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Hi Folks.

I’m getting in pretty deep on a serious upgrade to my race car, so I thought I’d share. Maybe I can help others, and most likely you can help me along the way too.



I’ve been belting my NA6 around Victorian race tacks for a few years now, and it’s been super fun. It’s been super reliable too, but some small niggles recently really got me thinking about the future. Also...

I’m going to Mt Panaorama!!!

So.... To cut a long story short, I have embarked on an epic upgrade project involving a new weld-in roll cage and a proper engine build. It’s going to be a fire breathing high compression big-bore VVT BP-Z3, taken from the 2000-05 NB8B. I’m lashing cash fairly liberally, but my budget isn’t unlimited so boosting is not on the agenda at this stage.

This is where the story starts. Out with the trusty B6 (which has a failed gasket)...



...and out with the bolt-in cage...



...and out with pretty much everything!!!



Why am I doing all this now? Well, as I mentioned, I’m going to Mt Panorama in late November to take part in Challenge Bathurst. It’s a regulatory trial, similar to the Phillip Island 6-hour. Anyway, I’ll be doing warp speed on the track with about another 60 cars of varying abilities, from Daihatsu Sirions to Porsches. The speed differential will be huge, and Mt Panorama has lots of concrete walls, so I’m keen for the warm fuzzy feeling of being in a fully caged car. Also, Bathurst is a power track, so what better time to go for a big bore engine swap!

So, I’ve made a start and I have a huge amount of work ahead of me, with not a lot of time to get it all done. It seems like a story worth sharing. I hope you enjoy it!!

Here are a few items that I’m expecting in the mail next week, to whet your appetite and get you interested...

Cheers,
Trav.










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What size bore and what compression? E85?

It is white, so this is an excellent start all round. Who is doing the cage? I saw that Brown Davis sell a 6pt weld in cage in bits for the DIY person.

Hey, great to see some interest!! Okay, answers....

1. I’ll be installing 85mm pistons, which takes the BP-Z3 up to 1930cc. According to Goodwin racing, more than that requires sonic testing to be sure that the bores are sound (I’m paraphrasing, so refer to their advice: http://gwracing.altervista.org/factors- ... 2015-.html)

2. I’ll be running the car on premium 98 RON unleaded.

Keep the questions coming!!


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Sorry, missed one question...

3. Compression will be approx 11.0:1. Fabre are supplying Supertech pistons to achieve those figures.




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Aaaand one more...

4. TrackArt are doing the cage. They have the skills and they have the capacity to do the cage in my required timeframe. I didn’t shop around widely, but they came highly recommended. I sought a quote from Lux Racing, but they were too busy to fit me in before November. They also came highly recommended.



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Also... Yeah! Race cars are white, right?!
So that you can plaster the sponsor stickers all over them.


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You should consider E85 in your build, your build is similar to mine. E85 allows more timing to be add without the risk of detonation.

What power/torque are you expecting from the build? What gearbox/diff ratio are you planning on running? What rotors/calipers/pads? Brake ducts? Aero?

Regarding E85, I haven’t actually given it much thought, but I won’t rule it out in future.

I got my hands on an NB 6-speed gearbox (second hand, not rebuilt) and a 4.3:1 Torsen 2 diff (second hand, not rebuilt), so those will go in with the new engine. I’m just going to put in some fresh oils and replace the input/output seals respectively. If the diff is a bit backlashy I’ll consider a rebuild at some stage.

As for power expectations... Who knows?!
In NA6 form my car made 78kW on semi-slicks on the dyno, so anything north of 100kW is going to be a significant upgrade for me. Realistically, 120kW is probably within reach. Figures like 140kW, and even 200Hp, have been bandied about, but I’m not holding my breath. I’ll be happy if it’s running and good to go for November.

Regarding brakes, I’ve got a full set of brake components from an SE: calipers/rotors/booster/master cylinder. I’ll probably run Hawk Blue Racing pads and braided lines (fabricated by my local Enzed guy).

Brake ducts? Not yet.

Aero? I’ve fitted an eBay Garage Vary Style front lip and an RS Style rear lip spoiler (from MX-5 Mania, I think), but that’s it for now. A proper front splitter, rear spoiler and diffuser would be nice, but they will probably happen much later (if ever). I don’t mind things getting loose at speed... That’s part of the appeal, right?? I’m more likely to get a Lightyear hard-top, because they are both slippery and sexy!!

Which brings me to a general comment about this rebuild...

It all started with the failed head gasket, and has snowballed into a full blown race engine build. I’ve never really been after massive horsepower, but that’s where I’m heading. In pursuit of reliability, I have ended up on the slippery slope of engine upgrades. As soon as you start spending money on an engine, more upgrades start to make sense. For example, if you commit to blue-printing, balancing, and good bottom end components, things like the ATI harmonic balancer and Boundary oil pump start to make sense.

