FYI FORD - MustangSteve's Ford Mustang Forum
The Internet's Most Knowledgeable Classic Mustang Information
IF YOU HAVE A QUESTION ABOUT CLASSIC FORD MUSTANGS, YOU HAVE COME TO THE RIGHT PLACE!
MustangSteve has over 30 years of Mustang experience, having owned 30 of them and restored several others. With the help of other Mustangers, this site is dedicated to helping anyone wanting to restore or modify their Mustang.... THERE ARE NO DUMB QUESTIONS!!!!!
Visit MustangSteve's web site to view some of my work and find details for:
FYIFORD Contributors' PICTURES - Power Brake Retrofit Kits for 65-66 Stangs - Classic Mustang FAQ's by MustangSteve - How to wire in a Duraspark Ignition - Mustang Ride Height Pictures and Descriptions - Steel Bushings to fit Granada Spindles to Mustang Tie Rods - Visit my EBAY store MustangSteve Performance - How to Install Granada Disc Brakes MustangSteve's Disc Brake Swap Page - FYIFORD Acronyms for guide to all the acronyms used on this page - FYIFORD Important information and upcoming events

You are not logged in. Would you like to login or register?

11/07/2020 9:49 AM  #1


Rear end gear choice follow up 67 coupe

I found a web site Blocklayer.com rpm-gear.aspx, this site gives you mph if you put in tire size, (215/70/14), rear
end ratio, transmission (4speed top loader,t-5 5 speed). When you enter the transmission type you can set the
specs for each gear (1st,2nd,3th,4th and 5th) if they are different than what comes up with trans type. (They have
been right on for the most part).  The top loader gears =4 are very close to the t-5 first =4 gears (t-5 a little bit lower)
I checked mph, at 2k rpm, with 3 different gear ratios in 5th gear. The 325 rear end= 2k,5th gear= 75 mph, 350 rear
end =2k,5th=70 mph, 370 rear end= 2k,5th gear 66 mph. I don't know for sure maybe it's the tire size ? I'm thinking
maybe modern driveline knows what their talking about. My wheels are styled steel, tires are 2 years old I would like to keep them as they are. I was shocked to see how high the mph was at 2k with the 325,350 rear ends. The 5th
gear is.63 in the t-5. Just wondering am I missing something here? I do like to do my homework before I pull the
pin and fork out the cash. What do guy's think?     mustang stu

 

11/07/2020 1:04 PM  #2


Re: Rear end gear choice follow up 67 coupe

Absolutely use one of the mph/rpm/gear calculators to avoid guessing. Being able to enter different diameter tires really helps. There are several out there from which to choose.


Bob. 69 Mach 1, 393W, SMOD Toploader, Armstrong  steering.
 

11/07/2020 8:14 PM  #3


Re: Rear end gear choice follow up 67 coupe

There used to be a MustangSteve calculator that included all the variables on the MustangSteve website.  Haven’t seen it for a few years.


Money you enjoy wasting is NOT wasted money... unless your wife finds out.
 

11/08/2020 8:30 AM  #4


Re: Rear end gear choice follow up 67 coupe

Or, build your own in Excel or any other spread sheet.  Takes about a half hour and a little basic math and if math ain't your thing you can steal all the formulas off Gargle in a couple of minutes.  Or, PM me your email addy and I'll send you mine.  Only think I didn't put in is the trans gears other than fourth/fifth.  And you have to measure your tires, mine doesn't have a data base of what the nominal diameter of all the tire sizes are...do any of them?...don't know?
Or...just use one of the zillion ones online....way simpler.

BB1


"you get what you pay for, good work isn't cheap, and there are NO free lunches...PERIOD!"
 

11/08/2020 12:15 PM  #5


Re: Rear end gear choice follow up 67 coupe

The calculators are a great tool, making changes at this stage is super cheap.

I went through a bunch of scenarios before I made a final decision on a gear and tire size. Don’t let 5th gear be the only deciding factor, keep first gear in mind too. What would the speed be in 1st at your typical shift point.


