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Re: Any Truth to the Rumor?

To: tigers@autox.team.net
Subject: Re: Any Truth to the Rumor?
From: TigerCoupe@aol.com
Date: Sat, 22 Jan 2000 15:38:49 EST
n response to a question from Don Story, Doug Mallory wrote:

> The deck height on a 260 will not allow a 302 crank.


It is perfectly feasible to install a 302 crank in a 260, resulting in a CID 
of 273.  The deck heights of 8.206 inches on the 221/260/289 and most 302s 
are identical (the 1973-76 302 was 8.229 inches).  This is because the 
shorter length of a 302 connecting rod maintains the same deck height by 
compensating for the additional throw of the 302 crankshaft.
  
For the 273 CID application, use 302 rods and 260 pistons.  In selecting the 
pistons, make sure that the skirts are not too long, or they will hit the 
crankshaft counterbalances.  (If you are installing a 302 crank in a 289, 
avoid this is by using 302 pistons.  Ford service pistons are identical for 
the 289 and 302.)  Or, if you prefer to use 289HP/Boss 302 rods, use 
aftermarket pistons with the wrist pin located nearer the top of the pistons. 
The important thing is not to exceed the sum of all the dimensions which make 
up deck height: crank throw, connecting rod length, compression height, and 
deck-height clearance.

The crank throw (stroke X 1/2) for a 260 is 1.435 inches; on a standard 302 
(not Boss) it is 1.500 inches.  Rod length for a 260/289/289HP/Boss 302 is 
5.155 inches; for a standard 302 it is 5..090 inches.  Compression height 
(distance from centerline of wrist pin to top of piston) for a 260 or early 
302 is 1.600 inches.  Deck-height clearance (distance between top of piston 
and block deck surface with piston at TDC) for a 260 or early 302 is 0.016 
inches.    

If we add the crank throw for a 302 (1.500"), the length of a 302 rod 
(5.090"), the compression height for a 260 piston (1.600"), and the 
deck-height clearance for a 260 ( 0.016"), we get a deck height of 
8.206"---same as a stock 260 or early 302.  Of course, after you have 
selected all your new parts (including damper, flywheel, rings, etc.), it 
will be necessary to take them all down to your engine shop and have 
everything balanced.

Dick Barker

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