The same goes for cooling... All of a sudden an oil cooler and a larger radiator are essential, to protect my expensive bottom end. It’s similar for the top end. I’m rebuilding a head and getting it ported and flowed, so why wouldn’t I skim it down to get some more compression and chuck in some 1mm oversized valves, to take full advantage of the extra capacity?! The answer is, of course I would!! And the ITB’s...? Well, I just want them. But if I didn’t fit them, I’d be leaving horsepower on the table, right?!

It’s a slippery slope, people, and I’m not even at the bottom yet!





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Scoota wrote:As for power expectations... Who knows?!
In NA6 form my car made 78kW on semi-slicks on the dyno, so anything north of 100kW is going to be a significant upgrade for me. Realistically, 120kW is probably within reach. Figures like 140kW, and even 200Hp, have been bandied about, but I’m not holding my breath. I’ll be happy if it’s running and good to go for November.

It’s similar for the top end. I’m rebuilding a head and getting it ported and flowed, so why wouldn’t I skim it down to get some more compression and chuck in some 1mm oversized valves, to take full advantage of the extra capacity?! The answer is, of course I would!! And the ITB’s...? Well, I just want them. But if I didn’t fit them, I’d be leaving horsepower on the table, right?

I have 204 RWHP and looking at your plans you will not even get close without considering E85! You will need some serious head work to even get close! What cam duration have you chosen? The head needs to be ported/flowed with the whole intake assembly including ITB's if using them. What intake length are you using?

Scoota wrote:I got my hands on an NB 6-speed gearbox (second hand, not rebuilt) and a 4.3:1 Torsen 2 diff (second hand, not rebuilt), so those will go in with the new engine. I’m just going to put in some fresh oils and replace the input/output seals respectively. If the diff is a bit backlashy I’ll consider a rebuild at some stage.

In a NA build the 4.3 will not give you the acceleration you need, consider a 4.8 or higher. There is no way you will get to the theoretical top speed as you will not have the horsepower to overcome drag. In my build I get 204kmh down the main straight of SMSP in 5th, never use 6th. This was with a 4.3 rear diff.

Scoota wrote:The same goes for cooling... All of a sudden an oil cooler and a larger radiator are essential, to protect my expensive bottom end. It’s similar for the top end.

You do not need a bigger radiator, in fact you can go smaller, most track NA MX5's use a 1/2 size honda radiator. The radiator size only helps when sitting in the pits.

Scoota wrote:Regarding brakes, I’ve got a full set of brake components from an SE: calipers/rotors/booster/master cylinder. I’ll probably run Hawk Blue Racing pads and braided lines (fabricated by my local Enzed guy).

Brake ducts? Not yet.

You will need brake ducts on the front! Make sure you grease the slider pins on the calipers after every few track days. Also swap the inners for the outers on the pads regularly to even wear out. I have had hit and miss results from OEM rotors, whatever you go with do regular checks down there. By the way why hawk blue?

Not too many people build serious NA cars anymore, boost is cheaper!


https://forum.miata.net/vb/showpost.php?p=5704021&postcount=24

Decide on a few things up front and it'll be easier for the rest of us to offer useful advice.

-Autocross, what class?
-Wheel to wheel racing or HPDE only, what class?
-Street only?
-Does it need to be emissions legal in any state? (what state)
-Must it be able to run on pump gas and if so, what octane?
-Must it run in a street car, (A/C, OEM alternator, col start driveability etc) ?
-Actual budget for everything connected to engine/power making hardware?
-Tuned by a pro or semi-knowledgeable amateur?
-You cool with the additional tuning/set up hassles of an IRTB set up?
-Does the car need to be quiet?
-Do you have a shop in mind that is familiar with race BP series builds?

Cost no object, I suspect someone could build a 300whp grenade that runs on exotic fuel. In the real world 150-190whp is doable within the budget of the most of us.

150whp is bolt-ons and a good tune. Above that you need to go into the motor.
160-165whp is just a little bowl work and compression.
170whp requires more substantial head work or mild cams or lots of compression, pick one.
185whp requires mild cams (still streetable in a VVT), compression, porting. Pick two.
195whp full head work, lots of compression and mild to medium race cams.
205whp+ is pretty much a full race engine with cams that would probably never idle for street use.
225whp+ so and the life expectancy begins to shorten. Perhaps 15-30 race hrs and you're looking at a $15-20K long block.

