Frames

[Joe L.]

Re: Frames - Interesting thoughts so far

Mike------

This subject has been brought up and discussed several times before on this board.

I'm quite sure that the holes and weld nuts were not added at St. Louis. I'm not saying that it NEVER occurred, but I'm sure it would have been the rare exception and not the rule. The holes and the weld nuts are installed at the time that the frame is manufactured. It's virtually impossible to add the weld nuts AS THEY WERE ORIGINALLY INSTALLED AND WELDED to the frame after it is completed.

There were at least several part numbers for the frames in any given year. The part number that you see in the AIM for the 1968 frame is that for the 68 frame with base engine and manual transmission. There was another frame for base engine and auto transmission. Likely, there were also frame part numbers for the big block frame ASSEMBLIES, standard and auto transmission. Unfortunately, these part numbers do not appear in the AIM. They are contained in the "Bill of Materials" for the options and we don't have that information for non-AIM-illustrated components of the option packages.

SERVICE parts information is no help here, either. For SERVICE, the frames were often consolidated into 1 or 2 part numbers---frome 68-on the only distinction between SERVICE frames was year model and auto or manual transmission. I'm quite sure that all the SERVICE frames had the holes and weld-nuts.

[Dave F.]

Re: Frames - Interesting thoughts so far

I have to ask: Is the difference in performance of having a rear sway bar on a small block worth the penalty in loss of judging points?

[John H.]

Re: Frames - Interesting thoughts so far

Small-blocks don't need a rear stabilizer bar - development engineers worked long and hard to develop the proper roll couple distribution for the small-block cars; adding a rear stabilizer bar without adding a larger front bar will just increase rear roll stiffness, resulting in earlier onset of limit oversteer (when it swaps ends). Catalogs and hot-rod magazines don't tell you that - they just want to sell "whizbang" hardware, and have zilch knowledge of vehicle dynamics.

[Joe L.]

Re: Frames - Interesting thoughts so far

Dave------

With either the standard or HD suspension, I don't think that the rear sway bar will improve the handling of a small block. In fact, it might make it worse.

Sway bars have to be sized and installed not as a "stand-alone" piece but as part of a fully engineered suspension system. That means that many factors go into the decision to use a combination of suspension components. Vehicle weight, weight distribution, shocks, front and rear springs, configuration of the front sway bar, and numerous other factors go into the design.

If I were going to use a rear sway bar on a small block, I would take advantage of GM's engineering and use only the 74+ FE-7 set up. This uses a 1-1/8" front bar with a 7/16" rear bar in conjunction with HD shocks/springs, front and rear.

All of the GM components of this set-up, except the HD rear shocks, are discontinued.

[Dave F.]

Re: Frames - Interesting thoughts so far

So, if someone wished to use a rear sway bar on a small block, using a larger diameter front sway bar would put roll resistance back in balance - right? In that scenario, what would be the resultant "street performance" characteristics?

[Dave F.]

Re: Frames - Interesting thoughts so far

Joe,

What I am faced with is the frame I bought to replace my rusted beyond repair 68 L79 is a 68 big block frame, complete with all suspension components, rotors, front/rear sway bars. I have the luxury of reusing the small block suspension, as it all can be salvaged, or use the big block suspension as it is all intact. All parts from both frames have been stripped and repainted (except for one set of control arms), so whatever I don't use will make for good swap meet stuff. From a "performance only perspective", which to use is the decision I'm wrestling with right now.

[Joe L.]

Re: Frames - Interesting thoughts so far

Dave-----

Unless the big block car frame had F-41 suspension, the only real difference in the suspension components will be the front springs, front sway bar, and rear sway bar. I would definitely NOT use the big block front springs for the small block car or you might well get an unsatisfactory ride height.

If it were me, I'd use the small block 3/4" front stabilizer bar and NO rear bar. You could try the big block 7/8" front bar and 9/16" rear bar, though. Then, if you don't like the way the car handles, simply replace the front bar with the 3/4" and remove the rear bar. It's not that big of a deal to R&R the sway bars.

Also, since the donor car is a 1968 big block, could you please check and confirm the OD of the FRONT and REAR sway bars on it?

[Dave F.]

Re: Frames - Interesting thoughts so far

Joe,

I am using the small block springs. The donor sway bars must be aftermarket - 1 1/8" front and 3/4" rear. I assume this combination really reduces body roll beyond comfort level (normal cruising use). Thanks for your expert advice.

[Timothy B.]

Re: Frames - Interesting thoughts so far

Check with Vette Brakes. They sell kits and have lots on info on sway bars sizes and recommendations. I have the kit that has a supposedly balanced front and rear bar for a small block, plus 'grand touring' front coil springs. If you go that route, you might consider the smallest rear bar and the appropriate front bar.

[frank mccracken]

Re: Frames - Interesting thoughts so far

As usual, John and Joe are dead on. I installed a 7/16 rear sway bar on my '65sb with a 3/4 front bar. The oversteer was horrible. I was amazed that a wimpey little sway bar like that would make any difference [good or bad] at all.

[Duke W.]

Re: Frames - Interesting thoughts so far

An anti-roll bar's contribution to roll stiffness varies with the FOURTH power of its diameter.

Bottom line, a 1/16" change will create a noticeable change in balance (oversteer/understeer), and going from no bar to even a small bar = BIG change.

Now you know why SBs did not have a rear bar. The change in the rear strut rod bracket in '68 lowered the rear roll center, which reduced the roll stiffness contribution from the spring, but when GM finally offered a rear bar on the SB in '75 as part of the FE7 package it was combined with a 1.125" from bar, which is FIVE times as stiff as the C2 base suspension 3/4" front bar.

Duke

[Tom R.]

Re: Frames - Interesting thoughts so far

I'm hearing conflicting information..."small blocks don't need rear sway bars!" yet the most depowered smallblocks could be equipped with the most massive front/rear sway bar in Corvette history. The latter of which was engineered by those engineers that had studied it for decades.

So, help us understand this incongruency.

[Duke W.]

Re: Frames - Interesting thoughts so far

C2 Corvettes with the base suspension were very neutral handling - just enough understeer most of the time to keep you out of trouble, but with very spirited
driving they could be tricky and were prone to swap ends.

In the mid-seventies GM couldn't sell much horsepower, so they put togther the FE7 Gymkana Suspension that had MASSIVE roll stiffness. They started out with the F-41 springs then stiffened it up more with big bars. By going to
a 1.125" rear bar they had to balance it out with a small rear bar.

If you want to increase the roll stiffness of a C2 SB a large amount, or
for whatever reason think it needs a rear bar, you better install the 1.125" front bar up front at the same time you install the 7/16" rear bar.

Duke

[Tom D.]

Excellent Discussion - Thanks *NM*

[Timothy B.]

Re: Frames - Interesting thoughts so far

The 1 1/8" front bar and smaller rear bar (I think it is 7/16") is what Vette Brakes sells as a suspension upgrade kit for small blocks, along with a 460 lb/in "GT" coil front spring. So far, I have the large front bar and springs installed. There is a significant difference already. I think I may have a go cart now...and I haven't decided whether I like it or not!