This edition of Turbo Edition evolved from a tech question about cheap, near zero dollar ways to get more boost and more power out of a turbo system. I am always a bit shocked at how quickly some people will bump the boost with no thought whatsoever to the fuel side of the equation or what the added heat in the system can do to performance.
The number one rule when boosting up a turbo system? Be sure there is enough fuel capacity on hand to meet the need. Retaining an optimal air/fuel ratio is key in realizing a power gain and ensuring reliability.
Intercooling is rule number two. When increasing the boost, intercooler efficiency must stay high. If it degrades, the resulting rise in intake temperatures will steal away the very power one is trying to gain. Further, improving intercooler efficiency will translate into more power...as a general rule a drop of 40-45 degrees in charge air temp will allow a 2-3 psi bump in boost without addressing fuel. This line of thinking can be seen in action in the form of water/methanol injection kits that enhance the intercooling effect and allow significant boost gains without an increase in octane quality.
With the public service bulletin out of the way, let's talk about boosting bumping methods. It's all about tricking the wastegate and there are two places to pull it off-at the spring or in the signal.
Spring Into Action
The spring version has to do with altering the pre-load characteristics within the wastegate. This can be done by shimming the spring with washers. Changing the spring rate on externally wastegated systems can be done in tandem with the original spring in the form of a helper spring or by replacing the spring altogether. Wastegate springs come as low as 3.63 psi and range all the way up to 23.2 psi so as you can see in the accompanying chart small, read safe, gains are a swap away.
External Wastegate Spring Ratings
Beyond shims, turbo systems with an integral wastegate take a little more cleverness but a few psi can be coaxed out of hiding. By affixing an additional spring externally between the plunger body and a mount fabbed on the shaft the resistance to pressure is changed and the gate will give up more boost. This is a sketchy, inaccurate way to boost up and integral wastegates are better off modded via shims or the signal method.
The other way to fool your way to more boost is by changing the pressure signal going to the wastegate. This is done by creating a leak in the boost signal line that leads to the gate. The pressure in this line initiates the valve. So a gate with a 9-psi spring modified with a hole that creates a 2-psi 'leak' will open at 11 psi. Back in the day mediocre aquarium bleeder valves were used to create a 'consistent leak.' They were marginal even in mild boost-up situations and often gave way to boost creep where the boost level increases past its maximum setting or poor spool-up because the gate would tend to start opening before maximum boost had been reached. There can also be sputtering when a resonance occurs between the wastegate valve and the orifice causing a choppy boost cutoff. Such components are best left with the fish.
Today's manual boost controllers, like those from Hallman, TurboXS, Turbosmart and Buschur Racing, are the ultimate evolution of the bleeder valve theme. They are made of quality materials and the bleeder orifice is solid, providing consistent control and adjustability, allowing for a wide range of boost levels. I do not believe in zero-dollar boost ups so I recommend a quality manual boost controller as cost effective, bare basics boost control ...people they are only $60 to $70. These units suffer none of the shortcomings of their now-fossilized forebearers.
If a manual controller is adjustable many enthusiasts may wonder what's up with electronic boost controllers (EBC)? Modern EBCs provide on-the-fly boost adjustments but their big advantage is how they control the flow at boost threshold. A manual controller relies on a pressure signal and the wastegate spring to manipulate the valve. An EBC has total control of the signal so, when set at 15 psi, it can hold back all the pressure until 15 psi is realized. Then it opens the gate valve in one emphatic motion. The result is quicker spool-up and a harder hitting boost/power surge.
Electronic controllers use solenoids or stepper motors to alter the signal pressure in the system. In a system with a wastegate running a 14-psi spring the EBC can be programmed to wait until 20 psi before opening the valve. The EBC's downside is cost with prices taching out at more than $700 for complex, full-feature units. A good do-it-your-self simple EBC like the GReddy PRofec-B, AEM Tru-Boost or Turbosmart e-Boost 2 can be had in the $300 - $350 range.
Electronic boost controllers max out at double the wastegate spring rating. So an external wastegate with a spring rated at 14 psi can only be boosted to 28 psi with an EBC. An 18-psi spring would have to swapped in to run up to 36 psi etc.
How much you plan on boosting up, the boost level you are starting at and the individual strong points and weaknesses of your system factored against the thickness of your wallet will help determine what style of boost controller is best for you car. The most important thing to remember is to get your turbo system tuned correctly each step of the way. Until next time, happy boosting.