Boost Control - Which One?

RarlyL8 · RarlyL8's Garage

I need eddicatin' on boost control.

I've looked at stuff on the web till I'm cross-eyed. Nobody has what I think I need, or I can't properly identify it.

Here's what I have and here's what I want: The engine is a simple '78 930. There are no computer controls, only CIS. The FUNCTION that I am looking for from a boost controller is to accurately measure the amount of boost being produced and dump the wastegate at EXACTLY that point. The object is to eliminate boost creep. Period. Nothing else.

Is there a simple and fairly inexpensive system out there that uses a solenoid to trigger the release of measured pressure to instantaneously activate the wastegate WITHOUT all the EFI crap?

1fastredsc · 10-18-2004, 07:09 PM

Your looking for an electronic boost controller, and they aren't cheap. The apexi AVC is a pretty mean boost controller, can map boost levels for each independent gear and controller lag with the soleniod. I believe they get cheaper from there.

TurboBert · 10-18-2004, 10:05 PM

Rarly8,
I use this hybrid boost controller (Dawes, about $45). I get no creep and you can set 1.0 Bar without changing your stock spring.

http://www.dawesdevices.com/boost.html

obrut · 10-18-2004, 10:15 PM

i use a dual stage unit from http://www.turbosmart.com.au/

nicely made, easy to set, sits in front of the wastegate and allows pressure to hit the wastegate at the set level - exactly what you're looking for

gave a nice little reduction in lag as promised

look 171 · 10-18-2004, 10:24 PM

Tell me if I am hijacking this thread, please. Can you explain how this works. Where does this device go. Why can a spring be good enough? For example, 1bar. When I am on full boost it does register 1.1 bar. Is that creep? Thanks, Jeff

beepbeep · 10-19-2004, 02:25 AM

Dawes device is mechanical device that will do the trick but don't expect too much from it. All "boost creep" stuff is somewhat exaggarated IMHO. Chances are that you won't feel a thing.

Correct way of doing things is fitting 0.7 or lower boost spring and using that pesky electronic boost controller to dial the boost from 0.7 upwards.

dean · 10-19-2004, 04:53 AM

An EBV won't fix boost creep. Boost creep is from a poorly designed waste gate piping. Boost creep is when your wastegate can't relieve enough pressure from your pre turbo exhaust and your boost goes over the set limit.

Jeff, I would put a mechanical gauge in to see if yoiur gauge is accurate.

Dean

dean · 10-19-2004, 04:57 AM

You must be talking about your wastegate opening early. I think it is an internet rumor that this happens. If I were you I would test the wastegate out with a gauge and air comp. Then if it is opening early then you can do something.
Dean

sammyg2 · 10-19-2004, 08:32 AM

Boost control? We doan need no stinking control

I use a mechanical device similar to the one pictured above, works pretty good.
It basically prevents any boost signal from getting to the waste gate utill it reaches a pre-set pressure, then it lets it all go. The idea is to keep the waste gate from opening gradually as the boost starts to climb.
Before I put this on the waste gate would start to open early and then gradually open further. The result was that boost would climb slower that it should have and then "creep" up slightly higher than desired.
After installing it the boost came on stronger and lower and leveled off where it is suposed to.
Not bad for $20 from e-bay.

look 171 · 10-19-2004, 12:48 PM

Dean, I have a big guage that replaced the clock. Are you talking about that one?

dean · 10-19-2004, 01:30 PM

Quote:

Originally posted by look 171
Dean, I have a big guage that replaced the clock. Are you talking about that one?

If it were me I would hook up another gauge to make sure that the one in your car is accurate. Then if you are getting boost creep you can deal with it if you want.

A wastegate that is working correctly doesn't open prematurely.

Dean

1fastredsc · 10-19-2004, 01:40 PM

Quote:

Originally posted by dean

A wastegate that is working correctly doesn't open prematurely.

Dean

I disagree on that one. My old 951 wastegate was functioning perfectly fine and would begin opening at 30% of the maximum boost, and open more, gradually, as the pressure increased.

sammyg2 · 10-19-2004, 03:29 PM

By design, waste gates will open partially at a lower pressure than it will take to get fully open.
The spring holds it closed. Air pressure overcomes the spring and opens it.
The spring, being a linear device, will compress a little when fighting a little air pressure and will open more with more air pressure. Exhaust pressure also mucks up the plans as it pushes up on the valve unless you have one of them fancy jobs where the valve is balanced to prevent this from happening.

Say you set it to control boost at 9 psi. It will probably start to open at around 6 psi, and be fully open at 8. If the waste gate or piping isn't big enough to pass all the exhaust gasses necessary, the boost will continue to creep up. The exhaust gets hotter and has more energy the longer you stay at full throttle, so that comes into play too.
The device I installed is also adjustable and has a spring loaded check valve that remains closed until a pre-determined pressure overcomes a ball seal and causes it to "pop" and allow the boost signal to hit the waste gate. It bleeds a very small amount of air when under partial boost. I guess that's what keeps it from doing the same thing as the waste gate.
That pop prevents the waste gate from partially opening before you want it to.
I was skeptical when I bought it and installed it, but the improvement is obvious. It does work on my engine, no doubt about it.

rattlsnak · rattlsnak's Garage

rarly, go to imagineauto.com, or call andial. Andial is probably the best one out there. HKS makes a nice one also.

sprbxr · 10-19-2004, 04:15 PM

The vacuum signal from the 951 is different than in a 930. The 951 has a cycling valve setup whereas the 930 doesn't.

RarlyL8 · RarlyL8's Garage

Sammy G is describing the "problem" that I would like to reduce.
When full throttle is applied everything happens too fast to notice any issues. It is only at part throttle when accelorating that I notice the wastegate opens a bit before it is supposed to. The boost gauge is very accurate. RUF type clock replacement unit connected to the engine, not the brakes. How do I know there is premature evacuation? My wastegate has a dump pipe - you can HEAR it.
A simple check valve type device would be perfect if it "pops" accurately.

obrut · 10-19-2004, 06:14 PM

"My wastegate has a dump pipe - you can HEAR it."

Ditto

"A simple check valve type device would be perfect if it "pops" accurately."

That's all my unit is - except it has two settings. Worked a treat.

RarlyL8 · RarlyL8's Garage

I checked out the website, looks good. Now where do I get that unit on THIS side of the world? Is it the same as Steve's Dawsdevice?
I don't wish to increase the boost level, only control the onset.

1fastredsc · 10-19-2004, 06:36 PM

Quote:

Originally posted by sprbxr
The vacuum signal from the 951 is different than in a 930. The 951 has a cycling valve setup whereas the 930 doesn't.

I know, but the setup i was fiddling with on the car was without the cycling valve, hence the reason for me to pull the wastegate out and find out what pressure it opens at. Before doing that, i always assumed that they stayed closed until a pre determined amount of pressure was reached, then went wide open. That helped me figure out otherwise.

sprbxr · 10-19-2004, 07:19 PM

My C2T racecar has the problem you have. It will overboost b/c the design of the wastegate plumbing on the B&B headers is horrible. The cure is modifying the collector area of the header where the wastegate pipe meets the collector. The stock WG can bleed off plenty of pressure if you can it there. Check www.turbo911.com There has been an ongoing discussion with pics showing how this shortcoming was dealt with.

BTW are you running headers or stock exhaust?