Sam's build thread

[sambb]

Gary this is MCA's scales from when they did the first Polo. That was with the spare/tools and back seats out and half a tank of fuel. In terms of weight split my car may be a tad lighter than that in the rear eg no muffler saved 6kg right at the back and I'd run with no more than 5-10 litres of fuel so maybe 8kg less weight just in front of the rear beam. I reckon my numbers would be very close to that though. I don't think they simulated driver weight though. So given those numbers does that change the 7kg/mm:8kg/mm recommendation you made earlier or does that still hold?

edit:to my calcs it looks like a 66:34 weight split

[sambb]

http://hillclimbnsw.com/pointscore.pdf

The pointscore or the years Hillcimbing finally went up. Despite missing rounds 3,4 and 5 because of the crash and not finishing in the points on day 2 (Rd2) at Panorama, I finished 5th/20 in class helped by a 2nd and two 3rd's. Initially I was filthy that the crash killed off my chances of doing the whole series but my results at the back end of the year and the fact that the car is way better now because it, have me pumped for next year where I can hopefully get up to Grafton and Kempey.

[sambb]

Ok so given 1191kg total, front:rear split of 776:415 kg and 66:34%. I'll work off 7kg/mm front spring rate coils with 317lb/in wheel rate. Notsoswift's rule of thumb says make the rear wheel rate 50%(1/2) higher again than the front wheel rate relative to the weight it carries on the rear.
The front then has 317lb/in wheel rate supporting 776kg = 0.4. The "50% higher again" ratio is 0.4 X 0.5 =0.2. 0.2 + 0.4 = 0.6. So for the rear 0.6 X 415kg = 249lb/in rear wheel rate.
To get that into spring rate 249/.8/.8 = 389lb/in (roughly 7kg/mm) rear spring needed. That's right in the pocket with Gary. I'll see about getting stiffer rears for sure then - split the diff. and get 7.5kg/mm ! bloody good. thanks guys for getting me a bit of clarity and schooling me on spring selection. thx

[simon k]

this all very good reading... since I only have detailed knowledge of classic minis, spring rates aren't in my vocabulary. I've only driven 1 polo, it's sitting in my backyard, and I only drove it around the block in 1st and 2nd gear before I bought it...

[Sydneykid]

sorry another question Gary - I always thought you just times the spring rate by the motion ratio. I didn't know about leverage ratio factoring into that same equation to get your wheel rate. Whats leverage ratio and how does it differ to motion ratio?

Movement ratio first, with a 0.9 to 1 ratio, if the wheel moves 10 mm then the spring only moves 9 mm. The spring rate is kg/s per mm, so less mm = less spring rate.

Next leverage ratio, the wheel/tyre has a lever effect on the spring, like a wheel barrow or your hand on a spanner, a longer spanner has more leverage. Again with a 0.9 to 1 leverage ratio that means a 10 kgs spring feels like 9 kgs to the tyre. The spring rate is kgs per mm, so less kgs = less spring rate.

A simple way to look at it is the movement ratio affects the distance (mm) and the leverage ratio affects the rate (kgs). So added together 10 (at the spring) x 0.9 x 0.9 = 8.1 (at the wheel).

Not all cars have the same leverage and movement ratios, the front of a Falcon for example, the leverage ratio stays the same through the travel but the movement ratio changes slightly due to the angle of the shock/spring unit.

Hope that makes sense.
Cheers
Gary

[sambb]

Ok thanks I think I get it. As long as I know to use it in that equation now I guess that's the main thing. I'll measure out the motion ratio of the beam next time I find myself under there. The beams bush casing is angled back towards the wheels in top view so I assume I'd still just measure from the centre of the casing? And do I measure the distance to the centre of the spring seat cutting an angle directly from the bush pivot OR is the distance taken straight rearward from the pivot to the side view point that intersects the spring seat (since the bush is well inboard of the spring)?

[Sydneykid]

I'm glad you said that because its worried me from the start that the front will be too stiff even at 8kg/mm. But my mates W172 clio is on 400lb/in fronts and it felt great which makes me think 450lb/in on the front wont be far off - just not sure.

Personally I always lean towards a softer spring rate, a slightly softer than perfect spring rate is tolerable and you can tune around it. But higher than perfect is always going to limit traction as it's much harder to tune around. On the basis of "more" swaybar and "less" spring, 400 lbs/inch is ~7.1 kgs/mm which is about where I'd recommend.

Based on my experience, Mark is as usual on the money, it's easy to overlook that a swaybar links the 2 wheels, so we can't look at one wheel in isolation, we have to consider both wheels. If we run a softer swaybar that means 2 things, the outside front spring will compress more so the inside front spring has to extend more to keep the wheel on the ground. If we run a stiffer swaybar that also means 2 things, the outside front spring will compress less so the inside front spring has to extend less to keep the wheel on the ground. Something to think about, a 200 lbs per inch spring takes 200 lbs to compress 1 inch and then takes another 200 lbs to compress another 1 inch. So the spring is pushing back at 400 lbs, another inch and it's pushing back at 600 lbs. Your car has approximately 800 lbs on each front spring, so whether it's a 400 lbs/inch spring at 2" compression or a 200 lbs/inch spring at 4" compression they are both pushing back at 800 lbs (to hold the car up).

