rear end ratio questions

[eschaider]

The Second Strike Gearing Calculator that MarkIV over at Time Machines pointed you at will give you a good way to model engine speed and vehicle speed based on your transmission, tire and rear gear choices.

The choice of how tall or short a gear/ tire/ transmission gear set package you use in your car will largely be determined by how much torque your engine produces at off idle speeds. If you have a 275 HP engine (probably at 4400rpm?) you only have about 330 or so ft/lbs of torque at that 275 HP rpm.

Most engines will peak their torque before they peak their hp so lets say you are somewhere around 350 ft/lbs of torque at peak torque. Your off idle torque will be significantly lower and you will need to crutch that with mechanical advantage in your overall first gear starting ratio.

How you go about doing that will ultimately come down to personal preference. The wide ratio TKO gearsets will provide you the transmission component of the mechanical advantage you need and then you just have to decide where to put tire size and the ring and pinion to suit your preferences. This is where the Second Strike Gearing Calculator is so helpful. Of course alternatively you could also solve the problem using the close ratio TKO gearset and a different arrangement for the other components.

In the end there are no absolute answers there are only personal preferences. The Second Strike Gearing Calculator will help you translate those preferences into parts choices. I believe you will find that it is much less costly to make a mistake and correct your selections in the modeling software than in real life.

Also worthwhile noting is that, modeling software is sometimes a bridge too far for some folks. All kinds of reasons for that but for some it is simply a bridge too far. It turns out that is OK too. In that situation you just proceed according to your instincts and buy the parts you think are most appropriate for your usage, put them in, drive the car and make changes as you see fit.

Either way you get what you want, which is what you were originally looking for — I think.


Ed