Hi Guys,
Looking to see if someone has a turbo with easy access, that can measure out the length of the wastegate rod. I may be looking into installing an aftermarket wastegate with much more pressure and better boost control.

My tuned SL65 AMG has always been making less boost than normal. On stock tune, it couldn't put out more that 13.5psi and fell to 7-8psi at redline. Made 464WHP/565WTQ on a dyno dynamics in 100% stock form.

With speedriven catless downpipes and billet BOVs and custom trunk tank, it still made same boost. I've replaced all the vacuum lines, added additional check valves in the lines that had check valves in them, and replaced all clamps for the charge pipes.
Boost pressure test shows no leaks with a boost pressure tester I built, tested to 25psi.
I believe I'm maxing out the boost solenoid, by tuning the ECU. We are able to hit 18-19psi at midrange and falls to 13psi by redline. While power went up fairly well, and I made 551whp on my dyno dynamics dyno on it's best run ever without air filters but still stock airbox, (12% lower than a local dynojet around the block) I still believe these turbos have more left in them. But possibly the backpressure is forcing the gates open at higher RPM, no matter what the boost controller is trying to do. Maybe my wastegate springs somehow weaken after 75k miles. I haven't tried adjusting the wastegate rod yet.

I've tried replacing the boost solenoid and map sensors with others to rule out any of those issues, no changes.


I'm debating on either adding an additional spring to the factory wastegate rod to raise the cracking pressure, or get Turbosmart Internal Wastegate with ability to change spring rates up higher, and a dual port to control boost better like an external gate.

See this link of how they make an actuator that maybe able to bolt on to our turbos. This is why I'd like to know the length of the stock rod. Modifying the bracket if needed is not a problem to mount it.

http://www.turbosmartusa.com/news/tu...-911-turbo-996

I wouldn't mind testing out the turbosmart dual port wastegates, if they work and allow me to run higher boost with less drop off up top, I can send them the stock wastegates, so that maybe they'll be able to make a bolt on kit for the M275 platform. If it doesn't change anything, then I'll probably still keep these wastegates on, and upgrade to billet impellers in the winter.


PS: Speedriven Downpipes and BOVs are badass. High quality parts, fit right up with no problems. The car sounds insane now, it's not crazy loud but growls really mean. You can hear the turbos spooling up pretty mean too, it's not the loud whistle noise like most large turbo cars, but more of a hissing/whoosh sound mixed.
BOVs are also nice, you can hear them, it's just a nice soft air release. Not too loud, but you know they're there when you get on it and let off.
I'll create a build thread for this car pretty soon.

You can just crank up the preload on your existing wastegate arms. I've got mine quite a bit tighter than stock. Which will definitely throw "boost pressure too high" codes if your computer is trying to limit boost for some reason.

My boost pressure limiters are turned up all the way at this point. No codes at all, increasing duty cycle of the boost solenoid stopped increasing boost.
I might give the stock wastegate actuators a try at adjusting them a few turns tighter. Probably a huge pain to get to, but should be doable with out the cats in the way.

I did mine when I had the downpipes off to remove the cats and install the cutouts. I cranked them up quite a bit. It sets overboost codes even with the tune. Presumably from the peak boost in the midrange being so high. I don't know how much boost it hits up top but it pulls hard (or it did until my coil started acting up...new ones on the way).

I was debating on adjusting mine during downpipe/tank install, but decided to leave them. Didn't want to mess with them yet at that point, in-case they were set properly.
Right now, if I put too much ice in the tank, my boost drop .5-1psi from cooling down the air, turbos cannot putout anymore pressure to compensate from the temp drop. I think it's gotta be wastegate related, most likely backpressure forcing it open and nothing you can do about it on the software side.

I kind of want to go with these dual port wastegates, and hook up the venting port of the boost solenoid to the 2nd port. This will stop any venting to the atmosphere, and instead help the wastegate stay shut at high rpm when backpressure may become on issue on these manifolds/housing setup. It will also take a lot more force to crack the wastegate open, which is not possible with the stock actuators. Adjusting them really tight might do it, but it will limit the amount the flap will open when boost does need to be controlled at lower rpm.

http://www.turbosmartdirect.com/Prod...mm-14-PSI.html

In my opinion it's not a problem. I've driven plenty of cars with welded wastegate flappers on stock turbos. Sure, they come on harder but it's not like you magically don't have a throttle body anymore.

It's normal for your boost to drop off with cooler charge air if you're running the turbos all out. Any cooling/pressure reduction you do post-turbo has little to no effect on the maximum mass flow the turbos can put out, because these are definitely limited by mass flow and not pressure head. You're always going to be limited by the air density at the compressor inlet until you upgrade turbos. I'm kind of with you though, I would tend to think that 550whp would be a disappointing number for a 65. I feel like I can get there even with the 600 turbos.

I'll be adjusting my wastegates this week it seems like and strap it back on the dyno.
551WHP is on a dyno dynamics dyno, it reads 12% lower than a local dynojet. That's about 620whp on a dynojet, pretty healthy numbers for a tuned sl65 amg. Issue is my boost is lower than anyone else with a tuned 65. Most people run 22psi, while mine can't manage to make over 19psi with the boost maps turned up really high. 20psi on a spike sometimes. Boost was confirmed with the obd2 map sensor readout and the dyno map sensor, identical pressure.

Does anyone know what the stock sl65 amg runs for boost exactly and confirmed it with an obd2 scanner/boost gauge? I've tried flashing various different software versions of the sl65 software onto my ecu, boost stayed at 13psi with all of them. I think that is too low.

If absolute max power on stock turbos is your goal I don't know why you're even fussing with the stock boost control. The actuators are super simple devices. Throw some check valves on the actuator lines, hook up a vacuum pump to suck all the air out and let her rip. No guarantee your compressor wheels won't explode, but it would certainly take the guesswork out of it without you spending all kinds of money on custom actuators that may not even solve your problem. It sounds like you've essentially got them cranked all the way up in the computer anyway so it's the same thing with the exception you'll have an extra 30 lbs or so of wastegate preload without having to fuss with the rod adjustment.

I don't want to run more than 22-23psi on pump gas. Race gas tune maybe run more, if possible with tons of ice in the tank, but that's not the priority yet.
I don't mind spending a little bit of money to get there, I don't want to explode the turbos or overspin them to the max. Turbosmart wastegate actuator allows you to change the wastegate springs super easy to get pretty much whatever psi you want as base pressure. I believe the factory ones start to open at 7psi, the rest is on the solenoid. Starting off with a 14psi actuator will improve spool up, up top performance and should be easier to control higher boost.
I want more boost, but still proper boost control

I will try and get some boost numbers on my car when I get the new coils on. I'm going to be out of town all week so it will probably be a week or two.

My stock SL65 did 17,5 PSI in the midrange and 11,5 PSI at redline.
The Power was just in line with the factory specs approx. 612 HP at the Crank on a MAHA3000 dyno (in Germany)

With ECU-Tune 20,5 PSI in the midrange and 14,5 PSI at redline.

The factory turbos are maxed out with this tune.

If you want to get more from the turbos I would recommend the BlackSeries Turbos with bigger Hot-Turbine housing and modify them with bigger wheels.

Or build new manifolds/headers with new turbos - and use every bit of space which is available in these cars.