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

RobL wrote:

Well - I don't think you understand how easy it is to sell Miata parts.

Off the top of my head - Seats are $50 each (these are good condition aftermarket).  Each straight body panel {hood, trunk, fenders, door skins, etc.} $20-$40 with a non-straight exchange panel from a spec miata driver.  Dash and in-dash controls - $40-60 total.  Carpet $20.  OBX exhaust $50.  Door glass $10 per pane.  CAI $40 with stock exchange. 

That's almost $450 in honest sales right there.

Having a big spec miata contingent and racetrack (NJMP) local makes these sales easy.

Honest RobL's Miata Parts?   hmm   Where is my bribe / booze?

No bribe?

10 laps!  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)

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

Team Sensory Assault wrote:

Honest RobL's Miata Parts?   hmm   Where is my bribe / booze?

No bribe?

10 laps!  big_smile

Damn, thought you would buy it...  wink

--Rob Leone Schumacher Taxi Service
We won the IOE at Southern Discomfort.
We got screwed at The Real Hoopties of New Jersey  and we took cars down with us.
We got the curse at Capitol Offense but they wouldn't let us destroy the car.

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

Team Sensory Assault wrote:

I would agree that red miata is a genuine $700 turd.  However, it is NOT a crappy $500 turn and there is no mythical hard top or even a soft top that will get you there.  In fact, it is so crappy I see no way you can reasonably sell off $200 of stuff.    MAYBE $100 and thats pushing it.

Remember this isn't some POS RX-7 that nobody wants parts from, it's a real sports car with pistons that has a very active used market in parts.  You can sell $200 in parts from a Miata without even turning around.

And those KYB AGX shocks?  DAMN!  I paid $400 for a set of just those shocks!  Jeez that car was a steal.

Quad4 CRX - Wartburg 311 - Civic Wagovan - Parnelli Jones Galaxie - LS400 - Lancia MR2 - Boat - Sentra - 56 Ford Victoria
Known Associate of 3pedal Mafia, Speedycop, and the Russians.  Maybe even NSF.

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

We here at Idiotarod Racing are going to bow out of the usual no-such-thing-as-a-$500-Miata discussion by reminding the reader that we sold off both the engine and transmission.  And air-flow meter.  And throttle body.  And ECM.  And starter and alternator and exhaust (it had a new serial-numbered California cat) and freaking everything.  Even at Pick-N-Pull prices, that math works out.

Now if you want to have the no-such-thing-as-a-free-snowmobile-engine discussion, that's different.

Scott

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

^^^ I'm all in on the snowmobile powered Miata. 

It could have been a snowmobile powered Boxster or Z4 and I'd have the same admiration and awe!

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)

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

I guess I promised a clutch-tuning post.  Sometimes present-Scott thinks past-Scott is kind of a dick.  And future-Scott is sitting someplace drinking a beer, so that's not cool, either.

Anyway, the drive clutch spring and the mass (and distribution of mass) plus the profile of the clutch weights control the engagement rpm, which is the point where the clutch starts to pinch together.  If things are set up properly, anything the engine does below the engagement rpm is ignored by the clutches.  How harshly the engagement happens can also be diddled with.  Race sleds are often set up with a fairly high and harsh engagement to prevent bogging.  Try that with a mountain- or trail-sled and you make a pillow and get some exercise digging back out.

Unfortunately, the clutch weights and drive clutch spring also have control (mostly) over the operating RPM under load.  Being that we are road racing, engagement isn't of primary concern to us as long as it is happening up in the four-thousands someplace to give us some overhead for blipping the throttle to keep the plugs from fouling.  As an aside, we were idling around 3000rpm instead of the factory-recommended 1900, mostly because we have a weak cylinder (the bore is all scuffed up) and it was dropping out and fouling at low RPM.

Operating RPM is critical.  I think I mentioned that the XLT engine is known for a weak crank.  It has roller-bearing mains (and rods) so the crank is multi-piece and pinned together.  Under high RPM the crank can twist and walk the pins out.  Various bad thing then occur.  But the power-band is also narrow.  It doesn't have to be wide because the clutches keep it close to a fixed RPM.  Polaris says 8500 +/-200 RPM.  The company that makes the aftermarket pipes and heads that are on the engine says 9000-9100 RPM.  Too much below that there's no torque.  Too much above and the crank is at risk of failing.

