Traction suggestions appreciated
Thread Starter
Pro
Joined: Apr 1999
Posts: 533
Likes: 6
From: Poinciana Florida
Front end advice ?
The C4 Vette IRS is a GREAT Drag Racing machine.... IF you know what your doing.
I am going to tell you what I know, what works for me and what I think of some mentioned suspension parts availiable for these cars. No BS and I'm not hiding anything about my 84 or what I have done to make it leave so well...
First thing. On the later model cars (89-96) GM changed the suspension. Everyone knows about the wider track width - but hardly anyone knows about the different brackets. The new brackets lowered the Anti Squat % that was built into the rear suspension. You need to raise the rear ride height about 1.5"-2" to get it back over 100% like it was in 84.
On my 84 I run a 28" tall rear tire which raises my cars ride height 1" to 1.5" taller than a stock 84... I also have the stock rear spring bolts bottomed out to raise the rear suspension another 1.5". Thats a total of 3" taller on the ride height.
Unfortunatly the DRM trailing arm brackets lower the AS % even more... They also place the Instant Center further forward.... They are totally the wrong thing to use for drag racing...
I do very much like the DRM camber arm brackets as they lower the inner pick up point for the camber arm so that the camber arm runs closer to parallel to the halfshaft. This reduces camber change across the suspension travel.. the eraly cars are terrible in this respect. The later cars are much better but the DRM brackets are about perfect IMO. That said I have never been able to find any used and I'm pretty cheap about some stuff.. espc when I can work around the problem.... Honestly I run the stock 84 brackets and just compensate for it by putting 1.5* negative camber in the rear end at ride height... then at launch the tire is pretty close to 0* camber.
Second you need a stiff rear spring.... the stiffest you can get. 84 Z51 rear spring is what I run.
Third you need real shocks to control all that spring rate.... Not some BS factory replacement stuff. I use Koni D/A SPA1 Alum rear shocks... $500 each and I had make new lower mounting brackets. You need the rebound cranked as tight as you can get it. Compression about 7 clicks from zero is my start point and then I adjust + - for track conditions.
Before the install of the Koni rear shocks I was having rebound problems with the stock Bilstine shocks... on a slick track the car would porposie after the tire broke loose.... I knew what the problem was but had to wait for the $$$ to cure it. For nearly half a season I raced on the stock 101,000 mile 1984 Bilstien Z51 shocks and the car ran great on killer track prep but on a slick track the car hopped on down the track like Flipper in the ocean.
Fourth I run extended suspension snubbers/bump stops. I have some from Energy Suspension (PN 9.9143) that I modified to fit.... Now when my car is squatted down on launch the half shaft is parallel to the ground... no angle at all on the inner or outer U Joints.
I run a 28X10.5S (Stiff wall) slick or a 275/60R15 MT Drag Radial on my 84. D44 IRS witha Yukon 3.90 rear gear and a spool. A1 Performance TH350 trans with a PTC 8" 4500 stall converter.
800+HP on nitrous.
I do run a progressive controller (LEASH Electronics) but use very little on a slick tire.... Single ramp, No delay, I typically start at 60% ramped to 100% in .5 second (yes 1/2 a sec). I did not have it at the start of the season and was hitting the car with everything right off the line.... My best 60ft ever actually came before I installed the progressive NO2 controller.
I have run a best of 1.247 60ft.
My average 60ft since I installed the Koni's is 1.27.... that is for 43 passes. FYI it's still under 1.35 if you count all season which is over 80 passes total. The car is very consistant.
The car runs equally well on the slick or the radial but the radial is much more track prep sensitive... The radial will also send my car up on the back bumper in a heartbeat if I don't chain the front end down (front suspension limiting straps). I don't usually need the front end limiters with the slick tire.
Biggest problem I see with your car is the 4L60 trans.... the steep low gear with all that power makes it hit the tire very hard for a very short peroid of time. Not much you can do about it without spending big bucks....
I like the tire your considering. Tall so it takes away some gear ratio. Radial so it's stiff sidewall but it's downfall is it's a 17" and has a short sidewall....
The biggest things you can change for free or cheap:
1) Ride height and Anti Squat. Just start jacking up the spring bolt.
2) Extended snubbers/bump stops. They were like $30 on Amazon and 20 mins time with a grinder to make them fit.
3) Rear Camber setting.... when you jack the spring up for taller ride height your going to add some negative camber to it just at the factory setting.... you really need a digital level to know how much (Smart Level is what I use).... Just spend some time on jack stands with a tape measure, the digital level and the spring/shocks disconnected to plot out your camber curve and see where you need to be to have 0* camber bottomed out on the bump stops.
I hope you can understand this and that it is helpful to you. Any questions just ask.
Will
I am going to tell you what I know, what works for me and what I think of some mentioned suspension parts availiable for these cars. No BS and I'm not hiding anything about my 84 or what I have done to make it leave so well...
First thing. On the later model cars (89-96) GM changed the suspension. Everyone knows about the wider track width - but hardly anyone knows about the different brackets. The new brackets lowered the Anti Squat % that was built into the rear suspension. You need to raise the rear ride height about 1.5"-2" to get it back over 100% like it was in 84.
On my 84 I run a 28" tall rear tire which raises my cars ride height 1" to 1.5" taller than a stock 84... I also have the stock rear spring bolts bottomed out to raise the rear suspension another 1.5". Thats a total of 3" taller on the ride height.
Unfortunatly the DRM trailing arm brackets lower the AS % even more... They also place the Instant Center further forward.... They are totally the wrong thing to use for drag racing...
