Cam, rear gear and torque converter relationship?

[69PaleHorse]

I've noticed a few threads requesting suggestions on torque converters, and rather than hi-jack those threads with this question, I thought I'd pose it here.

What exactly is the relationship between the cam, the rear gear and the torque converter?

I am going to assume that the cam helps to determine the powerband, therefore, the torque converter should be spec'd to work with that. But I'm not sure I understand the rear gear aspect.

The reason I ask all of this, is because I will be putting in my new B&M Street and Strip C4 soon, and it will need a torque converter. The cam swap will be done in the near future as well (probably along with the EFI swap) but I doubt my 3.00 gearing in the back will change...so what do I need to know here? What suggestions do y'all have?

Thanks!

 

[SadbutTrue]

It all is geared to get you in your powerband faster. A well built engine is built around a specific RPM (ie, built to make power from 2000-6000 rpm, or 4000-8000, etc). The heads, carb, cam, intake, and even displacement will all reflect this (if you do it right... this is why parts matching is important, why pairing a stock cam with AFR heads isn't a great use of money, why a huge cam with stock intake and heads is a massive waste of time, etc). The cam is probably the most influential part as far as power band goes. When you buy a cam, make sure all the parts (Engine and throughout the drivetrain) are matched to it (usually cams are rated, like above, in power ranges. if you match this to your intake and then pick carbs and heads according to mathematical rules/common sense, you should be good to go).

A torque converter, in simplest terms, defines the beginning of your powerband. A 2k stall converter engages at roughly 2000 rpm, depending on the motor. This is great if you have the aforementioned 2000-6000 rpm motor, because you'll be making big power instantly. If you had a stock converter (around 1500 rpm, i think), you'd have about 500 rpm of mediocre power before getting to the good stuff.

Rear gears do something very similar. They allow an engine to rev faster, especially off the line. This has the same effect... it can get you into your power band faster. 2.8 rear gears won't work in a high rpm/high hp application, simply because it'll take years for you to rev to those high rpms. But plug in some 3.73s and you're there in no time, and they'll help you stay there.

Sorry for the book, but yeah.

 

[jerry S]

you could do that

The cam is probably the most influential part as far as power band goes. When you buy a cam, make sure all the parts (Engine and throughout the drivetrain) are matched to it

or you could have a custom grind cam done up after you have flowed your heads and matched a carb to your application.