Hello all! I've got a build list together for an N/A motor that I was advised by Ed from 949 to float past here. A bit of backstory is in order I assume because I'm posting an N/A build on Miata turbo, I just have always got the best advice here. I've done the whole turbo car thing two times now, it's a riot. I've put down 350whp, blown up several 5 speeds and one 6 speed, broken diff housings, and blown up basically the entire driveline. While dumping my money into an endless hole sounds great, I've had my turbo car fun and I'm ready to just build a Miata with a "pure" driving experience. The crazy turbo builds makes a great car, but the charm of the Miata is lost. As Ed stated best, I've experienced the miataturbo.net circle of life. With that in mind, I don't really have a power goal. Chasing numbers is a game that always gets expensive fast, and I've played that game several times. The main goal here is to have a responsive, rev-happy, and playful motor that lasts ideally around 100k miles before oil burning or leak-down tests become problematic. Not super concerned about low-end torque, If it's an issue I'll put a shorter diff in it. I am well aware of the limitations of a 1.8 N/A motor, I'm not expecting 200whp, if I had to throw numbers around I guess 150-175 hp is the "goal". I live 15 minutes away from the now demolished Blue Ridge Parkway and Western NC Appalachia has several absolutely beautiful cruising roads, I'd like to have a car that doesn't pressure you to go 100 mph everywhere.


The current build list is as follows, going in a 99 NB1 with a 5-speed and an MS3


General Desires

• 7800 rpm redline
  
• Ideally it will run the A/C compressor at idle, now might "idle" with the A/C on be 1500 rpm? I don't really care. I have a Miata with A/C for once and it's nice.
  
• 100k+ Mile rebuild interval in relation to leak down results and oil burning
  
• Nice high rpm powerband
  
• 150-175hp (don't really care, just want it to be rev happy and fun)
  

Bottom End

• BP6D block 60k miles (very slight surface corrosion on bores, in my dumber years I would have ran it as it sits.)
  
• New Mazda .25mm overbore BP6D pistons
  
• New Mazda OEM rings (.25mm overbore)
  
• Either ACL race bearings (I don't think I need a super hard bearing) or king tri-layer. Some help here would be appreciated. Will use Mazda OEM if recommended.
  
• Mazda OEM head gasket (fellas is a head gasket top or bottom end?)
  
• stock rods
  
• stock crank
  
• Stock main bolts (Do I Need Arp for 7800 RPM)?
  
• .020 off the block for 10.3:1 CR and better quench (93 Limited no e85)
  

Top End

• BP4W Head
  
• Maruha +1mm oversized valves
  
• Mazda OEM valve stem seals
  
• Maruha 10mm lift 272 duration Exhaust cam
  
• Maruha 10mm lift 264 duration Intake cam
  
• Maruha SUB lifters
  
• Maruha Adjustable cam gears
  
• Maruha reinforced Kevlar timing belt
  
• I need help on spring selection, I've heard differing things about Supertech springs, I've ran them before and the massive 3mm washer on the bottom scares me with 10mm lift.
  
• Custom built ITB's using motorcycle throttle bodies
  
• Goodwin Header
  
• Simple 2.5 inch exhaust with a vibrant resonator and a Manzo axle back (I highly recommend the vibrant BTW)
  
• I am porting the head, I've done 4 already that made great power. I know the drill with these heads.
  
• New valve guides (192K mile cylinder head)
  

Insurance Policy

• Boundary gears In VVT housing
  
• Fluidampr with 60-2 tooth pattern for high rpm resolution
  
• Blueprinted bottom-end
  
• Balanced crank
  
• Swapping to the BPD6 block for the larger thrust washer (that's why the original stock BP4W was removed)
  

How does this all sound? The car this is going into is a simple setup with Teins, a roll bar, and a Sparco sprint with MSM sway bars. By no means a race car, just something fun.

I have already ordered an entire Mazda OEM gasket kit, pistons, rings, cams, SUBs, valves, cam gears, header, and other aux items (timing belt, water pump, idlers, ect.) I don't want a lightweight flywheel, I think the mass helps with the already unfavorable harmonics the BP engine produces in the bottom end. However, I'd consider doing the 1.6 clutch/flywheel if it will hold the power due to the slight weight drop, or would consider a slightly lighter flywheel if there is an alternative.

The main things I need help with are bearing selection/bearing clearance suggestions, valve springs, and piston-to-wall clearance. Should I just use stock running it out to 7800 rpm? I'm fairly confident stock injectors are ok correct? I can always check the duty cycle later I reckon and throw some yellow tops at it if necessary. I feel like I need the upgraded damper, it's never a bad idea and I'm willing to spend the money.

