MkII Cortina Perana V6 racer

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Gavin RS
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Re: MkII Cortina Perana V6 racer

Post by Gavin RS » Tue 29 Nov 2016, 09:06

Going to be 1 awesome car that.
1984 Rover Vandenplas V8 (Historic Race car)
1986 Rover 3500 Vitesse with 4.6lt from V8 Developments (UK Import Ex London Police Car)
1982 Rover SDS V8 manual
2009 Ford Territory ST,
2006 Ford Fiesta 1.6 Auto, daily driver

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KSF
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Re: MkII Cortina Perana V6 racer

Post by KSF » Tue 29 Nov 2016, 16:51

Tx guys, maybe one day we can put our cars on track together, Gavin's touring car Rover and Nic can flip coins for a while to see which one he wants to enter... :D

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KSF
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Re: MkII Cortina Perana V6 racer

Post by KSF » Tue 29 Nov 2016, 17:33

Somewhere after the steelworks and while the Cortina made its way back, I finally got back to the Sierra's build. The shocks had been waiting for a couple of months, so they went in first along with my freshly modified and painted springs. I need to still drop the front to check ride height, maybe do an adjustment, but the engine had to go in before that can be done.

This pic is out of sequence as I also did brakes before I borrowed the Cortina's wheels for a quick check of the back.
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In this pic the mudguard is actually resting lightly on the wheel. The rims I got for the car has a 20mm offset (these are 0mm), so it will fit in well enough. The front remains the bigger question mark as there the space is less. Some rolling and shaping is allowed though, just not modifications like cutting and adding material.

Just a quick word on rideheight. You don't need to run the car so low that it starts to scrape along, in fact that is far from optimum. Apart from the obvious ground clearance, one has to also think about what happens to suspension travel and suspension geometry. You can always reset the static CC&A, but once you have lowered a car more than 50-60mm, the suspension arms are running at quite different angles to what they were intended to be, so camber, castor and toe changes as it travels up and down at this new and much lower position may not be in the acceptable or desirable range anymore. In extreme cases, the front end may now be operating in a range where bump steer starts rearing its ugly head and on something like a semi-trailing arm rear end, you are at the steep part of the camber gain and toe change end of things. Same can happen on the dual wishbone suspensions commonly used.

In more formal modified racing (like Wesbank modifieds of the 80's) guys would then also alter the suspension pick-up points and relocate then higher on the bodywork to compensate for this. That is not a simple thing to do and obviously well outside of what Fines (and probably even Classics) will allow.

Also a quick note on spring rates: For popular cars you can go on line and find preferred spring rates. Be sure you know if it is the wheel rate or the actual spring rate listed.

If none of that is available, a reasonable rule-of-thumb starting to point is to take the cars mass at each wheel (you need to know the weight distribution between front and rear for this). From that you can deduce a desired wheel rate (spring rate effective at the wheel).

For a modified racing car, you can use that mass per wheel as a per inch rate. Meaning if the front end has 300kg's per wheel, then your wheel rate should be 300kg/inch or if converted to the better known lb/inch, 660lb/in. Or simply 660 pound springs as it is commonly known. Nearest commonly available would be a 650.

For McPherson struts that is just about the spring rate too. For swing arm and wishbone suspension, the wheel as leverage on the spring, so the required spring rate to get a 600pound wheel rate will need to be multiplied. Depending on exact geometry, probably by around 1.5 (or more), so you look at a 900lb spring.

A typical 6-cylinder RWD saloon in modified trim might weight around 1100kgs and have perhaps a 65/45 front to rear distribution. Assuming it is McPherson fronts and swing arms or wishbones at the rear, you are looking at using 780pound at the front and 800 pound at the rear. This would be a quite hard set-up and to make it work properly will required an extensive rollcage with suspension pick-ups and probably a full rose jointed suspension. Anything less, and the monocogue and suspension bushes will be doing too much flexing.

So for us mortals who don't build those types of cars, we back off the spring rates a bit and would use perhaps 500-550 pounds at the front and 550-600 at the back. For a road going car, the original numbers can be halved and you'll get a fairly firm, but not bone jarring ride. These numbers are illustration only and would also just be a basic starting point.

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Waterhond
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Re: MkII Cortina Perana V6 racer

Post by Waterhond » Wed 30 Nov 2016, 08:19

This threads is getting better and better !!

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KSF
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Re: MkII Cortina Perana V6 racer

Post by KSF » Thu 01 Dec 2016, 16:42

So the suspension was in and the ride height looked to be in range. Final adjustments of camber and toe will be done when the car is on its own wheels and all the bits and pieces are added. These early XR6's also had an anti-roll bar at the back. I took mine off and put it aside, in general racing cars don't respond well to ARB's at the back (they try to pick up the inside wheel anyway) and also the OEM part was so thin, you wonder what it actually does.

