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=24Decide 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.
