I'm thinking of picking up a first gen rx7 and completely replacing the chassis and upgrading the motor. But wheel base, and configuration will remain aproximately the same (struts in the front, 4 link + panhard solid in the back) I'd upgrade the rear springs to be coil overs and upgrade to 4 wheel disk brakes. The question is, will it be fun? Will this front engine, rear wheel drive solid axel street only dune buggy be fun? Should i go through the (extremely) extra effort of making it a mid engine? (all new front end, new rear end, porsche to be specific, mated with the rotary engine) Or should I continue as planned but just raise the suspension and take it off road? But RWD has to be horrible off road.. I think it could be fun though, to have a front engine RWD. It would basically just be a drift sled, made to drive sideways as often as forward. The thing that draws me to the RX7 is the cheap price, tons of performance upgrades (drop in turbo'd engines) Absolutely featherweight engine with plenty of torque. I have also over the years considered doing the same thing to a subaru, the boxer engine and awd makes it pretty appealing, i'll look for the availability of a suby but i've found an rx7 for $450. Any comments or suggestions?

Quote: Original post by bzroom
I'm thinking of picking up a first gen rx7 and completely replacing the chassis and upgrading the motor. But wheel base, and configuration will remain aproximately the same (struts in the front, 4 link + panhard solid in the back) I'd upgrade the rear springs to be coil overs and upgrade to 4 wheel disk brakes.

This isn't a terribly bad idea, though an engine swap will probably be more work than it's worth. If it's your first swap, you can definitely do worse than swapping a 13B into an SA22C but I'd do a lot of research about it first. The disc brake swap is not difficult, the FB GSL came with discs in the rear which should be sufficient.

Are you upgrading from a 12A carbureated engine to a fuel-injected 13B? There's a lot of wiring work involved in that swap, so I wouldn't pick it as my first job. If you're thinking of a turbo 13B you might as well just Megasquirt it and then start budgeting for new apex seals once you get the bright idea to crank the boost.

One bonus of having a nice new rotary engine (I recommend a crate motor rather than a JDM or junker pull, if Mazdaspeed makes 13B crate motors along with their four-banger crates) is that you can get a nice bridgeport done without worrying about making your car undriveable.

Quote: The question is, will it be fun? Will this front engine, rear wheel drive solid axel street only dune buggy be fun?

Fact: It is literally impossible to make a rear-drive car that is not fun. The solid rear axle kind of sucks, but I think you're going to find that on any mid-80s Japanese sports car that wasn't a Z.

Quote: Should i go through the (extremely) extra effort of making it a mid engine? (all new front end, new rear end, porsche to be specific, mated with the rotary engine)

Mazda rotary engines are so far behind the axle they might as well be MR cars already. It's not worth the effort.

Quote: Or should I continue as planned but just raise the suspension and take it off road? But RWD has to be horrible off road..

RWD used to run rallies for decades before Audi showed up with the Quattro S1. You should be fine.

Quote: I think it could be fun though, to have a front engine RWD. It would basically just be a drift sled, made to drive sideways as often as forward.

Sure; the rotary engine is a fantastic choice for drift use because of its absurdly even torque curve.

Quote: The thing that draws me to the RX7 is the cheap price, tons of performance upgrades (drop in turbo'd engines) Absolutely featherweight engine with plenty of torque.

The naturally aspirated 13B and 12A are not what I would call "torquey" but with a turbo and a bridgeport they have more than enough power to get what you need.

Quote: I have also over the years considered doing the same thing to a subaru, the boxer engine and awd makes it pretty appealing, i'll look for the availability of a suby but i've found an rx7 for $450.

I strongly do not agree with purchasing any SA22C that cheaply.

Rotary engines have to be taken special care of, especially the pre-Renesis and turbo models. That includes stuff like not shutting the engine off before it gets up to temp, rattling the engine up to redline a few times a year, and checking your oil frequently (once every two fillups at least). A good RX-7 owner will know this and take good care of the car, and would likely expect a higher price as a result.

$450 wouldn't even buy you a straight frame around here. Even though it's a project, it's always best to buy the nicest example you can afford, and triple or quadruple your budget. You may well end up spending enough money to afford an FD in the end and get benefits like ABS, electronic fuel injection and twin turbos.

If it were my project (and thankfully it isn't, because I'd run myself into the poorhouse on gasoline, leave alone the blown motors) I'd go with an FC Turbo II with a rebuilt, bridgeported motor.

A more affordable FR option would be a Miata, of which rotary swaps exist, and my own fantasy project cars are the Datsun 510 and 240Z.

Subaru is also a great plan; the naturally aspirated models are highly competitive in amateur rally, and swapping a turbo motor into a 2.5RS is not too bad except for the wiring. I'd recommend looking for a straight 2.5RS and then consider upgrading if it works out for you.

Well it sounds like you have a pretty good idea of what's going to happen, disks from a GSL (done it before), 13b FI turbo, i'm not worried about the wiring i'm a lot more worried about the chassis.

