hey guys anyone have a tube chassis 3rd gen. im thinking of building one with chrome molly. ive looked at art morrison, ed quay, art, s&w, and some other cages and chassis. ive found chrome chassis at 2100. thats not too bad when a cage is 500-600. i wana see pics and any install pics would be great. i might just sell the spohn tq arm and panhard bar i have and go fast. i wana build it as a 10.5 tire car.

 

A complete tube chassis for 2100? Pray tell where did you find this because i want one as well and have trouble finding an actual web presence or shops that advertise doing the custom work.

 

You might as well just plan on using a full fiberglass one pc body like a Funny car does and use a pre-engineered chassis like Morrison.

3rd gen platform is a unibody. You will have to cut out the entire floorboad and start from there.

I have actually started this same thing with my Austin '67 Mimi Cooper, but it is much smaller and lighter to work around. I have braced everything and completely cut out the entire floorboad and plan to cut off the entire nose of the car next then use a fiberglass removable nose piece. (A major divorce- two years and going still- has put this project on the back burner unfortunately)

the body shell will be attached to the chassis and joined via brackets to the upper structure (body and cage tied together permanently). The suspension is completely custom and engineered.as I would also recommend for a 3rd gen project like this. Otherwise, just do not waste you time if you plan to keep the same factory pickup points. It takes alot of knowledge in vehicle dynamics to do correctly, as well as fabrication skills.

 

Dollar for dollar buying a used roller is A LOT cheaper than building a back-half car. If you truely want a 10.5 legal car, then you will need stock steel roof/rear quarters and the stock front suspension lay-out. If you intend on keeping up with the class and being legal, you will need a 25.2 CM cage. A properly done 25.2 will run you north of $5k, and that's just for the empty chassis/piping, no hardware.

With the current heads up scene in many areas being as it is, personally I would look towards building a 275 radial car.

I personally do not believe in CM, therefore my car is MS and will only certify to the 25.5 specs.

 

What's wrong with CM?

 

^ CM is not any lighter than MS. When building a chassis it will be lighter because it is "stronger" and therefore allowed to run a thinner wall thickness. Stronger + thinner material = more brittle. I'd rather my cage bend than break, and a second impact at the same point can/has caused moly to fail. Plus, the fatigue rate is higher; there's a reason pro-stock guys start slowing down with one season old chassis - they say "old pipe" for a reason.

In a double rail, full tube pro-mod type chassis the total weight savings of moly is around 100-200lbs. Since we're required to weigh 3000lbs in 10.5, most any purpose built car will need balast anyway.



Here's a link to my PB album of the camaro; I need to update it, but not much has changed. http://s455.photobucket.com/albums/q...tlaw%20camaro/

 

Yeah, I know that...

But I never thought about it like that...

 

2100 is just the tubing from art morrison. i still have to build it.
im not plannin on runnin any class style racing. just want a chassis car.
its gona be a pg car with a sbc twin proably twin 76s. the floor and firewall are ate up with rust prety bad. so id have to replace the floor pans anyway.

 

shagwell thanks for the pics your car is like what i wana build
like this

 

Unless you're very skilled in welding up a tube chassis kit in a proper jig, like buying a rollbar/cage, the kit is the cheapest part. Having a rollbar/cage installed, you can usually estimate $100-$150 per point. To have someone weld up a tube chassis kit properly, I'd expect it would cost at least $20,000 considering it's about $10,000 just to do a back half. That would be just to weld everything up. Hanging the body and buying/installing front and rear suspension should add another $40,000. If you buy a CM kit, you'll need to TIG weld everything

It's not uncommon to have $100,000 invested in a tube chassis car. As mentioned above, a CM chassis is lighter but because CM is brittle, it's more prone to cracking. If buying a roller or turnkey, it's worth the extra cost if the cage/chassis has a valid certification.

You don't "need" a tube chassis car or a CM cage unless it runs quicker than 7.50.

