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: 13194 

    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


    '37 Dodge sedan

    Thread Starter: PNW Rodder

    Alright, here's the story: In March of this year, I decided I wanted another hot rod. I talked it over with the wife and we decided we'd like to...

    34_40 Today, 03:35 AM Go to last post

    the new look for the 32 this year...

    Thread Starter: roid


    johnboy Yesterday, 09:45 PM Go to last post

    1955 Crown Vic Build

    Thread Starter: F-350Luoi

    Just thought I would start a build thread for this 1955 Crown Vic. It's not my car I am just doing the body and paint. The owner has a mechanical...

    johnboy Yesterday, 09:40 PM Go to last post

    I'm a proud owner of a 82 Z28

    Thread Starter: 53 Chevy5

    Went and checked out the Z28 and as far as I could tell, it's in real nice shape with 107K. The owner has owned it since it was almost new and it's...

    40FordDeluxe Yesterday, 08:49 PM Go to last post

    It's like it's January day #92 Here

    Thread Starter: 53 Chevy5

    We were blessed with 6 inches of snow again last night/this morning and get to experience a temp of 6 degree tonight. I put my skidloader in last...

    40FordDeluxe Yesterday, 08:43 PM Go to last post

    chevy fleetline

    Thread Starter: shine

    looking for a 1949 - 1952 chevy fleetline 4dr to build . not interested in finished car or some chopped up project . want a barn car or pasture art ....

    40FordDeluxe Yesterday, 08:41 PM Go to last post

    1947 Biederman Truck Fender Repairs

    Thread Starter: MP&C

    Tonight in the shop we started the repair work on the front fenders for the 1947 Biederman Truck, seen here for reference: The fenders are...

    40FordDeluxe Yesterday, 08:39 PM Go to last post
    Mike P-938

    1965 Dodge A108

    Thread Starter: falconvan

    Yet another fabulous old heap showed up on my doorstep. Plans are pretty minimal for this one; leave it stock, get it mechanically right, and drive...

    Mike P Yesterday, 06:24 PM Go to last post
    Mike P-938

    57 Plymouth

    Thread Starter: Mike P

    A few days ago I got a letter from my High School Reunion committee. I made my 25th reunion, and our 50th reunion is a couple of years off in 2020....

    Mike P Yesterday, 06:17 PM Go to last post
    Chevy Lady-41777

    Ended up going to a funeral today

    Thread Starter: Chevy Lady

    I ended up going to a funeral today,a teacher I had in the 5th grade and she was good to me.She had cancer very bad and passed away on Monday.It was...

    Chevy Lady Yesterday, 05:42 PM Go to last post

    40 Studebaker frame and suspension

    Thread Starter: 40$tude

    Just moved here from the newbie section. I am starting on a 1940 Studebaker Champion 2dr Sedan. I have considered several frame and suspension...

    rspears Yesterday, 12:26 PM Go to last post

    the Official CHR joke page duel

    Thread Starter: john gemmer

    this page for any jokes you have to post try to keep them clean this was sent to me today just thought I would share:( :p :D :LOL:...

    fitzwilly Yesterday, 10:52 AM Go to last post

    Custom Non-Optima,....Battery Box ?

    Thread Starter: FUNFER2

    With the mixed reviews of Optima batteries, I guess I'll stay with the group 34 Interstate battery I've used for many years. I haven't seen many...

    firebird77clone Yesterday, 08:31 AM Go to last post

    Damn Noisy trailers

    Thread Starter: DA34GUY

    Quick 500 mile trip yesterday, and this came home

    DA34GUY Yesterday, 05:31 AM Go to last post

    41 chevy radiator

    Thread Starter: chevy3755

    was wondering what you folks are using for a radiator for a 41 chevy car.......there seems to be plenty for the trucks of that year....thank you Larry

    chevy3755 04-20-2018, 06:38 PM Go to last post

    Induction Engineering valve covers

    Thread Starter: Racer610

    small block chevy valve covers to make it look like a big block. early 1980 low production not many made .will post picture soon

    Racer610 04-20-2018, 06:07 AM Go to last post
    53 Chevy5-8625

    3 inch mini buffer

    Thread Starter: 53 Chevy5

    Looking for advice on a decent one for occasional use. I prefer and electric one and I've been looking at this...

    53 Chevy5 04-19-2018, 07:46 PM Go to last post

    Sad news.....

    Thread Starter: techinspector1

    https://www.usatoday.com/story/life/movies/2018/04/15/actor-r-lee-ermey-full-metal-jacket-dies-74/519273002/ .

    NTFDAY 04-18-2018, 06:57 PM Go to last post

    Hello from Ontario Canada.

    Thread Starter: F-350Luoi

    Just saying hello. I have been in the auto body repair business for 35 yrs. I have been on my own for the last 21 yrs. For the last 5yrs I have been...

    34_40 04-18-2018, 05:29 PM Go to last post

    40 Studebaker street rod

    Thread Starter: 40$tude

    Hi, I'm Roger and just acquired a 40 Studebaker Champion 2dr Sedan to street rod. I have been in the autobody and paint industry for nearly 40 years...

    techinspector1 04-18-2018, 05:24 PM Go to last post
Links monetized by VigLink