Go Back   Ford Truck Enthusiasts Forums > Performance, Engines & Troubleshooting > FE & FT Big Block V8 (332, 352, 360, 390, 406, 410, 427, 428)
Sign in using an external account
Register Forgot Password?


Welcome to Ford-Trucks Forums!
Welcome to Ford-Trucks.com.

You are currently viewing our forums as a guest, which gives you limited access to view most discussions and access our other features. By joining our community you will have access to post topics, communicate privately with other members (PM), respond to polls, upload content and access many other special features. Registration is fast, simple and absolutely free so please, join the Ford-Trucks Forums community today!





 
Reply
 
LinkBack Thread Tools Search this Thread
  #1 (permalink)  
Old 08-02-2005, 10:48 PM
biz4two's Avatar
biz4two biz4two is offline
Post Fiend
 
Join Date: Sep 2003
Location: Albuquerque
Posts: 5,237
biz4two has a great reputation on FTE.biz4two has a great reputation on FTE.biz4two has a great reputation on FTE.biz4two has a great reputation on FTE.
Talking 390 compression ratio...What?

Hey guys,

How do I find the compression ratio to my 390? Tell me what I need to provide...and I will try to get it for you.

1976 F-150 4x4 390 reman. from local FORD dealership. Do have some upgrades...what do you need to know???

Thanks a bunch!!!
__________________

2012 FORD F250 SD CC 156" Lariat FX4 6.2L BOSS 4x4 4.30s
2003 F250 SD SC 142" XLT FX4 V10 Auto 4x4 3.73s -- Traded
1976 F150 LWB Custom 4x4 390FE NP435 3.50s
Reply With Quote
  #2 (permalink)  
Old 08-02-2005, 11:07 PM
xfordman xfordman is offline
Elder User
 
Join Date: Sep 2004
Location: Grain Valley Mo.
Posts: 863
xfordman is starting off with a positive reputation.
Biz...I'd like to know the answer to that also. I have the same truck 390, same year even. I hear they are very low compression but when I do a compression test I get 175 psi. I woulda guessed that to be at least 9 to 1.

__________________
XFM...
__________________
Retired from Ford (KCAP)
1953 F100.....5.0-AOD
2005 Ford 500
2002 HD Road King
Reply With Quote
  #3 (permalink)  
Old 08-02-2005, 11:09 PM
Randyb12 Randyb12 is offline
Posting Guru
 
Join Date: Jul 2003
Location: Eureka, Ca.
Posts: 1,268
Randyb12 is new and has a neutral reputation at this point.
you need to call the dealership you got it from and ask them. There are so many things that affect CR there is no way to tell you unless you remove the heads and take alot of measurements.
__________________
The Blind Guy
http://members.***.net/randy-barnett/
Reply With Quote
  #4 (permalink)  
Old 08-02-2005, 11:16 PM
FalconStng FalconStng is offline
Elder User
 
Join Date: Feb 2005
Posts: 669
FalconStng is starting off with a positive reputation.
so true. Pull the head, measure the stroke, measure top of piston to deck height, cc the pistons, cc the heads, know the head gasket thickness....calculate...lot's of fun...LOL. The stock truck 390 is about 8 to 1....I've heard anything from 7.9 to 8.2.

Good Luck,

Tracy
Reply With Quote
  #5 (permalink)  
Old 08-02-2005, 11:30 PM
biz4two's Avatar
biz4two biz4two is offline
Post Fiend
 
Join Date: Sep 2003
Location: Albuquerque
Posts: 5,237
biz4two has a great reputation on FTE.biz4two has a great reputation on FTE.biz4two has a great reputation on FTE.biz4two has a great reputation on FTE.
Talking

Ok...so does the cam effect the comp ratio? Or valve springs? Intake manifold? Pushrods? Timing chain? Water pump? Carb? FelPro gaskets, etc. Truck runs great on 86 octane...in case that matters.

Let's assume my 390 was rebuilt with "stock" pistons...and the "stock" valves. After all, I did order a "stock" 390. The only mods I have done to the engine are what's listed above...

Does that help any??? I really do not want to pull the head to find this out...especially since they will need to mill it (or at least check if it needs to be milled)...always told that was a good rule of thumb to have checked.

I'm just looking for something that might be close...
__________________

2012 FORD F250 SD CC 156" Lariat FX4 6.2L BOSS 4x4 4.30s
2003 F250 SD SC 142" XLT FX4 V10 Auto 4x4 3.73s -- Traded
1976 F150 LWB Custom 4x4 390FE NP435 3.50s
Reply With Quote
  #6 (permalink)  
Old 08-02-2005, 11:42 PM
Putt's Avatar
Putt Putt is offline
Posting Guru
 
Join Date: Jul 2003
Location: Colville, Washington
Posts: 2,166
Putt is starting off with a positive reputation.
Static compression ratio is not affected by anything you add to the outside of the engine. It is a calculated number that depends on the bore, stroke, head chamber volume, head gasket compressed volume, piston deck height, piston head style(dome, flattop, dished) and likely a couple other things I forgot!! The camshaft will affect the effective or running compression which can change the compression test results. ie. a long duration cam will cause lower readings than a short duration cam all other variables being equal.

