What would you do? 2 engines, 1 turbo

[93supercoupe]

Ok heres the quick run down.

I got my 1988 325 from the original owner, 100% stock with 260,000 miles. Runs mint

I get a deal on a turbo setup, built head, and stock 2.5 block in running condition, but otherwise unkown condition.

So i gather all my parts, get the megasuirt built, ect....

SOOOOO what i did was took the built head, Oringed my stock SETA block and added head studs and boosted it.

Before i took it apart, compression should #5 in rough shape, but not too bad. But now that i been beating the shit out of it with boost for the past 2-3weeks, its looking like its getting worse. It still runs perfect, and hasnt lost any power, but is showing excessive blow by threw the valve cover vent.

The car is my daily, but i do have a shit box Toyota truck i can drive.

So, if you guys had a good 2.5 and a bad 2.7 and was looking for 450whp, what would you do?

Ideally, i would take the 2.5 block that is out of my car now, hone it, ring it, and put my 2.7 rotating assemebely in it. But is the .2 liters even worth it? Because if i leave it a 2.5, i could rebuild it now, and have a complete bottom end ready to go right back in, rather then taking the 2 apart to make 1.

Pics

Day 1, all stock running on MS


Day 5 all done

[93supercoupe]

Sleeper status

[LowR3V'in]

That coil bracket looks really cool. Have any more pics of it?

On your question. The 0.2L would be felt off boost BUT
once the turbo wakes up it won't matter. 1psi difference? Just a wild guess.

[93supercoupe]

I agree, the .2 liters wont be missed much, but i dont know, this is my first BMW.

Ill grab some pics of the bracket, its super simple, just a square 1/8 plate with some cutting.

Side question, what fails on M20's? ring lands? rods? whats there weak point?

[93supercoupe]

no help? opinions welcome. What would you do???

[ChefSkinny]

I don't think it's so much the .2 liters, but the drop in compression that is beneficial to you. I'm not an expert but when I did my limited research while trying to decide what to do myself, most of the 2.7 franken motors are lower compression using stock parts which is great for a turbo build.

[einstein57]

Keep the 2.7 and just hone the block and put in new rings. The car will be down for a week tops. The internal dimensions of an eta block are larger to compensate for the longer stroke of the crank. If it were me i'd order new forged standard oversized pistons. That will make it a 2.8L

[93supercoupe]

Keep the 2.7 and just hone the block and put in new rings. The car will be down for a week tops. The internal dimensions of an eta block are larger to compensate for the longer stroke of the crank. If it were me i'd order new forged standard oversized pistons. That will make it a 2.8L

thats what im leaning towards.

I know most car makers have there bearing sizes stamped on the block somewhere, is that the case with BMW? Assuming my bearings arent spun, i should be able to throw in the same replacement bearings, correct?

Im really not liking the way the 2.5 is looking at me. There are many un answered questions. The motor has defenitly been apart, but is extremely dirty on the outside, ect.

[ak-]

I agree, the .2 liters wont be missed much, but i dont know, this is my first BMW.
Ill grab some pics of the bracket, its super simple, just a square 1/8 plate with some cutting.
Side question, what fails on M20's? ring lands? rods? whats there weak point?

I think lowrevin is right when saying the difference in feelz would be just off boost driving.
Assuming your tune is great, you'll melt a piston before bending a rod so Einsteins idea is superb.

I'd do the 2.7/8(pistons) with the lower comp and add Meth to the equation for your 400+ goal.

[93supercoupe]

decision decisons.

I guess my decision will be based on my next profit sharing check, as that will be un-wifed income.

I think ideally id like to take my current 2.7, get some forged pistons, and do a decent rebuild. The head is titties, so id prolly just resuface that.

You guys typically do oil pumps? bearings? or just ring and hone them and call it good?

[einstein57]

If your going to have it apart replace the bearings. Oil pumps will go 350-400k miles no problem but its "cheap" insurance to replace it early. $180 IIRC.

[93supercoupe]

If your going to have it apart replace the bearings. Oil pumps will go 350-400k miles no problem but its "cheap" insurance to replace it early. $180 IIRC.

do you know if bearing codes are stamped anywhere on the block? Or do i have to measure them all?

[einstein57]

No clue. I was going to have the crank polished and have the machinist measure what size new bearings are needed. I probably will have him assemble the short block.