In a straight line a swaybar does nothing, doesn't add to the spring rate. A swaybar only works when there is roll, whereas a stiffer spring is always a stiffer spring. A softer spring allows the tyre to more closely follow the road surface whereas a stiffer spring can cause the tyre to skip over the ripples and bumps, hence losing traction.


Cheers
Gary

[Sydneykid]

Ok thanks I think I get it. As long as I know to use it in that equation now I guess that's the main thing. I'll measure out the motion ratio of the beam next time I find myself under there. The beams bush casing is angled back towards the wheels in top view so I assume I'd still just measure from the centre of the casing? And do I measure the distance to the centre of the spring seat cutting an angle directly from the bush pivot OR is the distance taken straight rearward from the pivot to the side view point that intersects the spring seat (since the bush is well inboard of the spring)?

I like to actually check it in a practical sense. So I measure the ride height (centre of wheel to guard is the industry standard), stick the car on jack stands, take the springs out, leave the shocks in, jack the suspension up to the ride height, measure the gap between the spring seats, then jack the wheel (hub) up 20 mm, then measure the gap between the spring seats, then jack the wheel (hub) up another 20 mm and measure the gap between the spring seats. The 40 mm at the wheel should relate to something like 30 mm at the spring seat. At the same time I like to measure the full travel, droop until the shock limits the travel and bump until the bump stops contact. Handy numbers to know for future reference.

Cheers
Gary

[sambb]

".....Your car has approximately 800 lbs on each front spring, so whether it's a 400 lbs/inch spring at 2" compression or a 200 lbs/inch spring at 4" compression they are both pushing back at 800 lbs (to hold the car up)."

Ok I get it now completely. So assuming everything else stays the same, its just that the 'more bar than spring' car has compressed further but the tyres see the same loads. thanks.

I have plan: I'll order some 7kg/mm fronts tomorrow. I'll fit up with 7kg front:6kg rear. If I'm happy with the 7kg/mm fronts then i'l send the unused 8kg/mm fronts back as an exchange for 7-8kg/mm rears. I'll probably hang onto the rear 6kg's for Sydney road drudgery though.
On the 8kg/mm fronts Josh recommended 4 clicks out from full hard so I assume I may have to take that out further for the softer spring.

[Sydneykid]

".....Your car has approximately 800 lbs on each front spring, so whether it's a 400 lbs/inch spring at 2" compression or a 200 lbs/inch spring at 4" compression they are both pushing back at 800 lbs (to hold the car up)."

Ok I get it now completely. So assuming everything else stays the same, its just that the 'more bar than spring' car has compressed further but the tyres see the same loads. thanks.

There are a couple of ways to look at it, holding the car up always takes 800 lbs. But (using my examples) the 400 lbs/inch spring will only compress 1" if it hits a 400 lbs bump, whilst the 200 lbs/inch spring will compress 2". So the softer spring has a better chance of absorbing the bump without disturbing the chassis. As long as there is enough travel available of course.

I have plan: I'll order some 7kg/mm fronts tomorrow. I'll fit up with 7kg front:6kg rear. If I'm happy with the 7kg/mm fronts then i'l send the unused 8kg/mm fronts back as an exchange for 7-8kg/mm rears. I'll probably hang onto the rear 6kg's for Sydney road drudgery though.

Sounds like a good plan.

On the 8kg/mm fronts Josh recommended 4 clicks out from full hard so I assume I may have to take that out further for the softer spring.

In simple terms it's pretty difficult to have too much rebound, the limit is when there is so much rebound that the spring doesn't push back hard/fast enough and the suspension jacks down until it sits on the bump stops. Conversely it's pretty easy to have too much bump damping, especially low speed (high frequency) bump. That effect is much like too high a spring rate, there's noticeable loss of traction because the tire can't follow the track surface vertically, it skips between bumps/ripples. That's why there is a ratio in the single adjuster that gives more rebound (than bump) for each click.

Too little rebound is easy to feel, the spring oscillates after hitting a bump, the chassis bounces off the rebounding spring. What we want is instantaneous settling, no bouncing, just bump, compression, settle. Watch a good V8Supercar hit a curb, there's no bounce after it lands and no skipping sideways.

Keeping the springs example in mind, the 200 lbs/inch spring at 4" compression needs the same rebound damping to control it as the 400 lbs/inch spring at 2" compression, as they are both pushing back at that 800 lbs. What is different is when they are compressed the same amount by a bump/curb etc. That's when the 400 lbs/inch spring needs more damping. But in total a 400 lbs/inch spring doesn't need double the rebound damping of a 200 lbs/inch spring. More like 20% more, plus the swaybar is a "spring" and it needs damping as well, which is why tuning the shock damping becomes an art, not so much a science. It takes a long time to learn what all of the effects are on a chassis of changes in damping.


