rascal

HI,

Though it was time to do a build log, even if only for posterity sake for when I'm old and sitting on the front porch in my rocking chair..
It might get a bit wordy, as I have a habit of doing, but its my build log so guess that shouldnt matter..


Car is a 1999 NB1.
I purchased this in 2009 with the sole intention to use it as a track car. (I've never been a convertible guy, but the platform was perfect so I put up with the convertible part)

This is on day 2 or 3 back in 2009. Car was stock as a rock with 61,000 miles on it.
I changed the wheels over to the kosei's (15x7 +17) just prior to taking the pic.


I'll try and keep it somewhat in chronological order, and may take me a while to catch up to current day.. (A lot has changed in 11 years...)

rascal

First order of day was safety, so a welded in half cage went in (it was still registered and full cages are a whole nother world of pain for registered cars down under, so half cage it was.
Also added a race seat and harness.



I had been running another car in sprints for the last 10 years, that made 160hp from a nat asp SOHC 1600 on twin 48s and weighed ~1850lbs.
I was hoping to do similar lap times to what the old car could do (would hate to go slower with the new car) but with reliability that the old car could only dream of.

So the MX5 was 400lbs heavier, and 50hp less at the wheels, so to match the times, the car would need to go on a diet (subject to class regs) and some power adders were on the todo list.

Though suspension was the first order.
A chat with Emilio, and some TEINs were on their way, along with locally sourced sways, and poly bushes all round, with offset front lowers for more camber.

Out with the old and in with the new.




Now safety and suspension was sorted, next up was to work on the power/weight ratio.

rascal

a mid suspension swap pic.

rascal

To get to my (assumed) required 160hp to match my previous car would mean some power adders.
So I went on the hunt for camshafts, and engine builders to modify my head to get it to flow some more.

This search back in 2009 wasnt very fruitful, and with time running out for my first track event, I decided to run with what I had and look to add to it as the season went.



So I added a cold air intake, taking a feed from a 2.5” hole drilled in the front bumper. (cos racecar)

This helped air get in, so I needed to help air get out too.

So on went 4 into 1 headers, and a straight through 2.5” exhaust to a single rear straight thru muffler.

I chose the exhaust size due to expecting to do cams/headwork and 2.5” seemed to be a good size to not have to redo when these arrived..

Initial ‘round the block’ test drive after fitting the exhaust showed that it was waaaaay too loud, so a resonator was hastily added in and this reduced the level down to hopefully get under the 95db limit at our tracks.



I fitted an Adaptronic E420c ECU, got it running, and it was off to the dyno to get it tuned, and to make sure I was under the power cap for the class I was to run in. The class limit was 90rwkw/120hp (which is ~100kw/135hp on USA dynos as they typically read 11-13% different for some obscure reason, but most likely just a different measuring method)



Back from the dyno and she was well under the 90kw limit..

rascal

To keep her cool with the astonishing level of hp it was now putting out, I fitted a 42mm alloy radiator in place of the original 10yr old factory one whose top tank was turning that lovely shade of brown suggesting its usefulness was coming to an end.

rascal

Now back at home, with the day of her maiden track voyage looming, the prep moved into the final stages.. Some new rotors, fresh hi temp brake fluid, some Hawk Blues and new R888s tyres and she was ready for her first outing..

rascal

First outing was at the best track in Australia (Phillip Island) and car was awesome.
Much better handling and balance than my previous (non Miata) track car, and I even managed to sneak under the club lap record, even though track was damp.

rascal

A couple of years (and 30+ events) down the track (pun intended) and the car developed a nasty habit of eating coil packs.
After going through three sets of (expensive) coil packs in as many months, I spat the dummy and moved to a COP system, using toyota coils off a 2000 Corolla.

After much deliberation, and a fruitless search for coil pack connectors, I decided to just cut off the connectors on the factory harness, and crimp on generic connectors, and just make a mini patch harness, should I ever need to go back to using factory coilpacks.



My patch harness, should I ever have to go back to factory coil packs. Plugs into the new connector I crimped onto factory harness.


My mate made up this awesome hold down bracket, using original valve cover bolts, and threaded holes to hold the COPs down.


This was surprisingly easy to wire up, (after initial worries about chopping factory harness) and worked fantastic, and my coil pack issues were solved.
(And 9 years & 100 events later still running on the same coils with zero issues - even now boosted)

rascal

Around 2013 I got tired of getting held up in corners by slower big hp cars, fighting to get pass them, only to have them pass me again down the next straight and I'd have to do it all again.
Whilst this can be fun at times, the events our club run are time attack style, therefore lowest lap time for the day is the winner, so fighting for track position with other cars just slows you down.

