Does anyone know how to choose the correct spring rate for a fast road SR20DET powered 1200?
And how do you choose the correct free spring lenght if you are going with coilovers.
I'm going tu use 910 struts, don't know what inserts to choose for them, and by the same I don't know how far I have to cut them. HELP

Use some "creative" common sense.

Let the manufacturers do the work for you.

Select front struts and inserts from a car with a similar weighted engine. Using a 120Y "aftermarket" sway bar will be good. The factory ones hit on the CA18 and SR20 sumps.

For power reasons (And weak springs on 1200s) You only need to "strengthen" the rear, which will normally involve going with one thicker leaf.

If you are using coilovers from another vehicle, try and make sure the donor car is a little heavier, and mount them on similar angles, and in approximately the same places to take into account bodyroll and leverage.

Using manufacturers R&D by using imitation rather than innovation, will save you plenty of time and money.

Otherwise going to a suspension specialist would be good, they have all of the formulas and experience. Unless you want to open your own suspension shop, there's really not much benefit in you learning this stuff.

Basically running "sports" rated equipment will be good enough for the street. Using adjustable Koni, Bilstein or KYB shocks will be good too.

Remember having large heavy brakes will add to the unsprung weight, who's effect is greater in proportion to the car's weight.

If you are shortening the strut tubes..use the new inserts as a measurement.

If you mean cut coil springs..don't do it (Unless your budget absolutely demands it).

Aim for using slightly shorter struts (total assembled length). Using a strut spacer between the strut and the balljoint will slightly lower the car and improve the roll centre of the car.

A good shock/spring combination only needs as much movement as the biggest pothole on the road surface.

Chris

As a starting point, try inserts out of a 4wd celica. They should be around 30mm shorter than the 910's

For the street, try 9-10 inch tall front springs, tack the lower spring platform in place, let it off the jack see if you end up with around 6 inches bump and 4 inches droop travel....
If not, grind the platform off the strut and move it accordingly until you do...
The spacer between the steering arm and the strut is only needed if your bottom arm ends up lower at the crossmember end. For road use, this arm can be 5-10mm lower at the outer (strut arm) end....
Spring rate....hmmm....I could only guess for road use, but say you put an extra full length leaf in the rear, try doubling the front spring rate....

The problem I have is with the stroke of both spring and shock insert. The stroke of spring should be shorter as the shock to prevent bottoming. At least that is what I think.
Once I have chosen a shock insert and I have cut the 910 strut, I can measure the stroke of this insert. I then know what free lenght the spring need to have. But how to be sure that the car will not drop to low?
For the spring rate I suppose I have to watch the spring rate for similar cars with the same engine. S14 or more NX with SR20?

A bottoming spring or a bottoming shock is BOTH bad. Both will mean you risk bending the chassis.

You should have a rubber "bump stop" inside the coilover to prevent either the spring or shock from physically bottoming out.

As for spring rate, many springs have a progressive nature, to provide soft ride and protection against bottoming out under heavy spring compression.

Always have more spring than required, thats why you never see springs close to the same length as the stroke of the shock. For soft springs, the cup on the strut should be 5-10mm more than the sum of the diameters of the spring material from top to bottom. This means that the spring can never bottom out.

Then it's up to the shock to stop itself from bottoming out, and the spring strength to assist, given a maximum load scenario.

Seriously, you should just use factory parts, or someone elses tested solution, and all of these considerations aren't required.

Chris

Quote:
Please give me an exemple of what you calll a factory part for my 910 strut?

Ok, you are "fixed" on using these 910 struts. These were on the 1980's Bluebirds here in Australia. This is part of your problem. I don't know of anyone else using these struts in their 1200. Does this not set off alarm bells for you?

Is the 910 strut assembly the best platform for your brakes and front suspension?

There are many reasons why people choose a strut for use in their Datto upgrade:
- Cost
- Availability
- Length
- Shock Absorber Availability
- Camber on Axle
- Availability/Cost of Brakes spare parts
- Ability to work with a known upgraded disk/caliper
- Availability of Springs to suit a 1200

I don't know what made you decide to use 910 struts. I can only think that you had them in your shed, and have chosen to use them based on Cost and Availability.

