What started as a deal too good to be true, this has been my most challenging engine build yet. After going turbo for a year (Flyin Miata kit with a 2560R and custom fabricated intercooler piping), Dylan decided he wanted to dial the car back to what made a Miata a Miata, the raw driving experience.
The Goal: 200 NA BHP
The Execution: 12.25:1 Compression 2.0L (85.5mm Overbore) ITB VVT
The Story: While scrolling facebook one day, a listing came up in one of the many Miata groups. A pre-built 2.0L that was set up for ITB's. This kit had some crazy parts in it from Tomei Cams, 85.5mm Pistons, Boundary Oil Pump, and best part was, all the machining and assembly was done! So we thought. Wanting to waste no time on a deal this good, Dylan and I hooked a utility trailer up to the back of my dads Toyota Camry (I have since upgraded to a truck of my own!) and made the 11 hour drive down to Raleigh to meet up with the owner and pick up the engine. Doing some research on the way down, Dylan manages to find the build list for the previous owner and we're shocked at all the parts. Turns out the engine was built, and then almost immediately sold due to military deployment, which is why it was never (thankfully) ran. It sat in the current owners garage for a few years until he decided to K Swap his car and let the engine go. The trip goes smoothly and we immediately rush back home to Rochester so that we can get a better look at the engine and see what we have.
The Inspection: I've learned over the years to always verify the work done if you can't verify who did it, and this was going to be far from an exception. As we sifted through the forum posts on this build, it was clear that it wasn't very well thought out. It looked more and more like a "buy the most expensive components and put them together" build, with the hopes that it would work and nothing would interfere. So we start doing some tests on the block to see what we have, also considering that it's been sitting for a few years, a health check isn't a bad idea. First step? Make sure nothing interferes when the engine spins over. High compression pistons, (unknown) head shave, oversized valves, and big cams are a recipe for disaster. Simple check on any engine that isn't a VVT, but this is. At base cam angle, everything spins over nice and smooth, so there's a sigh of relief, maybe this guy did the math! Next step, simulate VVT at full cam advance and try again. So we re-time the engine and set the VVT Cam 3 teeth advanced and spin it over carefully. Not even close to TDC, the wrench gets tight in my hand. Game over, engine has to come apart. Sure, we could have run without VVT in the tune, but what's the point. And if that's wrong, then what else is wrong? Better safe than sorry, especially when you plan to spin something to near 8000 RPM.
The Teardown:
Bottom End - After a moment of silence, it's time to just tear this whole thing apart. The deal was too good to be true, and it's time to find out what other surprises are in store for us. We immediately pop the head off, and it's arguable if those head studs were even torqued all the way. As we lift the head away, what's staring at us besides the wall on Cylinder #2. Completely pitted out, likely from water sitting in it for years. Normally this would just be an annoying problem that can be solved by running overbore pistons and machining through the damage. However, as this is already 85.5mm and stock is 83mm, there is no material left to bore though, and no bigger pistons that can physically fit in the block. That means we have to do something I've never seen on one of BP build. A sleeved Miata block. While we're there, we clay the pistons and reinstall the head to see just how far off we are with valve clearance. Due to the head shave, high compression pistons, +1mm oversized valves, and high lift Tomei camshafts, the valves are hitting not only too soon on the piston, but the valve reliefs are too small radially. The only fix for this is what's called fly cutting the pistons in order to open up the reliefs. And it's all 4 reliefs (intake and exhaust). Wanting access to the full range of VVT, there is no other way. So not only does the bottom end need to be re-sleeved, the pistons need to be re-machined. At this point, everything else has to come out, so all parts of the bottom end go out for re-work. Crank gets polished/balanced, Main and Rod bearings get measured and replaced with new ACL Race Bearings, new OEM thrust washer, and I balance the rods. Meanwhile the block and pistons are at a "performance" shop getting the custom work done, but I'll get to that in a minute.
The Head - The bottom end was a disaster, so let's assess the top end. There isn't too much to screw up here thankfully, but there's still a few things, especially when going oversized valves. A quick check of a valve job is to flip the head upside down and shine a flashlight through the intake/exhaust ports to see if you can see light around the valves when they're closed (cams out is easiest for this). At this point, to no surprise, each valve looked like I was witnessing a solar eclipse. What also looked weird to me was that the valves were sitting fairly proud of the valve seat, like the seats hadn't been cut to accept the larger valves, because it turns out they hadn't. Whoever assembled the head had just thrown the bigger valves in and assumed that meant you'd get more flow. Not a huge deal, since cutting seats for oversized valves should be no problem for a "performance" machine shop, you'd think, but again we'll get to that. Just some things to note here, the engine also had SUB (Shim Under Bucket) Lifters. I didn't bother to measure shim clearance at this point since it would change with the valve job anyway. But, off to the machine shop we go, plan in hand and a path forward.
