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Sounds like a reasonable plan to me. Not sure why you're calling the swaybars wimpy, the front in particular is pretty large on the gymkhana suspension. The only other things I'd suggest considering are:
- Ensure bushes and balljoints are in good condition if you're not replacing them.
- I'd spend the money on shocks. I think after tyres, shocks are one of if not the biggest factor in handling and ride. Kyb's are good for the money, but I'd recommend Bilsteins if you can spring it. They'll last forever and work very well. I have Bilstein Sports all round and they handle great and still ride well despite my gymkhana front springs with a coil removed. Bilstein HDs will ride a little smoother.
- That leads to the next point, what are you doing for wheels and tyres?
- After all the above, some aftermarket upper arms in the front will allow you to gain extra caster which will help handling and feel if you can swing the $.
My '80 originally had the Gymkhana suspension. I converted to the comparable rear composite spring and later to the front monospring conversion to gain both adjustable spring rate and ride height.
It costs a bit more than new coil springs, but the adjustability is worth saving for IMO. I took a couple hundred pounds out of my '80, so ride height was a concern. I have is nearly as stiff and low as it can go. Bilsteins are a perfect match.
A few observations over the years that might be of interest with my 78 L-82 4 speed and the OEM gymkhana suspension versus how the suspension is today. The stock gymkhana suspension with the 550 OEM GM front coils, Delco shocks, and 7 leaf steel 292 lbs rear spring was very stiff and road terribly. I changed the rear steel spring to a 360 VBP composite in 1986 and still have that spring on the car. For most of the 80's, 90's, and 2000's I drove the car with the 360 composite and stock GM 550's with eventually Bilstein Front HD's and rear Bilstein Sports...the ride was a vast improvement over the GM setup....A 360 composite will ride MUCH better than the steel 292 rear spring. I chose Bilstein HD's in front at the time since the 550 springs are very stiff to begin with and used Bilstein Sports (30% stiffer than the HD's) to quell some of the bouncy feel I had in the rear with the 360 composite..it worked perfectly!
In the mid 2000's I replaced the OEM rims with 17's (255/45/17 ZR tires) and the ride, steering response, and handling was transformed....everything was so much smoother. The car has the OEM 1 1/8 inch front swaybar with poly bushings all around and a rear OEM GM style rear 3/4 inch sway bar with poly mounting bushings (the GM gymkhana sway bars are not wimpy by any means and were HUGH in the late 70's/80's)plus competition adjustable heim joint strut rods (no they do not hurt the ride) but dramatically reduce unwanted rear suspension movement. The ride bordered on too soft for me....
Fast forward to 2014 when the OEM L-82 was rebuilt by me into a 355...The front end raised noticeable with the AFR aluminum heads. In 2015 I cut a half coil off the MidAmerica 550 front springs but the reduction in height was not enough. Last week I cut another half coil off the driver's front and it appears the height is good now BUT I have not taken the car out yet and still need another half coil off the pass front coil. Cutting the half coils did noticeably stiffen the ride BUT as mentioned earlier, the last iteration of the suspension bordered on being soft and with the BHD's in front may be just right for me. I eventually may need to go with a 420 rear composite once I get all these changes sorted out...
Having read your comments about a soft ride being desired, I think that the 330 rear spring with Bilstein HD's may be perfect for you. In the front I would go 460 springs since you probably will have to cut a half coil or full coil for ride height which will get the spring rate probably right around the OEM 550 lbs rating along with Bilstein HD's like I have. Add a great set of 17/18 inch ultra high performance tires and hopefully you hit the sweet spot for what you want in your C3. The gymkhana sway bars are really quite good and will not effect the ride just the lean when turning....
- That leads to the next point, what are you doing for wheels and tyres?
- After all the above, some aftermarket upper arms in the front will allow you to gain extra caster which will help handling and feel if you can swing the $.
I already put 18" nitro 5 Sport Muscle wheels on it; and kumho ECSTA 245 50r 18s on it on all four corners; they fit without rubbing with full wheel rotation. (The 79 and later C3s have more fender clearance for 255 width tires). The tires are fantastic the wheels are not the greatest quality and they're heavier than I would like.
Sounds like a reasonable plan to me. Not sure why you're calling the swaybars wimpy, the front in particular is pretty large on the gymkhana suspension. The only other things I'd suggest considering are:
- Ensure bushes and balljoints are in good condition if you're not replacing them.
- I'd spend the money on shocks. I think after tyres, shocks are one of if not the biggest factor in handling and ride. Kyb's are good for the money, but I'd recommend Bilsteins if you can spring it. They'll last forever and work very well. I have Bilstein Sports all round and they handle great and still ride well despite my gymkhana front springs with a coil removed. Bilstein HDs will ride a little smoother.
