Sams Polo 3.0

[simon k]

mine isn't hitting anything Sam... I didn't even grind the welds back

[sambb]

oh good news. I thought of you RE that noise you'd been hearing and wondered if this is what it was.

[sambb]

Ok this could get a bit numbery. With the silver cars rear beam sitting in the garage I thought I'd run a tape measure over it and accurately measure the movement ratio. I'd measured as best as I could previously but with the beam in the car, and I must admit there was a lot of 'by eye' going on, and to be honest I buggered up the calcs.
This is my rear beam and if you take each measurement as from the centre of the rear beam bushing out to the centre of the spring platform and centre of the axle, run vertically then the meaurements are:

bush ---> axle = 400mm
bush ---> spring platform = 370mm
370/400 = motion & leverage ratio = 0.925



It could be that you are meant to run the tape measure point to point producing two different angles rather than in the same plane like I did but I think this is correct.
I'd been operating on previous calcs that the rear ratio was between 0.8-0.85. With rear 8kg/mm (447lb) springs I'd thought I was at a wheel rate of 286lb (@0.80) but actually I was at more like 382lb! You can see that a small change in beam ratios makes a huge difference to the wheel rate.
Given that my front wheel rate is 316Lb, no wonder the car had felt more balanced with the thicker Whiteline front bar in it compared to stock. The car had seemed to benefit with it I assume because it was bringing the front up to 'meet' the rear.
My 6kg/mm (335lb) rear springs are looking more and more like the go. At the more accurate 0.925 rear ratio 335x0.925x0.925 = wheel rate of 286lb/in. Coincidentally these lighter springs will put my rear wheel rate exactly where I THOUGHT it had been with the 8kg rear springs.

So I'm now thinking I wont need to go up to the whiteline front anti roll bar as I think the only reason why the car felt better with it was because of excessive rear roll stiffness. I think i'll stick with the stock front bar - basically keep the front just as it had been and I'm sure it'll be sweet with the new MCA valving. Shouldnt have sold my stiffer bushes for the stock FARB..... dumbass.

[sambb]

So After speaking to Gary about the above measurements he set me straight that direct linkage length ratios rarely reflect actual suspension movements. For instance the base of the spring platform sits lower than the stub axle and obviously scribes a tighter arc than the wheel does when compressed. In side view when the wheel rises, the spring platform is in an arc that kind of moves back before it starts to move forward again. The stub axle which is higher than the spring base will scribe a different arc and only ever moves the wheel forward in the wheel arch. From what Gary said you really cant take a snapshot like the above post. The only way is to put the rear up on stands, remove the springs and dampers, jack the beam to its running position and then measure incrementally at different compression heights how far the spring platform moves relative to the wheel centre to build a true picture. ie its a lot more dynamic than one measurement. I'll do it properly for once and it'll be interesting to see if there's any camber gain in the rear end on compression too - looking at the angle of those rear beam bushes, I doubt it.

My refurbed, re-shafted, re-valved MCA's have arrived back in my hands:

They also came back to me with new bases. Initially it appeared to me that I'd been provided with two RHS bases as the droplink flanges were both on the same side. But MCA said thats pretty normal to do it that way now, you just angle the flanges slightly towards the nose of the car and if need be one droplink will fit to the inside and one to the outside of each flange. I was satisfied with that. The only other thing though is that the flanges are drilled for 12mm droplink balljoint pin/bolts and any of the OE and superrpo stuff is 10mm. I already have some12-10mm adapters off Eddys sherical drop links so I can easily adapt those to fit no problem.
Only thing holding me back is deciding whether or not to run 6kg springs with the stiff bar or 7kg again with the soft bar. argh!!
AND whether I should hold off on fitting my modded wishbones at the same time so that I can engineer a way to run the droplinks directly onto the wishbone rather than needing strut mounted flanges at all. And again, changing to that system I'm sure will force a change in the FARB so I'm all a bit snookered!

I think we talked about this in my previous Polo's thread but if the droplinks are moved onto the wishbone directly under the ends of the FARB rather than acting off the struts flanges, they'll be acting on the wishbone 1/2 way along its length. I would have thought that would make it easier for a set amount of wheel movement to twist the FARB because it has more leverage over it than previously. That would necessitate a thicker bar to create the same roll resistance as before wouldnt it? input please!!!

[sambb]

and to the parts I've advertised I've also added
-APR 2.5inch dump+cat for anyone who's looking to go to stage 2
-a Mocal 8 row oil cooler with Mocal thermostated sandwich plate including the correct length spigot for the 1.8T 20V
-a one piece aluminium Forge front strut brace
-a secondary air pump SAI with pipes and the combi if needed.

[Sydneykid]

I think we talked about this in my previous Polo's thread but if the droplinks are moved onto the wishbone directly under the ends of the FARB rather than acting off the struts flanges, they'll be acting on the wishbone 1/2 way along its length. I would have thought that would make it easier for a set amount of wheel movement to twist the FARB because it has more leverage over it than previously. That would necessitate a thicker bar to create the same roll resistance as before wouldnt it? input please!!!