On the alignment specs, it will of course vary between cars, tracks, drivers, tyre&rim size and type etc and so on. But in general, the semi's we use like a fair bit of camber, so you aim for between 3.5 and 4 deg's all round. One can later on fine tune this to suit. On a road car this would probably very aggressively eat the inside shoulders, so not recommended. Also, as in most things, there are compromises to be made and too much camber will not only lose cornering grip, but also braking ability and stability. So you cannot just go big, same as the suspension where you cannot just go as hard as you can get it. Tracks might look smooth from the outside, but they are actually quite far from it. And it is almost alive and evolving through the months and years where the bumps are and how sharp or deep they are. Then the bad parts gets resurfaced, and it is all new again.



To quote Andy Rouse (I think, although probably many have said this): "Its not that simple.... , if only it was."



I don't have a suitable pic here, so below I add in one from my Sapphire built years ago. The struts look about the same in any case.
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This was what it first raced with, but quickly proved to be too soft.

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KSF
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Re: MkII Cortina Perana V6 racer

Post by KSF » Thu 01 Dec 2016, 17:49

Next up on the car was to get the brakes on. This is one of those areas. A great deal can and has been said about what brakes and brake parts you need for racing.

What I am doing on the Sierra as a start, might raise lots of question marks, but here it is.
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At the front, stock standard 3l brakes. Discs, calipers, pads from Midas, rubber hoses. The discs I am using here had been grooved.

At the back, I took off the drums and replaced with the solid discs and calipers off a Sapphire (the hub carriers must be replaced to get the caliper mountings. These carriers was among the parts I swapped Wanegofast for the seat). STD rubber hoses.

For biase control, the std pressure reducer. In this car's case I used the one that was on there, but reversed it. For the drum brakes, it acts as a step-up, but for the discs you need a step down. So it went in backwards. They are not all identical in sizes, so I will see how this works, maybe change it for another later on.

STD brake booster and master also for the moment. No fancy brake fluid, just cleaned the system and replaced it all with Ferodo's DOT 5.1 fluid. This set-up has and is being used on several Sapphires and Sierras racing at K. It does run a bit hot and pads don't last very long, but as long as you have the 5.1 fluid in, it seems to work. So I am going to at least try it before changing it.

On the Sapphire I never even tried the OEM set-up, probably bought into the hype of big brakes and multi-pot calipers. There I went straight to big discs (330mm) on the front and also cross drilled them. On them were the calipers off a BMW 330i. At the back was also vented front discs off a 320i BMW along with its calipers. It was overkill and also I got my maths wrong on the biase, could never get the back to not lock up when you really stand on the brakes. They were eventually replaced with a 4-cylinder Sierra discs with a Ford Bantam's calipers. That along with the FORD pressure reducer AND a Wilwood biase controller got the set-up balanced. That worked very well, pads also lasted very long. But then racing against the other Sapphires with the std brakes, there was no advantage under braking, they could brake as late and although they had to change pads more often, my modified and bigger brakes came to nothing, no gain.

I say all that because while there is no denying that spending your money on a well sized Wilwood set-up of discs, calipers and braided hoses, along with the R1000/liter full synth racing brake fluid will yield very good results, that should not necessarily be your starting point. Such a set-up is quite expensive, so if you don't need it, spend that money elsewhere. Also, by simply looking at a higher performance or bigger/heavier production car, you can put pretty decent brakes on without breaking the bank. It just takes some thought and planning. In years gone by (quite a few by now!), even Wesbank modified racers used production car brakes, just with harder pads.

Some braking principals (it is a huge and very much specialist field, so I type out high level stuff of basics).
Perhaps the first thing to say is that braking performance is not about how many pistons you can fit in there or even how big the pistons are. Brakes are simple hydraulic systems and of more importance is getting the ratio of caliper size from front to back right and then also matched to the master. If you just wanted more clamping force, then simply fit a smaller master cylinder or bigger booster. Simpler and cheaper than 8-pot calipers.

Heat is the killer and normal production car brakes cannot work at the very high temps. You can fit improved pads (harder), but will still end up with discs that will warp and crack, and if they don't, the hard pads will eat them for breakfast. But hard pads, the expensive fluid and probably braided hoses can get you out of a hole.

Better option is to fit bigger discs and bigger calipers. What you are looking for is a big pad, not a big piston so much. Too big a piston and your brake pedal will be long anyway. Along with a big pad will eventually go more than one piston, because the pad can only go that wide before it needs to get longer to get extra size. Then you end up where the biggest piston that can fit in there will not be able to produce an even force over the full length of the pad. There is where more pistons are used.

