112.8mph Lucky Poos Needed

strtdv

Good to know. I'm going to be using mine for road driving, I'm still at the stage where I'm just tidying it up a bit, but once I finish that and get a major service and waxoyl done I'll be looking for some modest performance improvements (ie K&N panel filter and catback exhaust), and was wondering if a fixed timing advance was a good idea as part of that.

Obviously if you're running a full aftermarket ECU that's even better, but it'll be a couple of years before I look to do that (probably at the same time as fitting a supercharger kit and full coilovers)

It really could become a money pit if you let it!

RiftAmps

TORSEN LSD

Ok, now that the car is running at the class bhp/tonne limit, we can't really do much more on that front to make it go faster. The next step, of course, is gearing.

We've always wanted to fit the car with a proper limited-slip Torsen differential - the car currently has an 'open' unit - but there is a very annoying issue (from a motorsport PoV) that has thrown a spanner in the works.

Here's how a differential works:

Fitting a LSD will allow us to get on the power earlier and send that power to whatever wheel has the most grip, something that we absolutely need in a race car.

The 'ratio' of the diff - how many turns of the prop-shaft relative to driveshaft - dictates amongst other things, how fast the car accelerates vs top speed.

Our car currently has a 4.3:1 ratio diff, so the prop shaft turns 4.3 times for every single rotation of the driveshafts.
Increasing the ratio will gear the car towards greater acceleration, whilst decreasing will increase the top speed, at the expense of acceleration.

Want lower revs at motorway cruising speeds? Go for a lower ratio, such as 4.1 or even 3.9.

So, as we want to make the car accelerate faster, we need a higher ratio diff. Guess what, Mazda didn't make one of those.

Fortunately, the crown wheel and pinion from the front diff on a Kia Sportage is exactly the same size as that found in a 4.1 MX5 Torsen diff. In the Kia, you can guarantee that the front diff was never used for off-roading so most likely has spent 100,000 miles free-wheeling around the outer suburbs of the local town.

The ratio of these is 4.625:1 in the UK, and 4.77:1 in the USA. Exactly what we need!

So I've been searching for a 4.625:1 crown wheel and pinion for ages now. I've phoned everyone, scrap dealer, breakers yards, MX5 owners clubs, you name it. No one has one, and if they do, they won't sell.

In a last gasp attempt at finding one, I found a very old FB post from the owner of an MX5 race team, advertising a cw&p from a Kia Sportage. I phoned him on the off chance that he could help and guess what? He had an already-converted 4.625:1 Torsen diff that just needed a rebuild. I HIT THE JACKPOT!


A deal was done for him to rebuild the diff and then sell it to me

It arrived this morning, and I can't wait to get it onto the car. I've had to buy a new prop shaft and driveshafts to get it all to fit as the original diff is from a MK2 1.8 MX5.

I've got three trackdays booked before the season starts to get used to driving with both a different gearing setup and a locking diff. All are at Donington Park so will be able to compare laptimes against our race there last September. Would be great to see by how much we've improved the car since then.

Here is the currently gearing for the car, with top speeds in each gear

.....and with the 4.625:1 diff. You can see the top speeds in each gear are lower, but we accelerate faster. It's the same principle as a pedal bike, change to a bigger gear on the rear - easier to rev and accelerate.

strtdv

Sounds ideal. I've the viscous coupling diff which at 80,000 miles I'm sure has completely failed to an open diff.
The torsen out of a 1.8 will be able to handle much more torque should you ever want to go down the forced induction route too.

steer

Enjoying this thread. I love motorsport, but have close to no mechanical knowledge, so it is interesting to read what you are up to.

There was a thread on a VW forum a few years ago about a bloke tuning up a VW Bora for trackdays, and it was quite similar in many ways - tweaking, upgrading, setbacks, money, breakdowns, repairs, tweaking. 

strtdv

I'd imagine that the lowered top speed is largely notional anyway unless you get an incredibly long straight with a tailwind, certainly with the stock gearing.

If it was turbo'd that would be a different matter.

