Re: New Race engine build
Posted: Fri Jun 28, 2019 9:38 am
el-saturn wrote:it isn't 12 bar - his gauge would (ef) indicate a ratio of 10:1 (ca) if the reading would've shown something between 9 and 10 on his instrument, so at way over 12 (where the needle stops) it could even be 14:1!!! plus, as i said, mine have a dome height of 5 to 6mm and schaffner "uses" 3,8mm for a 11:1 compression - i'm also just thinking about shaving off 2 (or so) mm with a mini mill (magnetical) as included (pistons centered at the very top and everything well covered to prevent shavings getting anywhere Sandy - .......... just maybe a crazy idea
Sandy I have never seen a compression gauge that reads in compression ratio. Everyone i have seen reads in PSI and bar and I think yours reads in bar, can you show a photo of the dial that shows the gunge calibration and the makers name. Regardless you need to calculate the actual geometric compression measured ratio as you cannot simply determine it by measuring compression pressure even if the gauge is marked that way. Once you have done that correctly and provided information on the details of the calculation and also provided details on the cam duration and timing you have, then it will be possible to advise how best to achieve the required compression ratio if a reduction is required.
There is no specific intruder height requirement for a specific compression ratio as there are to many other variables. You need to also allow for e.g valve cutout diameter and depth , intruder cone diameters, gasket thickness and bore, engine bore and stroke, head thickness and combustion chamber volume and then what compression ratio is acceptable depends on the cams and the fuel you will be using and how its then best achieved depends on all the preceding data. Not a simple exercise.
If you don;t believe me then talk to your engine specialist Schaffner and if he does not believe me then get him to contact me for some discussion as i am always happy to discuss the best way to build a good twink and sometimes I learn something new which is always good.
I guess you could use a magnetic mill to reduce the piston height in situ if needed and if that is the best way to reduce compression but you would need to firmly lock the pistons with wedges in the top of the bore as they can wobble which would give a mill a real problem. I have been involved with a lot of in situ machining on large industrial equipment and it is never an easy exercise and need real expertise to do well.
cheers
Rohan