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Chassis rail extensions

Started by _greenmachine215_ , May 10 2008 10:43 PM

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45 replies to this topic

#1 _greenmachine215_

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Posted 10 May 2008 - 10:43 PM

Hey fella's,

Ive been thinking of ways to strenghten up the chassis of my hatch, Im putting in an injected 6.3L so that means mountains of tourqe which means twisting chassis

I have thought of purchasing a chassis bolt on kit from castlemaine rod shop,

But also have seen a few forum members doing the chassis rail extension mod,

I just want to know if anyone knows the legallity's of this, It means chopping out some floor pan to fit the extension, would this be something that an engineer would need to do for it to be legal on the street, Because its not something you can just change back for roadworthy,

Heres a couple of pics i stole from 355LX.

Any information would be appreciated

Cheers :spoton:

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#2 _moot_

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Posted 11 May 2008 - 08:12 AM

mine are engineered in nsw.

Edited by moot, 11 May 2008 - 08:13 AM.

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#3 Toranavista

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Posted 11 May 2008 - 09:14 AM

Nice job. What specs for the RHS did you use?

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#4 LS1LX

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Posted 11 May 2008 - 11:55 AM

I wouldnt bother unless your pushing 500+ HP or a big block full of torque.

A 383 isnt going to make that much TQ that you will twist the thing. You will need slicks and a 5000rpm converter before you start twisting the chassis.

On the street with street tyres you won't twist a thing.

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#5 tinkers

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Posted 11 May 2008 - 12:37 PM

Original question about the legallity's of doing it.

As a guess I would be asking an engineer about it.

edited since I cant read either

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#6 TerrA LX

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Posted 11 May 2008 - 02:32 PM

They are good chassis and suspension strengtheners but I do not think they will stop torsional twist without a cage or at least triangulated.

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#7 _the gts_

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Posted 12 May 2008 - 03:30 AM

I dont think it matters where you are, they need to be engineered.

They are ok in WA with engineering. my engineer didnt even look twice at them.
mine are i think 50x75x2.5.
there is a percentage rule with differing thickness when joining two sections of structural steel. I cant remember what it is though.

eg. you would not be allowed to butt weld 5mm wall thickness material to 2mm.

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#8 _HatchmanSS76_

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Posted 13 May 2008 - 01:55 PM

Extensions would require engineers cert.
The Rod shop kit comes with a certificate so if it ever got questioned. Bounus with the rod shop kit is no cutting of the floor too.
As for if it's necessary? Short answer, YES. Not sure if you could see mine twisting when we used to run it down the strip before I had the kit installed but I could definately feel it from in the car. The kit reduced that by heaps to where it wasn't noticable in the car any more. That includes before I started using slicks.

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#9 _moot_

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Posted 13 May 2008 - 01:58 PM

the rod shop one hangs under the car and looks ugly. do it properly

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#10 _youngy_11_

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Posted 13 May 2008 - 05:12 PM

Yeah I agree, I would definately put them in.

I got mine installed just incase in the future a big Hp motor is fitted but also mainly for stiffeneing the chassi, I have been told that the A9X race cars did this as well. Can someone clarify?

I think the guy from the drop tank mob in victoria?? I forget their name, they are well known

Cheers

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#11 ls2lxhatch

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Posted 13 May 2008 - 07:36 PM

I fail to see how the extensions could have any significant effect on the bending or torsional strength of the chassis. It would appear that the purpose of the extension is to reinforce the lower trailing arm mount.

The Rod Shop chassis kit reinforces the lower trailing arm mount bolt and then extends the length of the chassis. It is then cross braced by the CRS gearbox crossmember. The result is an increase in bending and torsional strength of the chassis and a reinforced lower trailing arm mount. It may be ugly but it is effective.

This is an extract from the Transport Industry Consultants engineering report on the CRS LC-LJ chassis kit dated 9 Oct 1989. I have not been able to obtain a report for the LH-UC kit but the design is similar.

Comparative tests were performed on the standard and reinforced vehicles. It was found that the bending strength of the vehicle is increased by approximately 30%. whilst the torsional stiffness in increased by approximately 40%.

Edited by ls2lxhatch, 13 May 2008 - 07:43 PM.

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#12 _scottya!_

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Posted 13 May 2008 - 07:46 PM

I'm of the opinion that the only purpose of the chasis extensions are only to add support to the bottom trailing arm mount as well.

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#13 _LS3torana_

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Posted 02 July 2009 - 07:07 PM

in my opinion, inserting fabricated chassis section to join your front and rear sub-chassis will reduce torsional twist as it will rigid up each side of the vehicle by not allowing a twist point between the two. hense reducing a twisting effect. The ultimate to reduce chassis twisting is two install a full cage, and unfortunatly the boys in blue arnt a fan of that!

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#14 _Squarepants_

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Posted 02 July 2009 - 07:22 PM

6 in a row!!! That's gotta be a new record!!! :tease:

Mod Edit: Sorry mate, I removed the five preceding posts Grant..

I reckon Axistr's chassis extentions would be the neatest job I've seen. It looks factory and I reckon would definately make a difference to body strength.

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#15 axistr

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Posted 02 June 2010 - 06:53 PM

Thanks Squarepants, I profiled them to the floor so there is no intrusion into the cars cabin, when I stonguard and painted them they look factory but best off all the strength and handeling was improved out of site, I dont like CRS design heavy and still has flex. I am punching 513hp and just over 500ft pounds of torque on 10" sticky tyres and eaton L.S.D

torana 048.JPG 1.56MB 158 downloads

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#16 Heath

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Posted 02 June 2010 - 07:01 PM

^ Did you get any better photos than that? I can't see shit lol

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#17 GML-31

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Posted 02 June 2010 - 07:20 PM

man Heath I only have 1 eye and I can see it...

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#18 rodomo

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Posted 02 June 2010 - 07:34 PM

Betterer?

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torana 048.JPG 50.73K 89 downloads

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#19 Heath

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Posted 02 June 2010 - 07:45 PM

Nah but I saved it and brightened it up in photoshop, now I see it well

I'm using a CRT on a kinda dark setting, and you guys are probably using LCD's

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#20 _nial8r_

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Posted 02 June 2010 - 08:39 PM

post a pic Heath so i can see it too Posted Image

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#21 Heath

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Posted 02 June 2010 - 09:38 PM

LOL

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#22 _niterida_

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Posted 02 June 2010 - 10:31 PM

Thanks Squarepants, I profiled them to the floor so there is no intrusion into the cars cabin, when I stonguard and painted them they look factory but best off all the strength and handeling was improved out of site, I dont like CRS design heavy and still has flex. I am punching 513hp and just over 500ft pounds of torque on 10" sticky tyres and eaton L.S.D

torana 048.JPG 1.56MB 158 downloads

Yeah that is the way I was planning on doing mine.

I may be wrong with this theory as I am not an engineer, but I think using the same method as factory will increase the twisting strength by using the floorpan as part of the structure. Cutting the floorpan and putting in a piece of RHS is relying more on just the RHS. I know this is still welded to the floor but the twisting location is now moved above the floor, rather than on the floor. Does that make sense ??

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#23 _nial8r_

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Posted 03 June 2010 - 09:12 AM

thx heath

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#24 ls2lxhatch

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Posted 03 June 2010 - 11:04 AM

How does extending the chassis rail make the rest of the chassis rail stronger?

If the factory chassis rail is flexing and twisting throughout its length then I can not see how adding a bit on the end will do anything other than make the lower control arm mount stronger.

Following the floor instead of going through the floor makes the sides of the extension so low that it is almost a flat plate for most of its length.