Matching piston size to comp ratio - Ford Forums - Mustang Forum, Ford Trucks, Ford Focus and Ford Cars
LinkBack Thread Tools Display Modes
post #1 of 3 (permalink) Old 05-08-04, 05:47 AM Thread Starter
tony xa's Avatar
Join Date: Mar 2004
Location: PERTH
Posts: 896
Matching piston size to comp ratio

How do you work out pistons to use in relation to comp ratio.
I want to use 3.850 stroke crank 6 to 6.125 inch rods and run my engine at 11-1
comp using 98 octane fuel . Heads will be 64cc
Would like to know in there is a formula that is used .
Any help would be great . Thanks

tony xa is offline  
Sponsored Links
post #2 of 3 (permalink) Old 05-08-04, 06:33 AM
Registered User
Join Date: Aug 2003
Location: perth
Posts: 661
Re: Matching piston size to comp ratio

This is how i would work it out tony.Firstly we need to assume your swept cylinder volume and this is worked out using the following formula. lets assume you have zero deck height for this example and that * is a multiplication sign. bore * bore * stroke * .7854. lets assume the following; 4.03*4.03*3.85*.7854=49.109. This figure represented here is the cubic inch capacity of one cylinder. We need to convert this to cubic centimeters somultiply the following. 49.109*16.387064=804.75348. we now know the swept volume in cubic centimeters. 804.75348 cc is now divided by our known combustion chamber size of 64cc and we now know that our c/r is 12.57 to 1. This is obviously way too high and it is clear now that we are not going to be able to achieve our intended goal with a flat top piston design .we have 2 options,those being that we can open up our chambers to suit or use a dished piston which is the preferred option here. again we can use simple math to tell us how much dish in cc,s we actually require to come up with 11 to 1. Using our known swept volume of 804 cc we can divide this by 11 and this figure will tell us where we need to be. 804 divided 11=73.09cc.this figure represents our combustion chamber volume inclusive of cylinder head chamber size of 64 cc.The dish in the top of the piston now becomes part of the combustion chamber.It is clear that our piston will need to have a 9cc dish machined in the top. hope this helps.cheers, russ
russxr67 is offline  
post #3 of 3 (permalink) Old 05-08-04, 06:40 AM
Two SC 61's = trouble
ebxr8240's Avatar
Join Date: Jul 2001
Location: Penrith,nswAus/Morrinville.NZ
Age: 63
Posts: 6,360
Re: Matching piston size to comp ratio

This will make it easy for you...

I needed 20 cc dish to get 8.5 to 1..

Don't be afraid to try something new. Remember, amateurs built the Ark...Professionals built the Titanic!
Tuned & maintained by "Peppertree Perfmormance". Dart block, Scat 4340 steel crank, Custom C.P pistons.Oliver rods.. Mal Wood twin plate clutch.. Twin SC61/2's,482 rwkw/ 645 rwhp..
Passengers, myocardial infarction material..
R.I.P Possum...
ebxr8240 is offline  
Sponsored Links

  Ford Forums - Mustang Forum, Ford Trucks, Ford Focus and Ford Cars > The Garage - Tech Forums > Engine Specific Tech > Cleveland Tech

Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
Thread Tools
Show Printable Version Show Printable Version
Email this Page Email this Page
Display Modes
Linear Mode Linear Mode

Similar Threads
Thread Thread Starter Forum Replies Last Post
EB Ė best Exhaust size / Diff ratio for EB II defective Exhaust 17 11-07-04 07:08 AM
Changing Diff Ratio tickford2001 Trans | Driveline 10 04-26-04 06:02 AM
EB XR6 exhaust valve size John_xr6 Exhaust 0 01-09-04 09:38 PM
Suitable diff ratio suggestions jAcKaL Trans | Driveline 12 10-28-03 12:13 AM
ED XR6 diff ratio BlownXR6 Trans | Driveline 14 11-14-01 03:00 AM

Posting Rules  
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On

For the best viewing experience please update your browser to Google Chrome