Ok another question about gear ratio....

I have a 351 W, slightly lopey cam, a 4 speed toploader and 15" 275 60's, I won't be doing alot of highway driving, pretty much around town and maybe occasionally 60 MPH tops, I want to be able to light em up when I want to, whats a good ratio? ya'll tell me cuz I don't know, that's why I'm asking

 

i would recommend 3.5s. get a limited slip at the same time.

 

With that tall of tire might wanna go deeper...like 3.80

 

Based on your overview and spec's.. I agree with rt. I myself would be looking in the 3.70-3.90 range.

That torque multiplication change alone will make you feel like the motor got a cam change. Should be able to add some extra timing down low and also volume to the squirter/s too.. which will give you even more snap when tuned to the new gears.

 

351 and a toploader? Dont think you'll have a problem Lighting em up with any ratio rear end.

 

true dat.. but a lopey cam will usuallt soften the power curve enough down low.. that the deeper gears will allow the cam to come in quicker.

Which is why I assumed he wanted to maximize his current combo and move towards a gear ratio that the cam mfgr probably rec'd in the first place.

 

Agree!

If your staying with an 8 inch, I have a set of 4.62's I will sell. I ran them with a small block and a toploader, lighting them up was never an issue.

 

That's what I was thinking but wasn't sure with those tires. Since lighting 'em up isn't an issue, I'd use an online RPM/ratio/speed calculator with the desired RPM at your cruise (60 MPH?) speed to select the rear end ratio.

 

Which gear ratio does your toploader have?

Is it the close rato toploader with a

2.32 1st, 1.69 2nd, 1.29 3rd, 1.00 4th, and 2.32 Rev

or a wide ratio with a

2.78 1st, 1.93 2nd, 1.36 3rd, 1.00 4th, and 2.78 Rev.

If it is the wide ratio I would say that the 3.5 gears that Bryant suggested is a good gear for what you want.

If it is the close ratio I would be more inclined too look at the 3.73 range...Remember in comparison too a C4 the 1st gear ratio on a C4 is 2.46:1 and allot of people tend to compare their choice of rear gear ratio too that of the C4 transmission ratio. So if you have the wide ratio toploader you have allot deeper 1st then the automatics do. And you especially dont want too go too deep on your rear gears because you will just end up making 1st the equivalent of a granny low and you will be doing a gear shift at 10 mph. Or starting out in second all the time.

But who am I too talk I am keeping the stock 3.0 gears in my car(yes i dont plan on changing them any time soon I like my 1st gear final drive ratio..) but I do keep thinking about the limited slip though..

 

I guess I need to confirm as to what I have, I was told it's a close ratio out of a Mustang, when I stop ordering parts and get some time I'll look and see what I can find out...thanks.

 

LOL... With 2:79s' and a stick, burnouts are a clutch dump away...I had 2:79s' in my Sprint with a healthy 351 / aod, and the car would cook em into 3rd gear no problem. I have 3:80s' and a trak loc in it now with the same tires...235/60-14s' If I stand on it a bit now...you wait for it to drop into OD so it gets some kind of traction...LOL... Go with 3:55s' if you plan to use the car ALOT. 3:80s' if you want to rip it up everywhere and still be a pleasant cruiser on the streets.

 

not sure where these "10 mph max in first gear" calculations are coming from.. but even a 3.27 geared 5 speed will run quite a bit faster than 10 mph before you need to shift into second. Most granny gears are well beyond 4.0 ratios for 1st and it would take really short gears in the rear of that car to limit you to those types of speeds. Especially if the car has any rev range whatsoever..then 40 mph 1st gear bursts isn't impossible at all.

Also need to keep in mind that it's not just about the first gear takeoff.. and the gear spread between 1st and 2nd will be softer and cause more rpm drop with taller rear gear and that should be taken into account if you're the slippery footed type that likes to ocassional downshift after getting up to speed a bit first. Much more opportunity for that type of driving on the streets.. than hauling rear from dead stops all the time.. and gears will often make the car feel faster than it really is due to the extra torque multiplication.

IMHO, putting anything less than 3.70 gears in combination with a taller 1st gear like that close ratio trans uses.. will lead you away from your original posts intention of making the most of the current combo. 3.50's are a good compromise.. but will feel a bit less than dramatic.. if you have decent rubber hooking up.. than the 3.70's.

Also IMHO.. you shouldn't have to dump clutches to get the cars tires spinning and/or hunting for traction.. and that's the whole idea behind torque multiplication in the first place. Match the cam to the gear and you will maximize the cars potential and make it feel like it's almost always coming into the cam instantaniously.. which will make it feel funner to drive as a result.

Unless.. you do put a lot of miles on the car or like to cruise at 75 quite often.. the shorter gears will give you your time and moneys worth almost very single time. While going too conservative can make you feel like you "coulda..shoulda..woulda" after all the hard work and money is spent. Been there..done that and I usually err on the side of overkill these days.