Here's another link to a tube chassis build. It's a T-bird but the body that's hung off the chassis could be anything.

http://smg.photobucket.com/albums/v6...428/?start=all

Here's the S&W chassis kit page. Third gen MS $1100, CM $2000

http://www.swracecars.com/Files/pdf/CATpg68.pdf

It can be a whole lot cheaper to just buy a roller that has a current chassis certification.

 

I've never heard that before. Are you referring to welds being brittle or the metal being brittle?

CM is no lighter than A36 mild steel. They both have a density of .284lbs/ci. However, CM is almost 2 times stronger than A36 mild steel.

Heres the material specs from Matweb:

4130:
http://www.matweb.com/search/DataShe...b2b6259&ckck=1

A36:
http://www.matweb.com/search/DataShe...df05129f0e88e6

 

I'll stick with the moly!!! I do specify normalized tubing when I buy it.... Moly cars can be built lighter because the tubing is stronger.... Look around at all the Pro cars, they're moly.... When welded properly and normalized tubing is used, it's not brittle.... NHRA went through all this a couple years back on the Pro Cars including the Pro Stockers.... Maybe it's not necessary for a street type car, but since when has "necessary" ever been part of building Hot Rods...??????

 

When you have an itch that you just can't seem to scratch. Thats where "necessary" comes into building a Hot Rod

 

Guess I'll probably take that as a joke or something.....Hopefully this thread hasn't deteriorated to implying somebody's an idiot????????

 

since i did the complete fram and back half cage, paint body, motor trans rear end in the s10 and its running 8s in street trim. i think i can handle the chassis build.
art morrison and a few others have a flat floor they build off of a ply wood jig. and there have been some very fast cars done this way. im looking only to go 7.50s. no faster.

 

Yeah, sorry about that. It was meant as a joke. After a long day of classes my sense of humor is that bad.

 

I use .120 wall DOM steel. In the end it will be lighter than a typical .134 wall HREW(typical MS) chassis, but not as light as .095 4130(CM). As I stated before, there is only 100-200lbs difference between a CM chassis and a typical MS chassis in a double frame pro-mod type chassis, thus even less difference if you use DOM, and even less difference in a typical single rail chassis.

NHRA went through nothing. They have never done nor had done any sort of materials analysis to prove any reasoning to require CM at faster speeds. In fact, drag racing is the only motorsport to require CM at faster speeds, most other motorsports' sanctioning bodies require MS at faster speeds due to it being less brittle and less likely to fail in a multiple impact/roll situation. - They have had the CM for anything 7.49 or faster rule for 30+ years and have never given any reasoning for it. - If you want a good topic, why do they cert based on ET and not MPH? I can gaurantee you the chassis does not car how quickly it hits the wall, only how fast it's going and how much weight it's packing when it does. Velocity is a fairly simple "theory" which the NHRA seems to not understand.

Higher strength + thinner wall is more brittle. I did not say it was going to break like glass, simply that a properly built CM chassis is more brittle than a properly built MS chassis.



Radical82 - Sorry if this came of as an "attack" towards you, it is not intended that way. Just pointing out some facts.

 

because of its hardness and type of metal ive heard chrome molly chassis will eventually quit working. 60 fts start to drop off and such. but i want it light then put weight where i need it to make it hook. motor will be a 357" sbc and twin 76s proably. im shooting for 1300-1400 whp.

 

Well, I guess you can put me and a lot of other chassis builders on the list of people who would like to see your engineering and metalurgical data on all this!!!! But, you're certainly entitled to your opinion.....

I've been involved with some of the NHRA track and lab testing, so I do know first hand that it has been and will probably again be tested...... All metal, moly included, are subject to embrittlement when they are welded and or heat treated improperly..... John Force has also started his own chassis shop with a full time engineer, a consultant who is a metallurgist, and a half dozen or so really first rate fabricators...nobody in pro racing runs a safer car or has more emphasis on design safety then Force Racing....There first house car debuted last week, and it's all moly.....

