Tuesday, 30 January 2007

They're Here......

Here's a grumpy Initial Citylink courier - he didn't like heavy things!

Never mind that though - what did he bring? Six lovely boxes of shiny new things!

In the boxes were: New vented front discs and solid rear discs:

Reconditioned Hand-brake calipers:

Reconditioned Rear Hubs:

Reconditioned front calipers:

Reconditioned Diff: Reconditioned rear calipers, New universal joints and new brake pads (EBC Greenstuff)

Plus lots of assorted bits and pieces - see the full list.
Everything checked off and accounted for and a new list of various odds & ends I'd forgotten has been complied!

Now I've got the replacement wishbone I need to crack on and prep and paint the last front corner and then I can start re-assembly - which reminds me I need to phone GD and check on the chassis delivery date and order some other bits (springs, shocks steering rack etc.)

Monday, 29 January 2007

At Last!

Phoned Wards today - everything is ready and the courier is booked. So day off booked for tomorrow - lets hope I don't have to sit around until 6pm - anyways the garage could do with a bit of tidying ready for the new arrivals.

In the meantime with not much to do I re-jigged the gearbox ratio / speed /rpm calculator spreadsheet (E-mail me if you would like a copy).


Thursday, 18 January 2007

30th and Counting........

Spoke to Wards again today. They did apologise as there had been some mix up with the handbrake callipers. As I'm away next week that gives them a few days to sort things out and I've been promised everything will be delivered on Tuesday the 30th!

So there will be nothing new to report until the 30th - then there should only be 4 to 5 weeks until my chassis is ready.

Then it'll get interesting!

Tuesday, 16 January 2007

Shiny Bits Imminent - NOT

Well a week has passed and again nothing from Wards - they gave me the impression that everything was finished?

So all I've done is clean the remaining parts - sprayed the front hub - waiting to paint the hub carrier, upper wishbones and pivot shaft when I get the replacement lower wishbone - whenever that might be?

So all a bit fed up really - however off on holiday on Saturday for a week so this will probalby be the last update for a while - unless by some miracle some shiny things arrive???

Tuesday, 9 January 2007

Shiny Bits Imminent

Spoke to Wards today, just waiting on the handbrake calipers... so should be here in the next few days - now I can really crack on! Not done much else other than pack the n/s front stuff away and put the offside stuff into degreaser to soak. I won't paint until I get the replacement lower wishbone so I can do it all in one go - that'll be the end of painting - thank god. Whilst I was on the phone I ordered replacment brake pipe brackets as my donor items were badly bent and I managed to break them trying to bend them back - yes, I was being a little optimistic. Funny how you never notice these things when you pick them up - still only a few quid.

Anyways.... just to maintain interest here's a short video about the Shelby Cobra Daytona Coupe - Gorgeous Car!

Sunday, 7 January 2007

The end is nigh?...........

…… of painting that is! It has been a productive weekend. Saturday I stripped, cleaned and acid etched all the components for the nearside front suspension.

The only bit of bother was cleaning all the old grease out of the front hub. I had soaked it in POR marine clean (1:5 with boiling water) for a day or so but getting inside to clean it out wasn’t easy. Solution – take one nylon toilet brush and some scissors – cut down the bristles so the brush is about 10mm bigger than the inside of the hub. Cut off the end of the handle so it will fit into an electric drill. Next find somewhere dirty (Not the utility kitchen sink like me!) and in a couple of minutes it’ll be as clean as a whistle. (Must remember to buy a replacement toilet brush before the domestic authorities find out!)

Having a nice clean hub I thought I might as well paint it. So out with the acid, masked off the disc contact areas, wheel studs and then paint. I used VHT calliper/drum spray paint – 3 coats 10 minutes apart and 3 hours to cure – much quicker than using POR15! Result – nice new hub.

Sunday was back to laborious painting by brush – at least there’s not much left to do now and the end results are well worth the effort.

So that just leaves one final corner – front offside. Allthough at the minute I’m missing the lower wishbone. Despite being careful three of the four spring pan bolts and the two shock mounting bolts were seized solid and eventually broke. Despite attempts to drill them out it started to look like a bit of a write off. Now seeing as it was only 25 quid for one from Wards there seemed little point in aggravating myself any further. Which reminds me – I forget to ring them last week to see where my bits are.

