My Twin Turbo

[T4T]

Castle Combe , hence me taking it steady .

Camp and Quarry corners - infamous for casualty toll .

Matt

[T4T]

Well ..........

The car survived two major driver errors by me - one into the esses and the other at camp - unscathed thankfully .

Car was brilliant , absolutely fantastic , need to adjust rear geometry slightly as the rear axle wasn't quite as stable as the front but still pretty good .
Going to go up a couple of clicks on the dampers as spring rates felt good just the car was a little wobbly .

All other regards the car was faultless other than it needs slightly more oil cooling on the engine .

Nothing too bad but hit 115C after 6 laps of quite gentle driving .

I was taking it steady with hardly any full throttle and pretty much short shifting all the time to keep speeds down ,
still managed my two mistakes though as I have always struggled to judge just how quickly the car is travelling as it accelerates so easily even in a high gear on part throttle .

Any way , the car was really good , awesome in fact , seriously impressed with outright mechanical grip .

Car completely balanced , no understeer or oversteer tendencies , just virtually perfect straight out of the box .

Any how , some photos of what getting it wrong looks like !!
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[T4T]

Looks like I might know what I'm doing behind the wheel doesn't it ?

Not really , as other than getting myself into the situation in the first place , after the last photo ,
ended up on the grass on the inside of the track at a standstill as the weight transfer grabbed the car after I caught the slide .
All caused by me not losing enough ( misjudging ) speed before turn in and having to keep the brakes on into the turn or not be able to get around at all !!

What a wally .

Still , all good in the end and really chuffed with the car's behaviour .

Same corner , later on , not messing it up !!

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Matt

[capri v8 driver]

Looks like you had a great day at the track and all your work pays off.

[T4T]

Photos gone ??

Matt

[capri v8 driver]

Looks like the link of the pictures is not valid.

[T4T]

Sorted photos .

Will be changing spring rates as well . 



Matt 

[T4T]

Not had anything to report for quite a while as too busy as always .
Changed front springs from 450lb to 525lb , changed rear springs to progressive 170-340lb , adjusted damper settings .
Lowered the car by 10mm all round and changed the geometry .
Now 2.75 degree camber with 5 degree caster at the front with parallel toe , 2 degree camber at the rear with 0.25 degree toe in ..........

Awesome !!

8th October on track again !!   

Matt

[T4T]

Track day was good , car significantly improved in the suspension department , but not quite there yet .....

Now putting 650lb front springs and just linear 340lb rears on . Geometry perfect now .

Discovered by pushing the car harder that we needed ducting for front brakes !!

Also managed to cook an ht lead !

Matt

[Marc]

Do you have any more info and pictures on the suspension and brakes you are running? 

[T4T]

Hi Marc

What would you like to know ?

Pics of most crucial things are at the start of the thread . other than current front brake setup and bias pedal box .

If you want some others let me know as doing a couple of bits on the car in the next couple of weeks so I can hit the track again this year !!   

Matt

[Marc]

Lol, I did look at quite some pages, but not at the first. 

Do you also have the coilovers revalved when increasing the spring rates? The springs you are using are quite stiff, but I guess that's OK if you only drive it on the track.

Did you have a Sapphire Cosworth front arb modified to make it less wide to fit together with the compression struts? And how are the compression struts mounted at the chassis leg where the arb also mounts to?

What kind of front knuckles are you using, XR or Cosworth? It seems like they are XR4x4 hubs. IMO you would benefit from using Cosworth 4x4 knuckles as they give a much better front roll centre.

[T4T]

Hi Marc

First page shows the compression strut/anti roll bar mount quite nicely on the original car shell ( this is turbotechnics ) .
The compression strut was the turbotechnics one but I changed to the more typical type used on cosworths to get rid of the bush in the track control arm ( again photo on first page
from when I was first building the car ) and yes the cosworth front arb was bent to suit .

My coilovers are going to be converted to 3 way once I have finished "developing" the car  and will be revalved at that time to suit the sprung/unsprung mass and spring rates .
Have to say though that it appears nicely damped , I think these were valved more for the harder springs than a road car might be ?

Correct on me using xr front carriers . I think probably I would benefit from cosworth ones but the car seems very well balanced etc with the current setup .

The car is not lowered by loads as trying to protect the cv joints so have never worked through the gains by changing .

Matt

Let me know if you would like anything else 

[Marc]

Thanks for the thorough reply. 

You have some great development in that car.    For my Cosworth 4x4 I had some special TCAs made to increase the roll centre more, while I already have the cosworth knuckles and don't run it really low either. You van check the angle of the front tca. If it is going down from the wheel to the crossmember it's not good for the handling.

[Marc]

I found another post from you 

I run coilovers as well .

Have been running 450lb on the front for the last three years but with an antiroll bar and compression struts , 170lb in the back .

It's actually very comfy - I don't have any suspension bushes either , other than poly diff mount .

Now I've been on track , changing to 525lb front and 340lb in the back with a 170lb tender spring to give me 1/2" of travel before the main spring takes over .

We'll see how that is on the road soon in a few weeks hopefully .

Matt

Were or are you using double spring rates on you coilovers? That would seem nice, to have a softer spring for the small bumps and a stiffer spring to limit body roll.

[T4T]

Hi Marc .

