Hey everyone - brand new here, first post, but a big question.

How much torque is too much for a first gen ragtop? How far can you go with subrames and a cross brace?

We are rebuilding the engine in my 1968 RS/SS Convertible - it came to me as, what appears to be now that we have seen the insides, a stock 376 LSX, 4.060 bore, 3.62 stroke, etc...... on the high end when it was fresh it was probably producing 425hp/450 torque. We plan on taking it up to a 427, guesstimating 600=hp/550 torque.

So - I'm wanting to hear from my fellow convertible lovers and see how far they have gone in terms of power, and what they have done to help avoid the body flex (like subrames and cross bracing and ?), and the results over time......

Any input is really, really appreciated. The car will be a cruiser and occasionally slammed, no track duty, no slicks, etc....

Thanks!

 

I don't think you are going to find a lot of guys that have pushed to find a limits. The value of the car and the safety issue of having a rag top really make it impractical. I am sure there are exceptions out there.

My RS/SS is not numbers matching. It does have a 350 out of a 69 SS in it so at one point I did a lot of research. Below is what I found.


The original designers of the first gen Camaro did not design it for a big block. The first car a chevy 350 came in was a 67 SS. GM designed the 350 just for the Camaro. It could not be ordered in a Corvette until 1968.

The idea of a big block Camaro came from marketing after the car was designed. Engineers did not want to do it but marketing won the argument and management forced engineers to make it work.

GM had to release a offset cross shaft for the upper control arm. This was due to frame sag, The subframe would bend in at the top and cause the front wheel to lean in. Dealers had 3 year old cars that could not be aligned. I though it was funny cause you could pull the frame cheaper then you could install the cross shafts but I think GM did not want customers to know their car needed frame repair while still so new. The small blocks would sag but not till close to 100,000 miles ( no I am not that old we learned about that one in alignment class)

Now the rag top was never designed to be a performance car. If you put a jack under a front lower control arm and start jacking you can get one tire pretty high off the ground before the second wheel will lift. When GM marketing tried to get a rag top Z28 engineering said no and won because they had cars they had twisted in testing and adding a stiffer suspension would just make it worse and that was going to be tuff to fix under warranty. There is one first gen ragtop Z28 but that is a whole other story.

Now my opinion.. 500+Hp in a ragtop is a waste in its stock form, the only thing it is good for is driving to shows, showing it off and driving it home. Although it may be better to trailer it. Because of the torque of the big block I would want at least the Hotchkis rag top support setup to really drive it worry free. That assumes you are 100% sure the connection at the rocker panel and the cowl is in like new condition. With anything over 350 HP in a big block I would want a add in chassis. I decided it made more sense for me, if was wanted a fast first gen I would just buy a hard top roller. The combination of the lack of structure, safety and value of an unmodified car made just leaving the rag top alone the right choice.

So the real question is what do you plan on using the car for? NHRA drag rule say you need a roll bar under 13.49. If you are adding a roll bar intergraded subframe connector seem like a no brainer and would box thigs in nicely but it would also kill the value of the car.

IMO the minimum a big block ragtop should have to drive worry free.
https://www.rickscamaros.com/1967-19...SABEgKMhPD_BwE

 

I don't think the LSX will be too much for a convertible. You can take it to a fab shop and maybe they can box in the frame in certain areas, but the car won't fold in half. It WILL want to twist. However, metal was a lot thicker back then. Also, that is why there is X bracing underneath the car, along with frame bracing because cutting the roof off very much affects the cars handling behavior. Some 80's A bodies lift a front wheel on full power take off. I don't think it will happen to your car but it will flex no matter how much you brace the floor. As long as you don't have a 850 ci race motor with 3 shots of nitrous I believe you will enjoy it very safely
Please post pictures!

 

Thanks, Chris. I agree with you. We will be welding in subframe connectors (probably Hotchkis), and the newer style cross brace. I think she will be plenty strong. Will definitely post pics as we get to putting it back together. Just a little mystery now as she went into storage for a few weeks as we build.