Its been a while and I hope you're concentrating
Tonight I've removed the balance pipe I put in and I've welded up one of the holes. I'm pretty sure I'll be making up some silencers of my own now, I'll be looking at copying something like the design of the Flowmaster exhausts I think.
I've finally done the weighing of the un-sprung weight of the car. This was a little tricky even with the simple method of removing the springs and lowering the wheel onto the bathroom scales. The trouble was the friction in the bushes. So I weighed it on the way down then continued to lower the car, then raised it and took another reading on the way back up (the average of the values is the true unsprung weight plus a little extra for the spring). I did this a load of times and got a very interesting result.....
The front unsprung weight was (a massive) 87kg per side, and the rear was less!!!! at 73kg per side. I didn't see that coming (with a heavy beam axle on the rear).
Now there are people who can build cars, and people who can drive them, then there are the rare skilled folk who can drive a car and can feel what alterations need making. I'm not one of them, so I was genuinely relieved to find there are some calculations you can do to get the spring rates in the ball part. Hence the all the weighing. The end goal is to find the natural frequency of the car front and back and bring these frequency figures close together. Here is the page I used from "The Race and Rally Source Book" Alan Staniforth: (If you're interested read between the red bits)
Now to cut a very long story reasonably short, you need to know
Axle wieghts
Unsprungs weights
to find the sprung weights of each corner of the car.
Then the coil spring rates
leverage ratios
leverage ratio ^2
Effective coil rates due to their angle on inclination (a little trigonometry)
to get the wheel ratio
then using the sprung weight and the wheel ratio, calculate the natural frequency.
Which is exactly what I did here:
The book is a little old but basic physics doesn't change, it suggests that for a road car the natural frequency (in cycles per minute) should be between 60 and 80, then 80 - 100 for a sports car, 100 - 125 for race cars. With the front being between 10 and 20 less than the rear. You can see mine in the sheet above. I was expecting to have to get stronger springs for the rear, but it seems the opposite is true I need to strengthen up the front end to get the balance right (show's I'm not much good at "feeling" what a car needs
)
The reason the front needs to be so much stronger on Scimitars is the fact that the wishbones weaken the effect of the springs by giving the wheels more leverage of the spring.
I've yet to decide which to buy but I'm thinking 450lb/in front and 225 rear to get the balance spot on.
Hope you took all that in
More to come.
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Topic: Scimitar MV6 (Read 91196 times)