The bars are certianly different between what constitutes a fast car though.. and to each their own based on the rev range capability and how they like to drive it.

 

wow mr roberts apparently you havent ever driven a tremec/T5 with 4.11 gears. You dont start out in first you start out in second...

With the 3.27 gear ratio of my TKO and my 3.00 rear end my final drive gear ratio is 9.81:1 in first gear (and yes alot of the mustang T5's actually had a 3.35:1 first gear ratio)

to put that in comparison lets look at the first gear of a C4 transmission, the first gear has a ratio of 2.46 now the closest numerical calculation I can get for an actual gear ratio is using 3.73 gears that gives me a final drive ratio of 9.1758.

But to give you a comparison too RPM lets say that we put that C4 transmission in front of 25.7" tires (p225/55r16 or the stock tires for my wifes 2000 mustang) and lets see with a 2.46 first gear ratio and those 3.73 gears that engine is doing the 1-2 shift right about 20 mph...or about 2500rpm

Now a good comparison is my car using the same size tire my 3.27 first gear and 3.73 gears in the rear end. Well in daily driving that puts my 1-2 shift at about 15 mph or 2500 rpms.. Thats really not that good of a shift point, especially if you drive the car more then once a month...

Now in real world terms right now I am shifting 1-2 about 20mph right now, this is about a 2500 rpm shift because this car is currently my daily driver(yes my choice the expedition sucks gas like no tomorrow and I am getting about 20 in my car), if I really stand in it and race and run the engine up to about 5000 rpm I shift from 1st to 2nd at about 35 mph and my 2nd to 3rd shift is about 60 mph with 3 more gears to go and If I really get pissed off or really want too win I can hit 6000 rpm, about the limits of my engine...ok as high of an RPM as I want too go and I end up doing the 1-2 shift about 45-50 mph,2nd to 3rd at 6000 rpms is about 75 mph...

With 4.11 gears I would be negating first gear and I would be starting out in second gear because my 2500 shift point would actually be about 12 mph. So now if you want to argue with me over a 2 mph shift point then go ahead its still way too low too be useful unless you are launching at 5000 rpms all the time, and on a street driven car that can get you in trouble with the police in some places...

So yes in the end planning of gears is very important dont just listen to anyone on the internet including me. Do your own research, figure out what tire size you want too run. Because you might just find out that those 3.80's will just be too much of a hastle in your weekend cruises around town, or that your 3.25's might be left wanting for a little more


I used the tire size on my wifes car as an example because it is only marginally bigger then the tire size that came on our cars from the factory. The C78-14's had a diamater of 25.2 inches but you are more likely too find the 25.7 inch diamater under most peoples cars.

 

mark. I wasn't trying to argue and only gave my opinion on the matter.. just as you did.. and tried to loosely adhere to the question originally asked with my own interpretation.

So, based on all that.. my previous comment.. "err on the shorter side of final drive ratio to get your money's worth out of the time and cost to change things" still stands. That will likely only change if more detail is given as to.. the style of driving, rpm capability, with greater emphasis on what constitutes "acceptable 1-2 shift points around town".

As for my qualifications to freely give my input or disagree with others?.. I've designed and built many cars through the years with pretty near 20 very fast and highly collectible(by todays standards anyways) Ford/Mercury stuff mixed in there. Well.. not all were very fast.. but the ones I kept a bit longer eventually ended up that way. lol

As for Mustangs in general of every generation?.. either I've owned them, worked on them, ridden in them more than a few times(some VERY fast ones as well and my buddy still has a 93/94 coupe with a 363 and fairly large SC that I originally did the TFS heads for.. and another with a 74 Mustang II that we 351W swapped more than 20 years ago).. or... have "friends with friends" that bring them around in small stampedes for street racing(quite literally.. and I tease the P outta them everytime we run into them because they pull into lots like they're towing each other.. AGAIN!, lol) and showing off for the girlies while the wives and kids are at home. Never said I hung out with the best crowds, eh?

I've also mod'd no less than 5 x C4's into Mustangs, Cougars, Comets, and Ranchero's with low gear pinion kits that change out to 2.75 1st gears(in fact my 71 Comet GT will get the TCI kit I have waiting on my shelf for 8 years now).. and those things are great for doing exactly what the OP of this thread is looking for with increased torque multiplication in 1st and 2nd ratios. Over the years from those experiences.. I like the 3.50's for fairly regular highway duty with shorter tires.. and 3.70's for the same with slightly taller "meats". Then for more rpm oriented builds I like to go with at least 3.90's.

Either way the OP goes there.. he will improve things for the basic requirement he originally stated. How much of that last "bang for the buck" he wants to accomplish remains to be seen. We also need to keep in mind that.. one mans ceiling.. is another mans floor and to each his own in that regard.

 

Ditto........................... Unless he's got a tall rear gear (2.79-3.08) and a close ratio toploader. Those two factors will kill the bottom end even with a 351.......................With a wide ratio's lower first gear, it should melt the tires with just about any rear ratio.