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Dusterbd13 UltimaDork
9/7/17 7:32 p.m.

So, the newest bad idea of the day involves a completely custom chassis.  

Constraints would be:

Front engine, rwd. Stick axle. Challenge budget. Radials. Street/autocross/track. Durable and easy consumables/repair.

Thats it. 

May go under a old 50s Plymouth savoy, duster, 60s dodge truck, sprint car clone from the 60s, etc. Body undecided, but probably not relevant to this conversation anyway.


So, what would you build, with what parts, and why?

Patrick MegaDork
9/7/17 7:34 p.m.

I would buy an 03+ p71 and make the chassis work or build new rails to tie the suspensions together for any of the bodies mentioned 

Woody GRM+ Memberand MegaDork
9/7/17 7:47 p.m.

Under your rules, I'd use the engine and transmission from a rusty BMW E30 and the rear axle from a V6 Mustang.

dropstep SuperDork
9/7/17 8:20 p.m.

Im no expert but my friends dad seems to go with s10 chassis for everything.

Ovid_and_Flem Dork
9/7/17 8:27 p.m.

Simplest solution would be using chevy metric front clip/rectangular square steel tubing for hack ala IMCA modified.

Stampie GRM+ Memberand SuperDork
9/7/17 8:37 p.m.

Get this and read it. Build everything yourself. Kick everyone's shiny with your cajones to the wall build. 

Appleseed MegaDork
9/7/17 9:24 p.m.

Go to the build section and find the Rice Rod.

Dusterbd13 UltimaDork
9/8/17 6:52 a.m.

In reply to Patrick :

Why p71? Its an option i hadn't considered and id like to hear your thought process. 

Dusterbd13 UltimaDork
9/8/17 6:53 a.m.

In reply to Ovid_and_Flem :

This was my first thought.  Parts are cheap and available, plenty of information out there.  But they run bias ply tires. Wed be running radials. 

Dusterbd13 UltimaDork
9/8/17 6:54 a.m.

In reply to Stampie :

Where my brain ended before the thread started. My concern would be durability due to scaling and weight. Your thoughts?

Dusterbd13 UltimaDork
9/8/17 6:54 a.m.

In reply to Appleseed :

Pretty much what inspired me.

Dusterbd13 UltimaDork
9/8/17 6:55 a.m.

The front runner in my brain right now is a rusty 55 Plymouth savoy and a motorhome 440. Just for what thats worth.

pushrod36 Reader
9/8/17 7:21 a.m.

Is this for a street or race purpose?

Apexcarver PowerDork
9/8/17 7:25 a.m.

gather miata suspension/diff, obtain Yahama R1 engine.


Obtain light body (target weight well under 1500lb)


Then make soup.


I have a spitfire and the miata parts so far.  Going to get moving faster once I make some Bugeye progress.


Had a good amount of internal debate of spitfire vs spridget. You could likely more easily do a spridget with a narrowed solid rear axle and can easily RHD convert for weight distribution. 



Think about it, I should be able to have a miata suspended/braked roadster weighing 1300lbs with 170hp, a sequential shifter, and 11kRPM.  



Patrick MegaDork
9/8/17 7:33 a.m.
Dusterbd13 said:

In reply to Patrick :

Why p71? Its an option i hadn't considered and id like to hear your thought process. 

Durable, cheap and easy to repair are in your requirements.  Big disc brakes, cheap 17"+ wheels, stout 8.8 rear axle.  Rides nice enough on street and competent handler, 115ish wheelbase mates to many older bodies.  And takes a rear sump oil pan like most engine options.  

maschinenbau GRM+ Memberand HalfDork
9/8/17 7:34 a.m.

Lot of thoughts on this.

I would try to keep the frame as simple as possible, fewer bends and Z's. In my hot rod, I needed the frame to be aesthetic. Under a big body, who cares.

Try to use a "drop out" front subframe that you can just bolt to a stick frame. Crown Vic is great for this, see classic Ford truck folks. Lexus SC300 front that I used is also great and easy to work on, but it has two offset mounting planes but that's not a big deal either.  The Lexus front end has HUGE amounts of camber adjustment built in.

 I don't recommend making your own front control arm mounting mounts on the frame. It will take way too long and you will never be satisfied with it, and there is so much geometry to screw up. Then you only have to worry about coilover mounts on the frame, which is much easier to figure out. 

