Backdraft Cobra AUS - The search for reliability

[spookypt]

As has been well documented over the last 6 years the general reliability of my Backdraft TD Cobra has been nothing short of woeful. (For the road going Backdraft Cobras Owners this is unlikely to apply as my car is a race car NOT a road car)
Some issues came from my ability and/or lack thereof and the learning curve of driving a dog boxed left hooker at speed. Some issues were due to simply bad design/fabrication and others due to its Achilles heal....the BMW mid case diff rear end and that Nascar 4 speed Dog box with a 1.630 1st gear.

So after Nats 2015 (my 5th Nats in the car) and having again not made it to Sunday I decided that its wasn't going to beat me..... Time to throw down the gauntlet. I preface this by saying like most, I have no real mechanical background I just learn as I go so this wasn't an easy challenge to take on.


So

First came ripping out the old mid case diff. Its a 188cm Crown wheel and was 4.27 ratio to try and counter the 1st gear ratio issue. I then sourced a 210cm large case 3.91ratiio'd diff and built an LSD and bolted in a new subframe. There was some fabrication work required but all in all a fairly easy conversion.
These diffs run in both the V8 and V10 and diesel BMW's with a high torque rating so I recon it'll be OK.

New diff complete. Bit of size difference



Then, as I was ripping out the 4 speed that had inbuilt pumps I had to make up new coolers with remote electric pumps and all the plumbing to go with it. I have almost completed that.



Then came the GB. I sold the Jerico and had to source something that would do the job. Some spoke about the T56 Magnum and there were a few other options like Hollinger and Modena. Although I have the Hollinger in my Daytona the offer to become a brand ambassador of sorts for a new Swiss GB manufacturer led me to going ahead with this 6 speed sequential from HGT Precision. And first gear is 2.60!!!
I know the PACE guys have some lovely bling but I recon they don't have as shiney a GB as I do.... YET! (Call me and I'll do you a deal)



So it now resides on my bench and I have 6 weeks ish to Rd 2 of the A series. The race is on. Im hoping I'll make it!

Spookypt

[stephen low]

Now that gearbox is an impressive piece of kit Spook!

Also gives me some inspiration, many moons from now, as to perhaps a planned diff replacement to improve on the 60+ year old Mark 10 Jag diff residing in my car.

Good luck with the reliability improvements!

[spookypt]

Thanks mate!

Once that's all done my next job is modifying the cage to suit a new hard top and then to make CAMS compliant and log booked.

[albanycobra]

I keep seeing those HGT boxes pop up on my Facebook page, send me some pricing .Some Kiwi's are into them as well. The box looks sensational for sure. Love your post and keep the detailed pics coming.
Oh how I dream of running a full sequential box in my GT40....

[spookypt]

Hmm sadly no options for transaxles mate. As a general guide in AUD for a 6sp with BH, GPsensor, shifter, TOB and flat shift sensor with geartronics control box allow about $16k + plus freight and GST customs clearance etc

I used my BH as its a reverse starter mount, I didn't need to worry about the geartronics control box either and once I sold my Jerico the actual cost for me to go this direction was almost the same as buying a new Tremec TKO! Lol

Of course I still need to fab up a fair bit of stuff and make a new tailshaft but the unit is good for over 700nm so it'll go OK I reckon.

[750hp]

Swiss GB - isn't that a porn site?

That gearbox looks stunning. Once the reliability is proven locally, I'd think there will be a lot of people questioning the need to spend $25k on a Holinger. Hope you've arranged a good spotters fee structure!

How long ago were the stripped down photos taken? I had no idea the rebuild had gone that far.

[Aussie Mike]

Hi Spook,

Looks good. Interested to know more about your diff cooler setup. I have the same pump for mine and am currently working on the plumbing.

what size lines are you running. I went with AN#8 and I'm hoping they are big enough for the thick oil

What kind of filter are you running? Wondering what mesh size and whether it's before the pump or after it?

Have you got a check valve in line to stop the oil draining back from the pump? I've mounted my pump down lower than the diff so haven't bothered with a check valve.

For the oil return to the diff does it just drain straight back in or is it directed to the crown wheel or center? I'm thinking about adding a tube to squirt the oil directly on the LSD center. (Hydratraks can generate a lot of heat)

Cheers

[spookypt]

Mike, all good questions and I hope my answers are of help.

Yes AN#8 lines on both diff and trans. Im running NULON Competition Gear Oil 75w140 which costs $45 a freeken qrt!!

The filters are from Golan Products. 10 Micron, KTM & Billet Fuel Filters in California | Golan Products
As per my comment in my earlier email in stock form they are actually a fuel filter and run a 10 micron element. When I went through my car I found these 10 micron elements were still in the housings. Great for fuel but not great for allowing oil to diffs. This is what I meant in my comments regarding fabrication. I remove the element and run just the spring loaded mesh that allows good flow but catches any fine metal frags. I've changed my set up a little as the pumps can be heat sensitive so it goes....diff out...filter....inlet low cooler in...outlet high cooler out...pump in..pump out...and back to inlet side high on diff.
No check valve as basically the pumps run all the time so they find the optimum level (as filled) pretty quick. Important to have a vent to catch can rather than atmo too.
The inlet side of my diff essentially flows directly on the LSD so now need for a direct spray. If the car was running the 12hr I'd be all for it but for what I do and plan to do I think I'll come across a lot more issues first before the diff overheats. Ive set up automated fans to come on the coolers at 95c and switch off at 90c so it'll get plenty of forced flow plus I have carbon shrouds around the coolers that get inducted air from the cars Naka duct while moving.
Hope that is of some help. Come to the Nats this year Mike and have a squizzy!!

