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 why??

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nigel breeze

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Registration date : 2007-12-23

PostSubject: why??   Tue Feb 09, 2016 7:03 am

"Dean from Los Angeles did use the "Holy Wonder" in 1968

I had that same sort of thought in 1968 when I was racing karts. I realized there was no where near enough exhaust area on the McCulloch kart engines. So I drilled 18 exhaust holes above the intakes. Vented to the atmosphere. After some experimentation I discovered that at low speeds the intake charge went directly out the exhaust, so there was no such thing as low end torque. Since is was ported directly outside, at low speeds, like at starting, it blew fuel out of everywhere and gave the distinct sound and visual impression of a blown head gasket.Once it came up on the pipe, it produced glorious amounts of power. It was named the Holey Wonder, not only for the holes, but for the unworldy sound it made at full pop. The conventional ported McCulloch would wind up to 12-13,000 rpm. This thing made 18,000 rpm. Won quite a few races with it.The rod wasn't up to the task I soon found out. It would last about 3 short races and break. Always at the top end of the rod. And then it would transform itself into an 18,000 rpm buzz saw. I still have scars from one of the grenade jobs. Piston ring life on an extreme ported engine is not long, but you live with the trade offs."

The original: http://www.landracing.com/forum/index.php/topic,3495.0.html

Trevor, does this sound achievable?? study
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john bass

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PostSubject: Not understood...   Wed Feb 10, 2016 6:16 am

Les ?,

"....18 exhaust holes above the intakes ... "

I cannot get my head around that comment ....

Any suggestion of what I am missing?
..

Cheers!


Last edited by john bass on Wed Feb 10, 2016 6:26 am; edited 1 time in total
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Trevor Amos



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PostSubject: Re: why??   Wed Feb 10, 2016 6:23 am

Why?
Yes, exactly Nigel, why, but is it achievable, the guy claims he did it so it must be, mustn`t it?

The first thing that occurs to me is, why was he allowed to race the thing with fuel and very noisy hot exhaust gas being blown around like that at lower engine speed? And, why would anyone try to solve one problem and create many far greater ones? Seems some people enjoy revelling in continued perversity! One thing is certain, without potential and significant breathing improvements elsewhere, the engine will produce far less power at 18,000 rpm than at 12,000. No mention is made of other porting modifications so meaningless revs making diminishing power is all too easy to achieve.
An example of that can be seen with the Aprilia engine. At 13,250 rpm 54 hp is available at the gear box output sprocket, by allowing revs to go up to 14,500 power falls to 47hp. In full race mode, gear changes were made at 13,250/13500 rpm and was counter-productive to do otherwise. Our guy can remember some very precise details from 68, but not apparently, the power output, conveniently perhaps.
The short circuiting of transferred gas at low rpm via the exhaust ports is to be expected, whilst we are not told the diameter of the 18 extra exhaust ports the combined extra exhaust area must be pretty big.
A good example of having too large an exhaust port at the wrong rpm can again be seen in the Aprilia. By blocking off the sub-exhaust ports, power below 9,750rpm was improved, but as rpm rose and blowdown time/area decreased power began to fade, at 13,000rpm the loss was 15hp. So both the Aprilia and the Holey Wonder confirm that too big, too early is not at all helpful.

Even way back in the 60s some Bantam competitors were claiming 12,000 rpm rocket ships, my best 52x58 engine could just get over 10,000 in the lower gears and a touch over 9,250 in top, never snapped a rod and it lasted all season running on R40. Trying to run that kart motor at 13,000 must have exceeded the rod safety factor by at least 2:1, the elongation at tdc is not sustainable hence the rapid failure rate at the weakest point. Mention is made of the engine coming on to the pipe and producing lots of power, that is strange as only the original exhaust port is connected to the pipe, but is handling far less gas as the additional 18 holes vent directly to atmosphere. Were Kart pipes that advanced back in 68, I seem to remember rudimentary things that didn`t seem to achieve much.
So in the end is this achievable, well it`s not achieving much if an engines only survives for three short races then self-destructs, and did the barrel get away unscathed amidst all of this carnage? A lot of questions left un-answered, so I have my doubts. However, full marks for trying and then keeping us entertained!

Trevor
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john bass

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PostSubject: Ah the intakes ...   Wed Feb 10, 2016 6:37 am

Thanks Trevor,

"The intakes" are the `intake ports´.... must be American English again...!

The whole thing sounds a bit like the fish I caught in the Wye -- which year would that be...?

It they were small holes I wonder if the boost of speed and power could be attributed to gas dynamics theory ?
where at high engine speed there´s suck when there would be blow at the lower speeds.

Er... uh ... um!
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john bass

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PostSubject: I think...   Wed Feb 10, 2016 10:25 pm

I think...

Shouldn´t do it too often -- it hurts....

If the size of the holes was correct there could be what the writer says....

Now -- what size hole would that be....??

CheerS!
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