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I'm adding a trinagulated brace inside each of the front guards of my 75 and plan to seam weld the major box sections in the engine bay.
My intentions are to use coil over style additional springs in conjunction with the standard torsion bars like RSR set up.
Now, is it worth while making a brace that go's behind the plenum chamber (V6) and links the 4 major box sections together?
Can anybody sujest any other chassis stiffening methods that ould be worthwhile? Bare in mind that it's a road car, so a welded in steel cage isn't an option

I wouldn't do that on a road car! If you have a minor collision on the front end, it's possible you have to write off the entire car due to lack of crumple zones. And if you retain the torsion bars, there's no need to stiffen the front end.

Track car: abslotely, road car: absolutely NOT!

Dennis wrote:I wouldn't do that on a road car! If you have a minor collision on the front end, it's possible you have to write off the entire car due to lack of crumple zones. And if you retain the torsion bars, there's no need to stiffen the front end.

Track car: abslotely, road car: absolutely NOT!

To late for the in guard bracing.
I do see what you're saying but I can't imagine the old Alfa is full of crumple zone technology.
I've also read numerous coments about coil overs forcing the chassis alignment out over time, even when retaining torsion bars.
1 of my favourite roads is feindishly bumpy and so the stiffened chassis seems like a good idea, especially at the front where it needs it the most.

what do you mean by in-gaurd bracing?

I've had coilovers (with torsion bars) on all my transaxles and never found any problem. Dutch roads are pretty good, but I do drive them hard. The only thing I've found is that the top mount of the coilover (no torsion bars) was bulged when I hit a very high curb straight on (both front wheels simultanous) and at serious speed (120 km/h) on a track.

What I meant by crumple zones, if you have a cross brace and you hit something, the opposite shock tower is bent outwards. That's when you write the car off... If you don't have a cross brace, most of the time it's repairable. The front of the engine bay (where the air filter box and washerbottle are in a GTV) is a pretty good crumple zone

Dennis wrote: And if you retain the torsion bars, there's no need to stiffen the front end.

Surely you don't mean that you don't load the LCA because you have torsion bars?
All the vertical load is transferred into the body at the LCA fixing points in the body and all road load will transfer the same route while driving.

I should have said stiffen the shocktower (with a crossbrace or seamwelding). Yoa're right.

It's a lot of work to do the seamwelding properly and totally useless on a roadcar IMHO.

Sorry for my ignorance but what is LCA

darryl longley wrote:Sorry for my ignorance but what is LCA

Lower Control Arm.
Pic of my inner guard bracing.

faaark me, never seen that before. Is that...meccanno?

If you are going to feed a lot of load into the top shock mount, I'd be trying to tie it back to something - maybe the firewall with support from a cross brace behind it (in the cabin) - as well as stitching up around the rad upper and lower (as that's all there is keeping the inner guards apart).

GTV27 wrote:faaark me, never seen that before. Is that...meccanno?

Nah, it's commonly referred to as "square steel tubing" and has been "drilled" to aid in "lightness". Or as the technically more sophisticated might say "reduce weight". .
I've seen this sort of bracing done on an Australian built/modified Skyline GTR that was intended to be used as a tarmac rally car (Targa Tas). Even tho it had a welded in cage that went into the engine bay, they still added similar bracing. It's also become quite popular for the Japanese fraternity like the MX5s and Silvias. I know that doesn't mean it'll work, but it does look like it will to me. Unfortunately I don't have any real means of testing its effectiveness.

GTV27 wrote:If you are going to feed a lot of load into the top shock mount, I'd be trying to tie it back to something - maybe the firewall with support from a cross brace behind it (in the cabin) - as well as stitching up around the rad upper and lower (as that's all there is keeping the inner guards apart).

There wont be a lot of load, max 200lb/in springs. Unless I decide to go stand alone coil overs so maybe 350lb/in springs.
The idea is to get the strong areas of the chassis to take some extra load. If the SZs can have coil overs with only bonding (glue) to help hold the chassis together and no exstra structural bracing, then I'm sure I can safely use additional coil overs and stiffen the chassis with come exstra steel and some strategic welding.

Are those cars you refer to McPhersome?

Mats wrote:Are those cars you refer to McPhersome?

The Nissan Silvia's are. The GTR is unequal length wishbone, tho it does have a big strut like tower where the spring lives. I know the MX5 is whishbone but couldn't tell you how the spring is orientated.
Incedentally. the Nismo built R34 GTRs used carbonfibre reinforcements that were the shape of the inner guard/firewall/suspension pick up points and they were bonded to the chassis inside the engine bay.

Ok some comments on your bracing.

First the lightening is not so good idea on the top&bottom sections of the tube.
The shocks (&coil-over springs) introduce a vertical load.
This is translated in a bending force in the blue line and the material which has to work against them are the top and bottom of the square tube.
The side you could lighten as they only function as spacer between the bottom and top of the tube.

What makes stiffness is the distance between the top and bottom wall of the tube. So more distance more stiffness. The blue line is an Alfa Romeo tube to get the stiffness in the shock towers.

If you had placed you tubing underneath the the ar tube (bleu line) it would work more effectively.
(Larger distance between bottom and top material)

The yellow line is unnecessary material.
If I push vertically against blue, red will become pull tube on. No way it ever wants to bend, so my opinion ... yellow is obsolete.

An X-brace above the engine is ok, it will help minimizing the banana shaping of you car during cornering, but how about the bottom... at the lower a-arm where the forces are introduces during cornering?

Resume do you really need all this for a road car? NO!

Cheers to all for there input so far.
Maurizio, I did wonder about the bennefit of the small (yellow) piece, but figures that it doesn't weigh much so it won't hurt.
The lightening was done after seing that holes drilled like that don't compromise bending strength by much. The tube is 30mm square, 2mm thick and the holes are 13mm spaced 20mm appart.

A brace undeneath has been considered, but it would have to be made from some pretty small stuff. Maybe 15mm square tube would suffice, even tho the car isn't as low as it use to be.

As for it's worth on a road car. Well there is no such thing as a chassis that is to ridgid, even for a road car. The engine is coming out anyway, so I see it as an opportunity to put some effort in where AR didn't.

I know that the RSR system can supposedly be used without additional bracing and maybe I am wasting my time. But I've never thought to myself when driving an Alfa "Gee, this car has a nice solid feeling chassis that should be able to handle massive spring rates. "

here some bracing of the lower parts...