Technical Discussion - (the non body thread)

[SkiRideDrive]

Hi guys,

Thought it would be nice to have a thread discussing the part of the car that's more important to me, and perhaps many others, the technical and mechanical aspects of the 818. Hopefully we can avoid any talk of body styles here.

1. One thing I was thinking about was the compliance in all the suspension bushing components brought over from the donor to the 818. Anyone have any ideas on preferred aftermarket bushings/materials which would reduce compliance in these areas and enhance feedback at the wheel? I feel like with the low weight of the car and with the right tires it will certainly put up respectable performance statistics. I am just hoping to up the "fun factor" by reducing as much compliance in the suspension/steering system as possible.

2. The other thing that I was thinking about is the proper tire for the car. The car will be quite a bit lighter then most cars on the road and thus most existing tires will have stiffer construction then necessary. Does anyone know what tires might work best in this sort of situation? I was considering having two sets, one for autocross/track days (possibly hoosiers), and another that wears a bit better for day to day driving.

Also really hoping that even though Dave ruled out any body style updates, he still keeps us up to date on the project's progress mechanically.

Thanks

[Flamshackle]

Good idea! I think on a technical note that many will quickly need a good baffled and winged oil sump as cornering G's will most definately be higher than standard.
Subaru's track raced over here all have a good baffled sump setup.

[bugeye_fever]

Not sure on the oil sump, but for bushings check out White line, Subaru's own Group N parts, or Turninconcepts depending on how hard you want to go. I have parts from all 3 on my Subie, no complaints.

Not sure about tires either, seems like the purple crack is always the way to go for autoX. I know alot of guys with lighter cars like the Hankook RS3 in the street tire classes. I do know what wheel I'll use though, that's the OEM 04 sti wheel. 17x7.5 bbs, strong and light.

[PhyrraM]

The stock bushings will be 'stiffer' when faced with the much lower weight. So, I guessing that even OEM stuff will feel like poly does in a stock WRX.

Outside of that, Subaru does offer a stiffer rubber for most bushing. They call it "Group N" and they were developed to compete in a class of rally racing that requires stock parts.

There are also true Poly bushing available from 3rd party vendors.

[spaceywilly]

Personally I'm worried about the steering. The WRX has a very slow steering rack and a huge wheel. Doesn't really lend itself to a sporty go kart feel. An STI rack or maybe a different rack altogether and a smaller wheel will probably be common upgrades.

[apexanimal]

while i'll go whiteline on a few bushings (alk, steering, etc) i'll be getting as many energy poly bushings in there as possible... b/c they're far cheaper than other companies that produce them for subies, and i like them...

tire wise, i'm thinking of likely going with a 205, MAYBE a 225 if the need arises (perhaps larger in the rear if traction is needed), and will likely go with the dunlop star specs or the new pss'...

[scartaan]

For those already working on donor cars, a more extensive list of what is needed and not needed would be helpful. For instance, there was one comment about saving hinges, but not if they were hood, door (front or rear), trunk, etc. Wiring harness- if the entire harness is needed, you have to completely dismantle the donor car to remove all the harness. Gas tank-exactly what is needed, as there are 3 or 4 different units bolted to the tank. As this information becomes established during the development of the 818, it would be very helpful for us.
Also, Kudos to Dave and the team for their hard work so far. The videos of the go-kart were fantastic and answered a lot of my questions. Keep up the good work!

[Flamshackle]

Personally I'm worried about the steering. The WRX has a very slow steering rack and a huge wheel. Doesn't really lend itself to a sporty go kart feel. An STI rack or maybe a different rack altogether and a smaller wheel will probably be common upgrades.

This is a very good point! I will be looking at these wee beauties to solve this issue...

http://www.speedwaymotors.com/Small-Body-21-Steering-Quickener,2030.html

I think a smaller wheel is in order also but will have to balance non power assisted with speedy steering ratios first.

[SkiRideDrive]

Interesting find.


This is a very good point! I will be looking at these wee beauties to solve this issue...

http://www.speedwaymotors.com/Small-Body-21-Steering-Quickener,2030.html

I think a smaller wheel is in order also but will have to balance non power assisted with speedy steering ratios first.