Speaking of which, have you any plans to get into the next power to weight class?
I know Skuzzle do some pretty serious natural aspiration tuning, seemingly able to get the 1.6 up to 170bhp at the crank, but it's more expensive than most "drive in drive out" turbo packages

RiftAmps

strtdv said:

I'd imagine that the lowered top speed is largely notional anyway unless you get an incredibly long straight with a tailwind, certainly with the stock gearing.

As you can tell by the title of this thread, the fastest speed we've hit has been 107.8mph - that was at the end of the Hanger Straight at Silverstone. On the second longest straight of the year (Snetterton) we hit 105.1mph.

The top speed in 4th gear for our car is 117.6mph with the 4.3 final drive, so we're not using 10mph of that gearing because there's not a straight long enough. By moving to a 4.625:1 ratio the top speed in 4th will be lowered to 109.3mph and crucially we'll get there quicker. The goal is to hit our top speed as early as we can so our average speed along the straights is higher. Time = Distance/Speed so that should give us lower laptimes.

The new Diff is being installed tomorrow and I'm testing at Donington the following Monday. Will put the theory to the test!

strtdv said:

I'd imagine that the lowered top speed is largely notional anyway unless you get an incredibly long straight with a tailwind, certainly with the stock gearing.

If it was turbo'd that would be a different matter.

Speaking of which, have you any plans to get into the next power to weight class?
I know Skuzzle do some pretty serious natural aspiration tuning, seemingly able to get the 1.6 up to 170bhp at the crank, but it's more expensive than most "drive in drive out" turbo packages

Now that we've bought the E46 328 we've decided to keep the MX5 in Class D. No point in moving up a Class if it's not a winning car as it currently stands.

If we ever did, however, we'd go the ITB route rather than a turbo. Much more driveable on a racetrack and would only need 166bhp at the flywheel to reach the 180bhp Class C limit.

strtdv

That sounds about right. The Skuzzle track packs seem to have ITBs and a very aggressive camshaft profile but I'd imagine it wouldn't be something you'd want to drive on the road which would rule it out for me.

Long term I'm faced with the options of either keeping my car stock (probably best for the resale value as stock early Mk1s are being rarer and certainly not losing value) or going for a proper quick B road car build (I'd be looking at lowered suspension, slightly widened track, forced induction up to about 170-180bhp at the wheels, 1.8 torsen diff, and a smattering of bits n bobs to make it look a bit more JDM ie offset plate and possibly a mild widebody kit). 

The former option makes much more financial sense but the latter would likely be more fun, and the car already has the factory JDM splitter and front fogs

RiftAmps

RACING RETURNS/TESTING

The 750MC have released the revised Roadsports calendar

The Silverstone race has moved from 8th Aug (F1 GP) to the 22nd August and they've added Donington Park to the end of the schedule.

My season now looks like this:

- Silverstone International 22nd August

- Anglesey Coastal 12th September

- Snetterton 300 17th October

- Birkett Relay (Silverstone GP) 24th October

- Mallory Park (Plum Pudding) 26th December

I booked 3 track days before the season starts and a final one before the Plum Pudding

- Donington Park 8th June

- Donington Park 25th June

- Donington Park 20th July

- Silverstone National 10th December

RiftAmps

Donington Park 8th June

The first test back after COVID, I took the newly diff'd MX5 to Donington Park for a full day running.

I had the GPS recorder going so gathered some great data and then could compare to my fastest lap in the race last year.

Might be difficult to see but the red trace is last year's race and the green is my fastest lap on Monday.

My minimum cornering speeds are pretty much the same but as you can see, the green trace shows that in both acceleration zones and top speed, the car is faster.

My fastest lap was 1.71 seconds faster. That's huge. Amazing. It's a combination of everything that we've done to the car since then, not just the diff.

I did an entire race stint on my own, at race pace. 45 minutes is bloody difficult and I was shattered. Felt good though and my pace didn't really drop off towards the end. Happy to do it for real now.

