Author Topic: Turbo Squareback - History & Rebuild Thread  (Read 19104 times)

Offline breadman

  • Members
  • *****
  • Posts: 636
  • mk2 breadvan 1341 turbo sleeper (currently snoring
Re: Turbo Squareback - History & Rebuild Thread
« Reply #150 on: July 26, 2013, 06:46:43 pm »
You must be extremely pleased with how this has turned out Andy?
Looking at the first pre MOT picture, who would ever think that this was a very quick road car that was also built for track day and 1/4 mile action? ;D
Glad to see you haven't gone for the race look with stripped out the interior and so on, looks so much better for it. Still looks very much like a basic Polo albeit an immaculate one.
Proper sleeper, great work.

Offline Andy

  • Traders
  • *****
  • Posts: 1494
Re: Turbo Squareback - History & Rebuild Thread
« Reply #151 on: July 26, 2013, 08:44:21 pm »
Thanks for all the positive comments!

Just got this back from Centre Gravity after a lengthy geometry setup on both mine and Yoof's Polos. Was an educational trip as well as a productive one. I don't profess to be a chassis expert, so please take the following in that context!

Interestingly, although the damping I'd set on the Gaz coilovers was out by a country mile - and my spring rates are on the hard side, my DIY geometry setup wasn't too ridiculous. String, spirit levels, rulers and measuring tapes can get you to a decent position if you've got a flat surface - though I think some luck and a straight shell also help!

Ride Height
I'd set my ride heights myself, turned out FR and FL were the same to the nearest mm, and RR and RL only 1mm out. Time with a metal rule and coilover C-spanners paid off. The car isn't low, but I'd set the ride height as a compromise between aesthetics and suspension travel - biased towards the latter. Feedback was that suspension travel is good.

Dampers
The car was put on a damper dyno, to check the damper effectiveness. Data from this, coupled with a test drive, enabled CG to significantly alter my randomly-guessed damper settings to something sensible.

Weight
Total car mass, with >3/4 tank of fuel and full washer bottle was 841kg. I have a full interior, no spare wheel, but things like interior rubber mats etc. in the car too. Put it down to half a tank of fuel, and it'd pretty closely match the official G40 weight. Not bad considering massive radiator, intercooler, big heavy exhaust etc. So far so good!

Most places won't touch the rear axle on the Polo, as the computer tells them it's not adjustable. This isn't the opinion of CG thankfully... I'd bolted on a straight-looking G40 rear axle, and aligned the brackets based on the original marks in the underseal. It appears that on a straightish car with a straightish axle that this is a decent place to start.

Rear Axle Before
Camber Left -1°52'
Camber Right -1°29'
Toe Left +0°12'
Toe Right +0°18'
So, it had some negative camber at the back - as most Polos that are straight and have been lowered will have. It wasn't even both sides (remember 60 minutes in a degree, not 100 - so 52' is nearly 1°) but not horrific either.
Toe out is, I believe, desirable to a certain extent on the rear of a FWD track car, as it helps the rear to grip mid-turn and aids turn-in. However, for a road car you don't want the rear to be too lively.
So therefore there was scope to improve...

Rear Axle After
Camber Left -1°29'
Camber Right -1°30'
Toe Left -0°01'
Toe Right +0°07'
As my axle and chassis seemed to be straight, no tweaking on the axle mounts was required - just Eibach shims behind the stub axles.
Rear cambers are now very even, and toe much more appropriate for a road car.

As most geometry setups reference the rear in one way or another, it's important to get this right! Then it was on to the front end - really the whole point of the exercise, as with Stage 3 frame and adjustable TCAs there's a lot more to setup than on a stock Polo.

Now here is where things are interesting, as I'd previously set camber and toe using some borrowed gauges, then taken it all apart and fitted Gaz coilovers, but I kept the TCA and compression strut lengths the same. This meant that on rebuild I had a starting point.

All I'd done on the rebuild was leave the TCAs as they were (I no longer had a decent way of measuring camber), measure the wheelbase to set compression struts (a crude way of setting castor) and got out the string and measuring stick to attempt to set the toe roughly parallel. The results were surprising!

