Visit our community sponsor

Results 1 to 18 of 18

Thread: Coupe A-pillar reinforcement

  1. #1

    Coupe A-pillar reinforcement

    Ever since I saw Lance Corsi's halo roll cage, I had imagined that I would do something similar for my coupe but I always heard that nagging voice from owners of roll cage-equipped street cars in my head about the need to wear a helmet all the time to keep your noggin from being bashed in on bumpy roads or from aggressive driving. Last week I finally removed the hard top from my body fitting stage, placed it upside down on saw horses and took a serious look at other options.

    For my decision, I tried to be realistic about conceivable scenarios versus the ultimate no-no which is getting upside down (or worse: upside down then right side up, sideways, repeatedly!!). Any coupe owner at this point will have stuck a flashlight up the A-pillar and said to themselves "holy s*#t, that piece of metal ends right there, not a third of the way up the pillar"!! Not the greatest thing if, like Lance postulated, you took out a deer at the knees. I then looked at the structure of the pillar's cross section, how it blended into the ducting of the engine's upper air intake tract and roof and an idea began to form: why not use some of that pre-formed 3-D hoop to help with strengthening the structure. Tossing the idea around with my race-car fabricator neighbor, we both liked the idea of filling that void with something substantial, impact absorbing and fairly light weight. A quick trip to the internet yielded pay dirt: 16lb 2-part expanding urethane foam. Trust me, this is not the same as "Great Stuff" from the hardware store. I got some today from USComposites, mixed up a sample, and HOLY CRAP that is exactly what I was looking for! You would need a hammer to even make an imprint on this stuff. Further research revealed that high-performance boat manufacturers have switched from sandwiched, marine-grade plywood transoms to this stuff with excellent results. Better yet, in an enclosed structure like the A-pillar, it bonds the outer fiberglass skin to the inner ducting to make one really rigid structure that I believe would seriously increase the safety structure of the car, probably even in the event of a roll over. My calculations show it should add a net weight of 6-8 lbs to the finished car. Not too bad!!

    Before I get too over-zealous, let me be clear I have NOT yet integrated this product into the car. I also acknowledge that there is no realistic way to substantially increase the structure across the top of the windshield besides a roll bar...but oh well, better something than nothing. Christmas duties prevail till after the holidays but let me share what I have done so far.

    First, I cut a slot into the ducting where the A-pillar duct meets the upper air inlet tract, made a cardboard template of it's cross section, then transferred that to a piece of fiberglass, cut it to fit and glassed it into the slot. This will keep the foam from expanding into the air inlet tract. Also, there is a quasi-bulkhead in the A-pillar at the upper windshield area that Factory Five placed to probably block off air flow downwards out the bottom of the pillar. This will necessitate placing the expanding foam from different points in successive pours, but that is an easy aside. I will document the process in it's entirety next week.

    I had also entertained the idea of filling the B-pillar with this product, but after careful analysis, have concluded this to be a futile effort: The B-pillar's structure has to be terminated by an (already existing) bulkhead where it intersects the upper air inlet tract, so any crash loads can't be transferred to the upper roof structure. This is also mitigated by the car's main roll hoop being only 5 inches behind this area. The law of diminishing returns prevails here.

  2. #2
    Sounds like a reasonable solution, debating the roll cage as well.

  3. #3
    Senior Member Canadian818's Avatar
    Join Date
    Nov 2011
    Edmonton, Alberta
    I've been considering foam in my S windshield frame. Very interested in how this turns out!
    Adam __________________ Instagram @brap818
    818 SRX - #91
    Arrived 01/02/2014
    First Start 10/31/2016
    First Drive 05/22/2017
    My widebody 13b-REW powered build thread

  4. #4
    I love this innovative thinking, Bill. Have a great holidays and post more in Jan.
    818S/C : Chassis #25 with 06 WRX 2.5 turbo, ABS, cruise, PS, A/C, Apple CarPlay, rear camera, power windows & locks, leather & other complexities.
    Mk3 Roadster #6228 4.6L, T45, IRS, PS, PB, ABS, Cruise, Koni's, 17" Halibrands, red w/ silver - 9K miles then sold @ Barrett-Jackson Jan 2011 (got back cash spent).

