mx5cartalk.com

Hi all,
I am starting this thread to help anyone that is on a budget like myself and wants to source them self a replacement head for their NB8a (BP 4W) 1.8l engine.

I have turbo charged my BP4w and take it to the track. I've successfully overheated two BP4w head and this is fatal for the poor little things . It causes the alloy that the head is made from to go soft (If a more educated member wishes to explain in detail please do), the result in both cases on my heads was the head warps and the valves no longer seal on their valve seats any more. So therefore i had no compression and the engine would not start.

As far as i have found (interwebs research) the BP 4W head has the largest valves and highest lift (cam lobe height) cams of all the BP 1.8L motors.
As far as i know the heads on the NA8, NB8a and NB8b are all different. I have not owned all three, again just what i have read online. (if anyone wants to share info on the differences please do) As far as i know the exhaust side is the same on all of them and the rear only has a different metal pressed in water feed/outlet that usually goes to the oil cooler. The fronts are the same. It seems only the intake side is different

So the BP motor came out in a lot of cars like protege, Ford laser.....and apparently a Kia ??? (if someone knows exactly which Aus delivered cars have a BP 1.8 in them please list em in this thread). I am basically going to got to the "pick a part" wrecker and pull off each one until i find one that will work......and if i dont loose interest I will hopefully post all my findings here for everyone's future reference.

Anyways..........

First victim !
protege 1996 model


I have to admit I aint the sharpest tool in the shed (prob hanging on the shadow board right next to the sledge hammer! ) So im bound to miss out on a whole bunch of details....

Radiator had to come out so i could get to the exhaust mani nuts.

You do realize that going from BP4W to a BP05 of the Protege is a downgrade, and plus your BP4W intake manifold will not work?

It all went pretty smoothly. I only had to get under the car to remove the plenum to block support brace. I always remove the head with the plenum still bolted on because its simply easier to do it that way.
(especially since i don't re install it on my own cars).


Upon immediate inspection the obvious difference is the cam saddles are different.... Below is the BP5w head and gasket off the protege.


once the rad was out i noticed that 'BP 5w' was on the side of the head....


sadly the inlet side was different to my NB8a head (BP 4w)....the inlet gasket off the protege head would not even fit over the studs on the inlet side of my NB8a head...
My appologies i didnt take pics because im a retard.

One thing that may be handy to know is the little black fuel rail spacers were the same! so i got some thing from this exercise as i had lost one of mine.



you can just see at the rear of the head that the pressed water outlet fitting has two outlets as opposed to the BP4w that has a single 8mm one.

No i didnt know that Spikes..... not for sure.....all i had was what i had read on the net......and lets face it if you believe everything u read online, then u def are the bluntest tool in the shed!
I prefer to find out for myself

Ive read that the valves are smaller in the BP5w head and the actual bolt on position was ment to be lower on the side of the head......but for $85 instead of $600, if the NB8a inlet manifold had bolted on then i would be happy to loose a little power. (i cant afford to keep tyres up to my power figure now anyway).

Im keen to go back to the wreckers and pull the head of something else.....Anyone suggest something (car with BP motor) ?? Dose anyone know what model Kia is supposed to have the BP ?

I've read of people using Kia blocks but not sure about heads.

So of coarse im doing this backwards...
So here is my NB8a head (BP 4w)



this is the pressed in steel water outlet i was talking about earlier....a line runs from this to the oil filter mount/cooler.



Intake side



The front



Exhaust side



Inlet port




Stepped injector seat/ hole 16mm dia

Here are more pics info on my NB8a head (BP4w)

This head is so clean because it was freshly decked,cleaned, valves seated and new seals put in for $410.....after i bought a noisy motor just to get the head for $400.......I did two 20 minute drift seshions ...split a water line and cooked it!
There was coolant in the cylinders......assuming because the head went soft and that allowed it to lift and thus coolant to get into the bores

Here are the valves from the bottom.... I guess "note" the 4w marked on the valves. Are 5w head valves marked with 5w ?


Sorry about the glare its on 33mm


Exhaust valve 27.5 or 28mm couldn't get the vernier on nicely

wazman wrote:Im keen to go back to the wreckers and pull the head of something else.....Anyone suggest something (car with BP motor) ?? Dose anyone know what model Kia is supposed to have the BP ?

I still don't quite understand what you are trying to achieve. You have a NB8A yeah? The only thing that is going to really fit with your intake manifold is a BP4W head. Sure you can use a BP05 head of a Mazda 323 Astina or the Ford Laser, there's also the BP26 head off the turbo'ed Laser and Mazda Familias but I wouldn't recommend going down that way.

