Transmission Ideas?

[Thorne]

Do we have any ideas of other gear boxes that might suite this build well? I'm really hoping to reach supercar level performance as I've got a already nicely built subaru. (400awhp turned up). I've broken quite a few 5 speeds including STi-RA gears. I will say my RA-box help up through YEARS of drag racing and rally racing and me beating the tar out of the box.

I'm also currently setup as a RWD subaru and i'm pretty sure I broke a stock wrx rear and I know i've already chewed up a front diff on 16psi.

[jimgood]

Here we go again...

Do you really think you're going to have as much stress on the transmission when you remove 1200 lbs of mass?

[shinn497]

Actually I am curious what to do beyond 300Whp.MY research shows this is the limit of the WRX tranny. The Sti can handle more but I don't know if that will fit. Early reports said no but we will have to wait.

The consensus before was that if you are really worried about the tranny, and want to keep the WRX 5 speed, buy a set of PPG gears.

[Xusia]

Maybe Mendeola will make an aftermarket transaxle for all the HP nuts out there -- Like they did for the GTM. If they do, it will likely be a year or two (based on how long it took to produce for the GTM) before it materializes. You could always build it with ~300hp when available, and go crazy later!

[autostang]

I am curious about this too, not so much for the power issue, but for the feel of the transmission. My least favorite part about my WRX is how it feels to shift. In comparison to many cars out there it seems to me that it is very clunky feeling. Its by no means a deal breaker, but it would be great if there was something that felt a bit higher end.

[Thorne]

I am curious about this too, not so much for the power issue, but for the feel of the transmission. My least favorite part about my WRX is how it feels to shift. In comparison to many cars out there it seems to me that it is very clunky feeling. Its by no means a deal breaker, but it would be great if there was something that felt a bit higher end.

If you do all the proper upgrades to the car the car will shift quite nicely. I ran STI-RA gears for multiple years and they held up pretty good. I'm more concerned about the diff than the gears.

02early03 box : Max power I would safely run stock weight 280awhp (I snapped second @ 280)
04+ 5 speed 300-350awhp driven nicely
STi-RA V6 350-375awhp
STI 6speed 500+


I think the lower weight will keep the gears alive assuming you don't have a 02 gear box but the diff I'm just not sure of. Plus the WRX front diff is open.

[Oppenheimer]

You are going to build a mid-engined supercar, to go drag racing?

Won't the STi gearbox work for you? I know others have mentioned about how STi box not ideal for this car, the gearing, it might be too big to stick out the back, etc. Not cost effective, overkill, etc. But all those downsides seem to be targeted for street or road race use. For drag racing, who cares if you have to swap gear ratios, hack the body (or even some of the sub-frame if it came to that) to get it to fit. Is even the STi box not string enough for your needs?

[StatGSR]

I see no reason why a set of PPGs and an aftermarket diff in a wrx 5spd case would have any issues with any of your goals..... or just about anybody's goals for that matter...

stop worrying people, there are plenty of options out there....

[riptide motorsport]

oppenhiemers got a point!

[3000gttom]

lol at listing peak hp as a limit for a tranny, anyone who knows what they are talking about understands its all about the torque, i dont feel like doing a bunch of fbd's so lets just look at this in the simplest way possible

because f=ma

you can start by multiplying the max torque it handles on the wrx by (1220/818)

another factor is air resistance, and assuming the 818 has a lower coefficient of drag you can have more torque at higher speeds too,

also 2wd has less traction than awd so half of the abuse that the tranny would get from awd launching is taken away too

ill be very suprised if these cars have tranny issues

[Evan78]

What are the issues to be considered when selecting a transmission? I don't know much, but here's the items that come to my mind:

• Axle alignment (fore/aft)
• Transmission length (too long in rear?)
• Axle splines (easy to solve with custom axles, right?)
• Bolting up to engine (adapter plate should handle most situations, shouldn't it?)
• Chassis mounting points
• Clutch actuation
• Shifter

How would the Porsche G50 fit? That's the standard solution for the GTM, right? How strong is it?

