2.7i or m20b25? Upgrade? Help. 86 325e

[UgkNW*]

2.7i

So let me start off by saying I'm not a mechanic. Don't have much experience, but have a Bentley and last will be doing all this with the help of a wyotech grad if that helps any. Lol

Oh and before you mention the search feature on this wonderful forum.. I've read and read pros and cons about how some think it's pointless unless you plan on turbo in future. Some say might as well go 24v instead. And so on so on.
I feel OCD and illiterate at the same time I need GUIDANCE.


So what I'm hoping for is a little advice. based on experience and knowledge. And relevant to my current situation. Anyways I'll go on..

I have...
89 325i stock. Parts car. Auto. 220,000 is where odo stopped. PO SAID He had refreshed the head 20k ago. Soon after torque converter went.
And busted oil pan. Battery is dead haven't even tried to start it lol. (I guess that's not that funny)

86 325e stock. Daily. 5sp. 248000 is where the odo died so not sure how many more miles is on as I've only owned it for a couple months now.

It runs fine aside from the normal high idle on cold starts. Reaches operating temp and idle dies down...

Daily is in for paint as well as a lil body work LOL. While all this goes on. I'm tempted to go 2.7i
Or just throwing the whole 325i motor in my eta.

So where I need advice is. Don't know much about both motors.
My eta runs. Late model doesn't. (Busted oil pan& dead battery.)

If I wanted to throw everything from my 325i from head up on my eta block. Do I need to have my block freshened up. Or could I just buy new gaskets timing kit radiator and head bolts and put together and be good?

Or should I remove eta block take to machine shop and have new rings and rod bearings & whatever else done.

Or I install oil pan to late model and drop that into my eta.?

The whole idea is to do this all as quick,as easy,and as cheap as possible all while gaining a little performance upgrade out of it all. My eta is my daily and I can't have it down much longer then what it's going to be for paint. With that said. Critics commence. Haha. But really any input is appreciated. Thanks.

I added some pictures to peak interest.

[e30austin]

Don't waste your time building a 2.7i unless you're going to boost. Just re gasket the stock b25 and drop it in. What color is your parts car?

[UgkNW*]

Pictures.

[UgkNW*]

Don't waste your time building a 2.7i unless you're going to boost. Just re gasket the stock b25 and drop it in. What color is your parts car?

Yeah thats what i was thinking too. even though having the eta block seems like its a upgrade kinda. also just debating of leaving my eta motor and getting a lsd and chip. i just need more even if it is almost none haha.

bottom link is the parts car

[djjerme]

on a side note - I want your drivers fender and bumpers if they are available still..

-as for the engine, if it was me, I would pull the B25 apart, check the bearings for metal flakes (in case it ran without oil when the pan cracked) and then check the cylinder walls for any scoring/out of roundness and lip at the top of the cylinder. If it all checks out, do a quick hone, some new rings, head gasket and then just run it as is. For the head, I would probably spring for a new cam at the least since cams can/do wear causing loss in power. It's not drastic, but it's worth it if you have it apart anyways, you can find new cams for cheap from online retailers.

You could probably do the motor rering for a grand or less if you shop around and there is no need for machine work outside honing and maybe hot tank.

Are you in Oregon or Washington? If you are around Portland, I can lend you a hand with the motor rebuild.

[e30austin]

Yeah thats what i was thinking too. even though having the eta block seems like its a upgrade kinda. also just debating of leaving my eta motor and getting a lsd and chip. i just need more even if it is almost none haha.

bottom link is the parts car

Your car took a good hit. What happened? An ETA with a 3.25 LSD and a chip is a lot of fun, surprisingly. I would just do that and drive it til it blows up, but in the meantime, have the B25 ready to go in case something happens.

[UgkNW*]

Your car took a good hit. What happened? An ETA with a 3.25 LSD and a chip is a lot of fun, surprisingly. I would just do that and drive it til it blows up, but in the meantime, have the B25 ready to go in case something happens.

Yea that's what I was thinking too. Also djjerme has also offered his help so I think that's what I'm going to end up doing.

And the dent.. About that. Ha.

Looked away while driving thru a residential area And hit a pole when the road slightly curved left... That's the short version.

[Andy.B]

Your car took a good hit. What happened? An ETA with a 3.25 LSD and a chip is a lot of fun, surprisingly. I would just do that and drive it til it blows up, but in the meantime, have the B25 ready to go in case something happens.

