In this case the only reason to run a solid FT is to restore the cylinder pressure, so the low-rpm performance is at least as good as the stock engine. I don't think any body makes a SolidFT in that 248 advertised size. The solid is about one cam size bigger at .050 than a similarly advertised hydro, because of the faster acceleration ramps.
I know you like your 268/268, but you only ever get to feel the power once below 100 mph, with those 2.21s. In the around town situation a smaller cam with a bigger reargear can and or will be way more fun because the engine is always spinning higher, closer to where the power is.
Here is another exercise
Say your current combo peaks at 5000/63mph. The torque peak usually falls at about 75% of the peak so say 3750, but you only have a VP of barely 100 so the bottom end is gonna be pretty lazy. Neverthless, the cam is waking up at 3750/47mph. Did you catch that?.....47 mph..... in 2.74 first gear.
That means the car is slooooow from zero to 47 mph, then waking up, and on the power by say 4500/57mph, peaking at 5000/63mph, and done by 5500/69mph. Then you put it into SECOND 1.54 ratio and the Rs fall to 4450 and you are back on the climbing part of the power curve to 75mph/4840 rpm;and into cruize-mode.
The next smaller cam
might peak at 200 rpm lower, and so give up maybe 15/20 hp, but with over 80% more TM with the 3.55x3.09=10.97, versus 2.21x2.74=6.06, it will flat out waste the current combo.......... in first gear.
Going two cam sizes smaller,
the engine might peak another 200 rpm lower, but again with 3.09/3.55 combo, the TM will more than make up for the loss of absolute power. Then when the manual combo peaks at say 4600 (5000 of the 268*, less 400), the speed in first will be just 34 mph, instead of 47. But the torque peak might be at 4600x75% so say 3450. That is 300rpm sooner, and the VP is up around 30% higher so that car is gonna be really moving, comparatively speaking. But it doesn't end there.
Running the tach up to 400 past the power peak, say 5000, and then dropping it into second/1.67 ratio, the Rs will drop to 2700 where with the current combo (2700=61mph in second gear), there is no power. But with this smaller SolidFT with its tight LSA,and now at 34mph there is plenty of power. But wait, that smaller tight-LSA cam actually power-peaks an easy 100rpm higher than expected..... and your ported heads are gonna stretch the Rs out maybe another easy 300 rpm, so now your peak might be around 4800/5000 and the shift point might be 5400, and that would be 40mph into second and the Rs now are 2950 in second gear. That's still a bit low, but again, the 130VP will slingshot you to the torque peak at say 75% of say 4800=3600 and the car is moving again.... all the way to 73 mph, for two full trips thru the power peak. And then you put it into overdrive and 75=2410rpm.
Now; this smaller cam with it's higher cylinder pressure, and way less overlap will be right at home at 75mph and passing many filling stations that you were used to stopping at.
This is just an exercise in using increased cylinder pressure by closing the intake so much sooner; 50* versus your current 60*.
The proper way to get the pressure up, is with a greater Scr;meaning hi-compression pistons. In your application,the engine doesn't much care which way you get the pressure, but you should. The more that you have to start with, the bigger the cam that you can run, before the bottom-end goes lazy.
With increased cylinder pressure, your engine/combo could be set up to run your 268/268/110, but I see no reason to. Your application calls for two gears for performance from zero to 60 mph to have a blast with, and a cruiser gear. As such the combo is limited to 3.55s and .73odx3.55=2.59 final drive. There is no reason to have a high rpm cam in that combo. It is just a bottom-end destroyer and a gas-burner on the hiway. I know you were impressed with the 19.2mpg, as am I,but imagine what it could do with an optimized tune.
And yes, you can keep the loc-up automatic, with the right tune, but you won't get BOTH equal performance and equal economy; to the 833od/3.55s. It will have to be biased a bit one way or another.
That's HotRodding.
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If I had your application, the first thing I would do is dump that 268 cam. Well that's maybe not true, the first thing to go might be the 2.21s. Ok maybe the cam,lol.
Then I'd decide on automatic trans or manual trans, and I would choose manual, cuz it's about an instant 2 mpg advantage, with all other things being equal.
Then I'd decide at what speed that's mph, I want the power to be at, and get the gears to put it there.
Then I'd decide solid or hydro, and I'd go solid, cuz I know how hard/expensive it is to get a 318 into the pressure zone, and the solid just makes it easier/cheaper.
Then I'd decide on how much torque to put at what rpm to optimally use those new gears, so I can pick a cam. And finally I would set the Scr to optimally use that new cam.
And finally, I wouldn't give a rat's behind about how much power it is or isn't making, cuz it will be smoking the hiway tires most of the way thru two gears anyway, so who cares about the absolute number.
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Your application is a natural for that 833od trans, one of the few combos I have seen like it. (early on, mine was another). But conversion ain't cheap. It would take several years to break even on gas savings before you start saving money.In the meantime tho, you would be having a blast around town.
If you decide to go 833od, I do have a spare complete set-up taking up space around here, less the floor hump. You would have to engineer where to put the outboard Z-bar anchor and the downrod, The pedal kit is out of a 68 Dart, so not sure if it will fit your FMJ chassis. There are guys on FMJ-body that have converted Dippys, and such, so you won't be alone. Just trying to be helpful, not pushing product..
Happy HotRodding
