Best method to remove and seal off battery boxes from '73 911?

[Jim Williams]

I saw only one other thread (Battery box removal?) that covered this, in a post by Chuck Moreland, but I have a couple more questions. (If anyone knows of other info already posted, please pass on the link.)

I'm looking for additional advice from those who have Been There, Done That.

This car has already been modified by the PO, so I'm not worried about committing any sacreliges here.....

A (factory) 3.1 liter engine is going into the '73, along with the front oil cooler lines and cooler. A fender cooler is planned to start with, a front bumper cooler already planned as an upgrade. Anyway, the battery boxes are in the way of cooling air flow for the front cooler and the brakes.

So, The options appear to be using a cut-off wheel or possibly a plasma cutter to remove the boxes. I know that some preparation will be in order to protect various items if a plasma cutter is used. The rotary cutter wheel seems to be the best option for neatness, but maybe more time consuming.

I assume it would be necessary to remove the front fenders for this, maybe not so much for the cutting, but for the welding to cover the holes lleft by the removal of the boxes. Is there a preferred method for welding the covers in place? I know that welding sheet metal requires some care, so would TIG or MIG be the method of choice? I'm assuming that welding the cover would be best done from the fender well side.

(For a thread on the 3.1 engine, check 911 Sc 3,1)

Thanks in advance for any thoughts on the battery box removal. Any photos in addition to the one posted by Chuck would be nice.

(Edit to correct link at top of post.)

[barney911rs]

I'll look and see what we did on my car this coming weekend when I'm planning some work. I don't recall how they were cut off, but I'm pretty sure we only used some aluminum to cover up the holes. I'll confirm that and see how we attached the cover material. I'll take a few pics as well.

[Jim Williams]

John,

I hadn't thought of bolting on a cover plate as opposed to welding, or of using aluminum (lighter, and rust-free!). Anyway, I'm open to all suggestions at this point, and photos would be nice.

[EarlyPorsche]

I have never done this myself but if I had to I would definetly weld steel in there. It would add rigidity and also seal off the holes well.

[boba]

I have to admit this is one area I did not do a good job of documenting as we did my build. I have the area in a few pics which I cropped to focus on.

The process was to cut off with cutoff wheel. Go back and clean up area make patch panel and weld in. I think it would be hard to do well with fenders on the car.

Having car on a rotisserie makes so many projects accessible.

Sorry the pics are not step by step, they are what I have.

[jpnovak]

you can easily do this with the fender on. Make your cuts inside the trunk. Use a cut-off wheel and cut just outside the lip where the battery box protrudes in the trunk. Should take just a few minutes to cut out.

Once done, have a help hold a section of cardboard inside the fender well. Trace from the outside. Transfer your pattern to sheet metal and cut outside your line. Carefully trim to fit. You are now ready to butt-weld the patch in place. I went one step further and rolled an "X" in my patch using a bead roller. This really adds some stiffness to the panel.

Welding can be done TIG or MIG. Lately I have been using the MIG to tack in place and then finishing with the TIG. Much less finish work this way. There is room to weld with the fender in place. IN reality, it is not that hard to remove the fender but does cost in extra time, especially when alignment upon remounting comes into play.


Don't forget you will have to weld a new stud for a light grounding post to the chassis. You will also need to fabricate a new fender and headlight bucket support since these were previously mounted on the battery box. This can be done with simple 1/8x1/2" flat steel stock.

btw, I only cut out the pass side for rust repair and oil cooler clearance.

I don't have any pictures handy to post. but will try to get some up soon.

[boba]

Jamie,

You are correct, I should not have implied/stated that you should take off fenders to do this. My view is colored by the fact that we did a total disassembly and had car on a rotisserie. This is not the norm and is not required to do most projects.

The process we used was as described by Jamie with the exception of all MIG on mine.

I for one have had to opportunity to see Jamie's work first hand and will testify to the extraordinary quality work he does.

Regards,
Bob

[jpnovak]

Bob, You are right about project scope. I assumed that the car was in good shape and was getting a drivetrain swap with the necessary oil cooling. If Jim is going to do more, removing the fenders will certainly make this process easier due to more accessibility. it will also make securing the oil lines much simpler. Of course, a right-angle drill helps with the access problem for this project.

Oh and thanks for the compliments.

btw, I will be doing this process in a few weeks on my new project. Currently the rockers are cut out on the driver's side. Once I make my way to the passenger side, the battery box will be removed as I hide AN lines inside the rockers in preparation for the new oil cooler. The cooler will go in place of the battery box just like you are planning. I will also be notching the bumper for more air flow using a factory technique used on the early ST's and RSRs. I will be happy to post pictures in this thread if you want.