So time to up the overall pace of the car, so I could gap them enough in the twisty bits that they were too far behind to catch me on the longer straights.
This meant moving up a class, which allowed me more power and some aero....


Power at this stage was 128whp, (AUS to US adjusted) with the motor being internally stock, just bolt ons.
I went with a mild-ish set of cams, (Specs of 220@50 268 deg .311" inlet, 226@50 270 deg .370 exhaust) as stock head wouldnt flow enough to use really big cams anyway, and a set of adjustable cam gears to dial them in fully.

Initial install of cams showed a jump to 135whp, with cam gear adjustment to come. Cam guy recommended 2deg adv on inlet, and 2deg retard on exhaust. I think I got that backwards, as this change instantly dropped power to 120whp.. Reverting to (correct) suggested orientation netted (after 26(!) dyno runs) a figure of 151whp, which I was plenty happy with given so few mods.



101kw +12% which appears to be approx diff between AUS and US dyno readings = 151whp..


Now power was up, it was time to add some aero.
Class regs allow rear wing and front spoiler/splitter.

So I sourced a 3D wing and another boot lid, so could drill holes in this one and keep my good boot lid for road duties. Also scored a hardtop to smooth the flow onto the wing, and some 8" rims for added goodness.


Bought a sheet of 12mm ply and cut to size, forming a rough mushroom shape providing smooth undertray back to front wheel centreline, and 3" splitter out front.


A quick coat of black paint to make it more waterproof, and a tad less ghetto.


A coat of paint for the boot lid, fitting the wing, hardtop, undertray/splitter, splats to cover the new rims and she was good to go...

rascal

A year on of running the new setup and times had dropped by about 2secs at each track
At the end of the season I plan what mods to do over the christmas break, and decided that running 151whp in a 185whp class was asking to get beat, so I sent the head off to be pampered.
Ported, shaved, bigger valves, heavier springs, as well as a set of bigger cams.

A few weeks later, I got that lot back and installed it all, heading off to the dyno full of expectation.
The first few dyno runs gave me a sinking feeling. Instead of the 115-120rwkw I was expecting it was spitting out 90!
A few hours of tweaking the tune, playing around with cam timing, etc only netted a max of 99kw.


WTF! all the time, effort, money on (theoretically) better parts, and I'd actually lost 2kw!


On the phone with the head builder and he couldn’t explain it other than maybe he had mixed up the set of cams.
So I pulled the cams and posted them back to him for measurement and checking.
A few days later and he came back that they were all in spec, and could only assume it was the std inlet manifold causing the problem as the 15 other cars he had done with same specs all made 115-120 but had ITBs
So the hunt for ITBs was on.

rascal

jenvey kits are ~$3000 here in Oz, and are too big anyway being 45mm throats. Overkill for a 185hp BP, so I looked into fabbing my own set up using motorbike throttles off a CBR600
But finding a manifold to suit was proving difficult, and all the homemade jobs looked wack, so the CBR option wasn’t looking good.
Then I happened to luck onto a Techno ToyTuning manifold that accepted AE86 Silvertop throttles for a bolt on option.
They are 42mm throats so a better size, and a local guy makes trumpets to suit.

So sourced the silvertops, bolted to the manifold and onto the motor. All going nicely. Now to size and fit trumpets.
There is where the biggest issue turned out to be. RHD mx5s (miatae) have a brake booster in the way of where you want the trumpets to go, and so you cant get enough length to make the ITBs work properly without some fancy (read $exxy) curved runner manifold.

Not gonna happen with my budget, (and class regs wouldn’t allow me to remove/move the booster) so I measured up and found I could squeeze 75mm trumpets in, and still have enough air gap to the filter.
Not ideal, and would compromise the power but best could do for now.
So got a set of 75mm trumpets made and put on and wedged the filter in.


Converted the MAP tune to a MAPxTPS tune, many late night road runs to get the tune sorted (my usual tuner was booked out) and booked yet another appt with the dyno.
Once again full of expectations that I had found the cause of my missing horsies.

Alas, once again spinning it up on the dyno showed power was still 99 and tweaking everything only lost power.

By this stage I am several thousand dollars in the hole, and not getting anywhere, so decided to admit defeat and stop throwing good money after bad, and just run it as it was.

So the next season would be 149hp in a 185hp class. Hopefully no-one with a built motor turned up otherwise I was toast.

rascal

A year of running this, and the christmas break again had me deciding what to do.

