Looking at the front coilover conversion kit for my 68 Barracuda. Any pros/cons going with either the 0-2in or 2-4in drop option? What is the difference between the single and double adjustment set up? Any significant modifying to make it work or is it a pretty straight forward bolt in system? Any rear suspension upgrades that would need to compliment the front? Also, any header fitment issues? I currently have Hedman tight tubes where the exhaust after the header flange slightly touches the tie rod ends.
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- Thread starter Mcfarlrm
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dano
Evil Handy Man
If you just want front coil over (i.e. no K member), Hemi Denny has a kit.
Appreciate the info. Looking for a full swap. Open to suggestions outside of QA1 as well.
@HemiDenny would probably be the best source of information on this. The various levels of drop will effect suspension geometry- bump steer, roll center, camber gain etc. With the torsion bar suspension a 2" drop spindle noticeably increases bump steer.
Suspension geometry aside though, the two major limitations on lowering the car are the header clearance to the ground and the tire clearance to the inner fender. I'm running modified torsion bar suspension in my Duster and am lowered about 2" from stock. At full suspension compression with 25.6" tall front tires, my tires just contact the top of the inner fender. So if I lowered the car further, I'd have to lose more suspension travel on compression. I also only have about 3.75" of clearance to the header flanges on my Doug's headers, which are one of the better ones for ground clearance. I probably lose ~2.5" of that under full suspension compression, so, that's not much ground clearance to account for an uneven road. My car is daily/frequently driven and a street car, it gets used on some pretty questionable roads, and I wouldn't go much lower than I have my car just because speed bumps and pot holes get to be too much of an issue. Show cars, race only and trailer queens could get away with being lower, but it wouldn't improve handling or driveability.
If you're talking about UCA's, single vs double adjustable means how you have to set the alignment. Single adjustable UCA's have to be removed from the mounts to adjust them. Double adjustable UCA's can be adjusted while still mounted to the frame, so it's significantly easier to set the car's alignment. If you're talking about coil overs, it double adjustable is adjustable on both compression and extension (rebound), single is typically only adjustable on extension. Obviously being double adjustable allows for more tuning of your ride quality. But even a good non-adjustable shock can produced a good ride quality if paired correctly with wheel rates, vehicle weight, etc.
For complete conversions I'd have to say the only two I'd look at are the HDK and the RMS. QA1 bought out Gerst, which was basically a knock off that had production issues. QA1 sorted the production issues and improved the design, but really I still think you'd be better off with the HDK. Both the RMS and HDK bolt in.
That said, ANY coil over conversion completely changes how the chassis is loaded by the suspension, and front chassis stiffness is already an issue on these cars even with the torsion bar suspension that carries all of the load in the crossmembers. So my opinion is that if you're installing a coil over conversion without stiffening the front chassis, especially between the frame rails and firewall, you're making a mistake.
And I'm sure everyone expects me to say this, but the only thing a coil over conversion adds that can't be done with the torsion bar suspension is the rack and pinion and some header clearance. From a handling perspective, anything you can do with a coil over conversion you can do with the torsion bars. There are pros and cons to both, and either system needs tuning and optimization. If you commit the time to tuning and optimization, either system will work just as well.
Suspension geometry aside though, the two major limitations on lowering the car are the header clearance to the ground and the tire clearance to the inner fender. I'm running modified torsion bar suspension in my Duster and am lowered about 2" from stock. At full suspension compression with 25.6" tall front tires, my tires just contact the top of the inner fender. So if I lowered the car further, I'd have to lose more suspension travel on compression. I also only have about 3.75" of clearance to the header flanges on my Doug's headers, which are one of the better ones for ground clearance. I probably lose ~2.5" of that under full suspension compression, so, that's not much ground clearance to account for an uneven road. My car is daily/frequently driven and a street car, it gets used on some pretty questionable roads, and I wouldn't go much lower than I have my car just because speed bumps and pot holes get to be too much of an issue. Show cars, race only and trailer queens could get away with being lower, but it wouldn't improve handling or driveability.
