190 replies to this topic

[fezzasus]

I think the first question is what does increasing the hole do? As the hole is increased in the direction of the applied compression forces rather than perpendicular to it, I can't see any increase in the perceived weakness and overall supported surface area in the direction of the applied compression force stays constant.

However. Forget what I have to say on the matter, here is a study on forces applied to formed structures with holes. http://www.moen.cee....rt Final R2.pdf

[NickB787]

How's this cut out not much larger than Lotus do

[Bargi]

Despite the general contempt throughout this thread is an interesting debate. It would be interesting to find out peoples opinion on making the hole a touch bigger and then epoxy bonding in a flange to the bottom or swaging the hole to add some rigidity. It could end up stronger than the OE holed panel.

Any answer to this option?

I would think that's better left to an engineer to answer

[Scuffers]

The best discussions are the ones back up with evidence. WHY is that ARB better, do you have any evidence that a rear ARB causes the car to break grip quicker. WHY will cutting out a larger hole for the fuel pump weaken the chassis. Do you have any evidence of this?

here in lies the problem...

at no point was I trying to suggest you buy X over Y ARB, I even stated that one suppliers 1" ARB is going to be dam near the same as ANO

what happens is that the usual suspects have to push their own product (or one they are associated with) and yes, I do fall foul of this myself.

However, if we get back to this thread, the point here is that no matter what has been posted so far, Nobody can honestly say top cut the tank hole out is a good idea.

the fact that it's totally unnecessary to do, it adds nothing to the performance or reliability of the car and yet has such potentially drastic effects seems to me to crossed the line between differing views on directions to take on performance items etc and darn right irresponsible advice that can have consequences.

(I am still utterly gob-smacked that somebody who owns up to being a structural engineer can post what he has, I actually would like to understand HOW he can put himself in such a position?)

as for evidence performance stuff is easy, you go by laptime on back to back testing for example, however cutting holes in stuff is a bit different, unless somebody is going to get access to Lotus FEA models, it's never going to be 100%, and in the bounds of this forum, it's not practical.

Yes, if you gave me a couple of tubs to write off, I am sure I could demonstrate the point, but who's going to pay for the tubs?

posting tech stuff on forums comes with some responsibility, something that some posts (like the fuel tank hole one) fall very short on.

[Scuffers]

How's this cut out not much larger than Lotus do

not sure what your getting at?

they don't come from Lotus looking like that.

[vocky]

so the reality is unless you crash into something which will bend the massive chassis side member nothing is going to happen if you fit an enlarged access panel on the fuel tank enclosing panel.

My car isn't going to snap in half if I go over a speed bump.

The chassis cross-member which holds the engine in place isn't going to fall off anytime soon.

The seat belt cross-member isn't going to allow my floor pan to fall off either.

My car, which is insured for all the mods, isn't ever going to be worth millions of pounds.

So all you are doing is trying to feck everybody off who doesn't follow your point of view, oh wait thats all you ever do on this site, you don't own a vx220, don't think you have ever owned a vx220 and doubt you ever will own a vx220. So why even bother coming on here

[chris_uk]

End of the day, lotus cut a hole in that panel to fit the pipes to the fuel pump housing, in doing so they effected the rigidity of the panel, so If someone was to enlarge that hole its not going to make any real difference to the structural integrity of that panel as there was already a hole there.. As long as you keep everything circular so not to create stresspoints (corners for eg) and dont cut through the crease.. there really is nothing wrong with making an already existing hole larger..

[anz3001]

im not going to pretend to be an engineer or anything but surely size does matter (at what point it becomes critical I dont know) an 8mm is surely different to an 8inch hole, which again will be different for an 18inch hole? is all this much different if we start talking about the floor pan for example? if I were to rip a hole in the floor pan say 4 inch could I just put a plate over it?

[Wolfstone]

I'd like to know which mod / admin saved Scuffers arse from being banned. ;-)

[chris_uk]

im not going to pretend to be an engineer or anything but surely size does matter (at what point it becomes critical I dont know) an 8mm is surely different to an 8inch hole, which again will be different for an 18inch hole?

is all this much different if we start talking about the floor pan for example? if I were to rip a hole in the floor pan say 4 inch could I just put a plate over it?

