mikey_audiogeek

Hi all,

I've dropped a few hints recently about my proposed suspension upgrade for my 944 S2, so I thought I'd better start a thread.

This thread is about fitting Lexus IS-F front suspension to a Porsche 944 S2. I am doing this conversion, and will post progress here.

I am happy to discuss technical details, and answer questions related to the modifications.

Here's where I started:

Known problems with 944 suspension, when racing at the level of TonyG:

• Geometry when lowered
• Non-maintainable balljoints
• Risk of cast aluminium arms failing
• Undersized brakes
• Bump steer
• Risk of cast hubs failing

To address all of these issues would cost in the region of US$4K. With this sort of budget, other componentry could be adapted to advantage.

Objectives in order of priority:

• Coolosity factor
• No mods to chassis mounting points or bodywork
• Use factory Porsche parts where practical
• Optimise geometry
• Use commonly available secondhand parts where practical
• Lighter than stock
• Cheap consumable parts (pads/rotors etc)

mikey_audiogeek

<deleted to avoid confusion>

mikey_audiogeek

http://blogs.insideline.com/roadtest...alkaround.html

http://blogs.insideline.com/straight...exus-is-f.html

http://www.lexuspartsnow.com/parts/l...201-53010.html

http://shopfigs.com/v1/index.php?rou...&product_id=59

http://www.clublexus.com/forums/susp...akes-on-3.html

mikey_audiogeek

Decision has been made to go with Lexus IS-F front suspension.

Brake calipers: 47730-0W030; 47750-0W030
Knuckle: 43201-53010 (R); 43202-53010 (L)
Balljoint: 43330-39625 (R) ; 43340-39505 (L)
Hub: 43550-53010 (R); 43560-53010 (L)
LCA: 48620-53020 (R); 48640-53020 (L)
Rotor: 43512-0W030 (both sides)
Upper arm: 48610-59065 (R) ; 48630-59065 (L)
F-sport bilstein: PTR13-53094 (L) PTR13-53093 (R)
Shock top mount: 48680-53050 (both sides)

Lexus data:

Front track = 1560

Front LCA width = 372mm approx. centre to centre (porsche 944 = 360mm)
Fore/aft pivot spacing = 286mm

Ball joint approx. 131mm below centreline (997 upright approx. 125?)

Front tyre (225/40/19) = 662mm diameter
Disc height 61mm
Disc diameter 360mm x 30mm

Wheel mounting surface 97mm outboard of ball joint

71mm from hub mount to wheel mount face

Bearing approx. 74mm dia spigot

V2Rocket

these RX7 arms?

mikey_audiogeek

Strut suspension based on Lexus IS-F parts:

No changes to chassis or sheet metal.

Custom parts:

• tie rod links (Lexus ball joint is on removeable steering arm)
• Strut mount (bolted to back of spindle)
• caster bush
• chassis brace (mounts to original caster bush mounting holes)
• wheel adapters
• custom brake lines
• custom sway bar links

Modifications to Lexus parts:

• Longer hub mount bolts (to mount custom strut mount)
• Top of spindle removed (to clear strut)

Carry-over parts:

• Front struts
• Top strut mounts
• Sway bar (upside-down)
• Wheels

mikey_audiogeek

[quote=V2Rocket_aka944;10062624]these RX7 arms?


Yep, they were considered.

For what I have planned, the Lexus arms are a better option. More to follow...

Thanks for watching!

Mike

mikey_audiogeek

Double wishbone suspension based on Lexus IS-F parts:

Some changes to chassis or sheet metal.

