Sam's build thread

[sambb]

The hillclimb site report just went up. No mention of us road reg cars I guess because the formula libre guys were doing some pretty amazing things. Malcom Oastler in the yellow OMS is the man. He was the head race engineer at Jaguar F1 when Mark Weber was there and also worked for Williams and Mclaren I think so he knows a thing or two about prepping an open wheeler. His car is an E85 non intercooled turbo Hayabusa making 350hp and the whole car weighs on 305kg.

http://hillclimbnsw.com/report-2017-rd-7-mantic-clutch-ringwood-hillclimb-2/

and here's my humble non open wheeler going around the bottom hairpin before the run up the hill. My net connection is stuffing up and I can't seem to upload so I'll get a vid up as soon as I can.

[sambb]

beam painted.out with the old.in with the new.on the scales. Naked beam without discs or calipers is 27kg.

[sambb]

The standard beam + whiteline 20mm RARB came in at 30kg = 3 kg heavier than the boxed beam. With the 4kg per wheel and 3kg saving there, my rear end is articulating 11kg less unsprung weight than a standard street car with a bar. Actually I think the beam weight saving has to be halved when working that out as its attached on one side to the chassis, but either way its a good saving.
I can definitely see the value of the UR cross brace. These flanges will be warping all over the place now the bushes have next to no give.
possibly my worst fears realised. The problem with solid bushing an angled bush housing is that the beam can bind. I went for these Polybush 44AX bushes because they appeared to have decent sized voids. When I got them the voids weren't as deep as I'd hoped and the centre steel sleeve is a much bigger diameter than the narrower pin in a Powerflex. Well they do appear to bind. The beam is happy hanging anywhere from 360-405mm (arch to hub centre) but below or above that the beam tightens up noticeably. My running height is a fair bit further up from that so I'll jack it up into that area tomorrow and get a gauge on how tight its getting and also on how stiff the beam is. The beam is WAY stiffer than stock without a bar and looks to be stiffer than with the bar. There wasn't much visible droop from one side to the other at all so I think the first drive is going to have to happen with the front bar on hard to square things up!
sorry a sideways pic. Just showing what the boxed part of the beam looks like that faces the fuel tank. Looks neat as and doesn't foul on anything.

edit: after another look the beam is unbound between 330-410mm. Above and beyond that you can feel it bind. eg rather than having to jack the beam to get it into a position to get the springs in and put the bolt through the damper I actually had to be doing the opposite -pulling down hard on the beam to do that.

[HaydEn]

That's a huge weight saving.

I was thinking the plate would weigh alot more. Whiteline must be a solid bar?

Sent from my Moto C using Tapatalk

[sambb]

Yeah I was relieved when it came in 3kg lighter and will be stiffer. Yep the whiteline bar is solid. On track when I run the enkeis (-4kg each corner) , new rear beam (-3kg assuming I won't need the RARB anymore), de muffler (-5kg) and rear seats out (- 20kg) and 10L of fuel at the most, the car is minimum 36kg lighter in the back end.
Its tempting to relocate the battery to the boot because of that but I still think I'd prefer to keep the HC20 I'm getting in the engine bay along with the 1L water coolant reservoir I'll be using for the water injection, because the light corner of the car is the left front and I don't want to make that worse. So because the rear is so light and stiff I'll hold off on fitting the Eibach toe/camber correction until I can get a gauge on what its like - because it'll have so much rear roll stiffness I think the oem amount of rear toe in might be a good idea to keep it well mannered.
MCA just contacted me and their new X series coilovers with a few revisions are ready. We're going to go front: 8kg/mm(445lb/in) and rear: 6kg/mm(335lb/in). Initially we'd talked about 9kg:8kg but I'm happier to go 1 step softer on the front as I may be able to retain the whiteline FARB and have some adjustability and it'll suit the hillcimbs better I think. The softer rears will work better with the stiffer beam and keep the ride tolerable. Its going to be a sled that's for sure. Just hoping I can get them delivered before my wife gets back from NYC cos I'm a dead man if that delivery gets spotted!

To other MCA owners, does the crown that shrouds the top of the strut tower need to be cut off for fit up so you can get access to the damper adjustment?

[sambb]

Props to Whiteline for helping me out. My whiteline adjustable droplinks haven't been in this car really since the rebuild. Where the top ball joints bolted onto the strut tower on my B8's they sat just a tad too close to the bracket. In normal driving this wouldn't be a drama but getting in and out of my driveway where the car onto two wheels sometimes I think it pulled some funny angles and caused some little tears in the boots. I called thrm to see if there was a boot kit or if they could be bought separately and they sent a new pair of the ball joints out to me for free which is pretty good service.

