Neil

and where did you get them from? Is Spohn the only one who has developed this kit for thirdgens?

86IROCNJ

Hey Neil, have you tried Art Morrison, or Ground Control? I believe they make kits for our cars, or did anyway. Also, I know of that "Orange Japanesse car" had a set on it. Purple anodized and everything. Do not know who made it for them though, never seen it before. So, how's the car running? Later-Bryan

RTFC

Here's a shot I have of one on a 4th gen, basically identical to our cars (disregard the text on the picture, it pertained to something else that I had saved on my computer)

AlkyIROC

Is the sheet metal at the top of the rear shock strong enough to support the car? Normally a rear coilover setup uses a seperate crossmember bar welded across the top somewhere for the shocks to attach to. I think a properly designed rear coilover kit for third gens should place the top of the shock where the top of the spring normally sits since that's already reinforced to support the car.

Apparently a company called www.autofabracecars.com has a good third gen rear coilover kit using adjustable QA1 shocks but they have very little listed on their web site.

25THRSS

I have the autofab rear coilover kit on my 4th gen and it is holding up just fine for every day street use and the occasional 1.5 60 foot at the track.

83 Crossfire TA

iTrader: (2)

I’d say no… I’ve seen the top shock mount crack and start to tear out on a 3rd gen setup for road racing with just a shock mounted there, that point is nowhere near as strong as the top of the rear spring pocket. It looks like that drawing is showing a reinforcing plate that bolts in, a better solution is to box the recess that the shock bolts to and then even possibly running a down bar from the roll cage/bar down to the boxed section, or at the very least tie it into the pinch welds near where the rear wheel wells are tied into the floor (the sheet metal is 3 or 4 layers thick there).

Neil

86IROCNJ, my car is running pretty good. Actually, after I put the ZR1's and 315's on I had to do a little "initiation burnout" shall we say and it was awesome at least it felt pretty awesome. The good thing is a buddy of mine video'd it! When he sends me the file, i'll post it.

Thanks for the pics and ideas. I like the idea of adding metal to the upper shock mount to make it sturdier. I'll definitely do that. The reason I am looking into coil overs is so I can tuck the 315's in without spacers. I have modified my lower control arms to accomodate the tire and as well as cut and pounded alot of the inner wheel well. As it stands now, I can put the wheels on without spacers, but there is only 0.25" clearance between the inner wheel well (where the coil spring is) and the tire. So, by going with coil overs I can get rid of the coil spring and knock that sheet metal out of the way and have more than enough clearance.

18inchboyds

check this out .

Neil

Very nice! Awesome pics! Thank you.

Neil

Ok, next question. What spring length did you use and do you know the part number for that shock?
I have been pricing these parts out and from Summit, those QA1 Promo Star shocks are $169.95, springs are $36.95 and the eyelet mounts for the shock (top and bottom) are around $15 a piece.

86IROCNJ

Hey Neil, can't wait to see the vid. I want to see the wheels on the car most of all. Anyway, back on topic, I believe those pics he posted were off of Spohn's site for the rear setup. Could be wrong though, but they look identical.

RTFC

Just so you realize, Those pictures posted are Spohn's rear coilover kit. Those are plates that are added in the pictures above to strengthen the shock mount area to support the load weight of the vehicle onto that rear shock mount. The pictures do not show the plate welded into place yet, but do note that it is a plate that is added and is not stock.

If you run a coilover into the stock shock mount without the reinforcement plate, that area will bust through in no time especially on a car that may have cancer.

Forshock 85TA

That looks nice. Us the place GM wanted the weight to go to. If that is the spohn kit: Steve, that was worth the wait.

Looks great

Neil

So, is the upper shock mount position relocated to where the stock upper coil spring perch is?

Forshock 85TA

Yes, in the spring pocket.

Neil

Hmmm, any idea as to how close the coil over assembly is to the sheetmetal which encloses the stock coil spring pocket (on the wheel side)? This is the metal that I must remove or pound in slightly for those meats!

91Z28-350

I'm not so sure about that. It looks like the stock location with a reinforcement plate. It doesn't look like the shock mount is relocated.

How thick is this plate? Essentially, can you revert back to standard shocks?

