Backdraft Cobra AUS - The search for reliability

[Donunder]

Got you in stereo Spook!

Shame there are so few takers from up your way for the Dec brekky. Of course you're more than welcome to join us at Shell Coro for our little convoy. Perhaps we can twist Muzzza's arm to bring the Stang too.

[spookypt]

Progress update:
- Clutch checked and overhauled
- Headers repaired and HPC'd

- Roof modded to fit helmet and roll bar hoop.

- Roof bulge profile and new Naca duct inserts both sides for diff and trans coolers. Fitting the windscreen and rear screen this weekend. Big thanks to Ash B Towmaster for the deal on some stout acrylic.

[spookypt]

Engine Update:
For those that knew my car it was a 372 dart blocked 351w. 13:5 compression 9000rpm (if you dared) and an absolute mongrel for maintenance.

Ive pulled the lot and have now flowed the heads and am working on the current combo.
440 cube
4 inch stroke
418 bore
11.5 comp
7000rpm
Im just flowing the manifold to ensure its capacity is up to the task based on what the heads are flowing.

Roll Cage:
Peter B is coming down to revisit at end of the month once the tops affixed in position and will measure up what we need in materials and design fab the cage itself. Then it'll be off to his place to get welded in.

Gearbox:
I have a new upspec'd GB arriving to update the old one (no cost - HUGE THUMBS UP HGT PRECISION) and will fit it with a new shorter shift arm and also a respec'd bottom linkage to give me even shorter throws. Compared to the Hollinger its such a different GB!!! Much smoother.

Once the car comes back from Peter B's I'll send the roof off to get painted.

Hoping by early new year I'll have GB in, roof painted, cage painted and just waiting on the engine to come back. I have to modify the door to swing open but haven't started on thinking how about that project yet.

[albanycobra]

Good update and lovin watching this Car develope

[spookypt]

Something of interest came about last night worth reporting. Those pesky hydraulic rollers that failed. For those that know the cam follower has a roller that runs around the cam lobe and his an internal needle bearing assembly. When they fail the needle collapse, go everywhere cause damage etc etc.

Well something new....now you can get these cam followers with rollers that no longer have the needle bearings and instead have a bush. Which means should you find some excessive play when doing a valve lash (issue) you can actually pull the manifold and follower, replace the bush in the existing follower and happy days!!!

Best thing since sliced bread. They will be going in my engine for sure!

[spookypt]

Also of interest was the heads just flowed way too much for the cubes it had. No torque! Great for oval track non stop 9000rpm but woeful for a circuit car. By all accounts this new combo may very well be an excellent circuit set up. I'm not rushing this build and I'm doing all the math to get it right. Quite enjoying it actually.

[deano59]

Originally Posted by spookypt

Something of interest came about last night worth reporting. Those pesky hydraulic rollers that failed. For those that know the cam follower has a roller that runs around the cam lobe and his an internal needle bearing assembly. When they fail the needle collapse, go everywhere cause damage etc etc.

Well something new....now you can get these cam followers with rollers that no longer have the needle bearings and instead have a bush. Which means should you find some excessive play when doing a valve lash (issue) you can actually pull the manifold and follower, replace the bush in the existing follower and happy days!!!

Best thing since sliced bread. They will be going in my engine for sure!

i saw a set of these bushers the other day and thought what a killer idea when the time comes for a cam change on my l98 it's something i def will be adding . i believe some engine machine shops have been turning these up as well in there own little engine building tricks ..

[spookypt]

Well despite spending most of my awake hours working Ive managed to now finally have the roof ready. Woke up at 4am Saturday and finished the sanding and put the bolt holes in the body to affix. Measure a million times...then drill.

What was throwing me was I just couldn't get it to line up as I wanted and then I realised the RHS A pillar was 25mm thinner than the left. So after lots more fibreglassing this is the end result. Gurney bubble for helmet and rear hoop clearance (I kept the rear hoop as its integrity with the existing cage will make CAMS log booking ALOT easier) naca ducts inserted for rear coolers, new RHS A pillar, rear lid with duck lip spoiler and all windscreen cut and predrilled once painting is done.

No I wait for Peter B to come down, work out the final design and order materials then its off to his workshop. Final pics of how it will look below less paint.

[Gav]

Originally Posted by deano59

i saw a set of these bushers the other day and thought what a killer idea when the time comes for a cam change on my l98 it's something i def will be adding . i believe some engine machine shops have been turning these up as well in there own little engine building tricks ..

You might want to re think that one Dean, you will have to pull the heads every time you need to change bushes.

[deano59]

Originally Posted by Gav

You might want to re think that one Dean, you will have to pull the heads every time you need to change bushes.

i think the longevity will be fine esp in a engine thats not a everyday driver or likely to be tracked .need to pull the heads to get to lifters anytime . i will talk to my engine man and ask his opinion on them i seem to recall that he had be doing this mod for yrs ..all taken onboard gav

cheers dean

[spookypt]

Flowed manifold and lost 2% against head flow so sweet fa. Getting some advice from SB racing engine builder about the build. He wasn't keen on those bushed rollers but we are still finalising our parts list.

I'll update the final configuration once it's all locked in.

[spookypt]

Big thanks to Peter B for taking the time to pop around and work out with me the best cage design that will comply as well as fit in with my existing cage work insitu.

Here's a rough outline of the design Peter has come up with.

[kyleb]

Originally Posted by Gav

You might want to re think that one Dean, you will have to pull the heads every time you need to change bushes.

