Topic: How we built the 2-stroke Miata.. some pics, links, thoughts and bs

First some pics that are on our facebook page:

http://www.facebook.com/media/set/?set= … amp;type=1

  Scott DeWinter was the diabolical nutcase who thought the whole thing up.  His brother is in the snowmobile industry and he comes from Alaska.. So snow-machines populate his dreams/nightmares.

    I will try to describe our build as time allows.   

   Suffice it to say that the car way out-performed our expectations, so much so we weren't ready to do quick fuel stops/driver changes and lost a ton of time off track.

  Top time was 2:11 to the fastest car's 2:03.     

   And yes, it is pull start and belt driven.

  -John

Gosh, my business card says 'Tech Tyrant'

2 (edited by ppressle 2012-03-26 01:35 PM)

Re: How we built the 2-stroke Miata.. some pics, links, thoughts and bs

We could always tell when you were ahead of us on the track by the smell. 

I wish I had a camera to film you using the pull starter in tech.

3 (edited by hoverducky 2012-03-26 06:29 PM)

Re: How we built the 2-stroke Miata.. some pics, links, thoughts and bs

Balto's origin story as I remember it:

I'd been thinking about a snowgo-powered LeMons car for a while, so I sent my brother $1000 and a request for triple that didn't suck.  A few weeks later I get back $1000 and a built-and-running-but-otherwise-a-mystery Polaris 600 mill complete with clutches, triple pipes, jack-shaft, chain-case (which we didn't use), and other hyphenated items.

He'd bought a complete sled locally (Idaho) and parted the thing out.  He apparently made pretty good money on it.  My folks brought everything back in the bins under their RV during one of their retired-persons' road trips.  Unfortunately Chris didn't come through completely on the "doesn't suck" part.  The engine has a reputation for twisted cranks and is only rated at 92hp.  Shrug.

I mentioned  to John that I had this pink engine laying around.  He expressed interest.

I was thinking Le Car or something, but a few months later, at the LeMons HQ party I think, John re-expressed interest and said that he had this body-wrecked Miata that he'd already written down beyond zero.  Now, I was really sick and he was totally hammered, so you wouldn't think the plan would stick, but somehow my father and I wound up in West Sacramento at the end of January for four days of stupid engine swappage, the first of quite a few.

We ended up playing the "how light can we make a Miata" game, which is kind of fun.  It is sort of weird how heavily the cars are built, actually.  None of it is in the body, either.  Stupid convertibles.  The de-weightification was helped immensely by the replacement of 550 pounds of Mazda drivetrain, exhaust, plumbing, and wiring by 88 pounds of Poo.  I mean, you can pick the entire engine and "transmission" up by yourself and walk it around.

It was a pretty easy swap, really.  The drivetrain is very simple.  The motor mount brackets and stuff are hacked together out of scrap steel and we built a simple tool to ensure the clutch center-to-center distance was right. 

The black body parts are takeoffs that came out of my junk pile, and we got the Polaris bits to talk to the Miata bits by cutting down the jack-shaft and a ruined Miata output shaft and welding the suckers together.  The front bearing is the stock Poo clutch-end jack-shaft bearing, the intermediate bearing came on the output shaft, and I bought a big sucker to support the Miata driveshaft snout.  Sorta worked.  We did burn up the intermediate bearing.  It sort of welded itself to the shaft, but it turns out stuff works just fine without it.  I think we will be adding some compliance to the rear bearing mount in the future.

Anyway, after two months of long weekends, the car made a couple of passes up and down Rice Avenue and into the trailer bound for Sears Point, and the rest is just a miracle.

I'm ecstatic that the car ran at all, much less finished.  It is also a joy to drive.  A bit strange, but in a good way.  All the drivers got at least one stint in the wet and at least one in the dry.

Regular Miatas make drivers into heroes.  What we have built is a machine that turns men into gods.  Any line, any time.  The outside passes in turns one and six are the stuff that giggles are made of.  We were running around 600rpm shy of the supposed torque peak, so we were a bit down on power.  Our top-end speed is also a bit limited, but it is race-able.  It would have been nice to have windshield wipers on Saturday, but I guess you can't have it all.