8.8 or 9" is tried and true. Common, cheap, discs available, easy to service. I went with 3-link (centered top link) and panhard bar because the axle I bought had already been modified for it. It is a ton of work to do that from scratch though. They make simpler 3rd link mounts that attach just to the side of the pumpkin. 4-link is easier to package, but 3-link with multiple bolt holes on axle and chassis side make it easy to dial in. They say 3-links don't bind as much and handle better, but I've heard the same about a properly setup 4-link. Or just use the stock P71 4-link setup with watts link. 

Body mounts. Don't drill through the frame rail like I am doing it just complicates things. Make little right-angle brackets that weld onto the side of the frame, then use any parts-pin body bushing. With a big body car, your frame design will probably be guided by where the mounts are on your body. So when looking at bodies to use, google some pictures of their original bare frames and see if the body mounts are on the same plane. This will keep the frame simpler. Or just cut the entire floor pan out and add some cross-members. You will have to design the body and frame at the same. 

And make sure to take lots of pictures and update your build thread at least weekly :) 

Stampie GRM+ Memberand SuperDork
9/8/17 7:44 a.m.

In reply to Dusterbd13 :

A lot of that scaling depends on the body you select and how you skin it. If you were to literally skin it with just body panels attached directly to the built frame I doubt you're adding a lot of weight. An real adventurous builder could even pull a fiberglass copy of the body with their newfound skills. 

If you decide it's going to be bigger then I'd do two larger frame rails like a traditional frame but build a roll cage to NHRA specs on top. Sometime like this:

Dusterbd13 UltimaDork
9/8/17 8:48 a.m.

In reply to maschinenbau :

If i build the savoy or duster, theres really no floors to go by. It would be a bodyshell and firewall sat down over top of the chassis and connected somehow. But VERY good points all the way around. 

Pat: good reasoning, and very simple.  Adaptable easily as well.

Stampie: im looking for an easy project this time around.  Stick built frame, body dropped on top, 50/50 eeight distribution, etc. Simple.

Rnd goal will essentially be a street rod set on kill on challenge budget. devil

chaparral Dork
9/8/17 9:04 a.m.

Two Corvette subframes joined by a tubular spaceframe. Draw it in SolidWorks and send it to G&H Diversified in Houston when they're ready to take outside work to have the tubes cut.

GTXVette Dork
9/8/17 1:50 p.m.

How about an early C4, I have bought a couple for under a grand, Jim (O&F paid half that ) or did you forget!  you may or Not Want to  Change the Body.

frenchyd HalfDork
9/8/17 2:57 p.m.

Depends on you and how much work you can finish.  I've built a few ground up race cars and the simplest took me over 4000 hours. 

Thats two years of a full time job. Plus everything else you have to do. Like earn an income live etc.   

Dont think you can spread it over time because you will lose interest or events will change priorities 

Dusterbd13 UltimaDork
9/8/17 3:51 p.m.

In reply to frenchyd :

Ive built a few ground up race cars. Few street rods ground up. Couple of frame off restos. Thats why im trying to split the difference on this one. Rough body, kill chassis, nice interior, low budget, done quick and dirty.

Im not sure if this will even happen. Got a couple in line ahead of this. Like a 70 duster and a 64 el Camino. 

wheelsmithy GRM+ Memberand Dork
9/9/17 11:37 a.m.
Dusterbd13 said:


Ive built a few ground up race cars. Few street rods ground up. Couple of frame off restos. Thats why im trying to split the difference on this one. Rough body, kill chassis, nice interior, low budget, done quick and dirty

+1 on S-10 chassis. There was somewhat of an expert on making them handle on this forum... Oh wait, that was YOU.  Also, P71 is a great idea. 

singledownloop Reader
9/9/17 11:57 a.m.

If you build a duster,or anything similar,look at this link http://www.schwartzperformance.com/the-gremlin/

This would let you build a killer chassis with excellent suspension.The duster,or similar unibody would act as a "frame jig" so everything is in the right place.Everything would be plumb and square.To make the frame complete and removable go ahead and use the same method using the rear subframe as your "jig" to finish it.After it's all welded up you could cut it out from under the car if you want a separate rolling chassis.The advantage for me is I can weld but don't have the skills to build a one off chassis.

A build like this is on my short list of projects to do.I'm going to do this to a chevette or 60's volvo.


sleepyhead Reader
9/9/17 8:37 p.m.
GTXVette said:

How about an early C4, I have bought a couple for under a grand, Jim (O&F paid half that ) or did you forget!  you may or Not Want to  Change the Body.

Pretty sure this is how Glenn Dodd built up the patina'd '46 Plymouth that ran OneLap a bunch of times

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