Front Axle Before
Castor Left +2°15'
Castor Right +2°17'
Camber Left -1°23'
Camber Right -1°18'
Toe Left +0°16'
Toe Right +0°16'
Positive castor of around 2 degrees is what we're aiming for, so the 'setting wheelbase' method I'd used seemed to be acceptable here!
Camber is presumably a product of the TCAs staying the same length from when I borrowed kit to set it up last time - and a dose of luck. This amount of camber is not bad for a road car either.
Toe was set to toe-in, though I was aiming for parallel. Not bad for the old fashioned 'string method' though. Definitely some luck in getting it equal both sides.

So the aim was for improvements, but bearing in mind changing any one parameter affects the others, this is a highly iterative process - and hence time consuming. The objective was to keep similar camber and castor to what I had, but had a touch of toe-out. Adding this toe-out aids turn-in, but also is supposed to assist traction, as under acceleration the front wheels have a tendency to toe-in on a FWD car - so a bit of static toe-out means your wheels end up closer to parallel when you put your foot down.

Front Axle After
Castor Left +2°15'
Castor Right +2°06'
Camber Left -1°22'
Camber Right -1°25'
Toe Left -0°09'
Toe Right -0°09'
These might not seem like drastic changes, but they involved cutting down one of the TCAs to get the right amount of adjustment, so weren't done in 5 minutes - and required adjusting all aspects of the front end, not just the steering arm!

So, nice numbers - but ultimately this is all bollocks if it doesn't drive very well. The test drive was an eye opener.

Conclusions
I need to do some miles to decide whether spring rates need softening up, but the work done to arrive at the current damper settings took the car from utter shite to tolerable. Now this is a toy car, so tolerable ride comfort might be acceptable if the handling benefits are there...

Now, I've gone from a soggy FK kit with no ARB to 325lb/200lb front/rear springs with no ARB - so it's no shock that body roll is massively improved. Damper settings were critical to making the car driveable with these spring rates though. If I can live with the ride quality, then I won't be bothering with an ARB - roll is much much much better now.

Conveying how the car now feels to drive is difficult, as this is more subjective and less science. Turn-in is improved - but was okay before from what I remember - better now though. Mid-corner stability and traction are greatly improved, and the rear end likes to follow you round a bend now instead of staying put. This is a big improvement for a FWD car.

I'm going to see how I get on with the front toe-out, as I've always had it set parallel before - so need to get some miles on to review this. I like the turn-in improvement it brings, and certainly traction is better, but I still need to get used to the slightly more active steering you get as a result. No bother though, CG will happily tweak if required in the future.

Before the setup I could throw the car around, but not with the confidence that the chassis balance now inspires. This surprised me, as I've owned this Polo for 13 years, so know it pretty well. It's still no sportscar, but it's an awful lot better than a 20+ year old shopping trolley ought to be! I now need to put miles on the car, and contemplate further tweaks to optimise.

Three words probably sum up what I think this exercise achieved - confidence, balance and control.

Review will follow in due course from Yoof once he's had his car back out on track. His setup was more involved due to track orientated nature of the car, additional adjustability, and what's presumed to be consequences of his Oulton crash on the rear of the car.
« Last Edit: July 26, 2013, 08:51:54 pm by Andy »

Offline Robin

  • Members
  • *****
  • Posts: 1178
  • 194bhp - 1341 Turbo
Re: Turbo Squareback - History & Rebuild Thread
« Reply #152 on: July 26, 2013, 09:39:46 pm »
Good stuff Andy. Chris certainly knows his shit and I am tempted on taking the polo to him for a session - just got to save some pennies to do so as I know he isn't cheap!!

Offline Alex

  • Members
  • *****
  • Posts: 1121
  • Hack
Re: Turbo Squareback - History & Rebuild Thread
« Reply #153 on: July 26, 2013, 10:10:25 pm »
Interesting stuff. It'll be interesting to see how you get on with it.

Offline Alex

  • Members
  • *****
  • Posts: 1121
  • Hack
Re: Turbo Squareback - History & Rebuild Thread
« Reply #154 on: July 26, 2013, 10:14:01 pm »
Mine was 828kg with a half tank of fuel, by the way, so fairly similar given we both have full interiors and factoring in the lighter square back shell offset by the intercooler etc on yours.

Offline z3i

  • Members
  • *****
  • Posts: 1484
Re: Turbo Squareback - History & Rebuild Thread
« Reply #155 on: July 26, 2013, 10:31:14 pm »
wow! thats a seriously harsh front spring rate! must be harsh to drive on the roads!
Just looked cg up and they use the stuff we use at work to align cars, kinematic diagnosis system 2. BMW approved. bloody good system!!
sometimes a little twitchy but dam good!

what were you saying about adjusment on the rear? do you mean where the rear axle is bolts? are the holes slightly elongated? and are the shims just those plastic bits?
car is so dam cool!!