Another question that I need help with. Can anyone with a standard front end/standard front bar and droplinks please tell me what the distance is between the driveshaft and the underside of the anti roll bar where it sits directly above it.? Now that the car is lowered a tad I want to set the adjustable droplinks so that this gap is the same because I'm not sure that the FARB mount on the MCA struts will be in exactly the same spot as on the OEM's. thanks

[Sydneykid]

The problem with solid bushing an angled bush housing is that the beam can bind. I went for these Polybush 44AX bushes because they appeared to have decent sized voids. When I got them the voids weren't as deep as I'd hoped and the centre steel sleeve is a much bigger diameter than the narrower pin in a Powerflex. Well they do appear to bind. The beam is happy hanging anywhere from 360-405mm (arch to hub centre) but below or above that the beam tightens up noticeably. My running height is a fair bit further up from that so I'll jack it up into that area tomorrow and get a gauge on how tight its getting and also on how stiff the beam is.

It should help the travel if you jack the beam up to the desired ride height before tightening the bolts for the bushes.

Cheers
Gary

[sambb]

Thanks mate. Yeah I did. I had the beam in there level with the ground (the old bushes would have allowed it to sag right down) when I torqued it up. I had another look at it today and it seems that it may have ok movement around where I want the rear ride height set up. Things will be different when the calipers, discs and wheels are on but I think it'll be less inclined to droop the inside rear a long way through corners due to the extra roll stiffness but also the stiction that the bushes has introduced.

[Sydneykid]

Thanks mate. Yeah I did. I had the beam in there level with the ground (the old bushes would have allowed it to sag right down) when I torqued it up. I had another look at it today and it seems that it may have ok movement around where I want the rear ride height set up. Things will be different when the calipers, discs and wheels are on but I think it'll be less inclined to droop the inside rear a long way through corners due to the extra roll stiffness but also the stiction that the bushes has introduced.

I haven't played with this model specifically but in general polyurethane bushes with well lubricated crush tubes should have next to zero friction and/or rotational resistance. There will of course be increase resistance to distortion due to the higher duro of the polyurethane (when compared to rubber). To offset that, the crush tube in a rubber bush has to be bonded to the rubber, so it does have noticeable resistance to rotation. Voids in the rubber do help to minimise it but it won't get down anywhere near zero like a properly lubricated crush tube in a poly bush.

If you are concerned with excessive inside wheel droop the rear antiroll should be sufficient to prevent that. The alternative is droop limiters in the shock absorbers.

Cheers
Gary

[sambb]

They should be ok. The main problem comes from the angled bush casings. In top view they are probably at 45 degrees to each other and in front view the casings angle upwards toward the rear seat bases slightly too. The crush tubes will allow up down articulation ok within a given range but then the angle of the bushes starts to force the bush to distort and then the poly, even just for up/down movement starts to lock up. Laterally I think they'll be unreal with no more of that detached rear end sog like before.
Yeah I had read a bit about droop limiters, everything literally from cables to internal damper ones, but figured I'd just go for more roll resistance from the twist beam than from the springs. Apparently limiters can be a bit abrupt in the way they limit droop (only read it have no experience) but if the bushes act to limit droop which I think they will (car is still on jacks with the beam just hanging there level with the ground) then hopefully its nice and progressive.
I just got the rear calipers back and don't know whether to slap it all together and go for a drive or leave it all in pieces and just wait for the coilovers to arrive. I think I'd rather drive it now so that I have a good before and after reference for what the beam is doing rahther than change everything at once but that means garage time tonight and I'm sick as. I'll see how I go.

[Sydneykid]

They should be ok. The main problem comes from the angled bush casings. In top view they are probably at 45 degrees to each other and in front view the casings angle upwards toward the rear seat bases slightly too. The crush tubes will allow up down articulation ok within a given range but then the angle of the bushes starts to force the bush to distort and then the poly, even just for up/down movement starts to lock up. Laterally I think they'll be unreal with no more of that detached rear end sog like before.
Yeah I had read a bit about droop limiters, everything literally from cables to internal damper ones, but figured I'd just go for more roll resistance from the twist beam than from the springs. Apparently limiters can be a bit abrupt in the way they limit droop (only read it have no experience) but if the bushes act to limit droop which I think they will (car is still on jacks with the beam just hanging there level with the ground) then hopefully its nice and progressive.
I just got the rear calipers back and don't know whether to slap it all together and go for a drive or leave it all in pieces and just wait for the coilovers to arrive. I think I'd rather drive it now so that I have a good before and after reference for what the beam is doing rahther than change everything at once but that means garage time tonight and I'm sick as. I'll see how I go.

