Author Topic: Sealing trunk area for NHRA requirements...  (Read 1734 times)

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cjshaker

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Sealing trunk area for NHRA requirements...
« on: December 29, 2020, 08:13:53 AM »
NHRA requires the trunk area to be sealed from the interior area when the fuel tank/cell is inside the trunk area. How do guys seal up their trunk areas, like in a Mustang? I thought about making a plate that went over the tanks recessed area, sealing it from the trunk area, but the fill would still have to be accessible from inside the trunk, so depending on how high the filler plate extends up, that could get a little complicated, and I'm not sure it would pass.

Making a plate to go over the center area between the trunk and interior wouldn't be difficult, it's a pretty flat, open area. But the wheelwell areas are pretty convoluted with braces and rounded areas that are hard to reach, like between the wheelwell and quarter panels. What's the best way to seal those areas up? Has anyone had issues with a tech guy over this subject?
Doug Smith


'69 R-code Mach 1, '65 427 MR, 2x4, 4-spd, 4.30 Locker
1965 Galaxie 390
1970 F-350 390

machoneman

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Bob Maag

Rory428

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Re: Sealing trunk area for NHRA requirements...
« Reply #2 on: December 29, 2020, 10:21:09 AM »
Doug, are you using the stock tank, or a fuel cell? If using a cell, what my buddy did with his Mustang, was use a small cell, below the trunk floor sides, and he then made a flat steel plate cover, that completely covered the big hole where the factory tank went thru the floor, and covered the cell as well. He then cut a hole, about 4" diameter, to access the fuel cells filler cap, and then found a large flange with a screw in cap, so to fill the cell, he would open the trunk, unscrew this large cap on the flange, to be able to pop open the fuel cell filler cap. The bottom of a fuel cell has to be covered with metal, to prevent punctures or abrasion in case of an incident, so if you wanted to keep a somewhat stock look from underneath, you could maybe cut the top of an old factory gas tank, place the cell inside , and make either a new cover for the top, or modify the top of the stock tank into a cover, and install an access cap. As for sealing the area behind the seat, and between the inner wheelwells, I wonder if a factory fold down seat trap door would be considered acceptable? Of course that does not address the huge space on either side, between the quarter panels and the outer wheelwells. Thats a large area, between the door jams and the tailight panel, and behind the rear seat interior fiberglass panels, that is wide open.
1978 Fairmont,FE 427 with 428 crank, 4 speed Jerico best of 9.972@132.54MPH 1.29 60 foot
1985 Mustang HB 331 SB Ford, 4 speed Jerico, best of 10.29@128 MPH 1.40 60 foot.
1974 F350 race car hauler 390 NP435 4 speed
1959 Ford Meteor 2 dr sedan. 428 Cobra Jet, 4 speed Toploader.

cjshaker

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Re: Sealing trunk area for NHRA requirements...
« Reply #3 on: December 29, 2020, 10:59:04 AM »
Rory, I had planned on using a cell, and eliminating the rear fill of the stock tank, mostly for my own safety (in rear end collisions or a roll over, that can be a very real issue). I also want to keep the capacity of a stock tank so that I can still do longer drives, and a cell that sits below the bottom of the tank area would drastically cut down on fuel capacity unless it was deeper, which would end up being very visible below the car and probably look hideous from behind. I have considered cutting open the stock tank and running a small internal tank for strictly 1/4 mile runs, like some guys do in Pure Stock, but that would end up being a huge hassle that would also cut down on capacity for street fuel.

Fuel Safe makes a cell that drops in for Mustangs. The filler looks like it might be low enough to fit under a flat plate covering the trunk floor (using an access panel to access the fill, like you described), if it's extended to the flat frame rail areas, much like you were describing (but not just the recessed area, like you were talking about). But GOOD GOSH are they expensive!! Starting out at $1600, it ends up at almost $2k after necessary options!! I'm not sure I like the internal pump either, although it seems to be a nice Aeromotive unit. Still, that's a LOT of money!

https://fuelsafe.com/early-mustang-comple-fuel-cell-enduro-cell/

I hate the idea of screwing or riveting panels all over the trunk area, but it would be a heck of a lot cheaper than that cell!

Bob, thanks for that link. It's interesting that they say not to worry about the 1/4 wheelwell areas because that basically makes the center panel worthless. I have no experience with NHRA tech guys, so maybe that's the norm, or maybe it just depends on the track tech guy? I'd hate to go to an event like Drag Week though, only to be told I can't run unless that area is sealed.

