Custom A arms (pic)

[ideola]

I cross posted this over on 924board.org, and there are some interesting opinions posted over there regarding the viability of this approach: 924Board.org :: View topic - X-Post: Custom A arms

Anyone considering these would probably be advised to read thru and consider some of the concerns expressed there. It would also be nice to hear from the creator regarding the concerns, and also to understand why $20 in used car parts with a piece of steel bolted onto the end justifies the $700+ price tag.

I'm not taking sides one way or the other. I still find this to be an interesting approach, but I think there are some important questions yet to be answered.

[xschop]

The arms themselves have to have the vulcanized rubber and inner compression ring from the rear of the factory arm machined off after being set-up in a Bridgeport mill. The RX7 arms are way thicker and lighter than the 944 alloy which is crap aluminum. I tried welding an adapter to a set of the Earliy arms and it blew thru because the alloy is too porous (crappy casting, that's why they are prone to break).
If you notice the stock RX7 control arms, they were designed with two large 12mm Dia. Grade 10 bolts and the replaceable ball joints bolt right on and off, the reason I chose them as a starting point.

As for strength, the Adapter plate is Cold rolled and annealed steel with a tensile strength of a whopping 54,000 PSI and I machined them even stronger than the RX7 factory bolt-on joints because the 944 conversion part is wider and can be used for EARLY or LATE offsets. I can even program my CNC to cut whatever offset you'd like at no extra charge.

AS for LOAD bearing, I hate to burst anyones engineering bubble, but the control arms on cars don't take the heavy loads, but the struts/springs support most the weight, it's the control arm area at the sway bar attachment points that take the beating, especially on the tracked 944. The sway bar attachment links are mounted parallel to the steel plate top or bottom if you choose to drop your X-member and Engine 1" for a lower Center of Gravity or putting in a V8 like I did. This is a far superior design than the Porsche link to cast alloy area that often breaks. Extended ball-joint pins ($200 set) on dropped/lowered cars are also scary and can bend themselves. This design eliminates them entirely.

AS for price, if you think you can build a set CORRECTLY with the right 944 control arm geometry (CMM fees are high if you can find one in your area even)......with NEW replaceable Ball joints and New Graphite-Impregnated Polyurethane and T-6061 Billet RX7 to 944 rear control arm bushing adapters for less than the $725 shipped Price tag....Knock yourself out

[ideola]

Maybe you should post this directly in the other thread at 924board.org since that's where most of the skepticism seems to be coming from.

[xschop]

This can be mounted on bottom, but is better to mount on top and turn the sway bar upside down. It is preload adjustable.....



Later I will post up the simple version using a solid mount on the bottom and sway bar stays in the stock position.....stay tuned

[Racerbvd]

So how is this project coming??? Are you open to trades for a pair of them???

Thanks,

[xschop]

This is a done deal. I will machine the adapter brackets to mount the stock 944 sway bar to the bottom of the control arm so all the 944 sway bar parts are retained.
I'm now finishing up the Dual Master Cylinder kit I designed for this car that deletes the Vacuum Booster.
As for trades, I will still need a Turbo nose with the lights and turnsignals. I already have the bumper bracket installed.

[flosho]

How about $300 shipped. $725 is too much money for a $12 oem mazda part and about $100 worth of machined metal.

[xschop]

Well, manufacture a set then.
If you can tell me the 4 critical dimensions within 0.003", I will send you a Bump steer kit with your choice of offset FREE OF CHARGE.....LOL

[flosho]

How many a-arm sets have you sold? Also, is there any type of warranty with these or are they as-is?

[xschop]

I stand behind ANYTHING I design. I will warranty them for 1 year of whatever you can throw at them. Your stamped steel arms are toothpicks compared to this design.
Here is a link to the Bump steer kits I designed for these cars. There is a simple strut tophat and X-member spacer version and Then I designed these arms to drop 1" and use the Tie-rod conversion parts to drop at the steering knuckle. Your spindles have to be drilled and REAMED to accept the 5/8" drop bolt (High Tensile strength) that accepts common 5/8" heim joints and uses INEXPENSIVE Toyota inner tie rods.....

X-Member Drop Down & BOLT-ON BUMP STEER KIT

[modenas]

i like it on my car so far, it hold the sbc well for the weight

[ideola]

Originally Posted by xschop

I stand behind ANYTHING I design.

So how many have been sold and are in use currently?
Have you done any computational analysis (FMEA), and if so, can you share it with us?
How about any real world testing (besides slapping them on a buyer's car)?
Any real world iterative wear inspection, and if so, at what intervals and using what methodology?
Are you insured?
What happens in the event of a catastrophic failure, particularly from a liability perspective?

I know "tone" is hard to convey in forum postings, so let me be clear: I don't mean these to be snarky comments. I commend you for the innovative design, and I for one find these to be very interesting and compelling. However, I also think these are good questions raised by others (that I wasn't intelligent enough to come up with on my own) that merit some consideration by any of your prospective customers.

