EBR

[Tom]

Okay guys, as being the one who asked for this thread, I figure I should be the one who kicks things off. As a disclaimed, I am not an engineer, engine builder or extremely knowledgeable about all things involved. However, I find motors and the science behind them extremely interesting.

The term EBR is one that I am familiar with to describe the ratio of pressure in the intake v. the pressure in the exhaust manifold.

In a normally aspirated motor, the cam is set up in order to incorporate overlap between the intake and exhaust valve. This is done through overlap or LSA. This is done to allow the air from the intake to push the exhaust gasses out of the cylinder. A cam with more overlap and duration is better suited to a high revving application (read: lower torque) .

Turbos make torque. Torque technically makes Horsepower. A problem with stock turbo systems, is that they are extremely restrictive in the exhaust. Often , in higher boost (+1 bar) applications, there is more pressure in the exhaust manifold than in the intake. This pushes the exhaust gasses into the cylinder and the fresh, boosted air out.

A common upgrade on turbo motors are the turbo manifolds themselves, namely a "pulse paired" equal length design. The "pulses" are the valve opening and closing. Assuming that the "shock wave" from the explosion travels at or near the speed of sound, a wave of pressure bumps back and forth in the manifold and if tuned properly, the wave will begin to travel away from the motor right after the value opens, sucking the freshly burnt exhaust out and the new air in. These manifolds when used with a divided housing turbo allow for quicker spool up than normal.

So basically, when applying tuning theory's of normally aspirated motors to turbo motors you can get the best of both worlds. Good power off boost and a broad power band when you are spooled up.

If anyone has anymore thoughts on this, I would like to heard them.

[daveyg]

Not a bad job of explaining something that can be very extensive and difficult to understand in a simple manner. Other factors though include heat transfer, exhaust pressure, etc. Heat = energy, thus, hotter exhaust *should* spool a turbo quicker than an exhaust that is allowed to cool. Thus, when someone uses an equal length, tubular turbo header, they should always use fiberglass header wrap, or insulating fg blanket, because a tubular header will allow the exhaust to cool slightly, through fluid heat transfer, when compared to a large, heavy, low flowwing, cast piece. Also the pressure in the turbo header is affected by the length of the header's piping. Granted a really long turbo header will allow the most high rpm gains, due to the freer flow characteristics, the turbo will not spool as easily because the header will need to build up exhaust pressure prior to spooling the turbine wheel, which will also cause more cooling of the exhaust gasses, which, again, is bad. So there really needs to be a happy medium to get the best midrange and top end. Most stock turbo car applications are built with low-mid rpm range operation in mind (the average, budget-minded consumer who doesn't really like to throw gears at 9,000 rpm) So it all really depends on what a person wants out of their car. If they want a mild mannered dd, they should stick with a turbo manifold that is shorter and a smaller turbo, that will give them quick accelleration, when they hit the go pedal, but if they want a high rpm track monster, they should go with the super expensive equal length tubular manifold and big turbo. There really is no wrong and right, only real important thing is what someone's goals and usage will be.

[Tom]

This is true. Generally, a low EBR setup likes to rev. That means less torque. Torque is what makes driving at lower (<100) fun. It is fun to get off the line in a muscle car. It is also fun to wind a motor out to 9K and grab the next gear.

[Tom]

Another thing. 99% of all honda turbo setups use a low EBR principles to make power. 600 hp is A TON to make out of 2.0 liters or less. That is a fact.

YouTube - 1014 WHP 55 PSI 2.0 @10,000 RPMS EVOLUTION 8 (http://www.youtube.com/watch?v=ESluRK3kdM8)
10K RPM Turbo EVO

[CHRIFFIN]

CUPCAKES

[Tom]

CUPCAKES

What about them/him?

[zex_cool]

Another thing. 99% of all honda turbo setups use a low EBR principles to make power. 600 hp is A TON to make out of 2.0 liters or less. That is a fact. wat is this gibberish your talking about?

[Tom]

wat is this gibberish your talking about?

High RPM motors move a lot of air. Big turbos move a lot of air. Thus, a high revving turbo motor can make a lot of power. If I recall correctly, the 1100 whp AMS Evo VIII revs to like 11K or something like that.