Also thanks guys for the input on bushings and tires.

[Mechie3]

06 and 07 steering racks are the same as the STI rack (same for 05-07 STI, 04 STI was slightly different). 02-05WRX racks are a slower ratio and have a different mounting method. I wonder how FFR is going to accommodate that. Q-rack also makes a quick rack, though I'm not sure if it can be run in a non powered manner. Usually when it's installed on Subarus it requires a power steering cooler as well.

Whiteline makes some steering bushings for the rack too. Some models have a rubber damper in the column while others (generally STI) use a solid steel link.

Top of image is a 99 2.5RS rack, lower is an 05 STI rack. Note the driver side bushing/mounting flange.

http://i50.photobucket.com/albums/f325/Smitch260/DSCN0243.jpg

I too am interested in a more developed need/don't need list. My car is coming back from the shop on a tow truck tomorrow or Friday and I want to get started.

[shim2]

Fairly certain STI parts are going to have to be custom fitted. It was on their website that you'd need either a Impreza or WRX donor. No mention of STI.

[PhyrraM]

Fairly certain STI parts are going to have to be custom fitted. It was on their website that you'd need either a Impreza or WRX donor. No mention of STI.

Website specifically says "Not STI".

This is because of the transmission and the front knuckles/spindles.

MOST other STI parts will work as-is.

[Mechie3]

^^ Correct, the transmission won't fit and the knuckles have a different bolt pattern (5x114.3 vs the WRX 5x100) and a thicker hub where the strut normally bolts onto. If you read my post carefully though, you'd see the 06+WRX and the STI share the exact same steering rack.

[slopoke]

what about the brakes on the STI? Are they compatible?

[PhyrraM]

'04 STI front calipers and rotors are a bolt on to any Impreza front hub/spindle.

'05+ STI calipers are a bolt on to any Impreza front hub/spindle. They can be coupled with the above '04 STI rotors.

Rear STI brakes also fit, but need adapters and careful rotor selection depending on your donor rear hubs/knuckles. Everything is well documented and readily available.

[projectrally]

Personally I'm worried about the steering. The WRX has a very slow steering rack and a huge wheel. Doesn't really lend itself to a sporty go kart feel. An STI rack or maybe a different rack altogether and a smaller wheel will probably be common upgrades.

This is something I've been thinking about from the beginning, too. The two biggest weak spots in terms of driver enjoyment in the WRX are the steering and the shifting. Obviously factory five are engineering a shifter solution, so we can only hope they picked something good. Does anyone have firsthand experience with the shifter from the GTM? I wouldn't be surprised if they use a lot of the same components...

The steering rack, on the other hand, has always been slow and just wrong for a sport sedan. Depowering the rack as they have done might help. So would dropping to a smaller diameter wheel. The airbags can't legally be used, so you might as well get a smaller wheel. The real solution, though, would be to adapt a rack from a Miata. Cheap, easy to depower, easy to find, and incredibly communicative.

[Mechie3]

Why can't the airbags be legally used? Not doubting, just curious. I like learning new things. :)

The WRX shifter has 4 different sets of bushings that can be updated in the event the reuse a lot of OEM shifter parts. Makes a big amount of difference in the feel.

[RM1SepEx]

the speedway 2:1 quickener would be too much.

Miata racks are 18:1 manual and 15:1 power and I prefer the depowered power rack

2005 WRX (my year) are 16.5:1 for WRX and 15:1 STI I'll depower the rack and it should be fine with a ratio between the two Miata ratios

so the rack isn't an issue

[flynntuna]

Just wondering, how will the distance from the engine to the radiator effect the water pump? Will it need to be upgaded or assisted?

[PhyrraM]

Just wondering, how will the distance from the engine to the radiator effect the water pump? Will it need to be upgaded or assisted?

While I can't say for certain, I can take a good guess that it won't be neccisary.