[xschop]

Hmmm, simple math. The RX7 2nd Gen was a Mazda 944 reincarnate. I owned an '87 RX7. The Car's dims were very close to the 944. The Factory control arms were designed way stronger than the 944 alloy control arms (2X the alloy). So I designed an adapter bracket with at least 2X it's strength. So you do the math. 4X stronger than the 944 alloy arm?
I will post up real world results in about 2 more months for my car with the IRON block 5.3l V8 installed. Believe me I won't go easy on this street menace and will be using it as a demo for the V8 conversion kit I designed. I will also be running modified EARLY STRUTS, LATE SPINDLES that I Cryo-treated and the LEXUS 4-POT MONOBLOCK calipers on my set-up. I will ask the 2 other users to post no-bull reviews also. One is still putting in his V8 and can't say when he'll be done.

As for testing. I will put these arms up against the stock stuff in a shear test anytime and even give a 50% handicap on load bearing for the factory arms.

[ideola]

The individual components may be stronger, but that doesn't necessarily mean the whole unit is stronger. Let's walk thru a hypothetical scenario. On a stock RX7, you hit a curb at speed; let's say the steel end holding the ball joint was designed by the engineers to sheer, snap, fail or whatever in a particular way. Now you put a much stronger steel piece there. That individual component may not fail, but what does it do to the alu arm where the stock bolt holes are drilled? What are the failure modes for the entire unit? Do we know? I don't think so. Too many variables to know for sure without empirical testing.

In the same situation, on a stock 924/944/951 with steel arms, the arm bends, and the catastrophic failure is relative minimized. This fact is precisely why many guys tracking their late 944/951 will revert to the steel arms (perhaps with some reinforcement). During a failure event, bending is much less catastrophic than breaking. We know the stock alu arms break rather than bend. How will these arms fail in a similar situation? Do we know? I don't think so.

So there's definitely some inherent risk here.

To be fair, I don't recall ever seeing anyone challenge the aftermarket suppliers of the chromoly alternatives to produce FMEA results or testing data. I'm not sure anyone truly knows what will happen to those during failure events unless they've actually broken one on the track. I presume that when they were designed, there was some basic calculus involved to determine suitable design and strength characteristics, whether that data is publicly available or not. So the question is, did you perform any such advanced mathematics? How is it that you're determining that the RX7 arm is stronger? The only thing I've seen is reference to weldability, which may not translate at all to structural strength.

[xschop]

The RX7 alloy arms are more than 2X the thickness of the 944 ally arms in the ribbing and I designed the bracket 2X as thick as the RX7 B-joint bracket. I have never seen nor heard of an EARLY 944 replaceable B-joint breaking, but have seen the alloy 944 B-joints pop right out the top of their sockets. They have PLASTIC bushings in them. The alloy of the 944 is porous and if you smack the sh%#& out of it with a hammer it cracks. I did smack the area of a spare RX7 arm and it SMUDGED and determined the casting process of the Japs alloy is far superior. I have machined many metals over the years and alloy casting is a science that the Japs have perfected. VW/Audi alloys are not as compact in the casing (porous)

I did choose the Cold-rolled steel that was annealed. Because un-annealed steel has a slight brittle factor to the metal matrix.

[Racerbvd]

Originally Posted by xschop

This is a done deal. I will machine the adapter brackets to mount the stock 944 sway bar to the bottom of the control arm so all the 944 sway bar parts are retained.
I'm now finishing up the Dual Master Cylinder kit I designed for this car that deletes the Vacuum Booster.
As for trades, I will still need a Turbo nose with the lights and turnsignals. I already have the bumper bracket installed.

A have a nose that needs some TLC and some light parts..

[ideola]

I'm not a mechanical engineer, so I don't know how to make heads or tails of the claims on either side. Here is one of the opposing viewpoints in the x-posted thread:

Originally Posted by Min

If a bridge fails, someone dies, and it turns out the engineer didn't do his due diligence, he can be sued for every last penny he's ever made. I don't see how it would be any different in this case, the guy is releasing a product that he figures will be good enough because cold rolled has a tensile strength of whatever, (oh guess what, when you anneal a metal the effects of cold rolling are reversed and it actually has a tensile strength of the softer steel it came from originally, woo woo material science. So this steel was cold rolled, and then annealed? doesn't have 54,000 psi tensile anymore, uhoh) Another point about the steel this guy is using is that, if its cold rolled, it has grains that flow in the direction the material was rolled, it has a far smaller tensile strength in the perpendicular direction of the grain. So if these steel pieces were not made with the grain flow in mind, they will also have a significantly smaller tensile strength (like, less than half, I can dig up some actual data if people want)

[xschop]

There are different annealing processes, methods. Most importantly is to remove the brittleness after heat treatment hardening. Cold rolled steel can be annealed in an oven to retain strength properties and making the material more machine friendly (remove brittleness). An annealed metal will bend during an impact as compared to a high tensile strength heat treated steel that will shatter more readily.....So a better material to use in the control arm adapters even....

[Racerbvd]

Originally Posted by xschop

This is a done deal. I will machine the adapter brackets to mount the stock 944 sway bar to the bottom of the control arm so all the 944 sway bar parts are retained.
I'm now finishing up the Dual Master Cylinder kit I designed for this car that deletes the Vacuum Booster.
As for trades, I will still need a Turbo nose with the lights and turnsignals. I already have the bumper bracket installed.

Needs some work & cleaning,

[xschop]

do you have the batwing and lights/markers?