Thank you so much for the support over the years and I appreciate any advice given to me!
~Mike

 

This sounds like the right combo for the power you're chasing. I would recommend OE main/rod bearings, I personally haven't experienced any issue with them at high power or RPMs, but I have had massive issues with "race" bearings.

Personally, I'd avoid the ITBs and just use a square top/S2 throttle body. I've built a few 160-180hp N/A BPs, and I don't think the intake manifold is a restriction. I did tune one to 180 and it was ITB, however it was a 2.0 stroker, so that's kinda apples to oranges. The other two BPs I built were bone stock bottom ends with a bunch of head work and cams.

If you're opening up the bottom end, I'd probably recommend forged rods for strength in high RPMs, but again, the ones I've built haven't had them, one's barely driven, the other blew up due to unrelated issues (hint: clutch in when you spin on track).

I'd highly recommend a lightened flywheel, nothing extreme, something like supermiata's 9lb option. That'll go a long way to your goal of "rev happy".

The 60-2 trigger wheel is over kill, plenty of options in the 36-2 range that'll be just fine.

Also, I'm not convinced the cam gears are necessary. Feel free to degree them and prove me wrong, but IIRC, the ones I used were set to "0", aka same as stock.

 

Like curly said, pretty solid list. I think main studs would be beneficial for that rpm, and I’m blanking on whether the BP6D bottom end has the MBSP but that’s also a good idea. Fully agree with Curly on forged rods for stability at high rpm, they are often lighter than a stock rod too, which will help with the revviness. Ditto going to a lighter flywheel, of even a light 1.6 spec flywheel/clutch. There are several options in 1.6 diameter that will easily hold that power.

Why not go with a VVT head though? They flow almost as well as a BP4W, especially given you’re already going for cams, big valves, and port work, yet they offer way more torque and/or drivability, especially given you want it to reasonably run AC at idle. Get a little stronger, smoother idle with less overlap, but also the torque and power jump from intake advance. Controlling it will be a cinch with MS anyway. Just some food for thought.

Can’t really comment on valve springs, I know the STs are popular within other brands’ engines, but also know some people on here have had issues on occasion. I do know the ubiquitous Volvo springs will not live long that that rpm and will lose seat pressure.

OEM bearings and OEM clearances will be fine. For rings and piston/wall, I’d do higher end of factory spec given you’re leaning towards factory pistons and rings.

As a parting seed to plant; have you considered the fabled 4-counterweight protege crank? Revviness is said to be divine. And for an N/A motor it would be plenty strong.

 

Thanks for the responses! If I'm going to be completely honest the itb's aren't a power thing. I just think they sound and look cool. I can make the manifold myself, and it's a bit of a personal challenge to see how If I can tune them well. If that doesn't work I will definitely follow your advice though.

In regards to not using the vvt head, I didn't consider how much that would help idle first off, and secondly I've already bought cams for a bp4w. Whoops. One of the turbo motors was vvt and it was very cool to see the effect on spool with vvt.

I'll definitely run some oem bearings as recommended and I'll see if I can squeak some rods into the budget. If not I'll just drop the redline down a few 100 rpm. Are eagles gonna be a decent option here?

I have seen the protege crank, however I haven't found anybody thats really ran it and said how good it really was. I'll look into that more.

the 9lb flywheel option sounds good, ill check into that as well. Thank you!

 

If you want 100k mile longevity then I think you need to wind back the rev limit somewhat. Rpm is what wears engines out.

fwiw, I have been here and ran a ITBd NB on track with cams, $$$ head work making 160ish at 7600 and whilst it went very well, you had to rev to the moon to make power and it wore out quick, even though built with all the good bits. cos 7600 all day will do that.

After deliberating what to do for iteration #3 (#1 was mild n/a which ran 9yrs and 90 hpde track events before needing refresh, #2 was ITBd rocket ship with all good bits that cost a fortune but barely lasted 3 yrs / 30 events) I now have an essentially stock motor (stock head, cams) so no expensive head work/porting, just with forged pistons for safety and run a rotrex pulleyed down to just 3 psi (long story but works) and it makes an easy 150ish, still more torque everywhere than ITBd car made, but is dead nuts reliable because it’s essentially a stock motor and I run factory rev limit of 7200.

 

Flip the cams. More intake cam, less exhaust. Also, why not higher comp or bigger pistons?
I have supertech doubles in my head with Maruha cams and they work well.

 

For longevity, get the damper, especially if choosing a lighter flywheel or raising the rev limit. Supertech light doubles will avoid valve float at higher revs. Get the valve guides checked and replaced if even barely needed. They are often an issue that creates oil burn and valve/seat wear.

