Fox ABC question

Hi All,

in my travels I have acquired a well worn Fox 40th anniversary stunt 35.. I am thinking about getting the ABC piston and liner for it. The question is how far should I go with this engine? Should I get the Hemi head and stuffer back plate or will this turn it into a combat motor?

Thanks

BTW: Great board, faster than the others and had no trouble getting registered..

LAST EDITED ON Jul-07-00 AT 12:32 PM (EST)

>Hi All,
>
>in my travels I have acquired a well worn Fox 40th anniversary stunt 35.. I am thinking about getting the ABC piston and liner for it. The question is how far should I go with this engine? Should I get the Hemi head and stuffer back plate or will this turn it into a combat motor?
>
Bob, the Fox 35 engine can never become a "Combat" engine with parts intended for that model (could be different when swaps of parts with other, older engines (Black Head, 36X, etc.) are considered). The Stuffer Backplate and Hemi Head hardly make any top end difference at all, and plenty of folks would say that they aren't needed.

The ABC setup does one thing extremely well. It gets rid of almost all of the vibration problems for which the stunt 35 is well known as being among the most poorly-balanced of popular old engines. (That started off worded awkwardly. Not a lot better after editing, but some, at least!)

LAST EDITED ON Jul-07-00 AT 12:56 PM (EST)

It is all a matter of what you want to get out of the engine and how much you want to put into it. The stuffer back plate can make a lot of engines run smoother. It depends on the amount of "bounce" on the rod on your particular engine--how much it may be hitting the back plate. The stuffer back plate helps solve this problem. The Hemi head--with the proper number of head gaskets--will also boost performance and still retain the essential characteristics of the engine. If I were adding the one, I would certainly add the other. The big problem with Fox, OS, (and a lot of others) is that deck height can vary from engine to engine--even in the same batch. Thus, you may have to experiment a bit on head gaskets under the hemi head to get it to your liking. Fox at one time made both .010 and .025 thicknesses in the head gaskets for the hemi head. We settled on two .010 for a stock engine that we put one on.

When you add up the cost of the ABC piston/cylinder and both the hemi-head and stuffer back plate, you are adding about $100 to the original cost of the engine. That gets back to the original question of how much you are willing to add, because when you are done you will have a good Fox, but you are still going to only have a Fox. It will improve, but won't drastically improve the power. I would also add an after market muffler (less weight, more power) and get rid of the stock needle (but, then, that is my preference. We are all different.)

The original Fox Hemi Head was based on preliminary work that wasn't considered a satisfactory solution by the designer, who elected to have Fox Company disassociate his name from the product. Are they still selling the original version, or is the current one in production any better now?

Bob: Fear not, because there is no danger of mistaking your leisurely Fox Stunt for a, say, Mark VII Combat Special.

As Len has commented, just retaining the conrod on the crankpin in a more orderly manner will improve things a bit, but don't expect more than about 300 rpm out of it, based on my limited testing. Ditto for the Hemi; in fact, I didn't get any rpm change, measuring it on the bench, at least. Others have reported some modest gains, however. And I don't think that the power gains from these two items are 100% additive, either. But try them, by all means.

Perhaps your greatest gains will be from the ABC setup, but, again, don't expect the world. There is no timing change here. I have one, not broken in yet, so I can't report with confidence how I really feel about it. But the ABC version is promising; the engine certainly sounds more powerful, if that's any indication of things to come when it is loosened up a bit.

LAST EDITED ON Jul-08-00 AT 08:55 PM (EST)

I've stayed out of this discussion so far, but I think I better bring up a couple of items that might have been over looked. First he said a well worn Fox. If the crank pin is already worn in a taper (which is likely) a new stuffer backplate will NOT hold the rod on the pin sufficiently. Check it with a dial caliper at each end where the rod sits if it is tapered over 0.005 inch The stuffer will be destroyed as there is just too much pressure exerted against it. If it is not tapered go ahead and use a stuffer plate. It will help increase the life of the engine. Second If the shaft is worn in the case, there will be some case pressure loss there as well as some vibration from that looseness, so you may not realize ANY boost of four cycle torque, The Fox hemi head was designed to provide a boost in torque in the four cycle range without getting runaway when it transitions to the two cycle mode in maneuvers.
I don't know for sure whether or not Fox has started production of the new updated Hemis or not. If they havent, I will rework the original one to my specifications if you pay packaging and shipping.(IF IT DOES NOT HAVE THE ROLL PIN OR ROLL PIN HOLE IN IT)
AS for the ABC P&C They ARE notably smoother with less vibration. ANY time you can reduce vibration, you WILL realize more power since vibration robs you of power. BUT I have four ABC set ups and all four of them are in boxes in the bottom of my work bench. I use the good old iron and steel shakers to pull my 50+ ounce 637 square inch NOVI III.
I am not discouraging ANYONE from going with the ABC. It just is not what I like.
Denny' M. M is in front unless I'm sorta backwards, or in reverse