Question on frame strength; How much HP / Torque can a '68-'69 vert take? I'm considering building a non-numbers matching car with a high performance 540 cu in engine mated up to a 6 speed transmission. However, the frame doesn't look strong enough to go over about 600 HP and the independent rear only about 500; (seen a lot of solid axle vettes out there). I like convertible vettes and they are my favorite car, but don't feel they can take the heavy HP...

 

Just take a look at some old pictures of vintage racing. A lot of the L88 racers were verts. Granted some had roll bars but others did not. I don't think the coupes are a whole lot stronger than verts. As for the rear it seems about 500 HP is it before mods are needed. Now if you are launching with slicks I'd say you are going to need some work regardless of power.

 

Just some information that may help.

There was a procedure written up for strengthening the frames for racing way back then. I think it was done by GM. Never seen the publication, but from what I heard, frame prep included welding up some seams and adding stiffeners. The factory 68 frame is not as stiff as a 69 frame as braces were added at the rear wheel kick-up points. Keep in mind that the birdcage also adds stiffness. The 69 frame is a hard bolt to the body. 1970? GM started using rubber mounts.

I wish I had the ***** to run 600 HP.

As for the verts racing, with the tops installed they had better aerodynamics than the coupes on account of the sugar scoop rear window on the coupes increasing drag. They may have even weighed a bit less.

George

 

I have about 525hp and almost 500 ftlb torque. But it is a small block. Your biggest problem will come from that manual transmission. If you are talking about drag racing "Forget about it". Automatic Transmission with a "FULL MANUAL VALVE BODY" will be faster and just as much FUN on the street. When I had my M-20 and went drag racing, I went home broken 95% of the time. That is power shifting of course. When racing you can't hold back or what's the sense . Put an automatic in the Vette and the car is AT LEAST a 1/2 second faster and going LOTA rounds and having LOTA LOTA fun. It's the best thing I have done to the car. With 4.11 gears I just had a 700R4, full manual valve body, reverse shift pattern, 3800 stall converter and ya know it's more fun AND faster than any manual trans. Good Luck, sounds like a great Vette your going to put together.

 

A lot, as stated MANY of the early C3 race cars were '68 L88 convertibles..

 

Roadracers that is. Probably because '70 & up were 454s

 

They do pretty well really. My '67 rag top has a little over 800hp and drives fine at the track. It runs 10.0s at right at 140 mph.(no cage or rollbar) Now I have added a killer Dana 60 converted into an IRS, but that was only for strength.

I did do some work on the frame when I had the body off the last time. I made/welded plates out of 3/16" steel to fully box in the "kickup" area and eliminate flex there. Before the mods, it did flex a good bit on slicks. It's much better now. The ultimate would be some sort of rollbar or at least bars that extended length of door area to just behind the front control arms. The car will twist on the long expanse area right around the bellhousing. There have been some threads here about adding the structual foam inside the frame rails like new cars have that sounds pretty interesting.

Anyway, overall they do pretty well. Any added stiffness is just icing on the cake.


JIM

 

JIM - meant to ask before, do you have a hardtop or do you run with just the ragtop?

 

Just the softtop. Gets a little wierd at 140 or so!!



JIM

 

i wanted to do this too but in a few years. i was thinking about buying a nice 68 or 69 and putting in a gm crate motor the 572. it has 620 hp. i was just gonna keep everything stock. i shouldnt have to modify it at all. it will do a really good burn out.

 

Go here - www.corvettefaq.com

Go to the "misc" section. You find the link to it in the column on the left side.

About 1/3 of the way down the page is the publication you are talking about. The link is entitled "Chevy Power Book on Corvette - In PDF format (caution: over 8 megs!)"

It is GOOD reading. A nice item to download and tuck away on the old hard drive.

 

657.08374 HP Slicked according to my calculations

 

Outstanding feedback guys. Appreciate the inputs!!!!

