Advice/Opinions? 2.8l stroker or stay 2.5l?

[Spaz!]

Ok I recently acquired an 87 325is and really like the car but I wish it had a bit more kick. Something in the 200hp/200tq range would be really nice. The car came with a spare 2.7l eta block that had slipped the timing belt and bent a couple valves. The 2.5 that is in the car runs pretty good but has a bit of a knock that really concerns me (though I have driven it a fair bit and it hasnt gotten any worse) and it fouls (oil) the no. 3 plug about every week. The po told me it had a leaky valve seal and comp test supports that but I have noticed a tendency to smoke under high load even after warm up.

My question is 2 part:

1. Does anyone have any input on the knock/valve seal issue?

2. What would you guys recommend as far as engines go? What are my options with either block? I have absolutely no interest in going to forced induction.

I know that combining the eta block with the I head will get a very low CR and I have looked at pistons but they are a bit pricey new and I would prefer not to get that far into a custom build for just 200/200.

[nando]

you aren't going to get anywhere near 200/200 with an 885 head swapped onto an eta block. if you're lucky, you'll have the powerband of a stock B25 wtih the low end torque of an eta. but usually you end up with an eta that makes more power but still falls on it's face after 5000rpm. it won't make a lot of difference if it's cammed, either (the compression will be too low for an agressive cam to work well).

that leaves custom pistons, and if you're doing that, you might as well use a bigger crank (89.6mm S52/M54).

another alternative is a 2.8 using B25 pistons, eta rods, and an 84mm M52B28 crank.

or, swap..

either way I don't see that 2.7 bottom end being much use to you if you really want 200/200 hp/tq. especially if that's whp.. no way, no how.

[stikrz]

not without a turbo. 885 head isn't enough anyway. Just do an e to i swap and then turbo. Calleraday.

[nando]

a turbo is way too much work for 200hp

[Spaz!]

a turbo is way too much work for 200hp

^^ Thats kinda what I'm thinkin! This is only a DD and I just want a bit more kick.

So basically I'm better off just ditching this eta block and getting a spare b25 to build out?

It sounds like either way I'm looking at a complete teardown and rebuild and if thats the case then I may as well go all out. What about boring? How far can you go with these blocks before you start boiling coolant?

[nando]

you can use the block to build a motor (they're the same). what I meant was, using the entire 2.7 bottom end, and bolting on an i head, pretty much garantees you won't see 200hp.

[e30rapidic]

I built and ran a 2.8 stroker for a while.....it was a great M20 "stock+" engine! Not blindingly fast but had much more low end torque with a smoother torque and power curves. I had it chipped, with 19# injectors and an M30 AFM. I'd say it was comparable to an M50 swap. Was pretty quick with a 4.10.

Only reason I got rid of it was I stumbled across an S50. As far as I know, the guy who bought (on this forum) is still driving it.

[Spaz!]

Nando:
OK so ditch the E rods and pistons and pick up a set of I rods and pistons to drop in the E block? Then use the I head, and what could I expect out of that? Whats this I read about shaving the I pistons? 2 or 3mm? Do you know which will give me what CR? I know I could do the math myself but I hate math :)

E30rapidic:
What all did you use in your build? Whats this about an m30 AFM and what does that require/gain?

Thanx for all the input guys and your patience. Im a complete noob when it comes to BMWs and I havent messed with recip's in a long time.

[nando]

I built and ran a 2.8 stroker for a while.....it was a great M20 "stock+" engine! Not blindingly fast but had much more low end torque with a smoother torque and power curves. I had it chipped, with 19# injectors and an M30 AFM. I'd say it was comparable to an M50 swap. Was pretty quick with a 4.10.

Only reason I got rid of it was I stumbled across an S50. As far as I know, the guy who bought (on this forum) is still driving it.

you can't build a 2.8 using an eta bottom end. not really a comparison - you either need an M52 crank or custom pistons to get a 2.8 M20. both will result in a higher CR.

spaz - you can't use i rods or pistons with the eta crank. the rods are longer and the pin height is different. they'd stick up over the deck 3mm too far. you can use B25 pistons, eta rods, and the m52 crank though (piston skirts will likely need mods, or knife edge the crank).

[Spaz!]

Also can anyone give me EXACT numbers for each of these components so I can figure these CR #s myself? I'm having a hard time finding reliable info on these. My owners manual gives me a bit of info and I have seen a few posts/sites but they all seem to have slightly different numbers.

What I have so far:

NOTE these are for STOCK parts, always check to make sure that these are accurate unless you absolutely know the history of the components you are using!

M20B27:
B/S:84/81mm
CC Vol.:37cc (200 Casting)
CR:9.0:1 (82-87 Eta)200 casting, 8.5:1 (87-88 Super Eta)
Piston>Deck: 0.2mm
Deck Height: 206mm
Piston Displacement: ???
Piston Comp Height:35.7mm (Eta) 36.2mm S-Eta)
Head gasket thickness: 1.651mm
Rod Length: 130mm
Rod Big End Bore:45mm
Crank Rod Journal:21.8mm

M20B25:
B/S:84/75
CC Vol.: 40cc (885 casting)
CR: 8.8:1 (US 87-90) 9.7:1 (euro spec 85-89)
Piston>Deck: 0.7mm
Deck Height: 206mm
Piston Displacement: ???
Piston comp height: 34.2 mm / 1.346 in
Head gasket thickness: 1.651mm
Rod Length: 135mm
Rod Big End Bore:
Crank Rod Journal:

[Spaz!]

Hmm I'll have to stew on that for a bit Nando. I gotta get to work now though. Can you give me specs for each crank and the missing/inaccurate info above? Also what about milling the I pistons down 3mm? I have heard of that but I dont know enough about it to know if its suitable for my purposes. Also I just checked my eta block and the pistons come up above the deck about 0.2mm (I didnt measure just eyeballed it) so this eta block may have been decked in the past or the specs I found are off. The deck does not look like it has been tampered with or if it was someone took great care in doing it.

[nando]

the piston crowns are too thin and the ring landings will be compromised. you don't want to machine M20 pistons.

it's normal for the pistons to come above the deck slightly at TDC

everything about the two engines is the same except rod length and stroke (and of course the piston).

[Spaz!]

the piston crowns are too thin and the ring landings will be compromised. you don't want to machine M20 pistons.

OK I knew there was a catch to that somewhere.

So what is the correct piston to deck clearance?
The specs I found say -0.01mm but these are definitely +0.2 or so.

[nomansland92]

Very good info so far and extremely helpful because I'm looking into building a motor for my ix but I also don't want to turbo.

[Spaz!]

Nice! its all about N/A power!