350 pushrod length swapping heads
March 25th, 2019, 09:25 PM
#1
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Join Date: Sep 2017
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350 pushrod length swapping heads
I got a 73 olds block with number 8 heads on it right now. I have some number 6 heads that I want to put on but I dont know what I should do about the pushrods.
Should I just buy a length checker pushrod and do it that way some how or is there a better way.?
Also what about bolting on the intake since the heads will be shorter?
Any help is appreciated
Should I just buy a length checker pushrod and do it that way some how or is there a better way.?
Also what about bolting on the intake since the heads will be shorter?
Any help is appreciated
March 26th, 2019, 05:53 AM
#2
Out of Line, Everytime😉
Join Date: Dec 2006
Location: Melville, Saskatchewan
Posts: 8,911
No, they will be the same unless the heads were milled a lot, the chambers are cast smaller, same overall height. Since you are probably going with .040" thick Felpro head gaskets, have the heads milled .020" to .030", the shim gaskets are .017-.018" thick. It will boost your compression some, put it closer to 9 to 1. Of course a CC check isn't a bad idea, anything can happen in nearly 50 years. I would also swap cams while in there, the stock one sucks and you probably need a new timing set anyways. I did the exact swap, heads were milled some, 62 to 64cc and .028" head gaskets put me at 9 to 1. Preload is fine but I have a stuck lifter, pretty sure. Even an adjustable valve train didn't fix it. The aftermarket cams do have smaller base circles which why a .030" mill wouldn't be bad with thicker gaskets. If you are worried you can buy a pushrod checker and see where it lies.
Last edited by olds 307 and 403; March 26th, 2019 at 06:01 AM.
March 27th, 2019, 11:10 AM
#3
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Join Date: Sep 2017
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No, they will be the same unless the heads were milled a lot, the chambers are cast smaller, same overall height. Since you are probably going with .040" thick Felpro head gaskets, have the heads milled .020" to .030", the shim gaskets are .017-.018" thick. It will boost your compression some, put it closer to 9 to 1. Of course a CC check isn't a bad idea, anything can happen in nearly 50 years. I would also swap cams while in there, the stock one sucks and you probably need a new timing set anyways. I did the exact swap, heads were milled some, 62 to 64cc and .028" head gaskets put me at 9 to 1. Preload is fine but I have a stuck lifter, pretty sure. Even an adjustable valve train didn't fix it. The aftermarket cams do have smaller base circles which why a .030" mill wouldn't be bad with thicker gaskets. If you are worried you can buy a pushrod checker and see where it lies.
I have an aftermarket cam in it right now, just dont know what it is because I dident put it in. So you think if i get them cleaned and milled .030 they'll bolt right on? And you really think I'm gonna only have 9-1 compression? I'm going from a 79cc to 64cc heads. With the small dish pistons I believe.
March 27th, 2019, 12:40 PM
#4
Out of Line, Everytime😉
Join Date: Dec 2006
Location: Melville, Saskatchewan
Posts: 8,911
Yes, with 14cc dish pistons .025" to .030" in the hole and a .041" head gasket needs about 62cc chambers for 9 to 1. I find the #8 heads CC at 77 to 78cc. Early 350 heads cc at 68 to 70cc untouched. Put in a 4.057 bore, 3.385 stroke and 4.230 gasket bore
https://www.google.com/url?sa=t&sour...ohf_GWsFWG6cGn
https://www.google.com/url?sa=t&sour...ohf_GWsFWG6cGn
Last edited by olds 307 and 403; March 27th, 2019 at 12:47 PM.
March 27th, 2019, 02:59 PM
#5
same but different
Join Date: Jun 2007
Location: Central Missouri
Posts: 2,861
Buying and using a checking push rod is the right way to go about this.
You probably don't need to do this but depending on any machine work done to the block, head or gasket + or -. The bottom line is, do the lifter plungers have enough travel to compensate?
They probably do, but you'll never know unless you measure it.
You probably don't need to do this but depending on any machine work done to the block, head or gasket + or -. The bottom line is, do the lifter plungers have enough travel to compensate?
They probably do, but you'll never know unless you measure it.
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