Sams Polo 3.0

[Sydneykid]

So because the base adjusters were different lengths all my old measurements for positioning them for correct droop etc were null and void. I spent today fitting them up.
My MCA's have 100mm of shaft travel before bump stop contact. The bump stop itself is 17.5mm thick.
At my guard to ground ride height of 630mm I set the base adjusters up for 38mm shaft droop and 62mm shaft bump travel. That 38mm of shaft droop equated to approx 40mm wheel droop.
But there's a problem i'll need to sort. At ride height and the springs lined up so that the beginning of their free coils are in plain view I was able to measure what the spring travel until coil bind would be. If I measured and added up the air gaps, or measured and added up the coil thicknesses minus the total available length that the spring could travel, I get a measurement of 67mm.
That means the spring will be binding 67-62= only 5mm into the bump stop.
I know this means I need to increase the droop to limit shaft travel in bump but I'm not sure by how much.
What I'm thinking of doing is taking the 17.5mm bump stop and taking a 2/3rd measurement of that assuming that by the time its 2/3rds through its travel it is pretty much arrested anyway. That'd give approx 12mm. If I add this likely max of 12mm of bump stop travel to my 62mm of shaft travel then I could potentially travel 74mm in bump yes?
So if the spring coils will bind at 67mm of travel then I need to add 74-67 = 7mm of additional droop travel on the shaft to make sure that its 2/3rd into the bump stop before coil bind.
That'd give me 45mm shaft droop and 55mm shaft bump before bump stop contact. That seems to be the best compromise between not running excessive droop/limited bump travel, yet still giving a good safety margin RE protecting against coil bind.
I know I need to go to better thin wire springs that sag less at resting height. These ones are 11.68mm di wire and are preloaded to get the desired ride height which hurts things even more. At the moment I just need to get operational until I do that though.
What do you think viewers............Gary!!!....

Sorry for the delay in responding, been doing some physical stuff for a change, rather than computer work. Stuff like rewiring the engine fan, fitting the brake ducting, new sphericals for the rear swaybar and best of all I cleaned all the junk off my garage work bench

As we have discussed previously on the front of a FWD car I allow around 2/3rds of the available shock travel (before bump stop contact) for bump (compression) and 1/3rd for rebound (extension, droop). With 100 mm of travel I would aim for around 65 mm of bump and 35 mm of rebound.

On the rear of a FWD car droop limitation is not a bad thing, so around 75B/25R is OK, even 80B/20R often works OK.

I don't know what bump stops Murray uses on yours, I run between 1,500 to 2,000 lbs/inch, in the trimmable V8Supercar style, commonly between 50 mm and 75 mm in length. Around 15 mm into that bump stop feels like a doubling of the spring rate, can't miss it. Your 17.5mm seems like a very short bump stop, I can't say as I have ever seen one that short.

To achieve more travel to coil bind is why we run the thinner wire less coils combination (eg; Eibach), the spring rate is the same (as the thicker wire more coils combination) but it places more load on the base spring steel material. The reason why the "less expensive" coil winders use thicker wire more coils is because they don't have to use as expensive (higher quality) spring steel as is the case with thinner wire less coils. Commonly with Eibach I can use the same rate spring with say 10 coils of 12 mm wire, 8 coils of 11.5 mm wire or 7 coils of 11 mm wire. Obviously the 7/11 has 43 mm more bump travel than the 10/12.

Happy to talk on the phone if you feel the need.
Cheers
Gary

[Sydneykid]

here's a shot of one on an early golf. Good pic as it shows it with a rear ARB fitted too. Seems like a lot of unsprung weight to add when the only real gain over shims is the ability to adjust rear toe easily BUT toe adjustment is a biggn

1976 VolksWagen Golf Mk1 Track Car Build Project - YouTube

Due to the motion and leverage ratios the change to the unsprung rate wouldn't be as much as you think.

Keep in mind that with the V links you would be moving the entire hub inwards or outwards ie; a lot more movement for less effect. Not just the front of hub outwards as with shims for toe out.