We use droop limiters on a number of race cars (mostly FWD and 4WD Production Cars where often the regs don't allow us to change the swaybars) , the most common method is an internal bump stop which can be selected to give some progression. This is not as abrupt as say a solid travel limiter like an alloy block or a steel strap. It's also handy to have adjustable rebound damping which can slow down the travel so that it takes longer than the wheel is unloaded to reach maximum droop. Plus it also can assist with a soft stop when it hits the travel limiter. Many ways to skin that cat.

I'll be interested in how reinforcing the torsion beam works out in regards to the anti roll rate. Personally I'd prefer to mount the swaybar on the body and have drop links to the control arms, no unsprung weight at all then, plus it gives anti roll adjustment which on the rear of a FWD car is a great handling tuning device. But I like the simplicity (and low cost) of your method.

Cheers
Gary

[sambb]

The reason why I did it was because as soon as the car three wheels it just glues the front down and I get awesome drive out of corners. Rightly or wrongly I just couldn't see how adding more roll stiffness with springs was going to aid in getting it to lift the inside rear. I figured less roll would just make it harder for the inside rear to lift because the beam allowed so much droop. I'd maxxed out the bar so to me the only answer was a custom 22mm bar (more unsprung weight) or boxing the beam so I went that way. But yeah I do loose roll stiffness adjustability so hopefully I can tune the rear end with track width changes (I was doing that a lot), the 1 way rebound/compression adjustability on the MCA dampers that are coming, and tyre pressure fiddling.
I'm getting the brakes on now so i'll hopefully have them bled tomorrow and i'll go for a run. Actually what I'm most scared of now is the welds just going ping! and letting go.

[sambb]

Yeah I've never seen a twist beam with an anti roll bar mounted to the body. I can understand why the factory don't do that when they can just throw a few more welds or gussets onto a beam, but its a wonder the aftermarket doesn't do it.

[Sydneykid]

The reason why I did it was because as soon as the car three wheels it just glues the front down and I get awesome drive out of corners. Rightly or wrongly I just couldn't see how adding more roll stiffness with springs was going to aid in getting it to lift the inside rear. I figured less roll would just make it harder for the inside rear to lift because the beam allowed so much droop. I'd maxxed out the bar so to me the only answer was a custom 22mm bar (more unsprung weight) or boxing the beam so I went that way. But yeah I do loose roll stiffness adjustability so hopefully I can tune the rear end with track width changes (I was doing that a lot), the 1 way rebound/compression adjustability on the MCA dampers that are coming, and tyre pressure fiddling.
I'm getting the brakes on now so i'll hopefully have them bled tomorrow and i'll go for a run. Actually what I'm most scared of now is the welds just going ping! and letting go.

Technically it's not the rear inside wheel lifting that increases the front end grip on turn in, it's due to the diagonal weight transfer onto the outside front wheel. The inside rear wheel lifting is just another symptom of that weight transfer. As long as the same amount of weight is transferred then it doesn't matter whether the inside rear wheel is on the ground on not. In fact keeping the inside rear wheel on the ground increases the weight transfer as the unsprung weight (of the inside rear wheel) wouldn't be working against the diagonal weight transfer.

Cheers
Gary

[sambb]

Yeah that's a good point re the hanging inside rear acting as a counterweight, I hadn't thought of that. Actually I should clarify inside rear wheel skimming the deck or at the point of un-adhering is the target in medium radius corners from what I've felt. That way it'll be lifting in tight corners to help the car rotate and still on the deck in fast open corners so that I make it to the others side!
A lot of what I've been guided by are articles written by Mark Ortiz who writes for racecar engineering. Here's one of his articles re FWD race car setup: April 2000 only some of it is applicable to what we're talking about now but was all I could find quickly.
He's written some other really good articles about using 'castor jacking' in FWD cars to help the inside front to get more front percent in a corner. Basically using lots of castor coupled with positive steering offset/positive scrub radius, jacks the diagonally opposite wheels of inside front and outside rear causing them to have more % (obviously the outside rear can't get more % when the inside rear is in the air but it'll help at the front when the outside front % goes up dramatically with three wheeling). Its primarily used in RWD race series that use locked rear diffs (eg supercars and lots of US stuff apparently) so that the car would lift the inside rear and enhance turn in but has benefits for FWD too. It seemed to make sense for FWD cars especially open diff ones (mine was at the time) so I thought I'd try it. The effects was pretty dramatic on my car. I have 6+ degrees positive castor and ran spacers at the front out to ET20. The car always felt great that way. A co driver at the eastern ck tarmac rally sprints couldn't believe how my car was turning in in the pouring wet on worn mediums. At the next round I forgot my spacers and the car was completely turd, like a different car pig understeering, not rotating and spinning up the inside front worse than before. I'll try to find that article.
Really I'll just have to drive it and see how it goes. If the rear is too stiff even with the front bar on hard then I won't run any castor jacking promoting scrubs if they are going to help it even more. Its going to be interesting that's for sure.