New Front Coilovers, Calculating Length?

[260DET]

For race car so lower ride height, less spring deflection under load due to heavier springs and the amount of droop are the main considerations. I have no idea how far the car sat down on the original springs/dampers at static ride height so without that the length of the new coilovers is guess work isn't it? Reducing the static ride height by say 1"/25mm would be a good start but how do I get there? To make things more interesting the new setup has less travel.

 

I'm thinking that to reduce ride height by 1"/25mm the overall strut level should be reduced by twice that to take account of less spring deflection, does that sound a reasonable guess? It looks like the sleeve should be just tack welded in place until the powertrain etc is installed and the car can sit on it's suspension.

 

At least our resident racer would have struck and solved this problem if only when working out the amount of droop required so I'm expecting some informed responses here 

[dat2kman]

Go check out a builders supply yard, grab a couple of bits of threaded scaffolding tube, a couple collars and a couple of lock rings.

Before removing, rest it on tye ground, and meadure distance between the top and bottom spring perch seats.

Rip your struts out,measure uncompressed free length, same perch to perch, theres your static compression height.

No pull struts apart, carefully grind perch off strut, slip said threaded acaffolding tube over, tack weld, fit lcking ring, then collar, machine disc to suit ID of springs, reassemble, using current strut top and perch.

PRESTO!

Coil-overs, then start playing with ride heights.

Start from there, then worry about shortening strut, thicker wire diam springs, and shorter length strut inserts, later

( Toyota MR2 are nice and short!)

 

You should know all this simple stuff,,,,,,

 

Crikey,,, I just noticed,,,, 3900 posts on here, of usefull knowledge, information and years of experience on lots of things Datsun!

Edited May 9, 2017 by dat2kman

[260DET]

That will be of use to someone for sure but it doesn't answer my question. Which is based on the fact that heavier springs change the ride height.

[Cozza]

Crikey,,, I just noticed,,,, 3900 posts on here, of usefull knowledge, information and years of experience on lots of things Datsun!

And 3785 of those arguing with Richard!!

[dat2kman]

We dont argue,,,, we have deep meangfull discussions!

[dat2kman]

That will be of use to someone for sure but it doesn't answer my question. Which is based on the fact that heavier springs change the ride height.

Correct!

Then, after you have installed whatever springs from whatever model Ferguson tractor you have chosen, you then wind the adjusting collars up or down, to get near to desired ride height.

If you have gotten close to limit of threaded tude, then you'd need to reposition tube over strut leg, in order to give more thread to make finer adjustments.

Thats why you just secure it initially with a couple of tack welds.

[d3c0y]

I went through this with MCA when I did my coilover setup. For optimal performance you want your control arms parallel to the ground, or as close as you can get them; that is what Murray Coote told me anyway. You might not be able to get it that low, like in the case of an S30 where flat rear arms is really damn low. Have no idea about setup for trailing arms at all though, sorry.

 

If you are going to run a cut strut with threaded tube welded on and a modern coilover on the front, you just get the shortest strut you can. The MCA struts ended up being plenty short enough in my application to the point that I was lengthening them to get the correct compressed length. For a race setup you only need about 60mm of bump travel and that leaves plenty of room for droop (80mm ish from memory). The old MCA site had a great article talking about what sort of travel you needed in both directions, but i don't seem to be able to find it anymore. 

 

Yes, I'm an MCA fan boy and if you buy their shocks, (which you should) Josh and Murray are more than happy to discuss setup over the phone to point you in the right direction. 

[260DET]

Agree that MCA are the best, the damper kit I got was custom for the Z31 but still needs the original front spindles which of course have to be welded on. I'm guessing that the right height will require the bottom of the supplied strut to butt up against the spindle with a small gap to enable a good weld plus there will be a welded in brace between the inside top of the spindle and the strut. It will all just be tacked in place at first.

[nizm0zed]

Correct!

Then, after you have installed whatever springs from whatever model Ferguson tractor you have chosen, you then wind the adjusting collars up or down, to get near to desired ride height.

If you have gotten close to limit of threaded tude, then you'd need to reposition tube over strut leg, in order to give more thread to make finer adjustments.

Thats why you just secure it initially with a couple of tack welds.

 

can we get this in the diy section? with pics please?

[260DET]

Correct!

Then, after you have installed whatever springs from whatever model Ferguson tractor you have chosen, you then wind the adjusting collars up or down, to get near to desired ride height.

If you have gotten close to limit of threaded tude, then you'd need to reposition tube over strut leg, in order to give more thread to make finer adjustments.

Thats why you just secure it initially with a couple of tack welds.

 

Yes, but if the kit you have has separate threaded adjustment for both spring and strut heights then you can adjust the bump/droop ratio independently of ride height. Last I heard MCA don't offer this but it has obvious advantages.

[dat2kman]

Yes, but if the kit you have has separate threaded adjustment for both spring and strut heights then you can adjust the bump/droop ratio independently of ride height. Last I heard MCA don't offer this but it has obvious advantages.

And THATS why you do a trial assembly first, with light tack welds, and once fitted, car set to near desired heights, then measurements at static are taken, allowances for bump and droop, measurements, and then calculate shock insert required dimensions, then off the scrounge the catalogues, then, once procured, section the strut, and reweld to suit the new shock insert

Like I said, have a look at the Toyato MR2 rear inserts.