Naturally, the car broke down twice. Firstly an exhaust bolt in the centre pipe fell out so I broke the noise limit and had to borrow one from a friend.

Secondly, and this was terminal, the starter motor failed so couldn't start the car without a bump start. Didn't get it figured out until it was too late so lost the last hour of track time before we had to go home.

There was a bloke filming the cars going around so he put together a little montage for me

Two weeks until the next one, I've already fitted a new starter motor so now we can find out what's next to break

TTony

RiftAmps said:

- Snetterton 300 17th October

Just up the road ...

strtdv

It's amazing how hard racing is on a car!

I don't know if I'd be able to afford the car needing something new every time I drove it..

I've just spent about £1100 getting mine mechanically sorted (clutch change and pilot bearing replaced, front and rear main seal, camshaft seals, CAS O ring, cam cover gasket, timing belt and water pump, thermostat, clutch slave cylinder, engine, diff and gearbox oil changed, 2 springs and a damper replaced, new anti roll bar bushings, and the whole thing waxoyled and stone chip layer renewed).

The brakes were renewed last year (new rotors all round, new rear calipers and the front calipers from a 1.8 for a bit more stopping power)

I'd hope that's all the major work done for the next few years (though one of the wheel bearings is getting very slightly noisy so I'll likely replace that in the next few months).

I'm not intending to track mine although I do "press on" on country B roads.

166 bhp would be just about perfect for an MX-5 I reckon.

I've shelved the catback exhaust idea for now as the garage I've had all the work done also offers turbo conversions and would put in a 2.5" decat exhaust at the same time as the conversion, so no point in spending the money twice.
Their conversion is good for 230-240 bhp at the flywheel provided the clutch and diff can take it, which is a fair bit more than I'd really need (I'd be happy with 180-190 at the flywheel)

RiftAmps

Pre Season Testing

After the first test at Donington, both Nick and I booked another at the same venue and also at Bedford Autodrome - a massive 3.8mile test track.

Both cars ran really well and at Bedford, the MX5 has never felt so fast/on point. We've switched our dry tyres to Nangkang NS2Rs which feel pretty similar to the Giti GTR2s but we can run a more aggressive setup with them, so another trip to Northampton Motorsport was in order.

In terms of driving - I've started trail-breaking with my left-foot which massively helps get the nose of the car to the apex and also balance the car at full throttle on corner exit. It felt a little strange at first but really only took a few laps to get the hang of and my top speeds at the end of the next straights are up, so a good thing to do.

The green BMW is running well and is now race-ready, bar a set of stickers and race numbers.

First race is Silverstone International on the 22nd and both cars are entered - the race is sold out at 44 entries with 2 reserves, so gonna be a great race

RiftAmps

Silverstone International - 22nd August

It's been a long wait, but our racing season is finally about to start I've not raced since the Plum Pudding on Boxing day so itching to get out there.

This Saturday, we're back at our local circuit, Silverstone, racing on the International layout running out of the F1 paddock.

I'm entered in Class D with the MX5, and Nick is racing the BMW E46 in Class C. So, an entire 45-minute race on my own. I'm gonna be knackered at the end of it!

The race is currently sold out with a capacity 44 entries. Huge grid!

Prep

Engine - Since the final test at Bedford, the car has been into MX5 tuning specialists BBR who are based in my town. Unfortunately, COVID has forced Skuzzle Motorsport out of business which is a massive shame. I hope Nick Bailey lands on his feet and keeps working in the industry, he's a nice chap and deserves to succeed.

BBR has the car on their dyno for a tuning session. As the engine spec has changed since the last tune it needed a tweak and now both the torque curve and BHP line are much smoother. Their dyno accurate measures flywheel power so we can accurately calculate the BHP/tonne. I told BBR that due to the weight of the car it couldn't produce more than 131bhp - they mapped it to 130.9!

Here's the printout.

