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Author Topic: 2 stroke comeback.  (Read 20519 times)

Offline Keltik

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  • Posts: 20
Re: 2 stroke comeback.
« Reply #165 on: June 27, 2021, 16:23:03 PM »
Crossplane crank for novelty purposes?

I'm sure there's an engineering reason to do it but I just want to hear what it sounds like.
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Offline Paul

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Re: 2 stroke comeback.
« Reply #166 on: June 27, 2021, 17:38:21 PM »
Quote from: Keltik on June 27, 2021, 16:23:03 PM
Crossplane crank for novelty purposes
On a 4-cyl 2-stroke? It would be terrible for vibration.
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Offline Jeff B

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  • Posts: 5176
Re: 2 stroke comeback.
« Reply #167 on: June 27, 2021, 18:00:26 PM »
Quote from: Paul on June 27, 2021, 17:38:21 PM
On a 4-cyl 2-stroke? It would be terrible for vibration.

I will have to have cross plane crank if I want even 90 deg firing order....
That was the plan....
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Offline Kakapo76

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  • Posts: 546
Re: 2 stroke comeback.
« Reply #168 on: June 27, 2021, 20:39:09 PM »
Quote from: Keltik on June 27, 2021, 16:23:03 PM
Crossplane crank for novelty purposes?

 

I am now fully aroused....  pop cou
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Offline Jeff B

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Re: 2 stroke comeback.
« Reply #169 on: June 28, 2021, 06:34:42 AM »
Am I missing something here? What's good about a crossplane crank? It's just the firing order....
I don't really want to go flat plane like a 4 cyl 4 stroke as that will be firing 2x cylinders at same time.
I'm not sure why Yamaha did it on their R1? It just makes an uneven firing order and sounds like a v4...
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Offline Paul

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Re: 2 stroke comeback.
« Reply #170 on: June 28, 2021, 10:37:49 AM »
Crossplane only really makes any sense on a 90degree V8.

Quote from: Jeff B on June 28, 2021, 06:34:42 AM
I don't really want to go flat plane like a 4 cyl 4 stroke as that will be firing 2x cylinders at same time.
I'm not sure why Yamaha did it on their R1?

Smoothness and vibration - controlling the opposite mass-oscillations.
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Offline Kakapo76

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  • Posts: 546
Re: 2 stroke comeback.
« Reply #171 on: June 28, 2021, 15:19:40 PM »
a good explanation of the relative merits.

https://www.youtube.com/watch?v=-s5bSQIQQsY&ab_channel=EngineeringExplained

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Offline Keltik

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  • Posts: 20
Re: 2 stroke comeback.
« Reply #172 on: June 28, 2021, 19:14:13 PM »
One consideration for your crank phasing could be running dual expansion chambers with cylinders paired together.  I think snowmobiles might do that kind of thing
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Offline Kakapo76

  • Website Member
  • Posts: 546
Re: 2 stroke comeback.
« Reply #173 on: June 28, 2021, 19:15:15 PM »
Hey Jeff,

I found a channel you might find interesting/ useful- got some cool experimental 2 stroke tuning stuff.

https://www.youtube.com/channel/UCHRXYmO1vdp-Bi1-w11R7WQ
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Offline powerband

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  • Posts: 19
Re: 2 stroke comeback.
« Reply #174 on: June 29, 2021, 13:14:02 PM »
Hi Jeff,
The Yamaha TZ750 straight 4 is 1&4 TDC then 2&3 TDC. Folan, a Swedish engineer built a 1,000cc twin both @ TDC for torque, then split crank to 180 for power, fast or slow tracks for MX sidecar racing.
Paul.
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Offline Jeff B

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Re: 2 stroke comeback.
« Reply #175 on: June 29, 2021, 13:30:18 PM »
Hmmm interesting, weren't the TZ 700s and 750s in essence 2x TZ 350s joined together? (2x seperate cranks)
I guess glavine 1,4 down and 2,3 up @ 180 deg will be the best for balance but I'm not sure if the crank will like firing 2x cylinders at once?
All the 2 stroke 4 cylinder outboards seem to fire at 90 deg evenly (cross plane crank)
And I think that would sound better,?
In motorcycles, the "twingles" always sounded a bit off....

* IMG_20210629_35977.jpg (40.13 kB, 432x768 - viewed 446 times.)
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Offline orac12

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  • Posts: 9
Re: 2 stroke comeback.
« Reply #176 on: July 08, 2021, 10:55:03 AM »
I think there is a couple different theories in the motorcycle world to do with big bang or screamer firing order setups. The big bang, giving more time for the tyre to relax and regain grip between combustion cycles.
Where as a screamer the combustion cycles are evenly spaced and provide more consistent power.

Not sure how it would affect a jetboat,big bang firing order might be hard on splines ? 
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Offline Jeff B

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Re: 2 stroke comeback.
« Reply #177 on: July 08, 2021, 11:02:11 AM »
Quote from: orac12 on July 08, 2021, 10:55:03 AM
I think there is a couple different theories in the motorcycle world to do with big bang or screamer firing order setups. The big bang, giving more time for the tyre to relax and regain grip between combustion cycles.
Where as a screamer the combustion cycles are evenly spaced and provide more consistent power.

Not sure how it would affect a jetboat,big bang firing order might be hard on splines ?

Yeah that's what I believed also.
An even firing pulse always seemed like a better option to me.
I'm not sure why Yamaha adopted the cross plane crank for their R1? Lots of mumbo jumbo about torque transfer and traction but I just cant like the sound it makes Haha.
I dont need uneven torque pulses or traction aid.....I hope....
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Offline orac12

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  • Posts: 9
Re: 2 stroke comeback.
« Reply #178 on: July 08, 2021, 13:02:39 PM »
I think the smoother output of the screamer setup would be the way to go in a jetboat.
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Offline Warwick Marflitt

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Re: 2 stroke comeback.
« Reply #179 on: July 09, 2021, 07:52:17 AM »
Next project will be 9 cylinder radial powered Gnome style engine...with a stationary crank,the block and cylinders all rotating en mass!! Jeff's trickiest waterjacket creation yet???
Power strokes evenly spaced across the cranks duration is more linear and smoother than twin firings at 180.... imagine a two pole electric motors power/torque delivery?? And then a 30 pole/cyl = one power stroke/push every 12deg of crank rotation probably why the Americans built the 36cyl 127litre  Lycoming XR-7755 5,000hp radial... hi-
« Last Edit: July 09, 2021, 07:54:25 AM by Warwick Marflitt »
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Warwick Marflitt
HJ53 752 Holden 3.8 V6 FloPro 19&17Deg Impellers

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