The most current (as in this week) testing and evaluation NHRA is involved in is with the top fuel classes, doing some testing with a single mag, smaller blower, and some smaller sized, harder compound slicks..... Interesting.... Would appear they are making some attempts to lower the cost of the top fuel classes....maybe to make a full field for all the national events in 2010....

PS--the actual weight difference between legal size and wall ms and moly is .76 lbs. per foot.....

 

The Morrison kit is really first rate materials for what it costs!!!!!! I've put a few of them together, with the right man doing the cut, fit, and weld it would be more then adequate to meet your needs..... One here locally running 7.90 class that is one hard hitting, consistent car to deal with when he's in the other lane-----please don't ask me how I know this!!!!

The S&W 10.5 kit is another very nice one to consider!!!!!

 

You need to look at all the CM pro car chassis. They only run those chassis for a couple of years before building a new chassis. The stresses they put on the chassis is hard on the CM. It's common to see an old ProStock car running in some slower class like SuperGas. Half the HP doesn't hurt the already used chassis.

Once you get into the speeds you plan on running, a couple of hundred extra pounds from a MS chassis isn't going to hurt you. As mentioned above, building it out of .120" DOM will greatly reduce the weight compared to using the thicker .134" EWS tubing.

Many of the fast cars have lots of weight added to the front to keep it down anyway.

 

The goal is to have a chassis package that works properly and makes the class minimum weight + a 20 to 30 pound cushion.... If you can meet that criteria with mild steel, leave the extra $$$$$$ in the bank. To be competitive at the Divisional or higher level takes every advantage you can get....

Btw, a properly set up chassis does not need ballast hung on the front to keep the wheels down!!!! If that's what it takes, something is wrong with the setup!!!!!

 

4130 (Chromoly) Normalized Alloy SteelMinimum PropertiesUltimate Tensile Strength, psi97,200Yield Strength, psi63,100Elongation25.5%Rockwell HardnessB92 4130 (Chromoly) Annealed Alloy SteelMinimum PropertiesTensile Strength, psi81,200Yield Strength, psi52,200Elongation28.2%Rockwell HardnessB82ChemistryIron (Fe)97.3 - 98.22%Carbon (C)0.28 - 0.33%Chromium (Cr)0.8 - 1.1%Manganese (Mn)0.4 - 0.6%Molybdenum (Mo)0.15 - 0.25%Phosphorus (P)0.035% maxSulphur (S)0.04% maxSilicon (Si)0.15 - 0.35%


4340 (chromoly) Normalized Alloy SteelMinimum PropertiesUltimate Tensile Strength, psi186,000Yield Strength, psi125,000Elongation12.2%Rockwell HardnessB100ChemistryIron (Fe)96%Carbon (C)0.37 - 0.43%Chromium (Cr)0.7 - 0.9%Manganese (Mn)0.7% maxMolybdenum (Mo)0.2 - 0.3% maxNickel (Ni)1.83%Phosphorus (P)0.035% maxSulphur (S)0.04% maxSilicon (Si)0.23%


8620 (chrome-nickel-moly) Alloy SteelMinimum PropertiesTensile Strength, psi97,000Yield, psi57,000Brinell Hardness201Elongation25%Machinability66%ChemistryCarbon (C)0.18 - 0.23%Manganese (Mn)0.7 - 0.9%Phosphorus (P)0.35% MaxSulphur (S)0.4% MaxSilicon (Si)0.15 - 0.35%Chromium (Cr)0.4 - 0.6%Nickel (Ni)0.4 - 0.7%Molybdenum (Mo)0.15 - 0.25% max


Here is the actual numbers on moy, normalized and annealed, as well as 8620 alloy....Numbers are as published by the ASE

 

Thin walled tubing in and of itself is a lot more prone to localized buckling than thicker walled tubing. This is something that is fairly common in the .095 and down tubing that is much less likely to occur with the .120. The moly just makes this worse since it is more prone to embrittlement and work hardening, normalized or not. Its just a basic factor of higher carbon steels that cannot be escaped. This is probably what some of the complaints are, there are likely locations on the chassis that are weakened and shifted over time and use. Its also something that can sometimes be hard to see, especially on round tubing. I dont know if the spec allows different tubing sizes, but I'd imagine they do and the locations that the tubing sizes change are going to be the first places to suffer this problem and ultimately fail. I would only pursue the weight savings capability of something like 4130 if cost/s are not a factor and weight is a major concern. If you are looking more for longevity, there is no arguing that a thicker walled mild steel will last longer.