[Niburu]

blowing the budget guys
which is half the reason why this car will be a success

[Evan78]

Who's budget? Just because FFR has a stated goal for what is possible doesn't mean everyone is going to build to that budget.

[Oppenheimer]

Who's budget? Just because FFR has a stated goal for what is possible doesn't mean everyone is going to build to that budget.

I would think the GTM would be a better fit for those with big budget aspirations.

Yes, many 818's will go beyond the base FFR budget, but there is no escaping the fact that the point of the 818 is less cost. The most expensive 818 builds will hardly reach the cheapest GTM builds.

[Evan78]

Doesn't the GTM weigh around 2500 lbs? And the kit is $20k?

There are two reasons to build an 818 right there. Just because you can afford a GTM and a big dollar build, doesn't mean it's the best project for a given individual.

I thought this thread is about transmission options. Is it necessary to go over everyone's goals, budgets, etc in order to tell others that the 818 is not the "right" car for them? It is a kit car after all...

[BrandonDrums]

lol at listing peak hp as a limit for a tranny, anyone who knows what they are talking about understands its all about the torque, i dont feel like doing a bunch of fbd's so lets just look at this in the simplest way possible

because f=ma

you can start by multiplying the max torque it handles on the wrx by (1220/818)

another factor is air resistance, and assuming the 818 has a lower coefficient of drag you can have more torque at higher speeds too,

also 2wd has less traction than awd so half of the abuse that the tranny would get from awd launching is taken away too

ill be very suprised if these cars have tranny issues

I agree except I think it would be LESS torque experienced on the gears at high speeds. Less wind resistance means less force of drag working against the engine and transmission to sustain or gain speed.

My argument otherwise is exactly as yours and I imagine it would be about the same cost and far more ideal to source an aftermarket transaxle vs trying to convert an STI transmission, modifying the chassis and body to make it fit only to want to swap the final gear to make the gear ratios taller so you don't have to shift more frequently than a mosquito to hit speed.

I've been one of the biggest guys to speak AGAINST the STI tranny for the 818. To be clear, my argument is about the overall gear ratios rather than the gear ratio spacing of those ratios. You'll want tightly matched gear ratios to keep it in the more narrow powerband that comes from a turbocharged engine. The STI tranny is great, don't get me wrong. It's just a monster of an AWD transmission with weight, size and technology as a result of being for an AWD application.

I just think for the worth of an STI tranny and then the costs associated with making it work in this application to end up cruising down the highway in top gear pulling 3200 rpm is not going to be conducive to a well balanced driving experience. Honestly spend the money to upgrade a 5mt if you're worried about it or see about getting a full aftermarket box which will be stronger and more compact than even an STI trans.

[PhyrraM]

A few facts, without getting into the variables of turbo spool....

1) The engine makes the same amount to torque regardless of what car it is in.
2) The gear ratios are the same regardless of installation.

1 + 2 = 3

3) The torque applied to the gearset will be the same regardless of WRX or 818 installation.

Consider the following:

The amount of time that the torque is applied to the gearset is less because the 818 will accelerate to shiftpoint much faster than a WRX.

The wheels may spin reducung the peak torque on the gearset in lower gears more in the 818 than the AWD WRX.

100% of the vehicles torque will be sent through a shaft small enough to fit inside a tradional layshaft cluster.


Pick your reality from somewhere in this mess. I'll wait to see a few built 818s before making transmission judgements.

[BrandonDrums]

A few facts, without getting into the variables of turbo spool....

1) The engine makes the same amount to torque regardless of what car it is in.
2) The gear ratios are the same regardless of installation.

1 + 2 = 3

3) The torque applied to the gearset will be the same regardless of WRX or 818 installation.

