Easy Q. (maybe) for 273 lovers...

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65Val

65Val

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Are the factory 2 barrel pistons the same weight as the factory 4 barrel pistons? In other words, can someone swap out the 2 bbl pistons directly for the 4 bbl ones, without rebalancing,etc.?

Thanks
 
If you are swapping pistons, even if they are the same part #... it can throw the balance off.
 
The 4 barrel pistons have a slight dome, so I`d guess they`re a little heavier. Don`t know for sure though?????
 
I was also wondering ,because ,if they ARE different weights, I guess the crank would be different from 2bbl to 4bbl. If thats so, how would you tell a 2bbl crank from a 4bbl crank? They are the same part number, yes?
 
I'm not a genius and don't claim to be, but in theory shouldn't you still be in balance if you put a new set of pistons in as long as they all weigh the same, even if they are different weight than the old pistons ? What I'm sayin is shouldn't the balance not really be affected but rather the gross weight of the rotating assembly.
 
wigsplitter74 said:
I'm not a genius and don't claim to be, but in theory shouldn't you still be in balance if you put a new set of pistons in as long as they all weigh the same, even if they are different weight than the old pistons ? What I'm sayin is shouldn't the balance not really be affected but rather the gross weight of the rotating assembly.
Click to expand...

Yes, if you were to draw a line down the crank center the combined weight of the pistons, rods, wrist pins, and rings should balance the opposing counterweights of the crank and in theory you should be able to do that. I think what 65Val is trying to do is see if he can swap out a set of the low compression, flat top pistons from a 2 barrel, 273 with 4 barrel, mini dome, 10.5-1 pistons without a balancing issue. I would guess the 4 barrel piston is a bit heavier but I think the wise thing to do would be to check the balance even if the piston is supposedly the same weight.
 
65Val said:
Are the factory 2 barrel pistons the same weight as the factory 4 barrel pistons? In other words, can someone swap out the 2 bbl pistons directly for the 4 bbl ones, without rebalancing,etc.?

Thanks
Click to expand...

The weights are different but the pins also are different, making the piston + pin the same weight. Balancing the motor gets the balance much closer to perfect. This makes it rev quicker, run smoother, and last longer, all things being equal. If your engine is apart it is something to seriously consider for the money. Also 68-69 273 pistons are .03 higher in the block to compensate for the open chamber heads. Cranks are the same. Only difference is Auto or manual.
 
Thanks guys. Those are the answers I was looking for.

Longgone...thats exactly what I was considering. I have a set of factory 10.5 : 1 pistons and was thinking of swapping them into my 2 barrel engine, but was concerned the balance would be off.

66fs...thanks for that info. I guess another possibility would be to swap the later 2 barrel pistons into the earlier block for a small comp. increase.

More food for thought.....(scatching head)
 
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