 

I've worked with moly cars for many years....and have yet to see any problems with flex and stress weakening on anything less then Top Alcohol and up dragsters and funny cars.... I've always heard the embrittlement stories, but never have seen a spec or a reference to define it as a problem area.... I use melt strips and pre heat techniques on moly, as does any reputable chassis man..... Not saying anyone is wrong or right on the embrittlement issue, just wondering where the specs and references for it come from?????

Flex and work stress are not an issue with proper design, except in areas on long wheelbase dragsters where flex is built into the chassis.... The chassis broke in half thing went away after young Schumacher's car broke in half--built with plain moly, not normalized moly, and the car had also been front halfed once.... IMO, not a problem with the materials used but more some poor choices on the part of the chassis man doing the work...

Maybe I just live in a different world or something, but weight is a concern on every car I build!!!!

I guess my question would be why would someone even consider a moly car if it were not being built to a certain weight for a specific class???? The "poser" cars will do just fine with DOM or EW.... Perhaps it's just a question of definition????

Back in my much, much younger days, I took some really ugly rides in 1600 lb. moly framed sprinters and never had a cage collapse!!! I did bend a couple of them terribly on the frame rails just ahead of the cage where the car was designed to bend when wrecked and the point where the car is front halfed after it's wrecked.... I know that that moly frame and cage is why I lived through them.....

So, what is the issue? Perhaps we just aren't talking apples to apples??? I don't see any reason why moly would not be used on a "real" race car designed and built to compete at the 7.50 or quicker level.... But for the street, I agree!!! Save your money and go DOM.....

 

no problem, man!!!!! I don't take any of it as a personal anything----I enjoy a good discussion, it's how we learn, right????

Oh yeah, in the NHRA rules there is a mph limit. Don't hold me to it, but I believe it's stated as an either/or rule; either 7.50 sec. or in excess of 135(?)mph....

Facts is facts, opinions is opinions..... Where is the reference material and the list of causes of embrittlement in moly tubing???? Not saying that it doesn't exist, but I guess from my schooling days, about the only embrittlement issues we studied were hydrogen embrittlement on externally treated (chroming) tubing and plate....?????

 

not trying to prove or disprove anything or anyone, I had this article from Hobar concerning embrittlement....their opinion is that the proper filler combinded with the proper pre and post heat negates the hydrogen issue::::