I was hesitant to throw more money at it to find the power,
Also the motor was developing an appetite for valve clearances, and I was getting far too much practice at reshimming them, so chasing power would only make this worse.

So decided to drop back a a class. Removing the ITBs, and a quick detune would put me at the lower class whp limit and run that way.
So off came the aero (not permitted in lower class) some quick fuel/timing changes to detune it and I'd be in a more competitive position in the lower class again. (rather than be constantly nervous of someone with a built motor showing up.)

rascal

The following season started off quite well, with the car very competitive, but a few events in and I noticed the car was getting slower in a straight line.

Compression checks were showing a drop off, and it became obvious that the coming christmas break would be a complete engine rebuild, as after 10 years of being flogged to within an inch of its life on track, the motor was waving the white flag

So this kick-started a whole new discussion in my head, about what to do.
I was wanting to stay in the lower class for a few more years yet, as there was more cars to play with.
And then after this period build a new big hp motor and go play with the big boys again in the higher class.
But the need to rebuild the motor sooner rather than later, threw a spanner in the works.
Also affecting this plan was that a short motor rebuild cost almost as much to build with std parts as it did with good parts, and most of the money was in the head, with my curr head most likely not fit to reuse.

So I decided to build a bullet proof bottom end, use a std head on it to save money and keep power down.
Put a mild set of cams in it which should get me back up to the class power cap, and run it like this for a few years.
Then all I need to do down the track was get another head built, with some big *** cams, and put my ITBs back on, onto my recently rebuilt tough bottom end, and I was good to go chase the big boys.

So off we went with that plan.

A new bottom end with forged rods and high comp pistons was built up (check out that piston dome!!)

A std head was fully reco'd and put on top with another set of cams, and the car went back together.

But it wouldn’t start!! Checked timing, fuel, spark, over and over and couldn’t find the cause.
Very long story short the new adjustable cam gears I had bought (from a reputable vendor) were manufactured wrongly, with the triggering nubs on the cam gear were 120deg out!!
so I had checked and rechecked the physical location of the cam gears, timing belt, retimed it multiple times, only to realise whilst the cams were timed correctly the nubs were misaligned.

note difference below!!


Lesson learned the hard way, not to trust anything!!

My tuner was once again too busy to fit me in, and with the season looming, I tweaked the tune myself again.
I noticed that the new motor obviously didn’t flow as well as the old one, as I had to pull fuel everywhere to get AFRs looking more normal.
On-track performance proved this to be correct, and the new healthy stock headed motor just didn’t have the zing of the old ported head version. (prob to be expected but I was hoping the cams would make up for this)
I was consistently half to one seconds slower at all tracks.
This was also the year COVID struck so three events down and the season was called off.
The car went to the shed and stayed there for what ended up being 6 months..

DNMakinson

iTrader: (3)

Enjoying your thread, Rascal.
DNM

rascal

thanks, I did think I was talking to myself for a while...

almost caught up to current day. And the rotrex...!

rascal

Having a car sitting in the shed for an extended period with an engine that you are not 100% happy with, and entry fee/fuel/tyre moneys piling up in my account (cos no events due to covid) meant it made sense for my plans to up the power sometime in the future to jump forward a few years!

The covid enforced down period was the perfect time to do all the upgrades necessary without having to find a rushed window between events, and potentally missing an event due to slow delivery of parts, services, etc.

So I sat down and went through my options.
My goal was US 185rwhp (= OZ 125rwkw), as this is the power limit of the class I wanted to be in. Anymore than this and it pushed me into the Open class, which would put me up against LS2 powered, slick shod, carbon fibre rocketships, and I wasnt interested in jumping into the money pit required to be competitive in that class!

So 185whp is somewhat easyish (the term is relative!) on a BP. Given I already had the compression, I'd just need to build a head with decent cams, and some good headwork, bigger valves, and slap it on and it should be there. The downside is that it would need to rev high to make the power, and revs is what predominantly shortens engine life span.

Having gotten over 10 years (and almost 100 events) out of the last rebuild, I'd hate to find I'm having to redo bearings/rings every couple of years, cos its now working much harder to make the power.
Also whilst it would make the hp cap, it would probably be peaky and I'd still be getting monstered out of corners for the first few car lengths by those pesky ND 2.0s with their big fat torque curves..

So the simpler option seemed to be a mild forced induction setup. Reasoning being I wouldn't have to rev it to the moon to make the power, so the engine should last longer, and it would fill in the torque curve a little so I wasn't at such a disadvantage to the ND 2.0s. I could also get away with not touching my brand new rebuilt head, saving many thousands in machine shop costs, as (good) headwork is expensive and I also wouldnt be throwing out the money I'd already spent on refurbishing the current head to std specs.

