Gear ratio

[MeanMachine]

My '71 started out as a 2-BBL 302 with 3.00:1 gearing and it would roast the (single) tire when I first got it.  I don't fear the gear, being that I don't have to commute long distances or cruise the highway.  The '71 is far from stock anymore and runs a 4.57 gear with a 28" tall tire.  My Mach 1 has the option of a 4.11 or a 3.70 gear, as I have multiple 'pumpkins' for 8 and 9 inch rears. 

Guess you can tell, I enjoy acceleration

 

[jpaz]

Nope, I have an FMX automatic, and a mild, almost stock "H" code ( has a 4v cam)....the original engine, under the hood complete with 2 barrel. You may be thinking that's just crazy, but the darned thing just runs too good, really. I DO have another engine in the garage, which I've been aquiring components for, to someday install in the car. My choices for the no.2 engine include one of Crower's "torque monster" cams, one of their mildest but better events than a factory 2 or 4 barrel cam, worked up Aussie 302c heads with dished pistons to match, an Edelbrock prototype 351c-2v runner intake ( rare pre-production item new in the box), a 600 vac secondary 4160 holley, and various oiling mods, con rod mods, etc. The major focus will be towards brutal low to mid range power and strength/reliability........exactly where I drive, as do most of us, whether anyone really wants to admit it or not. When I do this I will remove the original engine complete, save it,  and swap in the new engine. As smooth and powerfull as I believe the new engine will be, I still maintain that the "H" code in my car currently is suprisingly strong as is.  

I have a Crower torque monster cam in my 4V 351 Cleveland with a C6 tranny and I really like it! My trans has a Trans Go  shift kit in it and wow, it really is very quick off the line and chirps the tires when shifting very easily. I can break the tires loose at a 45 roll. But it has very good street manners too. Runs nicely in traffic and I have about 13-14 inches of vacuum at idle.

 

[Spike Morelli]

Jpaz,

         I run a Trans Go "re-programming kit" in my FMX as well, and I love the firm shifts. Mine will chirp the tires as well if I'm on it. Glad to hear some feedback on Crower's Torque Monster. You know, on this site, you hear many varied stories and opinions about what components people use, or want to use, but I build engines for a living. I searched through most of the Name Brand cam grinders offerings we buy from , to see what cams they had. I bought the Crower based on comparison of how really pragmatic the choice was for street driving, as well as the fact that Crower stuff is always top quality. The Aussie heads allow all of the positives of the 4V heads, but with the port velocity needed for street manners. I have bushed my lifter bores with a Wyandorf kit, some restricting of cam journal oiling, external line to bring oil to the back of the block, Icon forged pistons to mate with the heads to bring compression down to street gas useage. Rods are bushed, bolted, polished and peened. There's lots of incidental stuff I've done, not that I'll ever need it all, simply because I can do it at work myself, and I don't have to pay for the mods. And it's not all for horsepower, Truly, there's a measure of overkill here leaning towards strength, road manners, and reliability, but it's expected from me when I assemble someone's racing engine , so why not apply lessons learned to the daily driver?

 

[jpaz]

I did get a bad set of hydraulic lifters from them though. I had the cam saver lifters in and they collapsed after about 1200 miles. Long story short they replaced them and I went with the normal lifters. I probably have about 1400 miles on the new lifters and no problems. Running great now.

 

[Spike Morelli]

 I have multiple 'pumpkins' for 8 and 9 inch rears. 

Years ago, when I swapped out the 3.00:1 open diff, to the 3.50:1 Trac-Loc, I bought a complete diff with the gears and Trac-Loc already in and ready to go. I put the original nine incher in the garage, and after a few years, i got tired of looking at it and moving it around. I GAVE it to a friend. Nowadays, it's the diff of choice. I probably should have kept it, as long as I still have the car.

 

[Chris Baumann]

That seems like a lot of $$ for a gear swap. Heck, you can get a ring and pinion set for $250!

A change to 3.50 would get the car away from a stop with more gusto at the expense of highway cruise rpm.

A stock 4V CJ engine is pretty peppy, are you confident in its health?

I had '72 Cougar, 351C 2bbl, fmx auto, 9" with 2.75:1, and I could do burnouts long and hard!!! Tuned well. With the engine and axle gears you have, you should be able to lay black stripes for days!!

