anybody running 3.08 gears in the t-bird rearend,i have the 3.27 and the stock mustang t-5,1st gear is like a granny gear,3rd gear I am pushing 3500 rpm at about 60 to 65,seems like the gearing is to low,milage is only 17 mpg,with stock ho cam,would like better milage.

 

The 3.08 is the rear that I first installed in mine. It came stock with the 93 Tbird and AOD automatic. I have the 4R70W automatic in my car, so its not really apples and apples to your situation, but I could see very little difference between the 3.08 and the 3.27 I now have. And I'm sure the cruising mileage is slightly better with the 3.08.

Mike

 

Granny gear? LOL I'm running 3.55s with a 6 speed and don't find 1st too low at all!

17 mpg is very low mileage for sure but I doubt it's a gearing problem because there are hundreds of 3.27s behind drivetrains just like yours that get much better mileage. You say you are running 3500 in 3rd why are you running around in 3rd gear? I think most guys turn around 2 grand at 60 in 5th so what are you turning in 5th gear?

You might want to post in engine performace all the details of your set up and ask for ideas on improving the 17mpg. If you are running a stock Mustang set up you should be getting at least as good of mileage as a Mustang.

 

I like my 3.08's. Nice cruise and they work fine in all gears. My mileage is a little better that several carb'ed 5.0's, I get around 20 in normal back country road driving. Freeway at 70 it's 19ish with a best of 26 while driving a tank out at 60mph for fuel mileage. Many 5.0 cars see mid teens on average. Also depends on how many GPM's you're seeing (grins per mile). The higher the GPM rate, the lower the MPG. Sorta an inverse proportional ratio thing.

 

The 3.08 gears may help a little but it is not the only thing what is driving that ^ 26mpg number because lots of guys get that with taller gears.

https://www.v8miata.net/engine-perfo...question-1111/

 

cvx_20,

Did you manage to install a 4R70W transmission in your car? I've been told that these do not fit so I am curious how you did this. Did you lose ground clearance?

 

Yes I did. It's been in there from the start, about 6 yrs or so. Ground clearance isn't an issue, clearance for the exhaust is tight, though. If you look at the engine/trans assy from the side view, with the engine leveled, the lowest point is the bottom of the bellhousing, which is roughly the same for stick versus auto. But the width of the auto, around the pan area, is significantly greater, and that's where the exhaust has to go. So the exhaust has to run fairly close to the trans, between the trans pan and the tunnel. But 2.5" pipes do fit. I'll try to come up with some pics.

See the latest blog page for exhaust pics: http://miatav8.blogspot.com/2014/06/...2-exhaust.html

Mike

 

cvx_20,

Thanks so much for this info.

 

I see this thread is a bit old, but I'll add a couple thoughts anyway in case someone is searching for gearing info for their V8 conversion.

The O.P. said he has the standard Mustang 5 speed. Assuming original equipment, that T-5 has a 3.35 ratio first gear which, just as he perceives it, is geared pretty short by V8 performance car standards.

In considering a swap from 3.27 to 3.08 rear gears, that only raises gearing by 5.8%; so if you were running along at 3000 rpm with a 3.27, a 3.08 would only drop you to 2826 rpm. Which, as cvx_20 correctly noted, is not really a major change.

An alternative to investing in a differential gear change might be a swap to a transmission with a higher first gear ratio. The Ford Racing T-5Z is a nice strength upgrade from the OEM T-5, and it has a 2.95 first gear. Swapping in this trans would raise gearing in first by 11.9% (twice as much as the proposed 3.27 to 3.08 rear gear swap). So 3000 rpm in the current first gear would drop to 2643 rpm...enough to make a significant difference.

Looking at it another way, keeping the 3.27 rear gear and swapping to the 2.95 first of the T-5Z would raise the overall gearing (in first gear) by the same amount as dropping all the way from a 3.27 rear gear to a 2.88 gear. (No such ring and pinion set actually exists; just using this as an understandable measuring stick).

The point is, first gear ratios have a big impact on suitability of overall gearing for any particular application. Generally, you see the "above 3.xx" gear ratios in heavy car/small motor factory scenarios...obviously the opposite of a V8 Miata conversion. So taller first gear ratios make a lot of sense here.

The T-5Z is rated up to 330 ft./lb. and has a track record of handling even more than that in V8 Miata conversions if it isn't power-shifted or otherwise shocked hard with really sticky tires. Tire slippage is kind of a "fuse" that helps prevents breakage with above-rated torque, unless traction is really good.

