new box chassis

farkamhall · Post by **farkamhall** » Thu Jun 19, 2008 11:11 pm

hi all. just on the subject of body strengthening and as we are taking the roof off our FB, we have to install a box chassis to stregthen the body etc,. the new chassis is to be fitted between the inner and outer sills so has to be fairly narrow but strong enough to do the job.we had planned on using heavy guage metal but this is going to add to the overall weight of the car. I remember reading somewhere about a suitable material that was light in weight but strong enough to be used for our purpose, would anyone have any ideas what it is called? thanks.dave

Post by **Blacky** » Fri Jun 20, 2008 8:14 am

There are different tensile strenghs of RHS , it may be what you are thinking of. Talk to your local steel supplier ,they may have some answers.

Smooth customs · Post by **Smooth customs** » Fri Jun 20, 2008 10:24 pm

There is no way on this earth that adding a box section inside the sills is going to give the needed addidional strength you think is needed.

This is not a chassis. Ratbox explained some of what was involved in his wagon project, and posted photos of his two door project.

What is the concern with weight???

Do you have an engineer involved in this project yet?

From your questions, you have very little grasp of what is involved.

STOP NOW, and spend some time to look at what you want and why.

I have over 35 years experience doing all types of conversions, and have built rebuilt and restored my fair share of convertibles.

Building a 4 door Holden version is one I would not even bother to attempt. For several reasons.

You have a reasonable sedan, if this is a first project start with simple jobs and work up to the bigger ones. Dont cut it up. Master the skills required and learn your limitations.
Build a nice cruiser out of it and start to enjoy what you have built

It is less frustrating and the disapointments are not as devistating.

farkamhall · Post by **farkamhall** » Fri Jun 20, 2008 11:12 pm

thanks for the comments smooth, as always, straight to the point but i would like to make some things a little clearer.,yes, we have an engineer involved in this and he has never done a conversion like this and has advised us to install abox chassis with extra stregthening for the door pillars, his recommendation was to use the same or slightly heavier guage metal as the present subframe, we want to make this stronger and that is why we are asking questions here, i thought that was the point of this forum? I may not have a complete "grasp" of what is needed but i thought that the more questions i ask the more insight i get. just because no one has ever done one of these conversions before should not mean it cannot be done. Sure, i am inexperienced but i am not rushing into it without trying to find out the rigt way to proceed and what is required. it would be nice if you could give me some of your 35 years experience by telling me how you would go about it as that is the advice i need. Please do not get me wrong, your comments make me look further into each aspect of the conversion and bring my attention to points of great importance which perhaps i had not thought of but with your experience you could help me to correctly determine how to build the chassis and with what type of material. as you have the experience i would appreciate any constructive advice as i do intend to continue with the project.cheers.dave

Smooth customs · Post by **Smooth customs** » Sat Jun 21, 2008 12:02 am

Get a new engineer
One with experience in the type of conversion you are wanting to do.

I am not saying he is a bad engineer, but one that has been there before knows what is needed. Not what maybe needed.

Will your car be a modified production, or will the mods required be deemed so radical as it will become an ICV.

This is something else you must know before starting.

I did offer you my best advice, and in no way was I putting you down with your wish to build what you want.

But seeing you are set on this we will start at the beginning

To get a better understanding of what you are up against.
Get a cardboard box, an empty one. Tape the top closed and place a phone book on the top of the box, and then lift the box with one hand under each end.

Then get a piece of cardboard the same size as the base of the box, place the phone book on it and repeat the method of lifting.

This will show you what happens when the roof of a car is removed.

Doing this will only show sag, if you try and twist and lift something else will happen.

Try and figure out how to make your sheet of cardboard strong enough to lift the phone book without any sag.

People have attempted what you are wanting before, and some with prior experience. But the amount of work required to achieve the end result and the methods needed deemed some of these a waste of time money and material.

Only a couple of manufacturers have offered modern 4 door soft tops and there is a reason for that as well.

The visuals are another point of interest in this type of build. Have you drawn it up or done some cut and paste versions, to see what the the finished car will look like.

I will post some photos of the minium you will have to do, tomorrow.

farkamhall · Post by **farkamhall** » Sat Jun 21, 2008 8:06 am

thank you smooth

mrs ratbox · Post by **mrs ratbox** » Sat Jun 21, 2008 10:58 am

is there any reason you want to do it as a 4 door and not a 2 door ?

farkamhall · Post by **farkamhall** » Sat Jun 21, 2008 12:23 pm

hi ratbox. i know this is not a logical answer to your question but it is the truth. We have had the FB for over 12 years, unregistered and just sitting around, and all of that time i have wanted to make it a 4 door convertible. 4 door because i like the idea of it. i know that i am being told it is not practical etc but what are dreams if you cannot put them into practice at least once in your life. if someone wanted to put a jet aircraft engine under the bonnet, i am sure people would be lining up to give encouragement and advice so why should this be any different? its unusual i agree but it is "doable" with the right help from people such as yourself, smooth and other who may be willing to pass on some information. I do take all the negative criticism to heart i am afraid, and get a little upset that people cannot share my enthusiasm for the project, after all, its my time and money that will be wasted should it all go wrong, all i need is any constuctive advice that you or others can provide from past projects of a similar nature, that would be really appreciated. cheers, dave

oldnek · Post by **oldnek** » Sat Jun 21, 2008 4:26 pm

Dave, Please do not take this the wrong way! I'm not criticising or condoling what you what to try to do, but a few points of concern.........