The other thing that can affect operating RPM is the preload on the spring in the driven clutch.  There are four index positions in our particular clutch, the total spread of which is supposed to be good for roughly 250 RPM.  I guess you can also replace the helix with one of a different angle, also supposed to be good for around 250 RPM.  Basically what you are doing is changing how sensitive the driven clutch is to load, or how willing it is to backshift.

Other tuneable bits include the at-rest sheave-to-sheave distance in the driven clutch, which controls at-rest belt slack (deflection) by riding the belt higher or lower on the driven.  It allows you to adjust for center-to-center distance error or belt length variation.  On our clutch it is three pinch-bolts and a little cam thing and is quick to do.

Then there's a similar adjustment in the drive clutch, though it requires shimming.  What you have here is control over how close the edges of the belt are to the drive sheaves at rest.  You want it as close as possible without dragging, because too much space means the belt will be at a higher radius when it does engage (so your low-gear ratio isn't so low) and the whole drive system will sort of be leading the belt.  Weights deployed further than they should be, that sort of thing.

Also pretty important is that the rollers the clutch weights ride against (the cam followers, if you will) are actually rolling.  Friction in the interface or flat-spots on the rollers can make the drive clutch sticky, playing havoc with engagement and operating RPM alike.

Likewise, if the driven clutch helix or the buttons upon which it rides are worn things won't work properly.

The driven clutch wants to be installed with very precise angular alignment to the drive clutch.  Axial alignment is important, too, but a little bit of axial float is also a good thing, as it reduces the chances of end-loading the jackshaft bearing.  As previously mentioned, the center-to-center distance can be somewhat adjusted around using the driven clutch cam thingy, though we still made a tool to try to nail it down as much as possible.

Clutch alignment issues can at a minimum cause the belt to run hot, which makes the belt slip, which makes it run hotter.  Eventually the belt either glazes and stops transmitting torque, or blows, which is bad and breaks stuff.  The original sled had two rubber snubbers mounted to the chassis to prevent the engine from rocking around too much.  It seems to have taken the snowmobile folks a long time to recognize the importance of clutch alignment, but they are finally starting to mount the jackshaft to the engine rather than the completely floppy aluminum hat-section chassis.

Our driven clutch is held together with a heroic snap-ring, but is otherwise pretty easy to mess with.  The drive clutch is taper-fit to the crankshaft, which requires a special bolt-like tool for removal, and has kind of a lot of spring energy trapped inside it.  It is possible to blow one's face off trying to service it if one isn't careful.  There are also portions of the drive clutch which require a torch and bizarre specialty tools for disassembly.

Belt changes: The belt can be replaced by hand.  Both the clutches are cantilevered, so the belt is not trapped by structure.  In a snowmobile, the ends of both clutches are accessible from one side.  On our installation, the drive clutch free end points aft and the driven clutch free end points forward.  Removing a belt requires rotating the two sheaves of the driven clutch relative to each other, then pulling on the belt, which drives it into the vee of the driven.  Holding the sheaves apart lets you pull the belt over and around the side of the driven.  At that point the belt is loose and you sort of snake the belt out around the various bits.  Pretty much do the reverse to get the new belt on.

Specific Balto-clutch tuning issues to follow.

Scott

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

We started out the weekend with desperately poor clutching.  The engine was revving out to almost 10K, so we did the only thing we could do that didn't require parts: pulled the driven clutch and dropped the helix spring preload from #2 to #4.  Paddock testing revealed no change. 

In our "application" The drive clutch is accessible from the side, but not the end, so we could easily get to the weights, but not the spring without pulling the engine.  Then there's that whole blowing your face off thing.  So a weight change it had to be.  Minimal research had revealed that we wanted about four more grams on the weights, so that's what we sent Fish to the nearest Polaris dealer for.  Unfortunately, the nearest Polaris dealer was in Citrus Heights.  So no testing for us on Friday. 