Offline Andy

  • Traders
  • *****
  • Posts: 1494
Re: Turbo Squareback - History & Rebuild Thread
« Reply #156 on: July 27, 2013, 07:40:37 am »
@Taylor: It's nowhere near as harsh as I expected - no worse than Yoof's cup car setup which is ~50lb softer at the front and ~30lb softer at rear. It was horrible until the damping was adjusted though. Going to see how I get on with it.

On the rear axle the brackets mounting it to the body have slightly slotted holes, so there is scope for adjustment as standard. On Yoof's car these got slotted further to get the alignment required. Getting this right is key to making sure the car doesn't crab around, and that the rear beam is perpendicular to the direction of travel - giving even handling characteristics.

Shims are bits of plastic put behind the stub axles for fine adjustment. Same as the scene boys use to get 999° of negative camber so they fit their wicked sick 15" wide BBS XYZ123s in the arches.

Offline z3i

  • Members
  • *****
  • Posts: 1484
Re: Turbo Squareback - History & Rebuild Thread
« Reply #157 on: July 27, 2013, 10:36:47 am »
Oh really? Wish id gone a bit harder, decided on 250lb springs front for my gaz coilies.
may swap them out for some harder ones in the future and get cg to set my damping up, their services looks spot on!

ah! Thats brilliant about the rear axle :) i always thought it was fixed and mines slightly out, so i can have a play at work

yeah my rear camber is negative 1.5, yours is 1.3 so will be investing in some shims.
haha yeah! So dam true! Though their shims are more like cheese wedges to get the very desired horizontal camber

thanks for that info mate :) will put it to good use when i get mine on the kds ramp
Cheers for putting your readings up, have something to compare mine too
if you dont mind me asking, how was the damper testing and setting up at cg?

Offline Alex

  • Members
  • *****
  • Posts: 1121
  • Hack
Re: Turbo Squareback - History & Rebuild Thread
« Reply #158 on: July 27, 2013, 04:11:33 pm »
Those slotted holes on the rear axle - could they be used to correct a leaning car?

Stuck record, I know.

Offline Jimmy B

  • Members
  • *****
  • Posts: 23
Re: Turbo Squareback - History & Rebuild Thread
« Reply #159 on: September 11, 2013, 10:46:08 am »
Looks perfect Andy - I'm very impressed with the build, nice to see us oldskoolers sticking with the old Polo base.

I move back from Germany soon. I'm hoping to lower my PY running gear into my white MK2 when I get back.

Offline Andy

  • Traders
  • *****
  • Posts: 1494
Re: Turbo Squareback - History & Rebuild Thread
« Reply #160 on: September 11, 2013, 08:01:08 pm »
Those slotted holes on the rear axle - could they be used to correct a leaning car?

Stuck record, I know.
Only just spotted this! Possibly could - if yours is leaning a bit because the axle is on the piss.

Offline z3i

  • Members
  • *****
  • Posts: 1484
Re: Turbo Squareback - History & Rebuild Thread
« Reply #161 on: March 14, 2014, 07:51:51 pm »
Hi mate, read through this and could only find your front spring rates, what have you got on the rear and how long?

having trouble with my suspension, got alot of body roll with a stage 2 sub 250lb front 180 rear

how do your spring rates behave on the road? is it crashy and squittery? i want less body roll but without the bouncing around through corners. trying to get the right rates for what i want

thanks dude :)

Offline Andy

  • Traders
  • *****
  • Posts: 1494
Re: Turbo Squareback - History & Rebuild Thread
« Reply #162 on: March 14, 2014, 08:09:39 pm »
I'd play with your damping. I dropped to 275lb front and 160lb rear for a bit more compliance, I have no front ARB (Stage 3 frame) and would say that body roll is fine.

Offline z3i

  • Members
  • *****
  • Posts: 1484
Re: Turbo Squareback - History & Rebuild Thread
« Reply #163 on: March 14, 2014, 08:16:28 pm »
Oh really? That's interesting! Ok I will do. I have found that if I turn the damping up any more it just bounces around like mad, I've reached a point where I can go no further before it becomes a god awful ride
Thanks mate :)