John  -- 67 Mustang Coupe 390 5 speed
 

11/08/2020 12:30 PM  #6


Re: Rear end gear choice follow up 67 coupe

there is another site which someone here on this site posted for me when I had questions about the same as your,  www.tremec.com/calculador.php    I am not totally sure about that address. I am going to use a 3.25 gear with my t10, but my plans include the t5 I've had setting in the garage for several years. at 70 the rpm will be somewhere around 1800 and 2000 rpm at 75/80 mph.
 

 

11/09/2020 8:21 PM  #7


Re: Rear end gear choice follow up 67 coupe

What cam are you using?  It will make a huge difference in how different gear ratios perform in fifth gear.  In my opinion, a stock STOCK cammed engine can use 3.0 or 3.25 gears, or even 2.80.  Any cam at all needs 3.50.  Powerful cam like a 272 or 280 or more needs 3.50 or 3.70.   I tried 3.89 once.  Too much gear for street use unless you just like shifting to second really quick.


Money you enjoy wasting is NOT wasted money... unless your wife finds out.
 

11/10/2020 8:19 AM  #8


Re: Rear end gear choice follow up 67 coupe

MS   The cam is a comp cam 268 high energy, edelbrock performer intake, 650 avs carb, on 69 351w 
9.5 to 1 ,cast iron exhaust manifolds (69) 2 1/4 exhaust, turbo mufflers. Cam specs are 1,5 to  5,500 rpm,
rear gears 9" 325 open, it will pull from 1,100 rpm in 4th gear. Thinking about first gen T-5, 1st 2.95,5th.63
from modern drive line. I just don't want to buy a 9" center section that won't work out with the T-5.
mustang stu
 

     Thread Starter
 

11/10/2020 9:14 AM  #9


Re: Rear end gear choice follow up 67 coupe

I'd use a 3.50 with that setup. 

 

11/10/2020 4:39 PM  #10


Re: Rear end gear choice follow up 67 coupe

"Just like navels...........everybody's got one"......IMHO
3.25:1 with the T-5 would be perfect for spirited driving around town and cruis'in!  For occasional drag racing then go to the 3.50/3.73-ish.
By the time you "wring-it-out" in 1-2-3-and shift to 4 you will be beyond ANY legal speed limit (and you still got 4 & 5)
351.........cruis'in to the bash....in 5th gear...the engine should be "up-on-the-cam"and SMOOTHLY loafing along.  Drop it down to 4th to pass and you can "suck-the-paint-off" anybody's driver side door. PLENTY of scoot.
Leave what you got in it.
6sal6


Get busy Liv'in or get busy Die'n....Host of the 2020 Bash at the Beach/The only Bash that got cancelled  )8
 

11/11/2020 6:43 AM  #11


Re: Rear end gear choice follow up 67 coupe

Oh, if you already have a 3.25 I wouldn't spend anything to change it.  I thought we were talking about going from like a 2.80 set looking for the balance of performance and highway RPM.  If it were a clean sheet deal and you were building the rear anyway I would prefer a 3.50.  If you already have a 3.25, as the saying goes "run what ya brung". 

 

11/13/2020 8:47 PM  #12


Re: Rear end gear choice follow up 67 coupe

TKOPerformance wrote:

Oh, if you already have a 3.25 I wouldn't spend anything to change it.  I thought we were talking about going from like a 2.80 set looking for the balance of performance and highway RPM.  If it were a clean sheet deal and you were building the rear anyway I would prefer a 3.50.  If you already have a 3.25, as the saying goes "run what ya brung". 

Sounds like a reasonable plan to me.  If it lugs down in fifth at speeds you think it shouldn’t lug down, THEN consider a swap.


Money you enjoy wasting is NOT wasted money... unless your wife finds out.
 

Board footera


REMEMBER!!! When posting a question about your Mustang or other Ford on this forum, BE SURE to tell us what it is, what year, engine, etc so we have enough information to go on.