Consider the following:

The amount of time that the torque is applied to the gearset is less because the 818 will accelerate to shiftpoint much faster than a WRX.

The wheels may spin reducung the peak torque on the gearset in lower gears more in the 818 than the AWD WRX.

100% of the vehicles torque will be sent through a shaft small enough to fit inside a tradional layshaft cluster.


Pick your reality from somewhere in this mess. I'll wait to see a few built 818s before making transmission judgements.

If that were true, there wouldn't be any guidelines for not using overdrive when towing in a pickup truck. More mass means more stress on the drivetrain and everything else. Reducing mass reduces stress and load on everything.

A good way to picture it mentally, is Imagine the 818 somehow weighed just 100 lbs. What do you think would happen then when all the power ran through the transmission? Now imagine the same engine and transmission installed on a fully loaded semi with the brakes on. WOT but the clutch slips before the wheels turn.

When a clutch goes bad, it starts slipping in higher gears vs lower gears, if you hooked the car up to a big honking U-haul trailer and tried to go up a hill, you'd expect the clutch to start slipping in a lower gear right? Is there suddenly more torque being applied from the engine than before? Yes actually, here's why.

When I was in Highschool Physics we did a basic experiment that applies to this particular debate. We hung up a piece of paper by a string from the ceiling and punched it with a piezo force meter or whatever taped to our fist to measure the force exerted on the piece of paper. Then we went down to the gym and carefully tried to punch with the same amount of force on one of those big punching bags and had the computer record that result to compare.

The force on the piece of paper barely registered despite all of our strength while the force recorded on the punching bag was magnitudes larger despite all of our concentration to punch with the same effort as we did on the paper. Newtons third law describes this phenomenon, every action has an equal and opposite reaction. The piece of paper was incapable of exerting the same amount of instantaneous force on our fist as the punching bag, it had so little inertia due to its low mass that it would accelerate faster than our fist was capable of traveling so the force was never fully exerted on the paper. The punching bag however stayed put long enough for us to exert as much force as we could muster with our fists.

Now, F=MA (force = mass times distance) as laid out in Newton's 2nd law might seem on the surface to negate the above scenario. However our arms, just as a engines are incapable of producing a force over an infinite distance, or change speed at an infinite rate. Therefore, the A in this equation can't adjust infinitely given the limitations of the input mechanism and F eventually decreases when mass decreases past a certain threshold. The arm is limited because it's connected to our body and we can't run that fast, the engine because of the mechanical limitations of handling rotational forces and the limited rate in which fuel burns within the combustion chamber. In order to get the engine to exert it's maximum torque, there must be something capable of exerting the same amount of force upon it. Torque is a force, Horsepower is simply torque over distance and time or force over distance and time. When the object the engine is moving is very lightweight, then you must use gears to decrease it's mechanical advantage so it can apply it's full torque on the rotational system through increasing the linear distance in which the object moves per rotation of the engine.

In a multi-component mechanical system such as a subaru drivetrain, there are actually hundreds of F=MA equations taking place. Each piston, rod, crank, valve, cam, flywheel, gear, diff etc has it's own mass and it's own mechanical dependency to another system. All of those dependencies aggregate to a resulting peak "A" or acceleration of the system. Absent of any resistant force aside from the mechanical system itself, the inertia of all the components and the limited speed in which gasoline can oxidize prevents the engine from immediately revving from idle to redline when you step on the gas pedal and also reduces the torque that can be applied at high RPM's. A good race engine like a Formula 1 engine makes very little torque compared to it's horsepower but can continue to apply that torque even at extremely high RPM's and can rapidly accelerate the rotational velocity of the engine because of more optimal mechanical dependencies.

