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

 
  • Static compression ratio, domed pistons, how to figure the math.

    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.
    This article was originally published in forum thread: Technical Repository started by techinspector1 View original post
    Comments 4 Comments
    1. Brent Mills's Avatar
      Thanks for the efforts, nicely done.
    1. vara4's Avatar
      Trying to confuse me again, HUH Tech HE! HE! HE!
      Kurt
    1. glennsexton's Avatar
      Am I the only one who gets this message?

      vBulletin Message

      glennsexton, you do not have permission to access this page. This could be due to one of several reasons:

      Your user account may not have sufficient privileges to access this page. Are you trying to edit someone else's post, access administrative features or some other privileged system?
      If you are trying to post, the administrator may have disabled your account, or it may be awaiting activation.

      Log Out Home
    1. pat mccarthy's Avatar
      well that only works when you have the cc of the dome nice but if you do not have the cc of the dome then there is abit more to the job
  • Recent Activity

    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 Today, 06:31 PM Go to last post
    53 Chevy5-8625

    Grandpaís Grand Prix

    Thread Starter: falconvan

    Hey all, havenít been on in a while and getting ready to start a new one. The young man that plays drums in my band inherited this 77 Grand Prix when...

    53 Chevy5 Today, 06:26 PM Go to last post
    rspears-21970

    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...

    rspears Today, 05:51 PM Go to last post
    rspears-21970

    Happy Birthday, Ray/Scooting!

    Thread Starter: rspears

    Happy Birthday! Hoping that you have a great day celebrating, and stay safe out there!

    rspears Today, 05:37 PM Go to last post
    FordyG-42440

    New guy from Utah.

    Thread Starter: FordyG

    Just thought I would drop by and say hello, I am somewhat new to the hot rod world with my own project but grew up around them, I am currently doing...

    FordyG Today, 11:02 AM Go to last post
    wrp-40096

    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 Yesterday, 07:39 PM Go to last post
    t-top havoc-33918

    Transmission cooler with or without factory radiator 'cooler' / warmer?

    Thread Starter: CZSteve

    Thoughts on plumbing in an aftermarket transmission cooler for my application / driving style & environment? Gen1 SBC Chevy 350 w/ TH350 tranny in...

    t-top havoc Yesterday, 04:25 PM Go to last post
    MP&C-23705

    Door latches needed!!!

    Thread Starter: MP&C

    Door latches needed!!! Our local fire department has a one of two produced enclosed cab 1937 Seagrave fire truck that is in need of some...

    MP&C Yesterday, 08:30 AM Go to last post
    johnboy-11976

    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...

    johnboy 09-17-2020, 04:24 PM Go to last post
    34_40-21919

    surging engine

    Thread Starter: cffisher

    my 91 Chevy 5.7 throttle it body has developed a surging I'm not sure what's going on I start it and it will run from 600 to maybe 2000 rpm just up...

    34_40 09-17-2020, 12:58 PM Go to last post
    Mike P-938

    Project Sebring GT Spyder

    Thread Starter: Hotrod46

    Well gang, it's time it introduce my latest project. I've been looking forward to this for quite some time, but other projects kept getting in the...

    Mike P 09-16-2020, 05:54 AM Go to last post
    RaysC3-42686

    Need help.

    Thread Starter: RaysC3

    First post here so take it easy on me. I have a 1980 C3 Corvette with a 79’ 350 4 bolt main that has domed pistons (dont know the exact dome...

    RaysC3 09-16-2020, 12:53 AM Go to last post
    36 sedan-34242

    Front suspension square with frame

    Thread Starter: rsinor

    How do I confirm front suspension is square with frame. Can I use radiator mounts, firewall locating V? All inside frame reinforcements and cross...

    36 sedan 09-15-2020, 06:26 AM Go to last post
Links monetized by VigLink