Doom Patrol wrote: ↑Sun May 17, 2020 12:54 pm
Thankyou WT, good advice as always. It's something I don't know a great deal about, I must admit. but with my lay mans knowledge I know the original 175 barrel was not designed for a packer. If you raised it would it not throw out the port timings?
The 39 mm compression height piston with 107 mm con-rod equates to piston crown to crankshaft centre @ TDC = 146 + (stroke/2)
The 30 mm compression height piston with 116 mm con-rod equates to piston crown to crankshaft centre @ TDC = 146 + (stroke/2)
Exactly the same, but the duration of the port timings will vary by very little. The overall critical dimension with a standard stroke:
146 + (58/2) = 175
In the scenario you may adopt:
The 39 mm compression height piston with 110 mm con-rod equates to:
piston crown to crankshaft centre @ TDC = 149 + (60/2) which is 179.
The 4 mm difference SHOULD mean a 4 mm base packer, but, knowing that the standard squish is notoriously oversize, the likelihood is that 3 mm would be better with adjustments to increase (if necessary) with base gasketting.
(I spend a lot of time matching the profile of the head to the piston in any engine build which is why I have a small lathe & fixtures with form tools. The 'head is a heat sink & can only do it's job properly if it is able to absorb the combustion heat well to give the piston crown an easier life. That also has the advantage of keeping the combustion area cleaner & shows the transfer flows across the crown upon strip down. Should anybody desire to know
Inevitably, squish optimisation may require that the combustion area volume require modifying by removal of material from the head. Not a difficult process, but an optimised engine will perform better & inspire confidence IMHO)
Despite claims for head gaskets of any generic design being now 'suitable', I never, ever use them unless they are of the enclosed, ring, type as in the case of a machined recess. But that is through my personal experience & desire to eliminate a weak point.