I'm no engineer, and do not consider myself to even attemp being one. But! being in the game for 28 years and seeing a vast array of vehicles, and having built quite a few of them myself, modified and having those vehicles engineered............there are a few things that concern me regarding what you want to do with your build.

1stly: as with what Paul has mentioned, find an engineer with experiance in the proposed conversion you want to undertake.

2ndly: personal opinion here, is that there is no way of leaving the standard B pillar or middle section between the doors, as is without the need to strengthen that area. (all the strength comes from the outer sill to inner sill and connect to the roof frame truss support) and that whole section is collar tied to the frame. You will be removing this and there is no way to regain that strength, without fitting Y uprights. Which will vastly increase the door frame support and reinforcing the floor area at the bottom.

3rdly: The sill panel will have to reinforced, internally and external, on the body itself, and these will have to tied in with the Y frames on the centre pillar. The strength here, has nothing to do with fitting or fabricating a chassis kit.

If you think about it you have to sustain the strength from the front windscreen all the way to rear screen, and try not to bow the roof line or floor pan.
With that, you want to cut the roof off, so imagine where all the strength has to lie.
The torsional twist will then have thought about, this is where the chassis kit will be required.

I totally agree with Pauls (Smooth Customs) comments. He has built a sqillion cars and I think he has a pretty good idea of what happens.
Not putting a downer on you, or what you trying to achieve, just a couple of points to think about.

Regards John

Smooth customs · Post by **Smooth customs** » Sat Jun 21, 2008 8:48 pm

Dave

You have asked for advice, and when those of us that will offer ours do.
You view it as negative criticism, because we are unable to show the same enthusiasm for your project as you. We have major concerns with what you are wanting to build and its ability to be achieved

John has offered his input, and has similar concerns with what you would like to achieve.

If you look at your previous posts and this one, and count how many people have looked in and read your questions. But then concider the few people that have tried to answer and offer advice.
Mostly because the answers you want are not the ones that are being given, and there are reasons why.

I was made aware you are asking the same questions on other modified vehicle sites, and depending on the site you seem to leave details posted here out.
Even changing the model of the car to that sites prefered preference.

The chassis kits that have been mentioned here and elsewhere are designed as an additional strengthener to an already full bodied car.
Not a means of support for a body that has had its structural integrity removed.

As I said last night, I will post some pictures. and these will be on later tonight.

farkamhall · Post by **farkamhall** » Sat Jun 21, 2008 9:14 pm

thanks oldnek, much appreciated input. Smooth, sure i have asked questions on other sites but i have never changed the model of the car, i have always stated it is an FB and asked the questions that i need answers to. the more input the more it determines how to proceed,i shall take all the comments posted here and give them serious consideration as i appreciate the effort you are making in pointing me in the right direction. thank you for your time and effort in the replies

Smooth customs · Post by **Smooth customs** » Sat Jun 21, 2008 9:24 pm

Dave

Here are a couple of photos of an upgrade in the shell strength of a Holden for a customer.
The inner sills are now made of material twice the gauge of the originals.
A new rail system was designed and made from 3mm material in a folded style, to look as if it was factory fitted. It was welded to the back of the main crossmember that the subframe bolts to and is joined into the rear at the front sprin hanger.
Internally it has another 3mm wall insert that is plug and stich welded in place before a top hat piece was welded in place.

The inner sill and new rail are tied together by outriggers, that are made and fitted in the same manner. Box crossmembers join the inner rails, one behind the transmission and another further back. And then the floors are welded to the tops of these

This is done to improve torsional flex, and improve the structural strength of the body.
And this is in a car that still has its roof!!

Craig · Post by **Craig** » Sat Jun 21, 2008 9:36 pm

I am half cut so this might not come out right

1 Find an engineer who has done something simmilar before not someone telling you what you want to hear

2 Listen to people who have modified MANY not a couple of vehicles before

3 DO NOT ask a question that you do not want to know the answer to

4 Pay someone to do the job correctly

Yes this is a great forum to get ideas and hopefully help others but not at the expense of safety

IT is not just a matter of cut the top off weld in a bit of steel she'll be right think of what will happen in an accident

My mates impala 4 door convetable yoused (is that a word) to pinch your arm in the door top on EVERY bump and the chasssie HAD been reinforced
Consider the forces involved in a head on

and it would have folded like me with a shit poker hand

mrs ratbox · Post by **mrs ratbox** » Sat Jun 21, 2008 9:37 pm

i think the 4 door thing can be done, i have ideas in my head but can't put them to paper, and don't know if they'de work in reality, side impact collision would also be scarey, i'de say you'll need a taxi rail type arangment aswell
i have seen pics of 4 door valiant and early falcon 4 door convertables

Craig · Post by **Craig** » Sat Jun 21, 2008 9:41 pm

shows how long it took me to type that 2 replys in between