ajrothm

I am hoping to get some advice for a rear away bar addition and maybe a front sway bar replacement on my 71' big block car. My car is primarily just a street cruiser and drag racer, however, we are planning a road trip in July and will be driving from Galveston area to Bowling Green, then to Deals Gap and try out the Tail of the Dragon, so I am planning on adding a rear bar to help reduce the rear body roll that the car seems to have. I will not be road racing or auto crossing, just some nice curves on public roads and I'd like to improve the feel of the car, particularly in the rear. The front end feels pretty well planted and minimal body roll considering, but the rear seems to have a lot more sway/roll.. After searching tons of threads on sway bars, I'm more confused as to what to try.

My car is originally an SB car, so it has the small front sway bar and no rear sway bar, so my first hunch was to just buy factory big block sway bars front and rear, add poly bushings and try that but I'm curious to see what you guys think. I won't be changing any main suspension parts, only sway bars. Also I will be on stock rally wheels with 245/60/15 BFG Radial TAs front and 275/60/15 BFG radial TAs rear, so it's definitely not going to handle great, I'm just looking for a bit more stability.

My current parts are as follows:
FRONT:
Moog 474 lb front springs
KYB Gas Adjust shocks
Rubber bushings
Stock SB Front sway bar with poly end links
Springs/bushings/shocks are 1 yr old and maybe 2k miles

REAR:
TRW 340# rear fiberglass spring (about 25 years old and 40-50k miles)
QA1 single adjustable shocks
Rubber bushings in everything, about 10k miles on it all




I normally drive around on drag radials all the time but will be going back to a fresh set of BFGs so I know handling will improve a lot with that alone, but now I'm thinking about the sway bars.. I don't want to make the car ride rough as it's mainly an around town car...
Would a set of big block sway bars and poly bushings be a good plan for my use? I just don't want to get to the dragon and have a car that is wallowing all over the road.

I may entertain replacing the rear spring as well just to put a fresh one on so I don't have to worry about a failure, but this ole TRW spring has been great, I kind of hate to change it. Car weighs 3660lbs with me in it and 1/2 tank of fuel.

Thoughts?
Thanks in advance!

jb78L-82

You will get all kinds of advice on this topic. Here is my story and advice after 37 years of playing with the suspension on my 78 L-82 4 speed Gymkhana suspended C3:

The car was a bone stock gymkhana suspended car when I started-stock front and rear steel spring, Delco shocks, front bar 1 1/8 inch and a rear stock OEM sway bar 7/16 inch with stock rear GM end links. The first major change was removal of the stock 7 leaf rear steel spring and the installation of the 360 mono spring in 1986-Like you its been on the car a LONG time. In 1983/84 I changed all the sway bar mounting bushings and end links to poly. I also ran front Koni oil shocks and KYB gas A just in the rear with this setup for about 20 years. In the 2000's I changed the shocks (Bilstein Sports in the rear and HD's in front), new 550 front springs, and the addition of a 3/4 inch rear OEM style bar with stock oem type end links (NOT the aftermarket rear bar end links that restrict trailing arm movement). No change to the front stock/OEM bar. The car handles great and is not tail happy-very neutral near the limit of adhesion.

I think that your front springs of 474 are too soft for a BB car and should be 550 for the right balance like the gymkhana SB cars especially with that BB engine (650-700 lbs). The rear spring of 340 is good for a gymkhana SB and perfect for the BB cars. I would add a rear GM OEM type bar of 9/16 inch which was stock on the BB cars and see if you like the ride, balance and handling. You can always go bigger in the rear later (3/4 inch like mine) if you find that the car understeers too much. If the car oversteers too much for your liking with the 1 1/8 inch stock size front bar, you can reduce the rear bar to a GM oem 7/16 inch rear bar (or no rear bar-not my recommendation for handling) or go bigger on the front bar-1 1/4 inch. Going with the stock GM size bars is probably a good starting point. I would also suggest replacing those front KYB's with Bilsteins (HD's or sports). The rear QA1's, I have heard are quite good but no real experience with them.

