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  #1  
Old 12-19-2011, 06:53 PM
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Mid engined v6 offroad racer build

I’ve been building and racing my own sedans and buggies for basic level motorsport here in Australia for thirty years, winning a few club championships and state titles along the way. A number of things have motivated me to do this new project.
I’ve just about finished building my V6 EG Civic and have decided to keep it just as a tar car. Dirt events take a fairly high and constant toll on bodywork, but as rallysprints are my favourite events and I wanted to return to them, I decided to build something specifically for them. Wanting no bodywork meant it’d have to be a buggy, and the four previous ones I’d made have given me good experience in how to do it. Looking around at the current buggies I couldn’t get away from how ancient most of the winners technology was, with most of them using VW suspension designed before World War II, floor pans over forty years old, and engines from the 1980’s at best.
If I was going to invest the time, money and effort this’d take I was confident I could construct a new bench mark, and race for outright victories. A front wheel drive buggy would be way too light in the rear to handle and drift well on the dirt. Although I’ve successfully raced rear engined / rear wheel drive buggies, I felt there had to be something better than the VW type rear end with an engine swap that’s been so done to death. That only left a mid-engined racer. I’d seen a few of these made by moving a complete front wheel drive front end to the rear, and the design and race performances I’d seen had always impressed me.I'd mapped out a basic chassis design incorporating what I thought was the best features from a number of buggies and build sites I'd cruised.
Then by chance a few weeks ago a good mate of mine told me he had a buggy chassis for sale - an old "Bushmaster"off roader. It had held a VW front and rear and didn't meet the new Confederation of Australian Motor Sport (CAMS) requirements for buggies because: 1) The diagonals are not within the main hoop 2) The rear braces have a curve in them 3) The roof is not covered nor braced to the floor and main hoop 4) The bar which holds the steering column isn't the same size as the roll bars. 5) There are no braces across the floor between the base of the front pillars nor half way between them and the main hoop. 6) The bar running up the middle of the chassis is too small. 7) It has no rear wheel protector side bars.
but it'd provide me with a lot of the right steel already bent to shapes I was sure I could adapt into my build. I love the sound of an angle grinder in the morning!

I built a levelled, raised false floor in my garage and have marked a 100cm grid onto it. This gives me quick measurements and ensures everything will be square. A perfectly flat floor equals a perfectly flat chassis floor. I've begun with the new centre rail and the cross member on which the main hoop will stand. The cross member is the width of the outside rear tyre track.
Next I've added the side floor rails and the cross members as CAMS requires - all made from 40mm square tubing.
The main hoop is then shown without a cross member and after I re-cut the old one into it. This design is one CAMS approves.
These fifteen 3mm gusset plates will strengthen the chassis and also serve as mounting points for the floor.
They avoid weakening the frame with bolt holes, and will allow me to drop the floor out when it gets full of muddy slop like I got buried in at Ansell Park late last year. I will employ them as needed throughout the chassis to eliminate any cracking at high stress points.
I searched the net without any preconceptions to find the most powerful, readily available, and most affordable car fwd car from which to derive a powertrain and suspension to move to the rear of my buggy. I’m notorious in my home town of Newcastle as a Honda nut, but to everyone’s surprise – I settled on a 3.5 V6 Magna with a manual gearbox as the ideal donor car.
I watch the car salvage auction listings up here almost every day, and within 5 weeks what I wanted came up, and I got it with a mere $350 bid.

It had rolled into an empty storm water drain, damaging no mechanicals but just about every panel on the car… perfect for my needs and virtually no-one elses.

With an electric winch mounted overhead, I was easily able to lift the body up and remove the entire front end.
The aluminium subframe locates most of the suspension geometry and would save me weeks of work.
I filled the shell with spare motors and car scrap and took it off to the metal munchers where I got $167 for it. This is a scary industrial site where cars go to die… and be re-born as god knows what or where.
I carefully positioned the powerplant and subframe squarely and level on my table lined up with marks for my 2 metre wheelbase.
Screwing the drivers compartment frame and cage in place on the table enabled me to design and fabricate a rear subframe before my welding mate came over for what’ll be a mammoth session. I picked up the six lower subframe mounting points.
After the lower frame I bent up the main rear chassis rail.
Then cut it’s supporting diagonals.
She’s starting to get a look about her that suits the name she’ll carry “Raptor”!