Filler Metal Options for Chrome-Moly Pipe

Chrome-moly pipe has become a standard in industries such as power generation, chemical processing and petroleum refinement, not only because of its corrosion resistance and high-temperature strength, but also for its cost effectiveness. In many applications, it is a viable alternative to a more costly stainless steel pipe.
Choosing filler metals to weld chrome-moly pipe requires the same principle consideration as with any material: match the chemical and mechanical properties in a way that yields the strongest, safest and longest lasting welds. Specific low alloy SMAW electrodes and flux-cored (FCAW) wires do just that. They provide the low carbon, low hydrogen properties that prevent welds from corroding and/or cracking on critical piping applications, as well as the necessary strength to withstand high pressure and temperatures. It just takes a little know-how to choose which is the right one for the job.
Mind Your ‘Ps’ To select low alloy filler metals, it is first important to understand chrome-moly pipe itself. Among the more common grades are P11, P21, P22, P91 and P92, some of which can withstand service temperatures over 1112 degrees Fahrenheit (600 degrees Celsius) and have wall thicknesses ranging from 1/8 inch to eight inches. The amount of chrome, molybdenum or other alloying elements determines the assigned grade of chrome-moly. These particular grades contain a range of 1¼ to 9 percent chrome and ½ to 1 percent molybdenum, with those containing more chrome providing the most corrosion and temperature resistance. Not surprisingly, the amount of chrome is also a determining factor in filler metal selection.
When welding chrome-moly pipe, regardless of the grade and/or the filler metal being used, it is important to maintain specific preheat and interpass temperatures. Consistent temperatures help conserve strength and crack resistance under extreme service conditions. Recommended preheat temperatures range from 250 to 400 F (121 to 204 C) according to the wall thickness (see Figure 1).Per AWS code D10.8-96, ‘Recommended Practices for Welding of Chromium-Molybdenum Steel Piping and Tubing,’ preheating practices should always be observed, even before tack welding. It is especially important to preheat prior to repairing P21 and above grade chrome-moly pipe that has been in service, as it may experience temper embrittlement or ductility loss. This can occur when the pipe has been exposed to temperatures above 850 F (450 C) for an extended period of time (ref. AWS D10.8-96, 5.1 and 7.2).
Maintaining interpass temperatures is also important. A range of 350 to 600 F (177 to 316 C) is typical, depending on the grade of chrome-moly and its thickness, but most importantly, upon the required welding procedure.
Post-weld heat treating (PWHT) or stress relieving is also recommended. PWHT requirements are generally 1150 to 1400 F (621 to 760 C) for one hour. PWHT helps rid the weld of hydrogen that may have been picked up either from the filler metal, the base metal, or the atmosphere, and can help minimize the chances of cracking. Most low alloy filler metals designed for chrome-moly applications will also provide recommended stress relieving temperatures and duration on the label or spec sheet.
No Reason to Get Stuck Low alloy SMAW electrodes are your best choice for chrome-moly pipe welding repairs, because they are easily portable (they do not require shielding gas). They can also reach into the small physical confines of existing chrome-moly piping systems.
As a rule, low alloy stick electrodes designed for welding chrome-moly feature low hydrogen levels, low spatter, fast-freezing, easy-to-remove slag, and good bead wash and tie-in, all of which are designed to make welding repairs fast and trouble-free. To obtain these characteristics, be certain to clean the pipe prior to weld repairs. Often chrome-moly picks up hydrogen during normal service, which can lead to cracking in new welds.
For P11 (1 ¼% Cr – ½% Mo) chrome-moly pipe, use either an AWS E8018-B2 H4R or E8018-B2L H4R SMAW electrode, as both are formulated for applications subject to high heat and/or humidity. They also resist hydrogen pick up that can lead to cracking or starting porosity. The E8018-B2L H4R stick electrode contains a lower amount of carbon, which further protects against cracking. Both electrodes work especially well on boiler and similar piping repairs that require weld tensile strengths above 80,000 psi. On the average they offer tensile strengths in the range of 90,000 to 98,000 psi.

 

I have some books on it here that have literally paragraphs explaining it (seems these type of writers cant be blunt and to the point), but do not feel like typing all that up right now. This is the only reference (nice and short) I've found to it on the net so far (my books are older, obtained from an old prof at college and most were printed prior to the 80's)

Moreover, in higher strength steels, comparatively small amounts of hydrogen lead to large changes in properties with respect to steels with lower strength [10]
# C. G. Interrante: Basic Aspects of the Problems of Hydrogen in steels. ASM, (1982), pp. 3-16.

This is most likely due to the fact that high carbon steels are more brittle than mild steels to begin with, although thats just my personal 2 cents. If you couple that with reduced section sizes people use because of the strength ability of the high carbon steel, you have a higher probability of failure. Does not mean you will have a failure as most of these things have a large factor of safety that should remove the possibility of failure, but its more likely to occur with that type of material.

 

quoting this kind of "cherry picks" your posts, but this is my point.