The ME221 ECU had a firmware update and now has the option for launch control - although it's just a switchable rev limiter. I've installed a toggle switch on the dash that activates it and it then sets the limiter to 3500rpm when the clutch is pressed. Using it is simple - activate the toggle switch, press the clutch in, then you floor the throttle and the revs sit at 3500rpm until you drop the clutch and off you go. It auto switches off returning the limiter to 7350rpm. Just got to remember to disable the master toggle otherwise it'll kick in every time I change gear!

Who's racing?

- RLM Bikesports Championship

- PBS Brakes Hot Hatch Championship

- Yokohama MA7DA Series

- Tegiwa Roadsports Series

- Protech Shocks Sports Specials Championship

- Zampf Helmets Sports 1000 Championship

Tickets

The club meeting is being held behind close doors, so no spectators are allowed.

Live Stream

All races are being live-streamed by Alpha Live on YouTube. Our Race is at 2:20pm.

I will also be live-streaming my race from inside the car using a GoPro to our Facebook page, check this link around 2:10pm - https://www.facebook.com/2RMMotorsport

Live Timing  - 

Qualifying - http://www.theresultslive.co.uk/750-motor-club/2020/silverstone-international-22-23-august/qualifying-4-saturday

Race  - http://www.theresultslive.co.uk/750-motor-club/2020/silverstone-international-22-23-august/race-5-saturday

strtdv

Glad to hear you're getting back to it.
I saw Skuzzle had closed down, definitely a shame.

RiftAmps

Silverstone International Race Report

Testing

Friday testing went very well. The new surface at Silverstone is very smooth and everyone was suffering from awful understeer. I couldn't believe how early I had to turn the car in so I could hit the apexes. Usually, for understeer, the fix is to stiffen the rear dampers but as I was already as the maximum I could go without the rear skipping under braking all I could do was soften the fronts instead. It seemed to work well and the front-rear balance was great although still had power understeer. My target lap time was a 1:30 and was very pleased to run consistently in the low 1:28s.

By the final session of the day, I was dialled into the circuit and managed to take Turn 1 (Abbey) flat with low fuel. I finished the day with a 1:27.2 lap time which I was very pleased with.

Qualifying

As the race was sold out and had 3 reserves, we had to actually qualify to start the race! All you have to do is set 3 laps and you're guaranteed a start. Fail to do that and a reserve would take you place.

Queueing up to go out and the car developed a fuel leak from the fuel rail. An injector o-ring had split. Back to the garage as the session started and I ran around the paddock trying to find a 6mm o-ring. Thankfully, it's an easy job to replace and despite my panicking, we managed to find one from another team and get the car fixed. I went out on track and managed to set 4 flying laps. oooof that was close.

Best thing? I didn't qualify last and managed to beat one of my competitors, Joshua Watts (BMW E30) by 0.05 seconds

Race

The organisers decided that due to the large grid, a rolling start would be used so I didn't get to try my launch control system out. Nevermind.

Unfortunately, I got shoved wide at T1 and had to take the escape road leaving me plum last going onto the Hanger straight. The next few laps were great as I was part of a 4-car train consisting of BMW E30, Toyota MR2, and another Mk1 MX5. Unlike last year I could stay with them which shows progress in both the car and my own driving. You can see how strong I was through turn 1 compared to them.

Starting at 9:45 on the video below you can see my favourite lap of the race, overtaking the MR2 into Farm, being re-overtaken by him down the Hanger straight and then my banzai overtake of him again around the outside of Stowe corner. Unfortunately, I was once again shoved wide at turn 1 as the faster cars came through and all of my work was undone. Spent the next few laps trying to chase them down but the safety car came out and then that's where it all fell apart. I lost a lap under the safety and then couldn't do much but bring it home. I finished in 35th position but last of the runners. Still, I've proven that I can be competitive, just need to stop making errors and be more aggressive under yellow flags to make up time.

I'm back to Silverstone on the National circuit in three weeks time. Not much to do to the car apart from a simple nut and bolt check.

Here's the race footage from Saturday.

RiftAmps

Silverstone National - 13th September

This weekend was meant to be my first double-header racing on Saturday at Anglesey with 750MC and then at Silverstone on Sunday with the BRSCC. Unfortunately, the Welsh government put a stop to those plans and the Anglesey event was cancelled.

