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Previous Next Up Topic Engines / Subbug - Subaru Power / Subaru Manxter (32854 hits)
By Jordan C 1295 Date 2008-12-15 01:34
Hello fellow Subaru buggy enthusiasts.  I own Manxter #92 and have recently "completed" it using a stock VW 1600 power plant.  I love my car, but I now that it is complete I am really disappointed with it's absolute lack of power.  The idea of slipping an EJ25 in the back of it seems relatively straightforward, but looking at the trans work that will have to be done I have an idea that I would like to use a Subaru 6-speed manual instead.  Has anyone done this with a rear-engine configuration?  If so, I would love to learn how it is done.

My dream for this car is actually to reconfigure it for mid-engine.  The Manxter seems like a perfect candidate for the mid-engine configuration because of it's longer form-factor.  There is plenty of room in the body (if I eliminate the all but useless rear seats) but after some careful measurement, it has become clear to me that I would have to either cut out the entire torsion section of the stock chassis, thus eliminating any structural strength it has, or having an entirely new chassis and IRS designed and built specifically for the car.  That seems dicey to me, but I am impressed with the talent on this site.  Maybe with your help it can be done?

Do any of you have any advice for me?  Which direction should I go in and why?
By Mel Adjusted Date 2008-12-15 04:11
I've seen just what your talking about... I guess I'm gonna have to break down and buy another camera... The ones I've seen were really simple and awsome.... Without the backseat there's plenty of room...
At my age.. Everything I buy comes with a lifetime guarantee..
http://mel-adjusted.zoints.com/
By @Jeff GS Date 2008-12-15 17:22
I agree - think the Manxter would make a perfect candidate for mid-engine conversion.  Lots of room to work with!  Plenty more than my 85" Deserter, that's for sure!

The Subaru trans, at least the 5-speed from the WRX, can easily be converted to run FWD and be used in a mid-engine layout.  I hear the auto works well in this layout too.....  :-)

Your real challenge will be the re-engineering of the rear chassis.  You've got the gist of it - basically will have to gut the rear torsion - remove it completely and engineer a fresh new rear frame.  I'd try to use the front end Subaru hubs and drive axles as well, make it an integrated set-up from one manufacturer.  Prepare for some serious modifications to pull this together.  Needed will be custom a-arms, mounting points for the arms, rear chassis, water cooled plumbing, well that's the short list at least!

FWIW, I spent about a year just learning about suspension geometry through books, sketches and eventually some susp. geometry software - before I settled on what I believe will be a good set-up on my GS with low roll centers and minimum RC movement during roll and bump.

BIG challenge going that route!  How about a more reasonable rear-engine layout?  Porsche trans, 944 trailing arms and brakes, 2.5L Suby, all more or less "bolt on" and readily available.  My project is going on 6 years now..... and I started with a mid-engine car!  Something to consider!

Jeff
By Tom & Kathleen I 639 Date 2008-12-15 22:18
I think this woud be a great way to go.  Having put a fair number of miles on a "coventional" rear engine turbo Subaru, one of the handling problems is the extra weight in the rear (maybe 75 #'s in our case).  The other issue is the amount of power available makes the front end "light" under acceleration.   You had better be going straight if you are going to "get on it".  Mid engine would help a lot with both of these issues.  The other drawback is the VW front axle beam.  That needs to be upgraded as well to A-arm.  I can imagine a shortened (14 1/2") rear engined old style Manx type is even more of a handfull. 

I disagree that the back seats are usless.  I have sat back there with another adult a few times.  Of course, we are not tall (under 5' 6"").  Tom   
Tom & Kathleen Manxter #16, Kick-Out SS #16 & FiberFab Buggy
Manx Club #1030, CVA, RBC, SCCA
By Jordan C 1295 Date 2008-12-16 05:20
I would love to see those Mel...

Thanks for the detailed reply Jeff.  Although your build is impressive, your experience is something I DO NOT want to repeat!  I am a pathetically bad metal fabricator.  It has taken me 3 years to build the car to its present state.  I don't relish another extended period of it taking over my garage.  In fact, whatever I decide to do, I will probably farm most of the work out.

Does the WRX utilize a front subframe?  I wonder if a stock WRX front clip could be grafted into a VW chassis replacing the rear torsion and frame horns.  That would allow me to bolt up the stock a-arms and drive axles & brakes.  The manxter's rear cage section would allow me to stabilize the rear of the subframe.  The trick would be where do I mount the strut towers?  There's nothing but fiberglass up in there!

