Bosch-Bomb, inside the gas tank?

[Packy]

I don't know if anyone can help me but I'm trying to come up with a better place for my bosch fuel pump than under the front cross member which holds the front suspension together. It would be fine but I am not going to use the stock steel shield because i don't see other race cars use it and it makes sense because not using saves weight. Not using this leaves the fuel lines and fuel pump exposed to the road below.

I want my fuel pump to be as low as possible and close to the tank so it doesn't need to be primed but I can't think of anything good except the smugglers box which I already have plans for.

I recently read from a few sources you can put this pump inside the tank. Is this true? Has anyone ever tried this? I have two gas tanks so I'm willing to cut one up to try it but thought I would pass it by ya'all before building a bosch-bomb.

Any creative solutions?

[midlife]

Most, if not all, modern gasoline cars have the pump inside the tank. This is actually safe due to the vapor pressure of gasoline. The environment is too rich to burn.

[Packy]

Maybe, I know it's not perfect stoichiometric conditions but wet gas definitely burns. i am scared and curious about how I can wire the sucker up inside the tank. It would have to be a completely sealed connector. I could use epoxy heat shrink tubing I guess. Do I need to wrap the rest of the pump?

[JP911]

Since it's a race car, you could switch to a fuel cell. This will allow you to either: A. put the pump inside the cell (many cells are designed to allow for this), or B. mount the pump next to the cell (easier with a cell because the pickups are on top).

[Packy]

Yeah, I was thinking that too but I'm keeping the cost down (good fuel cells are like $2k). I have another friend who builds race cars and works on exotics during the day and he told me I should just keep my stock tank and add a fire system to it. He said I would be fine, sooooo I'm going with the pump in the tank idea.

JP911, do you have any links or pictures of how people modded their bosch pump to work in a fuel cell? This seems to be the way I want to go and just fabricate my tank to work with it.

I couldn't get a good search on it.

Thanks,

-P

[JP911]

The way to do it with a fuel cell is to install a surge tank, which contains the pump. You can check out some examples at Fuel Safe's web site. Here's an example that includes a pump: Collector, ST100-HP

[lin7310948]

my 911 has a big inch sbc with efi. i originally tried a ppump in the smugglers box but even on isolation pads it sounded like a beehive when activated. using an aftermarket ford lightning fuel pump hat, i mounted two wahlberg 255 lph fuel pumps internal to the tank. very quiet and not that difficult to mount. the fuel pump hat is a billet aluminum prewired unit from Fore precision products.

[rvanderpyl]

Pumps mounted inside fuel tanks, need to be designed to be mounted in a fuel tank. You don't just take an external pump and drop it in the tank. You don't say what you are supplying on your engibe, original CIS, Carbs??? In any case, you should be able to easily find a in tank pump from a speed shop, and use a pressure reglator to set the output to what you need.

[Todd Simpson]

C'mon, weight savings? That shield is a pound or two 6 inches off the ground. I can't imagine any performance difference. The shield probably even improves aero a bit.

Thom Fitzpatrick (VintageBus.Com - 1949 to 1967 VW Buses - 1949 to 1967 VW buses) used to make a fiberglass shield.

911/912/930 Steering Rack & Fuel Pump Covers

[Packy]

OOOoooo, thanks guys. This is all good info. I'll probably just buy the fiberglass part which is way easier and when I get some extra time go with the in-tank pump mod.

[jlex]

I don't know what it's like underneath your car, but when I changed the fuel pump on my '85 Carrera last weekend, it was my impression that the metal shield probably helped give some stability to the uniframe construction. I had a difficult time getting the last bolt on as the sway bar, shield and body didn't line up exactly so it was off for a couple of days... but I didn't feel comfortable driving it around as my opinion is it adds torsion strenth where it's needed.

[rvanderpyl]

No the shield is a shield, it is not needed to provide strength. Early cars didn't have them as their fuel pumps were mounted in the back so there was no need for protecting the fuel pump, in addition the cross member was steel, not aluminum, so it wasn't as easy to damage.

[Packy]

A lot of the early race cars don't have them too(935s, carrera RSRs, etc.). I'm going to have a cage welded in sooner or later so I think this will supply the torsional rigidity if any is lost. Do any of you guys know if the earlier cars with the fuel pump in the back had priming issues? I think my 79 SC has two pumps - the one in the back left in the engine bay and the one on the front cross member by the tank. The one up front is suppose to be a strong pump from what I read. Very popular for its time.

[Britain Smith]

Race car or not, I would run the sheild to protect the fuel line, brake lines, etc. I had a steering rack come loose on my at a race and the shield caught all the bolts/washers...it saved my ass.

-Britain

[Packy]

yeah, good call. Now I'm thinking I will make a large diffuser/splitter for under the front bumper and just carry it back to protect this area as well. I need to take a better look at it first but this was just an idea.

I was thinking of using something lighter than aluminum, like that corrugated plastic or maybe fiber glass - cheap, light weight and replaceable.