If you have a torque monster motor, the Tremec TKO 600 is a tempting option. It is rated at 600 ft./lb. and has a 2.87 first gear...even better than the T-5Z for this application, IMHO. It is also available in either .82 or .64 fifth gear ratios, optimizing for track or highway respectively. Compared to the OEM T-5. the TKO would raise gearing in first by 14.3%...which, paired with the 3.27 rear end would give the same first gear speed versus rpm as the OEM T-5 with a 3.35 first gear and a (theoretical, non-existing) 2.78 rear end ratio. So the TKO with its 2.87 first running the same 3.27 rear would drop our 3000 rpm example with the current setup all the way down to 2553 rpm.

The fact that it is difficult to get enough rubber under these cars to put all the torque to the ground also emphasizes the advantage of considering transmission choices with a taller first gear ratio, as it will lessen first gear wheel spin. It becomes an even better choice if running a fairly hot cam, as the rpm at legal highway speed with a .63 or .64 overdrive ratio can get too low for a cammed engine if you start dropping to something like a 3.08 or 2.73 rear gear, rather than swapping to a taller first gear ratio in the tranny instead.

Finally, when pushing the pencil to decide what you want in your own setup, also consider rear tire height, as there is enough difference in heights between sizes used on these cars to noticably impact overall gearing.

 

Wow great write up sunshine! Too bad OP seems to have checked out.

So this made me have to go back and look at the gear ratios on the 6 speed and I wondered if anyone puts a T56 behind the 5.0. Perhaps that would be the ideal solution? Other than the cost...

My T56 is 2.66 1st gear and a 0.50 6th and I turn about 1500 at 60 with a 3.55 rear and 25" tall tire. Even with the normal 23" tall tire I still find 1st very useful. Seems to me that would be a great fit for the 5.0 and really not much more than a T5z.

 

First of all great write up. Second of all, I think I can agree with this, I have a stock mustang T5, with the low first gear, but with a 2.73 rear end, and honestly, the 1st gear is perfect. I do find that the remaining 4 gears, are slightly high, the 5th gear is kinda useless unless you're cruising on the highway...


I wouldn't mind 3.27 rear, with T5Z, would give a similar 1st gear as i have now but with lower 2 to 5

 

Gabriel what you have there actually sounds like a pretty good combo to me. As I understand it the ideal shift points are to go from max HP to max TQ and I would imagine the gear ratios in the T5 would come pretty close to doing that for you. 2nd might be a hair on the low side for autox but probably not too bad. If you do that sort of thing even. The + side for me would be on the highway. I have a bad habit of driving 50 miles to get a 99 cent ice cream cone with my sweetie... So what do you turn at 60 in 5th?

 

I have the z box with 3.73s in my 91 stang gt, and they are well matched. I think with the smaller Miata tires, 3.27s and z gears will be great (it's what I'm doing).

Jason

 

In my opinion, the T-56 could be a logical fit for a mildly cammed, big inch stroker motor, one that makes a boatload of torque but isn't built for high rpm. The range between the lowest and tallest ratios in the T-56 is very wide, a 5.3 to 1 reduction. So, if you use a differential with gears tall enough to put the power to the ground in 1st gear, 6th is going to be REALLY tall.

There is no way to avoid the fact that the T-56 gear ratio ------ is really wide. That can be just fine with a motor with short cam timing, smaller ports, etc. that runs efficiently and smoothly below 1500 rpm or so. (I had this T-56 in a new, stock '95 Z28 Camaro with 3.55 rear gears; because of the engine's flexibility, it worked great and delivered 27 - 29 mpg at a 70 mph cruise, around 1200 rpm IIRC).

On the other hand, a motor with big ports, valves, and a rumpity-rump cam that wants to be around 2200 - 2500 rpm at cruise for smoothness and volumetric efficiency won't be at all happy lugging that .50 overdrive. You'll end up in 5th all the time except at jail-baiting cruise speeds.

The reason I suggest a big inch torque motor as a match for the T-56 is that this box brings a penalty in cost, size, weight, and power transmission loss compared to the T-5Z. Just from memory (so don't quote me), I believe the T-56 is in the neighborhood of 125 lb. compared to the T-5Z at around 75 lb. The additional power loss through the larger gear sets of the T-56 might be somewhere around 5 - 8 HP, depending on maximum engine rpm.

So, if you have a mild-cammed 5.0L, it makes more sense to me to go for the overall efficiency of the T-5Z...cheaper, smaller, lighter, strong enough, and more efficient. The T-5Z provides a 4.6 to 1 gear ratio ------ between 1st and 5th which, again, geared tall enough to put all the power down in 1st will still provide a tall enough 5th for relaxed cruising.

The bigger, heavier trannies like the T-56 or Tremec TKO600 start to make sense to me when you move up to an engine making, say, around 400 ft./lb. or more at the crank. The T-5 may theoretically transmit more power to the wheels, but if engine torque is high enough to eventually break it, no power gets transmitted at all, right?

