ideola

I posted this over on 924board, and solicited some feedback from Scott @ Harco, who suggested I post here as well. Here goes:

A friend posted a link to this video on my FB timeline:
http://expeditionportal.com/explorin...a-porsche-356/

It got me thinking about the two 1982 "parts cars" that I have sitting in the shop right now. Would be really great to make a 931 Rallye style car out of one of them. I'm thinking no paint job, stick with the badly faded guards red, and trick it out with a lift kit, skid plates, light bar, and fresh S2 turbo motor.

How hard could it be?

Potential donors pictured here:


I do NOT want to do one of the super-wide GTR Rallye cars, as I have TWO super wide projects in the works already. I would rather do a narrow-body version, similar to these:



Based on Scott's initial feedback, it seems very very doable:
- Strip the chassis down to nothing
- Get ride of all electrical load not absolutely required
- Skid plates
- Freshly rebuilt S2 931 motor (3 donors available on stands right now)
- adding an inch or two to ride height
- box-weld the A-arms and trailing arms
- slap on some rally tires
- add a rally light cluster

Couple of questions:
- How critical would track width be? As much as I like the flares on the first car pictured above, I'd like to avoid cutting up my good 931 sheet metal, as well as the add'l expense. Would the narrower track width of the 931 be a serious impediment?
- How important would it be to put in a cage? Bearing in mind, I'm not building a competing car, just something to do some off- / over-roading in like in the video link above.

ideola

V2Rocket

notch the spring plates and index the bars to raise it 1-1.5", there should be just enough room for that much.... may have to find another shock to fit though, but im sure theres some super beetle or buggy shock that would work.

strut spacers for the front end

tall skinny tires...

ideola

ideola

So the 6Jx16" Fuchs that I have should be a great starting point for wheels then...

V2Rocket

i'd use a set of 4 944 spare wheels (steel)...they are 5.5 or 6 wide, and the wheels are cheap.

imagine taking a big jump (unexpectedly?) and crashing down...a steel wheel would only bend, whereas an alloy could crack...

they are heavier but the strength/durability is worth it IMO, for this application.

Scott at Team Harco

Hey Dan,

I'm getting some conflicting messages here. You say it won't be used for competition and yet you are worried about track width being an impediment. Impediment to what? If you are really worried about this - you could install longer wheel studs and 10 - 20mm spacers to give a little more track. In reality - this will do more for looks than anything else.

Same thing for the cage. Unless you are planning on using the car in sanctioned racing/rally events, there is no real valid reason for a cage. I would suggest that a harness bar or a 4 (or 5) point roll bar with horizontal tubes for the shoulder harnesses would be a good thing to install.

You may also want to be a little conservative on the lift. There is no advantage to more lift unless you are traversing large rocks or really rough terrain. If you bang the skid plates once in a while, you are probably fine. It would be a different story if you were constantly riding on them.

Keep the questions coming and, most importantly, keep the build progress coming.

One of these days I'll get started on my 944 RallyCross build. I will be sure to document it here as well.

Scott at Team Harco

Those would be good with winter tires. Let's talk size when more is known about available clearance. Finding 16" rally tires, that won't break the bank, is a problem.

ideola

Wheel selection is critical because of the narrow body. What are the best sizes to target for rally tires? 15"? 16"? With the narrow body, I can put just about any late offset wheel on the car, but things like cookie cutters won't work without widening the arches.

What about suspension setup?
- Spring rate up front? Stock 931 springs OK or should I go stiffer?
- Stock 23.5mm T-bars OK, or should I go stiffer?
- Dampers: I tend to be partial to Bilsteins...are standard issue Bilstein HD's OK or should I go with something more rally oriented?

Brakes I'm not overly worried about. I'll start with stock binders and upgrade to wilwoods or brembos if need dictates.

Scott at Team Harco

You're over thinking this. I live by the KISS principle. If you need to throw more money and technology at it later - burn that bridge when you get there.

