manual tranzilla

[Nemesis Destiny]

I just had an idea for a manual transmission from hell. The purpose of this would be to improve performance over the 4-spd auto while providing better efficiency for highway cruising.


1) Install a 5 speed gearset into a 6 speed housing.

2) Have someone custom fab a taller 6th gear. Insert where the 6th gear would normally go.

3) Install tranzilla into SVX and enjoy both faster acceleration AND improved fuel economy on the highway. 2000rpm @ 75MPH?

Am I full of crap or is this actually do-able?

While anything is possible, with enough money. It probably wouldnt be practical in an older car to invest in such a project. But I drive a '92. There are many people out there with a lotta love for the SVX. Machining a tranny would be pricey though. A killer Idea though.

[Nemesis Destiny]

How much machining would really be involved? I know next to nothing about it, so I may ask some silly questions or make some retarded assumptions. I am in fact, oversimplifying, I'm sure...

Would the gears from the 5 speed not just drop right into the WRX 6 speed casing (we know this part fits)? Then all you have to do is have one gear made, no?

[SVXer95]

Why not just use the 6 speed. It is a pretty close ratio tranny. The 6th gear is for highway cruising...

[Nemesis Destiny]

The reason is this:

I have examined the gear ratios that the close ratio 6-speed uses, and while I'm sure it offers impressive acceleration, I have noticed that its 6th gear ratio is close to or identical to the 5th gear ratio in the 5 speed. Why not the best of both worlds? Decent acceleration of the 5 speed, plus the better highway mileage that a 6th gear can provide.

The high gear on the manual trannies offers higher rpms (by several hundred rpm) on the highway than the automatic, even with the .738 5th gear and the 3.90 final drive. It would be even worse with the 4.44s or 4.11s and/or the stock 5 speed .780 top gear.

If smallcar can swap into the 5 speed a .738 5th, why couldn't they, or anyone else, swap, say, a custom .550 gear into the 6-speed housing? That would provide wicked highway cruising and possibly ~35mpg.

I know if you throw enough money at it, you can do just about anything, but by 'do-able' I mean, could this be done realistically with off-the shelf parts or existing, proven mods? The only thing that would need to be custom-fabricated would be the snazzy new 6th "cruising" gear.

[svxsubaru1]

I dont know if the 5spd gers would work in the 6spd. Also what is the final drive in the 6spd, compared to the 5spd. I dont know if i would want to put stock 5spd parts into a 6spd trannie, i would think you would want to go aftermarket for the 5spd gears, or at least put some STI ones in. So you wouldent have to baby the trannie around as much.

[Nemesis Destiny]

Well there you go; if Subaru makes STi gears, you're all set... as long as they make the size(s) that would be required. I don't imagine that a performance line of parts like STi would produce gears for highway cruising, but you never know.

Realizing the cost of almost completely customizing the gears in a MT, you wouldn't save much dinero. It would take a fair amount of time and money. It would definitely take you awhile to just break even on the cost, in terms of the money you would then "save" from the taller gears versus what you spent on the gears themselves.

[Nemesis Destiny]

Yeah, I realise that. If I was all about saving money, I would never have bought this car, maybe a civic instead.

No, for me, this is all about the efficiency. If I have to replace my blown automatic at some point (soon) anyway, why not do it in a way that suits me?

I dunno, I was just throwing this idea out there to see if anyone had thought of this before, or how practical it really was. I know a 6-spd STi transmission is about $6k CAD, plus the other required parts to mount it in an SVX, plus the labour, etc.

[SVXer95]

If I had my druthers (and the cash), I would do what Mychailo did and go with the STi type Ra gearset for the five speed. You have incredible strong and closely matched gearing. Put this in the standard 5 speed box and toss in a limited slip front diff, then worry about a cruising gear if your truly want it.

I think he is selling Ra gearsets too...

[NomadTW]

why not just get an sti 6mt and put a taller 6th gear... that would certainly be less expensive than trying to get just the housing, and put the gears in it and then fab on a 6th gear.

and i doubt that the 5mt gears would go in

the 5 mt is the 4mt with an extra gear.... the 5th gear is not in the same part of the transmission as the other 4, if you've ever seen one apart it looks like it was just added to the casting... because it was.

the sti6 is not built off of the 4mt that has been around for 30 years, so i doubt that the gearset would just drop in

[Nemesis Destiny]

That's not a bad idea, though the change in ratio from the 6MT's 5th gear to the proposed new 6th would be VERY abrupt. Particularly since the 6MT 5th is a shorter gear than the 5th in the 5MT, and I wanted to go taller than that.

Still, I'm sure they make many different gearsets for many different purposes. I just have to find the right ones, I guess.

[NomadTW]

then what you need is a JDM STi 6mt, i believe that it's ratios are not as short as the usdm STi 6mt

[UberRoo]

The ratios between the highest gears is usually very close. Whichever transmission you use, just get a custom gear. These folks would probably make one for you, and I'm sure there are a dozen other shops that would.

The savings are not there, but I love cruising at 70 with the engine barely above idle.

[Nemesis Destiny]

Thanks for the link.

Like I said, if I were looking for savings, I would have bought a different car!!!

But, yeah, that's it exactly... highway cruising with low, low revs. Kinda like the air-cooled Chrysler-tank-engine-powered V16 hot rod that Jay Leno built... Customised Allison 6-speed automatic that can cruise at 80 MPH @ 900 RPM! When you have 1,500 pound-feet of torque on tap you can do that....