Ok so I have read a bit on here about " seam welding. But how far do you go i:e do you do every seam on the car or just the chassis and engine bay. Really like the way that baz said to do it by drilling more spot welds so you still have the factory look.

Thanks for the help.

There are specific areas you need to do. Are you planning on doing it yourself?
My suggestion is to provide your location and perhaps one of the members can help you out by visiting and suggesting where you should have the work done etc.

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1972 Datsun 1600, S14 SR20DET Engineered (204rwkW @ 17psi.)
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#SR20Datsun @SR20Datsun

Yes mate I will be doing most of the work my self. I am able to use a mig or tig welder properly. Just need a little guidence as to how far I need to go. I may be doing a little track work with the car and don't want the paint cracking as with some other people's 1600 I know.

You've gotta figure out what is most important in the shell for what you're doing, obviously the engine bay around the strut towers is pretty important and also pretty easy to access but that definitely isn't all you can benefit from. There are cars around that have every joint strengthened up with weld, my friend has an old sports sedan built by a sh*t-hot auto engineer back in the 70s and every join is fully seam welded.

The most common technique would be to stitch weld everything that you think is important that you have access to.

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1973 H230 Wagon, 'ILL-260'
1975 911S Targa
1978 Torana Hatch
1999 GXE10

Be very careful doing it, and how much you do it.

Most full steel/uni-body (steel mono-construction) race cars are no longer fully seem welded. It was common practice back-in-the-day, BUT, you won't find too many nowdays.
It stopped being common place when it was realised that you can very easily distort the body/chassis during welding, regardless of weld procedure, unless you have access to some kind of jig or chassis bench to hold the car some-what in alignment during welding and then stress relieve after welding.
Once welded, it also makes it very, very difficult to repair the car if it happens to have an accident or even if you find that the alignment of suspension pick-up points is out after welding, you will have a real hard time trying to use a chassis bench to pull to correct.
Also, having been & done it myself, it is easy to burn a couple of rolls of MIG wire into a shell. Stop & think..... each roll of wire is 15kgs - you can easily add 30+kgs of (arguably) un-neccesary weight. And if you want to use the car for competition and be competitive, you don't want to do that.

Cage design & bolt in braces can be just as effective (often better).

By all means weld the weak points, but think long & hard before just jumping in gun-ho & start melting wire.

Great. Mig is the go all the way. My recommendation is to use 0.8mm wire. The stitch should be approx 1" long about 3-5" apart depending on where it is and where the spot welds are. Make sure you stitch and don't weld the whole thing in one long continuous weld. I actually used a stitch for the stitch if that makes sense. You 'pulse' the stitch with the welder. So spot, spot spot etc. until you make a full 1" long. Puts less heat into the area and you get less distortion with just as much penetration if you set it up alright.
Tig will put too much heat into the chassis, same as Oxy. I'm sure you're already aware of this though, so no issues there.

My suggestion is as follows:
1. Pretty much all spot welded panels/box sections/chassis rails welded to the underside of the car. These are prone to holding water and rusting the spot welds out, so you loose strength.
2. The side rails box sections where the struts are / front guards fit over. If you see my build you will also notice I have added a strengthening section here to triangulate too. I ended up putting extra spot welds on these box sections too.
3. As suggested previously, the struts towers in general require welding around the critical areas (such as the top and down the sides)
4. Front chassis rails to the associated connecting sheet metal. As states previously only weld the back 3/4 and leave the front 1/4 not welded just in case an accident does occur and you want to get it repaired. Same goes for all the rear chassis rail/box section/panel sections.
5. The castor rod mounts.
6. Inside the car, the triangular brace on the back seat area and associated panels around here (flexing a bit doesn't help for the cracks you fondly recall)
7. Shock towers in the rear of the boot (depends on if you are going coil overs how much you will go). Pay particular attention to the areas around the spring mounts too.
8. Folded sheet metal seat support member which goes from the sills to the gearbox tunnel across the floor. I welded in extra plates per CAMS requirements (70x40mm 3mm thick) into the floor for the seat mounts too.
9. Seam weld the gearbox trans tunnel to the firewall (the join that is factory welded, but needs some extra here)
10. Around the C-pillar (try not to get much heat into it to mind the lead wiping)
(that's all I can think of at the moment)

Be careful of porosity. Making sure the whole area has been cleaned makes life a hell of a lot easier. Sand blast (using garnet) is the best way, but wire brush is probably the quickest and easiest.

There are a few threads on here discussing the benefits and negatives of seam welding and whether it's worth it (as stated above).
http://www.ozdat.com/forum/viewtopic.ph ... 0&start=15
http://www.ozdat.com/forum/viewtopic.php?f=37&t=12549
You will see my responses, and I stick by them. 40 year old spot welds are getting old, despite the fact that our cars perform reasonably well in torsion and beam tests.

This thread here:
http://ozdat.com/forum/viewtopic.php?t= ... engthening
is a ball tearer with some good input from a few members on here. Some of these mods are probably just as good as seam welding, but just remember that when adding reinforcement you are making something stronger than something else which may fail/bend/tear etc.

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1972 Datsun 1600, S14 SR20DET Engineered (204rwkW @ 17psi.)
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#SR20Datsun @SR20Datsun