This bigger pad will run cooler than a small one, even on the very same disc. It is because for the same force exerted, it is spread over a bigger area. I am struggling a bit to find the right words to explain this, but imagine dragging your hand with palm down across a carpet. And put about 10kg weight on it. Your hand might get warm if you drag it far enough. Now do the same, but support all of it just on the tip of one finger. You might actually blister your finger, so much hotter it will get. And yet, the same force as a applied and the same amount of drag was generated. The surface pressure is hugely different.

The bigger disc in itself present more surface area to the surrounding air, so will get rid of heat quicker. If they are cross drilled, then even more area is exposed. The vent holes and also the grooves you see on some serves the purpose of venting gas from between the brake pad and disc surface at the high temps.

Don't neglect the rear brakes. You hear if often that the rear brakes do almost nothing. It is not true. It is almost true for the guys who race shopping trolleys (FWD hatchbacks), but on real cars the rear brakes does a lot. Nominal brake distribution is around 80:20 front to back. To get that you need caliper piston diameter ratio of around 60:40 front to back. Discs size front to back does not need to be identical, but same order of magnitude makes it easier. And vented if possible.

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Re: MkII Cortina Perana V6 racer

Post by KSF » Fri 02 Dec 2016, 16:25

I thought of another way to explain the big pad vs small pad principal and it is something we have probably all done and experienced. When you fit new pads onto used/worn discs. I know these days more and more they get replace at the same time, but it was not always the case. When the new very nice and flat&square pad meets the old disc, it is not making contact everywhere, just on the higher areas. So it reacts a bit like a much smaller pad. Initially, if you try and use the brakes hard before they are bedded in properly, they overheat quite quickly, causing a very hard brake pedal and even rapidly fading brakes.

Back on to brake theory and selection, another big influence on brakes and there performance is the size of wheel you use. If you take your std car on its standard brakes, then fit wheels that are larger in overall diameter, you start to challenge the brake capacity. It happens because even though everything else (speed, car weight, tyre grip and so on) is still the same, to generate the same stopping force, the brake has to work harder. The bigger wheel now has more leverage on the disc, so to generate the same force at the tyre surface, the discs needs to be clamped harder. More force, more surface pressure, more heat. And you don't even need a lot of increase in wheel size to cause this. It is very well demonstrated by the guys with 4X4's that fit those huge off road tyres, 33" and more. But the same applies to saloon cars. If you go up by more than probably 5-10% in wheel diameter, you need to up the brake disc size just to get back to what you had before, never mind improving braking.

Here some old pics I found from the Sapphire build some years ago.

Brake discs... the smallest on top is the std 260mm Sapphire, next in line the 285mm BMW I initially used at the back and the 330mm used at the front.
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These were also cross drilled. I copied the pattern from the E46 M3 I had at the time (their std discs are cross drilled, also 330mm fronts). Then drilled for a couple hours.
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We do this for fun, apparently!

At the end of it and after a clean-up skim, it looks nice though.
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That along with the 17" rims I decided was essential and would really make it very fast looked the part.
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In my defence, I did not do my homework properly and only once I had it all on the car and ready, I found out you cannot get semi's in the very low profile I wanted. (You can now, but it helps very little.). So the overall diameter was quite a bit more than what I had planned for.

Cross-drilling: Also something a lot has been said about. Some insist you cannot do it as the discs will crack. Perhaps, but I have done a lot of these now and so far, touch wood, none have cracked. 5mm holes and then a chamfer with an 8mm drill. (Is chamfer correct? Spellcheck does not agree somehow).
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That is how the car went racing first time out. I discovered pretty early on that although those big wheels generated oodles of grip, it blunted straightline performance a bit. Just how much I found out later, when the modified engine was replaced briefly with a stock standard one. The car was completely dead and listless, might not even have kept up with a 4-cylinder Sapphire.

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KSF
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Re: MkII Cortina Perana V6 racer

Post by KSF » Fri 02 Dec 2016, 17:25

It was not just gearing, that is usually the first thing one thinks. The gears were much shorter than a std car. It took some head scratching and I doubt I am fully on top of exactly what all plays a roll, but here is what I think: First off, the semis are stickier than road tyres, so they have increased rolling resistance. (I had a spare set of wheels, same size, but on Conti Sports, significant difference). Second, they are a lot heavier than std size wheels. This is more significant than one might think and the result is two fold: First you have to also accelerate that extra mass along with the car, but second and an even bigger impact is that you have to also accelerate the wheels rotational speed to speed up the car. A big heavy wheel acts like a big heavy flywheel. The force (or torque rather) required to speed up a flywheel is non-linear, the higher the speeds, the more force is required to accelerate at the same rate.

