Curious as to how to determine if the chassis is stable or fit for autocross for a car without the stiffening add ons.

To help determine this ....pictures and a description of the current chassis would be helpful.

The stress imposed on the car will depend first on what tires you choose to compete with, to state the obvious. If you compete in stock street (including tires) you do not need to improve the original design. This also assumes you have little to no serious rust issues.

Grippage is what causes the most stress on a chassis at AX.

Those g's have to go somewhere.

I AX'd my car for two years on 16x7s with semi slick 205/55 Toyo Proxes R1Rs.

The car had no chassis stiffening or reinforcement and I had zero issues. I mean, apart from me being a sh*t driver. The car was "rust free" though.

Also depends on how competitive you want to be... it’s a slippery slope...

Loose as a goose, but fun. No stiffening.

That ultimately leads to an 8-point (or more) roll cage!

Absolutely! Depending on the condition of your chassis. Rust is the primary concern. I have 18 years of autocrossing on mine.

I've been surprised by how well 914s have held up to autocrossing for all of the discussion about weak chassis, etc. I think part of that was driven by the weaknesses discovered in circuit racing and major loading at very high speeds over long distances.

After 255,000+ miles, with many hard miles on all sorts of sticky tires that fit into standard fenders, I have yet to see a chassis crack other than The Crack commonly seen on the driver's side inner longitudinal—which was very small and easily welded up. And someone told me they all do that…

Go ultra wide on tires, or simply wide slicks, and YMMV…

i am curious, ive only run 2 autocross sessions in my 914, and i have 16" fuchs, 6" up front and 7"rear, 205/55 but indy 500 firehawk tires which are a 300 wear rating so i could go own to 200 and add some grip to the rear which got loose a bit 2x last time,
but front stuck tight and handled great so would i gain anything or loose to put 7" up front? stock 2.0 motor with factory sway bars front and rear, sport bilistein rear shocks and 100# springs, really very little body roll,- so i have a feeling that wider not always better, i may add 2 degrees negative camber in rear by lowering a notch and add just a bit of toe out up front for next time out, add some 200 rated toyo or such and just get it balanced out. anyone else have any thoughts on the additional widty, 6" vs 7" up front? btw in rear with the 205 on 7" rim gives me 8.5" of tread contact on the ground! and btw last time by my end of session i had closed the gap and tied the other 914 driver in our class that was running on 8" and9" flared car with suby motor, double my HP output


--- oh quick edit, to answer the question of the OP i had my rust issues addressed with all new floowrs rear longs and jack points that repair and some additional metal really tightened up the chassis i did not opt to do any of the more extensive longs stiffening. but, if i were going bigger track and full time ax car then i guess it would benefit for for 5-6 fun days a year i think thats way overkill - but maybe if you are in there already then do that if you can do it yourself, , but i will not do that to this car.

^ Manufacturers like BMW and Porsche have been known to play with wheel width inside the same tire size to adjust balance (e.g., 996.1 C2 and 996.2 C2), and sometimes even front to rear on the same car (e.g., E36 M3). Might be beneficial, but there's a lot that goes into it.

If you've got the nose dialed, and the tail at a point where you can get the car to pivot, and you're beating a far more powerful, more prepared 914, I might just drive it and get better at using that pivot to your advantage—unless it's really bad, that is.

Took a peek at your car, and it's beautiful. Nice to know it's also being used.

Try disconnecting your rear sway bar for more rear grip. Counter intuitive I know.

@914Toy

thanks for the reminder, i had been told that by someone else too, so will do that and see how it balances out

Betty was still autocrossing her 914 after 32 years and 400,000 miles. Still kicking butt with it too.

And @DRPHIL914 , we never disconnected the rear sway bar in her car. That car was dead neutral in a corner, and she could put it wherever she wanted it to go. She can drive over the base of a pylon, and not knock it down.

I definitely don't agree with the "disconnect the rear bar" crowd. They do that, then put stiffer rear springs on the car, which increases the roll stiffness. Just stick with the softer springs for a better street ride, and keep the rear bar hooked up.

Clay

After everyone's comments I decided to lift the car and take a look. From the bottom, I found holes at both hell holes about 3 inches diameter. Im assuming this is where the drain holes used to be. Difficult to tell how bad the rust since its all completely covered in undercoating underneath (Ziebart?). Also a slit hole 3 inches long where the battery tray rests on the inner fender. Next I will take off the rockers to see if there's any rust there. Jack points and jack holes look ok. I'll take pics when I get a chance.

These areas will need to be repaired at some point but are these areas critical to chassis integrity?

Steve Nieslony cracked his right suspension ear @10 years or more back with race tires. As @SirAndy said, it’s grippage that does the deed...

This is not going to be fun to hear - you won't have a functional race car unless that is fixed - and its probably worse then it looks right now.

You are going to need to get in there with a wire wheel on an angle grinder and take it back to bare metal and see how far the rust goes. The longs are the backbone of your car, and if the rust gets bad there your car can literally fold up - especially with the added strain of racing. Fix it now while its small.

Zach

Jack your car up with factory jack point on right side and get the rear tire off the ground and see how the door is to open and close. If you cannot get to that point you have trouble

Bob B

My rule

Never buy a 914 without pulling the rockers

Never own a 914 without pulling the rockers twice a year

You will find more rust

I’ve ripped out 2 suspension consoles that were not rusty on the track
Bracing on the suspension consoles is the only way to keep them from ripping once your tires and grip go up to that level