 

[Chris Baumann]

Nope, I have an FMX automatic, and a mild, almost stock "H" code ( has a 4v cam)....the original engine, under the hood complete with 2 barrel. You may be thinking that's just crazy, but the darned thing just runs too good, really. I DO have another engine in the garage, which I've been aquiring components for, to someday install in the car. My choices for the no.2 engine include one of Crower's "torque monster" cams, one of their mildest but better events than a factory 2 or 4 barrel cam, worked up Aussie 302c heads with dished pistons to match, an Edelbrock prototype 351c-2v runner intake ( rare pre-production item new in the box), a 600 vac secondary 4160 holley, and various oiling mods, con rod mods, etc. The major focus will be towards brutal low to mid range power and strength/reliability........exactly where I drive, as do most of us, whether anyone really wants to admit it or not. When I do this I will remove the original engine complete, save it, and swap in the new engine. As smooth and powerfull as I believe the new engine will be, I still maintain that the "H" code in my car currently is suprisingly strong as is.

 

[Chris Baumann]

I had '72 Cougar, 351C 2bbl, fmx auto, 9" with 2.75:1, and I could do burnouts long and hard!!! Tuned well. With the engine and axle gears you have, you should be able to lay black stripes for days!!

Just a reminder guys,, All 71-73 Cats, and Horses, with 351C ,,even 2bbls, are pretty snappy, I've owned 5. If it's not seat of the pants snappy, something is probably off, or wrong. '73 with spacer plate for EGR, can bring with it, all kinds of tune up issues. Vacuum leaks specifically!! There are no knowne replacements. My advice:: IF not switching to aftermarket 4V, intake and carb, then pick up a 70-72 351C 2Bbl cast iron intake from junk yard, and grab that spacer plate and carb also. You won't be dealing with a burned out one Also, why your tinkering, put in adjustable crank gear timing set, and the gasket set. Advance the gear on crank 4 degrees, Yep, do it. All cars this old need new timing set anyways. Put a new water pump while your there too. Yes, expensive project, but good stuff. Your '73 Cougar or Mustang, will. Thank you, in the 48 states,

Here's what I have in my 71 M code; 4 speed top loader. 3.25:1 now with Traction-Loc (used to be a one-wheeler-peeler) rear axle. Stock intake with a Holley 670 street avenger carb. Distributor is a factory motorcraft with altered limit slot (L10) and Pertronix Ignitor II module and matching coil and Autolite 25 plugs. Timing is set at 14 deg. initial, L10 = 20 deg. crank for a total of 34 mechanical plus about 4 deg. vacuum on top. The carb is basically stock other than larger squirter #35 and primary plates drilled for idle a/f ratio. And yes I can spin the tires with ease, not that I want to as tires here cost too much. I chose not to swap the gear ratio, but kinda wish I'd gone with 3.50:1.

As for the rip off artist who wants 3 grand, he must have a mortgage way too big or a mistress on the side. Run, Forest, run.

 

[Stanglover]

Chris Baumann, nice to see a new member sign up. Your input is invaluable.
However there is a section for introductions and if you could, please go there and introduce yourself and your car with pictures. We LOVE pictures!
While I'm here, a warm welcome from SW Ontario, Canada.

 

[c9zx]

Find a real mechanic. Or invest in some tools and shop manuals and lean how to do the basic stuff yourself. I hope you get it sorted out without too much drama. For what it is worth I'm not a fan of Edelbrock carbs. Chuck

 

[Stanglover]

Find a real mechanic. Or invest in some tools and shop manuals and lean how to do the basic stuff yourself. I hope you get it sorted out without too much drama. For what it is worth I'm not a fan of Edelbrock carbs. Chuck

FYI, this is an old post from 2020. Our new friend revisited it with his thoughts.
And for me too, not a fan of Edelbrock carbs, they just look wrong (for a start).

 

[kcmash]

I am in KC also, hopefully we can meet up sometime.