I fully agree that properly welded CM is as strong/stronger than MS, but the continuous stress of the power being loaded/un-loaded and thus the weight being pushed/pulled/drug in different directions on the chassis/cage results in material fatigue. Also, since when has the NHRA checked the chassis shops/welders credentials as to his abilities to properly weld CM? I don't get to involved in the metalurgy studies, I'm the first to admit that's over my head. I base my knowledge directly off of the cars. The pro cars(mod/stock/etc) all update chassis when the "pipe gets too old". You'll hear the phrase from driver's and crew chiefs. If you've ever had a chance to look at any of their logs you'll see it too. They start loosing some ET at the chassis ages and has more runs on it, and no re-tune can find it. The chassis is simply shifting around too much as the power is being applied.

A TT small block with the intent of running any heads-up outlaw type class will be required a minimum weight of around 3000lbs, and will be applying at least as much, if not more power than a Pro stocker. Almost 1000lbs heavier + more power = more fatigue.

Knowing some people who have/do sit on the SFI cert boards, I can tell you the NHRA's sole involvement with a spec is to pass or reject whatever is submitted to them, based off of their insurance policies. The pro teams don't run a chassis long enough(time wise) to have any structural issues with CM, therefore they will never have a reason to test a heavier material. The all-mighty NHRA does not "bite the hand that feeds them" thus thier "full throttle" pro teams are all that matters to them. - If you're involved with any outlaw/heads-up type racing, then I'm sure you know how far past due the recently released 25.3 spec is. The board that designed that spec has had it ready for a couple years now and has been awaiting the NHRA political red-tape BS to get it approved.

The Specs do list an MPH, but the certification tags are all based off of ET, and 1/8 mile times/mph are "x" lower configured off your calculated 1/4 mile ET. - If my chassis can handle a 200mph impact in the 1/4 mile, then it can handle a 200mph impact in the 1/8 mile.

 

weight specs:

1-5/8" tubing
.120 wall = 1.929lbs per ft
.095 wall = 1.552lbs per ft

difference = .377lbs per foot

source:
http://www.alro.com/DATACatalog/Upda...pe.pdf#page=11



The NHRA spec for MS is .112 wall thickness. Typical EWS/HREW tubing is .118 wall, but has a +/- spec of .008, and will also thin out on the back side of a bend. For those two reasons, .134 wall thickness is comonly used. - With DOM steel, you can use .120 wall, as the spec is +/- .0, and it will not stretch as much around the back side of the bend(not enough to be below the required .112).

 

Because of the variances in production and the distortion/reduction in wall thickness created by the bending process, it is generally accepted that in order to meet the NHRA spec that .134 tubing be used... The tech folks will reject a car with cage material NOT meeting the criteria....maybe not at the local track, but when you get to a Divisional or National meet the inspection process is much more thorough, and cars have been rejected from competition for a too thin of a wall thickness on a bend or bends.... DOM does stretch on the radius', all metal does!!!

I don't consider it sound advice to suggest using a material that may or may not at the discretion of NHRA be "legal".... .120 wall DOM is not the reccomended material to use by any of the chassis shops that I know of currently building cages that are guaranteed to meet specs..... In theory, all of your numbers are great, but in the practical world of building drag cars guaranteed to meet specs, things are a bit different.... I've never had a car fail to meet spec and been doing this stuff for more then a few years....

We do all have the ability to make our own decisions, but for me I'll stick with what I know works and is acceptable to the NHRA techs!!!! The wrong guy on the wrong day can really make your life miserable!!!!

 

In the late 70's and 80's it may have been an issue--but filler material spec and quality has improved immensly since then...As well as a lot of us learning better construction and better, more accurate pre-heat and post weld heat methods.... The chassis' of the Top Fuel cars are very, very stringently inspected, complete with lab analysis of the materials used in the build.... We've learned and improved in all areas since the 80's!!!!!

