When I purchased my 1972 Mustang I was lied to about the the condition of the mechanicals on the car so now I have some hard choices to make on what direction to go. first I took it into a shop to get the 351C actually running and after a couple of months I got the car back and am pretty disappointed with its performance.
What should I consider on the pros and cons of a rebuilding the existing engine not knowing the history of the motor, should I just do a crate motor?
Opinions on switching from the C4 to a manual or C6 when I increase the horsepower?
71ProjectJunk is spot on. Before condemning the engine look at the data card your door jamb. It will have info on the rear axle ratio, and once you have that you can Google what the rear axle code is for your 72 Mustang. Our 1969 Shelby GT500 has a very powerful 428 CJ engine in it. But, it is also a factory air conditioning car. When Ford built those if a Shelby GT500 had factory A/C the only rear axle ratios were 3.0:1 or 3.25:1 in order to get the engine RPM fairly low in order to prevent the A/C compressors from failing due to too much engine RPM. So, as powerful as that engine is, and as much torque it has where it can still tun pretty fast, it has nowhere near the off-the-line acceleration as it would have had with 3.91:1 (or better yet 4.11:1) for rear axle gears. But with the lower gears and stronger acceleration comes a lower upper end in top speed, and much higher RPM at 60 MPH. The upside to a steeper gear is the engine runs at lower RPMs at 60 MPH, and that makes things nice for cruising. Thus, I am not planning to get lower gears for the Shelby's rear axle.
Our 73 Mach 1 came with a very steep 2.79:1 originally., The prior oner swapped in a 3.5:1 TractionLok rear axle before he built the engine for street strip. I deem that to be a good compromise ratio, so I do not plan to change it. Our engine used to spin at 2,900 RPM at high way speeds, a little higher RPM than I liked. So when the original C4 auto tranny began to slip in its 1-2 upshift at wide open throttle I decided to swap in an AOD. Now I run closer to to the best of both worlds, decent launch performance, and really pleasant cruising. And the 60 MPH cruising engine RPM is now a mere 1,850 RPM or so.
Then we have the 73 Mustang Convertible with a 302 2v, a C4 tranny, and just over 21,000 original, well preserved miles on it. The rear axle is also 2.79, and I do not plan get lower gears as my purpose for this cars is not tray to race it. I can't tell how what I ought to do to further make a sensational car to drive and pee. I know 302 engines can perform when steep gear is an approach carmakers, . With those Ford was able to the Windows 7 Messenger run grot. So is the Mach 1. We now have the best of both worlds, a snappy bit of performance on the low end speeds with the 3.5:1 rear axle TractionLok unit, along with the OverDrive gearing of the AOD. I would, in fact be able to go as low as 4.11:1 rear axle ratio for even more exhilarating low end performance, and the AOD would still run at a reasonable engine RPM at 60 MPH.
Anyway, I sincerely suggest you find out your rear end ration before throwing big money at the engine looking for snappy performance. If you are running at rear axle 3.0:1 ratio, or an even steeper 2.79:1 ratio, you will be fighting an unwinnable war, even with a built engine. It is purely a physics play where the car will have certain leverage realities, which is what gearing is all about (leverage).
Have fun in whatever you end up doing.
Attached is a photo of our 1973 Mach 1's data card showing a code of "3" for the original rear axle ratio - a very steep, performance killing 2.79:1 ratio. It now has a 3.5:1 TractionLok rear axle gear set - which provides very snappy performance. LeftClick on the photo of the dataa tag to show it all. The Rear Axle Code is in the right lower quadrant.
. There are some smart folks about to ask some smart questions.
