Sam's build thread

[sambb]

Very happy boy. I finally got around to finishing the re-shimming of the rear beam. I did string lining before and after and now have an exact (across a 15in rim) 2mm of toe out on each rear giving 4mm total rear toe out. I also added some more neg camber at the same time and look to have - 2.2 degrees. Also swapped out my standard worn rear discs for some meatier yet used DBA T2's. Very stoked because if I'd stuffed up I wouldn't have had time to get another set of shims and fit them up prior to Bathurst in early March and re shimming can be a tad stab in the dark as far as accuracy goes when you are re shimming a car that was previously shimmed, so to land on the exact figures I wanted was great.
Absolutely loving the string lining too. I have two (front and back) aluminium bars drilled exactly for the string spacing. I just use fishing clips to hang swivelled sinkers off the lines to provide tension on the 80lb yellow braided fishing line which is dead easy to read off against a steel rule. All that is needed is to unroll the lines, place them on jack stands marked for hub centre height, and because the strings are a set width I know the measurements to stand the strings off each sides hubs and can get it all squared up start to finish in 30 mins. Once I'm very close I elastic band the alu bars against the stands and then get it down to as accurate as I can before I start measuring the alignment. The actual measuring of the alignment once its all positioned only takes 30 seconds per wheel.
Surprisingly the car felt a bit more predictable in the wet through a few test corners than previously. Seemed to want to steer/rail its ar$e around the corner rather than be inclined to slide. It is very responsive on turn on too. Nothing can really be gleaned at street speeds though but so far feels good and its sweet knowing that it is definitively aligned properly at the rear rather than getting some paid for bodgy numbers from an aligner that you just cant trust. Next thing is to check that with the extra tuck that the extra camber has afforded, whether 215/50/15's will now fit. If not I'll have to stay with 205/50/15 medium rears on the circuit and 195/55/15 softs for the hill climbs. Still not certain but I'm pretty sure that although narrower and very second hand and chewed up, that my softs work better than the 10mm wider mediums at the rear in hillclimbs.

In other news here is a great vid with Mr Mountune talking about Rallycross engine tech. Its interesting that if they run single throttle body, they are making use of dual plenum inlet mani's similar to the VWR Volkswagen Racing and Dahlback style ones used early days on 1.8T 20V's. They run the camera past one at the start of the vid.


https://www.youtube.com/watch?v=QdM6oZK1Gd4

[Sydneykid]

Rallycross regs are complex and as a result there are specific engine specifications engineered to suite those regulations. As a result you see "unusual" hardware that is designed to specifically overcome some limitations imposed by the regs. From memory the VW's ran in the category that mandated restrictors of a predetermined size. One of the engineering solutions to help with overcoming the limitations of a restrictor is to make the inlet plenum as large as possible, kind of like a boost storage tank. This helps with maintaining boost while playing with the throttle opening to control the traction. It also delays the response on rapid throttle opening a little to avoid the car breaking into uncontrollable wheelspin. All rather specific rallycross requirements that are not exactly desirable in circuit race cars.

That's why circuit/track cars have the throttle bodies as close as possible to the inlet valves, as we want instantaneous throttle response. Hence the need for multiple throttle bodies.


Cheers
Gary

[sambb]

Ah ok. I'd read that one of the advantages of the dual plenum intakes was that you could run a single throttle plate yet get very even flow distribution to each of the cylinders. But I'd seen flow bench tests done on the Dahlback where despite the EVEN flow distribution to each cylinder, the TOTAL flow was quite restricted compared to a traditional side feed single throttle body plenum I guess because the actual runners are fed through slits in the main plenum.
Like you say perhaps they have a place on air restricted engines where they can perform a certain function below the threshold where the air restrictor exposes its total flow shortcomings too? An interesting rule though where you can have single throttle plate DBW or cable throttle ITB's but not both. That would have to be a balance of performance rule you'd think. Yeah I guess you have to be careful looking at a race engine and lifting ideas from it without knowing what rules they are trying to engineer their way around.

[Sydneykid]

I don't know the restrictor sizes for rallycross but they most likely would in the range 32 mm to 36 mm, which is similar to rally cars. Which means 270 bhp to around 380 bhp maximum. That's why maximising WOT airflow isn't an issue, what is their main concern is is transient power after there have been throttle position changes. Hence the large" storage" plenum.

You could increase the max airflow limit by increasing the width of the slot, tricky to get too with a die grinder though.

Cheers
Gary

[sambb]

any IPRA test days/rounds coming up Gary where second hand tyres might be up for grabs?

[Sydneykid]

any IPRA test days/rounds coming up Gary where second hand tyres might be up for grabs?

Round 1 of the 2020 NSW State Championship is on at Wakefield Park 29/2 and 1/3, I'll ask Billy to quarantine any suitable 15"tyres for you.

Cheers
Gary

[sambb]

that'd be unreal. let us know when IPRA comes to SMSP. A friend of a friend may be running a Clio 182 that he's just put together and I'll be curious if the little mk2 escort turns up that had its engine built by an engine shop near me.