Can confirm, an eta with a good tune and a 3.25 is great. An intake for a little engine noise, and a 325i exhaust (from manifolds to tailpipe) can be done for cheap and help the eta breathe better to take advantage of the chip.

On the other hand, a 2.7i with an eta bottom end and i top end/fuel injection is fantastic :devil:

[mikebloco]

A 2.7i is a better dd engine. It has that little extra pep to get up to speed quicker and keeps going past were the "e" engine would fall off.
With the stock i motor if I wanted to make it move I was always in between 4,000-6,500 rpms and my mileage sucked

[djjerme]

It depends on how you built the 2.7i. If you started with a non-SETA bottom end and slammed an 885 head on it, I would imagine the gas mileage was fantastic, considering your compression ratio was barely 8:1.

Now, that being said, you might have lost a little grunt off the bottom end with the i cam and less compression ratio. So that is where gearing it down a bit in the rear can help compensate.

The other option is starting with a Super ETA bottom end and sticking an i cam and FI electrics/intake to it. Then you can keep the compression ratio for a little more tq then the other combination. Though, this will kill your gas mileage in comparison.

[Andy.B]

I don't see how compression ratio will affect fuel economy. The compression ratio doesn't change the volume of the cylinder, or how much air is sucked into that cylinder on the down stroke. And the amount of fuel added is based on engine temp and air flow, not the compression ratio.

I have a 'low compression' 2.7i, and my fuel economy is shit.

[djjerme]

The compression ratio doesn't change the volume of the cylinder.

Actually, it does.

It also affects the amount of air/fuel compressed. The more you compress the A/F mixture, the more energy it can produce with a controlled burn. BUT, the more you compress it, the increased risk of an Explosion - which is bad, that is detonation or more commonly called "pinging."

In order to combat pinging, the ECU will back the timing off, and try to increase the burn time and in some cases allow more fuel vs air to dumped in to the cylinder (depending on the system) which causes a richer run condition - and thus poorer fuel economy.

With a lower static compression ratio, there is less risk of detonation because the compressed volume is less volatile and so the ECU can lean the mixture out and advance the timing a bit more without detonation.


Here's a random link I found that somewhat explains the same thing, but mostly looking at newer cars (i.e. those with direct injection..etc. not our ancient Motronic 1.3 system.)

http://auto.howstuffworks.com/compre...el-economy.htm

[Andy.B]

Except the motornic 1.1/1.3 dme is too dumb for any of that.
It is pre programmed. There is no knock sensor. It is not adaptive to detonation, only a minor amount of fuel trim in response to o2 sensor readings at partial throttle. The stock dme on a 2.5 stuck on a 2.7i is going to behave exactly the same, with the same ignition timing, and same fuel trim based on airflow/temp/throttle position/narrowband o2 reading.
Nothing based on detonation, compression, etc.

If you are getting it tuned on a dyno within an inch of its life to walk the line of detonation, then you probably didn't roll in with a low compression 2.7i.

[djjerme]

What do you think detonation results in? Higher exhaust temps and incomplete combustion. Which is picked up by the O2 sensor and the temp sensor..

This is going nowhere.

If you truly believe they are not related in any way, then it's not my job to try and convince you.

[Andy.B]

I understand that they are related. You don't need to convince me of the the physics of ICE. It's a question of the capabilities of the stock motronic 1.1/1.3 system. I'm not a tuning expert, but I know a little bit about the nuts and bolts of older bosch fuel injection systems. Until someone with a more intimate knowledge of the motornic systems logic proves otherwise, I don't believe that the motronic is dynamic enough to make a noticeable effect on fuel economy in response to a minor change in compression.
There is no long term fuel trim. At idle, closed throttle, and wide open throttle it is running open loop. It only has MINIMAL fuel trim at partial throttle to regulate emissions, and boost engine longevity, not performance. For that reason, it is not tuned anywhere near close to detonation being an issue. Dropping compression doesn't magically make it more aggressively tuned or adaptive, and a single narrowband o2 sensor isn't providing accurate or fast enough data to even let it walk that line.
For all intents and purposes, it might as well be a carburetor and distributor. Yes, you could advance timing and/or lean it out with a lower compression ratio (and feel it at the fuel pump), but that carburetor isn't doing it on its own.
I just don't believe that all things being equal, and the car being driven the same way, you would see a notable difference in fuel economy between an eta 2.7i and a seta 2.7i.