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Well, I've been keeping a build thread on CT for a while now but after having a chat with richbike I thought I'd wander over here and get some opinions as well :)


As a bit of a catch-up I bought my little Mk4 for a grand as a rolling resto, but it turned out to be not so good at the rolling part so I thought I'd crack on with the resto.


Progress-to-date I've tidied up the rust on the body, rebuilt the engine (2.5l from a PI saloon with a Burgess head & balanced bottom end), fabricated lower rear wishbones a la Marcus/GT6M, gathered all the bits I need for the suspension (GT6 all round with CV axles and trunnionless fronts), swapped a quaife LSD centre into the diff (got to blow my money on something), welded a mount for the big saloon OD gearbox that came with the engine and fabricated a roll hoop.


The original plan for the car was to swap a 6-cylinder up front but retain the overall weight and distribution of the stock Spitfire without moving the engine back 6" in the chassis. To that end I've drilled holes (saves surprisingly little weight), spent lord-knows how much on very pretty alloy bits, bought a £20 fibreglass bonnet of eBay, swapped to a GT6 fuel tank and plan to put the battery where the Spitfire tank was.


Currently based on various bits of spurious maths I'm looking at a weight of ~760kg and a weight distribution of 53% front.


The latest idea comes from the idea of solid-mounting the body to the chassis. My thinking was that rather than bolting it on with alloy spacers, why not just weld it in place? I'd say it's an old hotrodding technique but I actually stumbled onto one chap who did it with a 50s Ford on a hotrod forum so I'd probably be telling porkies. The big Healey did it though :)


To add stiffness I'll box in the area between the chassis and the bottom of the floorpans, essentially broadening the chassis rails as they neck in at the middle. I've also got a hardtop that I've stripped back to just the outer shell and welded onto the body (at the rear at the moment, the front's a bit frilly. That'll get proper boxed in sections around the perimeter to add strength.


Probably a boondoggle, but someone's got to try it to see if it's worthwhile :)


Onto some pics!







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So! Long time no speak. Among other things during lockdown I've been scouting around my old forum haunts, finding out which ones are still alive and updating on how the projects are coming along  a lo

Thanks for the pics  that looks like a very neat setup for the linkages. I hadn't thought of getting rid of the box/plinth thing that the fibreglass boot has for the standard locking mechanism. Will d

Excellent drawing there. Deserve a medal for Services to Sideways. Got any @Nick Jones?

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Interesting project.  I've been watching it on CT.  We've done something similar with the back suspension on my son's Spitfire, though that'll stay with the Triumph 1300 for a while.


My impression of the Spitfire after years messing about with Heralds and Vitesses is that they are already alot less flexible.  I'd think that the hardtop alone makes a substantial difference, especially welded.


As regards welding the chassis to the body - yes, why not?  My approach would be to do this after final assembly to the chassis in the normal way with bolts and spacers, making sure that doors fit properly etc, then welding short bridge sections afterwards.  The donor car that became the basis of my Vitesse had the body welded to the chassis which made it feel very solid and up together even though it turned out to be far rustier than the Herald I was comparing it with..... Was an absolute sod to dismantle though!



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Yeah that was the plan with the body :) shim it up right on the chassis (I'm fairly certain it's slightly tweaked) so that the door fit and then weld an angle between the body and the chassis. It'd be a fairly permanent fixture when it's in place so I'd better make sure it's decently rust-protected!


It'd be cool to see your rear suspension setup as I'm sure there's differences that I might be able to learn from :)

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  • 3 weeks later...


I have been stealing the odd hour here and there to make a collapsible rotisserie to mount the body onto which I'll post up once I've finished.


However, I have been thinking recently about chassis stiffness, specifically the area just before the bulkhead which I'm pretty sure is a major area of flex when the front suspension is compressed.


On most racecars I've seen they simply extend the rollcage through the bulkhead to meet the suspension towers, which I'm sure works very nicely. However, as I'm not having a full rollcage I'm fairly certain that welding/bolting a tube straight between the front towers and the bulkhead (upper drawing) would be a significant safety hazard. I can see in a front-end collision that it would either punch straight through the bulkhead or cause the bulkhead to fold/buckle in towards the driver's feet.


