Dyno Summaries? PBRV???

[Hoplee]

I was trying to think of a way to quantify the breadth of a specific engine's power band. The effectiveness of an engine is not merely a product of max hp and torque. Hondas and Ferraris may put out massive hp and comparatively little torque, but a muscle car may present an entirely different balance, especially one with a big block!

How do we describe an engine to include these factors? I have proposed two "Power Band Reference Values" below that simply attempt to summarize the difference between the maximum horse power RPMs and the maximum torque RPMs, as well as the maximum hp RPMs and the redline RPMs, IMO giving one an indication as to how said engine will behave and be most properly geared.

However, I feel that it would be even better to somehow multiply the PBRVs proposed below by a percentage defined by the difference between the maximum horse power and torque values.

Thoughts?

Mustang GT Dyno Summary v407/377 (Spiney's version)

Invoice:
Race Exhaust
Race Cams

Readings:
407hp @ 7000 RPM
377 lb-ft @ 4500 RPM
redline @ 7500 RPM

Power Band Reference Value*:
2500 RPM
*difference betwen power RPM and Torque RPM=P.B.R.V.

P.B.R.V.TWO^:
500 RPM
^difference between hp RPM and red line RPM=P.B.R.V.TWO

Mustang Boss Dyno Summary v425/510

Invoice:
Race Intake
Race Exhaust
Race Block

Readings:
425hp @ 5200 RPM
510 lb-ft @ 3400 RPM
red line @ 6400 RPM

PBRV ONE*:
1800 RPM
*difference between power RPM and Torque RPM=P.B.R.V.

P.B.R.V.TWO^:
1200 RPM
^difference between hp RPM and red line RPM=P.B.R.V.TWO

[BarbecuePete]

I keep looking at this thread and thinking of ways to use the numbers, but I think you ned more than the peak values for HP and torque... I think really you need HP and torque figures for all 3 values..

So for the mustang GT...

407 HP @ 7000 rpm = ?? lb-ft
377 Lb-ft @ 4500 rpm = ?? Hp
Redline = 7500 rpm = ?? hp = ?? lb-ft

I think these figures would give more of an accurate idea of how an engine produces its power and how broad the power band is in comparison to the available engine revs..

Ah... I've had an idea...

Redline - 7500
Max torque Rpm - 4500
Diff = 3000

3000/7500 =  40%    PBRV 2 = 500  Peak torque = 377

500* 0.4 = (200) * 377 = (75400) / 407 = 185.25

Boss (same calcs) = (562.5) (286875)   675

Need to test more cars but think higher numbers would relate to engines with a low reving narrow power band and high torque and as such require long gearing / FD. Lower figures relate to wider higher reving power bands which don't require such long gearing... possibly 

[bimmerlovere39]

Alternatively, you could do a dyno (pick a gear, run from ~1k rpm to redline, watch replay in stop motion, and record hp & torque readings at approx rpm intervals.  I used 250 for the dyno below, 500 would probably work.)



I don't think I saved the data, sadly    But if you saved data, I'd think you could throw the cars' data on the same graph and get a comparison.

[Hoplee]

without an in-game dyno, I think that the easiest way to sum up an engine requires simply recording the information already provided instead of coming up with a formula that spits out an abstract solution.

for example, the following information pretty much sums up the engine in question:

407hp @ 7000 RPM
377 lb-ft @ 4500 RPM
redline @ 7500 RPM

From those three lines and 5 numbers, we can pretty much tell what kind of engine we're dealing with. I'm afraid that I'm re-inventing the wheel by coming up with new variables and associated definitions/formulas.

Thoughts?

[bimmerlovere39]

I'm with you - those three lines tell a lot.

And if you need more, I stick by my dyno method... I don't know what you meant by it not being in the game    Its just telemetry + excel

[bimmerlovere39]

Heidi - 2005 BMW Motorsport M3 E46 - S54 3.2L I6

Power: 381hp @ 7900rpm
Torque: 300lb-ft @ 4900rpm
Redline: 8500rpm
Rev Limited: 8900rpm

[BarbecuePete]

Looks like the power and tourque go a bit weird after the redline on both those dyno graphs with a little rise back up, I find that on most cars going way into the red before shifting means better acceleration because when you change up your revs drop to a higher point in the rev range where the engine is producing more power... how well it works though seems to depend on how many revs you have before you hit the rev limiter, I think I have some cars with only around 250 rpm between the redline and the rev limiter where others im sure have over 1000 rpm, my B class Cobalt springs to mind, Im pretty sure that has a redline around 6200 rpm but revs right up over 7000rpm...

[Hoplee]

excellent point Pete, now you've got me wondering if 'fuel cut-off' is directly related to cam upgrades or simply the engine in question...

[bimmerlovere39]

Fuel or Ignition...

Hop, I'm not sure I understood your post.   

[Spiny Anteater]

As someone who likes the Cams & Valves upgrade, I have to say that Hop is onto something here. There is a lot less "headroom" above the redline before the rev limiter kicks in when you have the Race Cams & Valves.

One thing I haven't checked though is how much (if at all) the rpm of the rev limiter rises with the upgrade.

[Hoplee]

Boss fuel limiter cut-off stock cams 7200 RPM
Boss fuel limiter cut-off race cams 7800 RPM

[Blooze]

I think these values may be of some value to those who don't mess with deriving an actual Hp-Torque graph from the telemetry (a la my Transmission Sheet). 

As for running up into the red...  as long as the current gear is outputting more torque and Hp than would be available at the entry point of the next gear, then staying in the current gear will be faster (tho the benchmark values will not reflect this.)

I have noticed that the torque / rpm values kind of jump around once the redline is breached, especially when the car's friction coefficient is approaching a stasis with the aero force against it.  It almost seems to me that they are modeling the Valves floating...

$

[bimmerlovere39]

I have noticed that the torque / rpm values kind of jump around once the redline is breached, especially when the car's friction coefficient is approaching a stasis with the aero force against it.  It almost seems to me that they are modeling the Valves floating...

 

Can you explain?

[Blooze]

Floating the Valves is something that happens when the engine is spinning faster than the valve train's ability to close the valve before the cam lobe hits it again.  This can be the result of inertia of the valve train parts (solved by lighter parts, titanium push rods and such, stiffer valve springs and so on.  A similar issue comes from hydraulic lifter "pump up" at higher rpms.  And with older ignition systems, the points can float the same way.

So, along with spinning main and rod barings, and overloading rod beams and wrist pins, these are the reasons there is a redline in the first place.

$

[Spiny Anteater]

As I understand it, it was precisely this problem which led to Ducati (and doubtless other manufacturers) developing driven valves on the MotoGP bikes - the valve springs just could not keep up with the engine at high revs, even with very stiff springs and light valves.

I'm really surprised that Forza has modelled this effect (in a good way) - just goes to show how it can still spring a surprise even after more than a year!