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7173Mustangs.com

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Joined
Jun 10, 2013
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Location
Tigard, Oregon
My Car
No car yet, on the hunt
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?
 

73inNH

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Jun 16, 2021
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My Car
1973 Convertible, Q code, 4 speed, 3.25, A/C, P/S
Give us a bit more info. Is the engine running well, but just a dog?
 

73inNH

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Jun 16, 2021
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My Car
1973 Convertible, Q code, 4 speed, 3.25, A/C, P/S
I wouldn't go to the rebuild yet. :). There are some smart folks about to ask some smart questions.
 
Joined
Jul 27, 2021
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644
Location
East Texas
My Car
1971 Mustang Mach 1 M code 351 4 speed
What engine, what transmission, and what rear end gears does it have? Does it run well? It just does not have much power? Please remember that by 72 most these cars came with the 302 2 barrel or the 351 2 barrel, neither of those 2 engines, especially with automatic transmissions and 2.79 gears were fast. The 302 2 barrel only made 140 HP, and I believe the 351 2V was 166 HP. These are 3500 pound cars without driver and at 140 or 166 HP with an auto and 2.79 gears they will be slow if totally stock. You would be lucky to run a 17 second quarter mile time with a 72 351 2V and 2.79 gears, the 302 would be worse. The engine may be running fine, it may not be down on power, they just did not make very much power, so you may have a good base to start with. You may not need to get a crate engine or pull your engine, some good bolts one, some rear end gears, and a good converter may just get you where you want to be. If you have the 351 C, it is easy to make 350-400 HP even with stock 2 V heads. Then again you may have a good engine, that someone built, and it is just tuned horribly. You would be surprised at what I have seen... I have seen newly built engine with very good parts, that definitely make power, be complete dogs on the street, because the owner was using a stock converter, with stock 2 series gearing, and incorrect timing advance. Need more info...
 

Roland

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Sep 14, 2014
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Location
Switzerland
My Car
1972 Mach1 351C Q-code gold glow, black interior
2v or 4v Q-Code? What carb, rear ratio, and exhaust system?
 
Joined
May 19, 2021
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Location
Fort Mohave, AZ & So Cal
My Car
73 Grande will undergo three phase build process. Phase 1 is to make roadworthy. Phase 2 is interior/exterior restoration. Phase 3 is ++ performance.
I think we need to know more about what was done over that month at the mechanic before we can help, other that the traditional bolt on stuff. If you’re not sure, post a copy of the paperwork they gave you; you can block out any part you don’t want to share. That will open our eyes to where you are.
 

piper62j

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Jul 6, 2014
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Location
34613
My Car
1973 Q-Code Mach 1. Full restoration in progress.
Even a 302 properly tuned for these light weight vehicles was peppy.. Start with the basics.. Do a compression test.. Fuel pressure test.. Carburetor clean out and adjust to specss. Inspect the distributor for a sloppy or worn cam lobe.. Points and condenser should be new and correctly installed. Spark plugs correct for the engine and gapped properly.. These basic inspections will determine what your next step should be.. Like everyone here is saying,,, We need more information from you on what you have and are trying to do..
 
Joined
Apr 24, 2020
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Location
Pittsford, NY
My Car
My all time favorite vehicle is our 1969 Shelby GT500
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.
 

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giantpune

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I'm running a C4 with a shift kit in my car, behind a hopped up 351W. I put them in 20yr ago. I've been beating on it since then, and its still holding up fine. Only reason I'd change mine is to a manual because they're fun to drive.

You do not necessarily need to run out and get a c6 or a manual transmission to handle more horsepower. You can build a C4 to do it just fine. That will save you some cost and headache of trying to get the correct adapters and linkages and driveshaft work to swap to a different transmission.
 
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