  5. #5
    Well, I have finished the initial expanding foam experiment and I have to say it has been quite successful. I now know more about 18 lb expanding foam than I ever thought I would, so let me share my experience with everyone.

    First, the good news:

    This product, as applied, should add a considerable margin to the safety structure of the car. The A-pillars turned out so well that I decided to fill in the upper areas between the duct work to increase the structural rigidity of the roof just behind the windshield. I plan to cover this area, as well as the interior portions of the A-pillars all the way back to just past the B-pillar with 3 plies of fiberglass cloth. This step will tie-in the pillars to the duct work and roof structure and add another level of strength for very little weight gain. While not exactly a crash test, I accidentally dropped the entire upper coupe structure off of a 3 1/2 ft saw horse onto the top of the windshield area of the left side A-pillar: it bounced, made a scratch and did no other damage. Pretty cool!

    I was close on my weight calculations, which were done before I decided to fill in the upper duct area. Each A-pillar absorbed about 2.5 lbs of material and the upper duct area absorbed about 5.5 lbs for a total of around 10.5 lbs. Adding fiberglass and resin for these structures should add about another 2 lbs. Overall, not a bad trade off.

    Now the bad news:

    Making successive pours on large open areas leads to different densities and difficulty in sanding these areas smooth. That's about it.

    What I learned:

    This 18 lb urethane foam only expands to about 2 - 2.5 times it's liquid volume, which is why it is so hard and dense. It also needs to be hot to perform properly. I have a heated resin cabinet, so I was able to get both liquids to about 85 degrees before combining, which is ideal. There were no problems with the enclosed A-pillar pours, however, a test pour for the open, upper areas revealed that the liquid quickly cools with exposure to so much surface area, so both the expansion ratio and the time to reach full expansion were affected. I was able to overcome these issues a two-fold approach: I preheated the larger areas first, and then instead of quickly pouring the mixed product, I instead kept it in the mixing container until it started to exotherm and just began expanding. Then I poured it into the areas where I wanted it to go. You have to be fast and precise here, because once it exotherms, you have about 20 seconds to get it placed. Messing with it after this point by trying to move it around can be counterproductive; it sets up VERY quickly. If you try to move it around too much with a squeegee you end up with very stratified hardness levels that are really difficult to sand properly. Having a partner here is very beneficial as your total start-to-finish time is less than a minute. Here is what I did: filled a container 5" high with lacquer thinner with which to accept the drill stirring attachment after mixing, my helper poured part B into the mixing container (it is thicker) and I put the stirrer in. Then he held the container and poured in part A while I began stirring for about 20 seconds. I took the container to the pour site and he immediately cleaned the stirrer in lacquer thinner. Repeat as necessary.

    The upper duct area between the two bulkheads took about 16 fluid ounces each, in two pours, as I was not sure how far it would flow before expanding. The bottoms of the A-pillars already had openings in them through which to pour when upside down, and each pillar took 12-14 ounces of product in the first pour and around 6-8 in the second pour.

    The upper structure took a lot of product, around 75 liquid ounces. This produced a lot of expanded waste but there are varying depths and shapes that must be dealt with. If I had to do it over, I would attempt the entire upper area in one pour. The important thing to remember here is that this product works best with a large or contained liquid volume: spreading it out over more surface area with thin pours is counterproductive and makes for VERY difficult sanding and shaping. Pour it all at once, let it make a big mushroom, and shave off everything that you don't need.

    Once this stuff exotherms, it generates a LOT of 160 degrees F!! My A-pillars stayed above 130 degrees for about 15 minutes!

    Being a newbie, and with untried techniques, I used successive pours everywhere. I had to get creative with placing the upper coupe structure in various positions to use gravity to help things flow properly.