A stock BB C3 has a nose heavy weight bias-51-52% F;48-49% R unlike my 78 SBC which is stock F48%:R52%. The added front weight bias will naturally make the BB cars understeer more than a SB car. You actually have a more built in safety cushion with the BB cars since most people do not like oversteer on street cars. Duntov much preferred the SB cars as the handlers of the the group since the slight rear weight bias of the SB C3's is preferable on the track. Just about every high performance and big $ sports cars sold today have a slight rear weight bias like the SB C3's!Just read an article on the new Mercedes AMG GT-$130,000-which has a weight distribution of 47%F:53%R-well I'll be...

Hope that helps!

ajrothm

Wow! Great post.. Thanks for that.
As for the front springs, I just put them in last year. I had been driving/drag racing the car with the original 150k small block front springs, they worked excellent at the track and rode smooth on the street but the car would bottom out over fast dips and wallow like a pig in turns. I went to the Moog big block replacement springs which were a good bit shorter, supposed to be 1" lower then stock ride height and I believe are 474 lb rate. The car drives 10x better with these springs. They did hinder my weight transfer to the rear wheels a good bit when drag racing but I think they will be a good compromise. I'm sure they are not ideal for pushing hard in the curves but I would prefer to keep the ride quality I have now and more importantly not hurt my weight transfer any more then it is for drag racing.

I think I will try the 9/16" sway bar for the rear, will that match up ok with the stock small block sway bar (15/16" I think) with poly bushings or should I jump to the 1 1/8" bar?

I will use GM bars, probably try to find some used ones on the forum.

redvetracr

I have what you want right here...15/16 front, 1-1/8 front and a 9/16 rear with most mounting hardware....send a PM if you or anyone else is interested.

jb78L-82

I don't know the stock front BB sway bar size but the BB cars did have a 9/16 inch rear OEM bar. If the car understeers with the GM bar installed, go to a bigger bar. I have poly upper and lower control arm bushings as well and with 255/45/17 ZR tires with the other suspension changes mentioned, the car rides MUCH smoother than my 10Z06….great ride, steering, balance, and handling. Let's us know how you make out….

Les

The stock bigblock set up would probably be just fine but it couldn't hurt to call Dick Guldstrand for advise. He has an extensive history setting C3 suspensions up and he knows what works with what, depending on your goals. A few years ago I called for some info and the person I talked to offered to put Dick on the line. My questions were basic so I felt no need to take up his time. Point is, at least back then, he was still there and available.

chevygod

Forgive me for asking, as I don't know, but is your BBC all iron, which is one weight on the nose, or heavily lightened with AL heads, intake, pump, etc, which is a more small block weight? This will affect weight and how the parts work.

I have an all iron big block going back into a factory big block car, and am interested in what you find, and how it relates to my project.

By the way, have always dug your car.

TheSkunkWorks

As such geometry alterations will affect your anti-roll stiffness requirements, I'd get the BFGs on it (no larger than 255s), lower your static rear height to locate the inner u-joints ~1/2" above the outers, and see where that puts you before attempting to better tune your chassis with spring and/or bar changes. Tires and ride heights are critical factors in the equation here, so IMCO until those items are in play it's a bit premature to prescribe treatment.

And, whatever your purposes, don't ever overlook that any spring/bar adjustment which changes the percentage of overall anti-roll stiffness being handled by either end of the car relative to the other will necessarily change its understeer/oversteer balance. My $.02, not that I have any experience with this sort of stuff...




.

ajrothm

Yes my big block is still iron headed, it does have an aluminum intake/water pump and radiator... But with AC so it's still very nose heavy.
Thanks for the compliment!

ajrothm

Good info. My train of thought is that if GM put a large front sway bar and a rear sway bar on big block cars, then I should probably have them. I could do 255s on the rear but I wanted the 275s to help lower the freeway rpms a bit for the 3000 mile road trip.

