tigerswaggerman wrote: Jul 12, 2025 3:30 PM
Thanks for supplying all this information turbodan!
Question, are you building a td e28 or just using the td manifold on a 2.7? edit: nm you're running the td IM on an ETA.
Why did you use the B25 flywheel instead of the TMS you ordered for this engine?
You are correct, td manifold on an M20. Not much eta left in this one, ended up being the M20B25 top end with the super eta bottom. Basically a long stroke version of the B25.
I didn't really know which way to go on the flywheel. I have the other build going on and I essentially tossed a coin on which one was going in which car. If anything I'm planning on going a little wilder with the other build. Bigger turbo, more boost, turbo cam, e21 intake manifold. Seemed to make more sense to me to use the super lightweight flywheel for that one.
What's the advantage of using the e21 intake manifold?
It has the shortest runners and largest plenum of all the different varieties of M20 intake manifolds. Should push the torque curve upward and extend the top end pull. Actual results are TBD but it will certainly do something.
I've been digging deep for information about the e21 323i and I've found that peak power was listed at 6000 RPM with the rev limit at 6700. On a 2.5l motor with bigger valves and boost running through it I really don't know what to expect.
There is one video I came across of a 323i revving past 7500 RPM, apparently on the stock engine. If I could build power to 6500 and hold it to 7 I'd be pretty stoked.
turbodan wrote: Jul 13, 2025 9:27 PM
It has the shortest runners and largest plenum of all the different varieties of M20 intake manifolds. Should push the torque curve upward and extend the top end pull. Actual results are TBD but it will certainly do something.
I've been digging deep for information about the e21 323i and I've found that peak power was listed at 6000 RPM with the rev limit at 6700. On a 2.5l motor with bigger valves and boost running through it I really don't know what to expect.
There is one video I came across of a 323i revving past 7500 RPM, apparently on the stock engine. If I could build power to 6500 and hold it to 7 I'd be pretty stoked.
Okay, super interesting. I rarely see any 323i for sale here in Canada. Almost always 320i.
I'm gonna keep an eye out for one.
I recently bought a turbo subaru loyale wagon that I'm trying to get running for the ski season. Would love to turbo one of my 528e cars.
Turbo 528 is a lot of fun, even if you just stick to the plain old M20B25 top end parts. Thats the standard setup thus far and it leaves little to be desired. All I can gripe about is the tendency for the B25 intake to build a lot of cylinder pressure in the midrange. Makes great torque but I would prefer to spread the power out and reduce the hit between 4 and 5k. If I can trade some of that hit for a longer pull on top with less of a spike in the middle I can run higher boost pressures without as much risk of detonation. On paper, the 323i runners should do just that.
That said, it seems unlikely that the 323i manifold ends up being worth all the trouble. Had to sleeve the injector holes down to 14mm, drill and notch a throttle body to fit the 323 stud pattern, chop off the IAC barb on the manifold to clear the TPS, plug the CSV port, and port match the manifold to the 885 intake port shape. Still need to tap in some vacuum line barbs and fabricate a bracket for the throttle cables to mount onto.
It has potential, and with this final frontier of M20 tinkering I can actually do something I've never done or seen done before.
Had a good run this afternoon. On the way back from mid day errands I ended up behind an e46 M3. I had just left the parking lot and I'm looking at my coolant and intake air temp. About 200 on the coolant and 145 on IAT, far from ideal. Its heat soaked, but regardless I have an opportunity to measure up against a substantial benchmark.
We set up rolling at about 40-45. I started off on in third and I think he did too. He got a jump until I spooled up, at which point he was slowly reeled in and passed by the top of third gear. Even though this shitty manual boost controller I'm running is dropping back to wastegate pressure by redline, the top end pull on this thing exceeded that of the S54 powered M3. I really need to get the boost leveled out, if it would just hold 200kpa all the way up I'd be happy and it would be faster. As is though, if it can pull on an S54 I can try to be happy with leaving well enough alone for a while.
Ordered up a TiAL MVI 2.5 internal wastegate actuator in search of more, steadier boost. The MBC was the most plausible suspect for my diminishing boost towards redline, or so I thought.
