compression test - Ford Forums - Mustang Forum, Ford Trucks, Ford Focus and Ford Cars
Ford Forum Ford Forum

» Auto Insurance
» Featured Product
» Wheel & Tire Center

Go Back   Ford Forums - Mustang Forum, Ford Trucks, Ford Focus and Ford Cars > The Garage - Tech Forums > Engine Specific Tech > Windsor Tech
Register Home Forum Active Topics Photo Gallery Auto Loans Garage Mark Forums Read Auto Escrow

FordForums.com is the premier Ford Forum on the internet. Registered Users do not see the above ads.
Reply
 
LinkBack Thread Tools Display Modes
Old 12-06-2004, 01:57   #1 (permalink)
347
Registered User
 
347's Avatar
 
Join Date: Jul 2003
Location: Sydney
Posts: 651
compression test

Is there any way of telling roughly what comp ratio I have from doing a compression test given I know the size of the comp chamber and the stroke?
__________________
What ever I have will never be enough !
Fear is only Fear itself !

http://members.optusnet.com.au/~two89w/
347 is offline   Reply With Quote
Sponsored Links
Advertisement
 
Old 12-06-2004, 02:25   #2 (permalink)
blue66coupe
Guest
 
Posts: n/a
Re: compression test

Depends heavily on cam specs also and what lash (if any) adv/retarded etc. Short cam might have 230psi big cam 170psi with same static comp ratio. I know there are formulae to work out dynamic compression ratio, maybe use these and factor it out. There is probably a simple formula to rough it out.. anyone?
  Reply With Quote
Old 12-06-2004, 02:44   #3 (permalink)
Registered User
 
xpc66's Avatar
 
Join Date: Sep 2004
Location: Brisbane
Posts: 155
Re: compression test

The ovious question is "why not just work it out the conventional way?".

To work it out using actual compression is very difficult. You need to know your leak down rate and volumetric efficiency at idle, plus your inlet valve closing angle, stroke and rod length to convert from dynamic CR to static CR, to name a few, but......

having said that if you run the engine at idle and measure the cylinder pressure and the manifold vacuum:

e.g compression pressure = say 42 PSIA, manifold pressure = 18"Hg;

18"hg = 8.8 psi, so absolute pressure going in (14.69- 8.8) = 5.89 PSIA

DCR = 42/5.89 = 7.26

with a little trig on the inlet valve closing angle of say 70°, stroke 3", rod length 5.09".

Dynamic stroke length =2.2"

CR = 9.5

Like I said it's easier and more accurate to work it out the conventional way:- using a reasonable calculator that takes into account toplands, dishes/domes, gaskets, deck to deck heights, etc.
__________________
Go the Brisbane Lions
xpc66 is offline   Reply With Quote
Old 12-06-2004, 05:29   #4 (permalink)
Two SC 61's = trouble
 
ebxr8240's Avatar
 
Join Date: Jul 2001
Location: Penrith,nswAus/Morrinville.NZ
Age: 61
Posts: 6,360
Re: compression test

http://www.rosspistons.com/calculator.php
__________________
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   Reply With Quote
Sponsored Links
Advertisement
 
Reply

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



Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
 
Thread Tools
Display Modes

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


Similar Threads
Thread Thread Starter Forum Replies Last Post
Boss 260 Compression test 00racer Modular Tech 10 10-18-2004 05:07
Help engine not firing after compression test utegirl Inline 6 Tech 13 08-29-2004 06:37
Results from Compression Test wildturkey Australian Falcons 8 04-15-2004 15:24
U.S.A.:Ford blasts Dallas cop car test Stacy94PGT Ford Worldwide News 0 09-18-2003 07:50
New SUV safety rules test automakers Stacy94PGT Ford Worldwide News 0 05-25-2003 03:17

Powered by vBadvanced CMPS v3.2.2

All times are GMT -7. The time now is 10:20.



Powered by vBulletin® Copyright ©2000 - 2014, Jelsoft Enterprises Ltd.
Content Relevant URLs by vBSEO 3.6.0
Garage Plus vBulletin Plugins by Drive Thru Online, Inc.