So, we're back to Silverstone again to race in the Clubsport Trophy - just like Roadsports, it's a 45-min multiclass race with a compulsory pitstop. I'm sharing the car with Nick so he can get an extra signature on his race license in time for the Birkett Relay in October. We're on the shorter National circuit this time (the scene of our infamous engine blow up).

Prep

Brakes - The EBC Yellow brake pads that we fitted to the rear were slightly too powerful for the brake bias in the car, causing a few rear lockups. We've gone back to Brembo road pads.

Cooling - The radiator fan stopped working last time out and the car got a little hot during pitstops. I've bypassed the auto-fan switch with a toggle switch on the dash so we can now turn the fan on/off as required rather than waiitng for the ECU to do it.

Who's racing?

- Milltek Civic Cup

- Mazda MX5 Championship

- Fiesta Junior Championship

- Hyperdrive ST-XR Challenge

- Mazda MX5 Supercup

- Clubsport Trophy

- City Car Cup

Tickets

The club meeting is being held behind close doors, so no spectators are allowed.

Live Stream

There is no Live Stream on the race weekend

EDIT: Yes there is! Race Qualifying at 11am, Race at 5pm.

Live Timing  - 

https://www.tsl-timing.com/event/203731

RiftAmps

Live stream link added above

RiftAmps

Silverstone National Race Report - BRSCC Clubsport Trophy - Car #221

Qualifying

No testing for us so went straight into qualifying. As I'd driven the car more recently than Nick, the plan was that I'd just do 4 laps or so and then swap over so Nick could spend the rest of the session getting up to speed.

Unfortunately, another MK1 MX5 immediately dumped engine oil all around the track so the session was red-flagged after 2 laps whilst they cleaned it up. Once we got back going I stayed out and did 5 laps before handing the car over to Nick.

We qualified 25th out of 40 cars and 5th in class. Very pleased with that!

Race

Same format as Roadsports, a 45-min race with a compulsory pitstop. This time our plan was to run 21-minute stints each unless the safety came out during the pit window in that case I'd bring the car in as soon as possible. Rather than a minimum stationary time for the pitstop, it was a 2-minute minimum time from pit entry to exit. Difficult to judge but we managed it at 2:02

I got a reasonable start and stayed with my competition (cars 78, 122, and 21) for a few laps before the first of three safety cars. I just couldn't quite stay with them after that but my lap times were very consistent. The second SC came out just when the pit window opened and fortunately the SC waved me by as it came out of the pits so we didn't lose a lap to the leaders. I immediately pitted and swapped over with Nick. We emerged in P4 in class and right behind P3, car 78.

Nick tried his best to catch them but they just had the pace on us that day. We were resigned to P4 until with 4 laps to go, we saw that #78 had a 4sec stop-and-go penalty for a pitstop infringement and crucially, hadn't noticed. If they didn't take the penalty they'd be awarded a 30second+4second time penalty after the race. If Nick could stay within 34 seconds of them, we'd get our first podium. With 4 laps to go, he was 10 seconds behind.

THE PODIUM WAS ON.

Or was it. Of course, it wasn't. Just our bloody luck that the clutch started to slip with 2 laps to go and Nick could do no more than bring it home at whatever pace he could.

We finished in P16/40, and 4th in Class, 53.6 seconds behind them (19.6 after penalty) so no silverware for us. Gutted.

Still, the car is definitely competitive now and we're on the verge of a podium, so let's keep pushing.

Onboard race footage

A new upgraded clutch in time for Snetterton on 17th October, and probably some other tweaks too.

the_jaffa

Interesting to see Richard Brunning of Bad Obsession Motorsport and Binky fame in their C1 on there.

I'm still loving this thread. Sorry to hear about all the misfortune but that's the way with motorsport. Hope you can get it all together soon though. That podium definitely sound on to me

Nitefly

Great stuff!  Why isn't this stuff on the telly?