- That leads to the next point, what are you doing for wheels and tyres?
- After all the above, some aftermarket upper arms in the front will allow you to gain extra caster which will help handling and feel if you can swing the $.
Originally Posted by NewbVetteGuy
I already put 18" nitro 5 Sport Muscle wheels on it; and kumho ECSTA 245 50r 18s on it on all four corners; they fit without rubbing with full wheel rotation. (The 79 and later C3s have more fender clearance for 255 width tires). The tires are fantastic the wheels are not the greatest quality and they're heavier than I would like.
Adam
Because of the switch to a composite spring and my low pro tires I think I'm going to go with a cushier ride shock like the KYB VBP specially valved shocks and not the Bilstein sports.
Sounds like a reasonable plan to me. Not sure why you're calling the swaybars wimpy, the front in particular is pretty large on the gymkhana suspension. The only other things I'd suggest considering are:
- Ensure bushes and balljoints are in good condition if you're not replacing them.
I've heard repeatedly on here how wimpy the stock Gymkhana rear sway bar is and how it can be confused for a brake line.
I'll take a look at the bushings, but honestly if they need replacing I have no idea what I'm going to do because that kind of work would drive me bonkers; I heard they're a beast to remove and I'd want to stick with rubber for ride quality and I don't have a press or anything to install new. -I'd have to pay someone to do it and it's labor intense. I'm hoping that as the car's only got 14.9k miles on it that they're good.... (sticking head in the sand on that one...)
Adam
Last edited by NewbVetteGuy; 08-11-2016 at 12:20 PM.
My '80 originally had the Gymkhana suspension. I converted to the comparable rear composite spring and later to the front monospring conversion to gain both adjustable spring rate and ride height.
It costs a bit more than new coil springs, but the adjustability is worth saving for IMO. I took a couple hundred pounds out of my '80, so ride height was a concern. I have is nearly as stiff and low as it can go. Bilsteins are a perfect match.
That car looks fantastic; I'd so prefer the tan interior "oyster" right?,
like the 80 front bumper, blue's my color, and the ride height is perfect; well done!
It's $79 for new front springs; and like $790 for the front mono spring conversion. I just don't see it as a good value based upon my goals for my build; it would steal funds away from other projects I'd much rather do. (I want that extra $700 in the engine so I can do a retrofit roller cam.)
There's a good start to a VBP front mono spring in the C3 parts for sale section for anyone interested in building one at a discount, though.
Adam
Last edited by NewbVetteGuy; 08-11-2016 at 12:18 PM.
- After all the above, some aftermarket upper arms in the front will allow you to gain extra caster which will help handling and feel if you can swing the $.
I don't understand suspension systems well enough to fully apprecaiate the upper A arm replacement but I see many people on here prioritizing it. I don't think they're going to end up on my car between now and 2019, honestly. I know I'm going to have to go way down the rabbit hole to start understanding the subtlities of suspension design; I'd rather just copy an assembled VB&P kit at this point.
It's one of those things that might be done in a distant future once I understand why / if it makes a difference and how much value I find in it given my goals, but I've taken it off the table for this build as I've got things that are going to add to my enjoyment of the car far more. Mine will be somewhere between a summer daily driver and a cruiser and it'll get an occasional beating out on some backroads, so I probably wouldn't appreciate a proper autocross setup suspension.
Adam
Last edited by NewbVetteGuy; 08-11-2016 at 12:25 PM.
I've heard repeatedly on here how wimpy the stock Gymkhana rear sway bar is and how it can be confused for a brake line.
I'll take a look at the bushings, but honestly if they need replacing I have no idea what I'm going to do because that kind of work would drive me bonkers; I heard they're a beast to remove and I'd want to stick with rubber for ride quality and I don't have a press or anything to install new. -I'd have to pay someone to do it and it's labor intense. I'm hoping that as the car's only got 14.9k miles on it that they're good.... (sticking head in the sand on that one...)