We couldn't have done it without help from Dave, Fish, Wayne, Lisa, Clint, and my aforementioned father, all of whom contributed labor, fab skillz, and blood to the build.  Turns out that Balto bites.  John's guys Hank, Darren, and Crawford did a wicked job on the cage.  It is a work of art.  They also put up with random idiots wandering around their workplace asking to borrow the tools they use to make a living, which is pretty cool of them.

There are more details if people want to know them, including insight into the black mysteries of centrifugal clutch tuning, but right now I'm headed for the pub.

Scott

Re: How we built the 2-stroke Miata.. some pics, links, thoughts and bs

So this means two snow machine motors would be better?

Daniel Sycks
Muttonheads!, nee Focke-eWe190 85-86-87-88 GTI
A Division of Cosworthless Racing. Sponsored by Marlburro!
http://www.facebook.com/pages/Muttonhea … 7122228200

Re: How we built the 2-stroke Miata.. some pics, links, thoughts and bs

hoverducky wrote:

There are more details if people want to know them, including insight into the black mysteries of centrifugal clutch tuning....

I have a couple of reasons to be very interested in that topic, if you've got any pointers.

http://farm2.staticflickr.com/1393/4733417200_c246d1d1e2.jpg

Index of Effluency, 2012 Pacific Northworst Grand Prix, Freewheelin' Pikers, 1967 SAAB 96
Longest Distance, 2010 Concours d'LeMons Box Wine Country Classic, 1982 MG Metro 1300
Second-Round Elimination, 2010 LeMons Pinewood Derby at Sears Pointless, 1978 H Special
Worst of Show and Fright Pig Supremo, 2009 Concours d'LeMons, 1980 KV Mini 1

Re: How we built the 2-stroke Miata.. some pics, links, thoughts and bs

While awesome, I was kinda hoping that they'd actually converted the Mazda's engine to a 2 stroke. 

I have this recurring fantasy where I convert a Mercedes 5 cylinder turbo engine to a 2 stroke diesel...

Tunachuckers: Returning to a race track near you in 2014!

7 (edited by Mulry 2012-03-27 06:49 AM)

Re: How we built the 2-stroke Miata.. some pics, links, thoughts and bs

The car was simply awesome. It caused significant brain confusion the first time I saw and heard the car -- looks like a Miata but what the eff is that sound? Then "it's got a snowmobile engine" and it all makes sense again. Only in LeMons.

My favorite moment was when the car got a black flag in the dry on Sunday. The driver pulled into judging and shut the car off (mostly because you can't hear anything above the racket that it makes when running even at idle). Jay gave the driver the business for a bit, then said something like "I want to see you start it with the pull start." The driver reached over and gave it a yank; the pull cord promptly broke off in his hand. Hilarity ensued; "Penalty served!" and they were out of there.

Awesome car, guys. It was fun sharing the track with you.

Pat Mulry, TARP Racing '67 SIMCA GLS 1000
"The SIMCA 1000 rear engined saloon is not a car which is going to be remembered in years to come for any particular reason.... It is not startling for its beauty, innovating with its design or particularly fast, economic or comfortable. However, it has been successful for SIMCA, especially in France."
--SIMCA 1000 Owners Workshop Manual, J.H. Haynes, 1973

Re: How we built the 2-stroke Miata.. some pics, links, thoughts and bs

I'm stunned it ran all weekend.....I figured it would grenade in specatular fashion at about hour 1...... 

Now I want to drive it!!!!!

Richard Doty
1984 Porsche 928 "Estate"
Porsche- "there is A substitute" Racing
Dirt Poorsche Racing #2

Re: How we built the 2-stroke Miata.. some pics, links, thoughts and bs

In my experience, when two strokes die they do it rather unspectacularly and occasionally impermanently.  Seizure seems to be the rule, and a little cooling down often frees them back up.

Scott

Re: How we built the 2-stroke Miata.. some pics, links, thoughts and bs

mechimike wrote:

While awesome, I was kinda hoping that they'd actually converted the Mazda's engine to a 2 stroke. 

I have this recurring fantasy where I convert a Mercedes 5 cylinder turbo engine to a 2 stroke diesel...

