I'm trying to calculate the exact compression ratio for my blown stroker motor and found this calculator on-line; http://www.csgnetwork.com/compcalc.html
I have all the information needed to plug in the numbers, except for "Head Gasket Bore Diameter"  I am not exactly sure what they mean and I don't have a set of Fel Pro gaskets to measure this dimension. Can anyone give me a number to plug in here? That is not a perfectly round area anyway so I am not exactly sure what they are looking for.

Also, there is no provision in this calculator for a relieved block. Is there a % reduction ( i.e. 1% or 5%) that can be subtracted from the calculated CR? 

Thanks,
Rono

  Ron Lane,  Meridian, ID

Ted knows that general number for h/gskt bore displacement figure, i dont think the relief amount is going to make a big difference regardless as the whole calculation is a general one.





  AussieBill            YYYY    Forever Y Block     YYYY

 Down Under, Australia

Thanks Bill;
You Blokes had an impressive fireworks display for the New Year...saw it on the Tele.
Happy New Year!
Rono

  Ron Lane,  Meridian, ID

Ron,

This is a bit off topic, but it's the calculator I found when I was rebuilding the motor and trying to select the cam. There's a bunch of dynamic calculators out there, and they don't all agree. This one's interesting in that it's an add on to static ratio.

I have no idea how this relates in practice to a blown application, but I found it interesting looking at different cams and rod lengths.

https://www.uempistons.com/index.php?main_page=calculators&type=comp&zenid=8e9027fc60bbc5227c417444b739f709

miker
55 bird, 32 cabrio F code
Kent, WA
Tucson, AZ

Rono.  Hmmmm...

What your formula is trying to do is determine the total effective volume of the combustion chamber you're using on your SC engine.  The last I knew, Rono, you're using a set of 5750-471 y-block cylinder heads.  Per JM's cylinder head chart, 5750-471 heads have 82 cc combustion chamber volumes.

NEXT, you're going to ADD to the 82cc combustion chamber volume the EFFECTIVE VOLUME of the cylinder head combustion chamber gasket areas that you are using with the brand of gaskets that you used when you assembled your engine.

Remember that the y-block has an i-r-r-e-g-u-l-a-r cylinder head combustion chamber perimeter shape AND that different gasket suppliers have varied their cylinder head gasket 'fire ring' contours slightly and consequently their actual perimeter gasket 'fire ring' lengths slightly.  Sooo... this is WHERE Ted Eaton has helped us generously.

EXPLANATION: Ted Eaton has calculated the cylinder head combustion chamber gasket volumes by actually measuring the perimeter length of each companies' combustion chamber gasket 'fire ring' AND also measuring the thickness of that same gasket material after compression caused by torquing the cylinder head bolts!
Ted's measurement has permitted him to calculate each of the various individual gasket manufacturer's effective combustion chamber 'fire ring' bordered combustion areas.  This combustion chamber gasket area has the effect of adding to the size of the actual cylinder head combustion chamber area.  In summary, the gasket area volume varies depending upon the gasket manufacturer's 'fire ring' dimensional length and how much that manufacturer's gasket material compresses when torqued down.

So, using Ted's cylinder head gasket chart, locate the gasket manufacturer and the particular gasket type from them that you're using.  Ted's chart indicates the perimeter length of the fire ring and the actual compressed thickness of the particular manufacturer's gasket.  Going across, Ted's chart also gives the cc volume that using that manufacturer's gasket will effectively add to the volume of your combustion chamber.  TG for Ted!  

Click on the link below to see Ted's cylinder head gasket chart listing head gasket combustion chamber volumes
http://www.eatonbalancing.com/blog/2012/06/30/head-gasket-volume-calculation/

Adding the gasket area volume to the combustion chamber volume gives you the effective combustion chamber volume above the piston.  IF your relief work on the deck of the block is 'significant', you'll need to measure it by forming a dam around it and using a fluid to determine the volume of material removed in ccs.  This figure would be added to the above calculation.  The same would need to be done if you had used dished pistons to lower the compression ratio because of using small combustion chamber heads when using a blower or supercharger.

Hope this helps.  


NoShortcuts
a.k.a. Charlie Brown
near Syracuse, New York

Rono.  Me thinks that you'll come-up with the answer you're looking for if you use their formula, BUT only enter your numbers for cylinder bore, piston stroke, and your determined number for total effective combustion chamber volume.

Assuming you zero decked your engine block...
Total effective combustion chamber volume with your y-block is
combustion chamber volume + cylinder head gasket combustion chamber volume + cylinder block deck relief volume

IF you did not zero deck your block, you have to take the in-the-hole piston depth (in thousands) and calculate the volume above the piston diameter using your cylinder bore size.  After doing that, add that additional number to the above 'total effective combustion chamber volume' to be more accurate.

Happy New Year!  