I guess the short answer is we can't do it without those values I mentioned.
__________________
Putt

1966 F100 4X2 428 4 and 3 sp. 2.75:1 rear
1965 Ford Mustang 351W/C4 auto
Reply With Quote
  #7 (permalink)  
Old 08-02-2005, 11:45 PM
Bear 45/70's Avatar
Bear 45/70 Bear 45/70 is offline
Post Fiend
 
Join Date: Mar 2004
Location: Union, Washington
Posts: 6,056
Bear 45/70 has a good reputation on FTE.Bear 45/70 has a good reputation on FTE.Bear 45/70 has a good reputation on FTE.
Compression ratio is the difference in the cylinder's volume at Bottom Dead Center and Top Dead Center. 1000CC at Bottom Dead Center and 100cc at Top Dead Center = 1000 divided by 100 = 10 for a 10 to 1 compression ratio. The cam can change cylinder pressures, but not compression ratio.
__________________
Bear 45/70

"Earth has its boundaries, but human stupidity is limitless."
Gustave Flaubert (1821-1880)
Reply With Quote
  #8 (permalink)  
Old 08-03-2005, 12:03 AM
Putt's Avatar
Putt Putt is offline
Posting Guru
 
Join Date: Jul 2003
Location: Colville, Washington
Posts: 2,166
Putt is starting off with a positive reputation.
Well said Bear! I'm too long winded!!! HAHA
__________________
Putt

1966 F100 4X2 428 4 and 3 sp. 2.75:1 rear
1965 Ford Mustang 351W/C4 auto
Reply With Quote
  #9 (permalink)  
Old 08-03-2005, 12:17 AM
biz4two's Avatar
biz4two biz4two is offline
Post Fiend
 
Join Date: Sep 2003
Location: Albuquerque
Posts: 5,237
biz4two has a great reputation on FTE.biz4two has a great reputation on FTE.biz4two has a great reputation on FTE.biz4two has a great reputation on FTE.
Talking

Quote:
Originally Posted by Bear 45/70
Compression ratio is the difference in the cylinder's volume at Bottom Dead Center and Top Dead Center. 1000CC at Bottom Dead Center and 100cc at Top Dead Center = 1000 divided by 100 = 10 for a 10 to 1 compression ratio. The cam can change cylinder pressures, but not compression ratio.
So, then my 390 is completely "stock" when it comes to the compression ratio...if that is true, then what was the "stock" compression ratio of a 1976 390 truck engine? Is it as low as 8 to 1? Or 9.5 to 1?

Thanks guys! We are close...
__________________

2012 FORD F250 SD CC 156" Lariat FX4 6.2L BOSS 4x4 4.30s
2003 F250 SD SC 142" XLT FX4 V10 Auto 4x4 3.73s -- Traded
1976 F150 LWB Custom 4x4 390FE NP435 3.50s
Reply With Quote
  #10 (permalink)  
Old 08-03-2005, 12:38 AM
Bear 45/70's Avatar
Bear 45/70 Bear 45/70 is offline
Post Fiend
 
Join Date: Mar 2004
Location: Union, Washington
Posts: 6,056
Bear 45/70 has a good reputation on FTE.Bear 45/70 has a good reputation on FTE.Bear 45/70 has a good reputation on FTE.
Most of the light truck 390 engines ran 8.6 to 1, while the car 390's ran about 9.5 to 1 for 2 barrel engines.
__________________
Bear 45/70

"Earth has its boundaries, but human stupidity is limitless."
Gustave Flaubert (1821-1880)
Reply With Quote
  #11 (permalink)  
Old 08-03-2005, 11:04 AM
biz4two's Avatar
biz4two biz4two is offline
Post Fiend
 
Join Date: Sep 2003
Location: Albuquerque
Posts: 5,237
biz4two has a great reputation on FTE.biz4two has a great reputation on FTE.biz4two has a great reputation on FTE.biz4two has a great reputation on FTE.
Thumbs up

BINGO!!! Thanks Bear...
__________________

2012 FORD F250 SD CC 156" Lariat FX4 6.2L BOSS 4x4 4.30s
2003 F250 SD SC 142" XLT FX4 V10 Auto 4x4 3.73s -- Traded
1976 F150 LWB Custom 4x4 390FE NP435 3.50s
Reply With Quote
Old 08-03-2005, 11:04 AM
Reply

Go Back   Ford Truck Enthusiasts Forums > Performance, Engines & Troubleshooting > FE & FT Big Block V8 (332, 352, 360, 390, 406, 410, 427, 428)

Tags
1976, 390, compression, engine, fe, ford, ft, ratio, truck

Thread Tools Search this Thread
Search this Thread:

Advanced Search

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 On
Trackbacks are On
Pingbacks are On
Refbacks are On
Forum Jump



All times are GMT -5. The time now is 07:28 PM.


Powered by vBulletin® Version 3.7.5
Copyright ©2000 - 2014, Jelsoft Enterprises Ltd.
Advertising - Terms of Use - Privacy Statement - Jobs
This forum is owned and operated by Internet Brands, Inc., a Delaware corporation. It is not authorized or endorsed by the Ford Motor Company and is not affiliated with the Ford Motor Company or its related companies in any way. FordŽ is a registered trademark of the Ford Motor Company.

vbulletin Admin Backup