Happy New Year to All
Cheers
Gary

[Sydneykid]

so after finally getting the MCA fronts corrected so that I could fit them up, I moved onto the back MCA's. They were untouched in the accident and had just been waiting to go back in once the front was stiffened up to match.
This time I thought I'd check everything properly. After adding up the fully compressed heights of all the platforms, shims, helper springs etc and the working spring I calculated the fully spring bound length between bottom adjustment collar and the chassis. I then fitted up the dampers without the springs and jacked the beam to check that the damper length/bump stop position was correct. It turned out it wasn't. The springs would have been coil bound and the bump stop was only starting to be active. So I had to wind the base adjuster down to lengthen the damper body. This increases droop and pushes the top of the damper body closer to the bump stop. Once I got it so that the bump stop was fully compressed and the spring was a safe distance away from being coil bound I fit it all up.
Thats where the problems appear.

Basically to get the damper body length correct to prevent coil bind, you end up introducing so much droop that the main spring whilst still connected to the helper is not captive over the adjuster. Now I could spin up a cone shaped aluminium guide to fit into the end of that adjuster cup to get around this, but the other fundamental thing wrong is seen on the damper shaft. The cable tie on the shaft shows how much shaft is taken up in droop and how much is available for bump. After taking it out for a test drive the insufficient bump travel can be seen here:


the tell tale cable tie has been pushed to just below the bump stop. While it wasnt going to coil bind and throw me off the road it was only a smidgen off really hardening up in a nasty way. Once out on a circuit pulling much bigger cornering G's and then riding up an outside kerb, this would definitely be going well into the stop.
SSSSssooooo whats the solution. It seems that the keeper arrangement coupled with a low ride height really restricts travel. I could increase ride height to gain travel but then the springs would fall clean out at full droop, and I need it to operate at that ride height.
advice needed!!!

Try relocating the helper/tender spring to the top and see if that helps with locating the main spring over the adjuster.

As per the post above, on the rear of a FWD car droop limitation is not a bad thing, so around 75B/25R is OK, even 80B/20R often works OK and I have used 90B/10R on production cars where we weren't allowed to change the rear swaybar. It may well be that, even with the shock length adjustment, there is is too much (droop) travel on the shocks. This is a common problem with "track cars" and easily fixed (by Murray) in using taller droop stops internally in the shock. They sit between the top of the piston and the top of shock body. Al you have to do is to tell them how much droop you want removed.

Cheers
Gary

[sambb]

thanks Gary. I'll have a good read over your replies tonight. I found this vid put out by MCA which should start at the bump stop bit. The footage where the strut is fully compressed into the stop are the same bump stops as whats on my car. When I was doing the checks on the rear they would compress to within 4mm remaining and be able to lift the car off the stand but are initially very compliant. They are 17.5mm free height and dont look trimmable.

The truth about Suspension - YouTube


RE the toe V links I've gotten in contact with Peter Jones who ran that Kamei inspired Golf Mk 1 to see what he says about them.

[Sydneykid]

thanks Gary. I'll have a good read over your replies tonight. I found this vid put out by MCA which should start at the bump stop bit. The footage where the strut is fully compressed into the stop are the same bump stops as whats on my car. When I was doing the checks on the rear they would compress to within 4mm remaining and be able to lift the car off the stand but are initially very compliant. They are 17.5mm free height and dont look trimmable.

I had forgotten about those, I look at them as being aimed at the "low rider" road car more than competition cars, move as a "save the piston from damage" philosophy. Whereas we use the bump stops as a secondary spring, particularly on the rear of a FWD.

For example if we have say a 400 lb spring in the front and then use full length 75 mm bump stop that is ~200 lbs at 15 mm compression then we have combined spring rate that progresses from 400 to 600 over 15 mm. That's good for jumping curbs etc.

If we have say a 400 lb spring in the rear and then use the same bump stop trimmed to around 50 mm that is ~400 lbs at 15 mm compression then we have a combined spring rate that progresses from 400 to 800 over 15 mm. That's good for limiting the rear squat, limiting the weight transfer off the front, but it's also still OK for curb jumping.

Not right or wrong, just different philosophy.

RE the toe V links I've gotten in contact with Peter Jones who ran that Kamei inspired Golf Mk 1 to see what he says about them.

My thinking would be that they are more useful for rigidity rather than toe adjustment, interested in the response.