You have chosen a combination that has not been tried by other people. You will need to answer many of your questions through trial and error, and this will involve cost and mental pain.

By following the combination of parts used by others, you don't need to understand the complex science of suspension systems.

In Belgium do you have many "Wrecking Yards" with Datsun parts for sale? In Australia, we have them, and most have a good selection of parts to choose from.

If you have only a small number of choices in what spare parts are being used, then this will constrain the solution that any of us can provide.

When shortening the strut tube, you are making changes that will require some degree of trial and error.

1. Say you cut down the strut to suit a 240Z insert.
2. What length spring does a 240Z use?
3. What weight is that spring carrying? Too much for a 1200. For B110 diameter springs you can use the 240Z, 1200, 210, 310, A10 springs. All of these the same diameter (different length, different load capacity). There are also 2 diameters of strut tube. Smaller 1200 ones and the larger ones for L Series equipped models.

If you are to use the 910 struts, then the spring cups will need replacing. I recommend using stanza A10, cups. As they are the larger diameter, and cheap and easy to find.

The 1200 springs (even aftermarket sports springs) have enough travel to cope with the shorter 240Z inserts. So I'd recommend using aftermarket lowered sports 1200/120Y springs, Stanza Cups, 240Z inserts, and cut down your 910 struts to suit. Assemble the struts with the cups loose on the strut tube, push the cup up until it holds the spring in place with shock insert extended. With a texta, mark the spot where the cup is sitting on the strut tube. Disassemble the strut, move the cup 5-10mm up the strut further, to provide some spring preload, so it doesn't rattle around when the car gets airborne over speed humps. Tack the cups into place in 4 spots. Reassemble the struts, and drive up and down your driveway and see where the ride height has settled. If it's ok, remove the struts and complete the welds around the circumference of the cups, then refit and go for a decent drive.

Chris

I am also using 910 front struts, I was recommended these by people in the car industry that use to run 1200's in rallys. I have carried out modifications upon recommended strategies. 310 sterring arms and bottom ball joints (which increase track width by 25mm) OE bottom arms, radius rods and top strut support. New 910 shocks and compressed 910 springs lowered to set camber but using original spring rate.

But heres the biggy, I have yet to complete this task which will happen one vehicle is reassembled with full vehicle weight, so I can neither confirm or deny whether this setup IS successful.

Damon

Ill be doing more or less the same. A mate of mine used asimilar set up , only he welded threaded pipe to the strut, and had two big nuts underneath the bottom spring cup to make the height adjustable. Then he had hillman avenger stationwagon rear coils either cut or compressed( I'll have to ask him) . Adjustable strut tops, 310lower arms modified to give adjustable camber, and he had cut and welded some 310 steering arms to alter the ackerman. When the time comes I'll hit him up for more info. But anyway that car had demon handling.

Quote:
As you can see, I'm not alone

Taking about availability of Datsun parts not only in Belgium but in nearly hole Europe, it is = 0
All Datsun and Toyotas have been sold to Africa regardless of rust, engine damage, missing parts. Africa took it all.
Only way to get a Datsun is buy one where they are still running for exemple PORTUGAL. You can compare it a bit to California, US. Much sun, few humidity, no salt against snow. Even better are cars from the isle of Madeira. That is were I bought my 2 B110 2door and 1 510 4door.

So if you need much parts for a conversion/swap you take it from another cars you bought before or you just buy a new ones.

You're right I had 910 still as NOS in my warehouse.

Quote:

This Is a fine description of what I was worried about. If the ride height is not good, if I have to lower the car a bit more.....what happens to my spring?....not enough preload! As I will work with height ajustable spring perches

I could use a helper spring to give enough preload at full suspension travel. But before using a helper, you have to choose the right main spring. That is what all this topic is about.

And don't forget I will use a SR20DET, so a 1200 aftermarket sport spring will compress to much under the more weight of the SR20DET. At least that is what I suppose.
Butr at least I know now that I have to start with 240Z shocks.
It seems that Tokico Illuminas are preferable to the Koni's as I read on the 510 mailing list.
Thanks to all,
Chris
To all 910 strut user keep the forum updated about your experience