Doug Smith


'69 R-code Mach 1, '65 427 MR, 2x4, 4-spd, 4.30 Locker
1965 Galaxie 390
1970 F-350 390

mbrunson427

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Re: Sealing trunk area for NHRA requirements...
« Reply #4 on: December 29, 2020, 11:07:21 AM »
Doug, we have these plates in both the Mustang and Cougar. They pass NHRA tech. Not sure if you have seen these yet?

http://tankarmor.com/search?controller=search&orderby=position&orderway=desc&search_query=mustang

cjshaker

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Re: Sealing trunk area for NHRA requirements...
« Reply #5 on: December 29, 2020, 01:01:44 PM »
Doug, we have these plates in both the Mustang and Cougar. They pass NHRA tech. Not sure if you have seen these yet?

http://tankarmor.com/search?controller=search&orderby=position&orderway=desc&search_query=mustang

Mike, no I was not aware of those. It still seems a bit strange that NHRA would be okay with the rubber hose connection in the trunk area, as that would be a major spill area if in an accident, but if it passes tech, then good for that. To me, that looks like a better starting starting point than what I had in mind, although I'm not sure if they would be tall enough to clear a top fill. I'll have to give it some thought. Thanks for that link.
Doug Smith


'69 R-code Mach 1, '65 427 MR, 2x4, 4-spd, 4.30 Locker
1965 Galaxie 390
1970 F-350 390

Posi67

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Re: Sealing trunk area for NHRA requirements...
« Reply #6 on: December 29, 2020, 10:21:21 PM »
On my car I have a 8 Gal (US) cell in the trunk that I had intended to be mounted low but then it was too low, looked like crap from behind and the sump fittings and lines were seriously exposed. Ended up mounted flush with where the factory tank top would be and aluminum fill panes to fill the spaces.

The bulkhead behind the back seat is the factory steel piece and I used windlace and black Right Stuff to seal any gaps. Only had 1 Tech guy ask be about the space along the quarters above the wheel wells and I said..  What do YOU suggest. He walked away and I've never been questioned since. Not sure how your trunk is but you can easily make a plate and seal it behind the seat area  without any major butchery. I can get a photo of mine if you like.

cjshaker

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Re: Sealing trunk area for NHRA requirements...
« Reply #7 on: December 30, 2020, 12:54:05 AM »
Dale, my trunk area should be just like yours, except I have the foldown seat (removed), so I have the flip up panel that separates the trunk from the interior. I don't really want to mess it up by trying to seal the panel to the car, so I think if I went that route I'd just rivet a panel behind the flip up panel and sealing it that way. It's good to hear that they don't make an issue about the 1/4 areas.

Still, if I can come up with a panel to cover a cell, with an access panel for fill, I'd prefer to do that. Then I won't have to worry about sealing around the rear down bars, panel etc. and it'll keep my flip up panel usable, which I do use on occasion. Got some thinking to do, but at least you guys have given me experience on what to expect. Thanks.

On the sump being exposed, I've noticed that on quite a few cars and sometimes thought that they looked seriously exposed. I don't like the look of them being exposed and hanging below the car, visible from the rear, but I think placing them anywhere else could cause me a fuel starvation problem, even if using a foam baffle like Fuel Safe uses.
Doug Smith


'69 R-code Mach 1, '65 427 MR, 2x4, 4-spd, 4.30 Locker
1965 Galaxie 390
1970 F-350 390

Posi67

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Re: Sealing trunk area for NHRA requirements...
« Reply #8 on: December 30, 2020, 02:22:09 AM »
I'll take some pictures in the next couple days. My car is legal so no need to do more. Battery in the trunk is another fuzzy area but if you use a gel cell like an Optima then things get simple. Steel braided fuel lines with an anti siphon vent tube will be your friend at tech. The better it looks the less they check and neither of us are running NHRA National events.

CV355

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Re: Sealing trunk area for NHRA requirements...
« Reply #9 on: December 30, 2020, 03:37:55 PM »
In my old GT drag car, we welded 12ga P&O steel in the trunk area to close it up.  It backed up to a rear seat delete kit that covered the panel and welds so you couldn't see it from inside the car.  If we wanted it to be visible, I'd have had a fab shop bead-roll an X in the center or something to stiffen it up so it isn't a gong. 

Of course, that trunk area is a bit more sealed up to begin with than 1st Gen Mustangs.  The quarter panels and wheel-wells will be the ugliest part to seal up here.  I'm planning on fabricating fiberglass panels that scoop inward and close off those areas to conceal the battery, fuse/distribution box, and other crap I have in there in our '69.  If I was putting the car on the track, I'd have these fabricated out of 16 or 18ga steel, maybe laser cut.  I'd weld in mounting brackets with dzus fittings (screws, riv-nuts, or even rivets would work too, but I like access) that the main panels can attach to.  Simple bulb seal would do fine here.  For any large gaps on permanent brackets, I'd run high temp seam sealer around the edges, though I've never seen a tech actually inspect gaps (at least they never did for me...).
« Last Edit: December 30, 2020, 03:39:52 PM by CV355 »

HR427

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Re: Sealing trunk area for NHRA requirements...
« Reply #10 on: January 04, 2021, 01:49:40 PM »
if you use aluminum, its gotta be .032

cjshaker

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Re: Sealing trunk area for NHRA requirements...
« Reply #11 on: January 04, 2021, 02:56:36 PM »
if you use aluminum, its gotta be .032

While technically that's true, several people have mentioned to me that thickness has never been checked by tech guys. Maybe if I were running in some pro class, or running really fast, that wouldn't be the case, but I certainly won't be in either of those categories. 
Doug Smith


'69 R-code Mach 1, '65 427 MR, 2x4, 4-spd, 4.30 Locker
1965 Galaxie 390
1970 F-350 390