I'm not sure that is a healthy fantasy life.. You may need some therapy, or some time alone with an OM 617...

Gosh, my business card says 'Tech Tyrant'

Re: How we built the 2-stroke Miata.. some pics, links, thoughts and bs

There is no such thing as a $500 Miata.   Snowmobile powered or not.  big_smile

Dangerous Banned Technology (NOLA 09), Judges Choice (Houston 2010), Organizers Choice (NOLA 2010), Most Heroic Fix (Dallas 2010), $100 from Jay's Pocket (Dallas 2010), Dangerous Homemade Technology (NOLA 2010), Ununhexium Legends of Lemons Status,  Index of Effluency (Dallas 2011), Most Heroic Fix - (Houston 2011), Index of Effluency (TWS - 2012), Organizers Choice (Dallas 2013)

12 (edited by Jer 2012-03-27 02:35 PM)

Re: How we built the 2-stroke Miata.. some pics, links, thoughts and bs

BS.  There are lots of $500 Miatas.  You have to pay attention and jump on them fast.  I personally have purchased four in the last three years.

Jer / Schumacher Taxi Service
2010 Spring CMP I.O.E. winner
2010 Sebring overall winner
1996 Miata, 1987 coROLLa

13 (edited by hoverducky 2012-03-27 02:43 PM)

Re: How we built the 2-stroke Miata.. some pics, links, thoughts and bs

Okay, centrifugal clutches:

To quote Polaris "The Polaris torque-o-matic" (really!) "drive system is a centrifugally actuated variable speed belt drive unit.  Blah blah blah." 

The system is comprised of the drive clutch, the driven clutch, and the belt between them.  The belt is basically a wide v-belt and the clutches are sort of pulleys, each of which has a pair of sheaves with angles that match the belt.  One sheave on each clutch moves axially, which changes the effective radius of the pulley by driving the belt out or allowing it to drop back in.

The drive clutch starts out with the sheaves held apart by a compression spring.  The ubiquitous P85 drive clutch contains three flyweights arranged radially and pivoted off the moving sheave at their outboard ends.  The back sides of the weights are cam surfaces which ride on rollers mounted on the fixed end of the clutch.  Things are set up so that the belt is slack and free of the drive clutch at idle. 

When the RPM rises (to around 4600rpm in our case) the centrifugal load on the weights pivots them outward, driving the moving sheave towards the fixed sheave, pinching the belt and forcing it out radially, which increases the belt speed.

The driven clutch is kind of weird inside, in that it contains a single spring which acts in both torsion and compression at the same time.  The spring acts on the "helix", which is a three-pronged jobby with helical ramps that ride on buttons in the fixed sheave.  It is keyed to the moving sheave.  Rotating the moving sheave and helix allows the sheaves to split apart and drop the belt to a smaller radius.  The spring can be indexed to the helix in multiple positions, which varies the preload and changes the effort required to split the sheaves.  The driven also has a cam thing on it which allows for adjustment of the at-rest sheave separation.  This can be used to tune initial belt tension and make up for variations in pulley center-to-center distance.

The drive clutch reacts mainly to RPM, and the driven clutch maintains belt tension while reacting to torque.  When things are set up properly the system freewheels until the engagement rpm, then immediately goes to the torque peak of the engine under full throttle.  As the road speed increases, the drive clutch effective radius increases and the driven clutch effective radius decreases to hold the engine at a fixed rpm.  It is approximately a continuously variable transmission which decouples at low RPM.

Under part- or no-throttle conditions the torque drops, which allows the system to kind of up-shift and the rpm will drop and become proportional to road speed until the engine RPM goes below the engagement threshold and the drive clutch pops all the way open, allowing the belt to freewheel.  Or the throttle is pinned, which down-shifts the system and away you go.

The drive clutch is bolted on to the end of the crankshaft and on a snowmobile the driven clutch is hung on a cantilevered jackshaft which reaches back parallel to the crank to the magneto end of the engine, where it is splined into the disk brake/chaincase assembly.  Two sprockets and a chain provide some gear reduction and transfer power down to the track drive.  Arctic Cat builds something called Diamond Drive, which uses a planetary gear box instead of a chaincase, and more recently Polaris has gone to cog belts instead of chains, at least on their high-end models.

