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7173Mustangs.com

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My all time favorite vehicle is our 1969 Shelby GT500
Welcome, and congrats on you getting the 71 Mustang. Many folks would tell you the 71 is a better vehicle as compared to a 72, much less a 73. I am not sure I would agree other than the more powerful engines in 1971 (Boss 351, for instance). The core vehicles between the 3 years are all really decent. The three years have some differences in their wiring and schematics, and for 73 the emission control system (EGR introduced in 73, with a dual diaphragm design for the auto trans vacuum modulator).

My Go To site for most of my manuals is Forel Publications. For all three years Forel offers colorized wiring schematics in PDF file format for very reasonable prices. The 71 wiring schematic is fairly sparse. The 1972 schematic is far better, and 1973 is really nicely done - considering what the schematics were like back then. I have made several corrections, and annotated my 72 and 73 schematics from Forel. The errors are not significant, and easy to see - none are major errors. It may be worth gettng the 1971, 1972, and 1973 schematics, as the 72 and 73 schematics are more detailed than 1971, and the changes between the three years is not horribly different. I often begin my schematic research in 1973 schematics, then look to the earlier schematics for 71-72 Mustangs, just to see if there are significant differences. I do that because the 73 schematics have more information re: connectors, splice locations, and ground locations. Their site is:

https://www.forelpublishing.com/clickbank/index.html

As for emission control/engine vacuum schematics (aka "calibrations"), the Shop Manuals do not include decent vacuum schematics until 1973's Shop Manual Volume 6. For prior years the Forel and Ford manuals pretty much totally lack any useful vacuum schematics. But, lucky us. The Mustang Barn put together some vacuum schematics for Mustangs and Cougars from 1967 - 1972, and offer the schematics for free. I took the time, with their permission, to collect all of their files into a single PDF file, grouped by year and sorted by engine size. I have attached that consolidated file to this post for you (and anyone else in need of that info) to download and use/distribute as you see fit.

I have also provided a file with two additional calibrations for 351C 4v engines, as the schematics not included in the 1973 Forel Shop Manual Volume 6. I do not recall where I got these calibrations from, but I may have annotated them to show where they came from. You may never need the info, but it is possible you may find someone else who may find then useful. They will not do you any good, as in 1973 the emission control vacuum calibrations changed fair significantly due to the introduction of the Exhaust Gas Recirculation (EGR) emission control systems. My hope is that you are able to share it with some person in need of 1973 351 4v engine calibrations in the future. I feel quite fortunate to have come across them, actually, as they are absent in the 1973 Shop Manual.

I look forward to seeing photos as you make progress with your project. Our 73 Mach 1 originally came with a 302 2v engine and a c4 auto tranny. the prior owner replaced the 302 with a 1994 351W (not C) with 1969 351W 4v heads, and a lot of some fairly tame performance upgrades that ended up producing 360 HP. He also replaced thed original 2.79:1 rear axle gears with a 3.5:1 TractionLok set of gears - a great move for lower end performance and great launches. The 3.77:1 gears you have will cause you to spin your engine at just a little over around 3,000 RPM at 60 MPH. If you find that to be more than you like, be glad you do not haver 4.11:1 gears! We were rinning about 2,850 or so RPM at 60 MPH.

I was okay with the RPM at 60 MPH, as I knew that was the price being paid for a nice low end level of performance. And I felt the 3.5:1 ratio was a reasonable compromise with performance vs street behavior. But, when the C4 began to slip at WOT in its 1-2 upshifts I decided to swap in an AOD. Wow! BEst of both worlds... A relatively low 3.5:1 rear axle ration when combined with the AOD resulted in retaining the low end performance, reducing our RPM at 60 MPS to about 1,850, and since the engine is not stock, it has plenty of HP and torque to push against the wind resistance at upper end speeds, which higher speeds I could not attain with the OverDrive gear final tranny ration (0.66:1 between the input shaft and output shaft). If ever you decided you want to go to an OverDrive solution, feel free to reach out for my list of parts and vendors we used, plus the many videos I took of the entire conversion project.


Ciao!

Gil
 

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351c1971

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Bayville ,NJ
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1971 Mach1
Thanks for the documentation. The annotated vacuum schematics are a big help.

My 71 was built for street cruising with a 3 speed wide ratio top loader transmission. I selected a 3.25 rear gear ratio which keeps the RPMs under 3,000 at 60 MPH. The 2.99 first gear ratio is easy on the clutch and provides a robust hole shot in 1st gear. I also added the quick change vacuum secondary spring tuning kit to the 600 CFM Holley 4v. This combination is a blast to drive around town.
 
Joined
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My all time favorite vehicle is our 1969 Shelby GT500
Thanks for the documentation. The annotated vacuum schematics are a big help.

My 71 was built for street cruising with a 3 speed wide ratio top loader transmission. I selected a 3.25 rear gear ratio which keeps the RPMs under 3,000 at 60 MPH. The 2.99 first gear ratio is easy on the clutch and provides a robust hole shot in 1st gear. I also added the quick change vacuum secondary spring tuning kit to the 600 CFM Holley 4v. This combination is a blast to drive around town.
3.25:1 is a decent street gear ratio that provides a nice low end performance without compromising upper speed performance too badly. The 3.5:1 TractionLok gears in our moderately built 73 Mach 1 are about as low as I would go with without an OverDrive tranny. By sappingin an AOD that 73 Mach 1 has retained its really nice low end performance while recapturing the upper end performance it used to ahve with its original 2.79:1 rear axle gears. Best of both worlds, truly. I could easily move to 4.11:1 rear axle gears with the AOD we swapped in, and still have really good higher speed performance without excessing engine RPM at 60 MPH. But, I m not after "better low end performance," so I will be keeping the 3.5:1 gears.

Your 2.99 1st gear ratio will certainly get some action at launch off the line especially with the 3.25:1 rear axle ratio. The AOD gear ratios are very close to the C4/FMX/C5 auto tranny for gears 1 & 2. The 3rd gear for a C4/FMX/C6 are all 1.00:1. Here are the gear ratios for the AOD:

First: 2.47:1
Second: 1.47:1
Third: 1.00:1 (Same as the 3rd gear for C4/FMX/ C6)
Overdrive: 0.67:1

It is amazing how a thing as simple as a gear ratio, in a tranny and/or rear axle) can alter the performance of a vehicle. A friend moved from his original 2.79:1 rear axle to a 3.5:1 TractionLok, like we have, and was shocked at how much more zip he has at lower speeds. He says it is like the 2.79:1 was fighting his every effort to improve performance with the engine. But once he dialed in a lower ratio the performance increase was like magic.
 

mach72

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May 29, 2011
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Oklahoma
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1972 mach 1 351 4V
Welcome I am in Oklahoma near Tulsa. I’ve owned my 72 for over 25 years and have done a lot of the work you are doing. Where are you located?
 

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Joined
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My Car
1972 Mustang Convertible, 351 C2V, 3 Speed Manual Transmission, Decor Group, Color Keyed Racing Mirrors. 6C Medium Goldenrod, White Knit Vinyl Bucket
Welcome from Connecticut !!
 
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