Gear ratio choice

[sea67n]

This is my first post outside of the build thread I have been running for my 67 Coupe, some great encouragement on there but thought a new post was more appropriate get some advice on choosing gear ratio....

Have pulled the 8 inch diff out in the course of the build, first time it has been out since I owned it which is around 17 years now. Previously had a very basic 289 in it with a C4 and just merely cruised around enjoying myself, and that attitude hasn't really changed..... but I need to make some informed choices and this is even less an area I know much about...currently the 8 inch is 2.79

I am still undecided on a 302 / 347 / 351w to go into the new build, but there is def an AOD going in. I have been having discussions re 8 inch, 9 inch, change of gear ratios, put an LSD kit into the 8 inch etc etc, in reality what is really a must do now ?  I certainly didn't have any issues cruising around as it was, but currently deciding where to funnel money into various parts of the rebuild and deciding what would be nice to have and what I should really consider a necessity..... all your words of wisdom appreciated in advance....

Sean

[shaunp]

If you are running an over drive and an engine with a cam you want a much lower diff. 3.25 min but if you want it quick of the line 3.5 or even 3.7 gears are cheap about $180 from summit, as is an LSD about $450 bearings about $100. 8" is fine. Unless you plan to do a lot of miles and or want to run a low diff, I'd leave a c4 in it. AOD's are not all they are cracked up to be. The fuel you save is not worth the drama often, I'm not sure what the fascination with them is, A C4 is a fine gearbox.

[GLENN 70]

I agree with Shaun on most of those things .Engine wise, well it comes down to what you are after power wise .A 302 four v stock engine doesnt have much go in a 67 ,a 347 will work well and fit with extractors the best    . If you just want a stock type engine with a 4 b carby ,alloy intake , up grade dissy and a set of extractors maybe a 351w and they fit in ok but the extractors are a bit of a problem fit wise  .A c4 auto is all you need with a 3.25 ratio diff if you are running 15 inch wheels and a 3.00 ratio with 14 inch wheels .Do you need a LSD diff ,unless you plan on hitting hard off the line ,and a LSD is useless they really are a wast of money ,a tru track center is the go .The 8 inch will do the job with the tru track but dont buy the cheaper gears as they will whine/be noisey ,so go for a very good brand not the elcheapos .A bit more info on what you want power you want will help us .

[Ron Mexico]

if you are going with overdrive, put in 3.8 in the rear. quick on takeoff plus you got a cruising gear on the highway
in 4th it will rev at 3000rpm at 60mph then drop down to under 2000rpm in over drive. (a little more for an auto)

I'm running a top loader 4 speed with 3.8 in the read (with an auto locker). i don't drive the car every day, the locker diff clicks when turning as the diff starts to differentiate but it hooks under torque.

wheels on mine are 17" with 225/45 tyres.

sometimes I wish I had overdrive to bring down the revs from 3000rpm on the highway but then again the power is ready when i put my foot down in 4th.

[Thirsty428]

I had an AOD with 3.7 Gears.
Good set up

[sea67n]

Thanks for the advice guys, Im not after a power monster, I wont be smoking it up taking off at the lights, in fact I doubt these wheels will ever be intentionally spinning away or sliding around corners. Whatever goes in will be relatively stock standard, some minor upgrades perhaps, 15 inch wheels have been on it and I don't think they can really go much bigger anyway as is. The Tru Track sounds like it might be a very good option to go with. I just want a beautiful reliable ride all over.......... I don't ever want to return to the old days for this girl where Id end up on the side of the road in the middle of the night with some weird 'old car' problem.   I have the other end of the spectrum with a B4 and sportsbike if I feel the need to see how fast I can go

[skev]

Any votes for a Gear Vendors two speed on the back of the C4?

[68pony]

Gear vendors is way to expensive, if you are going to spend the money on gear vendors your better off going down the AODE/4R70W electronic 4 speed  auto path , just google 4R70W into classic mustang and you will see plenty of info, this is what I have, computer controlled with lock up converter in 3rd and 4th gear , I have a 9 inch Detroit locker with 3.7 gears and cruises at 2,200 rpm at 110kph with converter locked, 3500 stall in trans , no converter flare on freeway due to converter locking so having a high stall is no problem, there are a few more on here going down this path, click on the link below for the computer and harness , this is who I used and were very good to deal with , they can give you more info, you will need to make a new cross member but they might be available now due to the popularity of this conversion,
http://www.becontrols.com/

[GLENN 70]

Ok just a nice 302 with some upgrades will be nice ,still a c 4 and still your diff with 3.25 gear ratio with your 15 inch wheels .As i said if you dont plan on spinning the wheels off the line, leave your diff and just change the ratio . With that ratio and 15s you will be 2,600rpms at 100klms or 2,400 rpm with 3.00 ratio .If you were out on the hwy every day then you would consider a 4 speed overdrive .A gear venders is for out right performance ,but you are only a stock type engine and not wanting to race . The true track is great but do you really need it .I am putting a true track in mine next week, but my car smokes the tyres and i go to the track sometimes .