Last edited by Redliner; 12-20-2011 at 03:50 AM.
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  #2  
Old 12-19-2011, 10:31 PM
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Quote:
Originally Posted by Redliner View Post
IVE TRIED TO CREATE AN ALBUM & POST PICTURES, BUT CAN'T FIND THE ALBUM LINK IN USER CP. CAN ANYONE HELP ME?
Hey Redliner welcome to the OFN.
The easy way to post pix is to become a member and simply post them. Short of that you need to host them someplace like Photobucket and then link them
It sounds like a heck of a cool project and I'm looking forward to seeing what you are building!
E
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Last edited by entropy; 12-21-2011 at 11:48 AM.
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  #3  
Old 12-20-2011, 08:13 PM
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A basic rule in steering geometry is that the swivel joints on the end of a steering rack must align with an imaginary vertical line between the inner mounting points of the front lower and top wishbones. If this is neglected the car will steer itself as the suspension moves up & down… “bump steer”. To avoid this problem (particularly in a narrow front framed car), requires that either a steering rack be shortened to match the chassis width, or that the frame be made to the width of a suitable rack.
Shortening a rack isn’t a cheap or simple exercise by the time you buy one, dismantle it, have it machined, and then re-assembled. I searched e-bay for shortened racks, but the few I could find were either tiny ones designed for miniature motor bike engine buggies, or expensive new speedway items. Most were overseas with high shipping costs and prices over $400. So I just kept on looking without much hope, until last week on the ninth page under “steering rack” I saw something that appeared short and looked like it might be suitable. It was in Victoria with only a few hours to go – not enough time to find out it’s width. But it was only $20 “Buy it now”, so I took the risk and grabbed it.
The driver sits further forward in a mid-engined chassis. This means there is no room to mount a rack behind the front uprights, as there isn’t enough room with the foot well being so far forward. I ‘d worked out what front suspension uprights I wanted to use, but realized I’d have to swap them over from left to right so the steering arms were in front of the hubs.
Two days later I had my cheap used part from a Peugot 205 Gti hatch, and it was only a little wider than my laid out chassis. As this hadn’t been welded yet, I merely had to widen the frame’s nose by 100mm and it was a perfect fit. For $20! Now I can fabricate the front end of the frame.


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Old 12-21-2011, 11:49 AM
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Are you going to stay with the factory drive axles and if so how much travel can you get?
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Old 12-21-2011, 05:22 PM
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Originally Posted by entropy View Post
Are you going to stay with the factory drive axles and if so how much travel can you get?
As far as strength goes the stock axles should be fine - given that the buggy will weigh far, far less than the Magna's original weight. This has proven the case in other similar builds by myself and fellow racers in my circles. I'm not sure how much rear travel I will get. I'll just max it out with the space frame being well above the shafts, and by the normal ride position and angles of the rear arms being lower than normal.... i.e. the suspension sitting much higher at standstill. This will all be assisted by fitting long travel coil overs too. The tracks I'm building this to race on are set up for rally cars so they're mostly graded and we don't have jumps. So it'll be ok even if I can't get as much rear travel in the suspension as needed in a pure offroad racer. By way of example any offroad buggies that have raced more than once in our type of events all lower their cars and soften the suspension by the next time they turn up.

Last edited by Redliner; 12-21-2011 at 05:24 PM.
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Old 12-23-2011, 03:45 AM
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I made a start on fabricating the front of the car. First piece I bent up was a big horizontal nerf bar to protect me and some of the front suspension. I made it a bit on the long side so I can trim it to size once the car is rolling and steering. I'll also brace it's ends back to the frame. Next bender creation was the lower lip of the "Rhino" bar which will be fitted with 3mm steel sheet to serve as a skid plate. It reminds me of one I made on and earlier pig hunting buggy. Still remember the sound it made when you ran over a grunter.


It's angled right up to match the angle the nose might get when landing from a big lift off.

Following pic shows the sort of strengthening I'll put in once the front's welded on. Triangulation is the strongest friend of any spaceframe.

Here you can see the 25mm straight bar I cut to go from the top of the front hoop curve to the floor as CAMS requires.

Then I triangulated it into the side "hip" bar so they're bracing each other.

Here's a place I can add triangulation with minimal weight increase and without obstructing my forward vision. This is gonna be one tough chassis - which should stop both it and me from breaking.

Last edited by Redliner; 12-24-2011 at 10:22 PM.
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Old 12-23-2011, 06:09 AM
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My pic above showing the bottom rail of the frame coming up at an angle at the front may concern some with suspension design awareness. Normally in a car with a lower wishbone like a clubman, racing car (or even a road car), the suspension moves up and down at 90 degrees to the horizontal. Even if it's lying over at an angle away from the wheel any coil or strut must move up and down in the same vertical plane in which the wheel does. So a discerning viewer of this build thread might think that with my frame coming up sharply at the front I haven't enough front frame low down on which to mount the front inner wishbone swivel point.

