1993ka24det

I want to pull more weight out of the front of my Exocet. The NB subframe weighs about 31.5 lbs. So, I've looked into doing all aluminum like a lot of new factory cars are doing. But the issue with that is Alum Infante fatigue strength, meaning that if the Alum bend any deg. that eventually it will crack. I have worked in the Aviation and or Composite Industry for over 20 years. I could take the time and make the subframe out of some type of Carbon structure, but that is some time to engineer a mould. I currently work in the Aluminum industry and work on carbon part on the side.

The Upper/Lower control arms push their load horizontally into the subframe, so I could design the load to go through the engine mounts and into the engine block/ the other sides suspension.

I'm asking for your input. If some pushes back on the idea, give your input in a scientific/Engineering way and I will take that into account.
I haven't corner scaled the car to know how much load will go through the suspension, but the Net weight of the car with me is 1718lbs. 1475 lbs empty

sixshooter

iTrader: (12)

V8 Roadsters front subframe saves about 10 lbs. The cnc aluminum control arms may reduce weight also.

curly

iTrader: (25)

Yeah, v8r subframe shaves about 10lbs, all of which I’d like back, not a big fan. there are certain areas I won’t trade strength for weight, and that includes the subframe. And battery.

sixshooter

iTrader: (12)

Lol, I'm using a battery from a riding mower.

curly

iTrader: (25)

Went through that phase too. Really pissed so threw away perfectly good 90-93 carpet, and with constant tender use, they’ll last. It only takes one no-start episode for me to wish I had a bigger battery. Most of the racing I do is enduro or class limited, where light weigh batteries and subframes won’t win races, but broken suspension or dead batteries will lose them. SoI should probably step out of the lightest-Exocet-ever chat, but thought I’d share my opinion.

patsmx5

iTrader: (16)

I think mine weighted 31.7 lbs. My plan is to drill holes and cut metal off of it to save weight. I think I can get 15-20% of the weight off of it without changing the strrength much. To get 30% weight removed I would loose a lot of strength doing that I think. Still, I bet it would be stiffer than the aftermarket ones I've seen that look pretty flexy.

1993ka24det

The stock subframe isn't the best engineered and it is way over built for the weight of vehicle, especially for a car that weighs 6-700 less pounds.

From your first quote, I've looked at the V8R kit and pretty much I have the same response that I had to curly. But I've talked to V8R about making more aerodynamic control arms, since round tube or squares aren't very aerodynamic. (I am in a open wheel car). I have plans to do 2 venturi tunnels on the car. I am running a 11lb Braille battery, since they are right around the corner from home.

as long as the load is spread horizontally and has a good reliable mount to the chassis. I have also thought of cutting all the welds on the subframe and make moulds of each piece, make them in carbon and glue them together. I'm planning on going heim joints on the control arms and get rid of that stack setup...Eventually.
I could also 3D print moulds and make a carbon intake manifold, since the car won't be boosted. The walls could be 3-4 layers of 5.7 oz. My biggest weight loss but would be more expensive, a k20 engine swap (about 32 lbs off the 1.8vvt)

doward

To echo other thoughts of the subframe not being the place to save weight:

Stock subframes tear and fatigue fail in cars raced at the pointy end of SM and faster.
Stock subframes are not bombproof and v8r's tubular design is worse, significantly.

1993ka24det

Where does the stock subframe crack? Show me the weak points ;-)

engineered2win

Not sure if you're being sarcastic or intentionally obtuse, but the front lower control arm mounts are a notorious failure point.

emilio700

iTrader: (3)

Stock reinforced subframe is going to give you the best stiffness to weight ratio and fatigue life. The V8R subframe is a noodle. That's isn't speculation either.

IMO, subframe is not the place to look for weight reductions on an Exo.

Brakes
Battery
Wiring harness
Driveshaft

HarryB

Brakes and battery are low-hanging fruit so I would start there. You will be surprised how much weight you can save.

Padlock

Having done a kswap... I think you may be surprised at just how close the kseries is in weight to the BP after you bolt on all of the required accessories to it to work in the miata chassis.. I dropped 43lbs from BP4W to K24 (while doing a lot of other weight reduction measures at the same time as long as I was in there). From the best documentation that I took for myself, of that 43lbs, 25 was for a lightweight battery, 5 was for removing OE seatbelts, 5 was for OE charcoal canister setup, 2 was for a lighter steering wheel setup (no airbag), 1 was for removing power antenna, 1 for various front end sheet metal, 8 for OE wiring that was trimmed out... If you do the math in adding all the sub-component measurements up, that comes to 47lbs, which is different than my measured 43lbs at on the chassis scales. I'd imagine the 4lb difference between my component sum and my measured chassis weight is likely due to not being 100% accurate with my fuel level between chassis measurements (I scale with ~1/2 tank).

In summary, I don't feel that I truly realized much of any weight savings with the kswap specifically.