I had posted this in the new member thread, however I thought these "calculators/graphics" might have broader appeal and decided to start a new thread

Here are a couple of online "calculators", revised from my "Mustang and Miata" days of 15-20 years back: the first charts M37 (or 56) theoretical top speed(s), it shows speed v. engine rpm in each gear assuming the engine could produce sufficient HP to attain that speed.

M37 Speed in Gear Calculator

Looks like this:



The othercalculates how much horsepower (at the wheels) would be required to push a M series to an indicated speed. It is based on the vehicle being locked into 5th gear as that is the gear in which engine output and top speed are most likely to be in alignment (for an M37). THe column labeled "RPM (JATCO 7-speed in 5th) 3.35 - 2.61" displays the engine RPM at the indicated speed (1st column) for the M37 (3.35:1) and M56 (2.611:1) final drive gears and the tranny being in 5th gear.

M Series HP v. Speed Calculator

It looks like this:



Many assumptions and assertions are made in the vehicle description" input section--I have based these on data from the web and other sources. However the formulae behind the calculations have proven themselves solid over the tears.

I welcome any comments/feedback...

FWIW -- I understand both the M37 and M56 have 155 MPH speed limiters as required by the USDOT--my SL500 had such a hardwired restriction , however in reality it topped out at 153.8 per my GPS...

Those are impressive graphs, thanks for sharing. I can see myself referring to them for an upcoming project.

Quick question - what would it take for you to replicate the last 2 columns of the HP required at speed graph for the M56? - Horsepower required and fuel consumption.


Also, I like the wheel and tire considerations. From your experience, how do those numbers compare in calculations versus real world application?
I know that the total vehicle weight is accounted for, but see, that could be distributed into rotating mass. Keeping all else constant, we can compare a RWD M37 with the base brake system and 18" wheels versus a RWD M37 with the Akebono rotors and 20" sport wheels (HEAVY).
It is easy to understand that lighter wheels are better for "performance" as a general term for acceleration, but rather counterintuitive is that larger wheels might be advantageous at constant highway speeds (like flywheels)
... I am just curious if that's a calculation you've done for any of your vehicles.

THe HP required to maintain a selected fixed speed for the M56 can be calculated by adjusting the total vehicle weight to that of the the heavier car, as required HP to maintain a speed is disconnected from acceleration (and therefore rotating mass) so no other changes are needed. I have dove work with acceleration factors on other vehicles, however the number of variables makes creation of a simple graphic webpage a less than -2-3 task.

The "speed-in-gear" number are just simple calculations, no guesswork so they are quite accurate--however the "HP v speed" calculations--though not rocket science (but not too far removed)-- involve a number of variables as provided and some "behind the page" assumptions as to their interactions; therefore those numbers have a bit more "fudge" in them. I would guesstimate they are ±10% though. I have tweaked those assumptions and the applied formulae over the years as empirical evidence has shown them in error.

FWIW my experience with MTs has been has been that one pound removed from the crankshaft flywheel/clutch assembly is worth five pounds removed from the wheels/tires. I installed a lightweight flywheel (9 pounds lighter than stock) in my '03 Mustang Cobra and it was a night and day difference...

In reviewing my work I found that the MPG calculations on the M series HP v. Speed Calculator were hardwired to 0.5 (lb/HP) B.S.F.C. (Brake Specific Fuel Consumption)) and 6.35 lb/gallon fuel density (100+ Octane fuel). These were viable parameters for my "03 Mustang Cobra running 15+ psi boost and the aviation fuel I had to feed it--however for our cars they were not valid. In correcting this I added "combo" boxes for selection of B.S.F.C. and octane, and set the defaults to values more appropriate for our cars:



I do not know what reasonable B.S.F.C.s for the VQ37VHR or VK56VD engines are, so I set it at 0.475 lbs/HP as a starting point--the effect on tHE MPG calculation s in minimal, however if anyone has any specific knowledge re: same I would love to have feedback. B.S.F.C. and VE (Volumetric Efficiency) are intertwined, and I suspect the VVEL M37 engine ha a superior VE as compared to other engines with less sophisticated vale trains...

I had an inquiry from a 370Z enthusiast asking if I could add options for the 370 to the Speed In Gear calculator. I have done so for both the manual and automatic transmission-- thought I 'd post about it here as well: