Wrong heads for a 273

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gzig5

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I just got the deal of the century on a 273 short block that came with a full gasket set. Really nice gentleman had it and gave me a tour of his shop after we loaded in my truck. It is/was the backup block for his streamliner dragster that has been restored and won't be racing anymore. Here is a link to that story, I thought many would find it interesting.
The Silver Bullet Dragster Comes Full Circle
In his shop along with some metal fab equipment, he had three front engine dragsters, two vintage SCCA type cars, Bonneville salt flats car, a 33-ish Ford hot rod, and all manner of other gas powered toys in there. It was a lot of fun talking to him.

So now I have a '65 273 block that has high compression pistons (I think) and seems to be thirty over because I measure 3.655" with calipers. Bores are a bit rusty but will clean up I think. He kept it oiled somewhat but it was not fully protected from the elements over the years. I have access to a set of heads 587 heads and intake from a 73 340 that I'm thinking of dropping on. I know that they are considered on the large size for a 273 but the 1.88 valves aren't all that much bigger and I'm thinking they might help it breath at higher rpm and let it sing. Thought I'd rub on the bowls a little and need to figure out how much I can shave the heads (with those pistons) to reduce the chamber size and keep compression. Just got it home and need to get it cleaned up but there are other projects in the way. For all I know at this point, it could be locked up, but I doubt it. Just kind of talking out loud and looking for some feedback.

I'm gong to try to keep this build low dollar. I'm not even sure what I'm going to do with it yet. Maybe I'll stick in my 73 Cuda for giggles. Might have to buy a car to put it in. Maybe a 67 Barracuda convertible, I like silver to match the other one...
 
I have run 1.88 intake 340 heads on a 273. Just don't over cam it. You will love it with a TQ. Mock it up and make sure your heads are centered on the bores to give you the most clearance with the intake valves. Mill the heads .040 and .038 on the intake side. That will put you at NHRA min chamber volume of 64.7 cc. Early 273 heads flow about the same as the 587 heads with the 1.78 intake valves. If you look at the 273 potential of what he ran, 10.37 sec at 142.85mph, you should be good either way. I love that dragster! Thanks for posting that article.
 
Sounds cool. 2 valve reliefs and a dome = Commando pistons
4 valve reliefs = regular 273 passenger car pistons.
 
Probably the safest heads to use on a 273. Use 2.02 valve heads and you have shrouding and clearance issues. Nothing that can't be fixed by grinding clearance on the bore edge.
 
I would approach it like this. There are way MORE wrong heads for the 273 than there are right. So be careful.If it was mine, you wouldn't catch me running a 340/360 port size head on one, or one with the 340/360 chamber size either. But that's just me.
 
I believe it will lower your compression a bit.
 
Valkman said:
I believe it will lower your compression a bit.
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Actually, in my experience, early 273 closed chamber head chambers measure between 63.5 and 64.8 cc. So if your milled 360 heads measure 64.7 cc, you are in the spread. Just have them checked for cracks before putting a lot of time and effort into any heads.
 
66fs said:
Actually, in my experience, early 273 closed chamber head chambers measure between 63.5 and 64.8 cc. So if your milled 360 heads measure 64.7 cc, you are in the spread.
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That's close to 10ccs. That's a pretty big cut. So so that he's gonna have to mill the intake too.
 
RustyRatRod said:
I would approach it like this. There are way MORE wrong heads for the 273 than there are right. So be careful.If it was mine, you wouldn't catch me running a 340/360 port size head on one, or one with the 340/360 chamber size either. But that's just me.
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It all depends on what you are doing with your 273.
 
66fs said:
It all depends on what you are doing with your 273.
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Oh yeah, I agree. If it was mine, I would TRY to put it together so there were no big cuts on anything. That way you wouldn't have any bastard parts. I would use either the 302 castings or the 5.2 Magnum castings if I was doing one......but I'm not so it's kinda a moot point.
 
66fs said:
It's .040 off a "never milled" head. Just mill the intake side of the head .038 while you are at it. No problem...
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Is that all it would take? Then you could probably get by without milling the intake. I've gone .030 before with no intake milling.
 