    Do NOT try to tape over a lower opening and expect it to hold as you pour through a higher opening!!! The combination of exotherming and expansion will overwhelm any kind of tape you can possibly think of (though silver metal duct tape comes close)! Ask me how I know!!!

    DO wear disposable gloves and be ready with both hands and Visqueen if you want to alter the inevitable expansion progress; DO NOT try to contain the expansion as it will blow apart your A-pillars or ductwork...always give it a place to benignly expand. I used two 1.5" holes between my duct bulkhead and FFR's windshield bulkhead, and then went with successive vertical pours to fill the rest of the A-pillars to let the expanding foam come out the ends of the pillars. It worked beautifully.

    Here is some documentation of my processses.

    First, I cut slots to place bulkheads where the A-pillar ducting met the upper air intake ducting. I used some pre-made 1/2" thick fiberglass/foam panels but you could easily substitute 1/2" thick plywood or purchase 1/2" foam insulation board from Home Depot. I cut the slots about 3/4" wide so I could look down into the area and see that I was actually blocking off the ductwork in it's entirety. I then epoxied them into place and glassed over them.

    Here are my two 1.5" holes through which I poured the urethane foam between my bulkhead and FFR's windshield bulkhead.

    Here you can see my bulkhead through the hole.

    At this point I had done the first pour fairly horizontally and was readying the area for the second pour. I put the structure fairly upright, poured the mix, let it start expanding then removed the lower metal duct tape to better allow for expansion.

    to be continued.

  6. #6
    Senior Member fastzrex's Avatar
    Join Date
    Oct 2015
    Oklahoma City
    Thank you for your investigation of this process. I have also wondered whether I should place more structure in the roof area but as you have talked about that places areas to hurt your head unintentionally (have done it in a prepared Miata). Look forward to your series of 'how I done it'!
    ~ Mark

    818C S/N 429ES: Start Date 1 September 2016
    2001 NB Miata LS3 V8 440 rwhp
    2004 Miata MazdaSpeed Factory Turbo

  7. #7
    This is another shot of the bulkhead I made, in place, ready to be glassed over. Before I placed them, I poured some thickened resin mix into the slot and generously slathered the contact areas of the bulkheads to be sure of good blockage and no gaps.

    Here is a piece of clear plastic (from the side of a plastic cup) taped in place over one hole. It resists the expansion just enough to let any expansion spread outwards underneath before pushing the plastic up.

    When you get it just right, it looks like this. This is the only one of the four like this; the others had little mushrooms of foam that I had to cut and sand off.

    This is the bottom of A-pillar after expansion.

    Upper duct area.

    I used 1/2" wide Frost King adhesive-backed foam stripping to limit where the foam would go laterally and I am preheating one side prior to it's pour.

    Here is the expanded upper duct. I left a slot in the middle to be able to start a contoured cut with a piece of bandsaw blade. It went excruciatingly slowly, so I got the bright idea of chucking the blade into my air saw and using an adjustable wrench to guide the other end. DO NOT TRY THIS!!

  8. #8
    Here is what happened to that bright idea. I was angling the blade at both ends correctly, but couldn't see what was happening below.

    The best solution I came up with was to use a Sawzall with a really long blade, cut straight across the gap as much as possible, then grind and sand the rest of the contour. It's kind of slow but it worked. I used a 3" 80 grit disc on my angle die grinder for the rough shape, then used a 60 grit 5" orbital sander to smooth things out.

    FFR thoughtfully provided a perfect template for this contour in the form of their outer door handle template.

    Here's the finished stuff, re-foamed and ready for 3 plies of fiberglass cloth

  9. #9
    Senior Member Canadian818's Avatar
    Join Date
    Nov 2011
    Edmonton, Alberta
    Great stuff! Thanks for the contribution. I want to use this on the "S" windshield frame, any idea how much I should order?
    Adam __________________ Instagram @brap818
    818 SRX - #91
    Arrived 01/02/2014
    First Start 10/31/2016
    First Drive 05/22/2017
    My widebody 13b-REW powered build thread

  10. #10
    Looks good. Is the ram air still functional?