[JadeMach1]

I am running a true track with 3.25 and 15 inch rims and it works fine with FMX and a stroked 351W. I am still getting  a little bit of wheel spin of the line if I am heavy footed with the accelerator.
 

If I was starting from scratch I would speak to the engine builder and get a recommendation for the stall convert and diff ratio before buying parts so that it all matches the torque curve of your engine..

If the package works together you will love car... If its wrong the driving experience will be comprised

[sea67n]

beautiful guys, thanks for the advice, a lot of thinking and balancing of budget to do..........

[Petey]

sea67n,
If it was good enough for Ford to use 3.0:1 LSD in Fairlanes and other medium performance cars, it's good enough to assume the ratio is fine for cruising and normal highway driving.
I would not use an FMX transmission because they are way less efficient than a C4 and not any stronger IMHO. If you plan to upgrade the HP of your engine substantially, I would suggest you just get the C4 overhauled to handle the extra torque. Value for money is what I am talking about.
As for the Gear Vendors unit, that is a serious bit of kit and really gives major improvement to performance off the line which is not possible with an FMX standard transmission because of the multiplier effect splitting the gear ratios. There is no comparison with cost or performance compared to any other transmission, but it really is over the top for a cruiser which is used for "normal" driving.
 PT

[shaunp]

Really unless you do a lot of miles in them I don't really see the need for an OD box, I'm mean how much fuel do you save, most of these cars don't do that many miles at all.

[peter9231]

Hello,
I have a 5.0 EFI engine with a BTR 97le 4speed auto in mine (3.0:1 Diff ratio)
Great for cruising 1400 rpm @ 100kph
Very easily returns less than 10 litres per hundred kilometres fuel consumption. (600 + kays to the tank )
If your diff ratio is 2.79 I think it would be to "tall" for overdrive transmission.
Go for 3.5 diff and you will get the best of both worlds.
Not convinced on durability of AOD autos they need to be set up correctly or they grenade easily.
Peter.

[derwin66]

I have 3.55 with a gear vendors overdrive unit attached to my C4 with 14 inch wheels and love it on the highway.  I put the gears in and it revved to high for my liking so I had to go an overdrive unit.  Best move ever

[68pony]

Really unless you do a lot of miles in them I don't really see the need for an OD box, I'm mean how much fuel do you save, most of these cars don't do that many miles at all.

Its not just about fuel economy, I do a lot of freeway driving with the missus, having that big 427ci reving at 2200rpm at 110kph is heaven compared to 3200 rpm, we can leave the panadol at home  ,i have switched the over drive off on the freeway and I can tell you f@$k that, for me it was also the gearing of the 4r70w , 2.84 first gear compared to( 2.40 with c4) with my 3.7 rear means rocket launch take off's , lock up converter on freeway also means my 3500 stall doesn't flare when cruising, but I do agree if your going for a mild set up a c4 and a 3.25 rear with tru track is more than enough it just depends on what your after.

[HEVEN67]

Im with 68pony 4R70W, as far as reliable Ford rated them at 500hp 500flb, they use them in F150's, not to be confused with the old AOD, those whom still believe in C4's and tall diffs still believe the earth is flat!
Overdrive transmissions, auto or manual give a increase in fuel economy by around 30%.....30%, that means 450ks from a tank full to 600ks. I rest my case.
luvhev

[GLENN 70]

Heaven67 you must be talking about me  ,i think sea67n is talking budget here .If i had the choice and dollars i would still go a c4 with a gear venders .A friend of mine has a 70 mach 1 with a c6 and has bought a gear venders to put in ,we just havent done it yet .

[shaunp]

Heaven67 you must be talking about me  ,i think sea67n is talking budget here .If i had the choice and dollars i would still go a c4 with a gear venders .A friend of mine has a 70 mach 1 with a c6 and has bought a gear venders to put in ,we just havent done it yet .

I know I'm living in the past, I just like Top loaders, if I was to change I'd go for a TKO, can't see it happening though, I'll just burn some extra fuel. Horses for courses I like old cars to have some of the things in them that made them great in the day.