However the front wheels on this buggy will NOT travel up and down at 90 degrees to the horizontal. If they did, I'd have to build those ugly high top strut mount points sticking up halfway along the bonnet to locate long travel shocks. That blocks road view and (I think), looks bloody ugly. In deciding to NOT use a VW trailing arm front end I had to search for a better design - one that I could both understand and build. Lots of surfing in cyberspace has led me to copy a design where the front wheels move BACK as they ride up. The coloured lines in this doctored pic show: red: the bonnet line defining brace that will slope down from the front hoop all the way to that big front bar; yellow: the top strut leaning right back with it's top mounting point off the front hoop, green: the lines at 90 degrees to the shock's travel along which the top and lower front wishbones will need to be positioned. The latter shows how much higher than a vertical travelling suspension the very front mounting points for the wishbones will need to be. Like I said at the very start of this blog - this will not be an old school build.


As this will be my first (and last), build of such a suspension, I'd welcome any geometry advice from you gurus out there with much more experience than myself.
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Old 12-26-2011, 03:21 AM
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This pic shows the second rear compulsory roof brace I needed to install going from the main hoop down to the hip rail. You can see how much tougher it makes the driver’s compartment than the old buggy frame I started with.

Once again I chose to add gusseting to make it even stronger which joins the brace into the diagonal within the main hoop, plus a tube triangulating the side hoop to the outer edge of than main hoop. Sorry about the masking tape – but it’s the only way I can keep fabricating before my welder and his MIG arrive without loose bits of steel falling on my head.

I added a second gusset plate to tie the rear roof brace into two bars within the main hoop, each bar strengthening the other.
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Old 12-27-2011, 04:05 AM
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Now for some lessons in steering geometry. A good friend of mine who’s built many race cars is following this build blog and rang to warn me of a problem to avoid. In a nutshell if I use Magna hubs in the front of my buggy by swapping the left to the right and vice versa I’ll end up with Reverse Ackerman. His call reminded me of a Datsun Bluebird my brother in law bought that’d had a V8 swap done on it, and they’d had to swap the front uprights across so they could put a forward mounted steering rack in it to clear the block. I drove that car and it was WEIRD around corners. He had a wheel alignment done, they discovered Reverse Ackerman, so he sold the car asap. But what is it???

Ackermann steering geometry is an arrangement of linkages in the steering of a car designed to solve the problem of wheels on the inside and outside of a turn needing to trace out circles of different radius. The intention of it is to avoid the need for tyres to slip sideways when following the path around a curve. Ackermann steering geometry is made by moving the steering pivot points inward so as to lie on a line drawn between the steering kingpins and the centre of the rear axle. You can see from the following pic of the Magna front hubs I am using on the back, that if you put the steering rack in the front of the axle line you need your steering arm rack holes on the hubs to be CLOSER to the disc brakes, rather than angled away from thems.


So what does this mean for my build? Basically to use a steering rack mounted forward of the front axle line means I’ll have to source a pair of front uprights from a road car of the same design, and with the Magna stud pattern of 5 x 114.3. Some likely candidates from my initial research suggests Mazda Rx7, Skyline R33 or R34, and Toyoata Hilux 2wd worth looking at in the metal.
Does anyone know if any of these cars have a forward mounted rack?

I cut more re-enforcing bars for the rollcage. Although these two going to the top outer edge of the main hoop aren’t compulsory why would you NOT have them? I’ve at last run out of steel to cut more framing until my steel merchant re-opens in the New Year, but I’m sure MIG man will be glad of that!

Last edited by Redliner; 12-27-2011 at 04:55 PM.
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Old 12-27-2011, 10:22 AM
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Thats an awesome build up your doing. Its nice to see different types of offroad equipment.

That VW buggy you posted a pic of is badass looking.

Keep up the good work.
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Old 12-28-2011, 04:10 AM
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My son races this RX7 series 6 and sent me pics of his suspension, which uses a front mounted steering rack. So with the same stud pattern as the TJ Magna it looks like I've found the front hubs and brakes I need to chase after for "Raptor".


Here's what his toy looks like. It used to be black but we vinyly wrapped it copying the Le Mans winning Rx7. Easier and cheaper than painting, and you can change it when you get bored.

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Old 12-29-2011, 01:58 AM
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Time to remove the rear steering rack and locate the tie rod ends. The other fwd power plants to rwd converted buggies I’d seen had all fastened the tie rod ends cut off from their redundant steering racks to their chassis. This requires exact locating, otherwise the car will steer itself as it rides up & down (bump steer). I would’ve done it the same way, except I was lucky enough to have a careful look two weeks ago at a brand new mid engined Clubman a club member had made for black top work. I’d already got a few innovative suspension ideas off his car as I walked around it at it’s debut. Then I saw he’d fastened his rear (non-steering) tie rod ends to the lower wishbones rather than the chassis. I instantly realised this was a much better method, because the tie rod arms would just move as part of the wishbone itself – eliminating any possibility of bumpsteer.
So the first thing I did was cut and shorten the tie rod arms off the rack, then I threaded them to take two large nuts.

