From:Dave Molnar e-mail:dave@impax.on.ca
Subject:RE: RE: New goodies Date:Thu Mar 17 09:44:45 2011
Response to:3393
Actually with these new pistons the feel of the compression on the kicker is still fairly light and easy to start. The combustion chamber is huge so no matter what you do mechanically the queeze will be limited. Yesterday I found a deluxe ricardo cylinder in the pile of Girard Fox's stuff I'm working on and by visual comparison to the regular cylinders there is not much difference in the combustion chamber - I did not think it was much but it is even less than what I thought. Rob Olsen mentioned that he had calculated the difference to be I think 2/10 of a point years ago.

The dome shape on my pistons do take up considerably more space. BUT just taking up more space and creating higher compression is not the be all end all solution.

There are many things to take into consideration like flow, turbulance (the more the better) flame travel, even the distance from the spark to the furthest areas among other things. Poor dome shape can actually have adverse affects on cylinder efficiency. The wedge shape I came up with does include a suggestion from Rob Olsen (thanks Rob!). Some of the theory being the combustion chamber and top of piston "gap" at TDC tapers slightly smaller towards the back thus increasing compression as the exploding gases expand without furthering "mechanical" compression. It appears that the performance has been enhanced and torque is impressive. I have to admit there may be and probably is some dumb luck involved as well!

The Rods are the same centre to centre. The pin diameter is 18mm. The cap and rod joint is serrated for exact placement. These serrations are like 1/4-20 thread rolling dies (1/16") and can be machined off to allow for 1/16" shims. The rod can be reworked to the original configuration by milling the width down and boring and honing the big end.

Some of you know that I do like to experiment. It is sure nice not to have to spend all that time fiddling around fitting all those parts together to get the rod properly swinging on the crank.

Ya - aluminum! This mix has 1% tin. Lets remember that Kohler, Techumseh, B&S and many others have been running aluminum rods on crankshafts for ever and ever. In many cases NO OIL PUMPS, NO OIL FILTERS, BIG TIME ABUSE, and in most cases (I know, I had a small engine shop for 5 years) PLENTY OF NEGLECT. These engines probably work harder in more adverse conditions than any others out there. Somehow they run for years like that even with crappy old oil.

Realistically: How much load is on those bearings? Hmmm... perhaps in this case 5.5:1 compression, long gangly stroke, 7.5 hp each maybe... 3,000 rpm... 1 1/8" wide bearings on a deluxe... Not much I say...

At this point this thing feels like it could run forever. Plenty of furthwer testing will happen this year. Maybe its time for a windshield and some bags...

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I like the pistons. I will bet they up the compression a couple of points. Do the rods maintain stock center to center distance or has the pin been relocated ?
Mark
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Some of you are aware that I have been doing some R&D on a new Deluxe high compression piston design and also some new "bearingless" aluminum rods.

I just returned from two week trip to Florida and am able to report that some 400 miles of testing has been done on this test motor at various speeds.

I am very happy with the results so far. These rods bolt right on the crank as is with .002 clearance. The pin is full floating and also bearingless. No more fitting and fiddling with shims and shells. The rods can be reworked back to the old shim and shell method if ever required. The rods are also available for KJs. The dome pistons are working good too. There is a bark and a bite I have not experienced before. There is tons of torque now too.

Email me if you would like more info on these parts.

BTW If you ever get to Ocala Florida - do the Don Garlits Museum! - Conveniently located close to Eustis!