mx5cartalk.com

Ok, so following will be a looong build thread, as I take my cars journey from initial purchase in 2009 right through to current day.

Car is a Grace Green 1999 NB8A. I purchased this in early 2009 with the sole intention to use it as a track car.
It was stock as a rock with 101,000 km on it. (little did it know what was in store for it..)
I changed the stock wheels over to the kosei's (15x7 +17) just prior to taking the pic below, on day 2 or 3 of ownership


I've never been a convertible guy, (my wife had one of the nicer ones for a while but it never did anything for me..) but the platform was perfect for my planned usage so I put up with the convertible part. ohh and the cramped bit, and the noisy bit, and the lack of power bit.
Yep as a road car an NB8A has a lot of shortcomings, but makes up for it completely once you get it hurtling around a racetrack, embarrassing much more powerful and expensive machinery.

Ha! Exactly.

Hooray! Peer pressure works

I'm looking forward to the drip feed of the evolution.

rascal wrote:Car is a Grace Green 1999 NB8A.

The Greenmachine lives!! Vicariously anyway ...

Yep as a road car an NB8A has a lot of shortcomings, but makes up for it completely once you get it hurtling around a racetrack, embarrassing much more powerful and expensive machinery.

Not sure I totally agree with the first part, but ...

I have told this story before but is is worth retelling, and totally reinforces the second part bolded above.

Many years ago, I was at SMP/Eastern Creek for a State Supersprint round on the GP circuit. The previous session I had been giving an old Mustang a hard time in the twisty bits, only to see him disappear into the distance on the straight. Rinse and repeat for the nest three or four laps

Next time out, there is a delay and we are all waiting around until they cleared a car, or cleaned up some oil, whatever, and the Mustang driver wanders over, and asks me 'please tell me that thing is a turbo?'. Cue much laughter, 'Nah, it's just a 1.8'. Priceless, as they say!

In the same vein, PI 6Hr some years ago, this Mustang hosed me off on the back straight, but I caught him on the entry to Lukey as he started to overtake some traffic, using the damp line. Anything a Mustang can do, an MX can do better, and with me sitting on his boot as we braked for MG, off-line and on the damp part of the track, he got the message that horsepower is nice, but it isn't everything!

Hey Russell! That's going a looong way back. I'm trying to remember what you tracked before this. Escorts?

Hey Phil,

Long time no hear...


Previous track car was a cough TG gemini cough

It was 108rwkw, 900kg and handled like a pig, despite the zillion dollars spent on it. (You can't make a silk purse out of a sows ear)
The MX5 was 150kg heavier, 30rwkw less and on exact same rims/rubber (wheels transferred over) ended up with a quicker lap time...

Needless to say I havent looked back...

rascal wrote: (You can't make a silk purse out of a sows ear)

....but you can make a mighty fast pig!

Having tracked the old car for 10 years prior to this, I had seen plenty of vehicles written off, and a few ambulances involved, so the first few things on the list of proposed mods were safety related.

Didn't think much of the chances of my body being much good if the car got tagged by another car mid corner and subsequently rolled as the windscreen would flatten in an instance and I'd be squashed in the process, so a roll bar was added.

This was a full weld in 4pt job, with diagonal, a harness bar and rear supports through to the chassis rails in the boot.

The slight increase in chassis stiffness this gave was an added bonus.

From my early days on track, I was amazed how much time you can gain just by being held in the seat properly and just steering, rather than being thrown around and having to brace yourself at every corner if just using a std lap sash, even one tightened with CG-lock style devices.

So also added a sparco sprint race seat (cos they bolt in with almost no fabrication reqd (just a slight elongation of two of the mount holes) and a 6 pt harness to keep me snug and in the right spot.

Now I was a little safer in the car, I could turn my attention to making the car faster..

So that would be a high hp engine so I could blast down the straights and enjoy much quicker laptimes, right?
wrong! More horsepower can be important for getting better laptimes, but its at the end of the mod list, not the start.