If you want rally tires - 15" is the only practical size to work with. Getting the right width and aspect ratio is the tricky part. Once you get the suspension, ride height and any fender clearance plans sorted - then install some wheel/tire assemblies to see how much real clearance is available. It should be easy to calculate the right tire size from this.

If you want to use the 16" Fuchs - you are going to find winter tires are probably your best option. There are many good winter tires out there that provide the "look" and traction in off-road conditions. They will wear faster than rally tires, but will be far more economical than 16" rally tires (assuming you can find any in the size you would need). For what it's worth - I think the Fuchs would be a great look for this project.

Take as much weight out of the car as you can. This by itself will mean less sprung weight and therefore increase the ride height. If you still want to sit higher, there is plenty of adjustability at the rear. The front is a little trickier. Spacers on top of the struts will raise the body. Do not go too extreme with this. A 1/2" spacer should be plenty. You may want to put spacers between the front crossmember (and "D" blocks - I assume the same as on 944s) and the body to reduce any unwanted suspension geometry changes. Again, moderation is important.

Bilsteins should be perfectly adequate for this. The tallest stock springs should be used (unless their spring rate is significantly less than other options). Remember taking weight off the car is effectively the same as increasing spring rate. Things you can mess with later are anti-roll bars. I personally like as little understeer as possible. A bigger rear bar and a small (or no) front bar will help the car to rotate.

Good that you're not too concerned with brakes. Good stock units with an aggressive pad should be all you need there. I'd have to see what compound it was - but I got something from PFC for my Talons that were super. 87 (or 97?) I think it was.

Focus on this: "weight is the enemy". Put back only what you need. Question everything. Anything that does have to go back; can it be lightened, made of different material? I've gone to some crazy extremes to take weight off of some of my race/rally car builds. The car below started at more than 2600 lbs. I took out 1100 lbs. I had to add 100 lbs of ballast to get to the class minimum. For you - there is no such rule. And for my RallyCross build there also is no minimum weight rule. I've got some more crazy plans for that car (whenever I actually get started with it... )

ideola

Great stuff, Scott. 15" Fuchs would be ideal, I only mentioned the 16"ers because I already have them, so they would be "free". 15" rims are plentiful for the 924, so even if I don't want to spring for 15" Fuchs at the outset, maybe some cookie cutters will work, with enough fender clearance (they stick out about an inch too far on the narrow body).

Good to hear about the suspension stuff too...so it sounds like I can just run stock components and not worry about dumping a bunch of money into suspension, other than the dampers themselves.

I would also be quite pleased to NOT have to put in a cage.

What are your thoughts on box welding the 931's steel a-arms and trailing arms?

Time to go raid the parts bin and see what I can throw together.

Scott at Team Harco

I am not very familiar with the steel arms on 924s. You need to answer some questions before you do that. What sort of punishment will this car see that you would consider this? And if you do think it is necessary - where now does the weakest link move to? Is it better for a ball joint to fail, or tear the crossmember apart, than to bend an A-arm? Are these components notoriously flimsy?

ideola

The idea of boxing the A-arms and the Trailing arms is because it was done on the Factory D-Production race cars. I also know many guys tracking 924s or early 944/924S (which all came with steel A-arms) who strengthen the A-arm seams. Seems like pretty common practice, so thought it might make sense to do for this application too...although you bring up a really good point about the next link in the failure chain. An offroad car might see more stress to the a-arm and lower suspension than a tarmac/road-race car, so maybe better to leave the a-arm as weak link, and replace as necessary...they are fairly easy to come by.

924RACR

We're definitely starting to see failure/weakness issues in the cross-member mounting to the frame rails (in the ITB cars). I'd consider beefing that area up. Though, admittedly, it may be more due to later impact loading than vertical/jumping...

kghaas

I Just started a thread on the 924bord as well.
Its about my new baby, a 931 which has done Rally Monte Carlo historique 4 times. (Not with me. I got the car 3 days ago..)
This is not a proper rally, but a regularity event. They do however drive at 7/10 at times. Sometimes at 9/10 when they have had a detour...

The cars are build according the original homologation papers. You might want to go that route with your project.

Monte Carlo 2014


New co-driver