So in an F1 or Race bike engine, the "A" has a much higher limit so the engine can apply much greater force on that piece of paper because it can actually keep up with it, meanwhile a big rig turbodiesel engine with the same peak horsepower as the F1 car can't apply the same force on a piece of paper given the same gear ratios as the F1 car. The gear ratios would have to increase tremendously which would reduce the torque applied at the wheels but dramatically increase the distance in which that torque can be applied. However, that also results in much higher stress on the gears. A race engine opts for revs vs torque because tremendous weight is saved in mechanical components due to the lower instantaneous torque experienced in the powertrain to achieve the same result.

Thusly, reducing the mass of a vehicle reduces the stress on the transmission given the mechanical drive-train and gear ratios remain constant. To achieve the same amount of instantaneous torque experienced by the mechanical components in a drivetrain when the mass is reduced, the gear ratios would have to increase proportionally with the decrease in vehicle weight.

Pick your reality indeed.

[RossLH]

1) The engine makes the same amount to torque regardless of what car it is in.
2) The gear ratios are the same regardless of installation.

1 + 2 = 3

3) The torque applied to the gearset will be the same regardless of WRX or 818 installation.

True, true, and also true. What you're not taking into account is the inertia on the output side and how that affects the impulse of shifting. Obviously a 3200lb car is more reluctant to change its velocity than an 1800lb car. Assuming both have identical clutch and flywheel setups, shifting is the same between the two, and there is no wheel spin, the 3200lb car (WRX) will have a MUCH larger impulse than that of the 1800lb car (818). Simply put, the 818 will be a whole lot easier on the WRX 5-speed than the WRX is.

Regardless of all that, I'll be calling up Andrewtech and having them build me a PPG dogbox. Necessary? Nope. Awesome? Entirely. Why? Because its my toy and I'll build it in excess if I want. And to reiterate, dogboxes are awesome.

[shinn497]

Brandom Drums you are making several physics mistakes, I don't have time to correct them, but I will when I can.

[Niburu]

I thought this thread is about transmission options. Is it necessary to go over everyone's goals, budgets, etc in order to tell others that the 818 is not the "right" car for them? It is a kit car after all...

Do you really wanna cut and reweld some of the main chassis components?
This is an engineered chassis, when you start hacking into it you're changing how it's going to perform, particularly in a wreck.

[Oppenheimer]

1) The engine makes the same amount to torque regardless of what car it is in.

I think Brandon did a thorough job of explaining why this is inaccurate. In the interest of exerting meaningless physical punishment against deceased equine I'll add my 2% of the smallest non-metallic US currency:

If you rev an engine in neutral, does it still make all its torque? When you run a car on a dyno, does it need to apply a load to perform the test?

Pedal a bike in a given gear at a given rpm with the back wheel off the ground. Now try the same thing out on the road. Torque can only be generated in response to load.

[bromikl]

Good luck keeping traction with two drive wheels at 300 Hp. I doubt the transmission will ever experience the max torque the motor capable of producing. If you're drag racing, you already know you need a PPG gearset.

[Evan78]

Do you really wanna cut and reweld some of the main chassis components?
This is an engineered chassis, when you start hacking into it you're changing how it's going to perform, particularly in a wreck.

Chassis modification would not be desired, but if the benefits make it worthwhile, why not? Just because it was engineered for one transmission does not mean it can't be reengineered.

With that said, nobody mentioned that route. I don't think we have enough info on the chassis to know if/when that would be necessary.

[Niburu]

With that said, nobody mentioned that route. I don't think we have enough info on the chassis to know if/when that would be necessary.

that's one of the point I'm trying to get to
we don't know enough until FFR realeases the CAD files and/or tells us what'll fit
and what sort of specs they've designed to

[Evan78]

Lack of information hasn't stopped much speculation elsewhere, I'm not sure why this thread should be any different.

[BrandonDrums]

Brandom Drums you are making several physics mistakes, I don't have time to correct them, but I will when I can.

I might have but the principle is correct. Its been a long time since my Physics years so I might have not correctly explained the mathematics but the statement is true:

Reducing weight while keeping engine power and mechanical leverage constant reduces the stress on the drivetrain. If that weren't true then vehicles would not have a stated towing capacity period and Lotus would not be in business.

