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M50B28 vs M50B30 Turbo

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I've been working towards a replacement engine for the M50B30 build I did about 6 years ago. On that build I don't know what was done with the stroker conversion (done by Sam at HellBM M50B30) - suspect it was just a quick fit of the rotating assembly without using many new parts. This engine has been running really well for over 110,000km's so far. I was going to build a replacement along the same lines but this time with more aggressive cams, porting and ITB's. The current engine makes 220kW @ 6500RPM and 343Nm @ 5500 RPM. The new NA engine might have achieved 270kW... However, an entry level turbo build could easily achieve this and be a much easier build.

So, I've now decided to go turbo and knowing nothing about what can and can't be done I'm looking for advice.

What I have for what was going to be a NA build is:
M50B25 Iron Block (was going to bore this to 86mm and with the M54B30 crank and aftermarket rods and pistons make a M50B32)
M54B30 crank (also have rods and pistons but don't expect these to be used for a turbo build)
M50B25 crank
M50B25 vanos head (although will likely lock the vanos and tune around it) - sick of rebuilding vanos units every 75k's
M50B25nv Intake
M50B25 Bored TB
S50B30 Oil filter housing and cooler
S50B30 ITB's + Plenum (currently for sale on Trademe - not anymore...)
Link G4+

If the RPM's are kept under 6500, could the M54B30 crank be used to make a M50B30 turbo or am I better to get a M50B28 crank?

My target is minimum 320kW from either 2.8L or 3.0L configuration. I'll be doing a fresh build with new bearings and +0.5mm oversize bore. New pistons will be required for the 0.5mm bore and if new rods are required I'll do that too.

At this stage all I'm looking for is the best rotating assembly option to be able to reliably make 320kW+ without revving too high (under 6500 for 3L and under 7000 for 2.8L options).

Looking to keep compression as high as possible and use less boost.
Anyone know ballpark compression requirement and how much boost would be required?
Also ballpark boosted rev range on either configuration?

Edited by wrs
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Still trying to find someone who knows about going turbo on BMW engines - there don't appear to be many people/business round NZ that have good experience with modifying them. It's possible the best resource I have is where I work. One of our software engineers has several turbo cars and a R6... The most similar would be his Supra with the 2JZ engine. From what I can see the M50B30 is similar enough to the 2JZ that I might be able to run similar compression, cams and turbos. He's getting over 400kW and races it from time to time at Hamptons... He took me for a ride and it's pretty mental - kind of what I'm looking for.

I did briefly consider just buying a complete package. Eg; HellBM has a low km turbo S engine for sale. Stock, they come with a DCT so would be a lot less messing around. It's a lot less fun than doing a build but probably similar in overall cost.

I think I want to do a build though, there's just something nice about doing it yourself even if you are just reinventing the wheel.

As a result of looking at what people are doing to 2JZ engines I'm starting to get closer to a combo that might work. I'm also considering using S50 ITB's as I have some and ITB's seem to work fine on the 2JZ.

I've decided I'm going to do a front bottom mount turbo. It will sit between the chassis rail and engine where the aircon pump used to be. This will keep the heat away from the M52 rocker cover and allow a nicer collector arrangement for the turbo manifold. I'm going to try to make a stainless turbo manifold. It may require a custom engine mount for the exhaust to go under. I'm starting to get ok with stainless tig so I'll give it a crack. I'm going to keep compression as high as possible to help reduce lag. The design will go straight for the target power with little headroom for more. This should maximise throttle response and minimise turbo lag. I'm now targeting 360-370kW but will have a boost limit switch to knock it back to 250kW and 300kW so it's drive-able round town and in the wet.

I'm considering buying part of a written-off coupe. Just the driver's side chassis rail and inner-guard so I can mock up the exhaust side of the engine bay. This will allow very accurate fabrication of the exhaust components and if required, an engine mount.

I'm also not going to go for what appears to the common trend in most modern turbo cars - get really good boost at low RPM and then stay flat or reduce torque as rpm builds. This gives a good push back in your seat initially and then not much more during gear changes. It's much better refined but I don't really like it. I want to target the traditional older-style M3 torque curve where peak torque is up round 6k rpm. I'll certainly be trying to fill in the bottom end a bit but prefer the raw feel of torque that builds right through the rev range and then a neck wobble as you change gears. For me this is more funner... Not sure how nicely this will work with a DCT though.

So not much progress yet, just a lot a research and a little bit of planning. I want to know exactly what I have to do before starting anything (except maybe setting up an engine bay for exhaust development).

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Remember Crunchy from here? He built a couple of BMW turbos at least.

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Sadly, no, never heard of him but a search of his past activity shows good things. Pity he's no longer here, looks like he's even deleted his username.

He does appear to be on instagram but I don't have an account. If anyone here has his contact details or knows him well, would you mind contacting him to see if he wants to help/talk to me? If he's ok with it then maybe he could contact me or you forward his details?

My TM auction for the S50 ITB's and plenum has just finished and I'm not going to relist it. I'll hold on to them until I find out if they can be used on a turbo build...


Edited by wrs

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