The fuel saving will also depend on the diff not being "too" high with an OD,  know of 2, 65 cars that drove from Brisbane to Melbourne basically the same spec, 302's exhaust, 600 holleys, the car with the AOD used little more fuel then the one with the C4, diff was to high and they labour in 4th, those AODs don't like changing back. I agree I'd go with a later model electronic box and bypass the AOD's completely or just stay with a C4 and compromise on the diff ratio. A code cars mostly ran a 3:1. to make them a bit quicker the a C code. They are just old cars.

[68pony]

Heaven67 you must be talking about me  ,i think sea67n is talking budget here .If i had the choice and dollars i would still go a c4 with a gear venders .A friend of mine has a 70 mach 1 with a c6 and has bought a gear venders to put in ,we just havent done it yet .

For the price of the gear vendors you can buy a rebuilt 4r70w and controller with harness, and if you need to rebuild your c4 the savings are even greater, the 4r70w are a dime a dozen in the usa , cheap as chips, and not hard to install , move on to the 21st century guys 

[Pinto Pete]

wouldn't mind one,  but not sure if you can fit one behind a 460..

[Petey]

Comparing the Gear Vendors unit to any other transmission mentioned in this post is like comparing a turbo charger with a supercharger. They do similar things but by a different method. The one major difference is lag from one and instant power from the other.  Cost benefit is relative and depends on the individual requirements.
Trying to argue that "Gear vendors is way to expensive, if you are going to spend the money on gear vendors your better off going down the AODE/4R70W electronic 4 speed  auto path" makes little sense. No standard transmission does what a Gear Vendors unit does and you pay for the advantages it brings. If you want all out performance off the line and double the number of gear changes with extra torque, then you can't beat a Gear Vendors unit. If a lower final drive ratio is all you want, go for the 4 speed auto.
PT

[StephenSLR]

Really unless you do a lot of miles in them I don't really see the need for an OD box, I'm mean how much fuel do you save, most of these cars don't do that many miles at all.

Not so much for fuel saving but like many of us, we do hit stretches of freeway and it's nice not to have it revving so high when your doing 110 clicks.

s

[68pony]

Comparing the Gear Vendors unit to any other transmission mentioned in this post is like comparing a turbo charger with a supercharger. They do similar things but by a different method. The one major difference is lag from one and instant power from the other.  Cost benefit is relative and depends on the individual requirements.
Trying to argue that "Gear vendors is way to expensive, if you are going to spend the money on gear vendors your better off going down the AODE/4R70W electronic 4 speed  auto path" makes little sense. No standard transmission does what a Gear Vendors unit does and you pay for the advantages it brings. If you want all out performance off the line and double the number of gear changes with extra torque, then you can't beat a Gear Vendors unit. If a lower final drive ratio is all you want, go for the 4 speed auto.
PT

Sorry dude your wrong, this post is about over drive , if you use the gear vendors as a under drive then you lose the over drive , yes it will launch harder as a under drive but remember the 4r70w has a lower first gear (2.84 ) a c4 has a 2.40 first gear so that advantage has been eroded some what , having extra gear changes between gears does not mean the car is going to go any faster either, no lock up converter in third or fourth gear with gear vendors , in third it locks at 80 kph so when going down the track you have instant drive and no converter flare, the ability to have 2 tunes , one for street and one for race at a flick of a switch, having the computer change gear for you at precisely the rev you want means no driver error and more consistent times, the 4r70w does everything a gear vendors does and way more.
  chris ps what im trying to say is as a all round package for street and race you cant beat a 4r70w

[shaunp]

Not so much for fuel saving but like many of us, we do hit stretches of freeway and it's nice not to have it revving so high when your doing 110 clicks.

s

 I understand  where all you guys are coming from, believe me, I've got 2 old cars that run overdrives, laycock-de'normenville units which is  basically, where Gear vendors would have got the basic design from, Jags had them since the early 50's and it's a must have in a 50/60's Jag, 4 speed with electric overdrive they work great, but that's how they came, My 65 3.8 S will cruise in at 130 mph all day  if you want to.

You won't convince me, to put one in my Mustang though, I like living in the past a bit, when it comes old cars, that's why you buy them. I don't mind if they rev a bit on the highway  or use more fuel, there are certain things/parts of cars that gain kind of legendary status over time Hemi's in mopars, Torque flite autos, Chevs have Power-glides and Turbo hydramatics, Muncie's and Saginaw 4 speeds, etc Fords had Toploaders, its  part of the history car for me I don't see any reason to swap out what is a good box. Just like Id never swap a Windsor for a modular or Coyote engine.

It is just how the hobby is, everyone has a different idea of what they want in a car, a lot of you guys want them to behave/look more like, a more modern car, I'd rather have them look like a "new" old and behave as well as they can with certain mods in the spirit of the car and as long as they are fast  loud & shiny, it's all good.