[skullandbones]

Maybe it would be helpful to start a new thread called "Transmission Ideas: Theoretical Approximations For Systems With Relations To Constant Mass Particle Physics But Excluding Special Relativity". At least, it would give you fair warning that the subject of "Transmission Ideas" might be broadly interpreted. This is meant light heartedly. So please take it that way. However, it does seem that often there are 818 threads that go on tangents and stay there instead of being brought back by someone in the discussion. In this discussion, there is really a great opportunity to discuss, for example, an existing gearbox that the 818 is engineered for with PPG gears (sorry haven't researched that yet). Another possibility is to look at boxes that might fit in the same area as the existing mechanicals. Are there adaptors or machinists that would be able to mate the transmission to the engine?

I don't think this is productive in general and it reflects on the forum by alienating many who would like to join the discussions or at least follow their progress for tidbits of information. IMO. WEK.

[PhyrraM]

Reducing weight while keeping engine power and mechanical leverage constant reduces the stress on the drivetrain.

The time is not constant. The reduced weight manifests itself as increased acceleration, not as reduced torque.

In any case, my actual point was to either be an early adopter and incur the expense (overbuild or break) or wait and see how many tranny actually pop. My secondary point is that Subaru never put more than about 130HP/140ish ft/pounds through a FWD/2wd version of this transmission, and that involves nothing to do with the actual gearset.

[RossLH]

In this discussion, there is really a great opportunity to discuss, for example, an existing gearbox that the 818 is engineered for with PPG gears (sorry haven't researched that yet).

PPG makes several gearsets that are designed specifically for the WRX 5-speed box. I plan on going all out with their straight cut dogbox.

[skullandbones]

Now that I know what they are, it sounds like the PPG solution may be "bullet proof" but it may be pretty radical for street applications but probably OK for track. There are disclaimers about how noisy it is so maybe it's like that sound you here when a dragster lets off at the end of the 1000 ft: wa wa wa wa wa wa!!! If you are able to insulate the cockpit maybe it wouldn't resonate too much. But I have had transmissions that sounded that bad and it drove me crazy.

Another thing about the transmission (transaxle) discussion is that the WRX is designed as a all wheel drive with the mechanicals being changed to rear wheel only from front drive. I see this as really a big deal from a design and engineering perspective. No matter that it works, there is no data to support the performance as a rear drive unit. From a known entity with all sorts of data to support it's performance, when you change it, all the data goes out the window. So nobody really knows how well the transmission will survive under the new "untested" conditions. I think the FFR prototype testing (mechanicals) will be as interesting as the body reveal. IMO, WEK.

[RossLH]

The straight cut gearboxes are very loud. The helical boxes really dont make much noise at all. I used to have a semi-helical gearset (MFactory short ratio) that made a rather significant whine, and to this day I miss it. I think its a great noise.

[Xusia]

Guys! Holy crap. Seriously.

Both engine torque and vehicle weight affect the transmission. A simple explanation:

In simplest terms, what causes parts to fail is stress (force). As in, when the forces applied to the part exceed that part's tolerance. Engine torque is NOT the only force acting on the transmission. In order to get the car moving (or make it move faster than it already is - i.e. accelerate), the engine must overcome any resistance to movement. The amount of resistance is DIRECTLY related to vehicle weight.

Now, a simple example: Consider how much torque & HP a transmission handle when it's not connected to anything (i.e. no axles, wheels, tires, nothing). Next consider how long you think the transmission in a bone stock Imprezza will last if towed a 20,000 lbs trailer all the time. If weight didn't matter, this shouldn't be a problem because the engine produces far less torque than the transmission is capable of handling. Common sense (or as I like to call it these days, UNCOMMON sense!) tells you this scenario would be a huge problem (if it were even possible).

