Is this mod allowed ??????
 

we run a 89 fox body in stock elim n/sa . my question is with the stock fuel tank removed and a fuel cell installed in the spare tire well it leaves a big open area under the rear of the car .also we do run wheelie bars .i read on another thread that theres alot of air being caught now by the rear bumper of the car .are we allowed to block this off under the car ?or fill the bumper with foam ????
thanks rick r.

Re: Is this mod allowed ??????
 

Rick - I had an idea recently of running the factory fuel tank plastic cover along with the tank support straps for this very reason. I have no idea as of yet if it will work as intended. Sure would be nice if I had access to a wind tunnel lol.

Re: Is this mod allowed ??????
 

You might get away with it (because no one will see it) but doing modifications to affect aerodynamics is not legal. An example that people often try to do is blocking off the backside of the grille, etc. These get booted any time they are caught.

Re: Is this mod allowed ??????
 

it makes sense that that bumper is acting like a parachute . i thought of putting an empty tank there with the cover but would have to modify it for the bars same with just the plastic cover .i might try to fab up a piece that attaches to the rear floor and bends down towards the bumper dont think the car will catch to much air by this but will stop the bumper from grabbing it also make sure its removable in case its not legal i guess its time to put the reading glasses on and go through the infamous rule book thanks again

Re: Is this mod allowed ??????
 

Not really sure how you would mount the factory gas tanks plastic cover, as it is sandwiched between the stock gas tank and the mounting straps. Without the stock gas tank, there would be nothing for the cover to be held in position with.
As for how much air would get trapped behind the rear bumper cover, I don`t know, but when I had my 85 Mustangs tank out, it sure looked like a big "parachute" to me. And the 87-93GT rear bumper cover hangs further down by a considerable amount.
I would really be suprised if NHRA Tech would allow any non factory paneling or other methods of trying to smooth out aerodynamic drag.

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I believe that if you run a fuel cell the stock tank must be removed.

Re: Is this mod allowed ??????
 

Rick,

just something to look at,

consider keeping the factory tank and adding a sump area to allow only running a few gallons. Maybe add an extended pickup tube from pump to sump. Doing so also gives the option to add more fuel if some temporary ballast is needed.

Re: Is this mod allowed ??????
 

x2

Re: Is this mod allowed ??????
 

Can the fuel cell be mounted in the front of the car?

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Why use a fuel cell? Any issues with the stock tank?

Re: Is this mod allowed ??????
 

Yes, if you're running a Corvair.

Jerry

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I wonder how racecars got built before the internet????????????

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A lot of trial and error. If one can get accurate information why re-invent the wheel?

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Or a Pro Stock. Then its mandatory.

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LOL! :) I agree Bob.

Too many times I believe that it is a requirement to wear an SFI approved Tin Foil helmet when reading some posts! :)

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wheelie bars in the way

Re: Is this mod allowed ??????
 

Good one Joe. The joy of Class Racer is that someone with no experience will get on here, ask a question and then argue when they get an answer that they don't like. The frustration that most long term class racers have is that cars show up that have stretched the rules within an inch of their life and NHRA finally throws up their hands and changes the rules to match the cars that have cheated. Case in point, FWD conversions, no way they were intended to be built the way they are today but NHRA would have been sued if they threw out all of the cars that stretched the rules. Look at where things are with cylinder heads. Before we blame NHRA for the rules being relaxed, think about why it happened.

Jim Caughlin
SS 6019

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Don't understand where all that came from. The OP asked a simple question and I haven't seen a single argument from him.

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Are the wheelie bars really necessary on a N/SA?

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Not really, and the amount of wind catching the rear bumper and slowing down the car would be minimal.

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I have no concrete evidence myself, but I would not be so quick to discount the effect of air being scooped up by these bumper skins. I've heard too many of the really quick Mustang racers describe the ballooning of the rear skin. It's a given we don't trap at the speeds they attain, but the effect/drag has to be present nonetheless. The problem is only magnified with our low hp vehicles.

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You might take some thin aluminum, pop river it to the trunk floor, and curve it down across the bumper opening. Paint it with spray can spray bed liner, and hope tech guys don't look for it. When Jere Stahl and Bill Stiles borrowed a friend's shop here in '68 to fix a *few* things to get through tech at the NHRA World Finals here in Tulsa, his Street Hemi Plymouth had a piece like that. They evidently picked that car apart, and didn't catch that. They had a lined sheet of notebook paper full of things to change. We were there from 6:00 pm until almost midnight. I have never seen anything like it. Jere must have offended somebody. No, not Jere. LOL

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That's funny Ed hehe. While I would not try anything that blatant, anything we do would probably be tossed if it were pointed out. I thought the idea of running the original tank cover/straps was a good one, but if scrutinized they would likely nix it saying it was part of the original fuel tank. In my defense I could at least say I was using factory pieces.

While not spelled out in the rule book exactly I wonder if it is legal to run a fuel cell under the trunk instead of inside the trunk? I have some ideas there lol.

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Since being discussed here, somebody might look under there.
Can you afford the weight of the factory tank, to hold the plastic piece in place? You could take out the gauge unti, and blow through it with something like an electric leaf blower for half hour or so to get rid of the fumes so it wouldn't be a fire hazard. Just use it to block air. I can tell you, that below 100 MPH, there ain't much there. Might be worth part of a MPH at best.

Re: Is this mod allowed ??????
 

Rich, the factory tank cover with a foam block between the cover and the trunk floor would keep things all snuggish. Or some release agent between the trunk floor and the cover along with some minimal expanding aerosol foam sealer would give a real custom fit.

And a can of satin black paint, if only obviously. ;) -Al

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"Why use a fuel cell? Any issues with the stock tank?"
Charlie Allen 7423 O/SA
7423 ET

What about what Charlie asked?
Myself, I'd get the car out and running. You can always try that later.

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Until I had my car back halved, I use the stock tank. On a Stocker, I can not imagine why not.

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Rich, I raced a 1989 Mustang GT in Stock for 7 years, I am changing it into a 1993 Cobra R,
I like that you are thinking about "outside the box" issues, but there are so many other things that are way more important that will provide better results. Go back and read some of Billy Nee's threads about dime-rockets.There is a lot to learn from those.

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Yeah, I'm just rambling on atm. Working on getting everything loose, light and with the least rolling resistance. I've already ripped the stock lines out of the car so I'm committed to a cell at this point. I don't fancy carrying a bunch of expensive fuel around for ballast anyway.

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I just put a fuel cell in mine, I will post some pics of my project soon, your deal is looking good!!!

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Take a look at this link for a fuel cell installation on a Fox body.

http://www.fast351.com/cartech/fuelcellbox/

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Questions should be directed to your division tech director. If it's a gray area get the answer in writing and throw it in your glove box.

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But is that Mustang a Stocker? I`d be suprised if NHRA would be OK with somebody cutting out most of the OE trunk floor, and fabricating a panel.

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Rory, I almost think you could slip that by ,with the same gauge metal.
Seems like a bunch of work to gain what? ..A usable trunk?
I always thought high and back (and simple) ..is best.

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That was a street driven car with a large capacity tank. He was having problems with fuel delivery when tank level was low.

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Where the tank is mounted and if the pump is above the tank sump can cause cavitation issues with a good pump. If the pump has to draw fuel up, it can boil the fuel (cavitate). Like Mark pointed out the tank being high and to the back is the way to go. How you fabricate the firewall makes a difference, and can look like it was factory installed.
Sean