Machining, Round 1: If this engine build taught me anything, it's that a Machine Shop is like a Barber. Find one you trust, and don't deviate unless you absolutely have to. I've been going to my local machinist (Shoutout Buck's Auto Parts in Henrietta, NY) for years and I've always had amazing experiences with him. Small personable shop run by long time dirt track/circle track racers and they have an insane attention to detail that I have yet to find anywhere else. That being said, they know the limits of their machining capabilities and what they're comfortable doing, and sadly sleeving and oversized valve stuff aren't on that list. The oversized valves were only a concern because he didn't feel comfortable that there would be enough seat material remaining. We've since come to an understanding that it's perfectly fine, but at this point he wasn't confident. So, per the recommendation of another local car guy, I took the engine to a shop about 35 minutes away. This place got me with all the flashy new tech, spotless floor to ceiling and a pedigree of building some fast drag cars. Dropped everything off with them, and I left feeling comfortable that these guys would be able to manage it all in the 1 month that they quoted me. Needless to say, a month goes by, no contact or anything, so I call and it turns out they never took any notes down of what I needed done. Not a huge deal, just annoying but we corrected it and moved forward. A couple weeks go by, they call me saying they aren't comfortable removing 0.200" radially from the valve reliefs because they're afraid of hitting the piston ring groove, but they'll do 0.100". No big deal, at least I had confirmation it was getting worked on. Another 2 weeks go by and I get a call that it'll all be done by the end of their workday. Being in a rush at this point, I left work early to drive out, and when I show up, they haven't even started what they said they would do, and the guy who had called me wasn't there. At this point I'm just fed up, but they said they'd have it done the next day and they did. The cylinder sleeve job looked great, the piston cuts were clean and tidy, and the head appeared to be well done. Time to put the engine together, right? Wrong. I head back home and think maybe I should check the valve job quality. They definitely cut the valve seats to fit the oversized valves, but when I hit the runners with the flashlight it still looked like a solar eclipse. Either the valves weren't cut to match the seat angle, or chatter from the cutting machine left a ton of low spots, but regardless it was a trash job.
Machining, Round 2: Thankfully at this point, I had complained to my normal machine shop about the quality of work and he offered to help me fix the other shops faults. Brought him the cylinder head and block and had him measure the bore to make sure they didn't mess anything up, and do a full valve grind/lap on the oversized valves. And it was done in a matter of days instead of months. Thankfully not a huge set back, but when you spend thousands on machining, you expect it to be done right the first time.
Assembly: Finally, it's time to bolt it all together and make some power! This part is going to get a bit technical with a parts breakdown, so bear with me.
Head Assembly - Head assembly is a fairly straight forward task. There's no clearances to measure until you've got it fully built, and every valve goes together exactly the same. This was a pretty cool experience for the build as it was the first time I had gotten to work with oversized valves (+1mm I/E), dual valve springs with titanium retainers, SUB lifters, and aftermarket camshafts. Most of the time it's a stock head maybe with some volvo springs, but this felt like I was assembling the Ferrari of Miata cylinder heads. Everything goes together smoothly, valves pass the light test, cams spin over nice. Awesome, finally a victory with this engine. For anyone who has assembled an NB Miata head, you know the next step is measuring valve lash. Not a hard process, just a little tedious and you have to make sure you get the math right. This is where we run into a little bit of a hangup. Being that a machine shop years ago had assembled this, they did what's known as "tipping the valves" to get the clearances to fit. So instead of exchanging the shims for the proper thickness, they machine the top of the valves down so they're physically shorter. This isn't bad in practice, just not my preferred method, and in this case it caused one major issue. The shims on SUB lifters straddle the valve tip, and since they had machined these, the standard 6mm valve shims would not fit as they would hit the retainer shim and possibly drop a valve. That knocks out 99% of SUB lifter options, as now we had to run the shims upside down so that they straddled the stem on the underside of the lifter bucket, which was 6.5mm (I believe, might have been 5.5). Not to mention now that the valves were properly seated in the head, they were "taller" than they should be and needed a shim thickness that wasn't available off the shelf. Thankfully, after a lot of searching, we found a company in Australia that was able to custom make the shims we needed in both thickness and lifter stem diameter. Again, not a huge issue, but the hits kept coming and it was definitely a mental exercise to keep pushing through all of them. Alas, the head was assembled and shimmed to spec.
Bottom End Assembly - While being definitely the most tedious half of engine assembly, thankfully the initial bottom end assembly went together perfectly, once we found the parts. We built this engine during the great bearing shortage of 2021 (also known as Covid), and it was impossible to find a set of bearings. Thankfully, throughout this entire build, Daniel Marshall from Bofi Racing was consulting us and helping point us in the right direction with parts, and he happened to have an open box set of ACL Race bearings on his shelf. 2 day shipping across the pond and we were ready to assemble it all. I balanced the pistons and rods (Crank was done at the shop), and one by one the rotating assembly went together. Everything was clearanced to a spec I was comfortable with (0.0018-0.0022 Mains and Rods, 0.017"/0.021" Top/Bottom Rings) and in it all went. After 3 months, we finally had 2 halves of an engine and we could see light at the end of the tunnel.
