Cobra and GT distributor and carb updates.

BlackSnake
Posts: 345
Joined: Mon Jul 13, 2015 4:09 am

Cobra and GT distributor and carb updates.

Post by BlackSnake »

Started looking into why the cobra idle has been racing after driving for a bit. Tom suggested the MSD advance weights may be the cause, so I decided that was a strong possibility since I’ve had problems with surface rust before on the mechanical advance in the Mallory distributor that was previously installed.

There was a bit of rust on one of the springs and between the weights. Enough to possibly have prevented the weights from fully retracting at idle, so I replaced the spring with a fresh light blue spring from the stockpile and wiped everything down with some lube. Also decided to replace the small red bushing with the large black bushing in order to limit total advance while I was in there.

Noticed the Holley carb was still leaking fuel from the front bowl even after I tightened the bowl screws before our recent ride. Looks to be the accel pump that’s leaking, so I ordered new pump diagrams and bowl gaskets that will hopefully solve that leak.

Since I was knee deep in distributors and carbs already, I decided to get on with the planned distributor swap for the GT. The Ford Racing 392w stroker crate motor came with the very large diameter cap MSD (PN 85840), which is pushed right up against the firewall/bulkhead. Not a good situation. Pictures below after I resize them.

Tom graciously provided me with a small cap MSD version (PN 8578) he had sitting in his garage with a recently installed steel drive gear perfect for my application. I owe you a bottle of single malt for that Tom…😉

Popped the large one out with less effort than I was expecting due to the limited clearance as installed, and dropped in the smaller replacement without a hitch.

Since that was the first look I’ve had inside the distributor on the GT, I was curious to see how it was setup in regards to the advance curve. Surprisingly, it had the smallish silver bushing along with the two heavy silver springs. Not at all appropriate for this motor, which needs light springs
(1 lt blue and 1 lt silver) to allow advance to be all in at 2500 and the large black bushing to limit advance to 18 degrees. Now the Cobra and the GT are setup with the same curves as appropriate for very similar engine configs.

According to Ford docs, this crate motor made best power (430hp/450tq) at 32 degrees total. That means initial advance needs to be 14 degrees, which I will set after I complete the install and fire it up. That may be a few days, or a week, since I managed to roll my ankle yesterday on the golf course and sustained a hobbling injury…😳
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mooreken
Posts: 591
Joined: Sat May 09, 2015 12:25 pm

Re: Cobra and GT distributor and carb updates.

Post by mooreken »

Sounds like good progress.
As I recall my MSD distributor came out of the box with the two heavy springs and the black button. So I think the DPO (dreaded previous owner) just dropped the new distributor in with no setup.

LookIng forward to seeing the GT on the road.
Ken
BlackSnake
Posts: 345
Joined: Mon Jul 13, 2015 4:09 am

Re: Cobra and GT distributor and carb updates.

Post by BlackSnake »

I'm not all that surprised Ken, the Weber carbs were bolted on with the standard jetting as delivered. No attempt to provide a basic and appropriate starting setup by the DPO (lol)... :cool:

I hope to have it up and running soon! :cool:
Tom Wells
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Joined: Fri May 08, 2015 7:34 pm
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Re: Cobra and GT distributor and carb updates.

Post by Tom Wells »

Mike,

Looks like really good progress!

That thing sorta reminds me of the Zephyr, where 1/16" is a big deal - you wouldn't think so, but it really is.

Really looking forward to doing a track day with you and the GT40 :-)

Tom

PS: I heartily recommend pulling the distributor after a few miles (100-200?) to make sure there's no excess gear wear. You know why I'm paranoid about that!
BlackSnake
Posts: 345
Joined: Mon Jul 13, 2015 4:09 am

Re: Cobra and GT distributor and carb updates.

Post by BlackSnake »

Will do Tom, I certainly don’t want to suffer the same fate…😉
BlackSnake
Posts: 345
Joined: Mon Jul 13, 2015 4:09 am

Re: Cobra and GT distributor and carb updates.

Post by BlackSnake »

So, as it turns out, the steel gear MSD installed on the 8578 distributor is intended for 351C (and others), not 351W as was assumed. Couldn’t understand why the distributor just wouldn’t drop fully into place, so I started looking at the units in detail.

The PN 85813 gear is approximately .180” larger in diameter than the PN 85834 gear installed on the large distributor. 😳

Guess I have more work to do. 😎
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Tom Wells
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Re: Cobra and GT distributor and carb updates.

Post by Tom Wells »

Ugh...

I sent mine to MSD for the gear replacement. Maybe you could do the same?

Looks like MSD 85834 will fit if the shaft is .531" Probably best to call MSD directly.
BlackSnake
Posts: 345
Joined: Mon Jul 13, 2015 4:09 am

Re: Cobra and GT distributor and carb updates.

Post by BlackSnake »

No worries Tom, I swapped gears around…success, it dropped right in this time…😎

Lots of room now, and hopefully the more aggressive advance curve will wake this motor up! 😉
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Tom Wells
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Re: Cobra and GT distributor and carb updates.

Post by Tom Wells »

Mike,

Here's the instructions for the gear install. Note especially the dimensions given on page 2. The penalty for being out of spec is, um, expensive!
121-85821.pdf
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Tom
BlackSnake
Posts: 345
Joined: Mon Jul 13, 2015 4:09 am

Re: Cobra and GT distributor and carb updates.

Post by BlackSnake »

I have that instruction sheet and took appropriate measurements. Should be fine.

Btw, I didn’t drill a new hole, I lined up the original holes.
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