Uncontrollable Boost - M20 w/ 6262

[Evan_VRM]

I did a compression test in March before really getting to work on this project, and since then have driven realistically less than 10 miles. I have not done a leakdown but the thing runs so dang good I am fairly certain it is healthy. I also have zero blow by. I know that doesn't replace the test, but my logic is that even if leakdown was at 30%+ adding boost would still add more power than we're seeing here.

Ignition settings are attached below. I also posted this on Bimmerforums and am being told my crank wheel setting (currently at 97*) may be off, which would be awesome. I watched the tuner verify it but looking back I am not confident at what he was looking at...

As for cam: non-adjustable stock gear. Definitely was correct before turbo'ing, although I suppose it is possible it jumped a tooth though I've never had that happen on an M20. Worth checking though.

[nomansland92]

Ya that's not right you should be closer to 350+ at 17psi. Have your down a leak down or compression test. I had a good compression test but failed a leak down one time, was a inlet valve leaking around the seat slightly. If you don't have a boost leak and your timing is reasonable and base timing is set correctly that air has to be going somewhere. Do you have a adjustable cam gear that's off, or cam/crank is off a tooth? Good to hear you got the boost control figured out though! Sent from my SM-G892A using Tapatalk

[varg]

Mind posting your ignition timing table and ignition trigger settings?

[Evan_VRM]

I wish I knew why these always upload sideways

[Evan_VRM]

Yeahhh... not so nice results on the dyno. First pull is at 10psi, second one was at 17. Tuner thinks the comp turbo is garbage. I’m scratching my head trying to figure out what else it could be. No boost leaks as far as I can tell, timing is dead on, AFR’s are good, exhaust is free flowing. It runs smooth it just doesn’t make any power.

[mikey.antonakakis]

Nice!

[Evan_VRM]

Well the problem is solved. Got the flange welded on there and it holds 9psi all day now. I plan on recirculating the dump pipe tomorrow though...

Aside from that the boost control solenoid is all wired up and she’s getting a proper dyno tune on Wednesday!

[mikey.antonakakis]

My setup looks very very similar to that last picture. My wastegate works so well it's getting blown open as it spools up with a ~9psi spring (VGT is a big factor there too). The same spring would be worth about 12psi at sea level, fwiw.
Main issue is the cast -> stainless weld, can be tricky to prevent cracking. Be sure to preheat and cool down very slowly.

[Evan_VRM]

I think I can make it fit under the hood. Obviously that pic is just one I pulled off google for an example, but heres another one of a similar setup on an M20. I've got an hour or so left at work before I can go mock everything up. If it looks like it'll work I'll drop off the turbo tomorrow and hope for some good results!

[varg]

Will that even fit under the hood? I know the design of the RSI header is sub-optimal but I don't rag on it because packaging is really a significant issue in these cars.

[Evan_VRM]

I'm thinking I am going to take the easy way out and weld a wastegate flange onto the turbine housing. Yes, there are drawbacks if I decide to switch housings or turbos altogether, but I know I will be able to control boost accurately and can have it done quickly without buying another manifold.

Appreciate the boost control table! Once I get things manageable on a spring I am definitely going to wire up my EBC.

[varg]

There's a pretty decent difference between a 6262 and a 6266. Turbine housing A/R has an significant effect too. Agreed on boost control, but my guess is the turbine and housing combination are the primary factor at play here. Very 'free flowing' and resulting in a good boost to exhaust pressure ratio, to the point that the wastegate is not effective due to it being a sub-optimal flow path compared to the turbine. It should be noted that a wastegate manufacturer will recommend vastly different placement than we have on these headers, as seen below in Precision's manual for the wastegate OP has.






^This is my boost control duty cycle table. Keep in mind my turbo is essentially an internally wastegated 5857 in precision's more sensible terms (The T3/T04E 60 trim designation is essentially gibberish if you want an intuitive sense of how big the turbo is) with a .63A/R turbine housing, and I still have boost control issues, but can run anything above 15psi with decent control by tapering my boost duty as seen above.

[SLEEPYDUB]

The issues is 100% the RSI Manifold
I have the same setup (6266 on an RSI manifold). With a 10psi spring it sees 13psi by the end of the rpm band.

What I have done is used my boost controller to level the boost. So for 20psi I have the duty cycle set to decline. So for instance at 4000 its set to 40, at 4500 39, at 5000 38, and 5500 37, at 6000 36, and so on.
You can play with these values to get it to level off at the boost pressure you want. But if youre trying to just run 10psi, you may as well be ready for it to creep to 13-14psi

[citizen_insane]

I can hold 0psi until high rpm then it still spools up to 7-8psi! How do I fix this?

You don't, there's no way to prevent making some boost at high RPM WOT. How much boost you make is a function of the geometry of your parts, the size of your turbine housing, WG passage and size of the wastgate. Most OEMs are shooting for near natural aspiration with WG fully open, but it is rarely achieved, they are usually making 3-5psi (even with large electronically controlled internal WGs).

Can you post a data log? Is it very suddenly spiking or does it slowly ramp up?

A smaller turbine housing A/R might help because it would increase your turbine inlet pressure and drive more flow through the wastegate. This come with the risk of increasing the pumping losses of the engine which will result in less power at higher RPM, so it will need to balanced against your peak power target.

[Evan_VRM]

I have a .82 A/R hot side. Maybe it’s not a super common combo, but I know the .84 6262 with RSI manifold was at least coming in the KAMotors kits for a while. I’ve seen at least one person running this manifold with a .63 A/R 6262 as well, which is partly why I’m so damn confused at this point.

As far as the wastegate- I can hear it opening, and it worked perfectly on the bench (opening fully, etc.) but I suppose it is possible that on the car it is not opening fully... I am not sure how I would test that. I have a 1/4” line going straight to the compressor housing. I suppose I could try to drill out the barb fitting on the compressor housing and see if that makes a difference.

Edit: and thanks again for the suggestions!! I appreciate any help I can get.