Thanks for the reply Tom, your feedback is insightful as always.  I have really studied your build carefully.  You guys have done a fantastic job documenting your build in photos.  It's invaluable for those of us following in your wrench turns.  Your advice on wheel sizing and spacing on the manxter forum really helped me get my car set up right, THANKS!  About the rear seats, I am 6'2" and all legs, so the back of my driver's seat is all the way up against the front of the rear seat normally. :/

Re-engineering suspension is such a scary concept to me.  I wouldn't dare unless I had someone with experience guiding me or I was following a tried and true design...

By Tom & Kathleen I 639 Date 2008-12-18 02:50
Very nice job on that car Jordan.  I see some new ideas at work such as the rear view mirrors and unique headlights.  Those new style Porsche wheels are also a different touch.

Thanks for the kind words.  We are always glad to help.  We have been helped in the past, and it is only right to pass it on.

I do have a question about how hard is is to steer your car at slow speeds with those very wide front wheels?  Kathleen's car with 7" X 16 with 4" backspacing is like a truck, but my clone with 6" X 16 with 5" backspacing is super easy.  What I am trying to figure out is it the width or the lack of backspacing that is the issue.  Whichever one it is, I would like to fix it.  Thanks!  Tom
Tom & Kathleen Manxter #16, Kick-Out SS #16 & FiberFab Buggy
Manx Club #1030, CVA, RBC, SCCA
By Bill K 96 Date 2008-12-18 16:38
Tom,  Do you think the additional wheelbase of the Manxter comes into play?
By Tom & Kathleen I 639 Date 2008-12-19 13:01
No, I don't think wheelbase comes into play.  I am talking about low speed times like parking and other very low speed maneuvers.  My FiberFab steers very easily and the Manxter is like an old non-power steering truck.  It steers easy with the wheels off the ground, so it is not the linkage.  We had a quick steer on both car also.  The only obvious difference is the backspacing and the fact that her car has 2"" if dish on the front wheels.  Lets get this tread back on track.  Tom
Tom & Kathleen Manxter #16, Kick-Out SS #16 & FiberFab Buggy
Manx Club #1030, CVA, RBC, SCCA
By Jordan C 1295 Date 2008-12-19 15:12
I don't know the definitive answer on the steering question but my guess is that both contact patch width and overall track width factor into steering drag.  My car steers fine when it's moving.  It is a workout to get in and out of a parking space though.  I don't think wheelbase is a factor at all, but of course I could be wrong.

I believe my front wheels are 7-1/2" wide and I had to use 2" wheel spacers in order for them to clear the shock tower on the front beam.  Even with this spacing, I have to limit the steering box with the bolts in the front beam.  Otherwise the wheels would rub the inside of the body when turned to the lock.  That makes parking a little dodgy sometimes because the car has a turning radius like a Hummer.  My steering wheel is 14" so that also plays a part as well.  The rear wheels are 11-1/2" wide and I'm running 3-1/2" spacers back there.  The rears are slightly inside the fender and I would prefer 4" rear spacers for a really flush look.  Maybe I'll fix that in a future upgrade to rear disc brakes.
By @Jeff GS Date 2008-12-19 17:57
Don't want to take anything away from Jordan's beautiful Manxter build - car looks fantastic Jordan and I can see why you might not want to mess with it!  A mid-engine swap is going to require some pretty major surgery - even if it's a total frame swap (you'll be cutting away major cockpit fiberglass behind the front seats!).

If you want to pursue a full custom frame swap I'd recommend you contact Eric Martin:
http://www.6speed.org/bradley/frame.html
(FWIW, Eric occasionally posts on the Yahoo Kelmark board)
I'm sure Eric could put you together either a full rear subframe, or full frame utilizing whatever combination of VW or Subaru parts you like.