In the Mazdolaris, the geometric relationship between the drive clutch and the driven clutch is maintained by flipping the driven clutch on the jackshaft, the clutch end of which is conveniently just an end-tapped 1" steel shaft with a keyway.  John had the brilliant idea of using the Miata tranny output shaft to interface with the stock driveshaft, so we just reached back to that with the jackshaft and didn't have to screw around with custom driveshafts and stuff.  This simplified the build immensely and kept it cheap.  We didn't use any of the chaincase crap.

Next up: clutch tuning.

Scott

Re: How we built the 2-stroke Miata.. some pics, links, thoughts and bs

Team Sensory Assault wrote:

There is no such thing as a $500 Miata.   Snowmobile powered or not.  big_smile

I see your smiley, but feel now is a good time to admit that Balto's donor was not a $500 Miata.  It was a -$2000 Miata.  John made out pretty well on it, from what I hear.  The right-front frame horn was accordioned pretty good.  It took some time with a torch, a hammer, and two Super Duties to make that side of the car long enough for us to even fit the motor.  It's still got that Gerard Depardieu thing going on.  There's a video out there somewhere.  Of the Ford tug-of-war, not Depardieu.

It was also a limited-edition 1991 BRG car, but the insurance company didn't seem to care.

One of the cool things about body-wrecked cars is that if you use the panels that were on them when they were hit, things line up nicely.

Scott

15 (edited by Evil Genius 2012-03-27 06:26 PM)

Re: How we built the 2-stroke Miata.. some pics, links, thoughts and bs

Pics:
  Clutch
http://i178.photobucket.com/albums/w279/Evilgeniusracing/100_5727.jpg
  Pull Start and collector
http://i178.photobucket.com/albums/w279/Evilgeniusracing/100_5724.jpg
   Pipes!
http://i178.photobucket.com/albums/w279/Evilgeniusracing/100_5723.jpg
   Balto!
http://i178.photobucket.com/albums/w279/Evilgeniusracing/100_5720.jpg
  Exhaust outlet
http://i178.photobucket.com/albums/w279/Evilgeniusracing/100_5719.jpg
   Spare transmission
http://i178.photobucket.com/albums/w279/Evilgeniusracing/100_5718.jpg

Gosh, my business card says 'Tech Tyrant'

Re: How we built the 2-stroke Miata.. some pics, links, thoughts and bs

And, more pics.
 
    Gauges... Simple
http://i178.photobucket.com/albums/w279/Evilgeniusracing/100_5717.jpg

    Two pedals and a foot rest
http://i178.photobucket.com/albums/w279/Evilgeniusracing/100_5716.jpg

    Three carbs
http://i178.photobucket.com/albums/w279/Evilgeniusracing/100_5715.jpg

    Driveshaft
http://i178.photobucket.com/albums/w279/Evilgeniusracing/100_5714.jpg

    Drivebelt
http://i178.photobucket.com/albums/w279/Evilgeniusracing/100_5713.jpg

Gosh, my business card says 'Tech Tyrant'

Re: How we built the 2-stroke Miata.. some pics, links, thoughts and bs

Needs 3 tiny turbos.

Jim C.
Muttonheads!, nee Focke-eWe190 85-87-88-97-99 GTDI
People wonder why I'm obsessed with cars.  I wonder why they are not.
08TMS45/52.09NL78/122.10GM16/51.10SP17/86.10NL3/13.11SP16/102.11NL28/74.12SP20/117.12VIR25/108.12NL12/47.13GM41/68.13NJ24/139

Re: How we built the 2-stroke Miata.. some pics, links, thoughts and bs

If this does not get a second motor or turbo powah you are not evil OR a genius.

Yeah... I went there. wink

Daniel Sycks
Muttonheads!, nee Focke-eWe190 85-86-87-88 GTI
A Division of Cosworthless Racing. Sponsored by Marlburro!
http://www.facebook.com/pages/Muttonhea … 7122228200

Re: How we built the 2-stroke Miata.. some pics, links, thoughts and bs

hoverducky wrote:

Next up: clutch tuning.