The same maths (leverage and movements ratios) applies to the swaybar as to the springs, if you are moving the link inboard then it will have an effect on the rate of the swaybar. You could try the measurements and maths, but I'd always recommend the practical route and measure the relative movements, how much does the wheel move compared to how much the swaybar moves. What I do is to remove the spring and reinstall the strut, then disconnect the other side of the swaybar and measure how much the connected side moves in comparison to the centre of the tyre (wheel studs). Swap over to the other link position and remeasure.

On the later BMW E36's the swaybar is connected to the strut leg and it preloads the swaybar when the steering is turned. So you get different amounts of antiroll depending on how much steering lock you have on, very undesirable. When we moved the links to the lower control arm (like the earlier E36's) we had to go up 2 mm (from 25 mm to 27 mm) in bar diameter to get the same amount of anti roll.

I think you will find that sticking with 7 kg/mm front springs was the right move with the larger swaybar.

FWIW, I think having the L&R links on the same side of the strut will make the pre loading worse.

Cheers
Gary

[sambb]

Thanks Gary. I'm at work staring at a spare wishbone trying to figure out how I can mount a rail across the top of it for droplinks to attach too. Ever seen anyone weld bracketry onto those pressed out wishbones without blowing holes in them?
And yeah I just cant get my head around those droplink flange positions on the MCA's. A bit baffled by that. Think i'll cut one of them off and get it re-welded to the other side if I cant sort a wishbone solution.

[sambb]

So I've been trying to figure out which of my two intercoolers is the one to stay with. The one off the old car is a SEAT sport - a large twin pass tube and fin with offset entry/exit of 52.50mm I.D seen in the last two pics.
The new cars one was a bit of a mystery till I found this old post:
Meet my Polo!
I new it was from APR but have since found out that they were APR's Golf Mk4 GTI intercooler. They were modded to fit the Polo as Guy Harding used one in a Polo tarmac rally car and then made a few and sold them. In the pic its the long single pass with short vertical fins. You can see where its end tank was modded to help it fit.
The other intercooler in the pic is a Forge twin pass. They were always touted as the one that produced the best cooling but from what I can gather this came at the detriment of flow restriction - something the APR doesnt seem to suffer from.
Now the SEAT sport (final two pics) I've run in the past is a bit of an unknown as I've never seen flow tests for it, but being a pretty a pretty thin cored twin pass with small offset entry/exit of only 50mm, surely couldnt outflow the APR. I've been driving around monitoring ambient vs inlet air temps as the new car has a scan gauge fitted and being able to see iAT's in real time is great. Yes the APR heatsoaks in traffic but not in a dissimilar way to the SEAT so I dont think there's much to seperate them there. The APR also fills the bottom grill but doesnt obscure any part of the radiator north of the crash bar so might actually help RE water temps. And on that I have noticed that this car does run a tad cooler than the last car that had the SEAT despite also having an A/C core, still running the water to oil heat exchanger that should drag water up if anything when up to temps and not having any blanking to fill the voids around the radiator. So there may be something in that. But if it flows 432 cfm at 48 inches then its well above the Forge which is a similar design to SEAT so should be the go. I'll have to have a proper dig around under the car but the APR also looks to have a 2/1/4in entry and a 2 inch exit which should be pretty easy to take out to 2/1/4in space permitting. So I think APR intercooler it will be.

[Sydneykid]

Thanks Gary. I'm at work staring at a spare wishbone trying to figure out how I can mount a rail across the top of it for droplinks to attach too. Ever seen anyone weld bracketry onto those pressed out wishbones without blowing holes in them?
And yeah I just cant get my head around those droplink flange positions on the MCA's. A bit baffled by that. Think i'll cut one of them off and get it re-welded to the other side if I cant sort a wishbone solution.

The lower control arm link is the superior solution. Is the inner most bolt on the ball joint too far outboard to use for the swaybar link? It doesn't have to be perfectly vertical with sphericals both ends.

If not tig would be OK on the lower control arm, easier to be gentle than a mig.

Cheers
Gary

[Sydneykid]

Intercoolers, arguably the most circular of references. Personally I'm not a fan of dual pass, the additional restriction always outways the extra cooling for me. You end up having to run more boost at the compressor for the same boost at the inlet valve. Which inevitably means higher airflow temperatures out of the compressor, so more cooling is needed. Whereas the single pass has less restriction which means we can run less boost at the compressor for the same boost at the inlet valve. Which inevitably means lower airflow temperatures out of the compressor, so less cooling is needed. And around we go in the circle.

Distilling it down, if you are running E85 with a boost (airflow) limited compressor then the single pass would be my choice. If you are Pump98 with a compressor with spare boost (airflow) then dual pass would be my choice.


Cheers
Gary