2.5l M20 vs 2.7l M20

[ATL_E30]

So I've decided i'm going OEM+ and sticking with an M20 instead of a M/S5X swap. I found an M20 out of a 89 325is local to me and just got it back to my garage where i'm ready to start tearing into her to see what I got. I'm planning on keeping this car as a DD + Mountain runs so nothing too aggressive.

What are the Pro's/Con's of building the 2.7l vs tossing the 2.5l in there?

From the Sticky post:

For the 1988 model year, the eta cars got a refresh from the factory. This included a newer Bosch Motronic version with adaptive idle control, a 325i head casting with the larger valves, ports, revised combustion chambers and water jacket, new pistons to fit the 2.7 L stroke with the 2.5 L head, a dual exhaust system and a 5300 RPM rev limit. Though it only made slightly more power in stock form, it could be easily boosted by bolting on a 325i head, a complete 325i intake manifold and throttle and plugging in the 325i engine control unit. Depending on which cam, chip and intake is used, the combination can make over 180 horsepower with the stock compression ratio.

As I see it I have three options:

1) Full refresh on the 89 325is M20 with 272 cam; full swap into E30

2) Mild refresh on the 89 325is M20 head + 272 cam; bolt on top of SETA block

3) Bolt 89 325is M20 head onto SETA block; SEND ITTTT :firehop:

Thoughts?

Thanks in advance!

[digger]

4) m20b25 piston + eta 130mm rod + eta 81mm crank + deck block 2mm + adjustable cam gear + + +

https://www.r3vlimited.com/board/showthread.php?t=421924

[ATL_E30]

4) m20b25 piston + eta 130mm rod + eta 81mm crank + deck block 2mm + adjustable cam gear + + +

https://www.r3vlimited.com/board/sho...d.php?t=421924

Hmm so just read through that thread and it looks like on post 11 there's a 2.7l and it's only making 120hp? So does that mean the quote in my OP is totally off about the 2.7l making 180hp?

[SkiFree]

So does that mean the quote in my OP is totally off about the 2.7l making 180hp?

I'd prefer to say that they are "optimistic".

[dsphil]

So I've decided i'm going OEM+ and sticking with an M20 instead of a M/S5X swap. I found an M20 out of a 89 325is local to me and just got it back to my garage where i'm ready to start tearing into her to see what I got. I'm planning on keeping this car as a DD + Mountain runs so nothing too aggressive.

What are the Pro's/Con's of building the 2.7l vs tossing the 2.5l in there?

From the Sticky post:


As I see it I have three options:

1) Full refresh on the 89 325is M20 with 272 cam; full swap into E30

2) Mild refresh on the 89 325is M20 head + 272 cam; bolt on top of SETA block

3) Bolt 89 325is M20 head onto SETA block; SEND ITTTT :firehop:

Thoughts?

Thanks in advance!

I did exactly #2. You only see gain on the top end range above 3500rpm. My mpg drop significantly. I would do #1 with a tune and call it the day.

[digger]

Hmm so just read through that thread and it looks like on post 11 there's a 2.7l and it's only making 120hp? So does that mean the quote in my OP is totally off about the 2.7l making 180hp?

The "I" head on eta bottom end as shown is not what you want. The "I" head onto SETA is only a slightly better option.

[ATL_E30]

The "I" head on eta bottom end as shown is not what you want. The "I" head onto SETA is only a slightly better option.

Slightly better than what? Stock 325i? I’m not looking for huge power gains or anything. Just going to be DD, but just want to give her a little more pep.

Swapping the head would obviously be the easier option, but if I would see better performance by just swapping the whole engine in then that’s the route I’d go... would just take a bit longer.


Sent from my iPhone using Tapatalk

[digger]

Slightly better than what? Stock 325i? I’m not looking for huge power gains or anything. Just going to be DD, but just want to give her a little more pep.

Swapping the head would obviously be the easier option, but if I would see better performance by just swapping the whole engine in then that’s the route I’d go... would just take a bit longer.


Sent from my iPhone using Tapatalk

Slightly better than the regular ETA with i head

I'm of the opinion that if you want to do a 2.7 that is better power wise than a stock b25 then it's the option 4. Which is more work than slapping on a head but it will meet your 180hp if it's executed properly .

[ATL_E30]

Slightly better than the regular ETA with i head

I'm of the opinion that if you want to do a 2.7 that is better power wise than a stock b25 then it's the option 4. Which is more work than slapping on a head but it will meet your 180hp if it's executed properly .

Gotcha, thanks for clarifying. The 180hp was more so a nice to have if it would be as easy as slapping the head on so that's why I was asking. I guess if it was that easy you'd see more people looking for the SETA blocks, pistons, etc.

[sert57]

I know you didn't list it, but I am quite liking my 2.8L build. definitely more work and money than a 2.7, but if you are disassembling the block for machining (to shave it down 2mm) the work get closer. I'm in atl if you ever wanna check it out.

I did a pretty moderate m20 build. I loved doing it and got a lot out of it, but sometimes I wonder if i should have just put the bottom end modification money towards itbs.

Of the options you gave - I speak only from reading other things and no experience - I'd go seta or b25 in that order. The others here probably now more than I on that front though.

[ButtJuice]

I mated a SETA bottom end with my 885i head and I like it a lot. I didn’t want to put too much money into the project because at the time I was a novice at car repair/modification. The added torque really wakes up the drivability and enjoyment of my late model.

I don’t have any mods (I.e. chip, cam, exhaust, etc). However the Sssquid chip is something I’d like to eventually purchase and install with the m30 AFM I have laying around.

[ATL_E30]

I know you didn't list it, but I am quite liking my 2.8L build. definitely more work and money than a 2.7, but if you are disassembling the block for machining (to shave it down 2mm) the work get closer. I'm in atl if you ever wanna check it out.

I did a pretty moderate m20 build. I loved doing it and got a lot out of it, but sometimes I wonder if i should have just put the bottom end modification money towards itbs.

Of the options you gave - I speak only from reading other things and no experience - I'd go seta or b25 in that order. The others here probably now more than I on that front though.

Nice, we'll have to meet up some time so I can check out your car and talk more. I just read through your thread and it looks like you definitely gained a lot of knowledge through your rebuild.

Still havent made a decision yet on the route i'm gonna go since havent had much time to rip into the b25 yet.

[ATL_E30]

I mated a SETA bottom end with my 885i head and I like it a lot. I didn’t want to put too much money into the project because at the time I was a novice at car repair/modification. The added torque really wakes up the drivability and enjoyment of my late model.

I don’t have any mods (I.e. chip, cam, exhaust, etc). However the Sssquid chip is something I’d like to eventually purchase and install with the m30 AFM I have laying around.

Thanks for the input! I think i'm in a similar situation, just want to wake her up a bit and not but feel like such a slush box.

[efficient]

dont forget ti swap the differential aswell if you do the 2.5 swap.