As for the steering - it likely is due to the increased scrub radius.  IIRC - the OEM VW wheels is something like 4" wide and 4.5" backspacing.  My rough napkin sketch shows this to be about 2.5" of negative offset.  A 7" wheel with 4" backspacing is 0" offset, or in other words the tire centerline is now "outboard" of the original VW wheel CL about 2.5".  If you're also running dropped spindles, figure on another 1/4"-1/2" or so of offset.  That, in conjunction with the quick steer adapter seems like it would make for some pretty tough steering and might give a bit of unwanted kick-back too.  The bottom line is not so much the offset - but where the rubber meets the road so to speak.  It's the scrub radius that matters and the bigger it gets, the more leverage the tire has against the steering wheel.  Scrub radius is determined by viewing the car front-on, and drawing straight lines, one down the center of the tire top to bottom to where it meets the road.  The 2nd is drawn through the center of the ball joints, again down to where it meets the road.  The distance between the two road-intersection points is the scrub radius.  The smaller it is, the lighter the steering effort required and easier to steer it will be.  OTOH, making it too near 0 makes the steering feather light, but also "numb" so you can't feel what the front end is doing (starting to slide, etc.).  A little scrub is good, and from what I gather somewhere around 1" to 1.5" is a good amount to shoot for (it's actually a percentage of the wheel width, but don't recall the number off the top of my head).

The trade-off to fixing it is wheels with increased negative offset - possibly limiting the turning radius available and having a narrower front track, not really desirable from a handling perspective.  Ideally you want something close back to the original OEM scrub radius.  The fix for the track width is to widen the beam, and moving the ball joint pivot points outboard, then running a higher negative offset wheel.  You still may run into turning clearance issues with this though (I think around 5" of backspacing is the practical limit with a BJ front end?)  Another option is to ditch the whole beam front suspension and run one of these:  :-)

http://a-arm.com/index.html
(He was working a "road" oriented kit, doesn't seem to be currently listed on the site....)

Not sure if it "fixes" any of the heavy steering problems - but it sure looks cool!

Jeff
By Jordan C 1295 Date 2008-12-29 20:59
Thanks for the compliments and the detailed reply Jeff.  If I am understanding correctly, the simplest solution to my problem would be to fabricate some 2" extended arms and remove the wheel spacers.  That would place the ball joints closer to the center of the wheel and reduce "scrub" width while keeping overall track width unchanged.  I would need new longer steering tie rods and custom brake lines as well, but that might solve the problem without completely replacing the front suspension.

Does this sound like a plausible solution to you?
By Mel Adjusted Date 2008-12-30 09:37
Jordan, I've converted 5 cars from rear engine to mid engine.. It's very do-able but you need to do some planning. From the front crank pulley to the centerline of the axle on the Subaru it's about 20". Thats pretty short. Being you'll be going IRS the entire rear suspension can be removed... If you hang loose a bit I'll order a Digital camera and get some photos for you. If you have someone in mind on doing the frame work it might pay to have them come down here and see how we build our racers.. You won't need the travel we have making the suspension easier and cheaper to build.. The racer costs $2,000+ a corner just for shocks.
Dare to be different... This I promise...If you go mid-engine Subaru and it's a turbo'd engine car, you'll mess your pants the 1st few times you drive it... Then you'll need a doctor to wipe the chit eating grin off your face.
I love pulling up next to Vett's, Porsches and Vipers... It brings tears in there eyes...

The Surgeon General says, Smoking V8's is OK.......
At my age.. Everything I buy comes with a lifetime guarantee..
http://mel-adjusted.zoints.com/
By dunelimo Date 2008-12-31 05:02
Why not leave it as rear engine and just install a Porsche 5 speed box and hang the Subi turbo engine from that---a lot less work than going mid mount and I would think at no more expence---I think you can buy a kit to install the Porsche trans into a VW chassis
By Sandsurfer Date 2008-12-31 12:42
Personally, I don't like all the engine noise you have on a mid engine vehicle, not to mention the heat.
Jerry....
By Mel Adjusted Date 2009-01-01 20:36
Everything has it's good points and bad ones...
Hanging the engine on the back makes the install much easier and cheaper but with that much power makes the front end very light and almost impossible to steer without cutting brakes under high power.
The mid-engine setup takes some doing and will cost more but as for handling can't be beat.
Anyone that knows me will tell you I'm a nut when it comes to hi performance and part of high performance is the handling. I've had all the 1,000HP cars that handled like a Sherman tank to last a life time.. I want a car to handle like a Formula 1 with the power of a AA/F Dragster.
What were talking about here is a car with a power to weight ratio of 3.5:1 which will put it in a class of cars that will litterly haul azz...
But we do have one thing.... and thats choice...
At my age.. Everything I buy comes with a lifetime guarantee..
http://mel-adjusted.zoints.com/
By Jordan C 1295 Date 2009-01-02 02:49
Thanks to everybody weighing in on this one.  So according to Mel, I need about 20" from centerline of axle shaft to front of crank pully on the subaru setup.  I don't know how much clearance to allow at the front, but I am going to take some detailed measurements make a few marks with tape on the body/chassis to analyze the clearance issues and I'll post my results for all to view.  Anybody know how much width and height clearance is needed for an EJ25T?
By Mel Adjusted Date 2009-01-02 08:24
If you can hang loose till daylight I'll do some measuring and than you'll have something to play with...
At my age.. Everything I buy comes with a lifetime guarantee..
http://mel-adjusted.zoints.com/
By Jordan C 1295 Date 2009-01-02 19:21
Awesome, I can't wait...
By Mel Adjusted Date 2009-01-02 20:26 Edited 2009-01-02 23:23
OK here you go..... The engine from valve cover to valve cover is 29",
                           With the stock oil pan to the top of the engine 22",   with/ short'n pan 18.750"
                           Engine fron bellhousing to front pulley 16"
                           From front pulley to end of tramsmission 44"