Upon Fish's return we busted out the clutch weight removal and installation tool (a four-foot 2X4) and pried the drive clutch closed enough to R&R the weights.  Surprisingly quick and easy.  It would have been impossible without the SAE hex-key set lent to us by the good people at Eyesore Racing.  You might not have heard of them, but they are stand-up folks.  I think they have a website or something. 

Anyway, Poo is an American company, but Fuji makes their engines, so working on a Polaris is like working on a mid-eighties GM car.  It turns out that a 1/8" allen wrench is the critical tool for Mazdolaris clutch tuning.  We used one both to remove the fly-weight pivot bolts and to lock down the clutch-end jackshaft bearing when the intermediate bearing (our previous axial constraint) decided it no longer wanted any part of the whole rotating thing.

Anyway, anyway, we got the new weights installed, but as before, paddock testing revealed no change.  Poop.  The strange thing was that we should have seen SOME change in operating RPM but didn't.  I think now that we were actually running up against an engine rev limiter, and that the things really wanted the engine at 12K or something.  Of course there is no reference to a rev limiter in Polaris' documentation.  At this point I was reasonably irritated and it was dark, so we decided to drink beer.

Later investigation revealed that our drive clutch spring is not stock like I thought it was.  Rather than bright blue like god and Polaris intended, it is bright blue with an intermittent red trace.  It's an aftermarket spring with an extra twenty pounds on both ends of travel.  We really needed an extra TEN grams on the weights.  So at 10:00am on Sunday while cars are filtering out on track, there we are making phone calls trying to locate the appropriate parts while Wayne, one of our drivers and all-around mensch, was already most of the way to Sacramento hoping for some direction as to where he was headed.  Wayne actually picked the appropriate parts up from the shop in Citrus Heights before we got through to the parts department, and he was on his way back before we got on track just in time for the green flag.

The early part of Sunday was, shall we say, characterized by full-course cautions.  We didn't have functioning wipers due to a certain dearth of amperage, the engine was still trying to rev itself to death, we couldn't get enough heat in the motor to get the temp gauge (which was only getting enough juice to work at full revs) off the pin, the radios had failed, and I was concerned about burning up the belt if I had to stop on the hills going into turns 2 and 6.  Things were going far better than I had expected.  The car was actually running and driving and passing other cars.

Trying to keep a vehicle with a CVT from revving up isn't easy.  Who knew?  I couldn't do anything about the visibility, or the engine temperature, or the radios, so I mostly just concentrated on the belt.  Oh, and not spinning.  A couple of you guys got to see my monster tank-slapper exiting turn 6 through the puddle.  One of you threw me a thumbs-up, which I appreciate.  Between getting up on the clutch and getting up on the pipe, power delivery is somewhat non-linear.

My solution to the potential belt-burning issue was to lay back on the straights during yellow flag situations so that I could maintain a bit of speed up the hill.  My apologies to the cars behind me when I was doing this.  I wasn't trying to mess with your race, I just didn't want to add another caution to the mess by having to take a strap.  I did get stopped on the hill into 2 a couple of times and learned that just booting the throttle works pretty well.  Nice little crab-walks result.

Eventually the spark plug in our low-compression cylinder fouled out to the accompaniment of rather disturbing crackles and explosions out the tail (side?) pipe and our triple turned into a twin.  I hit the pits at just about the same time that Wayne arrived with the new clutch weights, so we stuck those in and I went back out.  Success!  Throttle mashing took the engine to 9100 RPM, then it dropped back to 8600.  A bit low, but conservative and completely acceptable.

The rise-then-drop is indicative of the drive clutch sticking somewhere internally.  Reversing the preload changes we made to the driven would possibly have put us a little closer to our 9000 RPM goal, but you might have noticed that it was damp Saturday night, and I didn't feel much like crawling under the car to pull the jackshaft.

