273 commando Build

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Yes this 273 block is coming along nicely ....but..... My attention is going to be put on porting and polishing the 920 heads.. I want some horsepower to be unleashed from those 920 heads. this past engine was a beast without any real porting done . so we will see how much more hp I can make or loose. I'm staying with stock valve size.
I have read articles from guys that built 273's and ran 273-318 heads with stock valve size and ran some really good numbers. don't know how much of it was really true though..
 
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stroker402 said:
Yes this 273 block is coming along nicely ....but..... My attention is going to be put on porting and polishing the 920 heads.. I want some horsepower to be unleashed from those 920 heads. this past engine was a beast without any real porting done . so we will see how much more hp I can make or loose. I'm staying with stock valve size.
I have read articles from guys that built 273's and ran 273-318 heads with stock valve size and ran some really good numbers. don't know how much of it was really true though..
Click to expand...
Feel free to check out my build thread (link below) Somewhere in there I have pics of my ported heads both roughed in and assembled. I may have more photos if you need. 2 things I regret, not putting the heads on a flow bench and not putting the engine on a dyno. Regardless of the numbers, it would be fun to know them.
 
stroker402 said:
Yes this 273 block is coming along nicely ....but..... My attention is going to be put on porting and polishing the 920 heads.. I want some horsepower to be unleashed from those 920 heads. this past engine was a beast without any real porting done . so we will see how much more hp I can make or loose. I'm staying with stock valve size.
I have read articles from guys that built 273's and ran 273-318 heads with stock valve size and ran some really good numbers. don't know how much of it was really true though..
Click to expand...

My heads really work well with just a bowl blend and gasket match. I also just clean up any sharp edges and casting flash. Heads are milled to NHRA min chamber size and are cc'd and equalized. I run stainless exhaust valves, 340 valve springs and Fel-Pro Viton positive intake valve seals (no machining required). Back cut intake valves. No one would believe how my 273 runs. All with an Isky E-4 cam. For more than that, @perfacar, @318willrun and @GTX JOHN know a whole lot more about porting.
 
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66fs said:
My heads really work well with just a bowl blend and gasket match. I also just clean up any sharp edges and casting flash. Heads are milled in NHRA min chamber size and are cc'd and equalized. I run stainless exhaust valves, 340 valve springs and Fel-Pro Viton positive intake valve seals (no machining required). Back cut intake valves. No one would believe how my 273 runs. All with an Isky E-4 cam. For more than that, @perfacar, @318willrun and @GTX JOHN know a whole lot more about porting.
Click to expand...
i kinda just did what you do, bowl blend/gasket match and the pinch area.
 
UPDATE UPDATE !! FOUND THE SMOKING GUN !

well I finally found out why the 273 was popping head gaskets .. check the pics out and see .
top balancer is the one that spun !

IMG_20241214_150145.jpg


IMG_20241214_150602.jpg
 
stroker402 said:
UPDATE UPDATE !! FOUND THE SMOKING GUN !

well I finally found out why the 273 was popping head gaskets .. check the pics out and see .
top balancer is the one that spun !
Click to expand...
Nice, good job! That would explain it. @Newbomb Turk nailed it at post #324. You should always take the time to find True TDC and centerline your cam when putting an engine together. I have found some 10* off without slipping. Those early harmonic balancers can be rebuilt, don't ditch them.
 
If you guys read my past posts I mentioned every time i matted it to the floor is when the gaskets blew.. probally because the balancer slipped another 4 -5 degrees. hence detonation.
as you can see the balancer moved almost 2 inches from tdc and then you add in another initial 18*.. I remember setting the timing numerous times back to 18* initial thinking the distributor was not tight and moved.. or chain was stretched...or never seen a balancer that spun . heard of it though. live and learn !
the273 only ran rough after the head gasket blew. like I said in previous post that every time i trumped the gas pedal to the floor quick is when the gaskets blew , It happened that way 4 times.
 
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Stroker,
So, the cam was not degreed and the key was not properly set in the keyway several times, or was there something that caused it to shear?
Richard
 
Richard Sweet said:
Stroker,
So, the cam was not degreed and the key was not properly set in the keyway several times, or was there something that caused it to shear?
Richard
Click to expand...
the key was not sheared or the keyway not boogered up.. that was All fine..... it was the harmonic balancer that went bad and spun . this 273 engine revved violently fast .
 
Plymouth 65 said:
273 Commando pistons are above deck pistons, you're closed chamber heads will interfere. You'll require really thick head gaskets or open chamber heads like the heads that came with that motor originally.
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The heads on 1967 273 and 318s are ALL the same,
Closed chamber. I have a 67 formula S and and the heads are closed chamber. 1968 they went to open chambers...
 
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