Uncontrollable Boost - M20 w/ 6262

[varg]

Try a boost controller in conjunction with that lighter spring for better control, but it might just be a runaway situation since more boost leads to more exhaust gas volume. Are you absolutely sure the wastegate is opening fully?

I haven't seen anyone else running the same combo as you like you mentioned, and don't know what size turbine housing you have so I can't tell you more about it being a quirk of your setup. You're only running a couple of degrees less advance than me at 200kPa and more than I am above 5,000rpm, so I don't think it's your issue. The design of this header does promote boost creep, that much is known, but I haven't seen a case as bad as yours and I haven't yet seen a header for M20 turbo applications that has the optimal routing.

[Evan_VRM]

Ha- I found your earlier post mentioning advancing timing helped with your creep issues and already tried it. I’ve attached a screenshot of what I’m running at the moment. I tried a couple more degrees of advance too but it didn’t help so I went back to the attached table. I have a dyno appt coming up but am in a bit of a catch 22- I want the tuner to find the appropriate timing but can’t bring it to the dyno if I can’t control the boost. Thanks for the idea though.

[LowR3V'in]

hey this is probably a stupid suggestion but what does your timing look like?
going too low on the timing will cause this on top of a crappy wastegate exit.

[Evan_VRM]

Update: I put a 15 psi spring in and set fuel cut at 20psi. It hit 20 faster than it was hitting 14.5 earlier. I don’t see any way to make this work other than changing the manifold. Sure, I could likely run a light spring and probably keep the creep to 17-18, where I want to be, but the spool up sucks because the wastegate opens so early.

The one thing I don’t understand is how other people are running this same manifold/turbo combo and able to hold anywhere from 13-17 psi without issue.

[Evan_VRM]

Thanks for the Input! No, I was not planning on running that low of boost long term. I just wanted to get everything dialed down low before turning it up. I’ll throw a 15lb spring in there and see if I can keep it under 20psi. If that works, I’m happy with that. But if it then wants to run 20+ I’m back to the manifold drawing board.

[varg]

Exhaust gasses have inertia, and the wastegate branch of this manifold or most like it makes spinning the turbo up unavoidable because of that. For any significant portion of the flow to take that turn and go down to the open wastegate there will have to be a more significant restriction upstream. I'm kind of surprised that you can't stay below 15psi because even with my little internal wastegate I see only 13-14psi at the limit with it open, but my 57mm turbine is more of a restriction than your 62mm turbine even if we're both using a .63ar housing. The best you can do with the current setup is make sure your wastegate is opening fully and run higher boost or run a bypass valve to bring the boost down. But really, with such a big turbo, good for ~700hp or so were you planning on running less than 1bar of boost in the first place? I'd ditch the screamer pipe in any case so you have a better chance at hearing detonation, I hate tuning cars with screamer pipes because of that.

[Evan_VRM]

Alright guys I am pulling my hair out over this damn car and am not sure where to go next. Please help me lol. I’m running a 6262 .82A/r turbo on a RSI manifold with a 46mm Precision wastegate and no matter what I do I can not control the boost over 5,000 rpm. It will stay somewhat near spring pressure (tried 4.5 and 7.5) until around 5,000 then spike to wherever I set the fuel cut, in this case 14.5psi.

I confirmed the wastegate is opening as it should and had a feeling the manifold design was the issue, so I removed the wastegate entirely this morning and found I can hold 0psi until high rpm then it still spools up to 7-8psi! How do I fix this? Will recirculating the wastegate make a difference? I’m just super confused because I know other people have run this combo before and not had this bad of issues. If recirculating the WG doesn’t help I’m not sure what else to try besides a different manifold.

Any help is appreciated.