Your right, a bigger hole would lower its structural strength but we are talking about making a 4/5" hole and extending one side by a further 2".

Were are not making a 5" hole into a 20" rectangle..

[Spitfire Engineering]

to then cut into that so close to the fold takes what little rigidity and strength away, this is basic structural stuff, you don't need to model it in CAD/FEA to see the issues (which is why I am amazed at a self-professed Structural engineer can post such bollocks)
I don't think anyone has suggested going so close to the fold, you started with the ill founded comments well before someone posted an image which showed an example which I agree is extreme. In fact to some degree it was a bit of a let off for you.
The basic technique of enlarging a hole and fitting a larger cover (shear panel) with several well positioned fasteners is neither unsound nor dangerous if done correctly.
They even use the technique to patch up structural panels of aircraft.

A flat sheet of ali has sod all strength against compressive loads without being formed, much like a sheet of paper won't support any load as a flat sheet, but if you put a couple of folds in it and make it into a channel, then close the open side (like the shear panel does), suddenly it can take compressive loads.

True, but then my son when he was 6 could have told me that.

You have to read what is posted Simon including your own posts BTW, if you cannot read or assimilate what is written you will continue to make the same errors both in judgement and in attitude.

so after all that, you actually agree that it's a stupid thing to do, but you just can't bear to say that in so many words?
In your first post you made a categoric, non conditional statement "you do realise that this is an intrinsic part of the chassis and that cutting it is massively compromising the tub don't you?"
Ignoring the attitude of the post, this is simply untrue and you were advised of this, If done correctly it is a perfectly safe and normal engineering technique even used by Boeing to repair damage in the pressure hull
If you increase the gauge of the shear panel you can even make this area stiffer than the supporting panel.

What I then said, which I will now expand, was that in the example shown, which is one of at least 30 or so I have seen, mostly all different, was not IMHO carried out correctly for several reasons, the main one being not so much the creep towards the edge but more the fact that tacking the panel on with a few fasteners will not allow the shear panel to take up the load correctly from the main panel when it starts to buckle. I would not start to guess (as I use a stress engineer who doesn't guess either) how many fasteners would be needed but if it was calculated and quadrupled I would not be surprised.

Other issues are the mismatch in form, especially over the edge. The two panels should be in contact as much as possible, and I suspect the fasteners themselves which need a minimum clamping force if to be effective in stoping any shear motion between the panels and also to have an ultimate strength beyond the combined panel deformation point. Button heads can have a torquing issue due to limited amount of purchase from the tool.

(I had already seen the picture and a few cars before this thread started, so I knew what was being done.)
And you knew this was the example being discussed did you? shame you cannot put your psychic powers to better use, I beleive the military need someone in near the Korean border at the moment.
If this were true then surely you would have noticed that some have carried it out quite correctly, at least two Elise owners even did the calcs.
Had you posted something like..
You may wish to consider the potential issues .. or
IMHO you should really get this looked at professionally … etc,
I'm sure that A. you would not have been caught out yet again not knowing what you are talking about and B. not annoying everyone with your attitude of superiority which is misplaced.


Look, I just don't get how anybody can defend cutting the hole out in the chassis, it's only done because people are far too lazy to do the job properly and drop the tank.
I agree, though not for the reasons of laziness, As to do the work on the hole correctly really needs good access from both sides and the use of a plasma cutter to create a smooth cut with no dinks in the edge. With the close proximity of the wiring and fuel lines underneath the panel not to mention the tank itself, then you really have to drop the tank, so, as you are back to dropping the tank anyway you could save a small fortune on the carrying out the work correctly plus you can swash the tank out and check for both internal and external corrosion at the same time.
In five years it will be time to check for corrosion again anyway, fitting a new pump at the same time is a bonus!

Like I have said before, it's no skin of my nose if you want to trash your own car, but to post up how-to threads for others to follow is pushing it.
So why not post a "how to do it correctly" post then? rather than incorrectly claim it is all wrong?

