I've seen graph after graph where good tuners are able to control the amount of torque an engine output and the horsepower independently. For example, if someone was running a non-stock turbo on the stock block, the tuner might want to keep the torque at 400 ft/lbs, but have the hp hit 520 on the top end. What is the principle behind being able to control the amount of the torque? And the same for hp?

Is timing a direct or inverse relationship when it comes to torque?
Is AFR a direct or indirect relationship when it comes to torque?
Is timing a direct or inverse relationship when it comes to hp?
Is AFR a direct or indirect relationship when it comes to hp?

ie. When you want to lower the torque in a certain range, do you increase or decrease the timing?

-Acree

 

hp is derived from torque.

tune for torque

hp is torque over time and rpm

 

Horsepower and Torque have a relationship to one another. On one car with the same gearing Torque at a specific RPM will ALWAYS yeild the same HP. You can't change HP independent of torque.

http://en.wikipedia.org/wiki/Horsepower

HP = (Torque X RPM)/5250 This equation is always true (for imperial units).

 

I understand that. But more specifically, let's take 2 hypothetical graphs. Both of them have full spool at 4krpm, and hit exactly 400 ft/lbs and decline to redline at 7krpm. Graph 1 hits peak HP at 450 hp, and Graph 2 peaks at 520 hp. How do tuners control this?

-Acree

 

It simply means that there was more torque at higher rpm than in graph 1.

Typically this means more airflow or timing was used, airflow being boost or the equivalent restrictions removed. This assumes you didn't get to MBT where more timing would actually decrease torque and thus HP would suffer, not to mention you engine would likely go boom at this point.

In you specific example if the maximum horsepower was at 7000rpm

Graph 1's torque would be 337.5 ft/lbs
Graph 2's torque would be 390 ft/lbs

 

The tuner, in most cases, can control tq spikes through solenoid/boost modulation.

ramp the boost slower, decreases the initial tq spike.

ramping it faster and sooner, causes for the onset of tq to hit earlier.

 

So in general you want to get your AFR's in order first, and then start messing with boost and timing to control output?

-Acree

 

in general start with a safe afr(rich) and low timing while slowly tuning yourboost curve then afr then lastly timing. then do it again to fine tune. of course if you will do mivec tuning you should do that before timing and afr as it affects both.

 

If AFR is equal, its timing or MIVEC (if equipped) first. Timing is the fastest way to remove torque, the second is drowning the motor down low depending on fuel or conversely leaning it out depending on fuel. Lastly is if you have rpm based boost control taking duty cycle out at a given rpm (ECU boost or something like an AVC-R).

 

See now that's what I was wondering. Great information. Thank you both.

-Acree

 

After thinking about it for a while, I kind of feel like an idiot for not noticing this sooner.

With the very nature of Horsepower being derived from a linear equation, you CAN control horsepower and torque independently.

Horsepower is directly related to the slope of the torque curve. IE. If your torque curve is perfectly flat, then your horsepower exhibits a steady rate of increase. If you can manage to decrease the torque curve with a constant negative slope, the horsepower will have a constant slope. That slope will be positive, flat, or negative depending on the rate of decrease in the torque curve, ie. the slope.

I don't know if that will help anyone reading or just confuse them more, but makes sense to me.

-Acree

 

My 2 cents...

HP and TQ are somewhat inversely proportional with the crossover point always being 5252 (at least for our cars). They can't be controlled independently as one is dependent on the other. Although, tuning for more torque down low will result in a "punchy" feeling car. Tuning for top end horse power will result in a (usually) a very linear feeling car.

Remember, it is all about compromise. Tune for a purpose with a goal in mind. Every car is different.

Paul

 

alot of factors make a diffrence. Ex> Turbo's , Displacement, Flow rate

 

You must be confused let me put it to you another way.

HP = Torque @ RPM

It is impossible for example to have 400hp and 400ft/lbs of torque at 3000rpm. You would need 700ft/lbs of torque to get 400hp.

If you want to know how much torque you need to get to horsepower you can run the equation in reverse like so.

Torque = (HP * 5250)/RPM

 

I'm not confused.

My statement was regarding each curve respectively, not the independent values. I should have specified. I understand that a certain torque number at a given rpm will always produce the exact same amount of hp. I'm saying you achieve the HP curve you want by changing the slope of the torque curve at given points in the rpm band. Now, the amount of control you can assert over the torque curve is obviously going to be very limited according to the setup and car.

I guess my main point is I now understand how you can control torque to either to different ends, from one extreme being a supra like cliff of hp, or a broad stock-like power curve.

-Acree