327i conversion question - pistons

[R3VN R3D]

Whats up guys,

I am researching converting my 325e to a 327i. I was reading the following info:

http://www.strictlyeta.net/technical/328i_1.html

The 2nd question talks a bit about the difference in pistons between the 2 engines, and some options to properly convert them. To borrow a quote from the site:

"the stock 325e pistons will not work with the 325i head because of the different design; the 325i has a domed cylinder chamber to match the domed pistons while the eta has a flat cylinder chamber to match the flat pistons."

And option 2 goes on to say:

"#2 is to use the 325i pistons and shave the top. 3mm is supposed to be the accepted tolerance with stock 325i rods, though I have also heard 2mm as well."

So, if I am using a 325i head with a 'domed cylinder chamber', then wouldn't I WANT to use the 325i domed pistons? Why would I shave the top of the 325i pistons if I am going to use a 325i head? Am I missing something?

Also, for the time, money and power increase, is converting to a 327i comparable to just swapping the engine for something else?

Thanks for the help.

[Flash]

it all depends on how much money you have to work with.
For the 2.7i, you would use a super eta bottom end or pistons by themselves, with a complete i top end. Basically EVERYTHING is a 325i except the crankshaft, rods and pistons.
Best bang for the buck? A M30B35 with a 325i wiring harness (extended).
You would need to source a transmission since the m20 will not work, and a little bit of work is involved but its nothing a seasoned enthusiast cannot do, plus there is tons of info.

[Brian 89 325i]

Find a 731 head, it will work with your stock "e" pistons and give you the proper CR. If you use the "i" pistons with the E rods and crank you end up being 3mm to close to the head.

HTH

Brian

[E30Idea]

Stock "eta" pistons and an "i" will work just fine, you just get a lower compression ratio than desired for an NA motor. This is a great combo for forced induction. Dive in and have a blast.

[ikkitousen]

Find a 731 head, it will work with your stock "e" pistons and give you the proper CR. If you use the "i" pistons with the E rods and crank you end up being 3mm to close to the head.

HTH

Brian

So if you use the "i" rods and crank, does that defeat the purpose of the eta block? Sorry honest question tho...<--- me = Nub!


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DAMN NOOB MONKEYS!!!

[884door]

Whats up guys,

I am researching converting my 325e to a 327i. I was reading the following info:

http://www.strictlyeta.net/technical/328i_1.html

The 2nd question talks a bit about the difference in pistons between the 2 engines, and some options to properly convert them. To borrow a quote from the site:

"the stock 325e pistons will not work with the 325i head because of the different design; the 325i has a domed cylinder chamber to match the domed pistons while the eta has a flat cylinder chamber to match the flat pistons."

And option 2 goes on to say:

"#2 is to use the 325i pistons and shave the top. 3mm is supposed to be the accepted tolerance with stock 325i rods, though I have also heard 2mm as well."

So, if I am using a 325i head with a 'domed cylinder chamber', then wouldn't I WANT to use the 325i domed pistons? Why would I shave the top of the 325i pistons if I am going to use a 325i head? Am I missing something?

Also, for the time, money and power increase, is converting to a 327i comparable to just swapping the engine for something else?

Thanks for the help.

No because the domed pistons would smash into the valves because of the longer stroke of the 2.7l.

As for bang for the buck I think it's unbeatable. IIRC Someone here dyno'd 155 whp with an i head and ecu, an exhaust and an ebay chip on a super eta, using a head they got from a junkyard. It probably cost less than $500 total for a 50ish whp gain if you go that route.

An engine swap could still yeild more power but not that cheap.

[RobE30]

nosignal is selling a 731 head. He's parting a euro 323 4-door. Pm him if youre interested in the head

[Brian 89 325i]

So if you use the "i" rods and crank, does that defeat the purpose of the eta block? Sorry honest question tho...<--- me = Nub!


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DAMN NOOB MONKEYS!!!

Yeah, if you use I rods and crank you get a super-low CR 2.5. The eta block is the same M20 Block ans the "i" block. Is called a stroker for a reason, you increase the stroke to yield more displacement. If you are going to build a motor the most common combos are "e" or TD crank, "i" or "e" rods with custom pistons. If you want to do it budget style with a proper CR, you go with "e" bottom end (block, crank, rods, pistons) and a 731 head. If you dont care about CR you can bold on an "i" top end (head, intake, wires, etc ala the motronic 1.1 - 1.3 thread) to your eta motor and still get pretty decent results.

GL

Brian

[R3VN R3D]

No because the domed pistons would smash into the valves because of the longer stroke of the 2.7l.

As for bang for the buck I think it's unbeatable. IIRC Someone here dyno'd 155 whp with an i head and ecu, an exhaust and an ebay chip on a super eta, using a head they got from a junkyard. It probably cost less than $500 total for a 50ish whp gain if you go that route.

An engine swap could still yeild more power but not that cheap.

ahh... so shaving the pistons has nothing to do with the shape of their tops, it has to do with the fact that the 'e' rods and crank create a longer stroke, too long for the 'i' head...
So, then if you shave the piston, can you have them shaved with a new domed top to match the 'i' head and maintain proper CR?

[R3VN R3D]

What if I used 'super e' pistons...?
Don't the 'super e's already have 'i' heads and 'e' crank and rods?
Those pistons seem to work well between the longer 'e' stroke and the 'i' head.

[884door]

ahh... so shaving the pistons has nothing to do with the shape of their tops, it has to do with the fact that the 'e' rods and crank create a longer stroke, too long for the 'i' head...
So, then if you shave the piston, can you have them shaved with a new domed top to match the 'i' head and maintain proper CR?

I don't know for sure whether or not you can shave them and still keep the dome shape.

What if I used 'super e' pistons...?
Don't the 'super e's already have 'i' heads and 'e' crank and rods?
Those pistons seem to work well between the longer 'e' stroke and the 'i' head.

That's the way to go but honestly it only going to put out a little more power and torque than an I head on E pistons and you'll have to pull apart your whole engine. I think the money you'd spend on the pistons would be better vested twoards a custom chip or a cam.

[Swede-E30]

Hi,

Here is what I did. (Do not shave the pistons!!! They are designed the way they are for a reason).

Diesel crank, but your Eta crank will work fine too.

Eta connecting Rods 130mm Vs. 135mm.

Late model 8.8 CR "I" pistons.

Shave block a minimum of 2mm to compensate for rod length and longer stroke from Eta crank. I shaved 2.4mm for 9.8 CR.


You will also need an adjustable timing gear to compensate for the shorter block.

Depending on your experience with engines there is a little bit more work going this route, but you end up with an engine using only BMW parts.

Are you looking to add a high lift cam? If so, make sure you have enough valve to piston clearance and always calculate with the head if you had it resurfaced.

Thanks!

[eta]

An eta bottom end with eta conrods, crank and pistons works with a 885 head. "i" conrods are 135mm long, 5mm longer than the "e" rods and when used with any pistons will cause the pistons to hit the head.

All 2.7i motors use the e rods for this reason. Read the 2.7i thread on this forum it answer most queries. Their are so many way do build these motors all with thier own advantages and disadvantages. If using a 731 head you will need to modify the headgasket to allow oil into the spray bar.

e pistons with 885 head drops the CR a bit but the combustion chamber is the right diameter at least. With a 731 head the combustion chamber maintains the CR but is smaller (80 diameter). As the 731 head flows less air than an 885 head you limit power to 170 hp maybe 180hp is the build is good.

[R3VN R3D]

thanks guys...

[ikkitousen]

NM I started a new thread instead of the Thread jack. My bad.

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DAMN THREAD JACKS!!!