Compression Ratio Modeling

[59elcooldsuv]

So, I measured the chamber in the top of the cylinder & drew in Autocad as a solid model and added the "valve relief" notch. The computer says it's 8.67 cu in or 142 cc

I did the same with the dome on top of my new pistons. The computer says it's 7.7 cu in or 126 cc.

Then I add 10.3 cc or 0.63 cu in for the valve area on the head.

This is what it looks like when I superimpose the dome in the chamber & subtract the former from the latter.

I guess all I need now is to fit pistons on rods & measure my deck height. So far, I'm getting either 9:1 or 9.6:1 depending on how tired I am & which number I leave out of the formula.

I hope this pic is visible. How's it look to you?

[Phil Reed]

That looks awesome!!!! I could tell exactly what you had....I used to be a draftsman in an engineering department so I could tell right away what you were drawing!!

Looks great!!

[Mr Goodwrench]

great job randy I teach autocad here in highschool you just gave my students a new assignment. :D :D :D

[SSpev]

Thats preatty neet! I 'm wandering how you got you CR? I must be missing something. You got 142 cc in cyl, 126 cc dome, and 10.3 valve relief. 142-126+10.3=26.3 cc There is about 55 cc missing. I don't think a gasket and deck clearance will get that much. Ruffly 20:1 CR:eek: Did you see the measurements I posted in the thread "magic quench numbers"? They are real with a 100 cc burette.

[59elcooldsuv]

I'm still trying to get a good set of measurements of the valve reliefs in the head. I'm sure that the 10.3 number is probably good, but I just have this compulsive need to verify it myself - just because I can.

I saw the numbers you posted, SSpev, and I wondered why there was so much variation. Was it from grinding the sharp edges off? Or from variations in the depth to which the valve seat is ground? Surely the castings don't vary that much?

I'm thinking of stopping at ToysRus to get some PlayDoh to mold into the relief.

I'm not exactly sure if I have all the numbers right yet. I still haven't actually written them all down in order. I keep trying to just punch numbers iinto the calculator without keeping track of what I'm doing - probably because it's about 11;00 at night when I'm doing it.

I do this stuff for a living all day so it's hard to talk myself into being precise at night. I'm just compulsive, I guess.