A l am sure if somebody asked Lotus to comment on the practice, I know what their reply would be, I also know that if one got involved in a serious accident where the Police took an interest, somebody could end up with problems (I have already gone through this with the Honda conversions, one customer had a Major head on, the Police impounded what was left of his car, then wanted chapter and verse on the conversion, the test data, product liability insurance cover, etc. - it does happen).
So if you asked Lotus about the Honda engine conversion do you think they would be happy with that? or would you point them towards Joe McArthy as the guilty party?
We all know that Lotus would never agree to any mod that they themselves did not issue so not really applicable.
As for the rest, make sure you do it correctly then.

As the Mods have obviously taken an interest in this thread, maybe they would like to comment on...

The problem Simon it is not just this thread is it? not even just this forum if fact, you posted a load of rubbish on both the ARB and the German toe-link thread, equally incorrect and with equal attitude.
If you continue to consider your considerable hands on experience as a substitute for a an engineering qualification you will continued to be shot down whenever you exceed you limited knowledge base, especially when you argue with individuals who have far greater training, knowledge and experience than yourself.
And just to remind you again I am a pilot not an engineer if you think I include myself in the above statement.

….. the abuse I have received within this thread?
Which of your personalities posted this bit then?

[NickB787]

How's this cut out not much larger than Lotus do

not sure what your getting at?

they don't come from Lotus looking like that.

Exige S has more holes in it

Edited by NickB777, 12 April 2013 - 10:49 AM.

[anz3001]

... forget that bit for a minute lol

Edited by anz3001, 12 April 2013 - 10:52 AM.

[vocky]

What I then said, which I will now expand, was that in the example shown, which is one of at least 30 or so I have seen, mostly all different, was not IMHO carried out correctly for several reasons, the main one being not so much the creep towards the edge but more the fact that tacking the panel on with a few fasteners will not allow the shear panel to take up the load correctly from the main panel when it starts to buckle. I would not start to guess (as I use a stress engineer who doesn't guess either) how many fasteners would be needed but if it was calculated and quadrupled I would not be surprised.

I must point out that I did extend the original hole in my own car to give very good access, it is a little extreme (I don't believe anyone else has made theirs so large) and I have asked the Mods to replace the offending picture with a more suitable (sensible) picture

But this is quote is total bollocks ......

massively compromising the tub

[vocky]

How's this cut out not much larger than Lotus do

not sure what your getting at?

they don't come from Lotus looking like that.

Exige S has more holes in it

that tub is dangerous and needs replacing, far too many holes in it

[siztenboots]

evora chassis , square holes even

[Dave E]

SQUARE holes, oh the humanity, well that the polar bears/ African children/ wild bees/ ozone layer/ economy/ South Koreans fcuked then

[NickB787]

What I then said, which I will now expand, was that in the example shown, which is one of at least 30 or so I have seen, mostly all different, was not IMHO carried out correctly for several reasons, the main one being not so much the creep towards the edge but more the fact that tacking the panel on with a few fasteners will not allow the shear panel to take up the load correctly from the main panel when it starts to buckle. I would not start to guess (as I use a stress engineer who doesn't guess either) how many fasteners would be needed but if it was calculated and quadrupled I would not be surprised.

I must point out that I did extend the original hole in my own car to give very good access, it is a little extreme (I don't believe anyone else has made theirs so large) and I have asked the Mods to replace the offending picture with a more suitable (sensible) picture

But this is quote is total bollocks ......

massively compromising the tub

Sorry Vocky my fault I chose the first picture which came up on a search

[chris_uk]

fcuking LOL!!

[Spitfire Engineering]

From what I have gained in dealing with this option (quite a bit as we have supplied replacement pumps for years) and IMHO, is that unless you need to change the pump very quickly i.e on track, then it is not a good option for the following reasons. 1. The tanks have a well known corrosion issue both internally and externally and do need to inspected. As you need to remove the lower shear panel to do this along with gear and H brake cables you are already 70% there and dropping the tank is not really difficult anyway. The average pump life of about 9 years (standard) is more than enough time to leave the tank without inspection. 2. the work is expensive to do correctly, the hole needs to be plasma formed and a new panel laser cut. up to 20 rivuts may be needed depending upon the results of the stress analysis. 3. you have to drop the tank anyway to carry out the work so you have only saved yourself a job several years away, in conjunction with 1. above this makes it rather pointless. 4. if not done correctly you may have a stress issue, worse, a chopper job will make a mess of the car and may even devalue it. However it is your car at the end of the day!