 

Thanks for the advice, I'm intending on getting all the guides checked, especially considering the mileage. Upon further review, 100k is a lofty goal. I'd be happy with 60k, that's about 3/4 years. What wears out here? In my experience it's been big end bearings on the rods. If the "rebuild" consists of checking clearances and rolling some bearings into it that's perfectly manageable for me. I've decided to put rods in it, I was on the fence before but I've been convinced.

I want an engine I have to rev out, so I'm not worried about lack of low end power. Trust me, I've had miatas that made HEAPS of low end power/torque. Ruins the car for me. I'm talking 200tw 245's can't put the power down. Not after that again.

Another factor to consider here, this car won't ever see a track. It's supposed to be a fun weekend car. It's not going to live at redline 24/7.
About the cams, I went larger on the exhaust to compensate for the bp4w's large intake flow bias. Is that incorrect on my part? The factory cams are also set up in such a manor. Just wondering why I would want to flip the cams.

 

If I understand correctly, the longer exhaust duration reduces the dynamic compression and you lose on the mid - top end at 4k+ rpm. This is admittedly where I start getting a bit lost in the theory and am relying on our dyno results where the intake cam duration is much longer than exhaust and the motor makes the sauce.

 

Sell the 272 cam and buy another 264. Sell the pistons/rings and buy a set of 1.5 mm over ST 11:1 pistons/rings. Do not deck the block and head more than the min to clean them. Make sure the gasket set is for a 99-2k or the two most expensive gaskets (head & VC) in the set will not work for your build. Use the heavy double ST springs. .0015”- .002” clearance on the main & rod bearings. Do not use main studs. Definitely buy valves. My recommendation is the 1mm over Manley. Another option would be the 2mm over ST intake with the 1mm over Manley exh.

The factory rods are very high class by today’s standards being that they are forged with adequate bolts and bushed small ends. With that said they are not worth rebuilding and will barely run to your rpm goal. They will not have any extra capacity for an over rev. The best option would be a light weight I beam like the Carrillo ProA or ProSA. The next best choice might be the K2 since it is the lightest H beam. Based on your questions do not port the head. FI is much more forgiving than NA. The throat/bowl dia to the nominal valve seat dia is critical.

 

Yes I'm aware of the 83% bowl cut. I can do a head no problem, I've done several heads for several cars over the course of several years. Not going for magic flow bench numbers I'm going for improvements in mid lift flow.

Already have purchased +1mm oversized valves, I'm aware of the bp4w head gasket + reroute combo.

Ill request if i can swap my 272° cam with a 264° cam and just run both as a 264°

I'm not dealing with forged pistons again. That's out of the question. If I have to lower the rpm limit to accommodate stock pistons. So be it.

I was under the impression closing up the quench area on these engines via head/block machining produced favorable results. Emilio mentioned that before.

 

The forged ST/Mahle pistons are lighter and use thinner rings. They are worth the hp gains. If you have a competent machine shop do the bore work they can work well on the street. There is a lot more to head porting than just the throat to valve dia ratio and I would use 88-90%. When porting for this application less is more. I also recommend manganese bronze guides and having the crank ground. The OEM bearings are better quality than the aftermarket units. A second option would be to run OEM mains and ACLrace rods bearing.

 

E-mailed Maruha, as recommended by a few people they are going to send me a 264° for both intake and exhaust. Thanks for all the help!

 

Got parts in, will be going to the machine shop beginning of January, then I need to order bearings, lash caps, valve guides, and valve springs.

 

Figured I'd post an update here, engine is headed to the machine shop friday and I've prototyped my itb manifold, last prototype is pictured and

I need to modify runner angle as well as runner length, I'll be milling it out on the hass machine from 6061alum

 

Well, my machinist ran into some medical issues and i had to find another one. So a 8 month waiting period came of that. The cylinder head is finally done, that took forever. Currently checking valve lash after getting all of the valves installed, springs all installed at a height I'm happy with. Bottom end went together well and my tightest PTV clearance was 3mm with maruha 264 cams, maruha oversized valves, and JDM bp6d pistons. Once I order all of my shims the engine will be ready for install! I just threw the front covers and the header on for the picture. Needed some motivation after this long wait!

 

It runs great!!!!!
Super fun powerband, sounds great, and is an absolute riot.



Stock manifold is a placeholder. Wanted to break the engine in on an easier to tune manifold than itb's. Yes the hot air intake is terrible, ive got a 180° bend on the way to move the filter to the cold side of the bay.