This one came with 18psi springs installed, which I figured might get me a steady 200kpa. For those following along at home, that's only 14.7 psi. At 5800 feet though, the same pressure ratio only makes about 11 psi. I need the equivalent of 1.2 bar to get to what would be 1 bar at sea level.
I had to fuck around a bit to get the actuator rod clocked correctly but eventually I figured it out and got it installed. Thought that would be the end of it but I shortly discovered that the same problem remained. Hits 190+ kpa on spoolup but drops to the high 170s by redline. What a bunch of bullshit.
I tested the recirculated BOV to see what variety of Bosch valve I had in there. It was a 710P which should be up to the task. I swapped it with a -108 that I had on deck for the td build. No change.
Next on my list was the compressor inlet plumbing. This was improvised and cobbled together, still comprised of a section of 2.5" OD tubing that was originally used with the GT2560R. I still wanted to use the CRV air filter, so I had to adapt it to a 3" tube and eliminate the 2.5" section. The CRV filter was adapted to a 3" ID tube, so the solution was simply to slip a 3" OD section inside and redesign the filter retention system. Of course I used JB Weld.
The BOV is not currently recirculated so it makes cool turbo noises on throttle lift. The compressor sound on spoolup is more pronounced and noticeable, which I do like. Datalogs indicate that boost is holding over 190 kpa to almost 6000 RPM. It is better, possibly good enough for now. It pulled an e46 M3 with less.
Next obstacle is the stock fuel pump and 30lb injectors. I have an extra set of 42's here so I'll probably plug em in at some point.
Heres a quick and dirty third gear roll on. Didn't wind it all the way out, this was already 2x the posted limit.
I pulled the motor out of the 88 this morning. It's never been opened up other than when I refreshed the valvetrain so I am thinking rod bearings, main bearings, maybe rings. Its not using oil so I don't expect to find any ugly surprises in there. I do wonder about the valves, I suspect I may have some leakage there. We'll see shortly.
These kevlar clutches are always amazing, take them apart and they still look new:
Cylinder number two looks a little iffy. It had water in it at some point prior to my acquisition of the engine. The rings had to clean all this corrosion off of the cylinder walls which takes a toll as these oxides are quite abrasive. The other five look quite good, so it is likely that a quick hone and fresh rings sorts things right out.
Since this engine had previously been installed in an e21 I was unsure if it was in fact a super e bottom end. After multiple transplants it is hard to say exactly what it is but it does have the correct pistons.
The block honed up nicely, cylinder number two has some cosmetic pitting, very slight and near the bottom of the bore. It ran reasonably well before, this will be a large improvement. I made a decision while it was apart to reassemble with M20B25 components. I had a very nice set of B25 bottom end parts on hand which was in better shape than the super eta stuff that came out. Specifically the pistons, the super e pistons showed scuffing on the thrust faces that I didn't like. They ran well, little bit of piston slap, but the 2.5 pistons were nicer so it's a 2.5 now. Makes little difference with boost, and the 2.5 does rev out better than the 2.7 with the same intake on both motors. Regarding the intake, I do still have this e21 intake here and am itching to put it on this thing. I probably will.
While I had the head stripped down I figured I'd lap the valves in a bit, the exhaust valves showed some pitting. Not the seats, just the valves. The intake seats had been cut by whoever did the head last, CCH is stamped in it and since it came from Florida I think it may have been Clearwater Cylinder Head. When they cut the seats, they seem to have slightly mismatched the angle as the intake valves were only sealing around a very thin strip near the top of the seat. I lapped them in a bit too to widen the seat to valve head contact band. Then I figured why not clean up the short side radius in these intake ports, the factory does some machining operations here but the casting and machining doesn't always line up perfectly. It's better now. I touched up the exhaust too, but the hot side didn't require as much work as the intake did.
The head is fully assembled, the pistons and rods are installed in the block. I need to clean up the crank and assemble the bottom end. As hot as it is in the garage right now I don't spend a whole lot of time in there but it's getting done, bit by bit.
