Oddball engines and prototypes

[Pursang]

Took a little finding..Link is here. http://www.trhkc.com/the-special-builders.html

Really fascinating, if you're interested in how very advanced some kart builders were, back in the 60's.

Who knows where karts would be now if suspension wasn't prohibited and/or there was a Formula Libre for karts.

Here's some pics of the Dent Special with self water-cooled Villiers.
Attachment 331608Attachment 331610 Attachment 331609

cheers, Daryl

[Pursang]

It's an Amazing thing about Kiwi Biker

No sooner does one post a (brilliant) idea, but someone out in the real world has done it.

Water-cooled YZ490





"I'd rather say they had a water cooled head cover. Coolant in the cylinder was hardly moving; cooling below the exhaust was non-existent. Not the best solution if you want reliable power." or something like that.

Cheers, Daryl.

[guyhockley]

Google "Dent water cooled conversion" Daryl. I can't post a link sorry - but it's in a vintage kart club site.
Similar to what you're doing but the alloy pipe seats on the lowest fin left on the barrel - and the head is air cooled.
As someone will say - it looks like sitting the barrel in a bucket of water - but it worked.
There's no sin in leaving the head air cooled - MZ's were like that for quite a while.

http://www.kartbook.net/group/vintag...ource=activity
for the aircooled head?
Long thread, good job none here go on that long....

[guyhockley]

Surely this must be the same Mark Mansell as the Victa kart bloke?
http://www.onthewire.co.uk/mm10cc.htm

[Grumph]

Daryl, if you're looking at running the Victa at Lake Gardener - with the known high ambient temps there - you may have a problem with straight water cooling.
It may be worth looking at pumping through a coil in an icebox - or going back to the waterspray as that might give a better return in terms of barrel temp reduction.

[Pursang]

Daryl, if you're looking at running the Victa at Lake Gardener - with the known high ambient temps there - you may have a problem with straight water cooling.
It may be worth looking at pumping through a coil in an icebox - or going back to the waterspray as that might give a better return in terms of barrel temp reduction.

Cool, no radiator out in the airstream either, that'll save some horses. Got to get through a Queensland Summer of testing first.:

Cheers., Daryl.

[Pursang]

After a couple of days of intense study & re-study, I feel like I'm almost, nearly, starting to get IT!

Frits has explained it so many times, in so many ways, to so many people, he deserves a Medal, or a Nobel.

It seems to be all about the "Juggle" between the Blow-down STA & Transfer STA .
And not any old STA, not Jennings, Blair, Bell, et al.
The current Optimum STA's were developed in the RS125.

The juggle comes in the angle.area part.
Creating plenty of port area enables you to reduce the angle (duration),
That reduces your port height,
That reduces your area,
That reduces your TA.....and you start again.

Blowdown STA is causing me some concern .
As far as I can tell, the 'Angle' only applies to the portion of down stroke above the transfer opening?
(Unlike transfer angle(duration) that is functional with the piston going down and up)

I'm developing an excel work sheet to help with the juggle, if not mathematically, perhaps by graphing to indicate the "sweet spot"

If any one has an Excel formula to calculate port height from duration, and would be willing to share, it would be much appreciated. The one I'm using seems to be' haunted' and constantly referring to the on-line ones is awkward.

Cheers, Daryl

[Pursang]

Here's a very hypnotic graphic that clearly demonstrates the differences in piston motion with even small changes in stroke.




Attribution:
By Patrhoue - Own work, CC BY-SA 3.0, https://commons.wikimedia.org/w/inde...curid=16032659

[Pursang]

Got it: For some reason it was recognising PI() as a legitimate function and then ignoring it in the calculation.

Now looks like this: =(C2/2)*COS(C28*3.1416/180)+SQRT((C3^2)-((C2/2)^2)*(SIN(C28*3.1416/180))^2)-(C2/2)-C3+C2

C2 is the stroke C3 is conrod length.

Cheers, Daryl.

[Pursang]

So here is my transfer STA worksheet.



Not surprisingly, it conforms with Frits' earlier recommendations, regarding transfer circumferential length, timing and a realistic RPM.
(It just takes a bit of a mental shift, to move on from 40 years of 40 year old two stroke theory & practice).

Thank-you Very Much,

Cheers, Daryl

[husaberg]

If any one has an Excel formula to calculate port height from duration, and would be willing to share, it would be much appreciated. The one I'm using seems to be' haunted' and constantly referring to the on-line ones is awkward.

Cheers, Daryl

bell and robinson have simple formulas for port height +duration as do jennings.
Robinson is in BBC though lol
pretty sure there is a Prof blair site with a calculator
or just get a copy of eng2mod
http://vannik.co.za/EngMod2T.htm

i think what you might find is the duration figures that Bell used together with the widths generally still fall into line with current ideals.
the greatest gains were made with shapes of ports and transfers.
I seem to recall Frits saying port timing on the aprilias was pretty much static for about 15 years.

[Pursang]

Yes I will have to get EngMod2T, I even watched adegnes's Video walk-through, very helpful.

I will need to cull some other projects, to be able to drop the cash.

The timings seem identical to AG Bell, but those were intended to make the power at 10,000+ rpm.

The Optimum STA's should enable the same, or more, power with a pipe designed for 7,500-8,000.

Efficient Transfer ducts, holding the head down (and as already determined, managing all the extra heat) will be challenges.

But also, I'm not trying to make 50+ hp for an hour, just 20 at the wheel for a few minutes.

Plus I can use methanol and supercharging, if necessary.

cheers, Daryl.

[husaberg]

Here's a very hypnotic graphic that clearly demonstrates the differences in piston motion with even small changes in stroke.




Attribution:
By Patrhoue - Own work, CC BY-SA 3.0, https://commons.wikimedia.org/w/inde...curid=16032659

plus 10....

[Frits Overmars]

After a couple of days of intense study & re-study, I feel like I'm almost, nearly, starting to get IT!
Frits has explained it so many times, in so many ways, to so many people, he deserves a Medal, or a Nobel.
Blowdown STA is causing me some concern. As far as I can tell, the 'Angle' only applies to the portion of down stroke above the transfer opening? (Unlike transfer angle(duration) that is functional with the piston going down and up)

You grasped it.

I'm developing an excel work sheet to help with the juggle, if not mathematically, perhaps by graphing to indicate the "sweet spot". If any one has an Excel formula to calculate port height from duration, and would be willing to share, it would be much appreciated. The one I'm using seems to be' haunted' and constantly referring to the on-line ones is awkward.

The math isn't that complicated Daryl. Here you go:

But the real problem is that port windows are not always simple rectangles; their chordal width may vary with piston position, which will make your Excel job a lot more complicated.

BTW: I've got a couple of medals but a Nobel prize is still missing. Do you happen to know anybody in Sweden?

[Pursang]

You grasped it.

Thanks to you.

The math isn't that complicated Daryl.

No, I got the math. The complication was Excel not playing PI

But the real problem is that port windows are not always simple rectangles; their chordal width may vary with piston position, which will make your Excel job a lot more complicated.

Quite right, and I assume using the geometric centre of the transfer area doesn't account for the piston slowing down and stopping at BDC.
Still, I'm not trying to re-invent EngMod. What it has done is allow a simple play around with the numbers, to prove the concept & the potential.
Now I want to look at a couple of other older engines in the stable.

A copy of EngMod2T is now sitting at the top of the shopping list.

BTW: I've got a couple of medals but a Nobel prize is still missing. Do you happen to know anybody in Sweden?

??? Cheers, Daryl.