The T-56 is physically REALLY large compared to the T-5. However, it obviously can be made to work under the Miata as the LSx guys are using them. Also in the good news department, if the T-56 is desired, that extra 50 lb. or so is carried way down low and near center mass of the car...the best place it could possibly be to minimize its effect on handling.

I personally lean towards the TKO 600 for the more powerful Ford engines, simply because I see it as the best set of compromises. The 2.87 first gear is tall enough to pair well with either a 3.27 or 3.08 rear, depending on the engine's powerband (rumpity-rump versus milder cam, respectively). It is larger and heavier than the T-5 at about 105 lb., but significantly smaller and lighter than the T-56, yet the TKO is actually stronger than the T-56 (except for the special, Viper spec model). The TKO 600 also gives you two models to choose from with the Ford input shaft, either a .64 overdrive for relaxed cruising with a reasonably mild engine or a .82 overdrive to provide more performance usefulness and to keep that rumpity-rump motor closer to its rpm happy place at highway cruise.

Jim, you mentioned running 3.55 rear gears behind the T-56 which does help a little bit towards making 6th gear useable with other than a stock, low rpm torque engine. However, if you think about it, the .50 6th gear is equivalent to running a 1.78 ring and pinion ratio behind a non-overdrive, 1:1 transmission...so even with the 3.55 rear gear it's still really, really tall.

Plus, with the T-56's 2.66 first and 3.55 rear gears you are at an overall reduction of 9.44 to 1 in first gear, crankshaft to rear axle speed. Now, if you instead run the TKO 600 with its 2.87 first gear and a 3.27 rear gear, you are actually 2% taller in first than the T-56 and 3.55 rear (better), plus now you have a shorter (better) overdrive, more useable for anything other than a stock torque pump. (By comparison, the TKO .64 overdrive with the 3.27 rear gear is equivalent to a 2.09 rear gear with a non-overdrive, 1:1 top gear transmission, as compared to that extremely tall 1.78 on the T-56.

Now, should you be running a more highly-tuned motor, the .82 overdrive version of the TKO 600 paired with a 3.27 rear gives you the same, 2% taller setup in first gear compared to the T-56/3.55 combo, and the .82 TKO overdrive ratio is equivalent to running a 2.68 rear gear behind a non-overdrive, 1:1 transmission. Now THAT's a very realistic final highway gearing for a performance motor. Plus, again, the TKO is smaller, lighter, stronger, and cheaper than the T-56.

Bottom line, for powerful engines I see the TKO 600 as the best set of compromises and, because of the overdrive gear choices, the most versatile. For smaller displacement engines of appropriate torque level I don't think you can beat the overall efficiency of the T-5Z. Also, I believe you can still locate an optional, .80 overdrive conversion ratio for the T5-Z, making it more appropriate for hotter-cammed, stock displacement 5.0L engines.

The good news is we have all these wonderful choices! Now if there were only more time and money...

 

There must be some kind of cosmic radiation in my computer. In the above post, everywhere I typed the word "S-P-R-E-A-D" (without the hyphens) it appears as -------. Even after I edited to correct it. Go figure.

 

1, I tried range and it worked.

2, I really like the way you think! Could you do and intro thread?

3, No question the T56 is a huge, heavy, expensive beast.

I have to disagree with you on the TKO but only for the cost. For that money you can get a T56 which will take all the power most guys run and I really like the 6 gears. Of course 6 gears is not needed and the car is easy to drive as a 3 speed but for a lot of situations the wider range in gearing is benefit to have. For me 90% of my driving is rolling down an empty 2 lane road around 70 and for that I like the .5 gear. I am not running a huge cam but big enough it bucks like a mule at low RPM if I am not careful so having the option to run in 3rd under 30 or 4th under 40 to keep it over the 1500 rpm buck zone is handy. But to all your other points on the TKO I totally agree with you. .64 overdrive is a great compromise for street (that big of jump would stink on the track though) and shedding 50 lbs no matter where it is in the car is a win. I would also imagine the bolting and plumbing would be much more straight forward to a 5.0 that the T56 would be.

The good news is you are spot on that you have way more power than is needed and that absorbs a lot of gray area in gearing that lesser cars can't get away with. The car really could car less if it is driven 2,4,6 as a 3 speed she just goes!

 

LMAO! I don't know yet... My RPM is not clibrated... according to the gauge when i punch it i'm shifting at 9000rpm... I'm pretty sure the pistons would come flying out of the 5.0 at that range heh..