Cheers
Gary

[sambb]

Ok so to finally sign off in the front suspension I needed to be certain that I was calculating spring coil bound height or more technically speaking spring solid height correctly. After muddling through all the spring design/spec sites it seems that for a coil over type spring the ends are 'squared and ground'. In a squared and ground spring you basically count the total number of coils, even if they are ground, so every single 360 degree turn in the wire and then times it by wire diameter. For squared and ground springs it seems that you can also count the number of active coils and then add 2 (which accounts for the right angled and ground ends). I hope I have that right!
So given that I was able to confidently enough set up the fronts to a 2/3rds bump/1/3rd droop factor. So under the bump stop I have 65mm bump travel, 35mm droop travel and the spring 10-12mm away from spring solid height (spring bind) when the stop is fully eaten up. Currently I'm still running strut to ARB drop links on the super stiff 24mm FARB as I havent gotten the wishbones modified yet.
Because the wishbones still carry stock ball joints in the stock locations, despite having the top adjusters set for max diagonally back/in caster I dont have enough neg camber for the track - just under 2 degrees. But on the street with the high front ride height its pretty damn sharp at the helm.
So the remianing things for the front end in the short term are to get the wishbones modded to take droplinks which will reduce my front end roll stiffness on the 24mm bar. Tgese also carry the audi TT RS ball joints which will roll centre correct and give me lots (probably too much) neg camber. I need to swap in my subframes that have the rear lower control arm bushes set in the max caster position for even more caster. Then I can get the track rims/tyres on there and check for clearances and control arm angles and decide on a final ride height.
Oh and the steering rack needs it Polo 6R superpro high duro bush added when I do the subframes too. Then she'll be tight as a drum. It does concern me that on the Audi S3 hubs I'm considering, that their steering arms are significantly longer than the Polo ones. I definitely dont want a taller effective steering ratio so it looks like those hubs will probably need a different rack to really take addvantge of them and at this point I have no idea - Polo 6R rack ratios anyone?

[sambb]

this years Goodwood 2020 horizontal hillclimb. Nuts! how do two 70's F1 cars get in the top 4 against all that more modern tech? And that GTR four wheel sliding. love it. I really need to get on a track soon

Full 2020 Goodwood SpeedWeek Timed Shootout final - YouTube

[Sydneykid]

Coil bind height is on the Eibach spec sheet, so I mostly use that. Otherwise I simply grab the vernier's and measure the gaps between the coils and then add them up, subtract that from the free height of the spring = the available travel.

You can always subtract camber with the strut tops if you end up with too much after the lower control arms with the TT ball joints are installed.

Longer steering arms will make the steering lighter, less lock and slower response to steering wheel inputs. You could measure and compare to get an idea how much, from the centre of the drive shaft to the centre of the ball joint.

I used to add some neg with the strut tops while I had the car jacked up to change to the track tyres, do the reverse when changing back to drive home on the street tyres.


Cheers
Gary

[Sydneykid]

this years Goodwood 2020 horizontal hillclimb. Nuts! how do two 70's F1 cars get in the top 4 against all that more modern tech? And that GTR four wheel sliding. love it. I really need to get on a track soon

Full 2020 Goodwood SpeedWeek Timed Shootout final - YouTube

The Calsonic R32GTR is hectic, it's 1,000 bhp makes my 700 bhp look weak, but I only have 2WD so I have an excuse

Cheers
Gary

[sambb]

decided to properly vent the guard liner behind the oil cooler.

there is the worry that if ever a hose comes off that I'll almost certainly crash with oil all over the front tyre but OEM's do it this way too so I'm cool with that.

Sorting out the new cars APR stg 3 tune (K04-001) with the upsized exhaust hasnt gone well. It basically is going lean eg 0.95 lambda during the spool up and boost peak. I'm not sure if this is a failing in the tune because I never logged it with the smaller exhaust it was intended for. But I suspect that the bigger exhaust allows the boost to rise much more rapidly than the 2.5inch dump and so the fuelling is lagging as load rises. Despite lowering the peak boost there's not much I can do to temper the steepness of the boost rise. I got stuck into Lemmiwinks and played with fuelling, but even with lots of primary fuel added and extra 'increasing loads' fuelling, it still is miles too lean in that area despite the rest of the rev range sitting at 0.82 lambda. So last roll of the dice in an attempt to jag it with the generic tune was to fit up my GFB OEM replacement fuel pressure reg. I had this on hand for in case I needed to do a custom tune anyway and for if I ever get around to fitting the TFSI turbo. It all slots in nicely, direct fit even with the gauge in place. I set it for 4bar base pressure while the vacuum line to it was removed ( I think thats the correct way) and once the vacuum line was refitted it dropped to about 3/1/3 bar with the car idling at -20 in Hg. I'm pretty sure thats how you do it and that you dont set it for 4 bar with the vacuum line attached.