But, if you don't have the knowledge, equipment, time, and money to build a moly car correctly then using moly should be avoided like the plague!!!! An improperly constructed moly car is a big wreck waiting to happen, but then so too is an improperly constructed or welded DOM or EW car----

Just a note to some of the "first time" builders who plan on racing NHRA and wanting to avoid problems at certification problem, take the time to get acquainted with your Divisional Tech folks, pay the $35.00 for the specification book for the spec you must meet!!!! I'm fortuanate in that over the years I've become friends with a number of the NHRA tech folks and always make a phone call, email some pics, invite them for a visit or all of the above anytime and everytime I have a situation with rules interpretation!!!! For the most part, I have found the Tech folks to be more then willing to help in making sure your car gets it's cert tag the first time through the inspection process!!!!!

I guess I could quote specs and references all day, but I think the most meaningful thing that could come out of this entire dialogue is that everyone building a car that has to meet NHRA specs and pass NHRA inspection learn a bit about what the process is and how to best build a safe car that will meet all the criteria.... Think I'll just leave all the theory and metallurgy discussions alone, everyone has an opinion and with enough research can cite a reference to back that opinion.... We used to do it in school and it got to be a pretty much useless discussion other then for filling in too much spare time in the dorm at nite!!!!

 

That same fatigue will occur in mild steel as well. You're forgetting fatigue life. They aren't building that car to last 1 million miles plus, they are builing it to last for a certain number of races.

Fatigue life is the number of load cycles a part is designed to handle before failure. I know that this corrolates to weight increases or decreases, but how I don't know.

Thats the extent to which I understand fatigue life, hopefully someone else can shed some more light on this.

 

I've done two complete chassis and 6 cages with .120 wall DOM MS, all passed their chassis certification with flying colors. Yes, it will thin as it stretchs around the outside of the bend, but even at a 180* bend I have not had any instances where it was below the minimum .112. (the lowest I've had in testing was .116 and that was a short radius 160ish degree bend of 1-5/8x.120 wall).

- I've never seen a chassis checked at the track, unless the person had a previous appointment for certification. Most chassis certs are done before the cars ever go to a race, you pay the fee, an NHRA(or IHRA) inspector checks the chassis and applys the corresponding sticker if the chassis passes. Tech at the track checks the sticker/date and then the other safety equipment(belts, suit, helmet, etc).

If you're even thinking of building a chassis/roll cage/roll bar, definitely spend the $35 and get the appropriate spec book from the SFI. - My car is cert'd 25.5 due to being MS. I actually have more piping than what is required for 25.2. I run almost strickly 1/8 mile outlaw/heads-up stuff, which makes a difference as well.

I 100% agree on your "dorm room" theory. Arguing metalurgy is similiar to arguing religion. Any one racing needs to be running a car that they feel is comfortable/safe for what they are doing. In my experience, I personally preffer MS. Too each there own.



All materials have a fatigue life/rate, just noting that a stronger material will have a higher fatigue rate especially when a thinner wall thickness is used.

 

Here's a good read on CM tubing troubles at NHRA... http://www.bmeltd.com/Dragster/tubulartales.htm

 

just got through reading that twice. Very good article.

 

I didnt say ALL the books were older, just most of them. There are still late references to it, for the same reasons. I agree that things have improved in general, but the potential still exists because even though the materials being used are a little better as far as purity they are not perfect nor are the ultimate/general properties any different. High carbon steels are just more brittle and do not take as well to fatigue, nothing new about that. Newer material doesnt make any difference on that front, CM is still more brittle than MS. Fact of life. Also, many of the older texts I have were already doing testing using fabrication and welding procedures not common then but commonplace today like the preheat, normalize, etc. Good design and excellent fabrication are a obviously a must to avoid any problems, but some inherent qualities cant be escaped.

Anyway, what specs are they using for the CM? Size, wall, etc? I'm curious.

 

Interesting read.

 

I talked to a Mechanical Engineer yesterday and he said that the reason CM is more brittle than MS is because is has a higher yield strength than MS. He also said that was a very broad stroke explanation, but I told that it made perfect sense to me and he needed not to go further.

 

Jon Asher wrote a very good article!!!! Never have understood McKinney's insistence on heat treated moly----I think he likes the heat treated moly's lack of elongation because the car is just a tad quicker on laucnch and 60'--Just a guess on my part, can't say it's anything McKinney ever said....