Adam
The reason the GM rear sway bar is on the smaller side is that a C3 SBC, not the BB cars, has the engine placed very far back in the engine bay behind the front axle resulting in an almost mid mounted engine resulting in a weight distribution of in the case of my 78 C3 of 48% front:52% rear. A rear mounted/mid mounted engine cars have a much higher tendency to oversteer (back end of the car out) than a nose heavy car like FWD ones and big engine over the nose rear wheel drive cars. To minimize the oversteer tendency from a fairly neutral balanced car like the C3 (almost 50:50 %), GM used a big front bar on the gymkhana cars (1 1/8 inch) which on its own would make the C3 understeer much without a rear bar. The small rear sway bar (7/16 inch) in combination with the slight rear weight bias (52% in the rear) in combo with the large front bar in theory should balance out the handling at the limit. Keep in mind that even the gymkhana cars were designed to UNDERSTEER at the limit as all cars from GM did back then after the Ralph Nader Corvair fiasco in the late 60's. C3 SBC cars even with the gymkhana suspension will understeer at the limit which is why with my suspension setup I use the GM front bar (1 1/8 inch with poly bushings mounting and endlinks...makes the bar act like it is a bigger bar) in combination with a 3/4 inch GM style rear sway bar....My car is almost neutral at the limit with a slight hint of oversteer when I cross the line of physics...very slight and very progressive..not sudden!
The reason the GM rear sway bar is on the smaller side is that a C3 SBC, not the BB cars, has the engine placed very far back in the engine bay behind the front axle resulting in an almost mid mounted engine resulting in a weight distribution of in the case of my 78 C3 of 48% front:52% rear. A rear mounted/mid mounted engine cars have a much higher tendency to oversteer (back end of the car out) than a nose heavy car like FWD ones and big engine over the nose rear wheel drive cars. To minimize the oversteer tendency from a fairly neutral balanced car like the C3 (almost 50:50 %), GM used a big front bar on the gymkhana cars (1 1/8 inch) which on its own would make the C3 understeer much without a rear bar. The small rear sway bar (7/16 inch) in combination with the slight rear weight bias (52% in the rear) in combo with the large front bar in theory should balance out the handling at the limit. Keep in mind that even the gymkhana cars were designed to UNDERSTEER at the limit as all cars from GM did back then after the Ralph Nader Corvair fiasco in the late 60's. C3 SBC cars even with the gymkhana suspension will understeer at the limit which is why with my suspension setup I use the GM front bar (1 1/8 inch with poly bushings mounting and endlinks...makes the bar act like it is a bigger bar) in combination with a 3/4 inch GM style rear sway bar....My car is almost neutral at the limit with a slight hint of oversteer when I cross the line of physics...very slight and very progressive..not sudden!
Wow; great to see someone with such a good understanding of such great complexity.
I had no idea that the weight distribution was so even like that. What I'm taking away from what you've said is "keep your L82 sway bars; don't @#%#@ it up by adding aftermarket giant sway bars".
A few observations over the years that might be of interest with my 78 L-82 4 speed and the OEM gymkhana suspension versus how the suspension is today. The stock gymkhana suspension with the 550 OEM GM front coils, Delco shocks, and 7 leaf steel 292 lbs rear spring was very stiff and road terribly. I changed the rear steel spring to a 360 VBP composite in 1986 and still have that spring on the car. For most of the 80's, 90's, and 2000's I drove the car with the 360 composite and stock GM 550's with eventually Bilstein Front HD's and rear Bilstein Sports...the ride was a vast improvement over the GM setup....A 360 composite will ride MUCH better than the steel 292 rear spring. I chose Bilstein HD's in front at the time since the 550 springs are very stiff to begin with and used Bilstein Sports (30% stiffer than the HD's) to quell some of the bouncy feel I had in the rear with the 360 composite..it worked perfectly!
In the mid 2000's I replaced the OEM rims with 17's (255/45/17 ZR tires) and the ride, steering response, and handling was transformed....everything was so much smoother. The car has the OEM 1 1/8 inch front swaybar with poly bushings all around and a rear OEM GM style rear 3/4 inch sway bar with poly mounting bushings (the GM gymkhana sway bars are not wimpy by any means and were HUGH in the late 70's/80's)plus competition adjustable heim joint strut rods (no they do not hurt the ride) but dramatically reduce unwanted rear suspension movement. The ride bordered on too soft for me....
Fast forward to 2014 when the OEM L-82 was rebuilt by me into a 355...The front end raised noticeable with the AFR aluminum heads. In 2015 I cut a half coil off the MidAmerica 550 front springs but the reduction in height was not enough. Last week I cut another half coil off the driver's front and it appears the height is good now BUT I have not taken the car out yet and still need another half coil off the pass front coil. Cutting the half coils did noticeably stiffen the ride BUT as mentioned earlier, the last iteration of the suspension bordered on being soft and with the BHD's in front may be just right for me. I eventually may need to go with a 420 rear composite once I get all these changes sorted out...
Having read your comments about a soft ride being desired, I think that the 330 rear spring with Bilstein HD's may be perfect for you. In the front I would go 460 springs since you probably will have to cut a half coil or full coil for ride height which will get the spring rate probably right around the OEM 550 lbs rating along with Bilstein HD's like I have. Add a great set of 17/18 inch ultra high performance tires and hopefully you hit the sweet spot for what you want in your C3. The gymkhana sway bars are really quite good and will not effect the ride just the lean when turning....