Not necessarily..
I was doing a cam change on my LS. Had spun the old cam to push the lifters into the pockets and then very carefully removed the old cam to then insert new cam, and then.... Thunk !! A lifter drops into the sump.
Apparently a heap of pen magnets and clothes pegs holding the lifters is the way to go.. Too late
I stepped back, had a bit of a think about it and decided to have a crack at re-inserting the lifter through the valley slots.
Made up holder for the lifter from a coat hanger and proceeded to fart around with the holder until the angles were right, then with the help of a pen magnet through the lifter bore managed to re-insert the lifter into the bore..
Should have been a proctologist Come to think of it... No.
Anyways... I doubt you can do it with all of he lifters but at least you can access some without removing the heads if need be.

[Tenrocca]

Originally Posted by kyleb

Not necessarily..
I was doing a cam change on my LS. Had spun the old cam to push the lifters into the pockets and then very carefully removed the old cam to then insert new cam, and then.... Thunk !! A lifter drops into the sump.

This is commonly known as the "Russian Roulette" method. Good job to get it back in though.

Easiest method is to lube up a length of 9.5mm dowel and shove in the hole that runs beside the lifters and it jams them in place.

[Modena]

Originally Posted by kyleb

Not necessarily..
I was doing a cam change on my LS. Had spun the old cam to push the lifters into the pockets and then very carefully removed the old cam to then insert new cam, and then.... Thunk !! A lifter drops into the sump.
Apparently a heap of pen magnets and clothes pegs holding the lifters is the way to go.. Too late
I stepped back, had a bit of a think about it and decided to have a crack at re-inserting the lifter through the valley slots.
Made up holder for the lifter from a coat hanger and proceeded to fart around with the holder until the angles were right, then with the help of a pen magnet through the lifter bore managed to re-insert the lifter into the bore..
Should have been a proctologist Come to think of it... No.
Anyways... I doubt you can do it with all of he lifters but at least you can access some without removing the heads if need be.

Good job on rescuing that one! Yes I saw years ago a cam swap tutorial without head removal, step 1; buy 16 pen magnets and grab 16 clothes pegs!

[spookypt]

Well I've hit another hurdle. My engine is based on a 372 dart block. The blocks come in 2different journal sizes. The 2 main bearing diameters: 302 (2.249”) or 351C (2.749”) allow choice of small or large journal crankshaft. As it was a NASCAR spec mine had the small journals so it'd allow the little light crank spin big, but that now makes my new build an issue as to go + 400 cubes I need the larger journal size.
I might be able to bore the block out to suit if the only difference in composition is the journal diameter. Worse case is a new block! Argh! I can always sell the current one etc but this refresh is starting to have a serious 2 at the start of the bill!

And yes for you darksiders I have considered LS but by the time you factor headers ecu mount gb input shaft etc etc it still end up being more costly. Nothing's cheap in motor sport. Just the jesel cam followers are $4k! Ouch

[albanycobra]

yeah.....I know the hurt.....get a new block and sell off the Nascar donk to someone who wants 9000rpm bills.....lol.
new blocks are only $2600 plus set up machining. I run a 72 351 stock block and its well and truly past its power limit with high 500s at the flywheel. My 414(408 scat) makes peak power at 6000rpm so should last awhile. if you go a new block then aim for 427 cubes and use CHI heads and build a Clev-or style motor.

[Aussie Mike]

I read about this some time back. It was interesting stuff.

I think they use the small journal on those motors to reduce oil shear. Oil when under a lot of load and squeezed through a tight space like between a bearing and a journal gets torn apart at the molecular level (sheared) and looses it's viscosity and ability to effectively lubricate.

Plain bearing cranks run on a film of oil under pressure to keep the journal metal away from the bearing metal. If the oil looses its viscosity the two surfaces can come into contact.

NASCAR engines spin at such high RPM that the main bearing surface speed is very high. Reducing the journal diameter reduces circumference and therefore the surface speed which reduces this shearing effect.

I think this is one of the reasons a 351C was a better choice for a high revving engine than a 351W. The 351C has 2.75" mains whereas the 351W has 3" mains. The 302W has much smaller mains @ 2.249"

To work it out determine the circumference of the bearing X the RPM

At 10,000 RPM the surface speed on the The 302W is 70,654 Inches per minute
The 351C is 86,394 inches per minute
The 351W is 94,248 Inches per minute (About 33% faster than the 302W)

Sorry I'm a nerd and the why? of things interests me.

Cheers

[spookypt]

That's very nerdy Mike but in a very cool way!

After much research today Im progressing down a new Iron Eagle Dart Block 9.2 deck with large (Cleveland) journals.

And there will be a nice NASCAR Iron Eagle Dart block with crank, cam, rods etc for sale very soon thereafter.

[spookypt]

Update without pics.
- Ive booked the door, hatch and roof in for painting late January once the car comes back from Peter B at Ontrack Eng. Im using a local painter involved in the local car scene here who comes highly regarded. (Not that an ace paint job is needed.)

- Gearbox number 3 has arrived and I'll fit it over the Christmas break. A new shorter shifter and custom shift clevis is also coming to make the throw even shorter. Cant fault HGT Precision. Buy one if you need to experience again A1customer service.

- Engine. Well this is where it gets interesting. Multiple opinions and thanks to all who helped. Big thanks to Brent Lynkins (Lynkins Motorsport) for his IP sharing as well. If the AUD was stronger I'd be keen to have him build me a motor.
Anyway long and short of it my heads and manifold way out flow my current cubes. In engine talk in my case that's "the capacity vs head performance will always leave it volumetricly inefficient and therefore thermally inefficient".
As my block has the 302 small journals Im progressing down the path of new Iron eagle Dart Block 9.2 with large journals and all the fruit thereafter.
All but the pistons will be in essence off the shelf. Will run std fuel too and drop comp to around 11-1.

So I'll end up selling a complete bottom end and about 250litres of Sunoco 116leaded race fuel. That'll go a fair way to cover some of the componentry costs.

Pics to follow after Christmas.

matt