The rear ride height is where it needs to be because when I drag race it, the rear of the car squats pretty good and my half shafts go parallel to the ground. If I lowered the car any more, the tires would go negative camber on hard launches and probably break U joints. So my rear suspension is dialed in pretty well for drag racing, which is my primary use besides street driving. I'll probably get the sway bars from RedVetRcr just so I have them and I can use them or not after I get the BFGs on it.

Thanks for the tips!

chevygod

So with your setup you are probably very close to stock, base level BBC weight (all iron, no A/C), so starting at a factory BBC suspension level makes sense.

And the compliment is well deserved.

Best,
Tom

TheSkunkWorks

You're welcome. Mainly, I just wanted to make sure that you know to proceed with skinning this particular cat with care, however you decide to go about it. Wouldn't want to see you or that fine machine get mauled as a result.

F4Gary

I discovered yesterday that my 72 LT-1 has a 3/4" front bar on it. I think it's supposed to have a 15/16" on it (F41). So I would be interested in one of your front bars. Would the 1 1/8" be even better than the 15/16"? I do a little local club autocrossing (slow speed parking lot type) a few times a year.

What does the forum think? 1 1/8"?

I don't have a rear bar.

TheSkunkWorks

The question is, how is your balance now relative to what you'd like it to be? Diagnose and then tune accordingly.


And, FWIW, it is entirely possible (even preferable where practical/tolerable) to sort out a C3 chassis w/o a rear bar.

F4Gary

It does understeer when I'm running through the cones. Duntov Corvette says to go at least 1" on a C2/3. They don't even sell anything smaller.

I wasn't planning on a rear bar, just either going back to what it had from the factory (15/16) or improve on that with the thicker bar.

jb78L-82

The simple answer depends on what the car is doing now? How much front versus rear roll does the car have and does it understeer, oversteer, or neutral at the limits of adhesion? If the car has oversteer or has too much front roll, a bigger bar might help. My 78 with the gymkhana bars 1 1/8 inch front and 7/16 rear OEM bar would understeer at the limit. I added a rear OEM type 3/4 inch rear bar and kept the front GM stock 1 1/8 inch bar and now is very neutral at the limit. Hope that helps!

roscobbc

Has anyone looked at the stock rear sway bar mountings on a BB car - irrespective of the diameter of any sway bar they do not look up to the job of doing really handling anything thicker than welding rods! .
Mine has F41 suspension. A sway bar too thick (and stiff) surely has adverse effects on individual rear wheel suspension rates and movement anyway (doesn't it?) When I went with 18"'s front and rear I had to remove rear sway bar as it touched inside of rear rubber. Removal didn't seem to have any adverse effect on handling - OK I have ally heads and other crap changing front/rear balance but with the far more rigid low side walls of the low profiles handling was improved significantly without doing anything else. If I'm critical the front end is a bit 'wallowy' at speed on major roads with 'wallowy' surfaces but other wise fairly neutral. Having said that, I find the 'loose' front end beneficial for drag type pullways - lifts front end up in air - transfers weight over rear end?

Hib Halverson

I think your spring package is soft for a BBC car but workable as long as you're not going to run the car real hard down the Tail. It will ride nice but don't lower the car any because you don't have high enough spring rates to support limited ride travel. Make sure your compression bumpers in the front are in good condition. You'd be better with 550-lb/in front coils and a 360-lb/in plastic spring rear.

Your shock absorber set up is the pits. KYBs are an awful choice for a performance shock compared to QA1s which are excellent. The first thing I'd do is get your shocks matched front to rear.

As for the bars, I'd go with the 1 1/8 OE front bar and the 9/16-in OE rear bar.

jb78L-82

You answered your question in your post. The rear GM sway bar has a purpose built different end link than the front sway bar end link so that the bar can pivot in a vertical plane and NOT restrict trailing arm movement which will effect handling-the reason it is different from the end links. Controlling the roll of the front engined car is much more difficult (thus a much bigger bar) than the rear since the engine's mass is forward...

jb78L-82

Same thoughts as my first post….