Matt

[spookypt]

Craig, no its not been stripped that far this time! Those pics just show the current roll cage design (basically a singe seat drag car/nascar design) and what I'm going to have to add to bring it up to CAMS spec.

I wont touch that until my hardtop gets here and I can design it properly. Probably a Peter Behag job at this stage.

[spookypt]

Busy weekend sorting out more stuff. Managed to fab up the shifter position and make a alloy cover to hide the old shift hole. Decided to add in a bit of a bling with the Backdraft RACING logo for $hits and giggles.




Its probably about 15mm further away from the wheel than perfect but until I try it properly its hard to say. It feels OKish where it is. Its a big bludger so I cant see it breaking or having trouble finding it! LOL
I have adjustment forward and back and to some degree left and right so I should be able to get it perfect in time.

Now I have to re-plumb the accusump into the passenger side well (never liked it where it was on trans tunnel) and then I'll set up the box with remote bleed on the TOB and measure up the trans mount rubber bushing. I'm hopeful of setting the TOB shims and bolting the box in this weekend.

[Donunder]

I hope this latest incarnation of your Backdraft gives you more enjoyment and satisfaction than it has to date Matt.

Over the years I've watched with many others as you've battled one problem after another and I have to say I admire your persistence and tenacity in trying to get it right, not to mention your willingness to throw the big bucks at it when required. I've often wondered whether it wouldn't have been better for you to have run a stripped down local RMC/Harrison/DRB with a worked LS of some description which would have given you satisfying and reliable club level racing at a fraction of the cost and grief the Backdraft has thrown at you, and indisputably more track time.

That said, more power to you. Your determination is something few would possess, and I can't wait to hear your car at full noise at QR when next you venture out. It'll be a sweet day when the thing rewards your brave efforts.

[spookypt]

Thanks Don, its all timing I guess. Back when I bought the car options where limited and more expensive. To get a car the calibre of what I bought here wasn't available for near relative money as the USD AUD was almost parity. Combine that with my previous house with no shed, my work load, some poor external advice and my lack of mechanical ability and understanding all made for the perfect storm. If I had my time again would I do it NO but hindsight is always 20/20 perfect.

I think my car is a great car, but its had issues that time and money needed to sort out. Sure it wasn't good out of the box but believe me the driver needs more than the car. I've watched Paul G and his gocart suffer similar reliability frustrations and I didn't want to feel that I had been gifted with the same stigma as he has been fighting so I decided to get serious.

I think now once I get these latest serious upgrades done there is one more thing to do and look at de-compressing the engine. It needs to lose some of its compression and HP to make less stress on all components including me. That's another job down the track.

I need the car to regain a + reputation rather than just a nice looking car that breaks everytime I pull it out of the trailer. Don't get me wrong, I enjoy my car, but its time it gave me back some love cause its been kicking me in the balls for 6 years and Ive had enough of feeling nadded every time I go near a race track! LOL

[Mrs flatchat]

Change the colour and race number and all will be good
--and in hindsight if I were you I would've bought a ride in a Porsche cup car-- you know, arrive n drive , no hassles
Mr

[spookypt]

I'm not a storage king tycoon like yourself Chris to fund such exploits. :-)
Besides I like to tinker and learn by my mistakes. I make many so I'm always learning.

[spookypt]

Finished off some more jobs.
All plumbing and diff breather complete


T Piece - 8 for temp senders and thermo on/off switch for thermo fans

Working through my shims requirements and have made up some -3 braided remote TOB bleeder hoses for easy bleed

Next job in line is relocating the prelube unit and making up the brackets for the valve and plumbing. Bit tricky this one.


After that I have to make room (I have none) for my shift counter display unit and then run the wiring and connect for it. Once that's done I'll make up the cables for the reverse lock out on the shifter for reverse engagement.

And then.......Its fingers crossed it all fits!

[Mrs flatchat]

We sure would like to see this on track SOON with us in sports car category
---and while you're still tinkering --the tracks seem to be having a crack down on noise, 95 db at 30 metres during a drive by at WOT

Mr

[750hp]

...well get your local political aspirant to make some changes to the noise levels at Morgan Park Raceway

[spookypt]

Couple more jobs done.

Got the shift counter in. Not an easy job as I don't have heaps of room, I didnt want to mount it behind the aero screen but it needed to be high and central so I made a bracket that clamps up to the steering column. All I can do is try it.

I then made up another aluminium cover that has the accusump valve attached so as I can prelube on start. I think it came up OK and covered a few holes in the trans tunnel too.


Now I'm setting up the accusump in the passenger area and running the lines. Should have that done in a few days. Then its GB in. Maybe on the weekend.

Spookypt

[spookypt]

Originally Posted by Mrs flatchat

We sure would like to see this on track SOON with us in sports car category
---and while you're still tinkering --the tracks seem to be having a crack down on noise, 95 db at 30 metres during a drive by at WOT

Mr

Got pinged at WP last year so inserted my glass packs and I was quieter than many. Shouldn't be an issue at all at MP or even Lakeside now.

[stiffy]

SpookyPT,

Looks great PT.

On the noise front, your car is beautiful but hurty noisy, better to be safe than

Sorry.

Stiff