Hows that for openers?
At my age.. Everything I buy comes with a lifetime guarantee..
http://mel-adjusted.zoints.com/
By @Jeff GS Date 2009-01-03 13:43
Hi Jordan,

On the scrub radius reduction - anything that can move the ball joints closer to the wheel would reduce it.  Seems to me lengthening the trailing arms is the hard way to do it?  I'd be more inclined to do a custom wider front beam.  I've seen widened beams where the added center section has (2) adjusters on each tube.  Since you'd need another set of torsion bars anyway for a wider beam, you'd cut off the outer half of each set and have independent torsion leaves for each side.  This would also allow a truly independent(ly) adjustable suspension, enabling corner balancing if desired.  Alternately, one can go with some sort of coil-over shock arrangement and remove the torsion bars altogether, replacing with free-rolling thru-rods (or internal sway bar), like the full-on off road set-ups.  $$$$ adds up quick though, whenever you veer away from near stock VW arrangements!

Jeff
By Jordan C 1295 Date 2009-01-06 05:07
Awesome guys.  Haven't had a chance to measure clearances yet.  Got busy with honey-do's. 

Jeff, a wider beam would seem perfect, but currently, the inside edge of the front rim is about 1/2" away from the shock tower.  That's why I added wheel spacers in the first place - I couldn't even mount the wheels without them.  Is there another way to mount front shocks on a ball joint front end?  Will modified shock towers fit under the fiberglass?

I am thinking one of those a-arm suspensions sound pretty nice.  I don't think Pete has a street version ready for prime time yet though.
By Tom & Kathleen I 639 Date 2009-01-06 23:12
Mendeola Signature Motors is making a A Arm front end that uses a Super Beetle chassis.  We saw the prototype last October, and they had a Black Manxter at the SEMA show with this equipment.  They hinted to me that they might sell the chassis with the front end separatley to help recoup the developemnt costs.  I have pictures if you are interested.  Tom
Tom & Kathleen Manxter #16, Kick-Out SS #16 & FiberFab Buggy
Manx Club #1030, CVA, RBC, SCCA
By Jordan C 1295 Date 2009-01-21 15:16
Very interesting Tom.  I will continue to ponder this front end question.  Given that my chassis is standard beetle I will probably pursue an a-arm solution from Pete (a-arm.com).

In the meantine, I did some careful measuring and marking with masking tape.  This is the best estimate I have made as to the size and location of a mid-mounted subaru engine utilizing the stock subaru trans as Mel suggests:



As short as that engine is, it is clear that either the stock torsion housing would have to be removed or the pan shortened to allow the engine to fit.  One of the main reasons I purchased a Manxter kit in the first place was the incredible strength & ridgidity of the design, utilizing the uncut stock chassis and full cage.  I know this is a Subaru forum, but this got me thinking outside the box...



How about a little Honda VTEC power?  It's close, but transverse mounted Honda engine appears to be shorter than the Subaru.  Here's more info...

http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&item=230319169667&fromMakeTrack=true&ssPageName=VIP:Watchlink:middle:us

What do you guys think?
By @Jeff GS Date 2009-01-22 12:48
Go for it man!
That VTEC engine and trans would make one sweet combo in the back of a buggy, and should occupy less room in the car as well (than a longitudinal layout).  Be prepared to engineer your own rear suspension though.  It's likely you'll still have to lose the rear VW semi-trailing arms and torsion bars and make some kind of new subframe to fit it in there, and tie into the roll cage.
The other thing to watch out for is overall height of the package.  In my mind one needs to incorporate an engine cover to conceal the whole engine package (as well as provide heat and noise insulation from the cockpit).  If the cover sticks up too high above the rear sides of the body it might look a little awkward.  Also keep in mind that exhaust manifold will be right behind the driver/passenger seats!