Sounds generally familiar so far, please continue!  In looking at the latest set of pics, however, I'm beginning to suspect your setup may have been designed with greater facility for adjustment than either of mine.

Index of Effluency, 2012 Pacific Northworst Grand Prix, Freewheelin' Pikers, 1967 SAAB 96
Longest Distance, 2010 Concours d'LeMons Box Wine Country Classic, 1982 MG Metro 1300
Second-Round Elimination, 2010 LeMons Pinewood Derby at Sears Pointless, 1978 H Special
Worst of Show and Fright Pig Supremo, 2009 Concours d'LeMons, 1980 KV Mini 1

Re: How we built the 2-stroke Miata.. some pics, links, thoughts and bs

So, what I am seeing is that you could gut the back of a small car.  Utilize *possibly* some sort of IRS rear setup with the belt drive bolted directly to the diff.  Line it up, incase the whole thing and walla!

Dang-it, yet another plan for a Festiva which I have never been able to obtain.......

Re: How we built the 2-stroke Miata.. some pics, links, thoughts and bs

Thinkkker wrote:

So, what I am seeing is that you could gut the back of a small car.  Utilize *possibly* some sort of IRS rear setup with the belt drive bolted directly to the diff...

A differential is overthinking things, but essentially yes, one could do that:

http://clunkbucket.com/victoire-de-citrons/

Index of Effluency, 2012 Pacific Northworst Grand Prix, Freewheelin' Pikers, 1967 SAAB 96
Longest Distance, 2010 Concours d'LeMons Box Wine Country Classic, 1982 MG Metro 1300
Second-Round Elimination, 2010 LeMons Pinewood Derby at Sears Pointless, 1978 H Special
Worst of Show and Fright Pig Supremo, 2009 Concours d'LeMons, 1980 KV Mini 1

22 (edited by psychoboy 2012-03-28 09:47 AM)

Re: How we built the 2-stroke Miata.. some pics, links, thoughts and bs

that's the same setup the silverwing honda scooter and most gas golf carts use.


http://farm3.staticflickr.com/2469/3573157479_8d17897718_z.jpg
the left end is the engine, the right end is the wheel...there's a gear reduction set behind the big end that gets everything down to correct operating speeds.

i've got a few cars that really want me to put this motor in them (600cc parallel twin), but i've having trouble with the packaging and reverse.

http://farm4.staticflickr.com/3389/3573158813_3ddf76203c_z.jpg


the packaging you solved nicely, but the FR layout is more conducive to that than my intended FF or RR applications.


....and what did you do for reverse?

Team OK-Speed
Regularly losing in Class A
Soon to start losing in Class C

Re: How we built the 2-stroke Miata.. some pics, links, thoughts and bs

Reverse, like electric start, is for the weak.

Mounting the driven clutch on the input flange of a differential for a mid-engine version was appealing until I realized that it is like 12" in diameter and would be the lowest point on the car.  A chain drive off the jackshaft would be pretty clean, allow flexibility in engine location, and make ratio changes a breeze.

Turbo would be too easy.  It is one of the two solutions the serious mountain sled guys have come up with and is actually fairly common.  The other solution is intensive cylinder porting plus ridiculous compression.  They are making over 200 horsepower on normally-aspirated one-liter engines at altitude.

Looking at those pictures, I'm pretty sure that rust wasn't there before Saturday...

Scott

24 (edited by psychoboy 2012-03-28 10:16 AM)

Re: How we built the 2-stroke Miata.. some pics, links, thoughts and bs

I wondered.

i've been scratching my head for a couple years trying to make an elegant reverse (slightly more necessary for a street car).

the best thing i've come up with thus far is a moving electric motor that runs against the driven pulley, or pulls a belt tight against the axle. the harley trike guys use something like that.

in a solid axle application...the reverse is built into the diff of gas powered golf carts.

Team OK-Speed
Regularly losing in Class A
Soon to start losing in Class C

Re: How we built the 2-stroke Miata.. some pics, links, thoughts and bs

Reverse:  Change the timing and start the engine backwards.  Wheeee!

Brrrrrrrrrrrrrrrrrrr.