So, my thinking is along the lines of drawing no.2. Two tubes, one welded/bolted between the little open box that houses the chassis mount (which on mine will be boxed in) and the chassis, and then a second tube from the centre of the 1st tube and bolts onto the suspension tower.


In a front-end crash, I'd hope that the point of weakness would be the centrepoint of the 1st tube, and it would fold there (well away from the driver's feet). I could even make the 1st tube out of thinner walled tube to ensure that that's the part that deforms. If it works as planned, it should actually make the whole thing a bit safer as it'd essentially be and additional crumple zone


Ideally I'd like to build a mockup and test it in a press, or model it in software, but I have the facilities for neither...


Ideas? Criticisms?post-2681-0-61756000-1463564901_thumb.png

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All you need is a spare spit and a decent brick wall.

But seriously, I wonder if the brace on the second design might make it more likely to remain straight in a crash and punch thru the bulkhead


What about a L or U shaped brace. Might add enough stiffness but collapse better under impact. Or design one with thin tubing...stiff under normal load but the slight bend might collapse it in the event of a prang.



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Problem as I see it is that there is not enough strength in the bulkhead to make it worth linking to it.  That front outer corner of the tub is pretty insubstantial and crushes easily in an accident.  What might work, giving strength and some crash protection to the drivers feet would be to put a vertical in each corner, above the outer body mounts and picking up on them.  Then run a beam between them above the tunnel and link back into the A pillars.  You might then have something worth bracing the suspension towers to.



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Not sure if I agree with your "point of flex" in the diagram even when rusty its fairly heavy chassis box section at that point, there's lots of other places that flex a lot more!.  The racing cages extended to the front towers as far as I'm aware are to stiffen the towers as they do wobble and flex more than I'd like.   I had considered a brace from the rear of the turret down into the corner where the chassis meets the front outrigger, its a very strong point that would be good to brace the turret from and would also feed any load into the chassis in the case of frontal impact.



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Ideally I'd like to build a mockup and test it in a press, or model it in software, but I have the facilities for neither...




Have you thought about trying something like Fusion 360 from Autodesk?  It can do "load analysis" and is free to "makers".

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An article in the TSSC Courier many years ago, by John Thomason, related the research done at a university engineering department on a Spitfire chassis.   In classic style, they fixed the chassis at the rear, twisetd it by weighting one side at the front and measured the twist along the length.    The part of the chassis that  showed the least stiffness by far was the rearwards part of the central spine, where it is narrowest.  

A criticism of this work is that the chassis should not be considered in isolation, and that the body contributes to the total stiffness, but it's a valuable and often unknown piece of research.   If you have access to the Courier archive - it's available on a CD for very little - the title is "Twisted!"   I regret that I can't extract a copy of the relevant picture from my scan


The mod you were considering has been used in the past, but only in conjunction with a full roll cage, so that the strut to the front suspension turret can carry stresses back into that.  As Nick says, the bulkhead itself, especially the entirely flat panel in front of your feet, has very little stiffness, or strength.


esexfi's beatifully done strut, that connects the turret to the front outrigger will, I fear, only act as a pivot.     The inwards stress on the turret is taken by the engine, so it tends to move upwards and backwards, which that strut can do little to control.




PS This subject, and the article, have been mentioned here before - search for "twisted", and there was an online copy iof the article that has since disappeared.

PM me and I'll send you a copy.  J


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Hi Simon

MOT tomorrow...at least it made it there this arvo.

Been contemplating over an MOT pint and at the risk of sounding like an old fart is there an economic and functional limit to how much one can retro engineer old motors short of turning them into something they were never meant to be.

Or do I just lack ambition;-)

Having said that you could weld a cage to the chassis then fit Ali/grp panels on top.

Actually maybe you could butcher a tub to bolt on to that....hmmmmmmm

If mine fails the MOT I might butcher it.

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Is that related to the work done in this article?



They talk about torsional stiffness and weld in a plate to improve the situation.  With a swing spring I'm not certain how much it would really help my car, but I dream about incorporating it if I ever get around to taking the body off mine.

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Well I was off fixing the moderns and all this discussion has passed me by!


