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Depends on what you want to accomplish. Rear sway bar is standard on a BB C2 to counteract the tendency of a nose-heavy car to understeer. I wouldn't recommend puting one on a SB C2 unless you want to increase oversteer.
If you are racing your car or are more concerned with optimum handling over optimum comfort, a rear bar can help you fine tune handling but typically requires a larger front bar to maintain handling balance. However, just asking about a rear bar without first determining your intended purpose and considering spring rates, shocks, tires and alignment misses some critical components.
you already have a larger than stock bar so adding the rear bar will give the car more of a neutral feeling when pushing through turns. I would think currently that the car would be under steering, front end plowing, when pushing through turns. I have a 69 small block with the 1 1/8" front bar and the factory 9/16" rear bar.
I agree with Mel that, with that really large front bar, your car probably understeers at the limit. Experimenting with various sizes of rear bars could bring your car's handling at the limit back to neutral or, preferably, with a slight amount of understeer.
But to what point and purpose?
You won't be racing the car so you don't need to have such a finely tweaked suspension. My suggestion would be to reduce the size of that front bar instead of adding a rear bar. I think you'll notice your ride comfort improving.
FWIW #1: My street driven '63 has its stock size front bar (3/4", 15/16".... don't know, don't care) and it is extremely comfortable with negligible amounts of body lean up here on Sierra road curves.
FWIW #2: That 1-1/8 front bar on your car is 46% stiffer than the front bar on my vintage racer (see avatar). I don't run a rear bar. Handling at the limit is darn near neutral and very forgiving of a no-talent driver like me.
Jim
Last edited by jim lockwood; 02-21-2019 at 02:12 PM.
Achieving the proper handling balance depends on who's driving, in my experience. A friend with a 67 BB Vette he autocrosses has a 1-1/8" front bar and some kind of rear bar and the car is nearly underivable for me; it over steers like a pig when I autocross it, but for him it goes great. I've tried nearly every combination of front and rear bars when autoxing my '67 327 and overall I like the stock setup best, with the OEM front bar and no rear bar. A close second, though, is to keep the OEM 327 front bar and add on the OEM 427 rear bar. The car feels more lively because it understeered less and you can easily get it to oversteer with the throttle; this works fine on the street too, although it roughens the ride a little, since a sway bar is an extra spring. So, yeah, a rear bar "helps" by making the car more lively to drive.
Achieving the proper handling balance depends on who's driving, in my experience. A friend with a 67 BB Vette he autocrosses has a 1-1/8" front bar and some kind of rear bar and the car is nearly underivable for me; it over steers like a pig when I autocross it, but for him it goes great.
Sounds like the kind of handling Dave McDonald would have loved..
I am planning on doing some handling up grades to my original 65. I WAS planning on buying Avon 205/70 x 15s but am re-thinking that because they may be too soft for my street driving.
I am going to put QA1 shocks on and do a sport type alignment.
I have been thinking about increasing the size of the front bar and adding a smaller rear bar but don't know if it is necessary for my street driving?? Will I be overdriving a good street tire? Currently I have Coopers on the car but of course they are not really a sport tire.
Get the tires and shocks installed. Install hard bushings in the front anti-roll bar links. Then tune the shocks. Figure out a course that has a lot of dips and bumps, and try it at various settings. You might start out with the softest, run the course a few times, then go to the stiffest settings. Those are the boundaries and you should be able to find something in between that meets your needs.
Only then do you start messing with anti-roll bars.
I believe you'll find the above setup has minimal understeer, is forgiving at the limit, (i.e. doesn't snap into oversteer at the limit or on trailing throttle as base suspension C2 small blocks are prone to do) and the ride will be about the same as OE, which his to say somewhat firm, but not overly stiff... actually rather pleasant compared to some modern sporty cars.
When doing chassis tuning you do ONE CHANGE AT A TIME, so you evaluate the result of that ONE change. Do two or more and you will be chasing your tail. I think you'll be happy with the above setup.
I upgraded my small block car to a larger front and added the rear bar and for me the difference in handling was negligible and I eventually went back to stock for a smoother ride. I may still have the upgraded bars if anyone is interested.
What do you like- inherent understeer or do you best lay it out oversteer?
What tire size type! You can add all kinds of spring pressure to your tires, either at the corners or enhanced by bars, and depends on whether they will hold! Narrow tires with bigger bars, never smart! But most guy get away with it, as they unweigh the inside as the outside looses grip and both slide way before the chassis capability!
Bigger sway way bars are best, if you go soft on the springs. And then only to the limit of your ultimate tire adhesion! If you add double adjust and dial the rebound, then you can improve inside tire tracking, as long as you have some extension in your mounting! The shock can lift your tire too, on the extreme!