[Sydneykid]

that'd be unreal. let us know when IPRA comes to SMSP. A friend of a friend may be running a Clio 182 that he's just put together and I'll be curious if the little mk2 escort turns up that had its engine built by an engine shop near me.

The Escort is entered for Wakefield, goes good in a straight line, doesn't stop all the great and doesn't handle at all. Like all leaf spring/live axle cars he needs to spend as much on the rear end as he did on the engine, then it might be half OK.

Round 2 at SMSP is 3/4 April.

Cheers
Gary

[sambb]

Cool I'll see about getting along to that round.

[metalhead]

Not heading to Ringwood this Sunday for a shakedown before Bathurst Sam?

[sambb]

No mate. Got kids nippers, cricket and tonnes of jobs around the house to tackle I’m afraid. Good luck. Keen to hear how the new engine goes.

[metalhead]

Fair enough. Yeh fingers crossed I get it sorted, should do. New lifters should arrive tomorrow, so hopefully I can get it all back together tomorrow night after work and have a couple of days to make sure it's happy before a shakedown at Ringwood. Just looking at the weather for Bathurst, they're predicting some rain on the Friday night at this stage, not ideal for camping.

[sambb]

Yeah who knows what the weather will bring. Its a strange place. We've had years where we nearly turned around in Lithgow because it was so bad we couldn't even see where we going, yet when we got that first glimpse of the mountain coming into Bathurst it had that gods torchlight thing happening directly on the mountain through the clouds. For the whole weekend not a drop fell on the mountain yet there were showers all around us - bizarre. You just cant predict it. If they are saying for sure that it'll rain I might buy a little throw in the air single man tent to put all the tools in.
I've never driven it wet and I always start to stress about the weather around now. Not a lot of grooves left in what is left of my semis so I wont be chasing results if its bucketing. Your 'Vette has traction control doesn't it? What are you worried about..... ha ha
Good thing is Pete will be up there before us.

Pete is pretty OCD and he'll have a site staked out for us that'll be a good'n.

He takes his whole house with him wherever he goes - awnings, marquee's, ground sheets, etc. So worst case if it is raining friday evening we'll have some initial cover on arrival which'll make setting up easy as. That's worst case scenario so even for that we'll be ok. If I cant find anyone to look after the kids on Friday I might not be leaving till 6pm! ouch I don't think anyone appreciates rattle guns at 10pm so it'll be a busy Saturday morning if that's how my Sydney getaway pans out.

[sambb]

Found this vid about British touring car suspension. Ive linked the vid to start when he's showing the front struts (RWD on this car).
Gary whats the go with the spring coupling. Looks to be heights adjustable but also allow them to run more or less active coils for an adjustable spring rate? is that how you see it?

https://youtu.be/SwZB6avlZ28?t=161

[Sydneykid]

Found this vid about British touring car suspension. Ive linked the vid to start when he's showing the front struts (RWD on this car).
Gary whats the go with the spring coupling. Looks to be heights adjustable but also allow them to run more or less active coils for an adjustable spring rate? is that how you see it?

https://youtu.be/SwZB6avlZ28?t=161

Yep, it enables them to change the spring rate faster. Removing the mac struts takes time plus after they are reinstalled it needs to be wheel aligned. The springs they use are specifically designed to allow for a reduction in the active coils ie; they are over spec'd when all coils are active by using larger diameter wire than would otherwise be the case. When the minimum coils are active then the spec is more appropriate.

A simple example, if I want, say, a 350 lbs/inch spring I can use 10 turns of 12 mm wire or 12 turns of 13 mm wire. In the 12 x 13 spring I can make, say, 2 turns inactive then the spring rate is, say, 400 lbs. Engineering wise that won't over stress the wire. If I did that with the 10 x 12 spring (ie; only 8 coils active) that would cause it to sag, collapse or possibly fail completely.

The downside is the increase in unsprung weight, obviously a 10 x 12 spring weighs a lot less than a 12 x 13 spring, plus there is the weight of the adjuster. It's trade off for the ability to adjust the spring rates quickly which is important in the BTCC because they have a rapid turn around in races. It's also useful for the smaller teams with a shortage of crew. Then there is dealing with the constantly changing weather in the UK.

The trick is engineering the spring design and then having someone good make them for you plus, being a one off, there is a cost. They have a flat end (closed and ground) to sit on the spring seat at the top and then an open wind (no flat end) at the bottom to suit the lock off seat. As such they aren't an off the shelf item last time I checked. If they were it would be good for someone like you with a combo road/track car to run it a bit softer for the street and then lock of some coils for a higher spring rate at the track. It's easy enough with my spring design program to work out how many coils = what spring rate and then just mark the coils appropriately.

They did something similar in the 90's for the BTCC using alloy wedges between the coils to make then inactive, Supercars do the same today.

Cheers
Gary