 

The canned MCA's will give bump/rebound valving adjustability, in both slow and fast cycling, but going on what you are doing, the regular range of MCA as built units, will be too long ( very low ride height Ferguson Tractor Z31 Spurting Sedan race car,,,,,)

 

What about fabricating a double A-arm wishbone front end, and run a coilover type body shock absorber?

I'd attach images, but Gav tells us the server s a bit chockers

[d3c0y]

They certainly do and it's what i have in my car. They even modified my original struts to suit.

 

I thought i would have the strut length issues, but i don't i have tons of room from the shock to the bottom of the strut tube, to the point that i have adjuster extensions coming out the bottom of the strut as i'm using inverted mono-tubes on the front.

 

 

 

[dat2kman]

Jake,,,, Richo is building a real racecar, with 40mm of ground clearance, and 700 donkeypower, Muzza's units just wont cut it!

[Cozza]

They are a sexy strut Jake. What spring rates are you running?

[260DET]

Have 3 way MCA's on the 280ZX, as I've previously mentioned several times they are great but back then they did not offer the strut height adjustment option which would be very handy now to avoid the compamises having to be made as a result of the Bathurst experience. 

 

Until the Z31 has all the heavy stuff in the height to cut the original struts is just a guess which is what the original post was about. The actual suspension performance on the track will obviously have to wait, if it's not up to scratch then MCA will fix them, that I am confident of.

 

Jason, what you made do with in Sc does not apply here, this is serious stuff not an old boys day out, see that your P car mate broke the MP Sc lap record the other day, lol, this is fun 

[d3c0y]

You don't need the heavy stuff in it to work out what your strut lengths are. I didn't realise that you already had the suspension, i didn't read your earlier post properly sorry. 

 

I don't think not going low enough will be a problem either. I looked back to my emails with Josh and the coilovers in the photo can make an S30 so low that the engine cross-member is about 30mm off the ground on their shortest setting with the setup in the photos. 

 

This is how i see it:

 

A) Get the fully compressed length:

1. Get your factory suspension, take the springs out and mount it back in the car

2. Attach wheel and tyre combo you are running

3. Jack the wheel up as far as you can go

4. If the strut fully compressed still isn't low enough (for your full bump length), just measure the distance to the closest fouling point.

 

B) Get approximate ride height (ideal length) by lowering the wheel until your arms are flat

 

C) Take into account the fact that you aren't going to be running factory insulators on the top and adjust measurements for the pillow ball strut top.

 

Your strut will need to yield you at least 50mm of bump travel + bump stop 15mm for a racecar with stiff springs.

 

Then you have the lengths you need the shock to be, just take out your new shock length from them and the remaining length, plus about 60mm of overlap for strength and adjustability, is the length to make the threaded tubes, or if you add it all up the new assembled length.

 

Ya dig?

 

Also I'm interested to know what the problem with your 280ZX's ride height is with the three way shocks? Was it too low? 

My experience is once your strut length is optimised, there is no real point in changing it. Ride height is another story but that generally comes down to how much total travel your shock has more than anything else.

 

I love this suspension stuff, I find it really interesting.

Edited May 11, 2017 by d3c0y

[d3c0y]

They are a sexy strut Jake. What spring rates are you running?

 

 

I went with 6kg front and 5kg rear then, which is 340lb and 275lb.

 

The blue strut isn't mine, we got three sets made at once, i just didn't have a pic without brakes getting in the way.

 

[260DET]

I'm a suspension fan too Jake, it's usually a greatly underestimated part of a track package. Chassis stiffness is part of that which is one of the reasons why modern performance cars are so good, while exceptionally good drivers can do a lot with an old flexy chassis most of us are not in that category and need all the help we can get. 

 

When MCA did the custom suspension for the 280ZX I had to tell them what length the struts had to be, my modifications had made it a one off. Because there is no separate strut height adjustment the spring height adjustment has to be used to change ride height and that changes the droop/bump ratio. For the Z31 I'm aiming for 50/50 rear 30/60 droop/bump front as a base line, the 280ZX is nowhere near that as a result of adjusting in a bit more rake for Bathurst. But keeping the front on the ground is a priority there, having the front move sideways at 200kph on Mountain Straight is a ball shrinking experience.

 

Thanks for the tips, of course the Z31's ride, suspension etc heights should have been measured before the car was stripped, not doing so has resulted in some guess work and frustration at the back too which otherwise would have been unnecessary. 

[d3c0y]

But you should adjust the ride height with the spring adjustment, but I'm sure that MCA would have told you that. So the only scenario i can picture is that your struts are too short and your springs are really stiff so you don't get any droop?Depending on how far off you are, you could make up some thicker top mounts to effectively lengthen the struts. Think about how thick the factory strut top insulators are.

 

Either way, for the Z31 you know the travel of your shock and you know your target bump/droop ratios so these are all static numbers, you just need to add them up. Then if you are still worried put a bit more length in to give you more adjust-ability.

 

I honestly don't think the stock measurements matter at all, you just need to know where you want it to end up.

[260DET]

The 280ZX is not going to be developed any more before Bathurst, the front splitter and undertray have been modified to eliminate (hopefully) front end lift and that's about it. While the suspension bump/droop setting are far from ideal there was no indication last time that handling was deficient, testing at Morgan Park is not much use because 200kph is about it there. QR full track might be a good place to test yours.

 

The 'where to cut' decision for the Z31 struts has been made but it will be tacked together first, with the range of strut adjustment available even I should be able to get it right enough.

[d3c0y]

I'm going to have tons of droop with my setup i'll be like 40/60 bump/droop. As long as my aero doesn't touch the ground too hard it should be ok.