Jeff
By charliew Date 2009-03-16 19:05 Edited 2009-03-18 16:25
I know this is sorta old but still a good thread. I started a rear 901 wrx conversion and decided the radiator deal was a big deal so it's on hold. I have since moved on to a 914 as it's already been done a lot and I can pick the best parts of several conversions and go from there.

But I'm still studying the buggy. I also have a 58/64 bug sedan thats been a pickup since 68. It can also use a mid suby motor and tranny. The pickup the easiest because of the rear bed and closed off cab already.

I think the 914 rear trailing arms or a modified version will do the trick. The deal would be to copy the 914 trailing arm mounts and incorporate them into a new rear pan frame. The 914 uses the 4 bolt vw pattern or can also use 911 stuff with 100mm cvs. Of course on the buggy the body will need some reconstruction. The tread width is within a inch on the 914 versus the bug but the buggy is not a problem. It looks like the complete torsion tube will come out and the fabbed rear will require a reglassed inside back of the fg body buggies. Hey they use mid engine speedsters chassis on some speedsters. My fiberfab already has a rear trunk but the floor could be removable. The buggy still has the radiator location problems though. The two radiators on either side infront of the wheels seems to look the best but will probably be the most expensive setup.
By Jordan C 1295 Date 2009-03-18 02:37
With the bug/buggy, how do you figure you can gain clearance for the crank pulley at the center of the torsion housing?  That's the reason I ended up deciding against mid-engine subaru.  The required surgery is too extensive for my tastes.

You could probably angle the engine upward to sit above the center of the rear torsion, but you would need a custom oil pan at least.  I have searched high and low for people that have done a mid-engine bug, but haven't found anyone using subaru.  There's a well-documented account of a front wheel drive volvo going into a bug and that seemed to work pretty well.

I thought Honda would be perfect because their engines are a dime a dozen and highly reliable.  The drawback for mid-engine is (as stated in an above post) that the exhaust manifold is on the forward side nearest the passenger compartment.  If you use a Volvo, the exhaust is on the rear side for a quieter ride.

I am still very interested in this concept, but my project is on hold for now while I do more research.
By Jordan C 1295 Date 2009-03-18 02:39
Also, you can get a stock T5 volvo with a turbo and five cylinders instead of four in the same amount of space!  Hondas don't develop a lot of torque.
By @Jeff GS Date 2009-03-18 12:03
A big problem with going with a mid-mounted Subaru is it's like putting a big "box" between the cockpit and trans/rear tires - that everything has to go around.  Nothing a LOT of thinking and figuring out can't take care of, but it takes lots of both (OK, it took me lots of both!) to figure it out.

The problems are chassis tube layout and how do you get the structure around that big box of an engine and back to the trans and rear suspension which needs a narrower width for adequate a-arm lengths.  Underneath doesn't leave much room either with the water pump inlet/hoses, exhaust manifolds and oil pan down there.  You're left with having to go very wide on the lower tubes, or have them wrap up close to the oil pan (as I did) between the pan and manifolds.  This gets trickier as you also have to figure out how the exhaust will route towards the rear, and somehow come together if running a single turbo - while clearing the chassis and rear suspension.  You start running out of room very quick!  The shift linkage comes into play as well, especially with the mechanical 914-based linkage I'm fitting.  A cable shift would possibly be easier to route.
You end up thinking about using "box" shaped structures for the chassis layout, which are the worst for structural rigidity.
I'd also do a full a-arm based rear suspension design as opposed to my trailing arm "Can Am" layout - too difficult to get trailing arms back there around the big "box".  I suppose grafting the 914 style trailing arms could be another solution (especially since it has similar engine layout) - just keep in mind the 914 has NO lower frame structure beneath the engine and trans - it's all supported from above and to the sides for the front engine mounts.  The 914 arm option may limit adjustability too?  Plus you have to make sure the mounting points for it are very sturdy, since the whole rear suspension is cantilevered off those points.
Some things to think about!
Jeff
Previous Next Up Topic Engines / Subbug - Subaru Power / Subaru Manxter (32854 hits)

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