|
Sponsored Links (Register now to hide all advertisements) |
|
|
Thread Tools | Display Modes |
08-11-2021, 02:02 PM | #1 |
Member
Join Date: Apr 2017
Location: Smithfield, Virginia
Posts: 76
|
engine compression
what should the compression read on a warm engine ('30 four cyl.) versus a cold engine?
|
08-11-2021, 04:09 PM | #2 |
Senior Member
Join Date: Jan 2019
Location: Germany, near Aachen
Posts: 1,158
|
Re: engine compression
Hi,
on my not tuned engine I measured: Cold: 4.9, 5.2, 5.2, 5.2 . Hot: 5.2, 5.2, 5.2, 5.2 . (kp/cm²)
__________________
Beste Gruesse aus Deutschland, Werner Ford Model A, Roadster, 1928 Citroen 11 CV, 1947 Hercules W 2000, 1976; (with NSU-Wankel Rotary Engine), Canadian version |
Sponsored Links (Register now to hide all advertisements) |
|
08-11-2021, 04:23 PM | #3 |
Senior Member
Join Date: Mar 2012
Location: Ohio
Posts: 1,969
|
Re: engine compression
On mine I checked it Sunday and the readings were 79, 80, 80, 80 LBS. Wonder what that works out to?
|
08-11-2021, 05:20 PM | #4 |
Senior Member
Join Date: Dec 2014
Location: Santa Maria, CA
Posts: 985
|
Re: engine compression
Compression numbers will depend on the type of head installed...stock or other.
__________________
Alan 1929 Special Coupe 1941 Pick-Up 1955 Victoria |
08-11-2021, 06:41 PM | #5 |
Member
Join Date: Apr 2017
Location: Smithfield, Virginia
Posts: 76
|
Re: engine compression
i'm a bit confused......book says 75 or so....mine is reading 100-110 cold and 100-106 warm. so...whats up with that? the engine was rebuilt prior to my getting the car but i have no information on details.
|
08-11-2021, 06:56 PM | #6 |
Senior Member
Join Date: Jun 2014
Location: Land of Lincoln
Posts: 3,131
|
Re: engine compression
Sponsored Links (Register now to hide all advertisements)
__________________
Don't force it with a little hammer tap, tap, tap get a bigger hammer tap done |
08-11-2021, 07:03 PM | #7 |
Senior Member
Join Date: Jan 2012
Location: Western North Carolina
Posts: 3,897
|
Re: engine compression
5.2 is in bars, I think, which is one atmosphere or 14.7 psi. So converting to psi yields 76 psi. 80 LBS is 80 psi, or pounds per square inch. 80 psi is equal to 76 psi within measurement error bands.
__________________
A is for apple, green as the sky. Step on the gas, for tomorrow I die. Forget the brakes, they really don't work. The clutch always sticks, and starts with a jerk. My car grows red hair, and flies through the air. Driving's a blast, a blast from the past. |
08-12-2021, 05:15 AM | #8 |
Senior Member
Join Date: May 2010
Location: Largo Florida
Posts: 7,225
|
Re: engine compression
Mine is 45# across the board, been that way since 1975 when I bought it. It was rebuilt in 1961.
|
08-12-2021, 08:27 AM | #9 |
Senior Member
Join Date: Jan 2016
Posts: 2,098
|
Re: engine compression
For a good approximate way to get what your number should be, number do this.
14.7x the head ratio number. Example: 14.7 x 6.1=89.67 psi or 14.7x 4.2=61.74psi. |
08-12-2021, 10:34 AM | #10 |
Senior Member
Join Date: Dec 2014
Location: Shawnee, Ok
Posts: 3,471
|
Re: engine compression
I have a 6:1head with the modern gasket, reading 95 psi in all tubes
This is after lapping valves, honing cylinders, new rings and pistons, also installed the adjustable lifters, did this about three months ago, no changes or issues so far
__________________
Keith Shawnee OK '31 SW 160-B |
08-12-2021, 11:08 AM | #11 |
Senior Member
Join Date: Jun 2021
Location: Pella, IA
Posts: 336
|
Re: engine compression
Some of these look quite high! Mine was supposedly rebuilt about 1,000 miles ago, is all stock, and is reading..... #1 60, #2 55, #3 55, #4 60. That is PSI. Should it be higher?
|
08-12-2021, 12:20 PM | #12 |
Senior Member
Join Date: Dec 2014
Location: Santa Maria, CA
Posts: 985
|
Re: engine compression
Looks like your numbers are right on the money - with a stock 4.2 head
__________________
Alan 1929 Special Coupe 1941 Pick-Up 1955 Victoria |
08-12-2021, 12:22 PM | #13 |
Senior Member
Join Date: Jun 2021
Location: Pella, IA
Posts: 336
|
Re: engine compression
|
08-13-2021, 07:54 AM | #14 |
Senior Member
Join Date: May 2010
Location: Long Island, NY
Posts: 3,466
|
Re: engine compression
To estimate the compression ratio from gauge readings, divide the gauge reading by the atmospheric pressure in your region. At sea level, Atmospheric Pressure = 14.7 psi. In Denver, Colorado Atmospheric Pressure is 12 psi:
79/14.7 = 5.4:1 55/14.7 = 3.7:1 62/14.7 = 4.22:1 Engine power & torque vary with compression. Theoretically, gauge readings below 62 psig at sea level (stock 4.22:1 Ratio) are indicative of less than 40 hp and less than 128 ft-lbs of torque. How much less requires power & torque requires dynamometer testing.
__________________
Bob Bidonde Last edited by Bob Bidonde; 08-13-2021 at 09:27 AM. |
08-13-2021, 09:00 AM | #15 |
Senior Member
Join Date: May 2010
Location: Largo Florida
Posts: 7,225
|
Re: engine compression
Compression is a good thing to know, for now and for the future issues.
But, as long as the engine operates as it should, who cares. Run it and enjoy it. |
|
|
Sponsored Links (Register now to hide all advertisements) |
|