As for rear gears, I have a 351 4V with a Edelbrock Performer II intake and a Holley 670 Ultra 4 bbl. I run a toploader 4 speed and 3:25 in the rear. It has plenty of pep off the line and drives nice on the highway too. I can cruise at 70Mph at 2000 rpm. I have a Boss grind to my camshaft and my car is very driveable, and fun. I do not race or do a bunch of burnouts. If anything, my local expert thinks I ought to go 750 or 850 on the carb.

kcmash

look for me........

 

[Ron Tanzi]

I have to chime in on the subject of H codes with 2.75 rear gears since that is what my car is and was stock. I still run the 2.75 gears but have been running a four barrel and non-stock cam for better than 20 years. I will testify to the fact that my H-code in stock form before I did anything to the engine and with a hard 103K miles on her could lay a long patch. As a matter of fact it was the first car I ever lit up the tires on when I was 15. The car was always good down low with the stock cam and 2 barrel. My late mother sure would hammer it often and I always enjoyed that. My father was more gentle and only occasionally opened her up. I think Ford knew what they were doing with that combination.

Ron

 

[Stanglover]

I am in KC also, hopefully we can meet up sometime.

As for rear gears, I have a 351 4V with a Edelbrock Performer II intake and a Holley 670 Ultra 4 bbl. I run a toploader 4 speed and 3:25 in the rear. It has plenty of pep off the line and drives nice on the highway too. I can cruise at 70Mph at 2000 rpm. I have a Boss grind to my camshaft and my car is very driveable, and fun. I do not race or do a bunch of burnouts. If anything, my local expert thinks I ought to go 750 or 850 on the carb.

kcmash

look for me........View attachment 79110

Interesting that your car only turns 2000 at 70 mph. I have the same set up as far as gearing goes and mine turns 2800 at 65. Unless you have a close ratio box, I think your tach is off.
As far as the "experts" say about carb size, they're talking out the back of their ***. A 670 Holley or the now defunct QF 735 is all they need unless set up for racing. Just my unqualified opinion.

 

[70cobrascj]

Lol my mistake.. i should have mentioned it. They were push rods... I never got the compression ratio stats.. He just was listening too it and said that it sounded healthy.. Im located in KC.... As far as I know it has the stock high lift cam... It accelerates pretty good on the highway.. Just the initial press on the gas starting it takes off its boggs down....Like pretty much telling me wth you trying to do too me lol Take off just doesnt have enough spunk

I’d like to know how a bent or broken push rod could get into the intake?

 

[Ron Tanzi]

Interesting that your car only turns 2000 at 70 mph. I have the same set up as far as gearing goes and mine turns 2800 at 65. Unless you have a close ratio box, I think your tach is off.
As far as the "experts" say about carb size, they're talking out the back of their ***. A 670 Holley or the now defunct QF 735 is all they need unless set up for racing. Just my unqualified opinion.

That is curious I have 2.75 gears with 235/60/15 tires and I cruise at about 2200 rpm at 70.

 

[Stanglover]

That is curious I have 2.75 gears with 235/60/15 tires and I cruise at about 2200 rpm at 70.

Yeah Ron, I didn't consider tire diameter nor did kcmash mention what he had, so yes it could make a difference. Mine are 245-60-R14.

 

[kcmash]

Well I will have to check mine. I am running 15 inch 245 60 series on original magnum 500 wheels. I ordered the speedo gear to match my gear ratio, so I thought my numbers were good. I'll have someone pace me sometime.

kcmash

 

[Ron Tanzi]

Well I will have to check mine. I am running 15 inch 245 60 series on original magnum 500 wheels. I ordered the speedo gear to match my gear ratio, so I thought my numbers were good. I'll have someone pace me sometime.

kcmash

If you have the Waze app it will tell you your speed via GPS.

 

[70cobrascj]

If you have the Waze app it will tell you your speed via GPS.

You can just use any speedo app on your cell phone they are very accurate

 

[Stanglover]

Well I will have to check mine. I am running 15 inch 245 60 series on original magnum 500 wheels. I ordered the speedo gear to match my gear ratio, so I thought my numbers were good. I'll have someone pace me sometime.

kcmash

I was thinking wrong speedo gear, but it sounds like you already considered that.
I know with my car, the GPS speed matches the speedo within a mile or two, so PDC.
My tach is a Rocketman's conversion and it is very close to my timing light tach, within 100 rpm, so again PDC.