Head Decking - How much & how far
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Head Decking - How much & how far
I'm looking to bost the CR of my old 400 (my Bronco's origional motor - not it's current), and I'm considering decking the heads. Currently Ive got the ?78cc? heads (stock) and I'm wondering....
1. How much can be decked off these heads safely.
2. Mow much to take off to reach about 9.0-9.5 :1 cr w stock dished pistons.
The block & pistons are in good shape needing a good cleaning and bearings. Thus my reasons for leaving it alone if possable.
When I get to doing this, it will be in conjuction with an appropriate cam & timing gear set, maybe roller rockers, already got the headers, exhaust, and intake. Probibly clean the thermactor bumps also. Nothing real radical, jsut enough to ensure maximum fun factor from today's outragous priced gas!
George in the Fl Swamps
1. How much can be decked off these heads safely.
2. Mow much to take off to reach about 9.0-9.5 :1 cr w stock dished pistons.
The block & pistons are in good shape needing a good cleaning and bearings. Thus my reasons for leaving it alone if possable.
When I get to doing this, it will be in conjuction with an appropriate cam & timing gear set, maybe roller rockers, already got the headers, exhaust, and intake. Probibly clean the thermactor bumps also. Nothing real radical, jsut enough to ensure maximum fun factor from today's outragous priced gas!
George in the Fl Swamps
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From: Delaware
You have to take 0.040" off the heads to get 9:1 from a stock 400. I don't know that you can safely go that far. You could go to Aussie heads, and open up the chambers to about 64cc to get 9.5:1. If you get more than 9:1, you should be careful with your cam selection.
What kind of cam were you considering? What kind of use do you plan for it?
What kind of cam were you considering? What kind of use do you plan for it?
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What I was considering was to pretty much follow the old HOT Rod article and was aiming towards mostly a Comp Cams 268 (I think). In the article I believe the target was about 9.0 cr or jsut over. Either way, it's to run on pump gas as a mostly daily driven street truck (79 Bronco currently w 33x12.5" tires). Nothing too radical.
fwiw - Somewhere I saw a referance saying that .072 could be safely taken off the stock heads. Frankly I have no idea what the max could be. Im considering this as a possable option to piston replacement since teh flat tops aren't the easiest to find (though there are sources) and mine are still in good shape. Basically trying to cover the bases.
George M in the Fl swamps
fwiw - Somewhere I saw a referance saying that .072 could be safely taken off the stock heads. Frankly I have no idea what the max could be. Im considering this as a possable option to piston replacement since teh flat tops aren't the easiest to find (though there are sources) and mine are still in good shape. Basically trying to cover the bases.
George M in the Fl swamps
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Joined: Aug 2001
Posts: 4,270
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From: Delaware
There are better cams than the 268H. The XE256 for low RPM torque and the XE262 and the 265DEH for mid range. These will work well with 9.0:1 CR. For real performance the 270HR is a good choice, although you will put out more dollars.
