chassis modifications

[Steve]

Hello all

I have recently purchased a GTD in bits from another club member. As my gtd chassis, is currently bare, I have the opportunity of making modifications to it before I commence cladding

So far from reading the advice and comments in the forum I have gleaned that the following are useful

raise steering rack height 7/16
provide support for 5 point harness across rear bulkhead
relocate rear upper wishbone mount up 80mm
provide support in fuel tank pods to strengthen for side impact
brace "hoop" to rear to reduce flex and stiffen roll cage
increase footwell depth

Are there any other mods I should consider whilst the angle grinder and welder are out??
does anyone have good images of these\mods on their chassis that I can use as a guide?

engine lowering. lots of discussion on the merits of lowering the engine mounts, but by how much before transmission angles, and road clearance became a major issue. This has a r21, and will be mainly road use, with perhaps a ttle track day time..........

thanks for your help

Steve

 

[Brett James-McCall]

Steve,
You need to search for Paul Bearman here on the forum and contact him. If not, I'll see if I can for you and see if he is OK to pass on his details.

Paul did some CAE analysis work on the chassis and came up with some other areas that can be improved, especially if you have a bare chassis. It was something like:

1. Weld in 1" tube across the middle section where the chassis turns in for the wheel arch
2. If you are putting a rod change in you can also weld in some tube accross the dog leg and also complete the triangulation on that side

I personally would also weld a plate in at the front if you were looking to put floor mounted pedals in, as retro fitting mine has been a pain.

I have some pics of what I did in the sills if you mail me.

Just out of interest, did you buy Simon's chassis?

Brett

 

[Brett James-McCall]

relocate rear upper wishbone mount up 80mm

Steve,
Can you let me know where you got this from. I've never heard that, and 8cm seems a lot! Thanks

Brett

 

[Julian West]

Hi Steve,

interesting questions! With regard to raising the steering rack, there is an interesting discussion on bump steer here http://www.gt40s.com/forum/gt40-tech-chassis-brakes-tires-wheels/19449-bump-steer.html#post171446

With regard to changing the rear suspension geo (80mm sounds like alot!) check out http://www.gt40s.com/forum/gt40-tech-chassis-brakes-tires-wheels/16176-gtd-rear-suspention-mod.html

Re bracing the roll 'hoop' I fabricated a full cage out of 50mm CDS & took the roll bar rear stays to the top damper mounts. this was *alot* of work but will increase the safety as well as adding some stiffness to the chassis.

I've attatched a picture of the mods I made to my chassis. If I were to do it again, i would leave a bit more room around the rear of the gearbox.

Hope this helps.

 

[Steve]

Brett, I think I may have misread the post, but did read howard jones thread on relocating the rear chassis pick up point for the top of the hob - I thought I read 80mm but must have misread that part.
Very useful images and ideas......keep them coming!!!. What I want to do is try to incorporate all the best ideas into chassis mods before I commence rebuilding the car, so need to understand what has really worked, what was tried, and didnt work. You chaps have so much experience that it would be stupid of me not to ask

I know much of this is in prior posts, but this sort of development is often undertaken with no info on forums unless someone asks.

 

[Steve]

brett
thanks for the heads up on pauls work, I will try to pm him.

yes simons car...........an old but completely unmolested and unused GTD......
having built a few cobras before I am not a novice, and fancied something a little more challenging, and as I have good access to a fabrication workshop, want to get the chassis work done right

 

[Steve]

Julian, thanks for your post, useful information. I think I saw a post of yours hwere you posted an image of a GTD with a similair mod, using the top of the suspension towers as a brace point for the roll bar. inevitably will stiffen the chassis considerably.

It would be easy to add lots of metal to stiffen, guess the trick is to stiffen the chassis without adding much weight, in order to gain torsional rigidity,

My other car is a 470hp ls powered cob replica, which has a good chassis, tubular and light, car before that was a 450hp cob with a twisty chassis heavy and ladder like, night and day driving experience............

 

[Steve]

Brett - found this in the thread (post 9) regarding the height raise on the rear location. Actually refers to 1.5 inch. rise in the mount, not 80mm as I mentioned (really should learn imperial measurements conversions better than that!)

http://www.gt40s.com/forum/gt40-tech-chassis-brakes-tires-wheels/16176-gtd-rear-suspention-mod.html

 

[Brett James-McCall]

Steve,
Where are you based?

Brett

 

[Brett James-McCall]

Also ref: rear mods, you should look at Mick Sollis's rear frame. Simon has one and may have shown you? It may save some time doing it yourself, especially as it already allows for the Renault box to be lowered etc.

I am going to have a look an d measure up against Simon's once I get my Audi box back.

Brett

 

[Steve]

based in midlands, but get everywhere

 

[Howard Jones]

Have a read of Derek Bells web page. Lots of good GTD suspension stuff there. Index Suspension stuff is in articles.

 

[John Lowe]

Steve

I would give Frank Catt a call at Wealden Engineering wealdenengineer.co.uk. 01323 843 839. He has been modifying GTDs for the serious driving fraternity for some time. Very approachable and helpfull guy.

Best luck - John