What is the biggest Cam to run with Paxton and automatic trans?

[zray]

Focusing on camshaft selection certainly is important. However, it won't matter which one is selected if you neglect coolant selection, coolant temperature, and airflow engineering, or airflow tuning if you will.

The vintage Paxton is much maligned due to longevity issues using the basic Ford type F ATF.  These days we are in a much better position to run a vintage Paxton, and have it last tens of thousands of miles. If I can accomplish that, anyone can. My latest vintage Paxton installed on a '66 Shelby was removed after 20,000 + miles of extremely hard usage, like running the Big Bend Open Road Race course flat out numerous times (off -season). The bearings, balls, and races showed no wear.

All thats needed to have legitimate vintage Paxton longevity are a few intelligent decisions made possible by advances in synthetic Type F ATF, and the use of an external fluid cooler.

After some experimentation I settled on the synthetic version of B&G Trick Shift.  It is not an additive, but a stand alone transmission fluid that is correct for any situation where type a F fluid is specified.  Next up is a fluid cooler. Craig C. sells a nice cooler kit, but if you can fit a larger cooler than he has in the kit, then do so.  The fluid cooler mounts in front of the engine radiator, and in my experience, has little effect on engine water temp. from it's blocking of the radiator airflow.

Once those items are in place start thinking about making an air diffuser to put on top of the carb (inside the Paxton bonnet). Without an air diffuser you will never get the most out of the Paxton and always be chasing down the inconsistencies in performance. I made mine out of a marine spark arrestor designed for an inboard V-8 using the 650 Holley. I removed a few layers a steel mesh, and drilled a few holes in the top of it. Eureka ! No more tuning gremlins and the performance improved from an inconsistent+ 50 HP to a reliable  +80 HP.

Getting 75-80% from a vintage Paxton is pretty easy. But getting the last 20-25% is hard to come by, but not impossible.





Z

[gt350hr]

   I can see why the diffuser ZRay used would work as the COBRA air box was designed with the Autolite 4100 in mind. The "original" Prototype air box used on the '65 test car was a large bread box design with a flat top and accepted a 3259 Holley. I ended up using one of those on 6S240 when I raced it. The "issues" ZRay noted went away with the early box and "back then" I didn't give it a second thought as to why. The COBRA air box has angles that match the choke housing of the 4100 and are the opposite of the Holley.
   Regarding the ball drive mechanism , looking at this in "modern" terms , I wonder if there is a ceramic ball in that size that would work . Less weight , less heat storage etc. I may ask Craig about that when I see him in a couple of weeks.
   Randy
   Content added to last paragraph to make sense.

[zray]

I tried the Autolite 4100 HiPo carb on my first couple of Paxton cars. I was never able to totally tune away the fuel (starvation) issues which were evident going around a long sweeper. That issue was part and parcel of the limitations a carb with side-hung float, which is one of the reasons why the early GT350's did not use the otherwise  excellent HiPo Autolite carb. When I went to a center-hung carb such as the Holley Street HP 650 shown above, those fuel starvation issues went away.

Paxton now sells an air diffuser of their own to be used with their gear drive supercharger for carb'd engines applications. I have the part number for it somewhere, but years ago when I tried to order one, it was always N/A or backordered.

I've never actually seen the Paxton brand diffuser. But interesting they did come up with one of their own.

Z

[shelbydoug]

Curt Voght built himself a carbon copy of the first air box. I don't know if he built more then just the one. Ask him at Cobra Automotive.

It's a copy of the one that shows in the original Press Release photos. I think it looks more appropriate.