Welcome to Club Hot Rod!  The premier site for everything to do with Hot Rod, Customs, Low Riders, Rat Rods, and more. 

  •  » Members from all over the US and the world!
  •  » Help from all over the world for your questions
  •  » Build logs for you and all members
  •  » Blogs
  •  » Image Gallery
  •  » Many thousands of members and hundreds of thousands of posts! 

YES! I want to register an account for free right now!  p.s.: For registered members this ad will NOT show

  • CHR Technical Library

    by Published on 04-28-2011 11:41 PM  Number of Views: 14426 

    Static compression ratio, domed pistons, how to figure the math.
    We'll use a 454 Big Block Chevy for this explanation. Let's say we're using the stock bore and stroke of 4.250" and 4.000" and production cast iron heads with 122cc chambers. The pistons are down in the bore 0.025" (piston deck height) and have a dome volume of 28.7 cc's (get this info from the piston mfg or figure the dome volume yourself: See Determining Piston Dome Volume). To figure static compression ratio, you need 5 different values...

    1. cylinder volume in cc's
    2. combustion chamber volume in cc's
    3. piston crown volume in cc's (+ or - or flat with eyebrows)
    4. piston deck height volume in cc's (volume above the piston crown up to level with the block deck with the piston at TDC)
    5. head gasket volume in cc's

    Let's take these one by one so that you and others will know how to figure SCR with a domed piston....

    1. We know that the bore is 4.250" and the stroke is 4.000", so we multiply (.7854 times 4.250" times 4.250" times 4.000" times 16.387) and find that there are 929.88 cc's in the cylinder.

    2. Anyone building a motor should use a burette and colored alcohol to "pour" the chambers and determine the exact volume in each and every chamber (yes, they differ one to the other, but can be equalized prior to assembly), but I doubt that many of you fellows do that. These heads are advertised at around 119cc's, but production heads will usually pour a little bigger, so let's call them 122 for this exercise.

    3. OK, we'll do a little play acting here. We will visualize taking a sharp instrument and slicing the dome off the piston, leaving only a flat plane crown with no eyebrows. So, here we are holding a lump of aluminum that displaces 28.7 cc's. We are now going to jam that lump up into the combustion chamber to reduce the chamber volume to 93.3 cc's. This will result in a piston crown value of zero.

    4. We have no idea what the piston deck height is on this motor, but let's just use a theoretical value of 0.025". So, we have a bore of 4.250" and the piston is 0.025" in the hole at TDC. Remember, the piston is now a flat-top, so we will simply multiply (.7854 X 4.250" X 4.250" X 0.025" X 16.387) and find 5.81 cc's.

    5. I'm going to assume that the decks of the block and heads are flat enough to use a Mr. Gasket shim head gasket, #1131, 4.370" X 0.020". This will put our squish at 0.045". Again, figuring cc's just like anything else that's round and has a thickness......(.7854 X 4.370" X 4.370" X 0.020" X 16.387) and find 4.92 cc's in the head gasket.

    Now, we add all our values together....
    929.88 + 93.3 + 0 + 5.81 + 4.92 and find a total volume of 1033.91 cc's.

    Now, we will drop out the cylinder volume and add the other 4 values together....
    93.3 + 0 + 5.81 + 4.92 and find a compressed volume of 104.03 cc's.

    Now, we will divide the larger volume by the smaller volume (1033.91 / 104.03) and find 9.94:1 static compression ratio.

  • Recent Activity


    53 Is back from the Body Shop

    Thread Starter: 53 Chevy5

    Here it is , after so much color searching it isn't as dark as we thought it would be, but my wife loves it. Now, so much to put together I don't...

    Hotrod46 Today, 07:09 AM Go to last post

    random stuff

    Thread Starter: HOSS429

    i started such a thread during our down time but it seems it`s not coming back so without further adu here it is again .. there are times i wish to...

    34_40 Today, 03:22 AM Go to last post

    Breaking in the new cam in my 76 Vette

    Thread Starter: NTFDAY


    NTFDAY Yesterday, 08:20 PM Go to last post
    53 Chevy5-8625

    Followed Me Home II

    Thread Starter: rspears

    I've been toying with the idea of another build, and have been watching for a stalled project and considering other options, but with no time frame...

    53 Chevy5 Yesterday, 05:53 AM Go to last post
    36 sedan-34242

    geering for ford 9 inch rear

    Thread Starter: tyler1967ss

    hi, new guy tyler here,recently purchased at auction 1967 chevelle with ford 9 inch rear super low geering, original 4 speed standard trans, 396 bb,...

    36 sedan 08-04-2020, 11:01 AM Go to last post

    New Old Guy From Oklahoma

    Thread Starter: Indy

    Hello guys and gals, Grew up around cars, my dad owned an auto supply and both my brothers were into cars and racing. I’ve had my Tbucket...

    Indy 08-04-2020, 08:58 AM Go to last post

    Another Build Thread - My '32

    Thread Starter: J. Robinson

    And so it begins...:HMMM: I finally completed my Track-T and accompanying build...

    rspears 08-04-2020, 08:34 AM Go to last post

    Happy Birthday Shine

    Thread Starter: NTFDAY

    Happy Birthday, hope you have many more.

    CR55 08-02-2020, 06:24 AM Go to last post

    1940 Ford Tudor Build Thread

    Thread Starter: 40FordDeluxe

    Hi guys, I'm gathering parts and pieces to make some big changes to my 40. This car was my uncle's car and I purchased it from the guy who purchased...

    rspears 08-02-2020, 05:51 AM Go to last post

    RIP MetalTwister - Bob

    Thread Starter: rspears

    Just now I noted a posting on the Instagram account for Metaltwister, who we know as Bob, and who recently relocated from SOCAL to Licking, MO saying...

    40FordDeluxe 08-01-2020, 10:29 PM Go to last post

    P-30 Truck/RV/Motor home Chevy 454 question

    Thread Starter: madscotsman59

    New guy here with a question that i'm having a hard time finding a correct answer for. I Have a 1989 Winnebago 33 foot motor home with a bad trans...

    40FordDeluxe 08-01-2020, 10:24 PM Go to last post

    1928 REO Coupe

    Thread Starter: Driver50x

    My uncle is having health issues, and is trying to sell his street rod. It has a Chevy 350/Turbo 350. Mustang II frond end. Functional rumble seat....

    40FordDeluxe 08-01-2020, 10:21 PM Go to last post

    FFR 33 Ford Hot Rod

    Thread Starter: wrp

    Had the car about three years now. Initially put it on the road as a roadster. This winter we decided to add the roof, hood, side skirts and front...

    wrp 08-01-2020, 04:27 PM Go to last post
Links monetized by VigLink