Someone clarify something for me re: HP vs. Torque

[Kevin Shasteen]

If I may...and no - I'm not going to kick this dead horse anymore (as it appears the buzzards & dogs are already licking the bones clean ), I would like to make a comment regarding your dyno you posted.

 

I'ld like to comment on what Dan illuded to. Remember that Peak TQ is a reference to "PEAK CYLINDER PRESSURES" while Peak HP is a reference to "PEAK PORT PRESSURES". These two elements can be boiled down to one variable:

 

1) Airflow Velocity

 

When dealing with an automotive engine our airflow velocity must operate within a number of other fundamental variables. Keep in mind your engine is not always operating at Peak TQ nor Peak HP. So if you dong understand the math - in how your engine reaches Peak TQ/HP: then you will misinterpret this "Harmless" discussion of Tq -vs- Hp and possibly be prone to making poor decisions when you choose to purchase components for power modifications.

 

Have you ever noticed the data screen you can toggle to on DD2000. I believe DD2000 calls it the "table" screen? It indicates:

 

1) Engine RPM

2) FWHP

3) FWTQ

4) Intake Manifold Pressure

6) Volumetric Efficiency (%)

7) IMEP

8) FMEP

9) BMEP

 

These underlying elements explain how Airflow Velocity is altered at all rpms. These nine elements are the most important indicators engine builders thru the years have identified and required to build a successful engine for whatever needs (intended purpose).

 

Understanding those issues and the fundamental elements that make up those issues will help you grasp why your engine has reacted the way it did with your modifications.

 

Have you read the posts on Corvetta's new engine? His engine builder defied the Hotrod Mags by putting 180 cc heads on a 383 destined to be a Weekend Warrior type motor with a cam duration in the neighborhood of 288 or something like that with 10.0:1 SCR (I believe) - whereas, if we were to follow the typical approach to building a 383 taught by the HotRod Mags, we would have put 220cc heads on that engine. So, why did his engine builder put 180cc heads on that engine? The answer has to do with the effect Airflow Velocity has on Volumetric Efficiency.

 

In other words, his engine builder is purposely building this engine so that its Volumetric Efficiency is at its highest when it needs to be - at the end of the Peak HP rpm range.

 

If his engine utilized those 180cc heads with the 10.0:1 SCR and a mild cam duration of 250: then his Port Velocity would be very high extremely early in the rpm range. If this mild cam were used in that set up, his engine would probably have seen Peak Tq at 2000 rpms and Peak HP at 4000 rpms. This means his Cylinder Pressures would Peak (PEAK TQ) earlier in the rpm range. This also means his Port Pressures would max out earlier in the rpm range (PEAK HP). Similar performance to your "Dump Truck" comment.

 

Instead, his engine builder improved his engine's Volumetric Efficiency to its maximum and matched its intended use by utilizing these smaller Intake Ports with the 383 displacement: and then installing an excessive duration cam (288 Duration). This allows the cylinders to bleed which delays Peak Tq and Peak HP. This means Peak Cylinder Pressures and Peak Port Velocity are both delayed. This delay is caused by a lessor Port Pressure earlier in the rpm ranges.

 

Regarless of how you build your engine - all you are doing is manipulating the Airflow Velocity (Peak Cylinder Pressure and Peak Port Pressures).

 

I said all that to say this: Your engine is reaching its Peak Tq early because of its smaller Intake Port Volume or because of restrictive intake/exhasut system. If you wish to push your TQ curve higher in the rpm range, you need to either:

 

1) Uncork your Intake delivery system

2) Uncork your Exhaust system

4) Uncork both the Intake/Exhaust system

3) Get a Cam w/a longer duration (still doesnt help the restrictive intake/exhaust

4) If Turbocharged - then trim your turbo to not build boost until a 1000 rpms later (providing you are happy w/your engine's current output).

 

Hope that made sense.

 

I dont know what performance calculators you are looking at - but when I wanted to understand these very issues you are grappling with I took John Lawlers book, "Auto Math Handbook" and Forbes Aird's "Auto Math Handbook" and put some of their chapters onto Excel Spreadsheets.

 

I took John Lawler's

1) Chapter 4 Brake Hp & TQ

2) Chapter 9 g Force & Weight Transfer

3) Chapter 10 Shift Points

4) Chapter 11 Quarter Mile ET & MPH

5) Chapter 13 MPH, RPM, Gears & Tires

 

From Forbes Airds book I took his Areodynamics chapter and put it on Excel.

 

FWIW - as a little encouragement when trying to understand all this stuff, the light bulbs didnt really begin to make any sence to me until I actually FORCED myself to understand Camshafts and BMEP (Brake Means Effective Pressure), and how the Cylinder Head's Intake Port sizing effects Airflow Velocity.

 

Once I actually understood Camshafts, BMEP, and the Intake Port then everything was immediatly clearified.

 

Of course all this "Immediate Clearification" was a prgoression of knowledge that I gained over a three year period of time.

 

Is that "period of time" it took me to grasp these issues equal to brain tq -vs- brain hp?

 

Sorry couldnt refuse that one.

 

Kevin,

(Yea,Still an Inliner)

[Guest bastaad525]

repeated kicking of a dead horse isn't so bad as long as you keep kicking from different angles

 

Thanks for the additional info... this thread has given me a LOT of info to wrap my head around... in a practical, useable sense, it really boiled down to just a couple of things, but in a being-car-wise sense, it's given me tons to think about.

 

Well at least now I have a better perspective on some things, like what to focus on with my own car to get what I'm looking for, and how different cars compare to each other (so I love bench racing what can I say). Definately a 'keeper' thread for me, going in my 'good threads' folder.