Potential FED Build

[lake_harley]

Here’s an excellent online racing calculator which helps decision making.  For tire diameter answer, you input proposed rear gear ratio, anticipated engine rpm and mph at stripe.  This calculator is user friendly and lightning fast with answers.

http://www.wallaceracing.com/Calculators.htm

I had a 1970s dragster with an 8-3/4 Mopar (489) rear with Mark Williams axles and spool and had no issues with it.  It would work fine for your project.

That calculator website is interesting. It might keep me entertained for days.    I just hope it doesn't get my hopes up too much since my "theoretical" FED calculates as being quicker than I might hope.

Lynn

[THE FRENCHTOWN FLYER]

LOL slowing it down is a lot easier than speeding it up. And cheaper

I built my RPU with 2.47:1 Bonneville gears in the rear, with a 4.56 waiting in the wings. It never got changed to the 456s. Its fast enough. And with the 1-2 shift spaced way out I can dial that puppy within a gnatsass by altering my shift RPM.

[Paul New]

I agree with the 4” ground clearance!  My first dragster I built had the 3” minimum it was difficult.  Buy the SFI specs 2.6A is good to 7.50 and you can build with mild steel tubing 2.4C is 6.0-7.49.  Of you decide you want to run a torsion front axle I have a brand new Mark Williams torsion bar and a wide front axle 44” king pin C-C if you may be interested

https://sfifoundation.com/drag-racing-chassis/

[jeff/21]

what ever you do make sure you can fit in the car with all your safety equipment on This year I had a chance to do something that was on my bucket list that was to drive a sprint car took the car out to run laps behind the shop street clothes just a helmet and arm restraints  everything felt good, next day we went to the race I got dressed Sfi 15 suit could barely fit in the car couldn't fit the steering wheel on didn't have time to re position steering or lower the seat!
All this to say You have to be comfortable!

[dreracecar]

Most people will tell you to use the Ford 9"--- except me.
 Chrysler 8 3/4 is a good choice for what YOU plan to do, They offer more room for your legs, good gear sets are available, less exspensive than a Ford build, Not that it really matters but a Ford eats up a touch more HP because the pinion is lower. Don't go with a diff, spools are plenty cheap these days for them and available in the popular spline counts. With todays tracks and tires they will handle 800HP easily
 Chrome Moly is so much eaiser to work with them DOM mild steel  and the cost difference is a couple bucks, Places like Aircraft Spruce sells Moly at a reasonable price and will/can sell only the amount needed without cutting charges (as in ordering 2 -6' pieces instead of a 12"). Proper planning and the material can be shipped in short runs instead of freight shipping a 20' length.
 Front torsion will add another $400+ to the build and not really needed because current rear tires do most of the work and a solid front end is fine, A piece of 1 3/4" X 120wall and the split front axle will slide in or you can split the 1 3/4 and clamp the full axle in place

[lake_harley]

Thanks again to everyone for input and suggestions. There are obviously differing opinions like front suspension/no front suspension, 9" Ford/8 3/4" Chrysler, DOM/4130. I'm looking forward to getting started and hope the project cars I have that need to sell first find new owners soon. I'm taking all the suggestions seriously and hope that I make some wise choices as I develop a build plan.

I did call the main steel supplier I used for my fabrication business today and got quotes on 3 of the sizes of tube I would need. Based on a rough estimate on the footage I would need of different sizes, it appears DOM would run about $150 to $200 less than 4130. I can pick up 4130 from Wicks Aircraft who is only about 1 1/2 Hr. from where I live. Not really a huge price difference.

Thanks.
 
Lynn

[Paul New]

I agree with Bruce an 8 3/4 would be perfect and way more comfortable to have your legs go over.

[wideopen231]

Main reason I would not consider anything but molly. Stronger with half the weight . Also added safety,its not always how fast you go it other car too. Minor cost increase in the big picture. At some point selling it will be in picture.

You have said motor will be mild combo,why have extra weight?

[jeff/21]

a friend has a gremlin with 8 3/4" powered by a 454 only break stock axles when he gets wheel hop(10x30slicks)
9" do eat more power as for housings they come in all shape and sizes from big, truck and fabbed ones to smaller early models and some aftermarket with small round backs

[afaulk]

Thanks again to everyone for input and suggestions. There are obviously differing opinions like front suspension/no front suspension, 9" Ford/8 3/4" Chrysler, DOM/4130. I'm looking forward to getting started and hope the project cars I have that need to sell first find new owners soon. I'm taking all the suggestions seriously and hope that I make some wise choices as I develop a build plan.           If you have a good deal on the Mopar rear end, get it. I had one with a spool and 35 spline axles. At 4.80s in the eighth it was no problem. Chromoly tubing and a good set of plans to work off, you'll have a car you can sell when the time comes. Longer is better if you decide to add more power later. Good luck and have fun.

I did call the main steel supplier I used for my fabrication business today and got quotes on 3 of the sizes of tube I would need. Based on a rough estimate on the footage I would need of different sizes, it appears DOM would run about $150 to $200 less than 4130. I can pick up 4130 from Wicks Aircraft who is only about 1 1/2 Hr. from where I live. Not really a huge price difference.

Thanks.
 
Lynn

[rooman]

Apart from the other reasons noted above, the biggest advantage in using 4130 is that by using .058 wall for the main frame rails you can slip fit decreasing diameter tubes to step the rails down from 1.5" at the shoulder hoop to 1.375" in the engine bay and then 1.25" for the front of the frame.

Roo

[lake_harley]

Thanks again for the additional input and suggestions. I can understand that 4130 construction is preferred for many reasons, including the convenient telescoping tube ability. I haven't decided to go 4130 or DOM just yet, but if building with .120" wall DOM, can transitions from one diameter tubing to another (1 1/2" to 1 3/8" for instance) be done with a butt joint and a stepped sleeve that has at least .120" wall at the smallest end? That sleeve would end up being 1 1/4" at the big end and 1 1/8 at the small end OD, with a 7/8" ID all the way through. I do intend to order the SFI book and that will likely clear up many/most of my questions, but for now I'm just considering options.

Thanks.

Lynn

[dreracecar]

Why are you making more work for yourself???  Even doing things for myself --my time is not free

[wideopen231]

^^^ agree. Its so much more simpler with molly.

 Piece of advise.Design around what you think is extreme you will want for car and build towards that chassis wise,then put in combo you want and you will have room to grow if you want latter. Speed is a drug and the more you get the more you will want,to a point. Myself I have never found that point.LOL Just its easier to do once then do and have to redo for another step.

[lake_harley]

OK....I concede (as I hang my head in shame), 4130 is the best way to go for numerous reasons and I should quit trying to take shortcuts or pinching pennies. I do wonder about my bender and dies being up to doing a nice job on .058" 4130. I have to pull out my bender and check, but I believe the 1.5" die I have is for 5.5" centerline radius bends. I don't know if it is too tight (no inside mandrel) to bend without kinks or ripples. I guess the only way I'll know is to get some tube and try it out.

The bender I have is a JD2, and if I recall from conversation with dreracecar on another website (the HAMB) that it isn't exactly the preferred bender to use anyway. I guess I'll just have to get some 4130 of a couple sizes and do some test bends to answer that uncertainty for myself. I do recall from previous use that my 1 3/4", 6.5" centerline radius die created an unacceptable, rippled inside radius on 16 Ga. HREW tube. I don't recall ever bending anything under .083" with the 1.5" die, but I fear the tighter radius on it will have the same problem when bending 4130. 

I know I keep saying it, but I do appreciate the suggestions and advice from everyone.

Lynn