Kerry

What does the lap belt mount to?

jester911

Lap belts should be able to mount to stock seat belt points.

RedlineMan

Hey;

This is Sean's (1957 356) car, for those that don't know. His interest now comes into clearer focus.

As for lap belts, they can mount in the same GENERAL area as the stockers. For cars without inner tunnel holes, that means some fab work. Interestingly, the same plate backing panel method works much better in the tunnel because the load path is more paralell to the panel, where the same thin sheetmetal has much higher strength. The load is rendered at a much more acute angle, and therefore does not localize the stress at the holes itself to the same degree. The inner and outer sills (rocker & tunnel) also have some properties of a beam to strengthen them.

However, for maximum effect, the lap belt mounts should be positioned to give roughly a 60* angle from horizontal. This gives the best performance regarding forward hip as well as inverted (roll over) retention.

Sean is 5' 7-8". His lap belt mount points will be moving to achieve that angle. I have also found that having the belts mount very close to the side of the seat helps in getting them tight. This seems to help the Schroth 2" belt noticeably.

chrisp

I haven't done this first hand but if you're running with stock seat rails (or wings as some call them) I would think you could take a piece of 1" round, flatten the ends and through bolt it to the rails (wings). Postion the flattened ends under the rails (wings) so as to not add unnecessary stack height under the sliders. You may need to space the sliders up a bit to clear the heads of the bolts.

There are numerous weld-in solutions but they're not very DIY friendly.

To me the floor pan is cosmetic and shouldn't be a place where subs or seats are mounted to.

Also keep in mind that the pan can be easily penetrated by an off course excursion + big rock. I have a sheet of 1/8" steel on top of a sub-structure of 1" square between my seat and the floor pan.

Russ Murphy

The sub mount bar on the GT-3 seats is very much like you describe, but it has a rectangular cross-section, about 2"x1/2".

NNH

BK sell something similar for GT3 seats, which a roughly square 1" x 1" cross-section. My impression is that the seat rails will give up the fight before this monster does.

Tom R.

i am in the process of installing a set of momo seats with the sparco/sabelt six point system in my 944 tubo that has a redline roll bar. I put the passenger seat in a while back. I had to buy the sparco seat adapter, which came with two tabs for the seat belt to mount to (instead of a driver or passenger mount). I installed one side of the six point to the factory mounting on the outer frame which also has one of the hip belts mounted to it. i mounted the inside hip belt and sub to the frame inside frame of the sparco adapter with the factory receptacle.

My logic - the sparco plate is held in by grade eight bolts, but the tracks and seat mounted to the plate are held in by sparco bolts that are not grade eight. so i think the four bolts holding the plate in (trying to get six in there should hold me in for DE.

Since the car is a street/track toy I am trying not to drill into the tunnel.

What do you think John?

Tom R.

the stock seat belt point in late 944s is the side of the seat.

David K.

Per the PCA Club Racing Rules:

"14. Five or six point competition harnesses, properly mounted, are required as detailed in Appendix B. Harnesses cannot be mounted to seat or seat rail. Mounting must be to the chassis backed by large diameter washers or to the roll bar. No two harness straps can be attached to a single mounting bolt."

My sub-belt has always been mounted with a cross bar to the sliders, I now need to mount it to floor per the rules. I could trap the 6-point sub-belts between the seat and the floor using the front seat bolt as the anchor point. This would put the mounting point for the sub-belt to far forward. See below per Schroth. Any suggestion?

M758

Here is a picture of the underside of my mounts. Gray are the 4 seat mounts and 2 gold colored are th sub mounts. Seat sits about a finger's space off the floor on the lowest side mounts.

The sub is bolted down rather than using eye bolts. Position is very close to the Scroth Diagram David K posted

RedlineMan

Hey;

I understand why the convention is to mount belts apart from the seat. It is, after all, quite logical. Seat apparati can and have failed in the past. You don't want something that you are relying on to hold your belts to come adrift. Center tunnels and inner rocker panels are not likely to drift too far. Club Race rules forbid any belt mounting to any portion of the seat. DE has no such restriction, but it would be wise to follow the CR edict here.

In most cases, the drilling of the center tunnel is of no consequence in any car. Most I have worked on had no assemblies or esthetics effected by this. I still feel it is proper to weld a plate in -vs- bolting one, but the sills are generally quite strong in the direction they will be stressed in belt use, and so the bolt plate method is acceptable.

However, this is not the case for sub mounting. Any load rendered into sheetmetal at any angle nearing the perpendicular, and/or not directly countered by any member of sufficient cross sectional or shear strength, is simply not likely to handle the load at all well.

Floors can and do bend quite easily. Think of it this way. You can easily put a floor jack right under any portion of the rocker panel and raise the wheels of your 2-3k/lb car right off the ground with little damage to the rocker other than essentially cosmetic. You certainly cannot do the same by placing the jack pad under the middle of the floor pan. Any belt in the system will see loads upwards of 1500lbs in an "average" biff.

It's really quite a challenge to mount a sub to something really solid. It takes room under the seat to fit some sort of manufactured assembly. Most Porsches don't offer that kind of room. I am in the process of building an assembly for Sean's car. Sean is not tall, but I have taken the opportunity to not only replace the fairly flimsy 911 seat mount pedestals with something more substantial, but also take the 2-or-so-inches of headroom available by mounting the seat lower. This has made the sub mounting more of a challenge. It is complete except for final sub mount positioning and drilling. Pics to follow.

Let me now pose this question. How do you properly mount a sub on a seat that is on sliders so it can accomodate different size drivers and maintain proper architecture for peak system performance???


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Reporting Live from Brockville, Ont., CA.

rfoulkro

Hi,
I had the same issues, in my rally car I added a 1.25 x .095 DOM bar across the floor pan just below the seat rails, welded on both ends. Add two tabs hoizontal.
Ray

RedlineMan

Hey;

We now have the seat frame completed and welded in.



The frame is about as close to the floor as you can get, and at the same angle as the stock seat mount ledges were. It is welded to the center tunnel and inner rocker. These fabricated units also pick up the second rear mount of the seat track for added strength.



Also note the new lap belt mounts. They are placed to give the proper angle of address of the lap belt to the driver. They are also place more inboard near the seat than the stock points, which aids in getting the belts nice and tight, and also makes for greater hip retention performance.

The last step will be to set the seat in place, mark the position, and then fabricate a cross piece of angle iron, tying the two central rails together, and giving a solid spot for the subs to mount.

Greg Smith

Why two rear mounts and not two front mounts? I'd rather have the added strength on the front of the seat incase I backed into a wall, even with a seatback brace.

RedlineMan

Hey;

With a seat back brace, the floor won't see much rear lateral load, if any. Porsche went with a double rear bolt setup (and from 6mm to 8mm bolts) somewhere around 1985.5 on all models. This is likely because they saw stress localized around the rear mounts from loads put through the seat back in offset or side hits.

As I've said before, I don't often second guess Porsche. They usually do things for a very good reason.