2.7 Rebuild info

[Gus]

search does nothing for me, so i have some q's

i am looking to build a 2.7 out of my 2.5 and a incorrectly built 2.7 (e pistons, 320 intake manifold/TB etc). i am hoping to take the crank and rods out without separating (as to not have to buy new con rod bolts) and put the 2.5 pistons on (after the skirt being machined, as they are out a pre FL) and rebuild the engine. what will i need to replace? headgasket set, head bolts, oil seals are what i have so far....what am i missing?

any genuinely helpful info will be much appreciated

[nando]

I would keep your i rods.. in any case this will require custom pistons, about $800 for a set.

[Gus]

i rods are 135mm...too long. dont want to get custom pistons as $$ and not really needed for my application

[Jordan]

Can you say really really low compression and next to no gains?

[Gus]

with 325i pistons? and e crank and rods?

[Jordan]

325i pistons, eta rods and crank won't work.

[nando]

i rods are 135mm...too long. dont want to get custom pistons as $$ and not really needed for my application

you can't use stock pistons. The point of the longer rods is for a better rod/stroke ratio, since you need custom pistons anyway.

[Gus]

so you're saying this Total BMW article is completely wrong?

[Jordan]

Budget strokers are teh suck.

There are 2 ways to do things.

Right.




































Again.

[madjurgen]

Whats the rod ratio for:

i rods and i crank

i rods and eta crank

i rods and s50b30US crank?

[Kilomph]

Gus, check out E30Tech.com, there's a lot of 2.7i information there.

[Jordan]

Whats the rod ratio for:

i rods and i crank
1.82

i rods and eta crank
1.67

i rods and s50b30US crank?
1.56

i rods and s52b32US crank?
1.51

i rods 135mm
e rods 130mm

i crank stroke 75mm
e crank stroke 81mm
s50 crank stroke 86.4mm
S52 crank stroke 89.6mm

The consensus amongst engine manufacturers is that a ratio of 1.50 is the lowest acceptable rod ratio for a street motor. Realistically, rod ratios between 1.65 - 1.80 are ideal.

[madjurgen]

Rod ratio is directly related to revability or the willingness to rev, correct? I know other things contribute as well, but all else equal...thats what controls it correct? Doesnt bode well for a 3.0L stroker using i rods and S50b30US crank.

On an offnote, how long are the S50b30US rods?

[nando]

Rod ratio is directly related to revability or the willingness to rev, correct? I know other things contribute as well, but all else equal...thats what controls it correct? Doesnt bode well for a 3.0L stroker using i rods and S50b30US crank.

On an offnote, how long are the S50b30US rods?

the other option is the M52B28 crank (84mm stroke) e rods (130mm) and i pistons.. but this gives you a pretty low r/s. I've been thinking it over and I'd rather spend the money on the correct pistons so I can use the longer rods and not sacrifice my revs. I want more torque, but I love the way the 2.5 runs from 4k+.

[Jordan]

M20B25
M50B25
S50B30
S52B32
S70B56

All use 135mm rods. Might be more, but those I know off the top of my head.

You are correct. The lower the rod ratio, the less willing to rev up and high a engine is going to be.