340 Heads on a 273 Block

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gljplc

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I would like to replace the stock heads on my 273 V8 with a set of 340 heads.
However, it seems that the tech books say that this would be a close
call because of the valve-to-cylinder wall clearance issues.
The stock 273 cylinder has a 3.63 inch bore and and the 273 heads have a 1.78 intake and 1.50 exhaust valves. The smallest valves on the 340 are 1.88 intake and 1.60 exhaust.
My 273 block was bored .030 on the rebuild.

QUESTION: Does anyone know if the 340 head with 1.88/1.60 valves has
enough valve-to-cylinder clearance when bolted to a 273 block bored .030 over to operate properly ???.

As always guys, any info is greatly appreciated.

GLJPLC
 
I would install late model 318 heads with a port volume of 138-140 with the 1.780 intake valves and just do some match and port work on the bowls and be able to still use the stock rocker assembly or go to a adjustable rockers.The 340 head with kill the small motor of 275 and the port volume is to much for your applacation.And if you did get a set of the 340 heads with the smaller valves it would still be to much.To keep the volocity up and the the cylinder capable of filling close to 100%and with a good dual plane intake and small 4 bbl carb,this will work great,Mrmopartech :salut:
 
what Mr M said. the casting number of the heads you want ends in "302". They can be gotten off any 87ish to '91 318, car, turck, van..Just make sure you get a crack free set.
 
i agree with those ho has writen before mee, small valves does not mean slow engine, velocity is king!
 
The 340 heads WILL work on a 273 with some careful modification. The Cylinder walls will need to be flycut about 1/4" deep from the top of the block and a max of .070 toward the side approximately 1-3/4" wide to clear 2.02 intake valves. I can send you a sketch of what I did if you are interested. As mentioned in previous replies, unless you have a specific reason for 340 heads, the smaller heads with a good cam selection will yield better general performance. The 340 heads will make a 273 provide decent power in ONLY high RPM. They will work, but are only recommended if you are aware of what results the additional volume, port size, and valve diameter yield on the small cylinder volume.
 
as Grim said...the tops of the cylinders will need to be "trimmed". If it were me, I'd look into 302s or Magnum heads. the 302s are total bolt ons..
 
grimreaper said:
The 340 heads WILL work on a 273 with some careful modification. The Cylinder walls will need to be flycut about 1/4" deep from the top of the block and a max of .070 toward the side approximately 1-3/4" wide to clear 2.02 intake valves. I can send you a sketch of what I did if you are interested. As mentioned in previous replies, unless you have a specific reason for 340 heads, the smaller heads with a good cam selection will yield better general performance. The 340 heads will make a 273 provide decent power in ONLY high RPM. They will work, but are only recommended if you are aware of what results the additional volume, port size, and valve diameter yield on the small cylinder volume.
Click to expand...

I have a problem with this, "It will work"
The 2.02 + 1.60 valves = 3.62 while the bore of a 273 is 3.63. Even with this notch, there isn't room I believe.
Above is the simple math of it all which leaves .001 clearance. Then theres the notch. Not that a max of .070 isn't enuff, but.........
 
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