  11. #11
    My apologies, this product is actually 16 lb foam and not 18 lb foam.

    I would think 1/4 cu ft would be fine for the S frame. Even if you had to buy 2 you'd still be money ahead of the 1 cu ft package.

    Yes, the ram air is still functional.

  12. #12
    Might actually consider this. To bad I have the windsheild already installed this would be a bit challenging

  13. #13
    Quote Originally Posted by 07FIREBLADE View Post
    Might actually consider this. To bad I have the windsheild already installed this would be a bit challenging
    Actually, if you're going to paint your car and don't mind glassing over the holes, you could duplicate 95% of what I did by drilling 3 1.5" holes and one 1/4" hole through your gelcoat on each side and pouring from above. You could omit the duct bulkhead and use a little squirt of Great Stuff about 4" in front of the duct intersection. This would act as a bulkhead so your urethane foam couldn't get past it. You would have to use 2 layers of metal duct tape to seal the bottom of the A-pillars but I think it could work well.

    If you're interested. I could do some measurements for the best places to make your holes.

    Even without the extra, upper area of foam behind the windshield, you'll have a lot of extra strength by foaming in the A-pillar ducts.

  14. #14
    Could you take measurements that would be great. I am going to paint or wrap haven't really decided yet. How do you plan on covering the inside now? Would you consider doing the whole top even where the aluminum goes. Maybe 1/2" thick enough were you could drill into and maybe install a rivnuts to hold the aluminum up. That's sort of the plan that's coming to mind for me right now.

  15. #15
    Interesting idea, though headroom is kind of paramount for me right now. I'm covering the inside of the A-pillars and B-pillars as well as the upper foamed area in 3 plies of fiberglass, then I'll put some kind of head liner microfiber material over that.

    Give me a day or so to get the measurements to you.

  16. #16
    Quote Originally Posted by 07FIREBLADE View Post
    Could you take measurements that would be great
    OK, here are some pics that pretty well describe how to address the expanding foam experiment from the gelcoat side of the hardtop. I want to emphasize that you will need to first experiment with a can of Great Stuff to study how it expands in an enclosed space.

    I gave it some thought and here's what I would do: procure a couple 1' pieces of 3" id pvc pipe. Drill two 1/4" holes about 2" apart about half way along the mid point of each pipe (about as far apart as the 2 silver dots in the photo). On one test pipe, squirt a 1 second load into each hole and measure how far the final expanded product reached from the hole to the ends of the test pipe. On the second test pipe, give it maybe a 1/2 second squirt into each hole and measure the difference of the total expanded length in each pipe. This process is to insure that your Great Stuff aft bulkhead does not impinge into the upper air duct from the ram-air opening above the windshield. Once you are comfortable with placing your rear Great Stuff bulkhead you are ready to address FFR's upper windshield bulkhead. Mine, on both sides, were quite porous and not at all effective if they were meant to keep air from flowing down the A-pillar. Drill a 1.5" hole just below the area shown below the silver dotted line at the top of the windshield point. You will now be just below that bulkhead and can squirt a little Great Stuff to close off the bulkhead. You have now created two separate volumes in which to use your expanding urethane foam. To close off the lower A-pillar, you'll have to get tricky with the Great Stuff and/or metal duct tape to close off the area around the steel pillar reinforcement.

    For the upper volume, drill a 1.5" hole in front of your rear Great Stuff bulkhead, mix your urethane foam product and pour into the hole. The windshield bulkhead will keep it from going down the A-pillar. Let is expand out the pour-hole, cure and sand flush.

    For the lower A-pillar volume, pour through your pre-made 1.5" hole and let it expand up the A-pillar and out the hole. Let it cure, and sand flush.

    Good Luck. PM me if you need any specifics.

  17. #17
    I guess what I wanted to say in that post is to use as little Great Stuff as possible while still sealing off the ducts. It expands a LOT and will be stealing valuable space from the much harder expanding urethane.

  18. #18
    Cool thanks for the pics and info. Should be implementing this over the next few weeks.

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts


Visit our community sponsor