Started measuring a bit on my car and discovered I have a 2.93LSD. Plan on running a TII engine/tranny. Anyone foresee issues with running such tall gears? 28.5% taller gears...lol...

 

thats really tall... but it depends on the weight of the car, and the tires.... light car with short tires will be fine, heavy car with tall tires might suck

 

3400lbs curb, now...225/45 17's. With a 13b it'll be closer to 3200lbs.

Will be running RTek chip, 720 secondaries, FMIC, SAFC, full exhaust and 10~11psi.

..and the most obnoxiously loud BOV I can find.

 

how do you figure you have a 2.93 rear end? Maybe a 3.93 that I think was in the auto cars

 

Just like not every RX has a rotary, not every rotary has an RX.

 

you want to spin your motor at around 1500rpm when going 80 or something?

and why would you need a safc and a rtek?

 

It's not a "want", but it doesn't bother me. This is more about the concern as to whether or not it could cause mechanical problems.

And, technically, 80mph would be more along the lines of 2500rpm.

The car it's going in has a 2.93 lsd rear and the car gets several of it's major functions from this rear end, so swapping out isn't cheaply or easily done.

I want the RTek for obvious reasons...I'm told that you still need a piggyback for fine tuning.

 

if you have an s4 t2 engine then you only need the rtek 2.1 for tuning. If you have the s5 t2 engine you will need the rtek and some sort of piggyback for tuning.

Either way though with the stock transmissions the 2.93 rear end gear is going to be a pain. The stock rear ends were either 4.3, 4.1, or 3.909. In my t2 going below 2k at speed is bog city once you get past 2nd gear.

 

Looking for an S5 TII specifically, but it really depends on what the importer sends me. I haven't even really looked into the 2.1 so I'm not sure of what all it offers.

It doesn't bother me to cruise around in 1st and 2nd...I love winding the gears out. This will just lengthen the experience. I'm hoping to be putting down 350whp by the end of the project so I don't think I'm going to have too many issues with power delivery.

Solareon...do you mind asking what you're putting down with your mods?

 

Just read up on the 2.1...sounds awesome except the $450 tag. I would have have to sacrafice a few other upgrades in order to get it.

 

I haven't dragged it to the dyno yet (lack of money/time) and it's not been really tuned in a whole lot with the 2.1. I'd estimate and say I am putting like prolly 260hp atm but my setup should take me to 300+. It's a heck of alot quicker than the gxl and I am starting to have some traction problems with the 205s I have on the rear.

 

With 350whp I think you'll be fine. When you consider stock TII has 200 chp and 3.9 you're more than compensating for the 28% difference. Stock 96 328 was 190 chp right? I think you'll have a car that will far out perform any other 328. I say do it!

 

Well the first setup will actually be a bit milder than 350whp. Initially I'll be running a large FMIC, 720cc secondaries, intake, full exhaust, and RTek chip, and about 11psi...which is alledgedly in the 250whp area.

I may splurge a bit and go with 720's all around, get a slightly larger turbocharger, and run a bit more boost, but I don't know yet...it's going to depend on what my budget looks like when it comes to buying the goods.

I don't think I'll really have issues powerwise...horsepower is horsepower regardless of the gearing. Launch may be a bit suckier but top end will improve a bit. May actually improve my fuel mileage lol since I drive 250 miles a week in a straight, no-stops line. I was just concerned about the stress added from taller gears.

 

If you do decide you want to use the Rtek 2.1, remember it isn't available for S5 TII ECUs yet. I realize you're talking about a completely custom setup, but using an S4 ECU with an S4 engine is much easier than trying to make it work with an S5 engine.

I'm sure the 2.93 rear end will be fine once you get up to speed, but right off the line, I'd say you're either going to be dumping the clutch or slipping the hell out of it. Your first gear will become almost as tall as second gear is with the stock TII 4.1 rear end. And turbo or not, a rotary at low RPM doesn't have the torque to easily get moving at low throttle. It's not until the mid RPM range & under load that you get the broad wave of turbo torque. I guess it's something to consider if you plan on doing much street driving with the car.

 

It seems more likely that I'll come across an S4 setup than S5, but I have to wait and just see what comes.

The torque thing, though, is what's pulling me between the 13B and the 1jz. If I go 1jz, the engine just out of the box will be at or exceed my horsepower goals. I want to use the 13B because I just find the engine more interesting...plus the LOADS of room in the engine bay is appealing...but I'm afraid I might regret the power delivery with the rear end I'll be running.

If I go 1jz, though, I'll just have to pick up another FC in the near future

 

The extra load the rear end gears cause will just come back positively in the form of better low gear boost response. Too small a tyre, too high a rear end ratio, and you soon find it impossible to build more than 3psi in first gear.

 

This seems a bit contradictory...taller gears are better for boost, or bad for boost?

 

Taller gears will let you make more boost & build it faster because of the increased amount of load placed on the engine, but that doesn't change how the engine behaves prior to making any boost.

 

I understood the higher boost under load part...that's why autos can brake-boost...I just didn't quite get the "never build more than 3lbs" thing...unless that's to mean that, normally, a turbo car doesn't build much boost in first gear BECAUSE the load is so low. That makes more sense to me and is likely what was meant.

 

Yeah, that's right. My car for instance will make about 10 psi in 1st, 11 psi in 2nd & 12psi in 3rd-5th. Also, the taller the gear I'm in, the RPM that boost builds at will be slightly lower. In 5th gear, I can load it up and go into positive pressure around 2500 rpm.

 

Taller gears means worse acceleration and better freeway gas mileage. Shorter gears are the reverse. That's about it.

For performance purposes taller gearing is no different than driving a 3 or 4 speed transmission: you won't have to shift as much but 1st gear will be slower and it'll be harder to stay in the power band. As for the engine, just remember it doesn't like revving below 1800 rpm.

I don't think it'll cause any problems, but if you're focusing so much on performance and not economy then it seems like you're wasting a lot of that power you're shooting for... unless you only want to brag about dyno numbers. For example a 400 HP Corvette has only a slightly better 0-60 than a 300 HP Mustang. A big part of that is tall gearing. In fact, a lot of people install shorter than normal gearing for performance reasons. You might be able to find an aftermarket source that provides gearing to change the final drive ratio without making you use an entirely different differential.

 

I'm not focusing entirely on performance...trying to keep an all around package (performance, simplicity, economy, etc).

Automatic 325/328's had a 3.91...may be something I try to pick up later.

 

I cant remember who makes it, But there is an adaptor to bolt a T-5 to a 13b. the 6 cylinder T5 for an S10 has a gear set of
T-5 | TII
1st 4.03 | 3.48
2nd 2.37 | 2.00
3rd 1.49 | 1.37
4th 1.00 | 1.00
5th 0.86 | 0.76

you may run into problems if you are pushing a fair bit of power

 

If I adapt, I'll adapt it to the BMW tranny...and I've been contemplating how to make that work but I can see anything but flywheel and throw-out bearing issues lol.

 

Well, some people even prefer taller gears so they don't have to shift as much. Like on an auto-cross for example. If you don't mind the drawbacks and/or you want to save some gas money (assuming 5th gear is still above 1800 rpm on the freeway), then it could be a matter of preference. Weigh pros and cons, etc. In the end it's up to you.

... Unless someone else chimes in and knows a mechanical problem I didn't think of.