View Full Version : Change SVO T5 5th to .63 from .78

04-29-2011, 12:57 PM
First so you know I did searched the driveline section and did not see this topic. Has anybody ever done a 5th gear swap to the SVO T5? Since this gear is mostly used for highway speed anyway this could help fuel econ. With a 3.73 final it should put engine between 1900 - 2400 for 55 - 70 speeds down from 2200 - 2800 for the .78 gear. If that keeps boost down it should be running with a lower bsfc increasing mpg. 1900 is just about a perfect rpm for boost building when you want to pass. It doesn't take a lot of HP to cruse at those speeds case in point the Pinto with a 2.0 at about 88 HP max and thats with AC! If the .68 hasn't been documented I will some day when the right doner parts come to me on the cheap. Unless it has been done and it is a disaster. Better yet some TQ curves vs BSFC and the components used (turbo, injectors cam...) would be perfect.

04-29-2011, 01:00 PM
I think it's a good idea, but will only benefit you if you drive nothing but highway and mostly flat. I have the stock gear ratio in mine and highway I've gotten 30mpg..others have gotten the same or better.

04-29-2011, 01:18 PM
you CAN do that... but there's a lot involved in swapping high-gear in a trans...
Most opt for the simpler solution of swapping the rear end gearset.

In the T5, the main shaft, and counter shaft have to come out, and all gears and bearings have to be removed to change 5th gear.

The other option is to look at one of the transmissions that already has the taller gear in it. There's a list of t5's in several places, I know there's one in the members area, that list ratios for each transmission, and what they were available in.

04-29-2011, 01:23 PM
I like the idea, I have been researching 6 speeds and thats going to cost $3200 clutch to drive shaft. However, I decided that since I only drive the SVO 6000 miles a year, the savings would take to long to recover. @ 5$ per gallon (its going to happen!) and getting 20 mpg combined driving cycle (worst case) I might spend about $1500/year on fuel average. If I got 25 mpg combined driving cycle then I would only spend $1155/year.
So I would save $345 per year or $28.75 per month.
Supposedly If I spent $3200 on an upgrade it would take 9 years and 3 months in fuel savings to recover the cost of the transmission upgrade.
IHO thats not really a good upgrade for savings... although, If the car had a higher top end... that could be fun.

Anyway, if it only cost $350 to do the ratio change to 5th gear, including labor, then I could recover that cost in 1 year. Now, theres a thought.

I have a pdf of the borg-warner WC t5 rebuild manual that I can send the enterprising individual willing to try the 5th gear swap.

04-29-2011, 01:44 PM
wow, when you use that much logic, I don't see how you manage to do any upgrades :D

04-29-2011, 02:27 PM
My first wife made me, MADE ME, sell my 1979 Mustang Scorpion Turbo 4. So rare I can't find any info on it except that maybe it was a GT with a dealer stripe and graphics package on it. BTW, I named my current SVO "Dorothy" after her, cause it is fun to drive the crap out of it, but it might be all messed up later. Ha ha.
Although the current wife is happy to let me do whatever I want, I still play it safe... just so I don't break the bank trying to do everything I want to do.
I am actually thinking of finding a convertible mustang to put the mother of all turbo 2.3L engines and a 6 speed into.

04-29-2011, 02:31 PM
I spoke with Bob Hanlon about this very thing. He informed me that the 0.63 won't work in our T5 without the modification as Eric mentioned. The lowest gear that you can just slip in to our T5 is a 0.73.

Switching to a 3.55 rear end seems a simpler option and would make 1st & 2nd gears more usable.

04-29-2011, 06:55 PM
So I looked at all the WC T-5 available for this set up and believe it or not a 3.27 and an 88+ 2.3 NA Mustang T-5 gives about the same as the 3.73 and the SVO T-5 in the first 3 gears, since all trans are 1:1 in 4th we are only talking about how to not effect the first 3 gears and make the biggest impact on the 5th. If you can't maintain boost going into 4th you already scattered the engine. If most of your miles are spent on the street and not the strip it gives you the same seat of the pants with the economy of a NA 2.3 just don't start from a dead start without Nitrous. Swap Gears and not have to rip into the trans. If you want to go crazy take out the .79 and drop in the .68 5th gear. I did some excel sheets (up loaded as txt) that used the Gear calc and the trans info to give the details on my madness. My goal is to have a daily driver that is 400 HP and 35 mpg. Although I do like the new Ford Eco Boost there is nothing like middle age school. Now all I need is a full throttle pull to see my TQ curve on my new engine set up to see what really will get it done.

04-29-2011, 07:00 PM
The thing you need to consider is when you drop the revs in 5(or 6th) that you are out of the sweet spot and end up using a lot more throttle. You are constantly giving it the gas to get it to move, not a lot of fuel savings are going to happen when you do that.

Alex L
04-29-2011, 10:24 PM
My goal is to have a daily driver that is 400 HP and 35 mpg.

fast, efficient, reliable. pick 2. 30mpg is fairly good for a 2.3t at stock power levels (http://forum.turboford.org/ubb/ultimatebb.php?ubb=get_topic;f=3;t=030327;p=1). im not going to go into power goals because i cant put up, so ill shut up about em.

i run that '88 2.3 na t5 in front of 3.73s; its pretty fun.

04-29-2011, 11:12 PM
I am commuting almost 100 miles a day, and of that about 60 miles is at 70 mph or better. My car sits right at 3k rpm staying with the flow of traffic. First gear is pretty close to pointless I have noticed. Some taller gearing seems like a good plan. I am guessing it would help autocrossing also, I bet on longer courses you run out of gearing pretty quickly. Jeff

04-30-2011, 11:58 AM
get ya'self an 86 gearbox and a set of 3.45's or 3.27's and call it good.

ohh........cruise control helps:):):)

05-01-2011, 10:51 AM
you CAN do that... but there's a lot involved in swapping high-gear in a trans...

In the T5, the main shaft, and counter shaft have to come out, and all gears and bearings have to be removed to change 5th gear.

You can't intermix the reverse arm or prawl in these boxes - you have to use same same through out.

And if you brake it is is NLA - so know what bolts are removed to access !

P.S. As Eric said "change the rear gear" and limit the boost !

05-02-2011, 10:46 AM
I put an 89 Mustang 2.3 na T-5 on my 86 XR7 2.3T as well. It was ridiculously fast and got 28mpg @ 70, 30mpg @ 60, and 32mpg @ 55mph. It had 3.45 gears. ALSO had a 3 inch pipe from the turbo and duals to the bumper, no cats, no mufflers. I kept the boost down around 12psi on the highway. The XR7 also had a rather amazing cruise control which helped. This car made 330HP, so you can have you cake and eat it too. The na T-5 took an amazing amount of abuse without any complaints! Everyone tells me that 1000 Christopher miles is like 10,000 anybody else miles... so I was very impressed with the na T-5 durability.