<a little side story> A few years ago I was at a party talking to friends and a guy there overheard us talking about our racing, and said he wanted to put his HSV on track as he said it would 'go good' there. I asked him what he had done with it and he spent the next 10 mins telling me all the engine mods he had done, with 300+ kw at the wheels. I then asked him what had he done suspension wise, and he looked at me blankly and said its all the factory HSV stuff so should be more than up to it.. Needless to say his PI visit gave a laptime over 6 seconds slower than my 80kw MX5, and a max of two laps before the brakes gave out. </story>

Way more important than power is handling. And that means good tyres AND upgraded suspension to take advantage of that extra tyre grip.

Adding super sticky rubber on std suspension wont allow you to gain the full advantage of the tyres as increased body roll will alter your camber angles for the worse, as well as make it nosedive under brakes changing the bias.
Equally fitting 1000lb springs on std road tyres also wont gain as much as you'd hope as you'll just slide off the track everywhere as the tyres cant keep up with the added stiffness.

After much deliberation on costs/value. I ended up sourcing a set of mid range Teins coilovers from Emilio at 949racing, for a price way less than local guys could provide. (it helped that the AUD was in the mid 90c USD range)

old vs new


These were a simple combined compression/rebound adjustment as seperate rebound/compression and low/high speed adjustments were overkill (and kinda pointless) for what I would be using the car for. Sprint sessions are typically an hour apart so track & weather changes can be significant enough in that time span to affect the outcome more than the fine tuning the multi way adjustable coilovers give.

I also added heavier adjustable sways,


as well as new stiffer bushes, to remove some of the squirm that rubber ones have.



Delrin options weren't available back then so I had to settle for poly bushes, and frequent greasing..

Also to help get more than the 1.5 deg max camber the factory eccentric adjusters could give, I also added offset bushes in the front lower arms.


Some nice fresh R specs tyres (R888 were the flavour at the time) some proper pads that would take the abuse

and a flush with hi temp brake fluid and she was much more suited to track work than previously..

So handling was sorted so time to give the rear wheel output a little bump.

Given the specs of the prev car, (and using its 1:58.1 best at PI as ref lap) I assumed I'd need a lot more horsepower to punch out similar lap times (no one wants to go slower in the new car..) so looked into cams and places to get headwork done. Given the extra weight this car was carrying I figured I'd need 120+ rwkw and then hopefully could work on weight reductions to get it down to previous times.

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 wasn't 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. The class limit for what the car was closest matched to at this point in time was 90rwkw. which I thought was the class I could run in till I get the engine built and go faster to chase those sub 1:58 lap times..


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 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.



I fitted an Adaptronic E420c ECU, got it running, and it was off to the Adaptronic listed tuner to get it tuned.
A day later I got the call that the car was ready to pick up, and excitedly headed off early from work to pick it up.
Open arrival, I got into the car, and turned the key and what seemed like 300 cranks later it finally started.. (hmm, not a good sign)
A blip on the throttle and the car almost died. hmm, another red flag..
I mentioned that this wasn't very good to the tuner, and he kind of shrugged and said that these Adaptronics are hard to get right.. (??)

He then got in the car and spend 30 mins tweaking things, before hopping out and saying that's about as good as it will get.

I jumped back in to drive it onto the trailer and had abut 5 goes to get it on, as any throttle application caused the car to bog.
He said it would be fine once I got it on track as the higher revs would mask this issue. Not convinced but out of options I loaded it up and headed home.

With only a few days left b4 my first event I didnt have time to find another (read better) tuner, so booked it in at our club approved dyno centre for a power reading, to a) see what it made, and b) ensure I was under the 90kw limit. (which I thought I should be well under)


As expected it was well under and I headed home to prepare for my first track day in the new car...

First outing was at (imho) the best track in Australia (Phillip Island) and the car was awesome.
So much better handling and balance than my previous track car, (not terribly surprising!) made it massively confidence inspiring, which is what you need to crank out a decent time in a low powered car.

