piston dome displacement
- Thread starter Blaner
- Start date
22cc is what the stock dome size is to my knowledge.
EDIT: SOB I thought you were talking about the head and not the piston dome, my bad. I'll see what I can find.
Wait? Are you sure it's not flat? I just took a look at my old Wiseco piston and it looks pretty damn flat to me....granted it just LOOKS that way.
Pistons are not flat.... they have a dome curve to them. The outside 1/2" or so is curved at about 9° and working towards a small area in the middle which is flat.
Honestly blaner, I've never really thought about the displacement of the dome on the piston... just worked the rest of the engine around it.
Honestly blaner, I've never really thought about the displacement of the dome on the piston... just worked the rest of the engine around it.
Hmm I will have to check sometime. Macdizzy even shows them as being flat in his diagrams. I know on 4 stroke engines this isn't the case.
Really? Because right here:
1989 Blaster Engine Rebuild - Part 10, Two-Stroke Software Review
He shows it having a convex dome shape and even quotes as saying that the dome is at 9.5°-10°
And not all 4 stroke engines have flat topped pistons either. Most of the "increased compression ratio" pistons have a large bulge in the middle of the piston to take up some of the combustion chamber. Direct injection diesels have a flower shaped well cast into the piston that IS the combustion chamber. Piston design and construction is wildly different depending on the needs of the engine
ya they are not flat, they are inclined at about 9-10 degrees but what does it displace? agreed Sic, ive also always worked around it cause ive never been able to work it out.
This is an obvious part involved in compression calculations, like if your stock dome is 22cc, you still need to add the volume of the cylinder that the piston is below deck--no problem, but we actaully also need to then subtract the volume the dome displaces to get a accurate figure. Once you have that, you exact compression ratio can can be calculated...
This is an obvious part involved in compression calculations, like if your stock dome is 22cc, you still need to add the volume of the cylinder that the piston is below deck--no problem, but we actaully also need to then subtract the volume the dome displaces to get a accurate figure. Once you have that, you exact compression ratio can can be calculated...
Most people include the piston displacement in trapped volume measurements. Macdizzy put the piston up to TDC, sealed around the edge of the piston with heavy grease, and then measured the trapped volume with liquid.
If you cannot change the shape and displacement of the piston dome..... you don't need to characterize it, only understand it and then work around it.
If you cannot change the shape and displacement of the piston dome..... you don't need to characterize it, only understand it and then work around it.
yes you can measure it physically, but for every practical experiment there is a theory component, the advantage of the theory is that you can calculate it without taking off the head. or in my case, i study in a different city to where my bike lives...so if i had he dome displacement i could work it out...
as my bike and i are seperated, i have to find things involving it to play with
...such as head calculations..
as my bike and i are seperated, i have to find things involving it to play with
...such as head calculations..
You could form a mold of the same size and angle as the dome and get a fluid displacement from it. After that, I'm guessing you would have to find the area of a parabola with 2 fixed points(start/end point) and then factor in 360 degrees of space for volume. If the top of the dome is flat you can do it close enough by making the center flat section a square and the 2 outer portions triangles and figuring from there.
The piston dome takes up approx. 5 to 5.5cc of volume on standard pistons depending on what size you have. The radius on the dome is around 186mm with a dome height of 3mm.
