EVO 7-9 Housing

The myth of lag being caused by a large exhaust or dump pipe

05.12.15 IN: How it works

To preface this article, we are purely talking about turbo-charged engines, NOT N/A engines.

We get people ALL the time saying “My mate says, if I go a big dump pipe or exhaust, I’ll get more lag” and “My workshop says, going too big will create bad performance with response”.

When talking to people about why our EVO parts out perform others I ask a very simple question. “ How does a turbo work in its most simplest form?” Most don’t really know.

There are 2 sides to a turbo and a middle, the middle being the bearing section, which we won’t being talking about nor, will we be talking about the compressor side in this Blog.

 

It’s the turbine side I want to bring back to it’s most simple form.

The way a turbine works in it’s most basic form is this. There is more pressure on one side than the other.  Simple. . . . The high pressure exhaust gases exiting the head want to find the easiest was to get back to atmospheric pressure. For that to happen the high pressure compressed exhaust gas must escape via pushing a turbine blade/wheel.  This causes the turbine wheel to turn.

Now to go back a step, if you had a turbo, which had 20 psi before the turbine wheel trying to escape and 20 psi after the turbine wheel, would the turbine wheel turn? The answer is NO.  This is because there is no pressure differential across the turbine . The 20 psi before the turbine wheel has nowhere to go. Now lets say we change to 20 psi before the turbine and 10 psi after, that gives us now a 10 psi differential. The majority of the energy that was in the exhaust gases prior to the turbo is now converted to rotational energy to turn the turbine wheel. The energy that was not used in turning the turbine wheel provides the outlet pressure. This gives the high exhaust pressure somewhere to go, and to spin the turbine wheel. The larger the differential pressure the faster the response of the turbo due to the faster the velocity of air passing by the turbine wheel.

When you fit an ARTEC 3.5” turbo back exhaust you are removing most of the pressure restrictions on the post turbine wheel side which in turn allows greater pressure differential gives you faster throttle response, more torque and more power!

 

Very simply, the greater the pressure differential across the turbo, the greater energy that can be converted to energy going into spinning the turbo wheel. Any downstream restrictions to flow are just wasting available energy.

 

I have included an image of a HP restricted GT500 engine from the 90’s. It is a Toyota 3SGTE. Please note the large 4” Dump pipe outlet. Would Toyota want to increase its lag, or would they be wanting as much response as possible due to their HP ceiling being capped at 500HP but Torque not having one?

 

Toyota large Flow