Ross pistons 4 for 100 a piece!  Or close to that anyway..  hmm wonder how much more to have valve reliefs cut in try for maybe 9.5:1-10:1..  Anyone interested in a group buy?  maybe go for 96-97mm bore?  Easier to get 4 people than the twentysome for Wiseco, course i don't know anything about the quality of Ross pistons..

Kropatchek wrote on 12/31/69 at 16:00:03:



Was this reply for me?  If so, i agree! 4 of us should get some domed pistons with, if necessary for the savage, valve reliefs so as not to destroy our valves with the taller pistons.  oh and more specifically increasing compression ratio involves changing the cylinder volumes at bdc and tdc.  a larger piston will increase compression because the volume at bdc has increased more than the volume at tdc.  just my two cents.  i just really want to up my power and was hoping to get a few people to bite on some bigger pistons.

Here are the results of some calculations for flat head pistons with no valve cutouts I did a while ago... VH = volume of the head, i.e. size of the combustion chamber

Bore(mm),Extra_Piston_Height(mm),Displacement(cc),VH(cc),CR
94      0      652.3      87.0      8.5 (stock)
94      1      652.3      80.0      9.2
94      2      652.3      73.1      9.9
94      3      652.3      66.2      10.9
95      0      666.3      87.0      8.7 (lancer?)
95      1      666.3      79.9      9.3
95      2      666.3      72.8      10.2
95      3      666.3      65.7      11.1
96      0      680.4      87.0      8.8
96      1      680.4      79.7      9.5
96      2      680.4      72.5      10.4
96      3      680.4      65.3      11.4
97      0      694.6      87.0      9.0 (woodworker ?)
97      1      694.6      79.6      9.7
97      2      694.6      72.2      10.6
97      3      694.6      64.8      11.7

I posted similar calcs previosly, but there was a minor msitake in the comp ratio for a 94 mm piston and 1 mm taller.

uh let me check these again...  I think these #s are okay,

VH is calulated by:
VH = VHstock-ExtraPistonHeight*(PI*(bore/2)^2)

CR is calculated by:
CR = (Displacement+VH)/VH

For the extra height pistons, this is saying that when the engine is as TDC, the piston will go above the cylinder and into the combustion chamber.  If we go w/ over bore pistons, we also need to know if they will fit inside the combustion chamber, as well as if they will smack the valvies. (unless I don't get it)

Okay, to get a little more serious about a group order, looking at these figures, and considering the previous post about a 9.5 piston from wiseco, i'm guessing we could do 96mm with 2mm additional height and minor valve clearances   that should get us around 10:1-10.4:1, i'm not sure how much compression we would lose with the valve cutouts.. i'm guessing those figures are with flat top pistons?  might be able to do a 2mm higher dome top and forgo any valve destroying problems..   the earlier decision for the 9.5's from wiseco was based on valve clearance right?  i think we could get away with closer to 10:1 with the right pistons and that with a 2mm overbore should give some pretty serious gains.. We'll probably need the higher duration cam to go with it.  Most likely need to run premium too..  SE GA has 93 everywhere and with a 2.5 gallon tank i'd be fine with that..  i don't think 10:1 would need any higher octane, and if we're not changing deck height timing should be okay.. shouldn't it?  hmm..  anyone else have any thoughts on this?  And anyone else ready to make a group order?  just need 4 of us, i'm in, cash in hand.  think i'll do the cam same time..  (gonna need a carb too huh? ...  maybe lancer wants to put together a package deal?)

here are the numbers for spherical dome pistons w/ no valve cutouts:

Bore(mm),Extra_Piston_Height(mm),Displacement(cc),VH(cc),CR
94      0      652.3      87.0      8.5
94      1      652.3      83.5      8.8
94      2      652.3      80.0      9.2
94      3      652.3      76.6      9.5
95      0      666.3      87.0      8.7
95      1      666.3      83.4      9.0
95      2      666.3      79.9      9.3
95      3      666.3      76.3      9.7
96      0      680.4      87.0      8.8
96      1      680.4      83.4      9.2
96      2      680.4      79.7      9.5
96      3      680.4      76.1      9.9
97      0      694.6      87.0      9.0
97      1      694.6      83.3      9.3
97      2      694.6      79.6      9.7
97      3      694.6      75.9      10.2

this is on the assumption that the head doesn't have to be messed with.

The formula I used for the dome is:
ExtraVolume = 1/6*pi*Extra_Piston_Height*(3*(bore/2)^2 + Extra_Piston_Height^2).  Got the formula from my math text...  Then I used the same equation for VH & CR as above.


Here is a link to the spherical cap volume. Equation 2

okay, so does the piston come all the way up to be flush with the top of the cylinder?  If so, it looks like the combustion chamber/head would have to be bored to accomodate an oversized, taller piston...  or am I missing something here?  It's not like the gaskets would be tall/thick enough to take care of that...

What I want to know is, what's our deck height?



link
Anyone know how thick the gaskets are?