 

#%#&%$ I have 658. I guess I'm out of luck
I'd like to see the formula for that

 

Details please?

 

Can we hear more of this

 

Can we see some pics.

 

Many, many moons ago...early-mid 70's or so, the Lingenfelters, Agamans and Coccuzza's of the world were running Super Stocker Vette's that required them to keep an IRS under there. We all know how long that lasts.....

So there were a few folks who looked at a bare Dana 60 housing for a Hemi with no tubes in it and decided it resembled a Vette chunk sortof. Not sure there wasn't beer involved in this discussion....but the advantage of the Hemi one is it has a pinion snubber mount on the nose that help you to build a front lount like a Vette uses.

So those guys got Dana 60's made into IRS setups. I found some old pictures of them in a Hot Rod magazine and started researching.

I located a NOS Hemi housing that had never had tubes put in it. I also found that *if* you were sponsored by Chrysler, you were provided a *special* posi unit that was even beefier than the Powerlok with 6 gears in it. I also located one of those...new in the box! From what I can gather, there were 24 of these ever made...most with spools. A couple went to Alaska for a road racer??? I know where one other is, but he won't sell it. Who knows where the others are???

The housing was modified to accept bolt on axle retainers fabbed out of billet. 35 spline axles were custom made that accept bolt on Spicer yokes to create the "inner" stub axle assy with bearings and seals.

There is an aluminum adapter plate that is 3/4" thick attached to the rear cover mounting bolts with countersunk screws. To that attaches the stock Vette rear cover.

I then modified the bolt in "sombrerro" crossmember to position the diff properly. This took a little work to maintain the correct geometry and to allow it to be a total bolt in deal. I can remove it all and bolt stock Vette stuff back in at any time.

The lower strut rods attach to the aluminum plate and they are positioned to control camber change through the travel. Work great. I gave measurements to Vette Brakes and they made me custom lower arms with Heim joints. I can also add upper bars, but I haven't got around to it yet.

I used Tom's outer 31 spline axles and I had halfshafts made locally out of 3.5"x.134 tubing using 1480 series Diesel Truck u-joints.

You can't get 3.07 gears for a Dana 60...but you can get 3.33.s and 3.54's and up. I wanted 3.07's for highway cruising and for the trans combo I would be using. So a set of Dana 61 gears were shaved on the ring gear back side to position it correctly. The pinion from the Dana 61 is the same as a 60.

Anyway, I did all the installation literally in my driveway. I built a new front mount to attach to stock Vette stuff. I used 1350 series ujoints on driveshaft. The stock Vette springs bolt to rear cover and lines up fine with control arms. It's been under there a couple of years now almost and so far so good! I haven't broken anything yet and it's not for lack of trying!!It's made lots of low 10 sec runs (almost a 9.99!!) at 140 mph and a few test runs past 150 or so and it works perfct. No vibration at all. There's been a few Forum folks along for those rides!

When I did it. it was really out there, but now that new Hemi housings are being made, someone that is just as crazy could do the same thing even easier!


I'm no good at posting pictures, but if you would like to see some shots of it, send me an e-mail.


JIM

 

I once got pics of someone who used a hemi D60, was that yours? If so, I still have the pictures then. It was a diff with custom adapters for the side yokes and all.

 

Probably me....

Has aluminum bearing retainers held on with 3 bolts. The yokes actually bolt onto the the splined ends of the stub axles.

I doubt there are too many others around. I was looking at the Tom's 12 bolt deals, but they can only go down to 3.73's and I wanted lower. Plus there just ain't much out there stronger than a Dana 60. Size matters!!

The Vette uses an 8.2" ring gear, the 12 bolt is 8.875, the 8 3/4" Mopar is just that, then the 9" Ford....then you get the 9-3/4" Dana 60! Anything past that you are into serious truck category. There was the Mopar 9-1/4" and some Fords the same way, but they are wierd and no good parts are available.


JIM