NoShortcuts
a.k.a. Charlie Brown
near Syracuse, New York

Charlie;
Thanks for all your help with this!
Well, I crunched the numbers. I'll provide them below and maybe you can double check my result;
Bore Size - 3.810
Piston Stroke Length - 3.610"
* Head Gasket Bore Diameter - 12.95"
* Ted's formula for the Fel-Pro Perma torque uses "sealing ring distance in inches" (12.95") which is what the formula I used is asking for I think.
Compressed head gasket thickness - 0.044"
*Combustion Chamber Volume - 82 cc
* I used the 82 cc for the 471 heads, but that would be for stock, un-milled heads, correct? My heads are milled 0.010" which would reduce the volume right? May
  maybe 75cc would be a more realistic volume #.
Piston Dome Volume - 0 (I had john Mummert cut the domes flat on my pistons)
Piston Deck Clearance - I did zero deck the block (it actually came out to 0.002" below deck)
 The calculator program uses Java Script which my old lap top doesn't have, but my wife input the numbers and came up with a 4.8:1 CR and that is without considering the block relief.
We re-ran the numbers using a Combustion Chamber Volume of 75cc (for milled heads) and got a CR of 4.95:1
Unless I'm missing something, this is pretty low compression which should allow me to run a little higher boost without detonation using pump gas.
The reason I am going through all this is because I unfortunately will be selling my complete blower set-up. I just cannot fit it within the narrow front part of the engine bay in my 37 coupe. The bracket interferes with the outer fender. I have been talking quite a bit with Y-Bloke and will be going with his blower intake and a 4-71 blower. I'll be posting pictures in the  classified section of our forum next month with a full description and price. I hate to do it, but it is what it is.

Rono

  Ron Lane,  Meridian, ID

Rono:  Just beginning to work with the info you've provided...

I.  Volume of the combustion chambers of your cylinder heads after milling...

The 'pads' on y-block cylinder heads when fresh from Ford were suppose to be 1.000 thick (theoretically)
IF they weren't previously re-surfaced until you had them milled, they should now measure 0.990 (theoretically)

Ted's website has an article with a chart indicating how much cut it takes to remove 1 cc of volume from the combustion chamber of different versions of  y-block heads
My quick read on Ted's chart is that on the 471 heads, a .0.010 cut would remove (almost) ~2 cc of combustion chamber volume.   (close theoretical calcuation)

JM's chart is  an indicator of what Ford was trying to produce combustion chamber volume-wise.  Those who do engine blue printing will tell you that chamber volumes on production heads DO vary, BUT let's not get too clinical about this...

IF your production 471 heads were 82 cc, let's say that they're 80 ccs now after milling .010 off of them.

Click the link below to see Ted's article and chart on y-block head milling to adjust combustion chamber volume...
http://www.eatonbalancing.com/blog/2013/01/30/cylinder-head-milling-for-a-1cc-reduction/

Okay?  I'll be back...  


NoShortcuts
a.k.a. Charlie Brown
near Syracuse, New York

Rono that 12.95" dimension is the circumference and needs to be divided by pi to give you a
gasket bore of 4.122"
I get 8.528:1 compression or there abouts.

Gary- Havelock, New Zealand.

Rono.  Quite sure that I've got the correct answer based upon what I've done with using your information and Ted's with their website calculator.

- I presently have not been able to post a copied and pasted picture of their data page entry form with my data inserted on it using our Forum entry page 
- My hope was to add footnotes for some entry numbers to help explain how you went astray in using Ted's information. 

Here's the short of what I did:

Bore / Stroke Designation Type  -  entry #1 = Inches
Enter Cylinder Bore Size  -  entered 3.810
Enter Piston Stroke Length  -  entered 3.610
Enter Head Gasket Bore Diameter  -  entered 0.000  [reason: using Ted's data here will not work for calculation of y-block combustion chamber irreg. gasket shape]
Enter Compressed Head Gasket Thickness  -  entered 0.000  [reason: same as above... program calculation will not work for y-block cyl. hd. comb. chamber gasket]
Enter (TOTAL) (EFFECTIVE) Combustion Chamber Volume In CCs  -  entered 89.62  [471's chamber volume 80 cc + 9.66 cc FelPro gasket chamber volume]
Entered Piston Dome Volume In CCs  -  entered 0.000  -  [reason  - flat top pistons per JM's machining]
Enter Piston Deck Clearance  -  entered 0.000  - [reason  - block was all but zero decked!  pistons grow with heat -are probably flush with deck in norm. operation!]

I clicked the 'Calculate CR' [Compression Ratio] button at the bottom of the data entry area...

Very Bottom of Data Page...

Calculated Engine Compression Ratio  -  Answer  -  8.52563590200843 : 1
Total (EFFECTIVE) Displacement Volume  -  89.62  cc  [this number is 471 hd. comb. chamber vol. + FelPro cyl. hd. gasket combust. chamber volume per Ted]

What has NOT been valued in doing this computation using this Internet calculator?
- we did not include a calculation of the volume of material you removed from the block deck in doing relieving work...
- we did not include ANY cc allowance for the space in each cylinder above the top piston ring and the block deck... Ted will tell you this is of measure, BUT...

IF you follow what I've done, GooD!  IF you don't, I'll go at it in explaining it another way, OR more completely... 
The reason Ted did all of his gasket calculations is that no existing computer program could process hd. gasket combustion chamber information and come-up with the cc volume for the area inside the fire ring area on the different y-block manufacturers' cylinder head gaskets.

Again, THANK YOU, Ted Eaton!


NoShortcuts
a.k.a. Charlie Brown
near Syracuse, New York