Custom parts:

• tie rod links (Lexus ball joint is on removeable steering arm)
• top arm
• caster bush
• chassis brace (mounts to original caster bush mounting holes)
• wheel adapters
• custom brake lines
• custom sway bar links
• Lexus F-Sport front bilstein coilovers

Modifications to Lexus parts:

• Top of spindle shortened and machined/threaded for top arm ball joint

Carry-over parts:

• Top strut mounts (converted to coilover mount)
• Sway bar (upside-down)
• Wheels

mikey_audiogeek

Porsche 964/993 RS uprights: Ackermann geometry incorrect
Audi TTRS: Ackermann geometry incorrect
Porsche 997/TT/Gt3: Steering arm geometry (bumpsteer)
BMW E90: Bottom arm geometry

951and944S

Doesn't a Lexus front suspension break your #2 priority...?

All this trouble for a street car...?

Tracking and racing 944s for the past 5 years, we have never broken a late a-arm.....nor a hub.

There are several manufacturers (and site sponsors) that sell serviceable ball joints... "maintainable" with grease fitting, replacement boots, etc.

You can even buy geometry correcting sets...$300.

I have seen pics of broken hubs, but again, never had a properly maintained one fail on our cars....Sebring, Daytona....tracks with a lot of elevation and off camber, Hallet, TWS....our home track is the notoriously bumpy Circuit Grand Bayou (formerly NPR)....one of our cars has 3 4/500 mile enduro races on top of tons of track miles all over the country, still, never lost a hub or a-arm.

Elephant Racing has a bump steer kit, in the event that you think that bump steer is going to limit your on street performance.

And 944S2 brakes are undersized.....?

LOL X S2....!

Your ultimate braking traction is limited by the size/grip of the tire and S2/944T brakes will bump the ABS or lock a tire at a whim....anything more is overkill unless you want to address cooling, and that, again, will only be necessary on the track. If you are causing fade and overheating on S2 brakes on the street, you are either one bad dude, or live in a gated community with direct track access from your driveway to Nurburgring.

If you are breaking the parts you mentioned or having trouble with the brakes on an S2 on the street, you need to get on the race track.

As far as being "low stress" on the duty of our cars, one has an overall win in the aforementioned LA400 and my son holds the track record for 944s at Texas World and 944/NASA PTD at both NOLA 1.8 and 2,4 mile configurations.

T

mikey_audiogeek

Noted. I have updated my original post accordingly.

Cheers,
Mike

LS1Porch

There was a thread on pelican (IIRC) a while back discussing the RX7 control arms. There were a number of engineering-type questions that went unanswered. Long story short, i'd trust my life with the 944 control arms and their known problems over the RX7 control arms and their possible problems. I hope you know what you're doing with the Lexus parts... A set of fabbed control arms designed for the 944 isn't THAT expensive.

mikey_audiogeek

Noted. Neither the RX-7 arms nor the 944 arms (factory OR aftermarket) are suitable for what I have in mind.

I will delete post #2 as it might tend to distract or confuse people.

Cheers,
Mike

333pg333

That may well be true and it’s great to have real world account of your racing experience but I’d be inclined to applaud when guys take a lot of effort to improve our systems. We do run on pretty antiquated suspension so I’m happy to watch Mike have a crack at his improvements. I’ve also heard of some of the maladies that he describes re arms and hubs breaking. I’d like nothing more than to update my car’s suspension both front and rear but that is for another day.

As for $4k being half the cost of an S2…not in the rest of the world and certainly not Down Under.

Good for you Mike. Look forward to reading on your progress. Do you think they could cope with larger than 330mm rotors?

Don't like the look of those RX7 arms. They're a lot lighter than our cars too.

mikey_audiogeek

Bloody typical - no matter what I write, everyone has to comment on the single photo posted...

Anyway, thanks for the words of encouragement Patrick, would appreciate your thoughts!

The Lexus IS-F rotors are 360x30mm and weigh 27lb, US$400/pair.

A dimensionally identical (diameter/thickness/offset) alternative is BMW E92 M3 rotors, two piece design (have a look) and only 22lb each but US$600/pair.

IS350 rotors are 330mm and the 4-pot calipers are cheaper than the 6-pot brembos on the IS-F. The front hubs are different too - IS-F hubs have more offset by 12mm.

Cheers,
Mike