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Jul 27, 2021
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Location
East Texas
My Car
1971 Mustang Mach 1 M code 351 4 speed
The AOD or the 4R70W can both be run with 2.75 gears with no issues. The Fox Body Mustangs with the AOD came with 2.75 gears and the AOD, and they run fine. The issue with that high gearing is that the car will be a dog out of the hole. Those AOD 5.0 mustangs with 2.75 gears would loose a 1/4 mile drag race to a Honda CRX Si, trust me I was there, LOL. The issue with high gearing is what camshaft you limit yourself to when you are building your engine, besides how the car will perform. The 4R70W has an advantage over the AOD in that the first gear is a 2.84, vs the AOD 2.47. If you are going to build an engine with aluminum heads and try to get 500hp out of it, you really can't run 2.75 or 3.00 gears. It will be a dog out of the hole. To get to 500hp you need a decent sized cam, you will not get there with a small "RV" stock type cam or a little bigger than stock cam, which you can use with 2.75 or 3.00 gears. To make a engine make power AND the car perform, everything is a combination. At 400 HP or below, using a cam with at most 215 @.050 you may be able to get away with 3.00 gears with a good higher stall torque converter, but you are still loosing a substantial amount of performance compared with 3.50 gears or lower, not to mention with a bigger cam. Now you will probably not get to 500 hp, with 351 cubes with a small 215 @ .050 cam, even with the best flowing heads, intake, and exhaust. The bigger the cam, the more gearing it needs and the higher stall speed converter you will need to use. As you move up in HP your torque curve moves up in the RPM range, a 500 HP engine will probably make less torque that a stock 351C 2V under 2000 rpm, but from 3000 rpm on up it will be night a night and day difference. If you are looking at a real 500 HP normally aspirated 351, you really will need at least 3.50 gears, in reality you probably need more, and a 3000 RPM stall torque converter for the car to perform at its full potential.
 

droptop73

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Grand Rapids, MI
My Car
73 Convertible
It sounds like a bunch of highway time for this one. Only MY opinion but I'd back down a bit on the horsepower dream for the sake of drivability. The overdrive automatics are a good option but nothing beats 3 pedals. LOL!! I drive mine several thousand miles a summer and these cars are fantastic on the road. I've known too many over the years that have chased power at the expense of drivability and the cars are rarely seen again. Like I said, just MY opinion.
 

AcesArneson

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Joined
Aug 17, 2019
Messages
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Location
Fort Mac, Alberta
My Car
1973 Mustang convertible H code 351C-2V Playmate Pink
Hi,

In the coming years I'm going to have my own 351C 2V rebuild, may I ask what you are gonna do with your 2V engine to get it to put out 450HP?

Cheers,
Vincent.
Hey Vinnie, my mechanic is rebuilding the motor but I can make some general comments. Really all this motor needs is to breath better to hit 450. I am replacing the stock 2V heads with Edelbrock RPM hydraulic roller heads. He will flow test them to see if he even needs to do any porting to reach 450, he think it will be ok stock but I am ok with some porting to balance it out if necessary. Once he finishes the tear down he will suggest a bore and stroke, as far as I know this engine has not been touched before and had less than 70,000 miles. So unless the crappy oiling system has increased wear it should only be a stage one bore. He is going to correct the oiling deficiencies for me when he starts the rebuild by restricting the first bearing oil flow and using tighter lifter bores to stop the flooding of oil in the heads. I can send out the full rebuild list after all the tear down measurements are taken and firm order list is composed.
I also found a company in the US that makes adapter plates to use a 302 intake on a 351C, so I bought a used GT40 styled intake from an old Mustang. It will have to be ported a bit to make sure it flows properly but it will allow me to install EFI on the engine. I found an EEC-V from a 2003 Crown Vic to run the EFI at the junk yard and pulled it off a couple days ago. I also found a 4R75E tranny from a 2009 Crown Vic interceptor that I pulled as well so I am sending that to the mechanic for a rebuild as so it can handle the torque. It will be nice to have an over-drive on the old girl since I will do a fair amount of hiway cruising with her. It's not going to be cheap but this will be the only rebuild I do with this car.
 

