mx5cartalk.com

Having competed casually in sprints on and off over a few years in various road cars, I decided that it was time to move on to the next level and use a properly track prepared car. I was all set to build my own from an MX-5 road car, but as luck would have it this race car came on the market at the right time. I'm a picky bastard and so would much prefer to do my own build, but buying an already prepared car has save me a considerable amount of time and money.

The car is CAMS 2F category and is log booked. The previous owner had been racing it in Prod Sports as recently as a couple of months ago, so the maintenance is up-to-date and essentially it is ready to jump in and race. This is in stark contrast to two or three other race cars which I had enquired about over the previous few months, all of which had been laid up for a while and would need recommissioning.

I want to move into circuit racing in due course, so having car which is already log booked is one less hurdle for me to jump later on. In the mean time I will continue with sprints while I learn the car and, most significantly, improve my driving. I'm heavily into data acquisition systems, and this car will also serve as a development tool for same.

Crucially for me, the car also has a mod plate* for the cage etc. (it just got in before the old Qld Code of Practice was abolished) and has registration history in Qld. I've got no interest in using it as a road car, but it is very handy to be able to drive it to events as I have got no trailer access at my property.

*The picky amongst you will notice a couple of minor things which are not strictly legal (as with any modified car, of course) but the major things are covered.

Here's a quick run down of the spec:
1990 NA6
BP-4W engine (build spec unknown)
MoTeC M48 engine management
5-speed gearbox
4.3 torsen LSD
TEIN dampers and coil springs
Whiteline anti-roll bars
NA8 brakes
3/4 cage

Anyway, here's what it looks like:













The wheels shown above on the car didn't come with it. They are BBS RSs left over from my BMW days, but they fit perfectly and have got race tyres on with some life left, so I'll use up the tyres before selling the wheels.

This is what came with the MX-5. I don't know what they are, but they're Chineese made and they feel heavier than the BBSs. I'll weigh them properly when the tyres are next off.





The car was built about 3 years ago by Romano, and generally to a fairly tidy standard. Inevitably there are a few things I identified straight away which I want to ‘improve’, but the first thing to do was to give it thorough check over for maintenance and safety items.

First job was to roll one of the front guards. They had all been done originally, but one of the guards was replaced recently after a skirmish on track and the replacement hadn't been rolled. It was just catching the tyre and I wanted to correct it before it got worse. I ended up rolling all of them a bit further so that they would not get caught when I use the BBS wheels (which are ET25 as opposed to ET40 for the Chineese wheels).





I can't stand working in a mess, so the next task was to fix some leaks. There was some oil grime over the front of the engine; difficult to be sure where it was coming from, but I suspected the camshaft oil seals. When chasing leaks you have really got to start at the top and work your way down. After I had dríven the car a couple of times I also found a tiny drop of coolant hanging off the front of the sump; I couldn't see any likely candidate for this other than the water pump. So I ordered the “Do It Yourself - 100,000k Service Kit” from MX5 Mania which is the water pump, timing belt kit, and all the seals etc., but I asked for a belt upgrade to a Gates Racing belt. This is the first time I have dealt with MX5 Mania and the service was excellent.

Here I am the day before heading up to Warwick for the Super Sprint event at Morgan Park. I wouldn't be the-day-before-race-day if the car wan't in pieces, would it! I changed the cam oil seals, but ran out of time to do the crank seal.



I also changed a front hub as I had noticed a slight bearing rumble, but no photos of that because it was well after dark when I got to that stage.

More updates coming soon…

Looks great on the bbs' mate
Enjoy

Look forward to seeing it at the track.

Interested to see where this goes.

How far down the road do you want to race? There's an MX5-only meeting at QR in 6 weeks... ;) Will be my first race meeting, along with a couple of other newbies to racing too, Magpie being one.

Looks great! Subscribed

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Trackphotos wrote:How far down the road do you want to race? There's an MX5-only meeting at QR in 6 weeks... ;) Will be my first race meeting, along with a couple of other newbies to racing too, Magpie being one.

I was planning for sometime next year. I am aware of the MX-5 Challenge race at QR in November (thanks for mentioning it too) and I'm giving it some thought. The main impediment will be bringing forward the budget to purchase race suit / helmet / HANS device etc. but we'll see…

Over the last few days I pulled apart the front of the engine to replace the crank oil seal. After after that was done and everything was clean I found a drip of oil forming in the middle of the floor of the sump, but it wasn't running down from higher up. Turns out there is a tiny crack in the floor of the sump, barely 5 mm long. I'm not inclined to remove the sump at this stage, so I have patched it from the outside using epoxy paste. Hopefully that works, at least for a while…

While the cam cover was off it seemed like a good time to improve the breather hose attachment. Someone had previously welded on a hose tail, but it was too short to attach the hose securely and the position of it also required a moulded hose with a very tight bend to clear the manifold. Not really an off-the-shelf-item. The existing hose is deteriorating and I couldn't get it to stay on. There are no markings on the hose and I suspect that it is not oil resistant.



I cut off the hose tail and had a threaded bung welded on in it's place. Location angle was critical for the hose fitting to clear both the inlet manifold and the strut brace, and also required me to remove the unused hose tail in the manifold and plug the hole to leave a flush finish.



