BBK shorty headers

Discussion in 'SN95 4.6L Mustang Tech' started by fast97gt, Feb 18, 2010.

  1. All true, except for one thing. Tq can be manipulated by gearing. Knowing that Tq is the only thing that will increase acceleration (except for lowing mass), one could just use larger and larger gear ratios to get more acceleration. The problem with this is what I was getting at above. More gearing makes more acceleration, but at a lower speed.

    Above I defined and proved why increasing hp is what you want to do if you are interested in increasing acceleration at any given speed.

    Obviousely increasing engine tq at a given engine speed will increase engine hp. However, engine tq does not move the car. The tq at the wheels does, which is engine tq multiplied by overal gearing. This makes engine tq meaningless without knowing the engine speed that its made at (or, more importantly, vehicle speed).

    Hp is different. Hp gets to the wheels the same no matter what the gearing is (ignoring insignificant changes in losses).

    This is why hp is a better measure for acceleration if you want a specific vehicle speed operating range.

    300 ehp, 250 etq will accelerate a car just the same as 300 ehp, 350 etq. You just have to set the gearing so that you get the same wheel tq for each car.
  2. They are two independent variables. Max tq and max hp are almost never at the same engine speed. When do you shift, to maintain peak hp or tq? Think about it. If you shift to maintain peak ENGINE tq, you are now in a gear with less mechanical advantage, less wheel tq, less acceleration.
  3. Ricky is correct. Remember he is talking about wheel torque and not just the engine.
  4. I agree with him. I just think it is important to understand that horsepower is *directly* related to torque. You can't increase horsepower without increasing torque. Pretending that isn't so is ignorant, not an insight.

    Nobody gets a dyno graph showing the actual measurement of rear wheel torque. Gear ratio is always factored in. Horsepower is calculated from the math that gives engine torque at the wheels based on rear gear ratio. Installing 4.10's increases torque to the wheels, making the car faster through the gears, but horsepower hasn't changed. It actually drops since shorter gears eat up more power through friction.

    The idea that changing rear gearing changes horsepower is ludicrous.

    Nobody said you shift to maintain maximum torque. You need to do the math in each gear to find out the ideal shift point. Based on torque, NOT horsepower.

    The relationship between torque and horsepower should be self-evident. The relationship between torque and acceleration vs. horsepower and acceleration is not so obvious. I needed to put an accelerometer in my car and test it on the highway to clarify it in my own mind. Botom line - peak torque is peak acceleration. Horsepower is a fabricated number that means nothing at the end of the day. Tourque at rpm and gear multiplication is all that really matters.


    But all I really wanted to know is how much factory GT headers weighed compared to BBK shorties. :)
  5. I've had both Long Tubes and shorties. I currently am running the BBK shorties. I understand the power difference but I'd rather be able to remove my transmission if need be rather than trying to remove a long tube header than remove the tranny.

    I trap the same MPH with the shorties as I did with the long tubes.
  6. Can the transmission be removed from the bellhousing with the longtubes in place or do the long tubes get in the way? I understand that some transmissions cant be removed from their bell housings from the outside, but my t56 can.

    Interesting... any other changes?

  7. 4.10 gears will make you accelerate faster in any given gear, but your top speed in that gear will be less than if you had stock 3.27 gears.

    No one said gears increase hp.

    Shift to maintain max hp output, and I think you will find that you are maintaining max wheel tq.

    Hp is not a fabricated number.

    It is contradictory to state that hp is meaningless and that rpm and tq is important. Horsepower is rpm and torque!

    Hp = rpm * eTq

    Why do you think hp is used to compare engines? Why do you think power to weight ratios are used to compare vehicles? Why not etq to weight ratio?

    Their is a good reason why it has been done this way and you are missing it.
  8. Never tried it, I got fed up with the Mac long tubes and the other headers that allow the tranny to be removed are a complete rip off.

    Other than the BBK o/r X connected to the shorties that replaced the shorty o/r H pipe, no other changes.

    Technically speaking, HP is a mathematically created number. It is not measurable. The only meaningful measurement taken from an engine is Torque. HP is a way to make people feel all warm and cozy about their cars.
  9. Would you buy an engine without knowing what its hp curve is?

    You cant measure an engines performance without knowing it's hp.

    Show me a calculation that shows an engines ability to accelerate a given weight through a 1/4 mile in a given time that only considers torque (and not engine speed) as a mesure of performance of the engine. Knowing tq and engine speed means you know hp by definition.

    I dare you.
  10. What are you talking about? You cannot measure HP. You measure Torque. Hp is a conversion of Torque over time. HP is a selling point. Torque is what moves the vehicle, not HP.

    You just posted a link that shows you are arguing with yourself.
  11. Read the whole thing before you respond.

    And again... I DARE YOU to do what I asked in post 69.

  12. One more thing... Both tq and hp can move things. BUT, hp will tell you how fast you can do it (time) and at what speeds. Tq wont do either without knowing more information (such as rpm) which would actually define hp.

    If you dont care about your ET or mph in the quarter, fine. The rest of us normal people do.
  13. To do what???You cannot measure HP. This is like speaking to a woman.

    What you do think spins the tires? Torque from the engine
    What do you think spins the rollers on the dyno? Torque from the engine

    What do you not get?
  14. Let's keep the myths to ourselves.

    You can measure hp. You would know that if you read ALL of the link I posted. What I dare you to do is to prove me wrong with science. Show me an equation that proves your point(s). I've given enough already.
  15. Here is something else for you to chew on. With the right gear ratios, a 500 ft-lb tq engine can put the same tq to the wheels as a 100 ft-lb engine. Do they both accelerate through a 1/4 mile the same? Maybe they do... Maybe they don't. You don't know without knowing the hp curve.
  16. to answer the question of wich will cross the line faster, wouldnt you need to know the weight that is being moved by the torque? like if you moving 100 lbs with 100 pounds of torque over a quarter mile vs 5000 lbs with 500 lbs of torque, will the 100lbs be first?

    i dont know the equations behind all this im just trying to logically understand it. all this argument on this thread is awsome information
  17. So you are finally understanding that engines only produce torque?
  18. Both would have to weigh the same for the comparison to be meaningful.

    The point is that the question can't be answered without knowing what the hp is for each engine.
  19. F = ma (definition)
    a = F/m
    F=eTq/r (definition)
    eTq=Hp/rpm (definition)
    a = Hp/(rpm*r*m)
    rpm*r = v (definition)
    a = Hp/(v*m) (acceleration is a function of vehicle speed, mass, and hp only!)
    m = vehicle mass
    Hp = horsepower
    eTq = engine torque
    F = thrust force at wheels
    r = factor including total gearing and tire size to convert rotational movement into straight line movement or tq into force