Yes , I was using two springs on the back as we wanted to reduce roll from 170lb springs but were worried about losing traction if we ran just 340lb .
On the road it was good .

When we went on the trackday in October we could feel the rear of the car rolling too much when transitioning ,
once the car settled on the stiffer springs (either squatting from throttle or leaning from cornering ) it was much tighter and as we had no issues with traction ,
trying just 340lb now .

Matt

[Marc]

Interesting. What lenghth and poundage springs did you use? As with double springs the combined spring rate is softer. Did you not use double springs at the front?

[T4T]

Hi Marc

I have always used soft helper springs on the front so the front main springs stay on the spring platforms .
The helper springs do nothing other than that ( as I'm sure you know already ) .

On the rear I started with just 171 lb springs - no helper springs required - part no. 300-60-30 . Installed height off the car was 295 mm .
I measured their free length off the car and compressed length with the car on its wheels .

As the new main spring is double the rate of the old spring I knew how much it would compress
and likewise the tender spring as it was the same as the original main spring .

Referring to the Eibach ERS catalogue to see what I could do I fitted 250-60-60 main spring and 70-60-30 tender spring .
All the info on these is on Eibach's catalogue .

This way I knew I would get 10 mm of travel at 171 lb before the tender spring goes coil bound and 342 lb takes over .

I still use the 250-60-60 but have installed 60-60-0002 helper to keep the spring in it's seats .

Hope that explains .

[Marc]

Thanks, that helps a lot!

I have been looking into using these double springs as I think it could give quite a nice ride on the road while still be very good on track. But the difficulty is in finding the right spring rates and lengths to combine.

I'm not sure if you are aware, but the initial spring rate was not 171 lb/in. It was actually 1 / ((1/171)+(1/342)) = 114 lb/in. This is because initially not only the soft 171 lb spring, but also the harder 342 lb spring is compressing. After the 171 lb spring is coil bound you indeed get the 342 lb rate.

I guess the 114 lb/in would be a bit on the soft side, so I'd rather have a stiffer tender spring. But to get a initial rate of 171 lb you actually need a tender spring that is 342 as well, it just needs to have much shorter travel than the main spring. Perhaps the 60-60-0060 would be a better tender spring. At least that would give you the initial rate of 171 lb/in. But I'm not sure if the travel before it coil binds is suitable.

Have you never thought of using tender springs for the front as well?

BTW, if you know the free length and compressed length you know how much Newtons are on the spring when the car is on its wheels. Do you still have that number? As it would be of great help!

[T4T]

Hi Marc , sorry , been a bit busy to reply .

When I read the above 114lb bit I could have kicked myself !

Absolutely correct , I just hadn't thought it through like that !
It explains exactly the way the car felt when driving .

Anyway as we suffered no traction issues now running 343lb with 11lb helpers to take up clearance .

Compressed spring height with the 171lb springs was 234mm so 66mm of compression from free length of 300mm .

Hope that helps

Matt

[Marc]

Those numbers definately help! The 171 lb/in spring is equal to 30 N/mm, so with a compression of 66 mm that means the load on the spring is 30 * 66 = 1980 N. I estimated it would be something like 2070 N. Was yours with a full or empty tank, and with jack and spare wheel present?

I was looking into the available tender springs a bit more. The Eibach 40-60-0060 is probably a suitable tender spring for the rear. It has a rate of 342 lb, so combined the main spring of 342 it will give a rate of 171 lb, before the 342 takes over. And with the 1980 N it should have about 14 mm wheel travel left before it is coil bound.

I was also looking at something that could be used for the front. I believe a progressive tender spring of 250-650 lb (Eibach 0200.250.250-650) might be good. When combined with a main spring of 600 lb it gives a rate of 312 lb until the main 600 lb spring takes over. I believe if should give 9 to 10 mm travel before it is coil bound, but that will depend on how much yours weighs of course.

I don't know if you also drive it on the road, as for only track use the dual rate springs might not be that great. But on the road it should give a much more comfortable ride, while still being good on track. I'm thinking of using these when I get a set of coilovers (which might still be quite some time from now).

[T4T]

Hi Marc

40 litres of fuel on board , no spare or jack as my fuel swirl pot , second pump and fuel filter live in the wheel well .

I am 56% front axle and 44% rear weight distribution .

I only really drive it on track now as it's too fast for the road and it may well end up being track only or even a race car !?



Matt

[T4T]

Haven't updated this in quite a while !!

Now have racing license and go racing with my mate in a TVR Tuscan with an ls3 engine and Quaife 69g sequential box . FAST !! 

Said car



Sierra was on track in April at Castle Combe again , learnt some more as starting to use it's performance capabilities .

Spring rates seem perfect now .

Now 318mm rotors and bells on the back and converted the front to floating rotors .

Front brakes need more cooling and rear brakes need ducting as well .

Now use CL RC8 pads up front and RC6 at rear - AWESOME !

In the middle of modifying bodywork to accept bigger rubber - namely 255/40/17 AR1 on the back and 235/45/17 AR1 on the front . Need the grip !!

Ordered custom step off gears again as changing diff ratio to 3.36 in a 7.5" .

Still as a heavier than standard road car aiming to get into the 1:12's at Combe .

Everyone involved thinks it's perfectly doable .

Find out soon enough !

Over winter probably remove as much weight as possible and fit roll cage .

Matt