If you're talking about UCA's, single vs double adjustable means how you have to set the alignment. Single adjustable UCA's have to be removed from the mounts to adjust them. Double adjustable UCA's can be adjusted while still mounted to the frame, so it's significantly easier to set the car's alignment. If you're talking about coil overs, it double adjustable is adjustable on both compression and extension (rebound), single is typically only adjustable on extension. Obviously being double adjustable allows for more tuning of your ride quality. But even a good non-adjustable shock can produced a good ride quality if paired correctly with wheel rates, vehicle weight, etc.
For complete conversions I'd have to say the only two I'd look at are the HDK and the RMS. QA1 bought out Gerst, which was basically a knock off that had production issues. QA1 sorted the production issues and improved the design, but really I still think you'd be better off with the HDK. Both the RMS and HDK bolt in.
That said, ANY coil over conversion completely changes how the chassis is loaded by the suspension, and front chassis stiffness is already an issue on these cars even with the torsion bar suspension that carries all of the load in the crossmembers. So my opinion is that if you're installing a coil over conversion without stiffening the front chassis, especially between the frame rails and firewall, you're making a mistake.
And I'm sure everyone expects me to say this, but the only thing a coil over conversion adds that can't be done with the torsion bar suspension is the rack and pinion and some header clearance. From a handling perspective, anything you can do with a coil over conversion you can do with the torsion bars. There are pros and cons to both, and either system needs tuning and optimization. If you commit the time to tuning and optimization, either system will work just as well.
a 2" drop (short answer) will allow you to lower your car 2" while keeping the same suspension geometry. HDK uses this to not only lower your car but to utilize a longer shock. Longer shock=longer spring= more travel (over all the other conversions available)= a nicer / less harsh ride.
modifications?....if you can drill a couple of holes, go to the advanced class, no welding, fully reversable.
rear is optional and IMHO the rear is about tire size and traction and would depend on your specific plan to use the car. I am a personal fan of rubber bushed leaf springs for a street car.
single adjustable gives control (stiffness) over both shock rebound and compression dampening with one knob, double allows you to control them separately. Popular in a drag racing application where you want the nose to rise easily (rebound) for weight transfer and you want the front to stay there (compression) to keep the car from porpoising / bouncing.
on header fitment.....imagine how easy it is to fit any header without the torsion bars, steering box, drag link, steering arm / idler to work around.
out of the box adjustability, drops appoximately 30 lbs ....manual steer vs OEM manual steer, way more on a power steering vs power rack and pinion comparison.
Sounds like a 2" drop option is the way to go here. This set up will be strictly for road use. No autocross/drag racing. Any suggestions on a power steering pump? What would be suggested to stiffen the front chassis?
additional stiffening for a street car?, nothing else is needed, just the HDK components. JMHO, unless your car is not a solid piece to begin with, the USCT stiffeners just add unnecessary weight.
an OEM (60's -70's) P/S pump works great. If you go aftermarket, buy one with the correct pressure (around 800psi), too much pressure will cause the seals in the rack to fail, not to mention a jerky / twitchy feel to your steering wheel. Holley makes some nice set-ups serpentine and V-belt depending on what engine you plan on running.
Using a 2" drop spindle changes the suspension geometry. No reason to misconstrue the facts in the name of brevity. If you compare the numbers between the stock spindle and a 2" drop spindle, they will be different. The "short answer" is it lowers the car 2" and don't worry about the rest, since most of your customers don't worry about suspension geometry anyway.
lol! The unibodies on these cars are about as stiff as a wet noodle. With a good modern radial and half decent suspension it’s readily apparent how flexible the chassis is, they were not designed to have the kind of traction that is available with a decent modern radial tire.
XV actually did a chassis deflection test back in the day and compared the stock chassis to one with their take on chassis stiffening. Their testing showed that the front of the chassis, from the firewall forward, was actually very flexible. Hence the need for some kind of inner fender brace/J-bar, lower radiator support, etc. And their testing showed that adding inner fender braces and forward chassis stiffening made a significant difference. Needless to say there are significant improvements to be made even just for a street car. Believe that article was published in the 12/2006 Mopar Action magazine.
I added subframe connectors, j-bars (triangulating the frame rails and firewall and supporting the shock tower), torque boxes and a lower radiator support brace to my lowly torsion bar equipped street going Duster, and the difference IS noticeable. If you take the suspension loads out of the crossmembers and put them entirely on the front frame rails using a coil over conversion without doing anything else and don't notice the difference you definitely didn't need to drop that kind of coin on suspension parts.
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