Skippydog

I have a few questions for you gurus out there. How come it is so much easier to raise boost then to lower it. And how would you go about lowering your boost If you had too. I searched the forum but i was comming up empty with any good explanation. Hopefully one of you can give me a lil ol insight thanks

dra_gon_lee

porting the wastegate will lower boost, also restricting the intake or exhaust will also do it, if you have the 87-88 with the mechanical wastegate. I think the 89-91 have a much better electronic wastegate, and a better wastegate design....

RETed

Do you understand the basics of turbocharger and wastegate control systems?&nbsp I think we need to go into a short dissertation on the matter...

How a turbo works is pretty straight-forward - the turbo turbine wheel is exhaust gas driven, which in turn is mechanically connected to the compressor wheel which pumps intake into the engine.

Now, this whole system would basically spin out of control without a control system.&nbsp There are two ways to control the turbo system:&nbsp 1) bleed off the compressor side, or 2) bleed off the turbine side.&nbsp If we bleed off the compressor side, we would promote the turbo to spin out of control - this will eventually destroy the turbo itself, so we bleed exhaust gas away from the turine side to slow the turbo down.&nbsp This is where the wastegate comes in...

The wastegate is nothing more than a mechanically actuated valve that bleeds exhaust gases away from the turbo turbine section.&nbsp The wastegate has a mechanically actuated valve that is either a "poppet" type (or plunger type) or an "actuator" type (or swing-arm type).&nbsp The stock FC3S turbo uses an actuator or swing-arm (internal) wastegate design.&nbsp Under vacuum, the actuator is held closed by the wastegate actuator spring.&nbsp This spring is specially calibrated to start opening at a certain psi of boost pressure.&nbsp The wastegate actuator is connected to a vacuum/boost source that will cause the actuator to open when it sees a pre-designed boost level.&nbsp Once there's enough boost pressure, the wastegate is opened.

Now that we got that out of the way, there is only two ways to lower boost:&nbsp 1) lower the efficiency of the engine/turbo, or 2) throw a softer spring into the wastegate actuator so it opens faster.&nbsp #2 is basically a non-issue, as the stock FC3S turbo wastegate actautor is a sealed design.&nbsp If someone has a way to swap spring or swap actuators, I'd like to hear about it myself.&nbsp Which just leaves with option 1 - lower engine/turbo efficiency.&nbsp Now how do we do that?&nbsp Easy - choke the intake or exhaust, and we get a less efficient engine and turbo...

Therefore, you wanna lower boost, choke the intake down (i.e. keep the stock air box) or run a restrictor plate in the exhaust system.&nbsp A friend used a 2" restrictor plate in a Racing Beat full 3" exhaust and got everything down to a solid 10psi of boost.



-Ted

Skippydog

Great thanks Reted that was exactly what i was looking for. I have read the ways to do it but an explanation of why is what i always have wondered. Im not a turbo guy in any means so this has been extreemly informable.

NZConvertible

Just to expand a little on Ted's excellent post (beat me to it ), boost controllers raise boost by bleeding air out of the wastegate actuator line so that the actuator sees a lower pressure, so it stays closed longer and boost is held at a higher level. That should make sense if you understood Ted's info. So the reason boost controllers can't lower boost is they would need to increase the pressure in the wastegate actutor line, and how ya gonna do that?!