I kept on racing like that, initially I had more things to worry about and I always wondered if the cornering and apex speeds I gained with the big wheel would not offset the loss of straight line acceleration and speed. Plus, to go smaller meant ditching the big brakes as only a 17" would fit. Also, I would have to go all the way down to 15" as 16" is a bad size for semislick availability. So I decided to stick with the big 17" untill they are worn out. Of course, contrary to what many tell you, it does not necessarily happen all that quickly. It has proven that on a reasonably well set-up car with balanced handling, they can last quite long. Add in that these were a bit oversized for the car, and they just would not die.

Eventually, much later, I wanted to try the change to see what it does. At the time I had some 15" wheels I bought for the Capri anyway.

So I sort of quickly cobbled together smaller brakes.
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The smaller BMW discs fits straight on and I made a quick and simple adaptor to fit the Sapphire OEM calipers. With worn pads, because full thickness would not fit over the thicker BMW disc. The 15" semi's, not a size matched set (205 front, 225 rears), I borrowed from a friend off his Lotus 7.
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Well, on the day the brakes were poor, those semi's were initially skating around all over the show. Handling was interesting and changed from leery oversteer to tragic understeer midway through race one. So I did not expect much (although it did feel a lot stronger on acceleration). It was a very big surprise then when I saw the timing sheets and I had improved my previous personal best by almost 2 secs. Two seconds is huge. Two seconds on a car already fairly sorted out is very difficult to get.

Just to back up that experience, in case one might think it was a fluke, my mate JS Custom more recently put together a Sapphire and used what he had available in his garage at the time. It happened to be a similar set of 17" wheels with semi's. The car did very respectable times, similar to mine on 17". So, just for a test, he put some 15" wheels with semi's on. I think he did go a full 2 secs faster, or very close to it.

I can list a few more guys at K who went smaller to go faster, but the point is probably made. It is another case of "It is not that simple, if only it was". In this case, you cannot just stuff the biggest and fattest wheels on the car and think it will make it fast. It probably wont.

It is still about brakes and in the next post I will finally get to the point of how and why! :D

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Waterhond
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Re: MkII Cortina Perana V6 racer

Post by Waterhond » Fri 02 Dec 2016, 21:58

Is there some kind of formula for brake size, force etc. when changing an engine ?

For instance, if I put a 300 horsepower v8 engine in a one ton bakkie that used to have a 65 horsepower diesel engine in.

What would the requirements be ?

Pieter.

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KSF
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Re: MkII Cortina Perana V6 racer

Post by KSF » Mon 05 Dec 2016, 12:37

Pieter,

Short question with long answer!

I don't have such a formula no, perhaps the brake specialists will have. It will be more than one formula or perhaps by now a nice bit of engineering software that will spit out the specs.

Minimum criteria for brakes (legal ones anyway) says you must be able to stop in a set distance with the full capacity mass of the vehicle. In your case, unless you also increase the vehicle mass substantially (the conversion on its own should not) and don't increase the wheel size substantially (maybe 5% in overall diameter), you're still good from a legal point of view, assuming the 65hp bakkie was.

But common sense tells you that won't do, unless you are a very special person that will never get carried away by the extra power and exceed legal limits on a quiet piece of road. Or get carried away while overtaking an 18-wheeler. So you have to allow for the extra speed you are now capable of.

A 65hp bakkie may have a top speed of maybe 130kmh or so, at 300hp you could probably top 230kmh or so.

You can quantify all that extra kinetic energy with some simply calculations , E=1/2 M V^2. Energy(J) = 1/2 x mass(kg) x velocity x velocity (m/s)

For the two bakkies above, that comes out to 975 000Joules and 3 066 667Joules respectively. A massive difference and the 65hp bakkie's brakes will have very little chance of stopping the 300hp bakkie safely from high speed. Or even just stopping it at all before cooking themselves.

That kinetic energy is in Joules (J), and Joules you can express as Watts (W) if you know in how many seconds you need to get rid of it. That would be your stopping time from top speed to rest. So you have energy divided by time = power. Now power, that gives you some grip on brake sizing beyond just how much torque can they produce and high performance braking systems are also rated at their continuous operation Watts (in their case kW). A very high performance car might have a 1000kW braking system.

Short of going to ask at a counter somewhere for a 1000kW braking system (sure to either get very blank stares or laughter), you can look at other vehicles of the type you have (one ton bakkies). The current (and recent) crop of DC bakkies have quite big brakes and you can find one of them with similar performance (start perhaps with the highest performance in the range) and calculate its total energy at top speed (velocity above is top speed divided by 3.6 to get from kmh to m/s). Compare to yours. If favorable, then go find a broken one at a scrapper and remove the whole braking system with all piping, valving etc and install on yours. Use the same size wheels or very close to it, paying attention to the speed rating of the tyres, yours needs to be higher than a TDi DC's.

If you have a specific bakkie in mind and not just a hypothetical, perhaps post a thread under technical, I am sure someone here has either done it or will have usefull inputs. I will be happy to supply some more theory and number crunching if it will help.

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