That is why you can't run a 3.625 bore gasket on a 273. You have to sandwich the gasket between 2 surfaces. Now put that gasket on to your head and see why you need that 3.95 dimension on a head gasket if your gasket fire ring is round.
273 commando Build
- Thread starter stroker402
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That is why you can't run a 3.625 bore gasket on a 273. You have to sandwich the gasket between 2 surfaces. Now put that gasket on to your head and see why you need that 3.95 dimension on a head gasket if your gasket fire ring is round.
I would think minimum diameter would be the 3.975" spec?
**edit** obviously depending on bore size.
**edit** obviously depending on bore size.
Pretty stinking close isn't it.
They didn't loose much compression with the closed chamber head and funny shaped steel shim gasket.
stroker402
1968 dart GTS convertible
what was the purpose of the funny shaped head gasket ? shrouding ?
As good as you could get, and have the heads seal.
The chamber is that big next to the valves, shrouding for sure.
Shrouding is when the intake valve comes close to the bore at the top. You have to notch the bore where the valve path is as it opens.
The combustion chamber can also shroud the valves.
That's what I always thought shrouding was. I never realized/thought the cyl bore itself could contribute to shrouding.
I'm still lurnin'.
I'm still lurnin'.
Dartswinger70
Well-Known Member
I know its an old post but i think these engines are cool worth saving as they are factory HiPo offerings
stroker402
1968 dart GTS convertible
sure would appreciate it if some of you guys that built theses commando engines with stock heads and bore 3.625 to see what head gaskets you all used.. because the 318 gasket or larger will not seal.. that is my observation. that odd ball combustion chamber is limiting how much gasket material is available there for clamping . that's why is pushing that gasket out near the valley edge . it's only 3/8" wide . imo ... keep in mind this is no stock 273 it's built and is dialed in for max hp. it revs like it's on Nitrous with the lightest pressure on the Go pedal.
Dartswinger70
Well-Known Member
I think there is a specific gasket set for those Toolman Mike may know.
stroker402
1968 dart GTS convertible
update
well I called jim at sce cometic gaskets he recommended a copper gasket 3.75bore .043 thick ... $132.00 each ..... 2 months to make . they would NOT require studs OR o ring As long as good mating surfaces.
they do not have anything in a small bore composite gasket.
well I called jim at sce cometic gaskets he recommended a copper gasket 3.75bore .043 thick ... $132.00 each ..... 2 months to make . they would NOT require studs OR o ring As long as good mating surfaces.
they do not have anything in a small bore composite gasket.
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Newbomb Turk
Well-Known Member
I’m going to say pass on the copper gaskets.
They are a ***** to seal oil and water. If you run a 16 pound radiator cap it will find places to breach the gasket and it will leak.
Same with oil pressure. Even if they are embossed. I wouldn’t chance it. I may try it IF I was using Evan’s coolant because it doesn’t make water pressure.
That would help with the water leaks but nothing for oil leaking.
I would call Cometic and use those.
Dartswinger70
Well-Known Member
Ask Uncle Tony didn't he put 273 head son his Bottle Rocket 318?
I think he did. Closed chambered 920's?
He's a dumb ***. "67-69 273 closed chamber heads" I love to fact check him and prove him wrong!
64 and 65 were closed chamber with the odd intake bolt angle
66 and 67 were closed chamber with the normal LA intake bolt thread size and angle
68 and 69 were open chambered with the normal LA intake bolt size and angle.
His description is at the 2 min mark here:
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stroker402
1968 dart GTS convertible
yeah I don't care for him either.
I've built more than a few HP 273's with Fel-Pro 8553 PT head gaskets. Used stock head bolts torqued to 85 ft lbs and never had blown a head gasket. 273 heads, 57.4 cc chambers, or small valve "J" 340 heads 65 cc chambers, TRW forged 10.5 pistons and made more power than you. Those 273's would take everything a 600 Holley, "67" AFB, and a "71" 340 TQ had to offer. Hate to tell you, but I'm pretty sure your block needs a minimum cut for the decks to be square and equalized. See posts 237 and 240.
stroker402
1968 dart GTS convertible
OK guys ! that's the plan then. I have another stock bore commando engine .. I will send off to machine shop to square up block. the heads I already did .
I don't usually think you always have to deck a block, but after 3 blown head gaskets (failed at the same place and the same way), and milled heads, there is something wrong with that sealing surface.
Exactly. I machined my heads to get the chambers down to minimum but I checked the deck with a precision straight edge and deemed it ok. The Surface was smoother than some of the above photos. Production machining back in the day could be quite crude. A worn out braised carbide tool with a burr on the end could really screw with the finish and accuracy. Those machining marks are a long ways from right and 60 years of engine use can mess with the surface flatness too.
They don't even look factory to me. Seams too coarse for what I've seen.
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