I was reading some topics on horsepower theory and found one that stated that horsepower is equivalent to valve area and that valve area is a far greater determinant of possible horsepower that cubic inches.
Is this true? Here's the link where I read it: http://www.gglotus.org/ggtech/hptheory.htm
From what I have read there it makes some intuitive sense but as with anything there is usually more to it than what's stated :D



[Modified by C5Noir, 4:28 PM 1/13/2002]

 

Horsepower is a function of RPM, RPM is a function of Volumetric efficiency (TQ), Volumetric efficiency (TQ) is a function of airflow, airflow is a function of valve size, cam timing, intake constraints, exhaust system limitations, etc ...
So I guess you could say that valve size is in the equation there somewhere...
Shirl :D

 

Interesting. But I beleive an indirect relationship at best. Other factors that must be considered are the camshaft which controls duration and valve opening closing events relative to stroke.

TQ is not specifically volumetric efficiency either. Its a representation of how much energy can be produced with each stroke, which means Torque is proporational to how much energy can be produced with a given angular displacement of the flywheel.

Power (HP) = TQ (in Newton Meters) x rotational speed (radians per second).

Each aspect of a motor contribute to power output. Not simply a metric such as valve diameter alone.




[Modified by kewlbrz, 11:59 PM 1/13/2002]

 

So, Kewlbrz,
You're not going to let me get away with lumping torque and volumetric efficiency together without an explination, ehhh... Well okay, I believe that you understand what I am about to say, but let me make my case for those that don't... :D
Technechally, you are correct in that TQ is not the same as VE, however if you plot them on the same rpm scale and lay the plots on top of each other you will see that they almost exactly mimic each other... In fact the curves WOULD EXACTLY fit on top of each other if both parameters were measured at the same location... The reason they don't quite line up is because V.E. is measured as airflow into the cylinders and TQ is measured no closer than the flywheel... The difference between the two is frictional losses, pumping losses and parisitic valve train losses inside the engine... In fact, as the comparison of these curves show, TQ is the direct result of V.E....
Why am I going to all the trouble to point this out? Because, armed with the VE curve and knowing that improvements in VE will be translated DIRECTLY into improvements in TQ and from there to a direct increase in (the king) Horsepower, you can attack those things that improve airflow into and out of the engine...
This insight provides clear direction to the objective... Without this insight, understanding how to make improvements in TQ and HP become not much better than black art and mystery....
The nugget to be gleened here for those that are willing to accept it is that, knowledge and understanding will always be superior to the savage and untutered mind... Learn it or lose....
Shirl :D

 

Shirl, so does the V.E. improvements that translate directly with torque improvements support why nitrous causes such massive gains in torque?

 

mreracer. I concur.

c5noir, nitrous produces insane amounts of torque with less rpms, due to enormous pressures in the cylinders at those low rpms. No work (power) relative to time is necssarily being acomplished since piston velocity is so low. Only a lot a energy. Torque goes down dramatically with nitrous as rpms increase.

 

Absolutely, NOX is just another way to pack more oxygen (and fuel) into the cylinders which is just another way to say that you have improved your VE...
The reason NOX results in so much TQ is because of it's unique property that NOX derived HP is independant of rpm... In other words, NOX adds a constant amount of HP on top of an engines naturally aspirated HP curve. I'll provide an example... If you had an engine that produced 100 hp at 1500 rpm, it's naturally aspirated TQ would be equal to 350 ft-lbs at that rpm. If you engaged a 150 hp shot of NOX on this engine at 1500 rpm the total hp would then be 250, but the TQ would jump to an incredible 875 ft-lbs... This is the reason why engaging NOX at a low rpm will break a lot of parts....
The above example can be verified using the following equations:
hp = (TQ X rpm)/5252...
TQ = (hp X 5252)/rpm...
As an interesting experiment, take any hp curve for an engine and plot it's naturally aspirated TQ curve... Then add a constant 150 hp to the NA hp curve and re-plot the TQ curve... It will be obvious why NOX is so potent in the TQ department at low rpm... You will also note that (the NOX) TQ and HP are still equal to each other at 5252 rpm. as nature dictates... :cool:
Shirl :D

 

HP for dummies.......suck.....squeeze......bang .......blow........the engine that does this best, makes the most power :lol: :lol: :cheers:

 

Interesting, that would seem to explain why variable cams have been so successful, as they effectively allow you to optimize "valve area" over the RPM range. Given the benefits of valve area optimization, why isn't it found on the corvette? I mean, if its cheap enough for a Honda Accord, why don't we get it on the Corvette???

