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Old November 4th, 2009, 07:54 AM   #1
offshore
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HP Discussion

I'm bored because I haven't gotten used to the time shift and keep getting up at 3 in the morning, and this site seems to have grown quiet so I thought I would start a discussion about a topic that has become confusing to me (some would blame it on age). As I was growing up with cars and learning about how motors operated if you wanted to create more HP you bored out your cylinders, installed larger pistons and valves, changed the camshafts and sometimes timing primarily to increase CI. Turbo's and super chargers were added as they became more popular and refined and HP gains were attributed to them by increasing CR. The basics though were you had a certain amount of CI that produced a certain amount of HP. Since I've purchased my Porsche I'm hearing all kinds of claims for add on's that create more HP. Cold air intake systems and sports exhausts are a primary one and although I can understand how a motor that breathes better can run more efficiently I don't understand how that can increase HP since CI, CR, torque and etc. still remain the same. Is there a formula that is being used to illustrate gained HP from more efficiency that I've never seen or is it all done by Dyno? Another claim I'm seeing is weight reduction equalling HP gain. I can understand this one to some extent because there will be a difference from a 200 HP motor pushing a two ton car and a one ton car but how does making the motor run more efficiently by pushing less weight relate to a HP gain? Is there a formula for turning pounds into HP gain? Under pulleys are a hot topic on other Porsche forums and claims of up to 10 HP gain are being touted. I can understand reducing the amount of power a motor has to put out to turn devices that have friction and slow it down but aren't you really just reclaiming lost power from these devices? I'm certain there is an easy answer to this that my absence from automotive technology has come up with but I'm interested in tapping into the brain power on this forum to see what your thoughts are regarding this topic.
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Old November 4th, 2009, 09:47 AM   #2
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My meager understanding about reducing weight and a HP 'gain' is a shorthand for saying it's "like" a HP gain. From what I can tell, the impact is as you stated... it favorably changes the HP/Weight ratio and therefore increases acceleration.

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Old November 4th, 2009, 03:58 PM   #3
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CAI (cold air intake) works because cooler air is more dense. So, as you add more air to the combustion mix, the computer reacts by adding more fuel. More fuel + more air = bigger bang!

Exhaust helps because it lets more gas flow. However, going too large can be detrimental. Of course you will do better with a full system than with a simple cat-back.
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Old November 4th, 2009, 04:39 PM   #4
offshore
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Quote:
Originally Posted by vitaminC View Post
CAI (cold air intake) works because cooler air is more dense. So, as you add more air to the combustion mix, the computer reacts by adding more fuel. More fuel + more air = bigger bang!

Exhaust helps because it lets more gas flow. However, going too large can be detrimental. Of course you will do better with a full system than with a simple cat-back.
Understand all of that vitaminC but unless I'm missing something bigger bang in same size bore and stroke doesn't necessarily equal more HP it just may mean a more efficient combustion and less gas mileage. Removing exhaust gases more efficiently just means a more efficient running motor not necessarily more HP. What I'm starting to think is a motor starts out with a certain bore and stroke producing a certain amount of HP. Inefficient air intake, exhaust and add ons like PS, AC rob the engine of HP. Adding more efficient systems regain the lost HP. Correct me on this but if I'm correct than many of the claims I'm reading are exaggerated. Doc and Dan where are you when I need you?
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Old November 4th, 2009, 05:07 PM   #5
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I think you are basically correct. Any engine is nothing more than an air pump. the more efficiently you get the air thru the engine the better it runs and the less parasitic losses.
so a better intake or exhaust will gain some power. But the engine only has so much power inherently.
so if a stock boxster motor can make lets say 250Hp at the crank, you take away some hp for restricted intake or exhaust, you take away for ancillary equipment, you take away for alternator or anything else that requires power to operate it, take away the friction of the tire patch, take away the losses in the drive line (trans and half shafts) and you end up with a motor that makes 200 or less.
So with a given configuration you are not creating HP as much a releasing drag on the motor to let it more closely reach it's true potential.
at least that is my take on it.
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Old November 4th, 2009, 07:15 PM   #6
offshore
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Quote:
Originally Posted by Docdanracy View Post
I think you are basically correct. Any engine is nothing more than an air pump. the more efficiently you get the air thru the engine the better it runs and the less parasitic losses.
so a better intake or exhaust will gain some power. But the engine only has so much power inherently.
so if a stock boxster motor can make lets say 250Hp at the crank, you take away some hp for restricted intake or exhaust, you take away for ancillary equipment, you take away for alternator or anything else that requires power to operate it, take away the friction of the tire patch, take away the losses in the drive line (trans and half shafts) and you end up with a motor that makes 200 or less.
So with a given configuration you are not creating HP as much a releasing drag on the motor to let it more closely reach it's true potential.
at least that is my take on it.
I knew you'd have the answer.
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