[Walt Fricke]

Jlex is right, and some of you are at least partly wrong. The shield doesn't add any significant strength to anything. But the two bars which connect the cross reinforcing member (the thing which holds the rear of the lower A arms, plus the steering rack) back to the chassis do. If you decide to remove the shield, be sure to keep these two arms in place. The whole front suspension is held in place under braking (the most Gs your car will ever see short of a wreck) by two long 12mm bolts, plus these two straps.

How much you can do here should be governed by the rules under which you plan to race, of course. Not all classes in all venues would allow removal of the stone shield.

Of course, good race car practice includes your idea of some sort of undertray. On my track car it has evolved, and now is three pieces: One as a lip on the spoiler and on back to the front A arm mounts. The second covers the area between the A arms, and the third from there back to the main chassis a bit farther back than the driver's feet (I no longer hold that part of it on with sheet metal screws out of consideration of feet).

The front bit will benefit from being replaceable, as spoiler lips are kind of hanging out there. The rest should be good for the long haul. Cardboard isn't really the thing, though. There will be some air pressure on it (which is why you want it). Some of my sections are reinforced with small aluminum angle pop riveted on.

Cheap, light, and strong are probably a pipe dream, though. As they say, pick two.

If you are building up a track car, you might look into buying a big sheet of pre-painted aluminum. The ones I am thinking of are used by the roundy round fabrication guys, who replace this stuff all the time. Comes in 4'x10' sheets. I had some work done using some of this, and got a largish (4x4? 4x6?) leftover from the project. I've finally used most of it up. It is even about the same red on one side as my car (plastic peel off protectant on the colored side, white on the other).

Walt

[Packy]

Hey Walt, thanks for your input. I was definitely planning on keeping those two straps in place but just wasn't sure what to put under them. Do you have any pictures of your splitter set up? You sound like you have it all figured out.

And do you know where I can pick some of that aluminum up? What gauge were you using and what grade was the aluminum (7075, 6061), though I guess it doesn't really matter. The gauge would help though.

Oh, and what class/club do you race in?

Thanks,

Patrick

[Packy]

By the way Walt, I lived in Boulder for 5 years while I went to CU and I also grew up in Denver. Now I live in Cali though, but I miss that place. One of the most beautiful mountain fronts on earth, IMO. Not to mention you're an 1.5 hours from 8 ski resorts and some of the best rock climbing in CO. Nice place to live.

[Walt Fricke]

I'll take some measurements and round up a photo or two.

But you need to consider the source: while I build my own engines, it is probably more apt to say I assemble them. With much of the car stuff it is kind of monkey see, monkey do. I can't do FEA, can't afford a wind tunnel, don't own a dyno or flow bench and am a cheapskate about paying for this good stuff, and am not very good at doing one change at a time with tight before and after controls to see if there was improvement.

What a guy can do is use his ingenuity to make servicing his car easier, and - in a modified class with few restrictions - shed weight. After a wreck jumbled up the front of my car (distorted the fuel cell, though it didn't leak a drop) I redid it with improvements on how I mounted many things. The first go around had everything pop riveted to everything else, so to speak. Structurally fine, but lousy for service or section or parts replacement.

By the way, rectangular fuel cells do not need to be all that expensive. Take a look at the ATL and Fuel Safe offerings. You can use a steel container and a plastic tank. I used the occasion of my rebuild to switch to an aluminum container, but the ballistic nylon bladders were beyond my budget. It is the ones which are specially constructed for a 911 (or other car) which are especially costly. Of course, they just bolt in, but it is easy to mount a rectangular 15 gallon (or probably one a bit larger) into a 911.

Absent installing a fuel cell, I'd leave the plumbing stock, or at least in stock locations. An aluminum replacement for the factory gravel guard (if your class rules allow) will keep stray race track debris away just fine. Of course, one virtue of having most of the parts up in the front trunk space is ease of access for troubleshooting and replacement. Fuel pumps don't last forever.

My racing is in PCA's GT-4 and D (stock SC) classes. I have long been active in the Porsche Club, and do more DEs than races. But I have fond memories of the one race I entered at Thunder Hill, and keep hoping I can get back again. And to Sears, Laguna, etc.

I am a rules guy (an attorney, no less), which may explain why I stress the value of reading all the rules you can if you aren't sure with whom you will race. Building to several sets of rules can be a challenge, but challenge is part of what makes us all tick and will leave you the most options open.

Walt

[Walt Fricke]

Packy

The sheet aluminum that found its way into bulkheads and decks and undertrays and various other places on my track only car measures 0.040-0.0385" depending on how hard I squeeze my caliper. It has been useful stuff - strong enough for basically bodywork purposes, but not so thick/stiff as to be hard to cut or bend or even roll.

Were it not for the fact that a bare steel door skin is pretty light (especialy compared to a real door), I might even consider making a door out of it (since my doors are just skins Dzused on). Be cheaper than carbon fiber! But the cost/benefit ratio I think would still be pretty unfavorable.

Walt