High CR pistons and squish heads chat…

Fast Eddie

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Can anyone please share pics of the kind of piston design required to achieve 11:1cr in a 750?

I’m interested in the crown shape etc.
 

SteveA

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I'm guessing no! But....the AN product made by Omega must be the nearest, the rest to be achieved by skimming heads and barrels as required.....

I remember talking to Dave Watson's engine builder, about 10 years ago before they were using JSM pistons in the 1007, they also had a 750, which I think was a short stroke 270 crank, a lot of machining was required to get over 11:1

 

Fast Eddie

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Thanks Steve.
I tried discussing pistons with Andover once and gave up.
Seems to me the design work was done by Mick Hemmings.
 
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Ive got a pair of what i think are hepolite powermax 750 pistons at .020" over. Came with a basket case bike, dont think they have been used. rooted out and photos sent
.https://drive.google.com/file/d/1upo9n8R2I6BBc5dSshpu67DT60kX5NiA/view?usp=sharing

 
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Mick did have some pistons made by Wiseco

My head (fully hemisphered) has been skimmed. It took a lot of mchining to get the compression back down to 11:1

They were the same design as the factory AMA race kit, same shape as the later 750 Shortstroke pistons, just a 73mm bore
 
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u7H9GrU.jpg
 

ZFD

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Our forged pistons were made along the lines laid down by my engine man Rudi Kolano who wasn't overly impressed with the Wisecos.

No idea who you tried to discuss our pistons with but I'd recommend you talk to Ashley Cutler.
Joe S.
 
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Look no further. 11.3 to 1 C.R. Currently available in 73 through 74.5mm - JSM forged lightweight domed pistons (185+ grams). Race proven. For long rods of course.

domed5long.jpg


domed11.jpg


with 3D underdome milling for consistant strength and maximum lightening.
domed17.jpg


As used in Randy Johnson’s land speed record breaker for SCTA 750cc production pushrod motors on gasoline (126mph at Bonneville in 2012 with a best one way speed of 128 mph).

Randy-Johnson-record-holder.jpg
 
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Thanks Steve.
I tried discussing pistons with Andover once and gave up.
Seems to me the design work was done by Mick Hemmings.
No, Mick had no input whatsoever, the design work was by Rudi, but it is close to the Wiseco HC piston but lighter despite being forged - not the normal offering they sold. Some say they are over the top on compression, but considering Wiseco had a similar piston, I doubt it.
You're more than welcome to come and measure one, and view the Wiseco piston that some say never existed.
Just about to order a third batch of Omegas, and no one has complained about them. One customers barrel broke during a race, the pistons survived and have gone back in.
 
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The old Wisecos are based on two stroke castings they used for something else. You can see the excess material for ring location on the underside.
 

Fast Eddie

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No, Mick had no input whatsoever, the design work was by Rudi, but it is close to the Wiseco HC piston but lighter despite being forged - not the normal offering they sold. Some say they are over the top on compression, but considering Wiseco had a similar piston, I doubt it.
You're more than welcome to come and measure one, and view the Wiseco piston that some say never existed.
Just about to order a third batch of Omegas, and no one has complained about them. One customers barrel broke during a race, the pistons survived and have gone back in.
What compression ratio do yours give in an otherwise standard head / barrel ?
 

ntst8

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Wandering around the topic, I was chatting to a guy who has built a very fast 750 track bike, he was helping with the head on my 961, and commented on how similar the 961 combustion chamber and valve sizing was to his race bike head. I didn't ask on the pistons, presumably flat top in that case.
 
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What is the dome doing to flow through the head and flame propagation. Given the plug location on the side of the combustion chamber it could be splitting the flame propagation.
 
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What is the dome doing? Its raising compression - winning races and setting land speed records. The dome is only 5mm tall. The combustion chamber is approx 22mm deep. You have a periphery squish band creating turbulance and an efficient reduced combustion chamber volume - tighter around the outside with the greatest volume in the center to concentrate flame propagation.
 
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What compression ratio do yours give in an otherwise standard head / barrel ?
It was designed to give around 10.4:1 they had all the drawings of the head, barrel and crank cases to work it all out. Side by side the crown is similar in size and shape to the Wiseco AMA, not the lower compression Wiseco. Photos will be in the next newsletter.
 
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Can anyone please share pics of the kind of piston design required to achieve 11:1cr in a 750?

I’m interested in the crown shape etc.
The crown shape will be determined by the cylinder head hemisphere but you'll obviuosly have to allow for valve cutaways. All you need to do is look at some 10:1 pistons and extrapolate.
 
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What is the dome doing? Its raising compression - winning races and setting land speed records. The dome is only 5mm tall. The combustion chamber is approx 22mm deep. You have a periphery squish band creating turbulance and an efficient reduced combustion chamber volume - tighter around the outside with the greatest volume in the center to concentrate flame propagation.
Most flat top piston engines have efficient combustion due to the flat top. Introduce domed pistons and squish and power may go up but fuel efficiency suffers due to incomplete combustion in the squish areas. The standard Norton head already creates turbulence.
 

Fast Eddie

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Most flat top piston engines have efficient combustion due to the flat top. Introduce domed pistons and squish and power may go up but fuel efficiency suffers due to incomplete combustion in the squish areas. The standard Norton head already creates turbulence.
Unless we’re talking domes designed to very closely match the hemisphere of the combustion chamber, they won’t affect squish.

The easiest squish to get on a Norton twin is by using the flat stepped area. Yes the stock head creates turbulence, but it tightening up the gap in the stepped area gets a nice bit of squish too.

Personally, I am convinced of the benefits of squish due to running a tight squish (approx 0.040”) in my 920, which runs 11:1 cr, without issue, on pump fuel.
 
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