Compressor surge under power with M30B35 with T04E-61. Too big?

[BONDOSPECIAL]

Hi guys, I have an e23 with a forged internal M30B35 engine built with an MLS head gasket, head studs, a TCD exhaust manifold, a T04E-61 (T350 wheel) turbo, 3" mandrel bent exhaust, Megasquirt, and wasted spark. It has a 265/6 trans. I have a Tial F38 wastegate that is brand new. This car is water/air intercooled with an ancient Cartech setup.

When I had this car running under 12 psi on wastegate only, it actually ran okay. It pulled smoothly and didn't do anything weird. Now that I am turning boost up over 12 psi (I tried up to 15-16 psi) I am having terrible compressor surge under power (part throttle and WOT) above 3,000 RPM, when the turbo is fully spooled. I tried turning boost up two ways - 1, using a DIY Auto Tune electronic boost controller and tuning, and 2, using a stiffer wastegate spring but leaving the boost controller off.

The compressor surge is audible as a flutter under power and you can feel the engine isn't delivering power quite right, and the boost log has a pronounced ripple in it.



Is it possible this turbo is too big for my engine? I assume T04E-61 means it's a 61/82mm wheel but I haven't measured it. My very limited understanding of turbo builds is that if I'm getting surge like this under power, the turbo is making more pressure than my engine can use.

If this turbo is too big, what should I replace it with?

Here is my engine bay. The Cartech intercooler might look retro-cool but I hate how it is in the way of the valve cover.



Thanks

Steve

[Dirtym30]

I just picked up a turbonetics unit for my m30 e28, 60/65 we will see how she goes.

Your turbo does sound a little large for a 3.5L

[turbodan]

I was doing fine with a GT3582R on a 2.7l M20, that's a 61.4mm compressor. For the short period of time I ran that system on a 2.5l M20 it would surge in high gears on spool-up, until the revs reached a point where the engine was moving enough air volume to get the compressor into the map. Would only really occur on the highway in 4th or 5th gear.

I don't know if a compressor map is available for your turbo so it's hard to tell for sure but in any case it seems unlikely that it's going to surge on an M30 even at 3000 RPM. If it is surging it will only surge until the engine begins moving enough air to get along with the compressor. By 4000 or 5000 RPM it's not going to be a problem.

[BONDOSPECIAL]

I think I identified the problem. Looking closer at some logs where I roll into boost in a higher gear, I only start getting the boost surge above 13 psi. I think the ancient, piece of crap Cartech intercooler I have, which has its own bypass valve, can't hold 13+ psi. It was probably originally intended for low boost applications. It looks like the bypass starts fluttering open above 13 psi.

I ordered a Turbosmart BOV and am going to replace the bypass valve with it and see if that solves my problem.

Will report back w/ the results. Thanks

[BONDOSPECIAL]

I took the 1980's cartech bypass valve (that I had vented to air as a blowoff valve) apart and found the rubber diaphragm was blown. I gutted the bypass valve housing and used its 1.25" outlet with a 1.25-1.5" adapter hose to hook up a Turbosmart V-port blowoff valve. I am still getting a fluttering sound and a ripple in the boost log when the turbo is fully spooled between 3000-3500 RPM and most noticeably at heavy part throttle. Full throttle and above 4000 rpm the boost log is smooth. So this does appear to be compressor surge and the only thing I can attribute it to is the turbo is a little big for this combo.

I am going to have a pro dyno tune this and see what he thinks about the compressor surge and whether its worth changing to a different turbo over.

[euroshark90]

I run a 6766 turbo on my built M30B35. I used to run a 6262 turbo with no surge. Sometimes when you wire the boost controler, you can reverse the polarity, and you can invert it in the boost controller settings if it is backwards.
My boost controller sounds like a compressor surge because it is pulsing out the extra boost at the vent port.
The 38mm may be too small for a wastegate as well

[Panici]

Where is your wastegate vacuum/boost reference line connected?

If it's in the intake manifold, try moving it to the compressor housing.

[BONDOSPECIAL]

My wastegate reference is hooked up to the compressor housing.

A few updates since I last posted. I replaced the Cartech recirculation valve with a Turbosmart V port BOV. The Cartec valve did have a bad diaphragm.

I also found my friend who helped me set up the Megasquirt had the vacuum lines to the DIYAutotune electronic boost controller hooked up backwards. That was causing the touchy adjustments because the controller was referencing off the atmospheric dump port instead of the compressor housing, so it would fool the wastegate into staying 100% closed for any duty cycle above 0. That is fixed. I can now control the boost using the open loop boost table where small adjustments make small changes in logged boost pressure.

I don't think the boost controller is wired backwards because as I increase and decrease the duty cycle in the open loop duty table, the logged boost goes up and down accordingly.

If I run this car flat out from a dead stop through the gears, I never get any surge. I can run 16-17 psi no problem and the datalog shows smooth boost pressure.

BUT. At higher load/lower RPM, going up hills under boost, it surges badly. I hear loud air fluttering sounds from the engine bay and the boost log shows rhythmic spikes as large as 4-5 psi. The surge happens in the 3000-4000 rpm range. You can drive through it but it sounds and feels terrible while you're doing it. Once the engine airflow catches up to the compressor it's happy.

I don't think the wastegate is too small. I am not getting boost creep. If I put 30% duty cycle in the open loop boost table from 3000-6000 rpm, the log shows I'll hold 17 psi the whole time within a tenth or two psi.

This turbo is a sh*tshow special that's been through several owners and I don't know for sure what's inside it, just what I was told. It was bought in "rebuilt 3,000 miles ago!" condition with the compressor wheel hitting the housing, the bearings were so bad. It had to be rebuilt to even run it. The manifold that came from the same engine was also so warped it had to be replaced. So I don't trust it.

I am thinking about starting fresh and buying a turbo that has known specifications. That will fit the T4 manifold flange and has a 4 bolt 3" exhaust flange to fit the custom exhaust I have.

[BONDOSPECIAL]

Here are a few logs to ponder.

Here is what compressor surge looks like in a higher gear. I don't remember if this was 3rd or 4th but I was cruising and gave it full throttle under some load. You can see surge from about 3000 when the turbo is spooled until about 4000 RPM.



And here is a log of me going through 1st, 2nd and 3rd, WOT from a stop on a level road. The compressor stays out of surge.



Here is the log of 2nd gear zoomed in from that 1st-2nd-3rd wot pull.

[marc79euro645]

Interesting log. I've not experienced that.
I tried an ebay t4 gt35 with an 63mm compressor iirc, and an .83 a/r turbine. It was too laggy for me, for the street. I posted about it a couple months back.I went to an t3 .69a/r and 61mm compressor iirc. I'm pretty happy with the turbo, but I've got other problems with the motor now.

[BONDOSPECIAL]

I went ahead and ordered a new turbo from Comp that is a modern design including an anti-surge compressor housing. Comp was able to supply a T4 on center turbine housing with a 4 bolt 3" discharge, so this should be a bolt-on for my car. I will update when I get the new turbo and install it and provide some logs, hopefully showing no more open throttle surge.