Too Anal? Fed tubing question

When I worked for G&B Fabricators we MIG welded Chrome Molly all the time. We used 7018 wire if that's any help.

But yes the Zman is correct on this one.

And there have many a chassis MIG welded and or stick welded that have been NHRA certified. Its not the process it is the quality of the weld they are looking for.

(OK edit damnit. I guess the rule book specifies TIG for chrome molly. Sorry about that its a rule that I evidently haven't kept up with.)

Personally unless you are winning races by .000X you won't gain enough by using chrome molly to make it worth the time and effort. I would use mild steel DOM. At least that's what I'm using on the Altered. Just don't over engineer it, IE build it heavier that it needs to be. If you have to spend the extra money you would have spent on the molly, spend it on a set of plans. Probably not a bad idea either way unless you have been at it awhile.

 

There are some articles out there that John Force is no longer useing chrome moly tubing after his last crash they found that it got britle when welded.

 

When I was younger they used to say if it isn't stress relieved after welding walk away from it. We used to shot peen all the stuff we built at G&B.

 

I found the article and it was talking about useing Heat treated chrome moly tubing.

 

Normalized (condition N) is what should be used in structual applications. This is a annealing type process that is sometimes refered to as 'aircraft grade' and makes the steel less brittle. Non-normalized is o.k. for high pressure and non-structual apps. but is more brittle.

 

Damn, I didn't want to open up another tig vs mig can o worms. The frame WILL be built by ME. Mig and mild steel only. Don't have access to a tig, have tigged but not a structural member or on moly. Built my roadster frame thats been on the road for years. Just want to learn ALL I can before I push the loud pedal. Thank you all for the info.
You guys up for another can o worms? How bout DOM vs ERW. I know ERW is cheaper, buuuuuuut, can the cheap stuff with a heavier wall compare to DOM. Ready..........GO!!!!
Danny.....what coupe? Not A.D.D. but F.E.D.itis.


Just read an old thread,who says you can't teach an old dumbass new tricks. Sounds like ERW would work at .134 wall!!!!!!

 

I like DOM over ERW al little more expensive but stronger.

 

I really hate to be OT here, but I dont wanna look like whats his face earlier in the thread. I never introduced myself...is it ever too late??

 

almost every form of professional auto racing except NHRA mandates DOM over ERW.

however if your trying to save a few dollars in materials, a lot of desert race guys use ERW in non critical areas with no bends.

personally i dont see the point... DOM is a higher grade(more consistant) material than ERW.... and thats the added cost from the extra manufacturing steps.

my steel rack just got filled with 500' of 1.625 DOM for an upcoming project... so that tells you where my personal preference is.

 

Any one?
Whats beter to drive 140"or 200" FED because i like to build one i already got the plan of Dave Tutlle

 

Here is your answer Mr. Slingshot. Lippy

 

If I remember correctly, you used to have to get certified by the NHRA to fabricate and TIG weld NHRA sanctioned chassis, I believe that you were given a cert. number and applied it to the chassis itself. There was also only a certain amount of times that this chassis could be punished down the drag strip before it was considered too stressed and bumped, I believe this may have been for 8.90 and faster classes and my book is an '82 rules book. There is no real physical way of looking at a weld and knowing exactly how it was done if it was done by a pro welder and a pro welder can damn near use a bic lighter to weld and have it look nice, you can x ray or put the weld under an electron microscope, but you have to carve the car up for that, so thats out. I'll have to see if thats still the case with the certified fabricator ruling. I know for a fact that my buddy bought a car with a pro built moly chassis, it had a cert number by nhra, that cars tag expired and it was bumped. My buddy put a huge engine in it made a few passes and was told he could not run any more due to the speed being excessive for the tags. You could run it but not under a 10. This was a while ago and things do change though.

 

this topic comes up every once in a while. First NHRA has a rule book that is very specific about welding,tubing types, & material strengths & thickness. Get a rule book & if you have questions there are numbers you can call for tech clarification. As to tubing - DOM is mandrel drawn & the thickness variation is minimal & ( it should) maintain its specified wall. By the way .134wall is refered to as 10gauge & 120 wall or 1/8th is 11 gauge. Tube sonic wall tests by NHRA inspectors is done on straight places not in the bend radius. If you are serious about building your own chassis contact the SFI foundation & get the specs for what you want to build so you wont be sorry later. The NHRA rule book although specific in most cases most certification is done using the SFI spec for your car. Issue of cert tags is done by a NHRA inspector & chssis build tags are attached to the frame by the builder. PLEASE GET A RULE BOOK. Bill Wallace RACE CARS CLOVERDALE IN

 

There is always so much confusion about FED chassis...If you are going to build a
car that will run quicker than 10 flat then it must be certified (assuming you want to
run at NHRA events) and the cert inspection is done per one of the SFI specifications.
SFI spec 2.6 is for FED 7.50 seconds and slower. 2.6 will take you to 6 flat and 2.2
is for top fuel FEDs and has no limit. SFI certs concern the motorplate back. They
provide about 6 different designs to choose from.

First paragraph of Basic construction practices calls out required materials and the
second indicates accepted joint welding process.

Get the spec you need...build to meet the spec...have NHRA inspector check & tag
it. Now you can run anywhere. The sportsman tag (like the 7.50) is good for 3 years
at which time you simply need to have it reinspected.

The NHRA rulebook is available online these days. Might have to be a member. It has
all the general regulations and tells what all the other safety related stuff is depending on how quick you plan to run. It also mentions how to contact SFI.
Good luck,
MB

 

To access the NHRA rule book via their web site you do have to be a member but a limited number of print versions are still available from them. Phone # is 626 914 4761.
The SFI spec number for slower than 6.0 cars is actually 2.4. I agree that it is worth buying the spec package from SFI if you plan to build a car--It works out to $38 by the time that they mail it to you. Pick the performance level that you want and get the appropriate specs.

Roo

 

Oops...typo there...my bad.