Q.
When welding butt welds on floor pans, what size MIG wire should I use, and at what voltage setting on the welder?
A.
When MIG welding automotive sheet metal, thin wire is better. Most often .023 solid wire is used with a 25/75 (argon/CO2) shielding gas. Some welders can not use .023 wire, so .030 wire can also be used instead but watch for burn through. The voltage setting is different on every welder and welding condition, just make certain you are getting good weld penetration without burning through. 
Learning a lot
I am building a 53 Ford F100 with 302 engine. I was planing on running straight pipe. Will the engine run better with back pressure from a muffler?
Dear Gordon,
Thank you for your patience while I got the expert response, here is what Mark has to say:
Most street engines will run better with a little back pressure, even if it’s accomplished with pipe diameter.
Although I am certain your neighbors and local law enforcement would appreciate some sort of muffler.
Performance cars often sound better with a performance muffler that generates a rumble rather than the raspy tone of open exhaust.
You can always install a set of electric cut-outs for those times you need to make a little more noise.
Wrench Safe,
Mark
Classic Car Restoration
I am welding floor pans etc .on my 1966 tbird and have the harbour freight ultimate 200 welder …brand new … cool welder … what settings do you recommend …. and yes btw i am a paid member let me know thks
i bought it to work on my project car
Scott Steele
Hi Scott,
Thank you for your patience, here is the response from the experts:
The HF Unlimited 200 welder is a great multi-process welder for the money, but we have not had a chance to use one yet.
We have a couple good friends that do have them and each claim the settings listed under the cabinet door are close but they also said they used a little more heat and a little more wire speed than the listed settings. Neither of them liked the way it welded using 110-volt, but claimed with a little practice they could lay down a nice bead.
They also prefer using (CO2/Argon Blend) gas with this welder as opposed to flux-core wire as it gave them smoother and cleaner welds with less spatter.
For TIG welding you should use a 100% Argon gas.
Because we do not have first-hand experience with this welder we can not make a solid settings recommendations, but suggest you use the manufacturers listed settings under the side cover as a starting point. When welding sheet metal I prefer .023-.025 wire size.
Wrench Safe, Mark
Classic Car Restoration Club
When welding with a MIG set up I have welded a lot of sheetmetal. Here is trick I have been using for most of my 50 years as a welder. I use this when I am welding sheetmetal that is one thickness and then go’s to a thinner thickness. You don’t have to stop and change your settings. If you are holding the cup of the MIG say a quarter of an inch from the metal being welded. If you pull the cup farther away say half of a inch so you have a longer wire that will make the welder run colder. It is like turning the welding machine down.
can you weld without a gas shield and if so what size wire
Hello,
You can use a flux-core wire to weld without a shielding gas supply. flux-core is exactly as it sounds – wire with flux in the middle. Consult your welding supply house when selecting wire, as some flux-core wires also require a shielding gas too. As the wire melts it burns the flux creating a gas cloud around the arc to shield the arc. It creates a lot more splatter and heat and I do not recommend use flux-core for welding sheet metal. Flux-core wire is available in sizes to fit most hobby welders, so select a wire size that is compatible with your welder and the material you intend to weld.
Hope this helps!
Mark
Classic Car Restoration Club Video Membership