 

Went for a cruise last night with this tread in mind. I have 3.43 final drive with the T56 behind an LS3 withe hot cam. I have zero complains about first or the overdrive. True I don't shift into 6th until about 65-70 cruising down the slab, but then the majority of the time I just quick shift up to 4th (1:1) and stay they to play on back roads. ...with an occasional downshift to 3rd to make quick work of a pass. A lot comes down to driving style and what you use the car for. I like to sit at 3K rpms and use the gas pedal like a slot car trigger and not bugger with shifting if not needed. ...just play on the loud pedal and grin!

 

I was wondering how you were doing Gator Bait. Welcome to the world of driving 50 miles for an ice cream cone! Or the ever pressing I wonder where that road goes? And bugs on your baby...

 

Last night was a 60mi round trip for some cheesy tater tots.

 

A good portion of your success in running tall final gearing with a warmed up motor is the magic of modern, electronic engine controls. The engine computer and its gang of sensors make even a feisty motor walk the line in a way that would never have happened back in my hotrodding heydays of modified AFB carbs and dual points distributors with mechanical advance curves.

In case anyone asks, we're currently living in the good old days!

 

No doubt about that but just think the youngin's will never learn to drive 3 footed and be able to feather the gas, brake and clutch at the same time like we did!

 

I hate how true this is. I fear the EPA/Gov bringing an end to our shenanigans. I mean...really...this much fun probably should be illegal!

 

Although it is quite in vogue now with performance vehicles (see it a lot on high dollar motorcycles), I typically don't care much for the flat or satin type paint finishes. However, as done on this car it looks positively sinister. Reminds me of that nasty bully in high school that grew up on the wrong side of the tracks and everyone would choose to cross the street rather than walk past him.

Fitting to the car's personality, I think. I like it.

 

I was looking for a picture I saved years ago but couldn't find it. It showed the gear clusters of a TKO 600 lying next to a T-5. The gears of the T-5 looked like pocket watch gears compared to the Tremec (see pic attached). The TKO parts looked like they must have come off of a heavy duty truck.

As a matter of fact...they did. Here's a true story that will arm you with knowledge so valuable that this and $1.75 might get you a cup of coffee at the local greasy spoon.

The TKO is actually a distant descendant of the old, Ford Top Loader four speed that was young when I was. As in, ancient. Borg Warner built the Top Loader; Transmission Technologies Corporation (TTC) bought Borg Warner in 1998.

Now, UPS has their delivery trucks fleet built pretty much to their requirements. Way back when, UPS wanted a durable, affordable, manual transmission with an overdrive 5th gear to increase fuel economy in their vehicles. The Borg Warner engineers were consulted, and rather than design something from scratch they pulled the dusty old Top Loader off the shelf, worked in some strength and materials upgrades to make it suitable for the vehicle weight, engineered a 5th gear overdrive into the tailshaft area and, Voila!...the UPS special.

Not long afterward, the Fox Mustang craze swept the nation and gearheads began building motors that ate their T-5's for lunch. The only practical gearbox alternatives back then were full-race boxes with dog gear rather than synchronizer shift mechanisms. Great for the strip, but the crazies wanted to drive their big-pony machines on the street.

Tremec, smelling money, wisely saw an unfulfilled market. They eyeballed their upgraded Top Loader/UPS truck transmission with the overdrive gear and marveled at how similar it was in service mission to their T-5...except built like a truck...literally. So with just a few tweaks the UPS special became the aftermarket Tremec 3550, which morphed with further improvements into the TKO 500, which, with more splines on the input shaft, closer spaced ratios, and better metallurgy in the shafts and clusters became the mighty TKO 600.

So the next time they ask, "What can Brown do for you?" Answer, "Thanks, you already did."

I see from Tremec's online .pdf brochure on their aftermarket boxes that I'm a little behind the times (no surprise) on my info:
http://www.tremec.com/anexos/File/TR...erformance.pdf

The weights I gave by memory earlier were a few pounds off; there's even a bit broader weight range than I remembered. According to Tremec, dry weights are as follows: T-5 - 75 lb; TKO - 99 lb; T-56 - 135 lb.

Also, on the fourth page of that .pdf, they list a newer, "T-56 Magnum" box that is good for 700 ft./lb. Now we have to add a blower just to keep up with our transmissions...darn.

I also noticed they offer that T-56 Magnum with optional ratios of 2.66, 1.78, 1.30, 1.00, .80, and .63. If you want 6 speeds, from a gear ratio suitability standpoint, that, in my opinion, is just about perfect. If your budget is as large as your ambitions, anyway.

The close ratios of that box would be fun to navigate, regardless of the fact that the torque/weight ratio of the Miata makes them completely unnecessary. So what? A V8 Miata is unnecessary; doesn't mean I don't want one.

For those already in possession of a T-56, I noticed they offer optional ratio 5th and 6th gear sets as pairs. One combo available is the .80 5th and .63 sixth. So, with the help of a good tranny shop you could potentially "roll your own" box with ideal ratios.