Then I made a strong bracket to be welded onto the wishbone to which I could bolt the arms. I drilled a small hole in the arm ends to take a split pin as a failsafe. I’ll weld the outer nut and a big washer to the rod, and use a Nylock nut before the split pin on the inside.

Although not crucial, you can see from above that the rod lines up with where it used to attach to the steering rack, which has now been removed. And what a heavy cow it was too!

Adjusting toe in and out on the rear will obviously be a cinch now.
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Old 12-31-2011, 04:52 AM
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Reversing the Gearshift
One of the things that attracted me to the Magna for this build was that the gear shift linkages were cables – rather than rods. This makes re-positioning the gearstick in front of the mid-engined motor (compared to behind the donk in it’s factory fwd set up), much easier. The cable collars were mounted at the back of the motor near the flywheel – but if I used the stock position the cables would have to be significantly lengthened, and the gearstick would be on the wrong side of the cockpit. So I put the cables on the other side of the gearbox linkages, changing it from a push / pull setup to a pull / push one. I did this through some pivot arms I made and a couple of turn buckles left over from a landscaping job. This reversed the shift pattern… which is just what I wanted.

Besides the cabling now going forward of the engine (instead of back), the cables would now enter the gearstick from behind it (rather than from the front). I spun the gearstick around the other way – two control reverses retaining the normal shift pattern, and cables that won’t need lengthening.
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Old 12-31-2011, 05:32 AM
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I bet your about brain dead surfing the webb to get all these parts?
My one question is about the angle of the front shock being the top tilted back instead of being mounted 90 deg to the horizontal. Do you think you will get enough dampening effect at that angle? Just guessing around a lose of 25% effectivenes? Maybe a higher spring rate, that's if you can find one in hyper space.
I may have missed how your doing your rear shocks. Do you have any concerns about your relatively short wheel base concerning the front shocks still rebounding or oscillating at a different rate then the rear when your hitting the bumps with the angled front ones. Or is this no big deal?
Really enjoying your build...makes for a fine read.

Last edited by rookieshooter; 12-31-2011 at 07:12 AM.
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Old 12-31-2011, 09:54 AM
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Titling the front shocks back would be no different to angling them sideways as far as reducing their spring rate goes. A friend has a scale showing the precise reduction in springing per degree of angling of the shocks. However I am NOT going to angle my front shocks back from the angle of swing of the wishbones. Rather, I am going to do the opposite and build my suspension so it pivots to the laid back front shocks, constructing the front inner wishbone pivot points at ninety degrees to the angle of the front shocks. Look again at the two green lines in my suspension geometry photo.

Here's a buggy sold here in Oz as a kit car, which I'm copying the front end off. Notice the angle of the front inner wishbone pivot points is NOT parallel to the ground as in most builds, but rather quite steeply angled to match the compression line of the shocks.


I'm not worried about front versus rear spring oscillation as this buggy will race on graded dirt tracks, not offroad goat tracks. Anyway I'm happy to leave sorting any issues like that until they arise (if indeed they do), rather than having to be 100% sure until I move off the drawing board. I'm the sort of guy who gathers as much info as I can, and then just plows into getting things done with self confidence that I will be able to overcome any unforseen problems that may arise. This has worked 95% of the time - but not always!

Glad you're finding my build of interest.

Last edited by Redliner; 12-31-2011 at 10:01 AM.
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Old 12-31-2011, 11:12 AM
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Got it. Just did not follow the first post well enough.
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Old 12-31-2011, 11:46 AM
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Great build! Interesting explanations of the steering geometry. I learned a lot.
Keep on going!
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Old 01-01-2012, 05:41 AM
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TIG Man Starts
My son James has just bought and learnt to use a TIG welder for the construction we both do on our race cars. TIG welding is slower than MIG – but stronger and more suited to delicate jobs. So I took the gear shift linkages I’d cut and a few other bits over to him and away he went.

Then it was back home to paint them with aerosol engine enamel. It needs no primer, is heat proof, and quick drying. By afternoon tea time I was able to assemble the welded linkage pieces and adjust them to clear where the chassis rail will go.

I also re-fitted a couple of engine brackets I’d lightened and painted as well.

If I’m lucky MIG man will turn up tomorrow and we can get into welding the main pieces of the chassis together.

Last edited by Redliner; 01-02-2012 at 02:17 AM.
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Old 01-02-2012, 02:17 AM
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I just watched today's Dakar and saw lots of vehicles with their front struts leaning back and the wheel going back as it went up. They're called motorbikes
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Old 01-03-2012, 12:51 PM
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Motorbikes are not what you should be looking at, are you going to use struts on the front? Even if you are, the KPI angle and caster doesn't have
anything to do with where it's mounted to the spindle... Here's a nice picture of what I'm talking about...

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