http://www.svtperformance.com/forums...d.php?t=231900
Welcome to the RED PILL, my name is Dave, 4+ year SVTP veteran poster and 03 Cobra owner/modifier. I have compiled this post through spending my own money, buying, trying, breaking these components. My own experience, my opinions, my conclusions.
I have owned 2 03 Cobras, the first a live axle, ported Eaton, Pullied, Bassani, PHP intake Convertible. The second is the car I have now, 670sae RWHP, T76 Hellion Turbo, Cammed, ported heads, built shortblock, custom return fuel, Viper trans and Level 5 IRS coupe. Now, on to the RED PILL.
The only cure for wheelhop is the system approach. The stock car has many flaws in the rear suspension system. Soft rubber bushings, flexible body structure, unsupported IRS mounts, soft springs in the vert, slippery tires, weak halfshafts and a fragile diff cover.
The basic premise is firm up the points of contact for each of the major components.
Below is a list of relationships so you understand where hop comes from;
*Differential case is mounted with soft bushings, allows it to rotate side to side and front to back, MM bushings cure this.
*IRS Cradle is mounted with flexible bushings, allows it to move in relation to cars chassis mounting points, MM polyurethane bushings cure this.
*Upper and lower countrol arms are mounted with flexible bushings, this allows the wheel to move forward/back when you only really want it to move up/down, MM delrin bushings, aluminum sleeves cure this.
*Toe link bars are very small diameter and flexible, weakest point of support for the wheel, allows wheel to turn in/out and move forward/back, using PHP toe link bars cures this.
*Rear IRS subframe mounts are cantilevered 3+" from the rear subframe, allows for up/down flex in the IRS cradle mounting point, using Billetflow IRS Mount brackets with backer plates cures this.
*Convertible springs are too low of a rate to work with us to reduce hop, using coupe rate springs helps.
All these parts moving and flexing and rotating...... it has no choice but to hop.
Luckily now, after several years of suffering, a replacment or improvement exists for everyone of those components.
Follow this proven mod path to a hard hooking but smooth riding/handling Cobra IRS.
The below mods are carefully arranged to help you out.
You should start at #1 and go straight to #6 for any car from
stock up to 500rwhp.
All those mods compliment each other and will dramatically reduce wheelhop on all surfaces. Do not ask me which of the first 6 you can skip, the answer is
NONE.
FOR WHEELHOP
Listed
in order of necessity/priority.
Stock to CPIE wheelhop mods
1)Billetflow Diff Cover Brace $160
2)MM Diff bushings $50 or $250
3)MMFLSFC's installed $250-300 installed
4)MM IRS Bushings $50 with 14mm bolts/nuts $15
5)Billetflow IRS Mount Brackets $50
6)Used coupe springs $50 (est) (only for verts)
7)Nitto DR $375-$425 installed
500rwhp and up
8)PHP toe link bars $410
9)Maximum Motorsports UCA/LCA Bushings $550
10)Level 5 shafts $1500
11)Strange ADJ Shocks $59ea from HBH Billetflow mount bushings $50
Any shocks other than stock coupe ones or Cobra R Bilsteins are to be used with this caution, It gives you a rougher ride on the settings which actually reduce hop, basically destroys the feel of IRS. And you get to crawl under there and adjust the valve between hop and comfort. Also please realize the possibility of the shocks actually breaking the eyelets.
EDIT 8-23-06 Mine actually just broke. This is a seriously dubious mod. My advice is don't do it.
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1)
Billetflow Rear Diff cover brace.
Numerous stock Cobras have grenaded the flimsy diff cover. The damage only gets worse as you mod these cars. Get a Billetflow Diff brace ASAP on any IRS Cobra and you will thank me later. They are guaranteed to never break or full refund. This is not a bullsh*t advertisement, this is a critical reinforcing mod to keep your diff/driveshaft/trans safe from breakage.
BF IRS BRACELINK HERE
2)
Firmer Differential Bushings like the ones offered by Maximum Motorsports. They sell a Urethane kit for $50 and a fancy adjustable Aluminum set for $250. There have been other companies that offer low quality urethane bushings that melt and deform in this location (diff gets pretty warm) but I have not seen a report of these MM Urethane ones yet. They may be able to take the heat, I cannot say for sure so no endorsement for their urethane ones yet. Their aluminum ones will work fine. Also any other source for aluminum bushings for here could be used as well. One last thing to consider is the noise of the diff (gear whine) will be transferred more and be audible in the interior depending on how loud your car is. I use aluminum here and have a loud exhaust and can still hear the gears. The front two are the ones susceptible to heat, the rear bushings can be delrin, UMHW, nylatron, urethane..... just reuse the aluminum sleeve from the stock bushing or something like it and it will work fine.
MM Differential Bushings LINK HERE
3)
Quality Subframe connectors like MM Full lengths. Have them properly welded in by an experienced installer on a drive on lift. The drive on lift is absolutely critical, if the weight is not on the wheels you are unknowingly permanently warping and binding your chassis. Other brands like Global West, Laurel Mountain Mustangs and UMI Performance have shown good results. I currently have HANS Force subframes and do not like them, way too much flex, pass on them.
4)
IRS Subframe bushings
from Maximum Motorsports. Others sell them but I have used three sets of these now (3 different cars) with excellent results. Be
CERTAIN to order the 14mm bolts and nuts when you buy your bushings. MM Sells only the OEM strength ones so no need to worry.
MM IRS Bushings LINK HERE
5)
Billetflow IRS Mount Brackets,
3-hole design with backing plates, available now from Billetflow. Sometimes called Mathis Brackets these are an important part of the system. The outer portion of the rear IRS mount bracket is cantilevered out away from any support and free to flex under load. William Mathis originally developed them. I was making a set of my own and cut out a simple cardboard template. While marking the holes to drill I tapped through the template using a hammer and phillips screwdriver. A very mild tap resulted in me piercing the inner wheelhouse metal. Further research showed this metal to be less than 1mm thick and very weak. I did not trust such thin metal to withstand the stress so I then developed a backing plate to make it a robust modification.
Billetflow IRS Mount bracketsLINK HERE
6)
Coupe rate springs or heavier (especially in verts). Coupe rear springs are 600 lb/in, verts are 470lb/in. 650lb/in Cobra R springs have been reported as giving excellent results. I experimented with cutting stock springs and found 1/2 coil cut circumferentially will approximate most commonly available lowering springs. Drop will be 1"-1.25" with 1/2 coil cut. 1/2 coil = one "C" shape.
7)
Drag Radial Tires M/T DR or BFG DR. Nitto DR are an intermediate traction DR, n
need some help