Hope this helps!
This helps immensely.
My only question is about buying the VBP 460 springs and cutting them down to get the ride height where I want it. It's my understanding that the spring rating and rebound speed is based upon the diameter of the metal making up the coil and it's height; the diameter of the metal for the VBP 460s and 500s are identical; my understanding is that if I buy the VBP 460 and cut it down to the height of the 500 all I've done is turned my 460 into a 500 (in lbs rating, rate of recoil, height and weight). Essentially the 500lb coil IS the 460 lb coil cut shorter. -In which case I'd be better off just buying the 500lb spring and not having to cut anything, right?
Adam
Last edited by NewbVetteGuy; 08-11-2016 at 03:44 PM.
Yes, the aftermarket 550s are essentially cut down 460s. If the concern is that the 550s might result in too high of an after weight reduction front ride height, there's nothing to be gained by starting with 460s which would require even more cutting. In any event, best to do a couple of extra mockups when cutting than to risk cutting too much at one time. Just bear in mind that the mechanical advantage of the front wheel rate vs. spring rate is approx. 2:1, which translates that you won't be cutting but about half as much loaded height from the coils as the amount you wish to lower ride height.
And, while you're on this, I highly suggest putting priority on "Z" and "D" suspension geometry based measurements during the lowering process rather than those which may be skewed by body mount issues or non-stock tire size variations.
And, while you're on this, I highly suggest putting priority on "Z" and "D" suspension geometry based measurements during the lowering process rather than those which may be skewed by body mount issues or non-stock tire size variations.
In addition to being a C3 Corvette suspension expert, you speak fluent Mandarin?!? Wow! (I have no idea what Z or D suspension geometry is; might as well be Chinese- but probably good to post this for the people who know what you're talking about.)
In addition to being a C3 Corvette suspension expert, you speak fluent Mandarin?!? Wow! (I have no idea what Z or D suspension geometry is; might as well be Chinese- but probably good to post this for the people who know what you're talking about.)
Adam
The "Z" and "D" figures are measurements that are referenced in the factory shop manual, when checking ride height. They rely on hard data points on the chassis, rather than body panels, which can vary from car to car.
In addition to being a C3 Corvette suspension expert, you speak fluent Mandarin?!? Wow! (I have no idea what Z or D suspension geometry is; might as well be Chinese- but probably good to post this for the people who know what you're talking about.)
Adam
Sorry about that. Didn't mean to leave you hanging there. My laptop battery died on me before I could post up the illustration below...
Update: Just had the 78 out for a nice long ride and the 550's with 1 coil cut are perfect and the ride is firm but not overly stiff...right for me since I abhor soft riding cars of any kind. Compared to my day cars, I for the life of me do not understand why GM used soft springs on the base corvettes..they float all over the place and bounce up and down. I would say now the 78 is not as stiff as my 2010 Z06 nor my 2012 Lexus IS350 F Sport but probably more in line with my Chrysler 300 with 245/55/18 ZR tires, front Chrysler Strut Brace, and Bilstein Struts/shocks.
Update: Just had the 78 out for a nice long ride and the 550's with 1 coil cut are perfect and the ride is firm but not overly stiff...
Thank you! (Great context in your explanations too, 'appreciate that, its helpful.)
This picture below shows the stock L48 coupe springs (original, I'm guessing) on the left, and the new 550 pound springs on the right. Are the orange marks I drew where the cuts you describe should be?
Stock L48 springs on left, 550 pound springs on right.
.....This picture below shows the stock L48 coupe springs (original, I'm guessing) on the left, and the new 550 pound springs on the right. Are the orange marks I drew where the cuts you describe should be?
Yes for a full coil..The cut should be in line with the top coil cut from the factory....
I can't believe C3's came with that coil with the base suspension wihich is the majority of cars..holy smokes!
Karol on this forum who I see at car shows has a 78 L-82 4 speed with th base suspension versus my 78 L-82 4 speed that came with the gymkhana suspension....The difference in ride with my 360 monospring, cut 550 coils, 17 ZR tires, Bilsteins is very dramatic...His ride height is MUCH higher than mine and his ride is MUCH harsher with an OEM stock base suspension. This is why I constantly tell people with base or sport suspensions, the ride components (monospring composite and great shocks (Bilsteins)) will make any C3 ride better than a stock base suspension car. Do not be fooled either by the monospring higher spring ratings than the steel counterpart...they are NOT the same and you can go much higher with the composite and it will STILL ride better than a much low rated steel spring.
08-10-2016, 11:29 PM