Following on from my last post I spent some time following threads on the UK Cobra Club forum regarding differentials and gearboxes. I came to the conclusion that the open diff / LDS debate is far from over and will probably go on forever! There was a lot of good info / advice regarding gearboxes and diff ratios and I found that although there is no definitive answer there were plenty of do’s and don’ts. What I did find though was that the combination of top gear and diff ratio was perhaps more important for a predominantly road based car. In summary I’m happy with my intentions – the net result (I think) being a slight bias towards acceleration rather than economy – fine by me. With a 1:3.54 diff and a 0.64 overdrive 5th I should be cruising at around 2000 rpm. This also means that the engine mustn’t be too “camy” - anything with a lumpy idle or “muscle car chop” won’t be on cam until after 2000 rpm which means it will struggle to cruise at 70.

Thursday, 4 January 2007

It's a Question of Ratios.............?

Haven’t achieved much over the last few days apart from getting some of the front suspension parts into degreaser to soak. I have however been considering gearboxes and have realised that much more thought was required than I envisaged. The gearbox of choice for Cobra replicas is currently the Tremec TKO as shown below:

However the TKO’s come in three flavours:
So which one to choose?.... there are a few things to consider:

The first is the Starting Line Ratio (SLR) also known as the Launch Ratio and is particularly important when selecting a gearbox and/or differential.

Starting Line Ratio = 1st gear ratio X differential ratio.

The optimum SLR range is 9-11 with 10 being the ideal. Less than 8 will result in excessive clutch slippage to get the car moving and greater than 12 will provide lots of noise but not much movement. These figures are based on an overall wheel height of 28” (This info comes from our friends across the pond) and therefore the SLR needs to be factored to take account of actual wheel size:

SLR = 1st gear ratio X diff ratio X ( 28 / Wheel Height in Inches )

So now I need two bits of info – diff ratio and wheel height. My Diff is 46/13 or 3.54:1 there were various ratios fitted to the XJ6 dependant upon engine size and intended market (2.88, 3.07, 3.31, 3.54, 3.57, 3.77, 4.09, 4.27, 4.55) the 3.54:1 is fairly common. A number of these diffs were available either as Limited Slip Diffs (LSD or Powr-Lok) as well as Standard (or Open) Diffs. There are many opinions regarding the relative merits of LSD’s and open diffs and it seems to be an eternal quandary. However, having read many arguments I am sticking with my open diff as:

1) In normal or spirited road use it should prove more than adequate and should also provide improved turn-in of the car as opposed to an LSD.

2) LSD’s can produce some unintended “end swapping action” especially when accelerating out of corners, as a result of wheelspin with the diff locked – both wheels spin = no lateral grip. With an open diff only one wheel should spin therefore the other should still provide some grip.

I reserve the right to change my mind after driving the thing!! - and should the open diff not be satisfactory then the Grand Plan would be to fit Quaife ATB internals !!!

Getting back on track – overall wheel height is needed next. Many people fit 18” wheels with low profile tyres. I will however be going for the “period look” with 16” wheels and taller tyres. Now I don’t know the tyre size for the 16” wheels but I know that the Mark IV GD can be fitted with 18” wheels and 285x40 tyres (to fill the larger rear arches). This gives an overall wheel height of 27” (26.97).

So – for my car the SLR will be 1st gear ratio X 3.54 X (28/27)

Or 1st gear ratio X 3.67.

The TKO 500 has a first gear of 3.27 giving an SLR of 12.00

The TKO 600 has a first gear of 2.87 giving an SLR of 10.53

So this appears to be a “no-brainer” – TKO 600 it is.

I suppose you should argue that with around 400 hp and 400 lb ft torque you should be looking at the 8-9 range as a more powerful engine will be able to cope with the taller gearing. Certainly if you look at the original specs for 427 Cobras (420hp & 480 lb ft) its SLR is closer to 8 than 10. The 289 Cobras (271 hp & 314 lb ft) SLR’s are around 9.3.

There are two TKO 600’s the 600 and the 600RR. The RR is the Road Race version without an overdrive 5th gear – this would result in higher rpm (and increased fuel consumption) at cruising speeds – so a standard TKO it is.

So – a TKO 600 will give me the following:

Obviously aerodynamics will restrict 5th gear maximum speed!! One last thing to calculate is the distance to 2nd gear. Using the Calculator provided by http://www.5speedtransmissions.com/ I have calculated the distance to second gear to be:

1) For a normal gear change at 2500 rpm and less than 50% torque = 19 Feet.

2) For a full throttle gear change at 6000 rpm and full torque = 55 Feet.

Now all the numbers seem fine to me, but I still have a nagging feeling that the overall gearing should be a little taller (i.e. numerically smaller diff ratio). I’ll have a rummage on some of the forums and see what comes up?