The big problem we were having was that pesky temperature.  It took all day to figure out that our inability to get up on the clutch and rev past 7000 RPM exiting, like, turn 6 wasn't plug fouling: it was over-cooling.  We were running so cold that it wasn't making any power.  Exiting 11 the engine was a touch hotter because of the hard pull through 9a and 10 followed by slow speeds through the corner.  It would rev properly off the line, the fall back off the clutch and drop to a pokey 7000 RPM near the end of the front straight.  Sitting in traffic would help for a while.  Things were peachy for a lap or two following a pit stop, then 7K again.  We have a 140deg thermostat, and it seems to be working, but the big ol' brass radiator sitting out front was just cooling too well.

The stock cooling solution is to circulate the hot water through two or three heat exchangers mounted along the underside and rear end of the tunnel.  The exchangers are little more than finned tubes, and are cooled by snow kicked up by the track.  These engines also seem to run really cool.  I would have theorized that a lot of heat comes out the exhaust with the oil and smoke, but even that seems pretty cool.  The triple pipes have a lot of surface area, and we've got the big-ass pipe running inside the front fender and passenger side door skin, so maybe that cools the exhaust down.  Dunno. 

For Sunday we bent up a couple of slices of drip tray and zip tied them in front of the radiator and the thing ran at 125 - 150 all day.  We left provisions for "tuning" the temperature, but turned out not to need them.  Problem solved.  I think we'll investigate a less-manual solution, though.

Sunday's warmer temperatures also had us running a bit rich.  The plugs said that we were tuned perfectly on Saturday, but Sunday they were more black than brown.  The combo of rich plus clutched too low plus dumping horsepower into our recalcitrant intermediate bearing (the jackshaft was blue by the time the bearing balls made their escape)* was limiting our acceleration somewhat and our top speed more.  When I got out of the car at 3:30ish top revs were down to 7800.  John reports that he was back up to 8600 after our emergency bearingectomy.  I'm looking forward to driving the car once we get it sorted out a bit.

Scott

* That parenthetical was originally phrased somewhat differently.  Use your imaginations.

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

Okay the rusty gears are grinding, I raced 2 stroke motorcycles for years in moto-cross, loved the ferocious power and light weight. We could source a super light vehicle (miatas are just too small for my XXL Frame) for Lemons money fairly easy but zero availability of snow machines in S Texas. PWCs are now 4 strokes for environmental reasons I think. Does anyboby still make a 2 stroke PWC? Thinking  of a 914 with the 2 stroke or a 2 stroke SHOgun clone.

TEAM TONTO, 7 cylinders of thunder!
Now with 4 big Losses!
Steve was right

59 (edited by X-args 2012-03-30 11:06 AM)

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

You should be able to find some Sea-Doo Bombardier/Rotax PWC engines. There's an 800 rotary-valve twin that makes good power, but stay away from the 950 time-bomb...

Cheapest would be the 580 or 650 motors...

Volvo PV544 - now with Chevy 3.9 power!
2007/2012/2013 Driver's Championship (what was I thinking!?) 124 races and counting
9/9/2022

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

Clark wrote:

Okay the rusty gears are grinding, I raced 2 stroke motorcycles for years in moto-cross, loved the ferocious power and light weight. We could source a super light vehicle (miatas are just too small for my XXL Frame) for Lemons money fairly easy but zero availability of snow machines in S Texas. PWCs are now 4 strokes for environmental reasons I think. Does anyboby still make a 2 stroke PWC? Thinking  of a 914 with the 2 stroke or a 2 stroke SHOgun clone.

You might want to call Aaron or Scott at ATS Racing in Denton. They mostly build up high horsepower MK2 MR2's for drag racing but they have a soft spot for high horsepower jet ski engines too. I suspect that if they don't have a 2 stroke jet ski motor available, they'd know where to find one. They used to race Lemons so they'll appreciate this idea.

Pat Mulry, TARP Racing #67

Mandatory disclaimer: all opinions expressed are mine alone & not those of 24HOL, its mgmt, sponsors, etc.

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

how did you get 500lbs out of a miata?

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

We got a lot more than 500 pounds out of it...

Engine and transmission are 450.  Then there's the exhaust, the battery, a whole lot of interior and useless body panels, virtually every bracket on the car, the wiring harness.  The list goes on.

The car weighs approximately half of what a stock street Miata does and there's more to take out.  We haven't had it on the scales since the completion of the build, but I think John intends to weigh it today.