The plan is to buy the car, salvage the windshield, then roll it over on its top. Hoist out the entire drive line (12 nuts, 6 bolts maybe?) and set it asside, i dont really care if it runs, it's just place holder.

I'd then create a jig off the bottom of the chassis, i'm hoping the chassis is fairly straight, if not i should be able to adjust/tweak the jig until *it* is.

Off to the junk yard for the body/chassis.

Then i'd be bending tubes and welding a tubular chassis to fit the jig, if it can mount to the jig, the drive line can mount to the chassis. (that doesnt mean it can drive :))

At that point i'd have to shell out some big bucks for really fancy hardware including a shiny new 13b, referbed trans, bling bling rims, aluminum radiator, plastic fuel cell, carbon seats, oh and put the windshield back in.. LED indicators/head lights.

I've always wanted to add a zillion bells and whistles:

Entirely drive by wire:
* Stall proof
* Launch control
* Auto shifting
* Torque/Rev limiting
* Turbo timer

That would require a clutch actuator and some kind of H-pattern manipulator, but it shouldn't be too bad.

Air Compressor: (though this is far too expensive and heavy)
* Built in corner jacks
* Air ride
* General air filling needs

On board battery charger, keyless ignition.

Would need a fancy steering wheel to control it all and a set of gauges, all though I think a tach and some small LCD off to the side would suit me nicely.

It all adds up but it sounds like a lot of fun.. In the amount of time it would take me to complete any of those steps i could easily save the money for the next.

I'm thinking i could build it for around $5k before the engine.

Early chassis concept, I have cooler lines for the bumpers now and possibly a square rail that goes straight back rather than protruding out on the lowest level to the side of the passengers. Also this design hhas ommited the tunnel, engine cross member, and forward strut bracing. But it is to scale of a SA.




[Edited by - bzroom on April 22, 2009 6:42:21 PM]

Goin to pick my rx7 up!

Bought an 83 for $600 Just needs a new starter, got one in stock downtown, should be able to get it installed tomorrow and then ill have myself a nice little ride for the weekend :P

Plus i talked to my friend at work who builds race cars and he said in the next couple months they'll be rolling their projects out and there WILL be room for me in the shop. I'm stopping by there sunday to meet and greet.

I can tell how you guys are just thrilled about this project, so I decided to post some pics.

The donor:



Just practicing with solidworks:


I plan to have Cartesian Tube cut and notch all my tubes. Going for dimensionally accurate rather than made-to-fit, for build efficiency.

And the suspension:


[Edited by - bzroom on April 27, 2009 7:54:47 PM]

I keep thinking, why would i use this old clunky stuff. It's really fun to drive around (well you have to have a loose definition of fun, or be a gear head), but it's not very original or even that performant.

Well i'm not gonna lie, these things hug corners like it's nobody's business. The acceleration is formitable, occasionally.. but the odomoter is except so come on.

But realistically it's a piece of shit. :)

The engine needs a carb at least, and a quicky cleaning, straight pipe, and new ignition and it'd be screamin.

Or a turbo 2 model, which means there's no point in me having this model in first place.

So fuck it, why not use a porsche transmission? or an audi, or anything i want. It's all custom mounted anyway, parts which are not on THIS rx7..

So basically, i can either go with the plan and make a complete replacement for the rx7 chassis. Or i can just create a car entirely from scratch, with a Turbo 2 engine, porsche trans, all custom suspension.

Or should i stay with the front engine RWD and again just go full race 4 link.

Some many decisions to make before i can even face problems to make decisions about :/

All these questions will be answered tomorrow when i visit my builder friends at their shop tomorrow. But. no i'm jk i'm done typing now.

I really need one of these: Measuring arm. Can somebody spot me?

Quote: Original post by bzroom
I really need one of these: Measuring arm. Can somebody spot me?

Just what do you need it for? If you're talking about lining up body work, then I can show you a far easier method to build something for it that makes use of spirit levels and plumb bobs.

To measure mounting holes on arbitrary engine blocks or other donor components, reverse engineering. In most cases calipers just aren't going to cut it. This thing will allow you to build a 3d model from a point cloud. Creating plane and circle features. with a few pokes of this thing you can generate a mounting bracket for just about anything.

Tonight i'll be lifting my car and pain stakingly measuring the suspension geometry. The mounting points, control arm lengths and orientations with plum bobs and a tape measure. That arm would make it a 15min job.

I'm thinking about picking up a 3 axis laser level though, might make the job a little easier.

Digitized the donor in my garage tonight with a tape measure and a piece of paper. Measuring arms are for sukkas :P





Just found this, at least it's not just like "f off!"
http://www.dmv.org/wa-washington/custom-built-cars.php

[Edited by - bzroom on April 29, 2009 4:33:34 AM]

Most license registries are OK with kit cars - there's an FFR Cobra with four inch side exhausts that drives around near my house.

It looks like you're on the right track, at least as far as planning goes. I was under the impression you were going to keep more of the RX-7 than you did.