mx5cartalk.com

After reading various pages on this forum and weighing up options for more power as well as being in the right place at the right time I have recently purchased a B6T for my MX5 and over the next few months I want to strip it down and build it up - hopefully to 200rwkw. I had a 200SX before with about 140-150rwkw and wanted more power. Now that I have the opportunity to build something decent I want to seize the moment.

I was thinking a T28bb would suffice, do you agree?

Would 440cc injectors suffice with a stock fuel pump?

I am going to get some head work done, but if anyone has any pointers on this they would be greatly received.

Cheers,
Ben

Hi Ben,
The stock b6t bottom end with the MX5 head will take 230 rwkw but obviously not for long. Just need a good turbo, FMIC, ECU and upgraded fuel pump, injectors, fuel reg. If you want response then try to stick to anything in the Garrett T25 range with 0.64 A/R and it will be great to drive. If you just want big horsepower than play with slightly bigger ones than go up to 0.8 A/R... will make the hp but will be laggy.

I would like to point out that any NA6 with more than 200rwkw will start breaking gearboxes, diffs or wearing out clutches. Also brakes pads may need an upgrade or bigger brakes especially if you plan to do track work.

200 wrkw

1ton car



good luck with that and i hope u end up putting the right suspension and roll bars in it!
dont forget the stopping part at the same time!

Thanks for the responses.

I know that there are bigger brakes that can be bolted in with no mod work and these are definately on my list of things to buy.

Anyone had experience with which clutches would be good for my project?

MX52NV, what are your thoughts on a strong reliable bottom end?

Am I better off using the MX5 head or the B6T head?

I'm not out to make huge power, but I don't want to cut myself short. This is to say that once and I say once it is all done I don't want to get in the car and wish I had done this or that. I would rather get the planning right now, source parts and build over the next few months so that the end result will be what I am after.

i think if ur going after a gtx engine or lazer engine u'll need to run a bt head regardless... i know for sure that the 1.6 gtx engine has a distrubuter which hits the firewall and the mx5 uses coilpacks
so the head off an mx5 bolts on (apparently) - scroll down and u'll see my thread here for the gtx engine swap for 1.6
alot of good info on there!

I had a big post, but I'll summarise. Why'd you buy a B6T instead of a B6 from an MX-5?

i think i worked it out to be cheaper to buy a normal b6 engine and just buy forged pistons and conrods ect. rather then buy an engine that ur only going to use the bottom end on... and u'll just need to overall all that crap anyway!

Reason for getting a B6T engine is that it only cost me $300 including an almost complete car and it will allow me to keep my car on the road (as it is my daily driver) whilst building something up.

Warpspeed thanks for the details, it has been a while since I was turbo shopping.

Thanks everyone for the continued responses, I really do value your opinions and previous learnings.

Is it possible to get an MX-5 B6? While the B6T is nice to have, I think the only advantage it has over the B6 is the rods.

The sump, oil pickup, intake manifold, exhaust manifold, turbo, distributor, leads, knock sensor, engine mounts, etc etc are all going to be useless to you. If you want to minimise car downtime, then you're going to want to get these sorted out on the engine. Although, it still is possible to just pull the bits off of your current motor at swap time, it's easier not to. I assume you won't be using the stock ignition system - boost pressures aren't going to be spark friendly, so I expect you'll get a DIS-2 or similar for your spark?

Seeing as you are going for high power, are you going to give the engine a full rebuild? Seeing as you have basically what is an unknown engine.


FWIW, I put a Familia engine into my car because quite frankly at the time, MX-5 BP engines were a ripoff. I saved a heap of money by using a BPT - I think the replacement worked out less than $800 (after buying the engine for $1100).

I don't think there's an easy way to get 200kw at the wheels with the 1.6.

There's so much to do to a B6 to get it to run 200kW reliably. Don't forget Dyno Shootout isn't always 'Everyday' or 'Track'...

And once you're making that sort of HP, think very long and hard about how you're going to deal with cooling - that's the real headache in the MX5...

Not to mention breaking gearboxes, and diffs if you retain the standard Mazda ones..

btw looking at the dyno charts.. looks like the B6 with standard intake hardware is flow limited from around 160-170kW at the wheels

It really comes down to what you want the 200rwkw for?

Are you just chasing a figure for bragging rights and dyno comps? If so that’s easy (despite popular belief).

Do you want to race the car on the track?
Not so easy, thermal management and reliability come into it, besides you won’t find many tracks where a 200rwkw will be any faster than a 160rwkw one, remember racing around a track requires brakes and suspension as well as power, it’s about balance rather than brute power. You may find the extra power you loose in making the car more reliable will pay off when you spend the money in other areas. Remember there are a lot of limitations in CAMS classes that will hinder you reaching the goal of 200rwkw.

