Spring Question With Shortened Struts.

[Chris Duncan]

Just need to run this by the forum to see if my thinking is correct

 

'75 Z. Shortened all 4 strut housings by 2" and put Bilstein Sport struts (34-184530). I shortened the struts above the spring perch and left the perch in place.

 

So using the existing spring does this not increase the spring rate just because it is compressed 2" more just to install it on the strut assembly?

 

What has happened is that it had stiffer springs when I got it and now that they are compressed 2" more at full strut extension the car is not sitting at or even near the middle of strut travel.

 

This is a Chumpcar so you can't just buy new springs or put threaded perches. Need to use/modify the existing setup.

 

So do I start cutting off coils or do I try to shorten the spring with the oven method shown in "How To Make Your Car Handle" by Fred Puhn?

 

What if a stock spring was used without cutting it at all, would it approach coil bind with the 2" shorter installed height?

Edited June 5, 2014 by Chris Duncan

[logr]

If memory serves, those struts are shorter than stock struts so you could be compressed even more than the 2 inches. Since springs are rated by the distance compressed and you just compressed them, seems they would be stiffer.

 

I would consider lowering the perch if you have room, if not, go to shorter springs by whatever method.

 

Considering the travel that a stock strut/spring has, I would really doubt you could coil bind a stock one on a shortened strut.

 

I happen to know of a chump car Z that has some prelude springs on it.

[johnc]

You increased the spring preload by whatever the spring rate is * 2.  Of more concern is that you are probably rebound travel limited.  That can create issues in back if (or when) you pick an inside rear wheel up off the pavement.  That leads to a spin.

 

You can carefully cut the stock spring perch off at it base, weld a ring lower on the strut tube, and then weld the stock spring perch back on that ring.

[Chris Duncan]

You increased the spring preload by whatever the spring rate is * 2.  Of more concern is that you are probably rebound travel limited.  That can create issues in back if (or when) you pick an inside rear wheel up off the pavement.  That leads to a spin.

 

You can carefully cut the stock spring perch off at it base, weld a ring lower on the strut tube, and then weld the stock spring perch back on that ring.

 

So would you go the same two inches?

[G-E]

If the spring is completely linear (swift springs are very close to linear for a lot of compression for example) then compressing the spring 2" before putting any weight on it would not affect the rate... realistically you are though, because most springs are really not very linear.

 

However by preloading it that much, you will probably have a really harsh ride, imperfections in the road will upset the car a lot more than they should, I'd say you'll probably want to cut a coil off... or as suggested lower the perch

[JMortensen]

I had some friends who used to do something similar with 510s. They wanted smaller OD springs, so they'd use 240 stuff, and they'd cut the spring perches off of a 240 and weld them onto usually 280ZX struts (disk upgrade that fits under 13's and has the right spindle angle). If memory serves they welded the perch so that there was no preload.

 

If you went the same 2 inches lower, you'd get back to stock, but that's pretty light springs. Stock in front of a 240 is something ridiculous like 83 in/lbs. Could you do the old Chevette spring upgrade? That's low buck, if you can find a Chevette...

[Chris Duncan]

The springs that the car came with are off something else (not a Z) and they are cut. They didn't do a very good job with the angle of the ends and they don't match the perches, so the springs sit a little bit crooked.

 

The whole conundrum is I have to weld on the perches, but to get the ride height spot on is going to be tough. I need some clamps to clamp below the perches so I can move them to determine where they should be. Of course the OD of the strut tubes is 2-1/8" so the clamp is not going to be anything off the shelf.

Edited June 7, 2014 by Chris Duncan

[Chris Duncan]

So we've got two options for springs from other cars.

 

Honda Prelude

 

Chevy Chevette

 

any idea what years/gen those are?

Edited June 7, 2014 by Chris Duncan

[tube80z]

Do you not have enough budget to get springs?  I have a friend who has a Z chump car and it has 2.5 springs.  You get a budget hit for your build but they can be used.  It was cheaper than what they charge for sway bars.  Another option would be to do the old muffler clamp adjustable collar mod.  A lot of 510s used to have that.  You can use that to adjust corner weights or use it to help with balancing the car.  

 

Another oddball option would be to use really soft bump rubbers to augment the spring rate.  Then use packers to adjust engagement.  Nascar tech comes to chump car.  My personal feeling is that there's a ton of aero that could be done to help make the car faster as well as get better mileage.  That helps you get to the driver time limit on a tank and helps to keep the lap times up.

 

Cary

[Chris Duncan]

The Bilsteins mean $100, urethane bushings $25, headers $50, fabbed camber adjusters $10, materials for air damn, rear spoiler $20, Lexan $20. That puts it near $500. Springs are $20 ea, so $80.

[tube80z]

I've been over this a lot with some friends who race the rolling craps Z.  Not sure where you did lexan but if it's for the rear hatch go back to glass.  I would not bother with poly and use new rubber bushings.  There are plenty of tricks you can use to make them stiffer.  For camber adjuster slot the strut towers.  Why are you using bilsteins?  You should learn the fine art of arguing about replacement parts and how you can modify those.  I would also think about spending $10 on a couple of heims in strategic spots.  Become a wood worker.  Plywood is the cheapest material to work with and you can make a really nice wood airdam.  The rear spoiler can be the rubber cover that fits in the rear bumper on a later 260 or 280.  For a 240 I guess you'll make a nice plywood one.  Laughing at the plywood I can send you some links of a guy that makes wood parts for his F1000 and DSRs.  He used to race airplanes and boats.

 

Springs and collars are $80 for the car and a gift for what you can do with them.  Use a replacement insert or learn how to make the stock wet struts work.  That's what people did in the old days.  You have to get creative and push boundaries.  We're not cheating or bending rules but we're taking everything as black and white down the center.  If you want shocks and don't want to fight lose the header.  Power is going to be less help than a better working suspension with higher rates.

 

I would then do a lot of aero based on plywood.  Vent the hood, open up the fenders by cutting and folding them (stock part still), splitter, and side splitters.  You could make a wood wing but I'm not sure what they would say about that.  

[johnc]

Use the clamp trick to figure out your ride heights and then weld the stock perch in that spot.  Try to come up with about 2" of droop travel at the shock.  Without knowing your spring rate you'll have to be careful about bump travel fr the coil bind issue.  Progressive bumps stops as mentioned above is a great idea.  Try every possible no point mod and cut out brackets, mounts, etc. to trim weight.  Did that on a customer's E36 BMW and saved 80 lbs.!

[tube80z]

Going along with what John mentioned there's a lot that can be done for free.  Years ago for showroom stock and similar race classes a lot of tricks were employed to make the cars faster.  Often crash damaged parts would be used.  These are parts that were strategically bent to attain a specific alignment.  You can bend the front steering knuckle to bump steer the car.  You can bend struts to get negative camber.  You can use a porta power to push areas of the car around.  A little here and a little there adds up.  You can decide of this is cheating/not ethical but it's all part of pushing the rules boundaries.  And along those lines you can lookup betafoam from DOW.