RTFC

Yes you can. If you look back up at my first post with the sketch I have on that, It shows the use of a re-inforcement plate to redirect the load of the coilover from the shock mount back to the spring area with the support of a 1/4" steel reinforcement plate. Whether it is bolted to or welded, the spring pocket is strong and a 1/4" plate extended towards the shock mount will handle the load of the car. Steve opted to make it weld-on with the use of the shock I bolt to position and hold the plate into place while you weld to keep things aligned. You can still use a conventional spring and isolator ack into the spring pocket even after the reinforcement plate is wellded in- hence the open pocket for the spring dimple- the car will just sit a 1/4" higher than before

FirehawkSS

iTrader: (2)

Whats the gain or the advantage to running a coil over setup on the rear wheels? Just curious because it doesnt seem like there is an advantage. It looks trick no doubt but i dont see any performance gains. If anything you want the spring perch to be directly on top of the axle for maximum spring efficiency. Moving it to the other side of the axle doesnt give you any advantages over the original location. They are both about the same distance away from the axle centerline. Maybe a little closer with the coilovers but is it enough to make a difference? Just curious someone please correct me.

german-motorsport

Neil are you sure about the prices?

ME Leigh

I agree, mounting the coilover like that is gonna cause some funky forces. Did anybody do any engineer analysis or even looked into these design questions. The spring force and the damper forces are now on the same side of the axle, with the spring force being opposite.

I'd mount the coilover directly on top of the axle and the other side to the spring pocket.

FireRed91Z28

i am looking into the spohn coil overs my self and i have 315s also.... anyone know the answer to this?

AlkyIROC

Nice pics and a question I was going to ask is already answered. I was going to ask how those upper plates are attached and later saw that they have to be welded in. At least that setup makes more sense than trying to use a coilover aqttached to upper shock sheetmetal.

Advantage of coilover springs isn't really a street advantage. Racers use them because they can quickly change spring rates by swapping springs (another tuning aid). Since they're adjustable, you can also adjust the ride height.

As for the angle, they don't have to be exactly straight up and down. Look at a few custom rods. They'll use a rear coilover for a clean simple installation and sometimes have them angled inward as much as 45*.

RTFC

To
basically answer your guys questions about coilovers mounted on the front side of a solid axle suspension, take a look at any late model NASCAR. Their suspensions are practically identical in link setup on the rears.

Neil and FireRed, The mount hole is the identical hole you can see pictured above in the pictures. That hole in the middle of the Spohn reinforcement plates for the coilover mount is in fact the isolator "hump" for the centering position of the factory coilsprings. The coilover is thus mounted into the original shock mount position which is only about 1" outside the isolator/sring contact (or "can") position in the chassis-HOWEVER- even thought it is that close, it is a step down in thinness from the top side and is not as strong by any means as the spring pocket only 1" away- hence the NEED for a reinforcement plate.

Advantage?- Motion of spring travel without bind, set corner weights exactly, set ride height exactly with varying spring rates, less unsprung weight for better handling and ride.

83 Crossfire TA

iTrader: (2)

Coilover in itself simplifies some of this, since the shock is just a damper for the spring, and having them working in the same location, against the same lever arm with the same range of motion makes life very easy for a designer to get in a reasonable ballpark.

As far as before the axle vs behind it… well, behind it gives it more mechanical advantage and you’ll need lesser rates then in front, but in front allows for more travel from a smaller assembly allowing for a marginal decrease in unsprung weight and some other small advantages.



Well, the adjustable thing I’ll buy, but the “quickly change” part is complete… well, I can jack the back of an f-body, and even with the stock, tall springs compress the springs by hand, pop them out and put a different set in in less then 5 min… no fastners, no tools…

perpendicular to the motion is the most effective, but mounting them at an angle can work as long as you compensate for some of the change in force vectors. I would suspect that to some small extent angling them some would actually have the additional effect of dampening some spring harmonics, but I don’t know that I’ve ever seen any evidence to prove that.

ME Leigh

Could you design away to mount the so that the torque arm is not needed?

83 Crossfire TA

iTrader: (2)

If you get rid of the TA you have to find another way to hold the rear from rotating in the chassis, either a solid link at the back of the LCA’s effectively making them traction bars or a 3rd link at the top of the housing. Shocks/struts are meant to compress/rebound so they aren’t going to do the job.

Neil

German-motorsport, yeah, I am sure about those prices, but it might be better to go with the Spohn kit, that way you get the re-inforcement plate and you don't have to worry about fabricating your own.

FireRed91Z28, by looking at the pics again, I think there is plenty of room to pound in the sheet metal to allow for tire clearance. I don't know if I would cut that section completely out because it looks as if it might be used to strengthen the rear frame.

Zerstörer

Can the 1 bolt at the bottom of the coilover support the whole car? Stock wize the springs rest on the perch thats welded onto the axle. moving the springs onto the shock places all the weight and forces on that one lower shock bolt. I would think that 1 bolt would be prone to snapping when the vehicle is in motion.