BicketyBam

My spreadsheet is at work, but here are the formulas that you can use to make the spreadsheet:

MPH = (rpm x tire diameter) divided by (gear ratio x 336)
RPM = (mph x gear ratio x 336) divided by (tire diameter)
Ratio = (rpm x tire diameter) divided by (mph x 336)
Tire Diameter = (mph x gear ratio x 336) divided by (rpm)

All of these formulas have you use the RPM's from 4th gear, which is 1:1. If you multiply the RPM result by .62 you will get the 5th gear RPM's

Here is how you can make a spreadsheet that calculates your speed at a given 5th gear RPM:
Type the follwing words in the following cells

A1 - RPM
A2- Tire diameter
A3- Gear Ratio
A4- MPH in 5th

Then put this into the following cells:
B1 - type in the 5th gear rpm you are using to determine your actual speed
B2 - type in your tire diameter
B3 - type in your gear ratio (3.73, 3.9, 4.1, etc.)
B4 - type this exactly: =(B1*B2)/(B3*336)/0.62

So in my case, at 2400 RPM, with a tire diameter size of 23.5 inches and a gear ratio of 3.90, I am doing 69.42 MPH
If you change the formula in cell B4 to: =(B1*B2)/(B3*336) you will then get your 4th gear speed at that given RPM.

I had to play around to get my tire diameter. I knew that with my stock gears at 70 mph in 5th gear I was doing a hair over 2,000 rpms (I guessed and called it 2030 rpms). That's how I determined that my tire size was approx 23.5.

If you have no clue about Excel spreadsheets, PM me and I will email you the one I have on my work computer.

Martinrulz

If you just install the performance tune do you still need 91-93 octane?

The Great Cornholio

Yes

BicketyBam

Technically, I am not 100% sure of the answer, but why would you choose to put anything less in anyway? The differnce in price is about $3-$4 a fill up. I have always put in super from day 1, but that's just me. I do believe that the performance tune slightly advances the timing, so to play it safe, I'd say yes.

mikeyb6927

Are the tuners worth spending the money on because i was thinking about splitting one with my dad who also has a mustang!!!

SilverGTV8

You can't share them. Once it is used on a car it is locked on until the factory tune is reloaded into the original car.

They are if you are not planning any serious engine mods in the near future. They can still beused then but aren't as effective and the tune is that would be used is beyond the capabilites of the handheld tuner.

Martinrulz

So the best thing to do is run the car almost out of with previous grade of fuel first, fill up with 91-93, then install the tuner?

Fat Nick

You can go in and change the one thing and install it and be done. The safe way is not mess with a/f or timing AT ALL until on a dyno.

Fat Nick

You can go in and change the one thing and install it and be done. The safe way is not mess with a/f or timing AT ALL until on a dyno.