Deck height and shims etc

Just "had" to measure all the deck heights and head volumes for all cylinders. All the head volumes were somewhere between 68 and 69 cc (68.5 on average). I used two head gaskets to measure the deck height + a feeler gauge. The deck height was then 3 mm minus the feeler gauge. Since the piston protrudes, this measure becomes negative.

On cylinders 1 and 2 the deck height, dh, became -2.75 mm and -2.65 mm on cylinders 3 and 4. By using two 0.06 inch shims I will get a CR of:

CR, cylinders 1-2 : 7.78:1
CR, cylinders 3-4 : 7.72:1

The shims coming with the kit are 0.04, 0.06 and 0.09. This will give 0.04, 0.06, 0.08, 0.09, 0.10, 0.12, 0.13 and so on. But, it does not give 0.11. With one 0.04 and one 0.06 I will get:

CR, cylinders 1-2 : 8.07:1
CR, cylinders 3-4 : 8.01:1

This is above 8:1, so I ordered some shims from CB Performance (0.01 and 0.02 just in case). A 0.09 and a 0.02 gives 0.11, and this will be a CR of:

CR, cylinders 1-2 : 7.92:1
CR, cylinders 3-4 : 7.86:1

The I (re) checked the rings, on both ends of the cylinders this time as shown in the new Aerovee DVD.

Deck height and spark plugs

The compression ratio for the Aerovee is set on the basis of 55cc head volume (I measured them to be 53). I got a pair of new Revmaster heads instead of the hopeless "Mofoco" head from Aeroconversion (if my sets of heads were just a bad batch, I don't know, but the Revmaster heads are like a Swiss watch in comparison). The volume of the Revmaster heads are 68 cc. This means I cannot use the table in the manual to set the correct shims. I also have the Great Plains manual, and I used the procedure to measure and calculate CR there.

CR = (swept volume + deck volume + head volume)/(deck volume + head volume)

and deck volume = 1/4 * (pi*D^2) * (measured deck + head gasket + shims)

Measured deck height is as described in the Aerovee manual. I will go for the closest to 8:1 from the lower side. 2cc head volume difference doesn't seem like much, but it represents a difference in CR of 7.94:1 for 55cc and 8.13:1 for 53cc for the same shim sizes.

This had me thinking. Why are the Revmaster heads 68 cc while the "stock" heads are 53-55? Did some googling, and the only reason I can find is the reduced squish band. The squish band is the flat area round the "dome" of the combustion chamber and it's distance to the piston at top dead center. Reducing this will increase detonation margins and generally improve the combustion process. This is done when the piston "squishes" out the mixture in the squish band into the center of the combustion chamber. This causes lots of turbulence, which improves the combustion and decreases the possibility for detonation. The Revmaster head are simply put a whole lot better. When calculating this band for a "stock" Aerovee head and a Revmaster head, the band for the Aerovee is 3.8 mm while it is 1.5 for the Revmaster (at CR = 8:1). 3.8 mm is (according to Google :-) ) not nearly enough to cause any "squish" at all.

Then another small problem came up. The Revmaster heads have the second spark plugs at a different angle than the Aerovee. The are drilled so that only a spark plug with 16mm hex will fit. The Autolite plugs have 18 mm hex, and the cup for the 18 mm hex is too large. Revmaster use the NGK DCPR7E. This is a 16 mm hex variant of the NGK DPR7E which is (almost) a direct replacement for the Autolite 4163 (used by Aeroconversion). The direct replacement is the one notch "colder" DPR8E. I went to the local "Mekonomen" and they had exactly what I needed, the NGK DCPR8E. Maybe with the Revmaster heads (and all the squishing) I will need the "hotter" DCPR7E, but starting with a slightly colder plug is always safe, while a hotter may not be.

  

Engine

Applied Permatex Aviation gasket #3 this time. The stuff from Wurth, looked good, but turned brittle like glass after a while.

Engine

On the verge to just buy a ULPower 260i, I decided to just put together the engine (again) and see how it goes. All clearances measures up with a little bit of trimming.

I like the concept of the AeroVee; build the engine yourself. As for the execution of this concept from Aeroconversions...