2.7i Questions

[malmeida1040]

I originally purchased a an 2.5 m20 harness and 173 ecu for my 86 325e. My plan was originally to reseal the whole engine and throw a 2.7 crank in it. upon disassembling the engine I discovered the block had some bad scoring on the cylinder wall. The 2.7 I currently have in my car is pretty solid. What Im wondering is can I swap the valve springs and cam and drill 2 more journals from the 885 head to my 731 head. I don't want to lower the compression ratio but I want to run the same rev range as a 2.5.

[digger]

your post reads a bit confusing. did you get just the harness and ecu? as your 86 325e should have had a "2.7" crank already so maybe you bought a whole b25 and wanted to swap the 2.7 crank into the m20b25 engine?

your 86 325E wont have a 731 head it will be a 200 head so swapping in the valvetrain from 885 to the 200 is not recommended though is possible

a nice m20b25 would be a better swap, to make a decent 2.7 you need to mix and match the b25 and eta (eta crank and rod, b25 pistons and a couple mm off the block and full 885 head)

[malmeida1040]

I have two engines a m20b27 and m20b25. i purchased the m20b25 off CL and it had been sitting for two years. originally i was planning on resealing it and putting a 2.7 crank in it as a "budget stroker." Upon dismantling the B25 i found some bad scoring on the cylinder walls. i don't want to go through the hassle of boring it and ordering custom pistons. my b27 is a solid engine just its way to slow for my liking and not enough useable rev range. the head off the m20b25 is good but will lower the compression significantly and i don't want to turbo it. so i was wondering if i can take the double valve springs and cam from the b25 and transfer it over the b27 head? if i make the switch to motronic 1.3 im going to have the same rev limit as a b25. just curious if swapping the valve springs and cam can be done or has been done. and what are the drawbacks to swapping the 885 valvetrain to a 200. sorry for the confusion.

[darvo]

Blocks are the same so you could use the whole b27 block with b25 pistons as digger said. And all top end and accesories from the b25.

You just need to deck the block a couple of mm as digger said. 2mm more or less

[digger]

I have two engines a m20b27 and m20b25. i purchased the m20b25 off CL and it had been sitting for two years. originally i was planning on resealing it and putting a 2.7 crank in it as a "budget stroker." Upon dismantling the B25 i found some bad scoring on the cylinder walls. i don't want to go through the hassle of boring it and ordering custom pistons. my b27 is a solid engine just its way to slow for my liking and not enough useable rev range. the head off the m20b25 is good but will lower the compression significantly and i don't want to turbo it. so i was wondering if i can take the double valve springs and cam from the b25 and transfer it over the b27 head? if i make the switch to motronic 1.3 im going to have the same rev limit as a b25. just curious if swapping the valve springs and cam can be done or has been done. and what are the drawbacks to swapping the 885 valvetrain to a 200. sorry for the confusion.

You can swap the valve train over if you address the oil holes but you still end up with the the small restrictive ports from the eta 200 head so it's not going better and quite a results will be quite a bit short than the low compression full 885. To be honest even with the stock 731 head which has bigger ports than the 200 head but smaller than the 885 is not a great option either.

[turbski]

how do you determine how much material is removed from the block?

[4x4_e30]

how do you determine how much material is removed from the block?

With a surface plate and height gage, preferably.

OP- Just get the head shaved down and slap it on the 2.7 bottom end. The 885 head will CC the same as a 200 when cut down to it's minimum spec. aka ~9:1 CR. It's not going to be much faster than a strong running stock 325i, but since you have a good 2.7 bottom end it would be the most economical choice. If you dive any deeper into the bottom end you might as well rebuild it, or get another 2.5.

[turbski]

Sorry. Should have been more clear. How is the 2mm figure found? Difference in height of the blocks? Height from crank to deck?
I understand the milling process, would like to understand how the amount to mill off is calculated.

[4x4_e30]

I'll go ahead and quote digger on this one:

ive measured two b25 blocks recently both 206.2mm. even eta block wasnt 206.7, it was 206.0 iirc

Deck height would measured be from the centerline of the crank to the deck, and I think it's safe to assume the main cap surfaces are on plane with that centerline.

[digger]

Sorry. Should have been more clear. How is the 2mm figure found? Difference in height of the blocks? Height from crank to deck?
I understand the milling process, would like to understand how the amount to mill off is calculated.

going from 75mm to 81mm stroke is a 3mm difference in crank throw (half stroke)
using a 5mm shorter rod means the following;

+3-5=-2mm

meaning 2mm off the block. its basically comparing the stack height to end up with the piston at the same position with respect to the block as the stock engine

this is assuming m20b25 pistons , eta crank, eta rod, 885 head

its a nominal number you want the piston and head to have a 1mm clearance (around the "chamfered looking part" )at the end of the day

[turbski]

Thank ya.

[malmeida1040]

You can swap the valve train over if you address the oil holes but you still end up with the the small restrictive ports from the eta 200 head so it's not going better and quite a results will be quite a bit short than the low compression full 885. To be honest even with the stock 731 head which has bigger ports than the 200 head but smaller than the 885 is not a great option either.

Wouldn’t decking the head 2mm retard the timing so I would have to run an adjustable cam gear to compensate?


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[digger]

It's a good idea to use one