stock compression?
Super Moderator
Joined: Apr 2004
Posts: 34,466
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Without looking it up, I want to say 8.2 or 8.4. They do this with a short piston from the 410. It sits .100 or so down the hole, so shaving the head isn't going to get you much except goofed up gasket sealing and custom push rods.
A compression calculator, millions of which are on line, can tell you the difference once you plug in the specs. You will have to try to figure out about what your new combustion chambers will be.
The 410 piston is a flat top with valve reliefs. You will have to do the math on exactly how far down the hole it is.
A compression calculator, millions of which are on line, can tell you the difference once you plug in the specs. You will have to try to figure out about what your new combustion chambers will be.
The 410 piston is a flat top with valve reliefs. You will have to do the math on exactly how far down the hole it is.
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Elder User
Joined: Feb 2015
Posts: 676
Likes: 0
From: south east kansas
guess i forgot to say that my engine is a 68 truck 390, but i have bored it.040 and the pistons sit flush with the deck, it has shaved heads as well(dunno how much though), pistons are dished for the valves
Super Moderator
Joined: Apr 2004
Posts: 34,466
Likes: 2,798
You asked for stock compression. You do not have a stock pickup motor.
You need to measure your combustion chambers. Also, do your pistons have a dish or just 4 cuts for the valves?
10.5 CR pistons were flat top with the valve cuts.
9.5 CR pistons had a small dish with the valve cuts.
Sounds like you used car pistons in your rebuild. Pickup spec pistons would be .100+ down the hole.
Compression calculators:
http://www.summitracing.com/expertad...ion-calculator
https://www.rbracing-rsr.com/compstaticcalc.html
You need to measure your combustion chambers. Also, do your pistons have a dish or just 4 cuts for the valves?
10.5 CR pistons were flat top with the valve cuts.
9.5 CR pistons had a small dish with the valve cuts.
Sounds like you used car pistons in your rebuild. Pickup spec pistons would be .100+ down the hole.
Compression calculators:
http://www.summitracing.com/expertad...ion-calculator
https://www.rbracing-rsr.com/compstaticcalc.html
Lead Driver
Joined: Aug 2003
Posts: 7,592
Likes: 10
From: **** hole San Jose ca.
Cutting/shaving/milling and you don't know how much. Now you'll have to possibly have your intake manifold shaved also for proper intake gasket sealing. If not it won't be long you'll be pulling the intake replacing the gaskets.
set your intake on the engine of bolted down heads and Check intake gasket gap clearance. If heads have been shaved more then .020 then intake should be milled to correct square ness fit of gasket.
Orich
set your intake on the engine of bolted down heads and Check intake gasket gap clearance. If heads have been shaved more then .020 then intake should be milled to correct square ness fit of gasket.
Orich
Hotshot
Joined: Jul 2005
Posts: 13,834
Likes: 25
From: Middle Tn.
Cutting/shaving/milling and you don't know how much. Now you'll have to possibly have your intake manifold shaved also for proper intake gasket sealing. If not it won't be long you'll be pulling the intake replacing the gaskets.
set your intake on the engine of bolted down heads and Check intake gasket gap clearance. If heads have been shaved more then .020 then intake should be milled to correct square ness fit of gasket.
Orich
set your intake on the engine of bolted down heads and Check intake gasket gap clearance. If heads have been shaved more then .020 then intake should be milled to correct square ness fit of gasket.
Orich
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