After removing the steel hose tail in the manifold the hole was just slightly too big for a 1/8 NPT plug. The only big enough tap I have got is M12, so I used that and made a grub screw by cutting off the end of a bolt and cutting a screwdriver slot. I didn't cut the thread all the way through the manifold at full depth, so the grub screw will lock against the bottom of the thread, and I used some epoxy paste to seal it in there permanently.





An interesting observation when I cleaned the steel shields before refitting them to the inside of the cam cover: There are three locations where the cam lobes have been making contact with the shields. Whoever built my engine had made a neat job of grinding extra cam lobe clearance in the head itself, but had evidently not checked the cam cover for clearance. Something to be aware of for anyone fitting high-lift cams. I gave my shilds a little ‘bump’ in the relavent places after refitting them.





I got all this done just in time to get out to QR yesterday for the mid-week sprint. The car ran well and there is no fresh oil underneath, so I'm very happy with that. However I now have plently of mud and stones to clean off after beaching the car in the gravel trap on the outside of turn 2. Yesterday was the first time I have dríven the car at a familiar circuit in the dry, so I was experimenting with tyre pressures and pushing hard to get a good feel of how it behaves.

Best time of the afternoon was 65.9 (Clubman circuit) and I'm happy with that for a first effort. Even without any data to look at I can tell that I am braking too early and too much, so I know what I need to work on next time.

neat little trick with the intake manifold hose, were you not concerned with a need to keep the pcv system?

beavis wrote:neat little trick with the intake manifold hose, were you not concerned with a need to keep the pcv system?

I don't run the pcv on my car. With wild cams the engine is hardly ever in vacuum anyway. I simply run 2 x 8an lines to a breather and vent to air. I did cut down the cover plates and opened up the breather channels in the cover to reduce the wicking effect sucking out oil. Seams to work fine with mostly water collecting in the catch can and I have zero issues unless I forget to empty it every now and then.

beavis wrote:neat little trick with the intake manifold hose, were you not concerned with a need to keep the pcv system?

The only purpose of PCV is emissions control – not required in this case.

About time I posted an update on progress.

The first (small) piece of good news is that the oil leak repair I made to the sump using epoxy past is holding up. The entire engine is now bone dry everywhere except for a small amount of oil on the right hand side of the block in the area of the oil pressure sensors. I'll be changing those sensors in the near future, so hopefuly that will be the end of the leaks.

I have recenty changed the clutch master and slave cylinders. This has cured the tendancy for the clutch to gradually engage while stationary with my foot on the pedal. As an added bonus, the difficulty I used to have selecting reverse gear when returning to the pits has gone away, so my gearbox is in better condition than I thought

Another piece of good news is I found that the old BMW wheels I've got fit perfectly, despite the offset (30) and the tall tyre profile (195/65/14). This has given me some ‘free’ road tyres so that I can store the race tyres off the car between events.





Next the bad news: At the last club track day at Lakeside I entered the Hall of Fame by leaving some red paint on the crash barrier. The rear let go with no warning as I was exiting the last turn onto the main straight. I immediately realised that I wasn't going to recover it so it was time to plant my foot hard on the brake and lock up everything to scrub off as much speed as possible before the inevitable contact. All things considered, I have got away with relatively little damage.









The rear tyre sidewall showed evidence of very light contact with the barrier, but the car still drives the same and there is no change to the alignment. Still, I've got some panel work to do, and I'm on the lookout for a lamp cluster and a number plate garnish.

With a deliberate brake lockup from 150 km/h all the way to rest the tyres have suffered somewhat. Admittedly they were well worn anyway, but they will now have to be retired from active duty. One of the flat spots is through both the canvas and the steel belt

Having seen this unfold you definitely saved the car from a bigger impact by locking up early. Glad to see it's relatively light damage. The car sounded terrific, did you discover the engine build spec?

Custardtart wrote:…The car sounded terrific, did you discover the engine build spec?

I've been able to identify the cams from markings on them, but that is all.

Inlet cam is Tighe 564C (10,4 mm lift; 255º duration at 1,25 mm lift)
Exhaust cam is Tighe 642C (10,5 mm lift; 248º duration at 1,25 mm lift)

The engine pulls well at full load, but there is work to do to improve the driveability at part load. At high speed and light throttle there are times when it is jerky due to being silly rich, which makes throttle control difficult. That should be easy for me to fix with some retuning.

At lower engine speeds and light throttle there are times where the engine is running roughly, which is making road driving a pain in the arse, but the overall mixture strength is not far out so there is going to be more to that than simple retuning.

I've noticed that there is a lot of noise on the signal from the throttle position sensor; maybe the sensor is worn. It's an NA8 throttle body, and the sensors for those seem to be exceedingly expensive, so I have got hold of an NB throttle body to try. New sensors for those, should I need one, are half the price.

I have also found that there is some timing scatter at certain engine speeds, which suggests vibration in the timing belt (since the crank position sensor is on the exhaust cam). Apart from the timing scatter, this will also give the ECU an erratic engine speed signal. There are parts on the way to change to a crank position sensor on the crankshaft. I will also be changing the cam position sensor arrangement so that I can run sequential injection. This will enable me to experiment with injection timing to improve combustion al low injector duty cycles.

And while I'm at it, I will also get the injectors cleaned to eliminate poor spray patterns from the equation.

Does it have adjustable cam gears?