I'm sure the question has been asked hundreds of times here, but I am looking for feedback on how much Hp and torque the factory drivetrain on a 73 can handle?
I'll try to sum this up quickly. I am performing a body off restoration on a 73 non #'s car and question how far I want to go with the motor. I'll spare you all the rant an sum this up quickly. The original block is long gone so I have been taking to my engine builder about a dart 400 block stroked with aluminum heads and a roller cam puting out 400 to 425 hp. Can the factory 4 speed, drive shafts and rear tolerate the excessive power, and do any of you have any recommendations on upgrades. The car will mostly be used for weekend drives but I can't guarantee it won't end up at the track once or twice.

 

If you only have 400 to 425 with a 400 Sb and a roller cam with good heads something is wrong. With that combo you should be in the 500HP range easy. The trans should be OK, I should know that Muncie pretty good. The rear and half shafts will need some well built components but can stand 500 HP as long as slicks are not used. It is not the HP that breaks this it is traction. I have seen 400 HP break everything on slicks.

Look at my combo. a 385 with a big solid flat tappet and good heads and I am just shy of 500 HP. You could easily be 500 to 550 with what you are talking. With a 400 block put in a crank and get at least 421 ci. If you are buying a crank might as well by a bigger one.

 

Gordonm, you can't say that!!! Even though 500hp is very possible he may want to go with low compression for cheap gas and small valves for low end torque IMO. The muncie will hold up if its in good shape. If its a Saginaw it will last as long as you don't power shift w/out the clutch. Good Luck and have a blast!!!

 

Starting line technique at the track will make a lot of difference in the life expectancy of your drivetrain.
If you dump the clutch at 4000 rpm on sticky tires, your gonna need a bucket for parts.

 

You are not going to put on aluminum heads and a roller cam and go with low compression and small valve heads. Why waste the money. A 350 with iron heads and a flat tappet cam can give him 400 HP. By the sounds of it he wants something with power. Aluminum heads with a roller cam is a waste of money on a 400 producing 400 to 425 HP.

It is a Muncie. It came out of my car. I can tell you it saw many a hard shift behind my old 420HP 350 at 6500+ rpm.

 

Hey Gordon Thanks again for the great deal on the trans and components.
After 2 to 3 years I have finally gotten the time and saved up some extra $$ for the project. I decided to go body off and build it right from the beginning. It may take a few years, but I'm in no rush, and I'm still completely scattered on where I want to go with it. Every one knows how these things tend to escalate and spiral out of control without a set plan.

I guess I was just being a little modest or humble on the hp numbers. My original thoughts were on a simple drop in gm fastburn 383 crate motor making about 425 hp. A dart block and rotating assembly paired with aluminum heads was suggested by Don at the shop that rebuilt the engine in my Green 73. A lot of this is new to me being a newbie at the Hp game but (Gordon you are right) , he said if you are looking to make 500Hp or more aluminum heads with big valves and runners and roller cam at around 11 to 1 compression this would be his suggestion. He cautioned me on the drive train strength and how I planed to put the power to the ground. How much money did you plan on spending and what do you plan on doing with the car were his exact words. So Now I need to make a plan so I'll be putting all suggestions and advice on the table.
My original plans were to build the car to drive and have fun on the street. At this point in my life I don't have time for the track. Then again the future is never that far away, and the track is the only place you can drive your car to it's or your fullest potential. So my plan is to build a car that can do both. There is nothin like goin through the gears to take your mind off things.

 

For the IRS you can use 3" shafts or 3.5", 31 spline axles, or Toms 17, the diff should have a polished and tuned posi maybe 12 bolt spiders fit, then there's the 12 bolt but that really isn't needed unless you're going over 500 hp, have sticky tires and will push the car hard.
As with all these projects money is the limiting factor.