@Richbike: I did wonder whether I might be able to pick up a jank chassis and body to test it. I've got a mate working for the MoD who's got access to one of those rocket-sled-on-rails things. A couple of pints and they might strap my rig to it :)


Did it pass its MoT? I tend to look down on cars whose chassis have been replaced with tube-frames with the bodywork hung on top. It's utterly unfair, but for some reason it persists...


Turning classic cars into things they were never meant to be is my raison d'etre. My latest hairbrained scheme involves an MGB GT I got of eBay for 99p, the Rover V8 I got with Spit no.2, the Jag IRS from my XJ40 that got hit by a tree, the disco transfer case and Subaru R160 I have lying around and some big knobbly offroad tyres. It'll be an MG Baja! (eventually).


@Nick Jones: that's a great idea actually. I was thinking how I can reinforce the bulkhead area without taking out all the space for my feet and pedals. If I can fit that kind of structure in then I'll do that.


If not, then the plan was to re-make the little chassis mount out of 3mm steel (and extend it upwards and outwards to make it a stronger anchor) and then weld the tube to that.


@Pomwah: I had a discussion about that on another forum but the conclusion we reached is that it's such a complicated structure and subtle variations in where I actually ended up welding things would mean that any modelling would only bear a passing resemblance to reality.


@JohnD: It's that article that got me thinking properly about where the chassis & body combo would actually have flex and how to combat it (there's a great diagram in it that divides the chassis up into sections and gives you a stiffness value for it).


One of the outcomes of that study was that a good idea was to weld a t-shirt plate similar to TRs over the rear neck of the chassis to stiffen it there. My thoughts is that that's precisely the area that the body has a ton of strength what with the rear 'seat' area being one big box and the axle tunnel being over the top. Moreso now that I've got my little roll hoop and the fact that it'll be welded directly to the body.


So do you think my design, coupled with a suitably reinforced bulkhead area, would do a better job of controlling movement of the suspension turrets?


@esxefi: I'd have though that that brace would still result in an area of flex as the brace reaches the chassis.


I really like the design of the door bars though. I'd thought about doing a full cage on mine but balked at the effort involved after making 4 iterations of my roll hoop just to get one that fits worth a damn. Definitely a steep learning curve.


How easy is it to get in and out with it there?


@Egret: That's a brilliant thread there, although the study John was talking about pre-dates it. I thought about doing a similar modification on mine (might still do it actually, currently undecided). The turbine guys had the luxury of having a relocated propshaft so they didn't need to worry so much about chassis clearance.


In order to make it clear the propshaft above and the exhaust below you'd probably have to make it so that it follows the upper and lower line described by the centre box section.


You'd be looking at a sort of wedge shape going back in the chassis, with an arch on the underside to clear the exhaust and a sloping upper section to clear the propshaft.

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@Nick Jones: I'd thought before that what I'll be doing with the Spit would go down a treat on Heralds/Vitesses (Vitessi) as well.


I've always thought that if I started my own Triumph tuning business (unlikely) I'd have a unibody Herald estate with an EFI TR7 slant 4.


Too many project ideas for my own good I think...

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For sure Heralds and Vitesses could use some "structural enhancement".  Especially the convertibles.  The tub has almost no structural worth at all when it comes to torsion and precious little in any other mode either.  Having run a (fairly rusty at the time) Herald saloon with and without a roof it was truely remarkable how much difference the roof made, especially given the the roof is a pretty floppy object itself.


That same area of the chassis would really benefit from some kind of plate or cross-member, but the need to thread a propshaft through there does complicate things badly.


I've also thought about adding a substantial cross-member right across the tub above the rear outriggers - which interferes less with propshaft but much more with the handbrake linkages.  I've also though about joining front and rear sections of the tub with a proper sill structure, but want to keep the chassis and outriggers looking fairly "factory" as the authorities are getting increasingly difficult about stuff like this.


What I do know is that if I park my car or uneven ground or with one wheel on a kerb, door fit becomes strange..... and this is a good rot-free one.  And the cobbled hairpins in the Slovenian mountains nearly dismantled it entirely......


You can do alot better than a Triumph slant four btw ...........



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No, JT never told us where the work he reported was done.

That thread - a single post and couple of pics, really - doesn't go into anything like the detail of his article.


Of course, and this may not help most people, a properly installed roll cage makes things a LOT stiffer.


Edited by JohnD
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