FFR has done the GTM. Many others have done mid-engined conversions with many, many different kinds of motors. I have never read anything about needing to upgrade the water pump. As long as pipes used are not creating excessive restriction, I would think the pressure produced by the pump to be more than sufficient because the largest restictions (thermostat and radiator) won't change.

[Flamshackle]

the speedway 2:1 quickener would be too much.

Miata racks are 18:1 manual and 15:1 power and I prefer the depowered power rack

2005 WRX (my year) are 16.5:1 for WRX and 15:1 STI I'll depower the rack and it should be fine with a ratio between the two Miata ratios

so the rack isn't an issue

STI rack and smaller steering wheel isn't an issue. But I wouldn't like a stock Wrx rack ratio.

the 2-1 ratio modifier was an example but not the only choice out there.

[RM1SepEx]

1993 RX7TT has 16.6:1 ratio
no one complains about the 18:1 or 15:1 Miata racks...
Toyota MR2 Spyder 13.8:1
BMW Z3 15.4:1 Z4M Coupe 12.8:1
Z4M Roadster 13.7:1

There is more to steering than the rack ratio
camber, caster, trail, toe...

is the steering arm on the front upright longer than usual requiring longer rack travel for a given turning angle?
If not than just some alignment settings and a smaller diameter wheel may do the trick

I'll get some steering arm measurements from the donor and compare to a Miata... :-)

[Flamshackle]

1993 RX7TT has 16.6:1 ratio
no one complains about the 18:1 or 15:1 Miata racks...
Toyota MR2 Spyder 13.8:1
BMW Z3 15.4:1 Z4M Coupe 12.8:1
Z4M Roadster 13.7:1

There is more to steering than the rack ratio
camber, caster, trail, toe...

is the steering arm on the front upright longer than usual requiring longer rack travel for a given turning angle?
If not than just some alignment settings and a smaller diameter wheel may do the trick

I'll get some steering arm measurements from the donor and compare to a Miata... :-)

I like you already!

I find the WRX steering to slow for my liking but your right, a smaller wheel will be good

[RM1SepEx]

Donor is sitting in the center island of my driveway... think 40 foot ID skid pad for a go kart... I "found" another subaru 16 x 7 wheel (doesn' match though... I'll be buying wheels? or a wheel) and will be able to roll it around next week after remounting the tire

Battery is charging... so perhaps I can get it to roll/drive around. Worst case I can jack it up in the island and take some measurements.

Part of the steering feel of a WRX is the speed sensitive power steering, it disconnects you from the "feel" of the tires and traction with the road. With a lighter car, no power steering mush between you and the tires/ground it should feel better. Use a couple inch smaller diameter steering wheel should make the turning "shorter" across the diameter of the wheel making it feel quicker.

It will be "heavy" when stopped but with any movement it should be fine.

The least ratio I could find in a steering "quickener" box was 1.5:1, that may work on a track but I would think may be a bit too touchy and twitchy for the street.

Just trying to use my engineering background, that's what makes such a project fun!

Tomorrow's "project" is driving to/from the open house and seeing the F5 crew again. I'm hoping to at least get a peek at what the 818R looks like in a single color w/o a windshield

next week, install dynocom 15000 dyno at a friend's house and move his existing bendpak 4 post lift to my house... Yeah
looking forward to buying his lift for my garage! He wants a bigger one to "load" his dyno
donor disassembly in a couple weeks???

[DrieStone]

I thought the WRX steering is so much better than the Eclipse GSX I had. The GSX steering has 0 connection to the road. The WRX is pretty good in comparison. I'd gladly take the WRX steering in the 818.

Of course my Lotus is a thousand times better... although driving through parking lots can be difficult (between the manual steering, the 0 rear visibility, and the non-convex passenger mirror).

[Smitty911]

SNIP Of course my Lotus is a thousand times better... although driving through parking lots can be difficult (between the manual steering, the 0 rear visibility, and the non-convex passenger mirror).

And the children continue to suffer. HHAHHAHAHA

DrieStone,

Just adding some good natured ribbing. ;) Like damn, it cost me almost $1,000.00 to fill up my yacht.

Smitty