Somewhat underwhelming in a straight line as expected, (going back down 35% in power will do that) but the ability to carry corner speed was phenomenal, meaning trap speeds at end of the straights weren't that much lower due to the higher entry speeds..

Wow, these cars were good!
and made me realise why they are the 'most raced' car in the world.

I even managed to sneak under the club lap record, even though the track was 'damp'.

Following the successful first event at PI, the next event was at Winton. A tight and twisty track compared to PI's fast flowing nature, and should be a good match for my new low powered but great handling mx5.

A dry day thankfully,


and I could really enjoy the handling capabilities of my new steed. I managed to get down to some consistent laps within the first couple of sessions but then my times seemed to be stuck around the same pace, and the harder I tried the slower my times seemed to get.
(One thing the extra grip from a dry track did show up, and something I barely noticed at the damp PI, was an awful lot of inside wheel spin. The car was running the standard open diff, so stiff suspension and R specs meant it was picking up the inside wheel out of corners a lot. In fact 7 out of the 12 corners. It became obvious that a lsd would be my next mod.)

Between sessions in the late afternoon, I sat down and had a think about where I was losing time, and it was almost all in corner exit, due to wheelspin. Adjusting the bars to stiffen the front and soften the rear helped to reduce it somewhat, but also focusing more on getting out of corners rather than on into them (the old slow in fast out thing..) made the difference and my last session proved to be my quickest, with a smoother style and adjusted driving lines showing on the stopwatch, with the last two laps my quickest for the day, nudging the class lap record lower by a decent amount.

Getting under the lap record two meets in a row was pretty satisfying, especially given my preparation for the event consisted of reversing the car out of the shed where it had sat since PI, washing it, checking fluids, which were all good, and loading it on the trailer.
A vast improvement on the old car where I'd spent the week before the event fixing broken things and then come home after the event with a new list of things to fix.

This time after returning home from the long drive down the Hume, I only had one item on the list, and it was an improvement item, rather than repairs; namely sourcing a lsd to rid myself of that horrible inside wheel spin.

Great work, and impressive analysis and problem solving for the best times. Also great to hear the car was being low maintenance for you!

ManiacLachy wrote:Also great to hear the car was being low maintenance for you!

This was the compelling reason to upgrade the old car to an mx5.

Whilst I don't mind swinging spanners now and then, spending lots and lots of time in the shed working on the car is a very poor substitute for actually being out on track driving, where I really want to be.
So whilst the handling/capabilities of the car were the main attraction to getting an mx5, the stories of reliability whilst doing this were the icing on the cake that helped close the deal.

My diff search began.

I wasnt a fan of the torsen, as while they make a good road lsd, ontrack they still manage to light up the inside wheel if it gets unloaded, so a clutch pack diff was my preferred weapon of choice.

After much searching, I found Centreline Suspension in Thomastown who had the required goods at a suitable price, namely a Mazdaspeed clutch pack diff, and the necessary inhouse skills to properly install and set it up.


Since the diff had to come apart anyway, I got them to throw a new set of bearings in, shim it up nice and tight, set the backlash, etc, and also do a 4 wheel alignment.
They also setup the Teins with suitable ride heights, and damper settings, to give me a good solid baseline for fine tuning at the track.


Research around my new toy had led me to Miata.net and Miataturbo.net which meant a pretty long rabbit hole of reading.
Some long nights wading through literally thousands of posts/links, absorbing as much of the info as I could contain on the do's, donts and nuances of the various miatae.


Part of this reading, on heavier sways bars highlighted a potential problem, namely cracking of the sway bar mounts. Seeing as I've always preferred prevention rather than cure, I decided to proactively act before my nice fat new bars added me to the statistics and so the subsequent order and arrival of another package from overseas made me confident that wouldn't happen to me anytime soon.


next event was at Winton Short track and I was really looking forward to my new diff setup, to see how much difference it would make,
and whether I'd still be lighting it up 7 out of 12 corners.... I hoped not!