Prehistoric boost control?

[Sean]

You can also easily limit your boost by removing the controller all together and running a small diametre flange between the joins on your dump pipe.

[blackster]

You can also easily limit your boost by removing the controller all together and running a small diametre flange between the joins on your dump pipe.

The OEM short cast dump on the SE is pretty small as it is, its outlet is roughly 2" connecting onto his 2.5" FM downpipe.

Sounds like you have wastegate creep, caused by the inability of the OEM wastegate on the IHI to control boost well when the system becomes to free flowing. An EBC or MBC wont control wastegate creep.

Its interesting to see the differences between FM and SPM as far as there intakes/exhausts/IC are concerned. SPM's type II SE exhaust system is supposebly limited at different points to control boost. By no way am disrespecting FM products.

If you upgrading to the FM IC you may experience pressure drop due to its size, but if its free flowing with cooler charge density that wont be helpful.

Some options:

1. Reworking the wastegate
2. Put the OEM airtake back on, physically restricting the intake
3. If your happy to run 12-13 psi, then the boost cut resistor mod and 305/330cc injectors will address boost cut and lean spiking.
4. Try the 02 clamp for hesitation

[Garry]

Why do intake and exhaust changes on the SE change the boost level? Isn't the stock boost controller fixed to run a pre-determined boost level?

[blackster]

Why do intake and exhaust changes on the SE change the boost level? Isn't the stock boost controller fixed to run a pre-determined boost level?

Isnt that like asking why does a intake and free flowing borla exhaust produce more power on turbo systems, secondly as a consequence does it alter boost level?

You would expect a properly sized and loaded wastegate to control boost according to flow. For example when you run straight wastegate can pressure with the OEM intake and exhaust on the SE its around 7psi, this doesnt appear to be the case when you add an aftermarket intake and exhaust.

The differences between SE/mazdaspeed aftermarket performance manufacturers highlight this exact issue. Company A have chosen to replace the dump and downpipe where as company B & C have only changed the downpipe. Interestingly its company A users complaining of boost creep which has been addressed by reworking the internal or adding an external wastegate.

All 3 companies basically offer intakes, IC and exhaust the main difference being the differences between the exhausts. When you start interchanging certain parts between the manufacturers you cant expect the car to comply according to there test rig.

[Garry]

Isnt that like asking why does a intake and free flowing borla exhaust produce more power on turbo systems, secondly as a consequence does it alter boost level?

It may affect the rate at which the turbo spools up and therefore change the power at specific revs points but I would have thought the maximum boost would be set by the boost controller, assuming the SE uses an EBC and the monitoring point for the boost controller is at the intake plenum? If the restrictions in the intake/exhaust were preventing the turbo from reaching it's target boost level then I can understand how changes would increase boost. I must be missing something.

[blackster]

It may affect the rate at which the turbo spools up and therefore change the power at specific revs points but I would have thought the maximum boost would be set by the boost controller, assuming the SE uses an EBC and the monitoring point for the boost controller is at the intake plenum? If the restrictions in the intake/exhaust were preventing the turbo from reaching it's target boost level then I can understand how changes would increase boost. I must be missing something.

Yes it does take the boost source from the TB inlet tee'd to the solenoid and then back to wastegate.

SPM exhaust raises boost to around 8 psi and the addition of air intake + IC raised boost to about 10.5psi with the OEM solenoid in place.

Is it the OEM boost solenoid causing the addition of 3psi? No, the boost settings on the solenoid cannot be physically manipulated with just running the OEM ECU nor can timming or fuel.

The power gain and hence the psi rise is the result of the intake, IC and exhaust changes. It is this flow that when it over comes the flow restriction in the wastegate, the wastegate cannot compensate for this leading to boost creep. A boost controller cannot control boost creep.

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.

http://www.turbobygarrett.com/turbobyga ... qs.html#t7

[Garry]

ah IC.....well there ya go

[Sean]

If it's overboosting, why not turf the mbc all together? I still don't see how any of the mbcs can actually lower the boost lever, the wastegate can is pre-set, you cannot lower it, only bleed off air to \"trick\" and increase it.

[blackster]

I had an intake leak at the GFB bypass valve. The turbo noise was actually the air leaking in at the valve outlet. I must have disturbed the outlet from the valve during the AEM installation. When I went to tighten it however I discovered a perished 'O' ring and had to make do with gasket goo. The valve is only 2 years old.

A leak around the piston will cause it to "leak boost", not give more of it causing a overboost condition (yes its an oxymoron but it makes sense), which what is basically happening to the OEM valve when you surpass stock boost.

If a leak is occuring around the piston in VTA set up not only would it affect performance, it becomes problematic at idle as vacuum is lost to atmosphere, giving rough idle and changes in AFR. There is no such thing as an atmosphere leak in recirculated valve unless you got the hose clamps holding the valve loose.

I still don't see how any of the mbcs can actually lower the boost lever, the wastegate can is pre-set, you cannot lower it, only bleed off air to "trick" and increase it.

Agreed.