Posted By: MO_PA
Compression ratio? - 02/28/15 01:51 AM
.040 over bore 440, 906 heads, .020 head gasket,
flat top pistons .120 in the hole.
Estimates appreciated.
Thanks!
flat top pistons .120 in the hole.
Estimates appreciated.
Thanks!
Compression ratio?
Posted By: 68LAR
Re: Compression ratio? - 02/28/15 01:55 AM
With 89 cc heads, MAYBE 8:1 CR. No too good.. 
Posted By: Cab_Burge
Re: Compression ratio? - 02/28/15 04:09 AM
Quote:You really need to CC at least one chamber in each head to find out what CC heads your working with
.040 over bore 440, 906 heads, .020 head gasket,
flat top pistons .120 in the hole.
Estimates appreciated.
Thanks!
I've seen supposidly stock uncut 906 heads have 91.+ CC in them with the carbon removed 
I've also seen 4.3 CC varience in chamber sizes on the same head, same differences on the other head with the thickness within .003 on both heads on both ends of those heads 
Once you get a idea on the CC size you have go to United Machines web site , AKA KB Pistons, Silvolite and click on there calculator tab and go to the compression ratio calculator and plug in your numbers to get a idea what you have on the compression ratio with your pistons and the specs. you put on here Let us know your results
Posted By: MO_PA
Re: Compression ratio? - 02/28/15 04:24 AM
United Engine Machine calculator comes up with 8.75 using 89cc head.
this should power a grocery getter 62 Sport Fury
this should power a grocery getter 62 Sport Fury
Posted By: BSB67
Re: Compression ratio? - 02/28/15 02:54 PM
It is about 8.4:1. You don't need to measure anything in my opinion, you have enough information. 86cc to 94 cc is 8.2:1 to 8.6:1, i.e. it really does not matter much.
Posted By: dogdays
Re: Compression ratio? - 02/28/15 05:12 PM
With a 90cc head the comp ratio calculates to 8.35:1.
With a 93cc head the comp ratio calculates to 8.18:1.
To get to 9:1 you need to lose 13cc of volume above the piston, meaning cut 0.053 off the deck or heads or move the piston tops up the same amount.
Key calculation, the 440 + 0.040 has a per cylinder swept volume of 918cc
R.
With a 93cc head the comp ratio calculates to 8.18:1.
To get to 9:1 you need to lose 13cc of volume above the piston, meaning cut 0.053 off the deck or heads or move the piston tops up the same amount.
Key calculation, the 440 + 0.040 has a per cylinder swept volume of 918cc
R.
Posted By: RapidRobert
Re: Compression ratio? - 02/28/15 05:52 PM
Quote:I'm assuming it is all together. What cam? Advancing it might build some psi. definitely dial in the dist subsystems (in order) when the time comes
.040 over bore 440, 906 heads, .020 head gasket, flat top pistons .120 in the hole.
Estimates appreciated.
Thanks!
Posted By: BSB67
Re: Compression ratio? - 02/28/15 05:54 PM
That is why I said "about". Three significant figures is a bit of a push even if you are trying to equalize combustion volumes at the typical amateur/hobbyist budget level.