I'm hoping that the slicker FPR might respond to boost signals a bit quicker than the 4 bar that was in there and miraculously the fuelling will fall into place. Logging to come! Failing that I'll have to weigh up whether I want to throw money at it with a stop gap custom tune, or just pull the turbo out and get the TFSI one in there. I do hope it works though because theres a twilight tarmac rallysprint on at Eastern CK on Feb 11 that I'd love to do, but not if I'm going to grenade the motor.

[h100vw]

Sam, have you thought about the fuel pump not being able to keep up. Plus the stock injectors are used by APR on that set up IIRC.

[sambb]

yep its still stock injectors. Did a back calc off the injector open times in milliseconds from the nefmoto logs and they aren't actually maxed at 6000rpm. They are at about 85% duty. I did think it could be the pump but at WOT at the top end its getting as rich 0.80 lambda so there's no issue with fuel flow when the injectors are at max duty. It was just that area between 2300-3300rpm on the boost ramp, after that the mixtures are ok. But that lean area was kicking off timing pull that would just never clean up throughout the pull.
Just now I checked the test log that I did on the way to work with the GFB fuel pressure reg and lo and behold the afr's are consistent all the way through. 0.83-0.84 lambdas but still going really rich at the very top above 5700rpm for some reason. The OEM 4 bar that APR specc'd with their K04-001 tune must have been on the blink. I'll just give it a squeak more fuel pressure rather than muddle around with Lemmiwinks and I'd say I'll be able to get it to sit on 0.82's the whole way through and then hopefully it'll take some more timing. Imperfect I know, but it'll do temporarily until I can get this turbo properly tuned by Dave with the good bits (EV14 550's, bigger maf) OR pull my finger out and get the TFSI turbo in there.

[Sydneykid]

No vacuum line connected is the proper process for setting fuel pressure.

Leaness at the early stages of boost build is not uncommon, where the airflow increases rapidly, the fuel demand follows as the torque builds. The low (comparative) rpm is also a factor, the combustion time is longer (than at higher rpm) so the burn has more time to complete. Which the lambda sensor sees as leaner than at higher rpm where any unburnt fuel is exhausted. Increasing fuel pressure is a common method of addressing the low (comparative) rpm leaness problem, but it does require some trimming at higher rpm to compensate. You are at the lessor of 2 evils currently, the engine is under the most load at high torque low rpm, so better not to be lean there even if it means being rich at higher rpm.

Cheers
Gary

[sambb]

Ok thats good to know. Logging is taking a while to do without a dyno but I'm zero'ing in on nice safe mixtures now. Because the injectors are stock and getting close to maxxed, I've left their pulse widths alone and have just climbed the fuel pressure to get more fuel in. Its at 4.2 bar ( a squidge over 60psi) so I think i'll stop there for fear of working the fuel pump too hard. The idle and partial load fuelling was resultingly richer but I was able to pretty easily pull fuel out of those spots and now the fuel trims are at nice low percentage levels. With that nearly done I can look at getting a bit more timing back into it and we'll see how it ends up. I think it'll tide me over like this for a while though until I get the suspension sorted.

[Sydneykid]

Ok thats good to know. Logging is taking a while to do without a dyno but I'm zero'ing in on nice safe mixtures now. Because the injectors are stock and getting close to maxxed, I've left their pulse widths alone and have just climbed the fuel pressure to get more fuel in. Its at 4.2 bar ( a squidge over 60psi) so I think i'll stop there for fear of working the fuel pump too hard. The idle and partial load fuelling was resultingly richer but I was able to pretty easily pull fuel out of those spots and now the fuel trims are at nice low percentage levels. With that nearly done I can look at getting a bit more timing back into it and we'll see how it ends up. I think it'll tide me over like this for a while though until I get the suspension sorted.

Keep in mind that the base fuel pressure is 60 psi then you have to add boost to determine what the fuel pump is pushing against. eg; 60 psi base + 20 psi boost = 80 psi.Cheers Gary