RustyRatRod said:
Is that all it would take? Then you could probably get by without milling the intake. I've gone .030 before with no intake milling.
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I just always mill both, not that much difference in money, besides I like how it cleans all the gasket surfaces up. I'd worry about something being off somewhere down the line I wasn't thinking of. Plus I know I'd be swapping some other intake or two or three just to see how I liked them.
 
My personal experience on bracket racing 273. Combustion chamber volume not measured in either case:

Stock 273 heads, (port matched to 340 intake gaskets), 10:5 to 1 factory Commando style pistons (forged TRW). Block decked (cleaned up cut), heads milled (cleaned up cut). Edelbrock Tarantula intake (made for 340) and Holley 600 CFM double pumper. Steel shim head gasket. Cyclone fenderwell headers and Isky camshaft. Best E.T. 12.72.

Same as above with 340 open chamber heads (2.02) and cylinders notched for valve clearance. Best E.T. low 13.00's.
 
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66fs said:
I just always mill both, not that much difference in money, besides I like how it cleans all the gasket surfaces up. I'd worry about something being off somewhere down the line I wasn't thinking of. Plus I know I'd be swapping some other intake or two or three just to see how I liked them.
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If you cut it and it don't bleed................................you didn't cut deep enough!!:rofl::rofl::rofl::poke:
 
dibbons said:
My personal experience on bracket racing 273. Combustion chamber volume not measured in either case:

Stock 273 heads, (port matched to 340 intake gaskets), 10:5 to 1 factory Commando style pistons (forged TRW). Block decked (cleaned up cut), heads milled (cleaned up cut). Edelbrock Tarantula intake (made for 340) and Holley 600 CFM double pumper. Steel shim head gasket. Cyclone fenderwell headers and Isky camshaft. Best E.T. 12.72.

Same as above with 340 open chamber heads (2.02) and cylinders notched for valve clearance. Best E.T. low 13.00's.
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I never ran the 72 340 head 273 at a track and never had headers on the car, but I can tell you that it was much faster with the 340 heads, cam, intake and TQ than the 273 heads, 284 duration TRW cam, Offy intake and 600 1850 Holley.
 
It would be interesting to know what the limit the 273 bore and stroke has as far as port flow. It can only use so many cfm and there's no reason to have more that can't be used. You would need to run a 273 at 8000+ rpm to use all that flow. All the manufacturers have done it. Boss 302, 302 Z28 Chevy, etc. If I ever have a reason to pull my heads I hope to flow them just to see what they will do.

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The problem with a 273 is you run out of rpm since your stock bottom end and valve train need to be addressed past 7,000 rpm. I think you hit 7,000 rpm around 1.88 J head intake flow, 200 cfm. But at that point you are over 400 hp. Theoretically...
 
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toolmanmike said:
It would be interesting to know what the limit the 273 bore and stroke has as far as port flow. It can only use so many cfm and there's no reason to have more that can't be used. You would need to run a 273 at 8000+ rpm to use all that flow. All the manufacturers have done it. Boss 302, 302 Z28 Chevy, etc. If I ever have a reason to pull my heads I hope to flow them just to see what they will do.

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I think 8000rpm would be a kick in the pants.

I'm going to ask the gentleman I got the motor from, a few details about the motor in the silver car next week if I can get hold of him. I know he built that injection system from scratch, but we didn't discuss the guts of the motor such as the cam timing, heads, etc.. Supposedly was making about 400+hp back in the late sixties on motor alone, but probably not regular gasoline. The cubes limit the peak HP but it could still be a fun engine in a light car.

This is sorta like when I go to a gun show and run across a great deal on a set of reloading dies and cartridge brass in a caliber I don't have, so I buy it. And then I go find or build a rifle in that caliber so I can use them. Now I have a motor, and I'll just have to find a light A-body to put it in at some point.
 
Although I had a forged crank, polished and shot-peened connecting rods (stock), forged pistons, a solid cam with dual valve springs, I would not dare pass 6,500 RPM with my 273 (too scared).
 
Before you start making plans on where it's going to sit, you may want to look at the crank first to see if it's the small register (stock '64-6 273 crank) or if it's been changed to the later large register for the later converter button. If it's going into a manual trans application, see if the crank has been machined for a pilot bushing.
 
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