Max CpS for pushrod OHV?

[Niels Abildgaard]

Have bougth some moped cranks as I cannot make suitable cranks myself.

http://www.ebay.de/itm/331421986002?_trksid=p2060778.m1438.l2649&ssPageName=STRK%3AMEBIDX%3AIT

Two goes into an opposed piston scheme and one will be modified for the scheme shown next.Desmodromics are nice but it is hard to beat a single crankmounted cam for simplicity

A BMW 801 radial did 3000 rpm/25 valve cycles per second with pushrod valves that must have been between 75 to 85 mm diameter.
My old BMW R 27 250 bike must have had valves around 25 to 30 mm and did 60 cycles per second.
What does V8 engines for racing achieve and how big are the valves?
I am trying to figure how fast a 14 mm pushrod OHV exhaust valve can be run in a 30 times 44 mm cylinder

 

[Niels Abildgaard]

Found this concerning pushrod OHV on the limit.
31 mm valve doing 70 openings per second.

http://www.scuderiatopolino.com/3-4-valvetrain.php

A 14 to 15 mm valve is 8 times less mass and opening half ie 16 times less force at same rpm.Loadbearing area is one fourth and as foces are quadrupled by going two times as fast it is my guess that a half scale of the Fiat valve train will be able to behave at 140 openings per second.

 

[stevehuckss396]

So are you going to build the prototype then?

 

[mu38&Bg#]

If you're turning only 30Hz (1800RPM) why is there much concern over valve train? 1.1L Detroit Diesel cylinders ran this fast with pushrod exhaust valves. Maybe I misunderstand the question. It seems that the sharp lip around the smaller chamber may cause flow restriction, heat loss, and I wonder about knock.

Greg

 

[Niels Abildgaard]

hello Greg.
My wish is not to build a model engine but to make functional model of a novel engine.
Two persons need about 80 horsepower to go places.
Optimum prop diameter at 200 km per hour is 1.6 meter.
Noise acceptable tip speed is 200 meter per seconds or less.
My favourite V2 two stroke direct drive is thus asked to give 80 horsepower at 2400 rpm or 40 cycles per second.
11 m per second piston speed means strokes around 135 mm and then two bores of 90 mm looks nice.
1.75 litre and a mean effective pressure of 8.5 bar will do.
WW1 V-engines working harder was 15 kg per littre.
40 horsepower past a single exhaust valve needs ca 40 mm diameter .
Question : Can a model 13 mm pushrod valve at 120 Hz function?

 

[mu38&Bg#]

I fully understand you're building a working engine. Detailed valve train design is more than I'm familiar with right now. Why would the valve run at 90Hz if the engine is 40Hz? I suppose that is roughly the equivalent operating speed for the open close cycle in the two stroke turning 40Hz. NASCAR runs 41mm exhaust valves with pushrods at 62.5Hz. (corrected from 125Hz)

Greg

 

[mu38&Bg#]

There is also the Mercedes Benz 500l engine built for Penske Racing team in 1994. http://8w.forix.com/penske-mercedes-pc23.html With a 97mm bore the valves would be quite large and ran at almost 90Hz.

 

[Niels Abildgaard]

Hello Greg and a Happy new Year.
The Mercedes had 53mm inlet valve working at 90 Hz,so 35 to 40mm at 40 Hz will be possible.
Very interesting reading and thank You for the link

 

[Niels Abildgaard]

So are you going to build the prototype then?

Hello Steve

Maybe,but first point is to make sure my phantasies are not hot air.
If a pushrod 40 mm valve can be operated 40 times per second it is not futile to scheme a model say 30 mm bore and 44 mm stroke with 14 mm valve and let it run 120 rps.
The rather crazy rulebender pushrod Mercedes engine from Gregs link proves that a 53 mm valve can be opperated at 90 .
As mental game it is more fun than TV.

 

[mu38&Bg#]

Niels, have you seen this? http://www.50products.com/english/index.html

Greg

 

[Niels Abildgaard]

Hello Greg
I have not seen it before and the link is the best gift I have had for years .
Thank You
It is nice to know that I am not the worst two stroke fanatic around.
Is Japaneese difficult to learn and can one get living there permission as 69 old?
Would love to work with that guy.
It is the sound of real power.

Niels

 

[mu38&Bg#]

It's an interesting design. It's too bad it seems there are none in use by modelers. The 1650USD (at 120Y/USD) must be a factor.

I too have engine designs I've been working on for years. It's at the point where I have to build it or just put it on the shelf and do something else. You can continue to try to design and improve with no end, but reality, for better or worse, quickly sets in when you have to build it. And of course, output and efficiency is proof.

You should put your latest posts here to keep on topic. Side valve is compact for sure. I saw something about a sidevalve four stroke aviation engine. http://www.dmotorusa.com/ They don't say much about BSFC though.

Greg

 

[Niels Abildgaard]

Hello Greg
You just started me on another CAD session.
That fourcylinder boxer flathead is best at 2400 rpm 78 horsepower.
Rotax marketing was rigth with the 912.
A sidevalve V2 is coming.
Two stroke of course

 

[Niels Abildgaard]

Number crunching.
Wanted 80 horsepower at 2400 rpm or 40 Hz.
My Mz of DDR origin ran at mean effective pressure of 7.5 bar for nearly 1000 hours and had one new sparkplug midway.
The Rotax 912 is 12 m per second max piston speed.
12 m per second at 40 Hz means strokes of 150 mm without reduction.
92 mm bore in 2 two stroke SV cylinders of 150 mm stroke at 7.5 bar mep gives 80 horsepower.
Enlarged,simplified and improved Harley actually.
A Polish moped crank, two Suzuki conrods and four pine car racer slugs of tungsten will make a beatifull 1:3.4 model

 

[Niels Abildgaard]

Hello Greg

Found this about flathead fuel consumption

http://www.d-motor.eu/nl/fuel-consumption-110.htm

This means around 190 gram per hph or 260 gr per kWh where Rotax 912 claims 280 before gearbox.

 

[mu38&Bg#]

More interesting photos to look at for you, Niels.

http://s1056.photobucket.com/user/uniflow/library/?sort=3&page=1

Greg

 

[Niels Abildgaard]

More interesting photos to look at for you, Niels.

http://s1056.photobucket.com/user/uniflow/library/?sort=3&page=1

Greg

Hello Greg

How on earth have You found them?
I was in contact with them about 8 years ago and have forgotten it.
They have come a long way since.

 

[mu38&Bg#]

I spend far too much time looking at engines.

 

[Niels Abildgaard]

Crank assembly with proper balance.
Some phantasies.