kens911

I opted to go with a waste gate with a low pressure boost spring and an electronic boost controller. I have been having a tough time getting it to work correctly. it is supposed to be set at 1 bar for high set-point and .8 for the low. so that I can switch between the 2 settings. It's a 46 mm and I have a k-27hfs turbo. It starts building boost around 2k rpm. I think the reason it is not controlling correctly is the fact that it will over run the waste gate to about .9 bar, even when it opens at the stock setting of 5 psi. So when I put it in the learn mode to have it read the stock setting it isn't reading it correctly. which I think is why it's opening early. I am thinking of possibly going to just a regular set up with a 1 bar spring. I am going to give the company that sells the boost controllers the benefit of the doubt and wait till I can get them to actually answer a phone on the support line before i decide, just to make sure I didn't set it up wrong. Does a Tial with a 1 bar spring start to open at a lower pressure than 1 bar or does it wait to open then pop all the way open?

A930Rocket

It would be nice if they stayed closed until whatever spring you have in there, but in reality, they start to open early. It's called boost creep, but I think a higher boost spring my help delay it.

kens911

well i thought the boost controller was supposed to stop that from happening but i hear it hissing around 0.5 bar

911rudy

It soundslike you have something else going on. I am using a mechanical controller and it over shoots a tiny bit but you can set the controller to compensate for the error, ie; set .9 to get 1.0. If you are hearing a hissing sound at .5 bar then you have a problem in either of two places. The connection to the WG or the BC. If you have a way to test the BC by itself then that will confirm its operability. Then that leaves only the hook up to the WG and the connection to the car's system.

Porschefile

What type of boost controller is it? Just curious but, from what you are saying I gather that you do have a .5bar spring in the wastegate? Depending on the boost controller, there are usually a lot of variables like "Gain" to mess around with which can have lots of effect on spool time and can affect boost spikes. Actually, if you have the gain set too high, spikes can be pretty common. Are you absolutely sure everything is hooked up properly?

kens911

it is a 5 psi spring in the waste gate which is .3 bar I am wondering of the waste gate is too weak for the boost controller?

911addict

Are you getting full power at all, or is it just blowing into space?

I have a similar setup and the mechanic is having a tough job finding where the power loss is. (At least we are getting 1 bar boost consistently, but its not being utilised).

PS: Currently I have the OEM headers, the B&B's are on order.

kens911

well it's a k27hfs so it will still run up to .9 bar even with the waste gate open

Arnie1

I have the same boost controller on my 89. I forget the name. Is it small black box with a blue lt face which provides both negative and postive vacumns? Mine works perfectly. It was set up using a dyno at Powertech. They tried to do on the road but it was too difficult because you needed long accelration runs. Once they did on the dyno it works great.

Porschefile

Oops, 5psi spring is what I meant to ask. Honestly, a .3bar spring is really soft. Typically you want to go with as stiff a spring as possible, at least to whatever your minimum desired boost level is. Also, just curious but, did you install the Tial valve seat with the wastegate? The valve seat is a little flange-like thing that has a raised beveled center and it bolts between the wastegate outlet (so that it sits up against the valve) and the header connection. Without that valve seat in place, there is around 1-2mm of open area around the entire valve head, which basically equates to an exhaust leak so you'd be loosing exhaust energy which could cause odd boost issues like increased spool.

pete77930

I always thought boost creep was when you set your maximum boost to lets say, 1 bar. and the wastegate can't flow enough and you end up getting say, 1.2 bar

nathanUK '81 930 G50

Agreed.

Ken did say he has a 0.3bar spring and is getting .09 bar of boost though. Was that with the ebc off ken? What happens when you connect the Tial directly to the IC (removing the ebc)?

A930Rocket

You guys are right. I had it wrong all this time.

From the Garret site:

What is boost creep?
Boost creep is a condition of rising boost levels past what the predetermined level has been set at. Boost creep is caused by a fully opened Wastegates not being able to flow enough exhaust to bypass the housing via the Wastegates itself. For example, if your boost is set to 12psi, and you go into full boost, you will see a quick rise to 12 or 13psi, but as the rpm's increase, the boost levels also increase beyond what the boost controller or stock settings were. Boost creep is typically more pronounced at higher rpm's since there is more exhaust flow present for the Wastegates to bypass.
Effective methods of avoiding or eliminating boost creep include porting the internal Wastegates opening to allow more airflow out of the turbine, or to use an external Wastegates.

Porschefile

A Tial 46mm wastegate is plenty large for the typical airflow volumes of these motors. Actually, most people could get away with a much smaller wastegate just fine in most cases (like their 38mm), but the 46mm is a bolt-on and a bit higher quality in materials so might as well go with the best! The only real problem I could see anyone having with boost creep on a 930 and w/ a Tial 46 is if the wastegate connection from the header was at some extreme/restrictive angle. An example of this would be having the wastegate connect to the header wg connection at a 90 degree angle which would add substantial airflow restriction and have the effect of decreasing airflow velocity substantially as well, which could in return cause the airflow to "back up" a bit and possibly cause creep. However, judging by all of the production 930 headers I've ever seen, that shouldn't even be an issue as they all seem to follow a similar design and have relatively unrestrictive (at least judging by pics and the few I've seen in person) designs.

It sounds to me like there is something else going on that is possibly not wastegate related. With EBC's, I'd highly recommend checking the "gain" as if it's set to high, spikes like this can be fairly common, also a high gain setting would cause the turbo to spool much more quickly as well, which sounds like what you are describing Ken. If you can figure out what type of EBC it is (there should be some kind of writing or words on the unit somewhere), I might be able to help you a bit better if you're not familiar with things like adjusting gain.

As far as EBC's go, Ken, since you mentioned the "learn" mode, I'm guessing it is either a Blitz SBC-ID, HKS EVC5, or Apexi AVC-R. Those are the only ones I know of off the top of my head that have an auto-learn function. There could be others but, it is still relatively uncommon. If you do have one of these, they can all be relatively tricky to get them to learn properly. Just some words of advice but, most of them will initially require you to be very abrupt with your throttle inputs so that they can properly auto-adjust the gain for appropriate boost response. Also, initially the boost response and overall boost level typically will not start out near what you are looking for so don't be alarmed. Technically though, I've only ever seen most of these "intelligent" ebc's start out on the lowest boost and gain settings and slowly adjust upwards. Usually it can take a good solid 20-30min driving around some desolate roads/highways with some very abrupt full throttle runs through multiple gears. No I did not just suggest breaking the law but, dynos don't typically produce the same load levels as actual road surfaces do.

pete77930

My GHL's used to give me boost creep like a M.F.'r
nothing a little new piping and some welding couldn't fix.