I do very much like the DRM camber arm brackets as they lower the inner pick up point for the camber arm so that the camber arm runs closer to parallel to the halfshaft. This reduces camber change across the suspension travel.. the eraly cars are terrible in this respect. The later cars are much better but the DRM brackets are about perfect IMO. That said I have never been able to find any used and I'm pretty cheap about some stuff.. espc when I can work around the problem.... Honestly I run the stock 84 brackets and just compensate for it by putting 1.5* negative camber in the rear end at ride height... then at launch the tire is pretty close to 0* camber.
Second you need a stiff rear spring.... the stiffest you can get. 84 Z51 rear spring is what I run.
Third you need real shocks to control all that spring rate.... Not some BS factory replacement stuff. I use Koni D/A SPA1 Alum rear shocks... $500 each and I had make new lower mounting brackets. You need the rebound cranked as tight as you can get it. Compression about 7 clicks from zero is my start point and then I adjust + - for track conditions.
Before the install of the Koni rear shocks I was having rebound problems with the stock Bilstine shocks... on a slick track the car would porposie after the tire broke loose.... I knew what the problem was but had to wait for the $$$ to cure it. For nearly half a season I raced on the stock 101,000 mile 1984 Bilstien Z51 shocks and the car ran great on killer track prep but on a slick track the car hopped on down the track like Flipper in the ocean.
Fourth I run extended suspension snubbers/bump stops. I have some from Energy Suspension (PN 9.9143) that I modified to fit.... Now when my car is squatted down on launch the half shaft is parallel to the ground... no angle at all on the inner or outer U Joints.
I run a 28X10.5S (Stiff wall) slick or a 275/60R15 MT Drag Radial on my 84. D44 IRS witha Yukon 3.90 rear gear and a spool. A1 Performance TH350 trans with a PTC 8" 4500 stall converter.
800+HP on nitrous.
I do run a progressive controller (LEASH Electronics) but use very little on a slick tire.... Single ramp, No delay, I typically start at 60% ramped to 100% in .5 second (yes 1/2 a sec). I did not have it at the start of the season and was hitting the car with everything right off the line.... My best 60ft ever actually came before I installed the progressive NO2 controller.
I have run a best of 1.247 60ft.
My average 60ft since I installed the Koni's is 1.27.... that is for 43 passes. FYI it's still under 1.35 if you count all season which is over 80 passes total. The car is very consistant.
The car runs equally well on the slick or the radial but the radial is much more track prep sensitive... The radial will also send my car up on the back bumper in a heartbeat if I don't chain the front end down (front suspension limiting straps). I don't usually need the front end limiters with the slick tire.
Biggest problem I see with your car is the 4L60 trans.... the steep low gear with all that power makes it hit the tire very hard for a very short peroid of time. Not much you can do about it without spending big bucks....
I like the tire your considering. Tall so it takes away some gear ratio. Radial so it's stiff sidewall but it's downfall is it's a 17" and has a short sidewall....
The biggest things you can change for free or cheap:
1) Ride height and Anti Squat. Just start jacking up the spring bolt.
2) Extended snubbers/bump stops. They were like $30 on Amazon and 20 mins time with a grinder to make them fit.
3) Rear Camber setting.... when you jack the spring up for taller ride height your going to add some negative camber to it just at the factory setting.... you really need a digital level to know how much (Smart Level is what I use).... Just spend some time on jack stands with a tape measure, the digital level and the spring/shocks disconnected to plot out your camber curve and see where you need to be to have 0* camber bottomed out on the bump stops.
I hope you can understand this and that it is helpful to you. Any questions just ask.
Will
The project is almost finished. I'm waiting for a set of trailing arm brackets(stock) to complete the project. Any advice on front end suspension? Perhaps front end limiters or chain down the drivers side front? Your views would be appreciated.
Safety Car
Joined: Apr 2005
Posts: 3,624
Likes: 431
From: Dale City VA
The people I have seen that have been able to make short sidewall radials work have a good amount of front suspension extension.
I think with the new Z51 spring, QA1 shocks, extended bump stops, raised rear ride height and the rear camber set up like I explained, your going to be fine with a little shock and air pressure tuning.
Will
Thread Starter
Pro
Joined: Apr 1999
Posts: 533
Likes: 6
From: Poinciana Florida
with your tranny gearing and short sidewall tire i would leave the front end like it is before changing anything.
The people i have seen that have been able to make short sidewall radials work have a good amount of front suspension extension.
I think with the new z51 spring, qa1 shocks, extended bump stops, raised rear ride height and the rear camber set up like i explained, your going to be fine with a little shock and air pressure tuning.
Will
The people i have seen that have been able to make short sidewall radials work have a good amount of front suspension extension.
I think with the new z51 spring, qa1 shocks, extended bump stops, raised rear ride height and the rear camber set up like i explained, your going to be fine with a little shock and air pressure tuning.
Will
Rvy
Melting Slicks
Joined: May 2001
Posts: 3,014
Likes: 18
From: Raleigh, NC
jonecap went a best of 1.51 on his 6 speed 96. And he probably went 1.55 a hundred times or so.
That's the quickest short time that I know of for a late model 6 speed car.
4.09 gears were the only change to the rear end. Stock half shafts, spindles, shocks, trailing arms, etc... He was on a 27 x 10.50 x 17 on the stock 96 Collectors Edition wheels.
That's the quickest short time that I know of for a late model 6 speed car.
4.09 gears were the only change to the rear end. Stock half shafts, spindles, shocks, trailing arms, etc... He was on a 27 x 10.50 x 17 on the stock 96 Collectors Edition wheels.