Scott

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

hoverducky wrote:

We got a lot more than 500 pounds out of it...

Engine and transmission are 450.  Then there's the exhaust, the battery, a whole lot of interior and useless body panels, virtually every bracket on the car, the wiring harness.  The list goes on.

The car weighs approximately half of what a stock street Miata does and there's more to take out.  We haven't had it on the scales since the completion of the build, but I think John intends to weigh it today.

Scott

oh, i did not understand until right now that you aren't using a normal trans also. it's just the CVT then the rear end.

neat!

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

hoverducky wrote:

We got a lot more than 500 pounds out of it...

Engine and transmission are 450.  Then there's the exhaust, the battery, a whole lot of interior and useless body panels, virtually every bracket on the car, the wiring harness.  The list goes on.

The car weighs approximately half of what a stock street Miata does and there's more to take out.  We haven't had it on the scales since the completion of the build, but I think John intends to weigh it today.

Scott

I do?  well, I guess I'd better get on that...

Gosh, my business card says 'Tech Tyrant'

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

I thought that's what you said last night.  But then, I _was_ drinking.  For all I know, so were you.

Scott

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

1548 lbs with about 1/3 tank of fuel.     So race weight with driver and fuel is around 1700# to 1750# ....       50.3 % on the rear tires with a 170 lb driver.  53% on the left side with said 170 lb driver

   Where is that damn Plasma cutter???     gotta get it down to 1600# race weight.   

  Car is currently being loaded into the trailer to go down to Laguna Seca for the Miata Club weekend... Should cause quite a stir....

Gosh, my business card says 'Tech Tyrant'

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

Ooh, porky.  Time for Balto to go on a diet.

Scott

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

hoverducky wrote:

I thought that's what you said last night.  But then, I _was_ drinking.  For all I know, so were you.

Scott

Hmmm......both Scott and the Evil one have limited memory due to "drinking"................no wonder we all get along so well!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!  I'm drinking RIGHT NOW......

what did I just say...err...type?

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

69 (edited by autoxmike 2012-03-30 03:05 PM)

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

A-mod (the top dog autocross class)  has been dominated for over a decade by purpose built cars using snowmobile engine/CVT powertrains.  Good to see them used in Lemons cars. Reminds me of childhood in NW Wisconsin. Everyone carried a spare belt in their snowmobiles... Still sounds wierd to hear a snowmobile engine/CVT from a car.

Mike
Hong Norrth
#39 TRON Gray/Orange MX-3, aka "Sumbich"

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

Thought about it a little more, a PWC motor swap is not gonna work, no clutch and CVT, gonna have to talk to the inlaws in Canada.

TEAM TONTO, 7 cylinders of thunder!
Now with 4 big Losses!
Steve was right

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

Formula 500 (was F440) uses Rotax power and CVT.  The cars are very light and are sort of like go-karts with suspension.

From what we are seeing, our application is easier on belts than the original one.

Scott

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

hoverducky wrote:

I guess I promised a clutch-tuning post....

Thanks!  I'll see how much is applicable to my own CVTs.

1982 MG Metro 1300: IOE 2015 Pacific Northworst GP, Longest Distance 2010 Cd'L Box Wine Country Classic
1980 KV Mini 1: Worst of Show and Fright Pig Supremo 2009 Concours d'Lemons
1978 H Special: Second-Round Elimination 2010 Lemons Pinewood Derby at Sears Pointless
1967 SAAB 96: IOE 2012 Pacific Northworst GP

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

I want to publicly retract my comments about there being no such thing as a Miata for Lemons Money.

Found one.  hmm

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)

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

The last one I found was perfect for a daily driver... $500 and all it needed was a front bumper!

Lorin Mueller
Scuderia Asino formerly Team Haulin' Ass - 83 Plymouth Scamp
Team Soccer Moms - 93 Dodge Caravan

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

! I've always wanted to drive a two-stroke car.

Would you consider me for a wrenching/driving slot? I'm a 2t tuner/kart racer, mechanical engineer with FSAE experience, and had the fastest lap on my team in my only Lemons race.