Cheers
Gary

[sambb]

I really appreciate the help you've given me mate. The main things have been the stiff spring/little bar vs softer springs/more bar argument for the front end, and also where to start regarding spring rates. I had a fair (not saying good!) idea of what the F:R relative stiffness needed to be but no idea on where to start eg 600lb,450lb or 250lb for the type of driving I do- so thanks heaps for that.
Hopefully if we cross paths at Panorama in march i'll have everything in and be PB'ing ha ha. There's still no calender up for next year btw.

[sambb]

Dead beam weld. They more or less all looked like this.

Someone was asking me about my airbox inlet. This is the outside of it.

Tilt your head to the left and that's what it looks like inside the inlet to the airbox. The inlet pipe flange has been flared and contoured to fit the inside of the stormwater pipe which itself is a bit flared. The convoluted tube fits into that.

Attacked the strut top dome today. Grinder access is difficult on the drivers side and it had to be finished with a handsaw which has left me with very little unmolested skin on my hands.

Dome off. Rough as guts yes. Main reason I did it was too see how tough a job it was going to be - didn't want to leave a day to do the MCA strut swap and find myself up until 3am because grinding/dressing the domes took all day. As it was the cutting disc went through like butter, so a grinding disc will square this one up pretty easily once the Bilstein is dropped and i'll do the passenger side on the day of the swap. Main thing is I was able to confirm that with just the dome top off (not taken down flush with the strut tower) there will be plenty of room to get to the MCA camber adjusters with allen keys. Leaving the domes sides on will hopefully allow me to slip some sort of rubber cap over the whole dome when its all sorted.
This pic also shows that there is a squeak of neg camber available if you push the strut tops across towards the engine bay when before you tighten up the strut bolts. Yes the top nut of the strut is lying at a decent angle due to the ball joint mod that gets me my camber and other things, but the whole strut top rubber mount is visibly across because the strut top bolts are smaller than the holes in the strut towers. Don't ask me for a number but there is a bit there that's free to take so why not
Hope all that made sense. My post job beers are kicking in.

[Sydneykid]

I really appreciate the help you've given me mate. The main things have been the stiff spring/little bar vs softer springs/more bar argument for the front end, and also where to start regarding spring rates. I had a fair (not saying good!) idea of what the F:R relative stiffness needed to be but no idea on where to start eg 600lb,450lb or 250lb for the type of driving I do- so thanks heaps for that.
Hopefully if we cross paths at Panorama in march i'll have everything in and be PB'ing ha ha. There's still no calender up for next year btw.

Your welcome, I have an idea that there will be a Polo in one of the race teams at some stage, so I was doing some early research that I could easily share with you. For next year I've been slowly reducing the weight in the Skyline whilst staying within the Hillclimb Class regs, almost finished that now. Changing from a wet cell battery in the boot to a lithium cell in the passenger floor will save me about 8 kgs and there's a few remnants of the HVAC system that have to be removed that will save another handful of kgs. I also need to move the power steering reservoir to a cooler place as I've changed to a smaller plastic one (in lieu of larger pressed metal) which when added to the shorter hoses should save a couple more kgs. The swap to the forged wheels will get it a bit under 1200 kgs (no driver) and with ~700 bhp it should keep me occupied. After it's tuned I want to do a track day to arrive at a basic set up and also calibrate the dash, I find that there's not enough track time and hence data at a hillclimb to start from scratch. If I don't make the first round I'll aim for something later in the year, hopefully catch up then.


Cheers
Gary

[sambb]

Yeah I here you re setup /seat time at the hillclimbs not being the right setting. A guy in one of his podium speeches called it the premature ejac... of car racing. A couple of the hillclimbs do practice days which might give you some mid year opportunities to test. eg Rd3 at Huntely had a practice day this year for the first time which had a lot of people there and they said they'd do it again. I know that Grafton, Tamworth, Ringwood and Queanbeyan do practice days too which might help you. Not sure about Huntely but they have very good security for the cars/campers overnight at the track in case you stay off track. Yep I'm sure well cross paths - I want to see your thing in action. If someone can rock up and beat Neville Shears in his GTR with one out of the same stable and some of those annoying evo's, many of us will be cheering!

[sambb]

Need some sump advice. Ive gotten my hands on this INA engineering sump. It has an additional 0.7L along the south side of the sump, aluminium sprung flaps for oil containment and a 'windage tray' of sorts that sits atop the oil pickup reservoir. I'll have to probably get the turbo oil drain modified to adapt onto the new fitting and also find a way to adapt the oil level sensor from the OEM sump onto this one.
Before it gets fitted up though I wanted to confirm a couple of things. Can anyone who has had the bottom off a BJX recently confirm that there is a plastic OE windage tray fitted like in the last pic? And if so can anyone with a bit of aftermarket sump knowledge tell me do I keep the sumps aluminium drip cover that fits over the oil pickup in place even if the engine already has a windage tray?

thanks
sam