Do you want to drag race the car?
Again that’s easy in a turbo MX5 you’d be looking to run in the sport compak classes, within the ANDRA rules you are allowed a lot of things that you are not allowed in CAMS sanctioned events. You are free to run whatever fuel you like, including high octane leaded fuels and nitrous oxide.

If you just want something for the street it’s possible to have a car that is capable of producing 200rwkw with relative ease. The trick is how often you use the full 200rwkw…

My car runs a stock bottom end, and until recently was my daily driver. With no boost controller (wastgate pressure around 11psi) it pulled 150ish kw at the wheels at the NSW Club Dyno day recently – this is exactly as I drive/drove the car everyday. When I was running my electronic boost controller and more boost the car has achieved better power figures.

I have used the exact same engine/turbo combination to make a smidge over 200rwkw in drag racing trim, but that is using Sunoco Supreme fuel which is a leaded race only fuel.

On the street 150rwkw is huge power for an MX5, it is capable to outrun a GENIII 5.7 in a Commodore and is relatively good on fuel and easy to drive to and from the shops or work with no thermal issues. Remember that the same power in an MX5 vs your old 200sx is a lot faster in the MX5 due to the considerable drop in weight.

As for building it there are a lot of people who seem to get their wires crossed between what the MX5 has and doesn’t have…

The MX5 bottom end has a lot of sweet gear as standard too, it is the EXACT SAME BLOCK as the B6T as comes with the alloy sump and baffles along with the piston oil squirters that Warpspeed mentions as being part of the B6T setup. The B6T has the advantage of lower compressions and thicker conrods – Given the stock MX5 rods are able to handle huge power anyway, I wouldn’t rush into buying a B6T bottom end.

Warpspeed also mentions the modern GT series of turbochargers, and I couldn’t agree more woth him, there are some great turbo’s in there and you could easily find a turbo with minimal lag capable of producing 200rwkw when pushed close to it’s limits, a GT2871R would be where I’d start looking, perhaps a tad on the big side, but it’s a small trade off for the big power potential. Again though I’d urge you to consider the loss of low down torque. If you want it to be a great MX5 to drive in traffic as well as windy mountain roads I’d be looking at the overall power under the graph, there are a lot of times I’d swap a few kw top end for some more grunt down low.

Again I agree with Warpspeed on the fuel pump, you’ll get out of trouble with a Walbro GSS342 and some bigger injectors, the RX7 550’s are big enough but their spray pattern is less than perfect, budget for a set of brand new injectors and you’ll never have to worry.

MX52NV mentions the other things you’ll start to break with this sort of power, gearboxes are reasonably common to break although it depends on how much you abuse the car, the diff will require an upgrade the 1.8 setup (atleast), brakes can also be easily upgraded to the 1.8 setup (both diff and brakes are bolt in swaps).

I upgraded my clutch when I went turbo and have got over 20,000 trouble free kays on it.

You’ll also need to consider a better radiator, and if you want to run high power consitently, a proper oil cooler and thermostat, the water cooling setup for the oil like many other mazdas have is not really sufficient for extended use of high power B6 engines.

Hope that’s given you some more to think about,

Sean, 200rwkw was a target that I have set based on being disappointed previously with my 200sx with 140-150rwkw, I am not after any bragging rights - this is purely for my own personal enjoyment on the street. Whether or not I achieve this figure will be answered down the track, but what I want to try to accomplish is to do things right from the beginning, i.e. I don't want to have it all running and think gee's why didn't I consider that or put that in etc...

I have just finished pulling the engine out the car and have realised that I have actually purchased a BPT rather than a B6T

Now with a BPT engine am I looking at the same constraints?

naturally the BP for the same boost will make more hp/torque than a B6

about 1bar or so should get you what you want...

I too am looking to rebuild my engine but currently am running 140rwkw in my '90... I cant even begin to imagine 200!

140rwkw is scary fast already if you can get the power down...
And as sean was saying SS's are even easy as.. my mate with a VX SS with 250rwkw is easily kept up with in a straight line..

I dont think i'd really want anymore power.. im just looking to build a strengthened engine so its reliable power, with out having to worry about the fact ive just increased my power by another 170% on components that werent designed too.

warpspeed... you were saying
\"The ordinary sohc EFI B6 uses a fairly simple forged crank with only a small counterweight at each end. The DOHC B6T uses a fully counterweighted forged crank with eight balance weights. An absolutely beautiful crank. \"
so im guessing by you comments the DOHC B6T crank is interchangeable into a EFI B6 bottom end??

Luke.

Sean: from what I remember reading the US guys seem to say around 350rwhp is the limit of the gearbox. So I would have thought the diff and flywheel/clutch from the 1.8 would be the only required mods for 200rwkw.