Boost pressure alterations are by far considered the most cost effective modification in almost any turbo car. There are issues to consider when contemplating an increase in boost pressure in an E15ET.
As we (should) know, as the pressure of the fuel/air mix rises, the volatility of this mix increases concordantly. This is the very reason any engine compresses the fuel mix immediately prior to combustion. This is also why a turbo used to pressurise intake air is a great performance tool.
increased air pressure
=increased energy output upon combustion
So more pressure is a good thing, right?
To a point. When intake pressures reach too high a point, the fuel/air mix becomes too volatile in the engine’s compression stroke… and it pre-emptively ignites as a result of pressure alone before spark is even administered. After spontaneous ignition the fuel-air mix burns haphazardly, causing damage to cylinder walls, pistons, and compression chambers. Furthermore the fuel-air mix reaches ignition point in the piston’s upstroke, and ignites immediately as the ignition threshold is passed. This is not necessarily, and often not, at the correct time in the engine timing cycle. Thus, as fuel in the cylinder explodes, it expands and attempts to force down against the piston and connecting rod, which is still being driven upwards against the explosive force by the crankshaft! Such conflicting forces can be described as akin to taking a plastic spoon between the palms of your upraised hands and forcing your palms towards one another. What this example shows you what opposing forces separated by your conrods do to the conrods! Warping, flexing, ultimate breakage of components…
Ultimately all I’m trying to say is moderate your boost pressures. That, and don’t just rely on my short description above – _learn_ what detonation sounds and feels like before you go playing with boost levels which challenge your car’s well-being.
Safe Boost Pressures
Increasing the boost in a non-intercooled (description of intercooling here) Pulsar turbo cannot be recommended. The risk of detonation is simply too real to ignore.
If you feel you must toy with the boost of a non-intercooled E15ET the most I could possibly recommend is 9PSI. This is the tolerance set into the safety boost pressure release valve venting from the side of the plenum chamber atop the inlet manifold. To tune to this boost pressure the most straightforward option would be to use a system such as the AutoSpeed wastegate restriction/bleed boost controller. Boost could be tuned to a point at which the safety pressure release valve opens when the car is approaching maximum boost under test driving, then repeatedly tweaked back a little and tested until the system is set to a tolerance at which boost comes as close as possible to tripping the release valve without actually doing it and letting all the boost go.
Intercooled Pulsars are a different story. Given heat caused by the compression of inlet air to high pressures is a contributing factor to detonation, removal of this heat from inlet air has two desirable effects. First, intercooling densifies the air, promoting more efficient combustion, and most importantly, removing the detonation-inviting heat from inlet air allows much higher boost pressures to be run. Exactly how much boost can be run before detonation occurs depends upon a number of factors. These include intercooler cooling efficiency, ambient temperature, engine ‘breathability’ or ease of high-volume flow, and more.
Personally I know of E15ETs running up to 30PSI…
Just do this…