The bottom line is that vehicle weight increases inertial resistance and is therefore a "force" that acts on the transmission (just like engine torque), and should to be taken into consideration. The 818 will weigh less than the donor vehicle, so if 300 hp is limit of the transmission in a WRX, it should be higher in the 818. By how much I have NO IDEA. I'll leave that the mathematicians!

[Evan78]

I'm sure everyone will agree that all else being equal, faster acceleration results in greater stress on a transmission, right?

I feel similar to PhyrraM - the same engine will result in similar transmission stress regardless of if the car is 2000 or 3000 lbs. The 2000 lb car will see the peak stress level for a shorter amount of time. The difference as I see it, is that shock loads will be reduced in the lighter weight vehicle.

[shinn497]

I'm sure everyone will agree that all else being equal, faster acceleration results in greater stress on a transmission, right?

I feel similar to PhyrraM - the same engine will result in similar transmission stress regardless of if the car is 2000 or 3000 lbs. The 2000 lb car will see the peak stress level for a shorter amount of time. The difference as I see it, is that shock loads will be reduced in the lighter weight vehicle.

Ummm you have a contradiction. First you say that greater accel = greater stress.

Then you say same engine = same stress regardless of weight

Then lighter vehicle = greater accel = less time = less stress

Your conclusion should be the same as exusia's.

Your first statement is wrong. Greater force causes failure. Acceleration is dependant on mass. If we lessen the mass, the acceleration increased, but the force remains the same.

out of all these arguments xusia's is the most correct.

[shinn497]

I want to add something that is confusing everyone.

Consider newton's 3rd law. Every action has an equal but opposite reaction.

If an engine acts on a gearbox they both feel the same force period. As long as the engine's power is constant, this will not change regardless of the weight of the car.

What the weight of the car will change is the time this torque is applied. Therein faster accel times = less load on the tranny.

The question is not if the tranny will experience less stress. It will. The question is if the tranny will break . What I'm (and I think most of us ) can not be certain about is how much force is neccessary and how long it will take. This is why impulse is important.(Impulse = force*time). It could be that tranny's are more resistant to impulse spikes...which would be good. Maybe not...

I think several people have said this in different ways and we're getting lost in the sauce. As someone that teaches physics for a living, this is not surprising.

[Oppenheimer]

Another thing about the transmission (transaxle) discussion is that the WRX is designed as a all wheel drive with the mechanicals being changed to rear wheel only from front drive. I see this as really a big deal from a design and engineering perspective. No matter that it works, there is no data to support the performance as a rear drive unit.

I believe there actually is already data on this. FFR is not inventing the idea of repurposing the AWD transaxle for 2WD. There are kits that convert the Subie transaxle to 2WD mode, and its expected FFR will use one of these commercailly available units in the kit (or fab their own, etc.) These can be used to covnert to FWD, or for creating a mid engine RWD car. FFR are not the first ones to do this with the Subie drivetrain. They are pioneering plenty of things with the 818, but this isn't one of them.

[skullandbones]

I stand corrected. Do you have any "vendors" that I could search that? I would like to check it out. In the meantime, I will see if I can find something. Thanks for the heads up. WEK.

[skullandbones]

Hey, I found one right away: "Bremar". I'll have to do some more reading. Thanks again, Oppenheimer. WEK.

[BrandonDrums]

Hey, I found one right away: "Bremar". I'll have to do some more reading. Thanks again, Oppenheimer. WEK.

Yeah, here's that kit http://www.bremarauto.com/products/s...onversion-kit/

lockingsleeve-259x300.jpg
blankingplate.jpg

I think there are a couple other vendors as well. However, I'm close to expecting that FFR will provide a piece as part of this kit weather it's 3rd party or if they just machine the part somehow in-house. That part will be needed to get the kit on the road and it won't be sold separately since FFR's motto is they give you everything you need with the kit.

It's just a sleeve and a plate, still some specific splines in there to work out but something that simple can be made for way cheap given the right vendor or tools.