273 rebuilt but way low compression

[Babyblue66]

This is just a tip for those that may be rebuilding a 273 or have and ended up with a turd.

So last May I bought a 65 Barracuda. Plans were to put in a big block, but the 273 was rebuilt so I've decided to keep it. It seemed way to sluggish, and I could tell the engine was out of balance, and cranking compression was 115-120. So I pulled a head to see whats in there. I know it new I have paper work too.

The reproduction pistons are .045 below the deck, head cc is 65, with a .039 compressed gasket its measures a whopping 7.7 to 1!! Even zero decked it would be about 8.4.

So now I have to get expensive pistons. So always have your heads cc'd, deck hight measured, and static compression calculated when building an engine. And balancing is worth every penny!

later

 

[Tarr]

Good candiate for a turbocharger or supercharger at low boost.
That is a common problem that people that buy project cars from someone that is just trying to turn a car and make a few bucks. All the hype they spew about fresh rebuild with new pistons usually covers up for not having real details about the car and parts used. You can put a 350 Chevy together with all new parts really dirt cheap if you try but it will be a turd also. Cheap parts can be compared to a Street Hook--. If you don't care what you end up with, don't complain. It's all about details.
Sorry. Sounds like you got told a truck drivers story. "You ain't gonna beleive this but........".

 

[perfacar]

hi, ran your numbers, comp is 8.07. easist way to fix this, is surface heads to 58 cc, use the mopar thin gasket-.028, comp ratio, is 8.96. if you look at the specs on the motor, pistons are set at -.011 down, .028 , gasket, 57.3 cc head, comp os 9.70. not bad for a low comp motor.

 

[Tarr]

I fed him the negative and you told him how to make egg sandwich's out of broken eggs. Although the turbo don't sound half bad.
Thanks.

 

[Babyblue66]

hi, ran your numbers, comp is 8.07. easist way to fix this, is surface heads to 58 cc, use the mopar thin gasket-.028, comp ratio, is 8.96. if you look at the specs on the motor, pistons are set at -.011 down, .028 , gasket, 57.3 cc head, comp os 9.70. not bad for a low comp motor.

I don't know what formula you used??, but what we use at the shop I work at, we build engines, we came up with 7.7. And with a web site calculator I came up with the same. Also has 4 valve reliefs you need to take into account.

Those specs are meaningless.

My pistons are down .045. I measured them. The heads are 65 cc.

 

[Babyblue66]

If you don't care what you end up with, don't complain. It's all about details.
Sorry. Sounds like you got told a truck drivers story. "You ain't gonna beleive this but........".

I'm not complaining. I didn't care about the 273. I've just decided to use it now. Either way I would have been buying engine parts. I'm saying the after market parts are often incorrectly designed.

 

[moper]

It's more likely the block is not as short as it should be. The parts are stock replacement, and as you note, there aint much for 273s. Also, as stock parts, its' common to not balance things. I don't have any use for stock pistons anymore. It's not worth the savings IMO.