I think the easiest way for you is just to get another BP4W head, and sort out your cooling issues..
What is your setup? How much power are you making? Do you have a coolant reroute?

I also just noticed that the injector hole on the 5w is not stepped and is in a slightly different location/angle (?).
4w


5w


The injector hole location on the 5w actually intrudes into the edge of the plenum runner bolt on location (for lack of better wording )


Dose anyone know if or which model mx5 the 5w comes on ?

What im trying to achieve is writing a thread that informs everyone of the cheapest bolt on option i guess. I guess its fair to say that i dont actually have a cooling issue as much as a "stupid s#%t happening" issue......ie me nudging other cars while drifting, breaking brakets that attach important things like intercoolers and bad luck with water line/ blocker splitting (me failing to notice steam coming out the bonnet so i do another lap on limiter! yee ha!


Have probably the best cooling setup that anyone has.....50mm ASI rad, no air con, no heater, 19 row oil cooler

It is a good idea. See what is a cheaper option than buying expensive mx5 parts. You could get an adapter made for the intake. I have seen them done before.
Do you want to see an nb8b head to compare the differences? I have one I pulled off yesterday.

Intercooler and oil cooler in front of the radiator. And it keeps overheating?

The BP4W head only came in MX5s.

The BG/BA 323 BP05 90-94 is the same as the NA8 MX5 BP05 94-97 in every way except manifolds, covers, water feeds and sump.

In 1996 mazda changed the 323 engines from HLA to SOBs in the BP05 engines. The MX5s got the same SOBs with the introduction of the NB8.

The BP26 head from lasers/familias 90-94 is exturnally the same as the BP05 head. The intake ports have little domes to change air velocity entering the piston chambers.

wazman wrote:Have probably the best cooling setup that anyone has.....50mm ASI rad, no air con, no heater, 19 row oil cooler

76mm PWR radiator, 9 row setrab (perfectly fills foglight hole), re-route, no a/c, no p/s and a Davies craig eletric waterpump with the factory one deleted . Plenty of race guys don't go through heads with good power. My cars a similar setup to a lot of turbo race cars. I'd get a stock head, have it hardness tested before install and setup some fail-safe alerts. I'm using a DL1 datalogger and I've got alarms setup for the dash 3 with it. Coolant is a bit trickier though... pressure would drop slowly I would think but the steam would keep it gradual. I don't know where you'd start so it doesn't trigger alarms when the water is just cold and engine is at low rpm. At least in racing you can scan gauges on straights...but drifting like you are I'd definitely want to make your life easier and have a light/beeper combo.

Here's someone putting a protege head on a miata, you can see the head casting and the second coolant outlet on the back plugged. Not a lot of information in the thread though.
http://clubroadster.net/vb_forum/18-engine-transmission-sponsored-track-dog-racing/38272-miata-protege-head-swap.html

^^^ In that thread the guy goes from a BP5w to a BP26 !!! The 96 protege i pulled the head off had a 5w head ! this is what im trying to clear up for Aussie info.
What year and model car to get the particular head you are after.

I see your cooling mod list and cry cause i could never afford that stuff oil coolers and rads are expendable items on a drift car anyway...... someone spins in front of you and you crush a core......lots of guys bring spare china cores to the track.

The pick a part wrecker I go to sells heads without cam gear for $45
Can get an ebay head gasket from USA for $70 ish

If I can pick up a NA8 intake cheap then I can be back on track fairly cheaply........ and if I cook another head then its just another $115 ish to fix !

some interesting stuff in here including an adapter plate to change intake manifolds.....
http://books.google.co.jp/books?id=wvnQbYLEj6wC&pg=PA34&lpg=PA34&dq=miata+head+bp+to+bp+4w+plate&source=bl&ots=8GvBX6_ZIi&sig=TXkKTpOqtRiFE2hXAVwZ8M6v-is&hl=en&sa=X&ei=QXnRUYvrAs7YkQXRq4CQCg&ved=0CE4Q6AEwBA#v=onepage&q=miata%20head%20bp%20to%20bp%204w%20plate&f=false

wazman wrote:^^^ In that thread the guy goes from a BP5w to a BP26 !!! The 96 protege i pulled the head off had a 5w head ! this is what im trying to clear up for Aussie info.
What year and model car to get the particular head you are after.

that thread is a bp-05 head to bp-26. surprized he had pulled a 26 off a non turbo LX. it must have had a head swap sometime in its life.

what aussie info are you trying to clear up? head switching between mx5s/323s/lasers has been done before. what info are extactly are you trying to find?