The power that these top fuel monster put out is just phenomenal though!!!! Don't know of any material that will stand up to it!

Fortunately, we arent' dealing with anything like that kind of power in a 3rd Gen..... I do know that I've been building moly framed cars since the mid 70's and have never had a chassis failure.... Normalized Moly with pre heated and post heated weld areas (not to be confused with heat treated moly (hardened) has always done everything it's expected to do, hook up the chassis and keep the driver safe!!!!

I have no idea if embrittlement is an issue with moly.....and if it is I sure do wish somebody would come by and show me on one of the cars I've built just exactly where it has created a problem cuz' I've sure never seen it!!!!! Every sanctioning body I know of specifies moly on the faster cars. It's stronger and lighter! Back to the original poster's interest, IMO a properly constructed moly tube chassis for a 3rd gen car is indeed practical if you're planning on powering it up enough to run in the sub 7.50 ET, 135mph range!!!!!!!

 

Its not that 4130 is brittle - its that it unevenly so. In the areas right next to a weld, the 4130 becomes brittle. Martensite forms. Mostly because carbon gets trapped in the rapidly cooling crystals.

To normalize the 4130 again you need to anneal the the area. Back in the WWII days, 4130 was welded with a oxy/acetylene torch. The extra heat (flames don't concentrate the heat like a TIG) help smoothly transition the weld area to the rest of the tube. Now, with small weld areas, the HAZ or heat affected zone is potentially very brittle. In fact, if you weld it wrong, you may actually start cracking as the area cools. (Don't use SS welding rods (308) or 4130 filler).

http://web.a-znet.com/~dave1w/maxim_disaster.htm
Even from a reputable chassis builder, joints fail right next to the weld... But the guy survived, so all was not lost.

Anyway.

Lincoln says use ER80S-2 (and apparently so does Experimental Aircraft Association). Search the web for a "Mr. TIG"
http://www.weldingtipsandtricks.com/welding-4130.html

I was told FAA says ER70S-2 for intersecting joints. I have no way to verify this.

The most reasonable advice I've seen was this:
http://www.netwelding.com/Welding%204130.htm
Basically ER70S-2.

Use blankets to keep the heat in. Pre-heat a bit (normalized flame - 350F), consider back purging (keep carbon away), make decent convex (bulge out) fillet welds, use gussets, ER70S-2, and let it cool very slowly (still air).

If you can find a place that can normalize the entire chassis, build a JIG from heavy steel and protect the JIG from heat when you put it in the oven. BTW, if you can find such a place, post details here. If you are going to normalize the whole chassis, consider a good pre-heat and weld with 4130 filler. (see link above).

If you are going to try to normalize yourself with a torch, be advised that this is hotly debated as well. Some say you can do more harm then good because you cannot control the temperature well enough. Others say even if you miss by a little, you are still doing better than nothing. All I can advise is use a neutral flame - no extra carbon, no extra oxygen or see if you can inductively heat it.

Bottom line, on a full chassis street car, don't bother. Saving 30lbs in cage isn't worth the hassle. If you are going to build a chassis from scratch, you might have a chance of doing it right. If you dig around the Morrison web site they still have the step by step build up they did of a '55 Chevy for Car Craft or Hot Rod.

Keep in mind that most professional racing teams barely have the resources to keep up with the maintenance of the cars - not a lot of time for pure R&D. Most of the R&D they do is limited to seeing if they can make work what the other guys are doing. John Force on the other hand has enough money to do some serious research.

Note the 2007 controversy over Top Fuel and heat treating is not making the chassis less brittle, its to make the chassis harder (they rapid cool). So they are heat treating to make the 4130 harder/stronger. Problem is that Force's chassis failed right near the heat treat.....

One last thought, there is some discussion that TIG welding with a pulser affects the size of grain growth. Search the Miller forums for "4130" and "pulse" Personally I like my old DC, transformer based machine for steel. Leave the fancy inverter for aluminum.