So on to the FI slippery slope it was. Having never ran a FI setup on track before, this meant lots more reading and research to be done...

rascal

So my FI research continued.
I spent many weeks trawling what seemed 1000s of forum pages, web searches, articles, even re-read through some early books from Fred Puhn, Corky Bell and Carroll Smith.
My direction was starting to become clear.

I briefly looked into a turbo (for about 0.000000000000001 of second) but although I have a couple of turbo road cars and love them, (so I'm not anti turbo by any means) for a track car in my case they suck!
Far too much time, money and effort to build & set them up properly so they don't break and are reliable, and too much maintenance to keep them that way.

(I do get the irony that I'm posting this on miataTURBO.net but meh, its my build thread so I can be derisive if I want)


So no turbo for me, that left supercharging for my hp fix.
FFS and TDR styles soon proved to be the two most popular avenues of thought to follow;


FFS - MP/TVS style blower, running fuel to cool the charge as no intercooler.
TDR - Rotrex, option of intercooler.

Comparing the two options, The TDR option seemed to be the simpler to install and control. I already had an aftermarket ecu so controlling the 5th injector for the FFS option was an extra hurdle I didn't need or want.

Also the power delivery of the Rotrex was more to my liking, having a nice linear power curve that made it feel very similar to the existing n/a motor, just more everywhere. And it didn't make any torques so my gearbox wouldn't be in any danger any time soon..

The final, and actually most compelling, argument for the rotrex was the sound, or more accurately, the lack of it.
Personally I hate the sound of MP style blowers that constantly whine their heads off, like a 1980s Gilmer belt drive tragic.
The rotrex, other than the BPV venting at closed throttle), was basically silent.

so, it is!!

rascal

So traded emails with Gary at TrackDog Racing for a while, and he was very helpful in suggesting a suitable parts list.


I didn't need their power cards to control the extra fuelling needed as had aftermarket ecu already and my current injectors were too big for stock ecu to control properly anyway.
I also didn't need their radiator as already had big alloy one, that was perfectly fine with the current 150hp with oil cooler smack bang in front and no ducting/sealing, so with some ducting and proper sealing (and moving the oil cooler) the proposed 185hp should also be fine.

TDR had a really nice intercooler setup but it was pretty exxy, and wouldn't work with my radiator anyway.

So since I wasn't going to use half their kit anyway, Gary put together a DIY kit of a C30-84, 85mm pulley as didn't need to extract every last hp. (or in fact much hp at all given my low class limit),mounts & tensioner, oiling kit.

Unfortunately, living in a little country on the other side of the world, meant an initially nicely priced package from Gary ended up being a horrendously overpriced option, once exchange rates, shipping, GST, and customs double dipping had all added their pieces to the pie.

This led me to research closer to home options, and it became apparent that the aussie distributor for rotrex could supply me a similar package for approx $2000 less.
Whilst I would have much preferred to get the TDR setup, being a known proven setup with excellent support, the $$ difference was just too big to ignore and I placed my order with the Aussie guys for their DIY kit, which was essentially the C30-84, brackets & oiling kit.
I'd just need to provide my own intercooler and intake/piping.


A few weeks later and I had this pile of goodies on the bench.




Time to get to work....

electroCrunch

I know it's only been like 5 days, but is the rotrex in yet lol?!

Sorry for the spam, but wanted to say I love the build so far, keep it up. There are not a lot of supercharged examples out there, I appreciate this thread...subscribed. I've been toying with the idea of supercharging my BP also, which mainly is to keep the heat down because I live in the desert and a turbo track build is big money all around and I'd be fighting heat (albeit turbo is superior in some ways over a rotrex, but has its drawbacks too). I was also eyeing the TDR kit because there are not really any other decent assembled kits out there using Rotrex (kraftwerks is long gone, hoping for a V2), and appreciate that you shared Gary from TDR will sell a custom partial kit if you already have ECU/injectors/etc...

Curious to see what you end up doing for an intercooler, and if you have any belt slipping issues. Watching closely. Good luck with the build and looking forward to some dyno charts.

rascal

Thanks. This is my first ever build thread (after 12yrs on the forum!) so trying to include plenty of information whilst hopefully not making it a dull read.
I'm adding pics where I can too, to help this aim..

<spoiler> Rotrex is in... </spoiler>

More info/pics on mounting and intercooler setup to follow shortly...