This is a very helpful and very detailed list, thank you for putting it together.

Emilio, could you give me your recommendation on valves for my new head? I picked up a stock VVT head with 160k. I am torn whether to do a stock rebuild with multi-angle job or to go for oversized valves. I'm not sure if the valves are worth the $$$ for me. The car is a weekend, sunny-day driver and doesn't see track time and 7200rpm redline. Forged bottom end, ARP studs, etc. Plans are to make less than 300hp, likely in the 270 range. What will valves do for me in terms of spool and how many more PSI would I need to make the same power bump as oversize valves would give? Just blew up another Churbo and looking heavily at a TSE EFR right now.

 

You are making it more complicated that it is. Valves cost more and make a bit more power. If they are in your budget, add them. If they are not in your budget, do not add them.

If you can add boost, then add boost. The equivalency is irrelevant.

 

Didn't Soviet make 450hp on a bone stock head?

 

Simple enough, thank you!

 

Be careful with the multi angle. While retaining stock valve seat width, there is not a lot of room to add a third angle. At least that was how my machine shop felt. I did end up with 3rd, but not much.

 

Out of curiousity if BP6D engines do not have bearings from ACL what bearings do people use?
Also is the NBFL a different engine from the BP6D in the NB?

I ask because I've been paid and a NBFL SVT engine has popped up which could be Phoebe's backup heart.

 

You read that wrong. ACL does not offer thrust bearings for the NB2. The rest of the engine bearings are the same for all Miata BP's.

No USDM car with NBFL chassis or engine code. Perhaps someone from Europe can answer that question in a new thread.

 

What thrust bearings do people use in VVT motors?

 

OEM VVT and MSM (from Jim Ellis site.)

ZJY111SK0 ------- (Oversize 0.25)
B6Y211SKY ------ (Oversize 0.75)
ZJY111SJ0 ------ (STD

Also, another place to get them: Mazda OEM Miata Thrust Bearing Set although they don't list the same part numbers.

 

Yah, OEM here.

 

^There you go RJ.

Also: NBFL = NB Face Lift.

RJ, all USDM 01-05 NBs have the BP6D motor that "we" usually call a "vvt motor" or "nb2 motor." "We" did not get any form of 1.6 in a Miata past 1993.

 

Thank you for the clarification all.

I will purchase appropriately although I do have one final question.
What is the dry mass of the BP6D engine give or take? stands are rated and so i don't want to mount it then the stand give way.

 

I don't think i've seen an engine stand rated for less than 500lbs, which is well more than any variant of BP.

 

No much i took mine in out out of my truck by hand. If i had to guess i would say 200ish lbs

 

It's an interesting question and also one that's commonly asked. But completely off topic. Your project sounds interesting. I would suggest starting a new thread for it.

 

Thinking of building a vvt head to run on stock bottom end for just spirited daily driving. Shave 20 thou, 3 angle valve job, port/polish, SUB lifters, springs, Tomei cams. Will get bigger injectors, plus new intake manifold and throttle body. At the end of the day, what do you think I will have after this? I just sold a supercharged V8 car and bought my Miata....so I'm a little mentally starved for more power.

Thanks,
Dale

 

Odd place for this question. Probably get more response by starting a new thread in this section.

Include the following info in your new thread: min octane it will see. Whether you have done compression & leakdown on your bottom end, intake manifold type, header brand, exhaust diameter, ECU type, Speed-Density or Alpha-N, comp ration of that bottom end. Good luck with your project.

 

Thanks Emilio...will do. Thanks for the bold as well...really drove home the point

 

March 2020 addendum:
As Supermiata no longer offers complete built engines, we thought we would share a few trade secrets.

Cylinder wall thickness

We would sonic test every block before using it for an engine build. We found the NA8 (94-97) blocks had the thinnest cylinder walls. NB1 (99-00) a bit thicker. NB2 (01-05) had the thickest cylinder walls so we only used NB2 blocks for our built engines. For F/I builds, we try to keep min thickness above .120". For N/A build, .100". Key areas are the thrust faces. In non-thrust areas, the walls can be much thinner.

In general, we would stay away from 85mm or larger pistons for high boost applications. Difficult to find blocks with enough wall to reach .120 in critical thrust areas with 85.5's so we stopped trying. A low boost (<12psi) engine could be fine with 85mm pistons. Much above 15psi and we stick to 83.5 or 84.0mm to maximize cylinder wall thickness. Power is coming from boost at that point, displacement not critical. For N/A builds, we like 85.5mm pistons.

Heavier bits
A high dome 85.5 piston can be quite a bit heavier than the OEM 83mm 9.5: 1 OEM NB1 piston for example. Beefier rods are a must when building a high compression, high revving bigger bore N/A motor.

To keep main bearings alive with all this extra mass and increases forces from higher revs, harder race bearings are a must. Thicker viscosity, higher film strength synthetic oil kept below 240° is a must. Cheap, low viscosity conventional oil without an oil cooler can see 310° and have nowhere near the film strength to keep the bottom end alive above 7500rpm. Modifying the oil pump to raise pressure 5-10psi is also a standard practice here.

 

How would you accomplish this?
Another thread on this site stated that shimming the relief spring would NOT increase hot oil pressure which seemed incorrect to me.