What CR???
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Senior User
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From: Six Shooter Junction
What CR???
Ok, I got my engine all torn apart and found out that my 460 is a mut with parts from 68 to 76. Thats not the problem, I have a D1VE block with D0VE heads and though that my CR was in the low 10s. Are the pistons for the 71 flat tops, mine arnt. I also found out that my block is bored .040 over, so this may be why my pistons have a oval shaped dish in the middle. So now i need to know what CR im going to have, is it still in the low 10s or now in mid 9s
Thanks in advance
Chase
1979 F-250 4x4
71 460 Holley650, MSD OFFROAD, L&L Headers
C6-B&M Transpack
Dana HD44Front/60Rear
35 inch Goodyear Implement Tires
4 inch Skyjacker System
Much more to come
[link:www.tarleton.edu/students/jwillms/ChasesOldFord.com|My Truck]
Thanks in advance
Chase
1979 F-250 4x4
71 460 Holley650, MSD OFFROAD, L&L Headers
C6-B&M Transpack
Dana HD44Front/60Rear
35 inch Goodyear Implement Tires
4 inch Skyjacker System
Much more to come
[link:www.tarleton.edu/students/jwillms/ChasesOldFord.com|My Truck]
Postmaster
Joined: Aug 2001
Posts: 2,882
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From: Nevada
What CR???
Easiest way is to identify the piston. Go to a machine shop that builds Ford engines and ask them. If it's forged, then probably TRW, now SpeedPro. Cast may be difficult, but as a last resort they can measure it for $$ and look it up in their parts books, which will also give the C/R with a 75cc head.
If not, you'll have to cc the space between the top of the piston at compression stroke and deck to use a formula with the head cc and gasket thickness. Not fun.
If not, you'll have to cc the space between the top of the piston at compression stroke and deck to use a formula with the head cc and gasket thickness. Not fun.
New User
Joined: Jan 2008
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What CR???
Are they single eyebrow or double eyebrow pistons?
[font color=red]Dennis
FTE Adminstration
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[font color=blue]78 F-150 429CJ,Silver,Explorer Pkg.
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Thread Starter
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Senior User
Joined: Aug 2001
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From: Six Shooter Junction
What CR???
Sorry for the delay but heres a picture of the piston. [link:www.ford-trucks.com/user_gallery/displayimage.php?&photoid=6284&width=0|Piston] Does anyone have a picture of the original pistons out of a 71 460 so i can compare, or maybe someone knows the cc's of this dish. Its a longshot but hopefully someone here will know.
Thanks in advance
Chase
1979 F-250 4x4
71 460 Holley650, MSD OFFROAD, L&L Headers
C6-B&M Transpack
Dana HD44Front/60Rear
35 inch Goodyear Implement Tires
4 inch Skyjacker System
Much more to come
[link:www.tarleton.edu/students/jwillms/ChasesOldFord.com|My Truck]
Thanks in advance
Chase
1979 F-250 4x4
71 460 Holley650, MSD OFFROAD, L&L Headers
C6-B&M Transpack
Dana HD44Front/60Rear
35 inch Goodyear Implement Tires
4 inch Skyjacker System
Much more to come
[link:www.tarleton.edu/students/jwillms/ChasesOldFord.com|My Truck]
Postmaster
Joined: Aug 2001
Posts: 2,882
Likes: 0
From: Nevada
What CR???
Looks like a regular dished 460 piston. 429s had flat tops with one or two valve reliefs.
Dish volume=12cc is standard on the 460 piston, get an eyedropper
Comp. Ht.=1.756 (don't know the piston, so I'll use TRW)
Head gasket thickness? (Don't know, I'll use .040, pretty standard)
Head gasket bore? (don't know, I'll use .046)
Stroke=3.85 (measure to see if crank was cleaned up)
Bore 4.40 (includes .040 overbore)
Compression height = 1.756+6.605(rod)+1.925(1/2 stroke)= 10.286
Stock DIVE deck = 10.322 (Don't know if it was decked as it was bored)
Deck clearance 10.322-10.286=.036
C/R with those factors = 10.69:1
1. You need to identify the piston to verify the compression height or have a machine shop measure it.
2. Verify the block deck height
3. Verify Head gasket compressed thickness and bore size
4. verify dish volume cc
Then go here (or any other site with a C/R calculator)
http://www.smokemup.com/auto_math/compression_ratio.php
No true answer until you get actual measurements, but this should get you started.
Dish volume=12cc is standard on the 460 piston, get an eyedropper
Comp. Ht.=1.756 (don't know the piston, so I'll use TRW)
Head gasket thickness? (Don't know, I'll use .040, pretty standard)
Head gasket bore? (don't know, I'll use .046)
Stroke=3.85 (measure to see if crank was cleaned up)
Bore 4.40 (includes .040 overbore)
Compression height = 1.756+6.605(rod)+1.925(1/2 stroke)= 10.286
Stock DIVE deck = 10.322 (Don't know if it was decked as it was bored)
Deck clearance 10.322-10.286=.036
C/R with those factors = 10.69:1
1. You need to identify the piston to verify the compression height or have a machine shop measure it.
2. Verify the block deck height
3. Verify Head gasket compressed thickness and bore size
4. verify dish volume cc
Then go here (or any other site with a C/R calculator)
http://www.smokemup.com/auto_math/compression_ratio.php
No true answer until you get actual measurements, but this should get you started.
Thread Starter
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Senior User
Joined: Aug 2001
Posts: 213
Likes: 0
From: Six Shooter Junction
What CR???
Thanks alot, Ill see if I can get the rest of that info to get a more precise number. 
Thanks
Chase
1979 F-250 4x4
71 460 Holley650, MSD OFFROAD, L&L Headers
C6-B&M Transpack
Dana HD44Front/60Rear
35 inch Goodyear Implement Tires
4 inch Skyjacker System
Much more to come
[link:www.tarleton.edu/students/jwillms/ChasesOldFord.com|My Truck]
Thanks
Chase
1979 F-250 4x4
71 460 Holley650, MSD OFFROAD, L&L Headers
C6-B&M Transpack
Dana HD44Front/60Rear
35 inch Goodyear Implement Tires
4 inch Skyjacker System
Much more to come
[link:www.tarleton.edu/students/jwillms/ChasesOldFord.com|My Truck]
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