I'm sure I'm missing something here, but can someone tell me the difference between a 2.5 block and the 2.7 item? I've read the article on conversions, which seems to suggest using the 2.7 eta black if doing a conversion - but the very same article says the 2.5 block is "more or less the same". So what's the difference?
Can I use a 2.5 block with 2.7 crank to make a 2.7 motor, or is the 2.5 block not as tall as the eta block? The article does say that if a 2.7 crank is installed into a 2.5 block, the pistons will stick out the top - but then it goes on to say that this is corrected with the shorter 2.0 rods and then decking the block.
So which is it? And does the block have to be decked either way? (Assuming I'm not just going to use the whole eta bottom end.)
Any clarification would be appreciated!
Which block for a 2.7?
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chu346
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The Eta block is taller.
Eta block, rods and pistons work fine together, other combination will need the block shaving.
Eta block, rods and pistons work fine together, other combination will need the block shaving.
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eta
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The eta block and 2.5 block are the same. There is a 0.5 mm difference in stack height of the 2.7 crank, 130 mm conrods and eta pistons compared to the 75mm crank 135 mm conrods and 2.5 pistons.
So it makes no difference what block you use. Eta crank, 130mm conrods and eta piston, 885 head stock exhaust, chip and all the other i bits will only net around 160-170hp. I have such an engine. It fine but using the 81mm crank, 130mm conrods, 2.5 pistons , decked block and vernier pulley (to adjust the cam timing) will result in 210+hp. Alternatively use the M52B28 crank, 130mm conrods and 2.5 pistons. No block decking needed and it will net more than the biuld using eta pistons.
So it makes no difference what block you use. Eta crank, 130mm conrods and eta piston, 885 head stock exhaust, chip and all the other i bits will only net around 160-170hp. I have such an engine. It fine but using the 81mm crank, 130mm conrods, 2.5 pistons , decked block and vernier pulley (to adjust the cam timing) will result in 210+hp. Alternatively use the M52B28 crank, 130mm conrods and 2.5 pistons. No block decking needed and it will net more than the biuld using eta pistons.
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daimlerman
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My 2.7 uses an ex 325 block!
There are detail differences,the so called 'steam holes' between the bores is one,but for all practical purposes B25 and B27 blocks are the same.
2.7 can be built in several ways,all have their supporters and all are correct. Just depends on what use the OP intends as to the correct way for him.
Piston choice is where things get complicated,the gudgeon pin position on 325 pistons is different in relation to the distance from the pin centre to piston top when compared to the eta piston,it is this measurment that makes it nessesary to 'deck' the block when using the 325 piston.
There are detail differences,the so called 'steam holes' between the bores is one,but for all practical purposes B25 and B27 blocks are the same.
2.7 can be built in several ways,all have their supporters and all are correct. Just depends on what use the OP intends as to the correct way for him.
Piston choice is where things get complicated,the gudgeon pin position on 325 pistons is different in relation to the distance from the pin centre to piston top when compared to the eta piston,it is this measurment that makes it nessesary to 'deck' the block when using the 325 piston.
Youth is wasted on the young.
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StuBeeDoo
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Use a 2ltr block and bore it to 84mm!! 
This is why I no longer drive an E30......
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E30BeemerLad
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