[68WarDog]

Over the years I have built several street 600/700hp engines with little modifications to the 68-70 A body chassis. I've heard that convertible chassis of the same years may require a lot of modifications to handle the same power/ torque level. I'm presently building a 455 that should be about 485-500hp and a little more in torque. I'd like to put this engine in either a convertible 69-70 A body or convertible 69F body. Other than body and suspension bushings, what other chassis strengthening will be required?

[steve25]

All the factory convertible’s have a boxed chassis for the run spanning the passenger section so your easily good with even a 550 hp motor, just don’t put slicks on it .

[69Customs]

Also too the 69 convertibles that had standard transmission had 2 extra braces bolted in the rear end area. Automatics didn't have them. Found that out when I went from an automatic to stick.

[68WarDog]

Originally Posted by steve25

All the factory convertible’s have a boxed chassis for the run spanning the passenger section so your easily good with even a 550 hp motor, just don’t put slicks on it .

Got it. It won't be race other than an occasional spirited jaunt.

[Sirrotica]

The convertible chassis are actually stiffer when ordered in a hardtop car, there used to be an option to order them new that way.

Hardtops are C channel along the rocker panels, the convertible chassis is boxed in that area. They will still bend because of the loss of the roof to stiffen the body. The best option we used when building stock cars was get a convertible car, weld in the cage and then weld a hardtop roof on it. Fine if you're wanting a strictly race car, but not for a driver.

Putting a street type roll bar in a convertible will help immensely with stiffening the whole car, but many people won't want to cut the car up and put bars in it.

There are ways to stiffen the chassis underneath with X members and extra bars tying the front and rear together, but it will not work as well as roll bar with struts running front and rear to triangulate the chassis. Losing the roof panels also loses a lot of stiffening from front to rear. If you compare a street car to a car with a cage in it, it's apples to oranges. It all depends what you want to end up with, how much work and money you want to invest, and what you feel you want to compromise.

Convertibles that are drag raced many times end up with wrinkled quarter panels without some sort of bracing or cage to limit twisting. I've even seen sedans, and hardtops wrinkle the quarters too.

[Radman]

NHRA rules for a roll cage are different for a convertible. Any one faster than 13.49 needs a 6 point roll cage the last time I checked.

[performerrpm]

a convertible F body may not appreciate the 6/700 hp quite aa much as an A body since its a uniboy. I woukd definitley add subframe connectors if you go that route. I used a convertible frame for my 65 prostreet car...definitley a better frame to start with.