I have a 289 Fastback with a C4 transmission and 3.0 Gears in a 9" rear. I recently bought a 302 engine that makes 450-500 hp. I was looking to get higher top end and want to make sure that transmission will be able to handle the hp. Any suggestions?

 

C4's can easily handle 300-400 horsepower and 450 lbs-ft torque. Most transmission specialists refer to horsepower when talking about a transmission’s limits. What’s really going to wreak havoc with a tranny is too much torque, since that twisting force from the engine is going to shock-load the internals. A transmission is especially vulnerable during a hard launch or a firm One-Two shift, especially if there’s a huge gap in ratios between First and Second gear. Once the car is underway and headed towards peak horsepower output, there’s less risk of damage to the transmission. So when deciding to keep the C4 or not, determine peak torque at launch, and not worry too much about the horsepower.

 

If your current tranny is stock, I would not consider using it for your new motor. A built-up C4 will work fine but you'll have to spend some bucks. Check TCI's web site to get an idea of how much tranny and $$ you'll need. A small block with that kind of HP probably has a pretty nasty cam. You'll need a stall speed converter to match also.

 

A built up C4 will handle that motor but you better get rid of those 3.0 gears. A 302 with that much hp will have no low end torque whatsoever and will be a real pig until you are moving about 40 mph. You're also going to need a torque convertor with at least 3000 rpm stall speed. With the 3 to 1 gears you will be revving under your stall speed at anything below about 75 mph. You will have huge slippage and heat problems.
Get a C4 built up with a 3000 - 3500 rpm stall convertor and maybe a set of 3.90s or 4.11s.
If you want top end get a 5 speed. The power band in an engine like that will be narrow enough that you will never get decent low end and decent top end with a trans that has only 3 speeds.
If it were mine I'd get a 5 speed manual with 4.11 gears. The best of both worlds. You will get a good launch and decent top end with the overdrive. As far as I'm concerned 3 speeds just don't cut it in today's world. Unless you never drive on the highway or never drive around town. With only 3 gears you can have low end or top end but you can't have both unless you have a 400 plus cubic inch torque monster.

 

Well put!