cc 4 strokes with 350cc 2s (roughly). I'd imagine a 700cc 4 stroke of RD350 power would be more tractable etc, the FZR400 is just peakier than the RD350 'cause the former is more highly tuned to get that power.

Mr. Dazzle wrote: Wed Mar 17, 2021 3:50 pm They're really good when they're in their 'zone' which is why you see them so much in applications where they can run at a set condition constantly.

Edit...the FZR400 vs. RD350 thing is an interesting point, they're similar power but in different states of tune. If you accept the 2:1 ratio you should be comparing 700cc 4 strokes with 350cc 2s (roughly). I'd imagine a 700cc 4 stroke of RD350 power would be more tractable etc, the FZR400 is just peakier than the RD350 'cause the former is more highly tuned to get that power.

The 350 two strokes were pitched against the 550 four strokes from a sales/marketing perspective in the early 80s, and performance wise they were evenly matched , but the 550s were easier to ride as the engines were smoother and required less gear changes - the 550s were dull to ride.

Yorick wrote: Wed Mar 17, 2021 3:49 pm Nearly all trials bikes were 2 strokes for awesome torque from zero revs.

My KX 500 isn't exactly a revmonster, never had a tacho on it (yet) but bet I've not had it over 8000 if that.
It does have an 86mm piston though but there's fourstrokes with bigger diameter pistons that rev way higher.
They don't have very long pistons though and are basically all top with a gudgeon pin and two thrust faces back and front.

On a twostroke theres a lot of cylinder wall to cover and uncover for each stroke so being oversquare doesn't help.

demographic wrote: Wed Mar 17, 2021 6:23 pm
On a twostroke theres a lot of cylinder wall to cover and uncover for each stroke so being oversquare doesn't help.

Until you start making DOHC Two strokes that is....but that forces you to have a super/turbo charger and probably direct injection. But WTF would you do that, you might as well make a 4 stroke at that point right?

Unless you plan to hook it up to a load which runs at a constant speed. Hence the Kawasaki patent.

Mr. Dazzle wrote: Wed Mar 17, 2021 6:28 pmUntil you start making DOHC Two strokes that is....but that forces you to have a super/turbo charger and probably direct injection. But WTF would you do that, you might as well make a 4 stroke at that point right?

Unless you plan to hook it up to a load which runs at a constant speed. Hence the Kawasaki patent.

I'm interested to see where that goes but wouldn't want to listen to one.
I'd rather hear a lecky motor on its own than a scooter variator constant Waaaaaaaaaaaaaaaah.

They need to make a 125cc version of it for teenagers to play with and learn about home tuning, big bore kits etc.