We have just touched 180whp on stock cams with an NB2 motor but it was not cheap. Based on the data from that experiment, I know 190whp on stock cams is possible with IRTB's, more compression and E85. At that point however, you should just feed it the cams it wants. We played with stock cams to gain a higher BFSC for endurance racing.

For most guys, I think a stock-ish cam NB2 build makes the most sense. Run as much compression as your fuel will stand, get the best ECU you can, build a Honda B series manifold grafted onto the Mazda flange, RB/Maruha/Maxim works header, fully port and polish the head. Forged everything, SUB's and heavier valve springs. That should net and easy 175whp or so, be safe to 8000rpm sustained, idle like a stocker and last 100 race hours.

Wow, thanks Magpie. There’s a lot to digest there.

It might take me a while to cover off all of your questions. Here is another installment that should fill in some of the gaps for you...

My cams are coming from “Cat Cams”, and they will have ~10mm of lift (I’ll attach a data sheet below). They are paired with new (presumably heavier) valve springs from the same mob, to suit the cam. “Shim Under Bucket” shims will be fitted, and the valves are all being replaced with 1mm oversized stainless steel jobbies. OEM valve retainers and locks will be used. I’m planning to stick to the 7,200rpm factory rev limit, for the sake of reliability. I’ve read a lot about harmonics at 7,500rpm and beyond, so I’m not keen to go there.

Regarding cam timing, duration, overlap and whatnot, here comes the contentious part...

I’m keeping the VVT hardware!!!

Yep, that’s right folks. I’ve never been accused of being conventional, and this is just another example. At every turn over the last month or so everybody has said “You’re ditching the VVT, right?”

Well, no, I’m not. I’ve been really torn about this, and it certainly does come with some additional hardship and risk, but I’m going for it anyway.

(I can feel the scorn brewing already)

I am pretty happy with my decision at this stage, but I’d be happy to hear your thoughts.

Discuss.






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Scoota wrote:I’m planning to stick to the 7,200rpm factory rev limit, for the sake of reliability. I’ve read a lot about harmonics at 7,500rpm and beyond, so I’m not keen to go there.

With the right valve train build the harmonics are not an issue, mine has a soft cut at 8,250 and will rev beyond if allowed. Heavier valve springs are not a good idea as this adds to the valve train mass and will impact RPM. There are lots of decisions to be made in a NA build

Once you get the engine done then it will be suspension to decide on...

If you are in Sydney in October stop in at WTAC and say hi, happy to discuss builds

This was with a 4.3 final drive and a 5 speed box. It is capable of a lot faster laps...

Magpie wrote:Heavier valve springs are not a good idea as this adds to the valve train mass and will impact RPM.

I disagree on this one. Not having enough spring rate is a lot worse outcome. The added mass from stronger rate springs is miniscule, and they’re effectively stationary objects, not being flung around like pistons or conrods do where weight would make more of a difference.

rascal wrote:I disagree on this one. Not having enough spring rate is a lot worse outcome. The added mass from stronger rate springs is miniscule, and they’re effectively stationary objects, not being flung around like pistons or conrods do where weight would make more of a difference.

There is a difference between heavier springs or spring rate. K = (1/2m)(v2) (kinetic energy) divides the mass in half (1/2m) but also squares the velocity (v2), hence an increase in weight has a bigger impact as velocity increases... Then you have F=MA to consider.... The springs are less than stationary. Yes the same appiles to other rotating mass components.

I agree stiffer springs are needed, but maybe consider titanium stiffer springs as well as valves made from lighter material. This way you are placing less stress on the valve train. I'm running a non-standard (not even Mazda) valves and springs combination...

Looking at the parts, and planned mods, I'm going to assume that you will get about 160hp on 98.

I can throw out some (possibly unwanted) advice, but keep in mind it is all based around an ITB car setup for racing.

With that in mind: (my 2c)

- Oil cooler, probably don't really need it if you aren't going to have a splitter covering the underside. (but doesn't hurt right.)

- Radiator, when you say bigger, I would just get better... I have a PWR core that is 2/3rds the size of a standard radiator, 42mm thick and water temp is not an issue.

- e85, can't recommend this enough, will run cooler and probably pick up some free HP.

- Brakes, loving hawk DTC-70/60, and lots of people use blues so sounds good.

- Semi slicks, just buy AO50's and be done with it, don't buy cheap tyres.

- Rev limit - I agree, I shift around 7,200 even though I can go much higher.

Questions:

Intake
- ITB details
- Trumpet length?
- bore size?
- airbox or socks or YOLO(no filter)?

Fuel
- Injector size?
- fuel pump?
- surge tank?

ECU
- got a tuner?

Exhaust
- Headers?
- and the rest...?

And realistically what is your budget, and does that include just the engine, or all the other bits to make a fast NA car?