Achieving the proper handling balance depends on who's driving, in my experience. A friend with a 67 BB Vette he autocrosses has a 1-1/8" front bar and some kind of rear bar and the car is nearly underivable for me; it over steers like a pig when I autocross it, but for him it goes great. I've tried nearly every combination of front and rear bars when autoxing my '67 327 and overall I like the stock setup best, with the OEM front bar and no rear bar. A close second, though, is to keep the OEM 327 front bar and add on the OEM 427 rear bar. The car feels more lively because it understeered less and you can easily get it to oversteer with the throttle; this works fine on the street too, although it roughens the ride a little, since a sway bar is an extra spring. So, yeah, a rear bar "helps" by making the car more lively to drive.
Autocross needs specialized setup, or you are just an also ran! I would have to watch a run, to help someone! Some guys benefit with stock seats to have big overkill bars, to maintain level, and oversteer the crap out of it! Some with OEM actually stay in the realm of the tires they have, softer, can handle the lean, etc. Where guys get fast, is not with bar changes, but more handling drive, and positive corner entry. A severely under steering car throws away generally the after apex, grip, and I have seen guys driving techniques induced beneficial oversteer to negate the plow. But that is rare! Oversteer on an autocross is just so wrong! I call that drifting!!!!!
Get the tires and shocks installed. Install hard bushings in the front anti-roll bar links. Then tune the shocks. Figure out a course that has a lot of dips and bumps, and try it at various settings. You might start out with the softest, run the course a few times, then go to the stiffest settings. Those are the boundaries and you should be able to find something in between that meets your needs.
Only then do you start messing with anti-roll bars.
I believe you'll find the above setup has minimal understeer, is forgiving at the limit, (i.e. doesn't snap into oversteer at the limit or on trailing throttle as base suspension C2 small blocks are prone to do) and the ride will be about the same as OE, which his to say somewhat firm, but not overly stiff... actually rather pleasant compared to some modern sporty cars.
When doing chassis tuning you do ONE CHANGE AT A TIME, so you evaluate the result of that ONE change. Do two or more and you will be chasing your tail. I think you'll be happy with the above setup.
Duke
Duke you are a race track guy!
On a flat parking lot autocross, most with the stock or slightly bigger street tires will never need to cure deflection! As why rubber and poly is generally adequate for these guys, and seems to get them satisfactory speed! The tire adhesion generally ain’t high enough to worry about deflection!
Also with softer street springs and big bars, they can never get shocks right enough to win. Most end up binding the main springs, with excess shock settings! They can get a decent handling car, but not race car capable! But boy does it feel stiff!!!!!
Your tips are great for an actual track!!!!! For tire tracking, it can be good to set up shocks and springs to just barely not bottom or ride the suspension bumpers (softer for adhesion). But that can be dangerous advice for these guys, as we both cut ours down or eliminate those bumpers. Most of these guys have full bumpers and at track speeds, we could be seeing big problems! All of a sudden, they have no more suspension travel, and can potentially wreck or spin or head for a guard rail or tree!
Last edited by TCracingCA; 02-21-2019 at 11:59 PM.
I spent 15 years tracking my Cosworth Vega, and it ended up a giant killer, embarrassing a lot of name brand sports cars, including those beginning with F and P. It took me a couple of years, which was eight track sessions to get it fully dialed in. As a mechanical engineer I have a good understanding of vehicle dynamics and Fred Puhn's "How to Make your Car Handle" was a big help and is as valid today as it was in the seventies when it was first published.
The following Hemmings Muscle Machines article has a good overview of the story.
There's also a brief Youtube clip of me dicing with an ill-handling 911 at Riverside. I'm currently working on converting about two hours or raw video into about a ten minute program.
I spent 15 years tracking my Cosworth Vega, and it ended up a giant killer, embarrassing a lot of name brand sports cars, including those beginning with F and P. It took me a couple of years, which was eight track sessions to get it fully dialed in. As a mechanical engineer I have a good understanding of vehicle dynamics and Fred Puhn's "How to Make your Car Handle" was a big help and is as valid today as it was in the seventies when it was first published.
The following Hemmings Muscle Machines article has a good overview of the story.
There's also a brief Youtube clip of me dicing with an ill-handling 911 at Riverside. I'm currently working on converting about two hours or raw video into about a ten minute program.
Duke
Pros like you should stay away from the amateur autocrossers, because you know too much!
Last edited by TCracingCA; 02-22-2019 at 08:22 PM.
02-20-2019, 09:14 AM