 

kewlbrz wrote: The reason they don't quite line up is because V.E. is measured as airflow into the cylinders and TQ is measured no closer than the flywheel... The difference between the two is frictional losses, pumping losses and parisitic valve train losses inside the engine... In fact, as the comparison of these curves show, TQ is the direct result of V.E....
Why am I going to all the trouble to point this out? Because, armed with the VE curve and knowing that improvements in VE will be translated DIRECTLY into improvements in TQ and from there to a direct increase in (the king) Horsepower...

I write: There are situations where you go into an engine and change the frictional losses without changing the VE and still get added TQ and HP. Those examples are few and far between, but one cannot disreguard from the theororetical point of view.

examples: lighter ring tension, Aluminum flywheel, longer rod/stroke ratios

 

thanks mitch, although I didnt say that. :)

 

Re: VE

From what I have seen there are actually 2 slightly different versions of VE out there.


If we represented VE as

Actual Airflow / Theoretical Airflow

- well, the actual is fixed, but theoretical is what seems to be interpreted differently - specifically some people seem to calculate theoretical airflow based on manifold pressure instead of atmospheric pressure.

I know, I thought this was some strange one off approach also, but it is the only methodology that explains the factory GM tables.

For example, here is one from a stock LT1

Reference: http://www.slowcar.net/shared/2000to7000ve.txt

Notice the general VE trends; not what you would expect with a classical
definition. Yet if you log your vehicle and calculate VE using MAP reading as the theoretical max instead of atmospheric it agrees pretty well with the values listed.

The reason for doing it like this? I don't know, just wanted to point out there was at least one other definition of Ve out there.

 

Exactly. My knowledge in this area is very minimal at best, hell I read up on camshafts at HowStuffWorks.com but it does give a nice explaination of how the Variable Valve Timing improves engine efficency on page 3.
http://www.howstuffworks.com/camshaft.htm

Some of you are just too smart, LOL! Glad to have the knowledge though, thanks!

 

Volumetric Efficiency = (Amount of air pumped every 2 cycles)/displacement

One might think that VE at 100 RPMs WOT would be 100%. This would be the case if the intake valve closed at BDC. Since this event is delayed to allow high RPM operation, the piston pushes some air back out the intake valve at RPMs significantly under max TQ. And therefore the low RPM operation has a TQ floor significantly lower than maxTQ. As RPMs rise, the pump-back is reduced and TQ rises until maxTQ, stays for a while, than slowly drops as other restrictions come into play at high RPMs.

Then One might think that 100% VE or greater is impossible. This is also not the case because of resonance effects in the intake (velocity stacks), exhausts (headers) can trick more mixture into the cylinder than the actual displacement of the cylider itself.

 

If you were replying to my formula you will notice the two are the same thing. I just said actual/theoretical.

Yours is amount of air pumped per 2 cycled. This would just be displacement if our engine was at 100% VE, otherwise it's just the actual airflow per 2 cycles. Displacement would be perfect (theoretical airflow) for a 2 cycle duration. So it's the same the as saying actual/theoretical.



I know what you are saying, but don't agree. If we could have a non-restrictive intake and square lobes on the cam then you close the valves here and do that, but working withing the context of available technology it wont work.

And good point on the greater than 100% VE point. This will generally only be at a specific RPM or RPM range though - since it is based on resonant tuning of the intake and exhaust - normally you shoot for this somewhere between your torque and hp peak, depending on what your requirements are.