Horsepower

[TheBlizzard]

I was looking for some full exhaust systems for my 01 GTP and came across an interesting article regarding horsepower in general. The article was written by Alex Borla (Borla Exhaust). He was commenting on one of his exhaust systems and said " it doesn't add horsepower, it just takes away less horsepower than a stock system does".

How many people believe that a certain production motor has 'X' amount of potential but it is held back by restrictive part? Someone could say that a larger free flowing exhaust is just releasing the power that is already there, so are you really adding horsepower or just releasing the power that is already there?

With forced induction and/or nitrous, you are giving the motor a power adder that wasn't previously there. Hence 'ADDING'.

So are bolting on cold air intakes and exhaust systems really 'adding' horsepower or just freeing up horepower that was provided from the factory?

Here's my take on the question. I think what he's talking about is latent hp. A 100% efficient engine and drivetrain can put out a maximum amount of horsepower. Some of that is used to overcome friction and some is used in overcoming intake restrictions, head losses, and exhaust back pressure (pumping losses), some is used in the drive train getting it to the wheels. So we have a lot of opportunities to reduce friction, pumping losses and drivetrain losses. Now if you put in power adders into the equation such as nitrous or boost, you are only adding to the maximum possible hp the setup could make.

The power adders work only as well as the basic efficiency of the setup you start with. So you want to make the setup as efficient as possible (reduce friction and rotating mass etc). Then add power whichever way you choose whether it be nitrous, turbo, or a supercharger if you don't already have one.

Anyway since its snowing like hell and there is nothing to do, lets here some of your brains rationalize this.

[93sc]

I think that he's right as far as saying that a free flowing exhaust frees up HP. But the way I look at it your changing something on your car which increases your WHP so your adding HP. Whether its HP that comes from the factory being stupid or from adding nitrous doesnt really matter cause it wouldnt be there if you didn't do something to bring it out.

[CVD]

Yeah, theres adding power vs adding efficiency. But it really makes no difference.

[TheBlizzard]

But when you make the engine more efficient you make more power? So you are adding horsepower or just freeing up horsepower that was already there by making it more efficient?

[93sc]

Originally Posted by TheBlizzard

But when you make the engine more efficient you make more power? So you are adding horsepower or just freeing up horsepower that was already there by making it more efficient?

It depends on where you stop. Do you stop with the CAI and exhaust or with the heads? Is getting a really nice PNP job on teh heads and reshaping the bowl adding HP or freeing it up? Is changing your feul maps freeing things up? Where do you consider teh line to be?

[TheBlizzard]

Thats kind of what I was getting at with the question.

[93sc]

Kind of walked that one around in a circle didn't I.

[1ViciousGSX]

Like it or not, all engines are restricted from the factory. It makes them safer, more reliable, more predictable, less prone to warranty failures, etc., etc., etc. Intake & exhaust systems are ussually restrictive, mostly because of federal noise limits. Tuning is always conservative.

An engine is nothing but an AIR PUMP. The more you can pump in and out, the more power you will make. Intakes, exhaust, head ports, valves, etc., etc., are all restrictions at one level or another. Free up air flow and you will make more power if the fuel increases to match it.

An engine that is naturally aspirated does have a power potential up to 100% of it's volume of air flow and the energy released by combustion of that air flow/fuel mixture, limited by nature of design and friction. But as any good engine designer or tuner will tell you, you can exceed this 100% limit by several means. Port designs in the head will actually help push additional air/fuel into the cylinders at certain rpm levels. This comes from the air mass moving at such a fast rate of speed that as the intake valves close, the rushing air mass keeps wanting to move into the cylinder, which builds up pressure behind the intake valve. Ever wonder why Mitsu intake ports keep getting smaller on the 4g63? This is why some cylinder heads can see over 100% efficiency, by tuning the airflow.

Turbo chargers and superchargers add to the air flow, helping make more power.