The 73 is a lo-compression engine.
With a standard 340 cam, the CCP is gonna be pretty low, which means the low-rpm torque will be low. which means it will take a lotta throttle to get it moving, and more a than usual amount of throttle to keep it moving. And that tranmslates to lousy city mileage.
The usual cure for the soft bottom end is a higher stall, and for a city-car, more rear gear....... which now make for lousy hiway mileage.
When a performance cam is installed, this can, and usually does make it worse.
There are only three cures for this sad situation;
1) more cylinder pressure so you can use less stall, and less gear, or
2) more stroke, or
3) less weight.
4) A finely tuned ignition advance system can help but there is nothing that can touch decent cylinder pressure. So once again, start with a compression test
Just so you know;
not very many years ago, I had a hi compression, alloy-headed 367, with a Final-drive ratio equivalent to 1.97, that at 85=2100 got 32mpgs on a certain measured day-trip. The cam was a Hughes HE2430AL that was 270/276/110. with an Ica of 61*, the pressure was over 190psi. I ran that on 87E10 full-time, with full advance. The cruise timing was close to 60*.
The point being; it is possible to get both power and economy. Just not with a cammed-up/stalled up/geared-up, 340; yur gonna need a different line of attack.
Thanks for the post. It does seem like it takes a lot to get it going which is what I think you are saying in your first point. You noted 190 psi, what does that refer to?
Thanks
Just so you know-2;
A long time ago, I put a 318 cam into a hi-compression 340, with the early 318 heads even,installed into a 65 Canadian-Valiant wagon that was a gangbusters city car.