[911pcars]

Hi Jim,
Since you don't seem to mind making front end mods, another option is to concentrate on the eventual front cooler location along with adding trunk-through brake ducts. This is a much more efficient air path for both systems.

Removing the battery boxes does reduce some front end weight, but their removal, IMHO, still results in a compromised routing location for brake ducting and a transfer of time better spent on installing a front cooler from the get go. You may find that the cost of installing a front cooler at this stage will be cheaper than installing a less-effective fender cooler now, then upgrading later. However, YMMV.

Sherwood

[jpnovak]

While on this subject... Has anyone removed a battery box and placed an oil cooler flat against the inner fender well while simultaneously making a duct inside the trunk to turn the air out through the batt box hole oil cooler? Basically 964/993 routing on an early car. This should give the high pressure air flow from the front of the car while keeping the cooler protected from frontal impacts and debris impacts from the front wheels.

I personally don't like the RS front bumper/oil cooler opening on a full street car. Plus if you run a non-tail rear the RS bumper looks heavy. I do realize the potential gains in heat transfer from this mounting location. I have not seen a good hidden install using a stock or S-style bumper. Not to mention that front ducting prevents use of a full-size spare (non-collapsible).

[911pcars]

Good idea, but where is the hole from which one harvests high pressure air?

The periphery of the battery box is fairly small. One would have to enlarge the opening for a suitably sized cooler that is already restricted by the available space behind the front fender.

If a stock front bumper is mandatory, then you do what's necessary. However, not sure Jim is going to paint himself into a corner with that limitation.

Sherwood

[jpnovak]

I see I have quickly taken this post OT from the original question. Sorry Jim.

I will move this to a new post.

[boba]

Jim,
Sorry for the hijack, hope you got an answer to your question.

Jamie,
I kind of like the ventilation on the Kremer ST for the 2 fender mounted coolers.

Sherwood,
I think Matteo did what you were talking about, ducting from front mounted cooler to fenders, on his build.

Regards,
Bob

[boba]

Did not post photo of Kremer ST.

[RWebb]

The Kremer is pretty but blocks a LOT of the air flow.

Search up the old threads where Bill V. posted pics of some major installs where side heat exchangers were used.

Exhausting the air thru the sides will work, but you want the [1] the biggest ducting you can fit.
[2] minimal turns and angles, and
[3] to dump it into the lowest pressure area you can find.

Hint: it is not the wheel well area... doesn't mean it won't be enough for you.

[Jim Williams]

Guys,

Thanks for all the inputs, particularly the ones that addressed my questions.

The main issue for now is to formulate a plan to get the boxes cut out and covered back over with a blank plate.

Even before that, tho, comes getting the engine into the car, installing the oil lines, and cranking it for the first time. A trombone cooler will go in first, simply because I happen to have one. Before the engine gets stressed, something else will have to take the place of the trombone, but first things first. I need to get the fuel injection and other stuff mounted on the engine so as to get it whole and stop falling over parts.

The oil cooler issue will have to come as a separate project after I get the engine in and the battery boxes out.

Then I can do a search on the oil cooler. I know there is lots of info posted here on Pelican, perhaps by some that have posted on this thread.

'73 photos:





Note the brake cooling ducts and the removable cover over the cut-out for the cooler.

Thanks to all for the info thus far.

[Zeke]

I made a plate out of aluminum, folded the edges so it fit over the flange from the inside and riveted it in place. I didn't really do this to save weight, I was just tired of welding. If you want a total seal, you can always use body caulk. And, if you want to modify your deal later, it's easy.

No pics, sorry. This was 3 years ago.

[barney911rs]

Jim,

Here are the pictures of what we did. This is on a race car, so it may not be suitable for a street car unless you did something to seal it better like milt said. Some of that industrial adhesive and a few sheet metal screws should make a water tight seal.

Driver Side

Passenger Side

[sundevil64]

Originally Posted by jpnovak

While on this subject... Has anyone removed a battery box and placed an oil cooler flat against the inner fender well while simultaneously making a duct inside the trunk to turn the air out through the batt box hole oil cooler? Basically 964/993 routing on an early car. This should give the high pressure air flow from the front of the car while keeping the cooler protected from frontal impacts and debris impacts from the front wheels.

Jamie,

I was thinking exactly the same thing! I just removed my battery boxes and while I was looking at it I thought, why not put oil coolers flush on both sides, although I would have to create some ducting and I want my full spare. I think if something is done down low low profile it could be done. Right now it is hard to mock it up with my front pan gone.

[sundevil64]

Originally Posted by boba

Did not post photo of Kremer ST.

Bob,

I really like this!

John