AcesArneson

Well-known member
Joined
Aug 17, 2019
Messages
54
Reaction score
18
Location
Fort Mac, Alberta
My Car
1973 Mustang convertible H code 351C-2V Playmate Pink
The AOD or the 4R70W can both be run with 2.75 gears with no issues. The Fox Body Mustangs with the AOD came with 2.75 gears and the AOD, and they run fine. The issue with that high gearing is that the car will be a dog out of the hole. Those AOD 5.0 mustangs with 2.75 gears would loose a 1/4 mile drag race to a Honda CRX Si, trust me I was there, LOL. The issue with high gearing is what camshaft you limit yourself to when you are building your engine, besides how the car will perform. The 4R70W has an advantage over the AOD in that the first gear is a 2.84, vs the AOD 2.47. If you are going to build an engine with aluminum heads and try to get 500hp out of it, you really can't run 2.75 or 3.00 gears. It will be a dog out of the hole. To get to 500hp you need a decent sized cam, you will not get there with a small "RV" stock type cam or a little bigger than stock cam, which you can use with 2.75 or 3.00 gears. To make a engine make power AND the car perform, everything is a combination. At 400 HP or below, using a cam with at most 215 @.050 you may be able to get away with 3.00 gears with a good higher stall torque converter, but you are still loosing a substantial amount of performance compared with 3.50 gears or lower, not to mention with a bigger cam. Now you will probably not get to 500 hp, with 351 cubes with a small 215 @ .050 cam, even with the best flowing heads, intake, and exhaust. The bigger the cam, the more gearing it needs and the higher stall speed converter you will need to use. As you move up in HP your torque curve moves up in the RPM range, a 500 HP engine will probably make less torque that a stock 351C 2V under 2000 rpm, but from 3000 rpm on up it will be night a night and day difference. If you are looking at a real 500 HP normally aspirated 351, you really will need at least 3.50 gears, in reality you probably need more, and a 3000 RPM stall torque converter for the car to perform at its full potential.
Thanks again for the input Junk, I am leaning heavily toward 3.50 gears. I found a 4R75E from an '09 Crown Vic and pulled it earlier this week, so pretty sure I wont empty my wallet at the pump by moving higher.
 

BUCKWHEAT

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Joined
Jul 22, 2021
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Location
Warson Woods, MO
My Car
1973 Gold Glow Mustang Convertible, 302 2V C4
as last production Grande, would your car be more valuable as a bone-stock restoration? just asking...
 

AcesArneson

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Aug 17, 2019
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Location
Fort Mac, Alberta
My Car
1973 Mustang convertible H code 351C-2V Playmate Pink
I am not rebuilding it to sell, I am rebuilding it to drive. As long as stock parts doesn’t inhibit making the car fun I will keep them on. I am also keeping all of the stock components I replace so if I ever do sell it in the future the buyer can always flip it back to original.
Dropped off the tranny and rear end in Edmonton and they are already rebuilt. Went with a 2500 stall and Dana limited slip with 3.5:1. I found an Offenhauser Port-O-Maroc intake that already has the injector bungs welded in. It was already running so I know it’s good welding so I scrapped the gt40 intake with adapters for now. It will still have an old school intake look with the MAF hidden under the air cleaner. Next I need to find someone local to modify my hood.
 
Joined
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Mustang, OK.
My Car
1972 Mach 1 Q code
2007 GT
1969 Cougar Eliminator B302
CSX 7000 Shelby Cobra FIA
2020 Edge ST
2002 F250 V10
450 2V flywheel HP can be done but takes some pro head porting and good cam and compression selection. The stock 2V heads stop flowing at .450 valve lift max. The early 1990s (92-93 IIRC) f-150 AODs had a more favorable gear set in them. The governor still limits shift points at WOT. If you are looking for 450-500 plus from 351CID look at 351c CC 4V heads and matching CR and camshaft. The alternative is open the wallet wide for the CHI heads and intake. The TFS head are a good alternative but, still not inexpensive. Contact Brent, at Lykins Motorsport for sound, results proven, advice if you want the big numbers. Just my opinions, I hope all goes well with the build. Chuck
 
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