For those of you interested, the bottom end was made up of:
- Supertech 85.5mm 11.0:1 Pistons
- Manley H Beam Rods
- ACL Race Main and Rod Bearings
- OEM Mazda Thrust Bearings
- Boundary Engineering S2 Oil Pump (72 PSI Shim I believe)
- ARP Main and Head Studs
- Gates Cast Impeller Water Pump
- All Mazda OEM Gaskets
The Final Assembly, Right?: It's finally time, we have two halves of the oreo, and the Cometic 0.060" Head Gasket is the cream filling in the center. Why 0.060" head gasket you ask? Because the OG machine shop years ago had done a 0.060" head shave, and we were trying to get 6" (0.040") for Jesus back between the pistons and valves. While I'd love to just bolt it together and go, we figured it was our best bet to to a dry run and make sure the pistons in fact cleared at full VVT advance. To do this, we took the old 0.045" head gasket and assembled the engine with some clay on the pistons. Set the timing to 3 notches advanced and started turning the engine over by hand. Just like before, the wrench locks up and we sit in disbelief, but comfort that we checked. We rip the head off and look at the pistons, and sure enough, the 0.100" fly cut wasn't near enough, and it needed about another 0.080". We had guessed at the 0.200" originally just based on thicker head gasket and properly shimmed valves, and it turns out it would've been perfect. So what's the path forward? Do we disassemble it all and bring it back to the worst machine shop ever for another 2 months of work? Or do I break out the carbide bit and my Milwaukee dremel (go team Red) and just do it by hand. If you're a patient person, you choose plan A. We aren't patient. So we taped off every opening, taped the gaps between the piston and cylinder wall and just started sending chips flying. Definitely one of the most nerve wracking experiences that I've had to go through when doing anything related to Miatas, and not something I would like to do again, but after a few cycles of "machining", test fitting, clay measurement, and vacuuming (not in that order), we had the clearance we were looking for. Minimum 0.040" from the bottom of the valve to the top of the piston, and a solid 0.020" from the OD of the valve to the relief pocket in the piston. Thankfully without busting through the ring groove, but I'm willing to bet it's pretty close. We also added some cushion by measuring with the 0.045" head gasket, and using a 0.060" head gasket in actuality. But it's finally time, new head gasket on with some copper tack spray, re-lube the ARP studs, install the head and finally, after months of battles, thousands of dollar, and countless hours, we're staring down the face of an 8,000 RPM capable 2.0L BP-6D.
The Final Package: What good is a built engine without it's supporting mods? People say that it's what's on the inside that counts, but that's not entirely true in a situation like this. It's time to bolt on the parts that you can actually see, and hopefully bring this whole build to life. This build has been the culmination of weekly phone calls with Daniel from Bofi Racing, planning, trouble shooting, dreaming, and most importantly keeping us planted in reality and helping us through the speed bumps we kept hitting, but a plan was in place nonetheless. Dylan knew from the beginning of this that ITB's were the answer for him, so in working with Bofi, a beautiful set of Jenvey ITB's were installed, along with a Fluidampr crank pulley, Racingbeat Header, and Bofi's OEM+ Racing Clutch Kit to give it that nice OEM pedal feel. Mated to a 6 speed transmission and 4.10 Torsen, this turned into to what I would have to say is my favorite NA build that I have driven to date. On the dyno it *only* made 178 WHP, which you could argue is around 200 BHP, but it feels faster than my NA K24 Swapped Miata felt when it made 200 WHP. Everyone argues about horsepower numbers and dyno charts, but the only thing that matters in the end is how the car drives, and to say this is a visceral car to drive through all the supporting mods Dylan has done is an understatement. As it sits right now, it's a turn key build with probably 5,000 miles on it, and it is exceptional.
Takeaways: What did I/We learn from this?
- I'm never suggesting anyone buy a "pre-built" engine that's not from a known builder (let me introduce myself!). I don't know the financials in the end, but it feels like from a personal time (Both mine and Dylan's) and a finances (Dylan's) side of things, it might have been more expensive than just starting with the VVT that we took out of his car. Credit is given where credit is due though, this build definitely took my abilities to the next level when it comes to both understanding of BP's and how to build them.
- Never cheat on your machine shop, and if they can't do it, do some more research before going elsewhere. There is one component to engine building that I out source to another shop currently (line honing), and I only went to them after consulting with other people who have used them AND talking to my machine shop about it.
- Have a good support network. I want to again give a shoutout to Daniel Marshall and the Bofi Racing crew. They're more than just a parts supplier, the knowledge base they have is unprecedented and I'm not sure if that engine would've been in the car and running if it weren't for the countless hours and late nights that Daniel worked with us. Whether it's buddies that come and wrench with you in the garage, or someone thousands of miles away on the phone, you can't put a price on good help.
- Dare to be different, sometimes. You wouldn't believe the amount of times I heard people say "why not just turbo it for the amount of work/money that goes into an ITB setup like that". Obviously the dollar per HP argument here is valid. His car could be making 400 HP right now for the time/effort/money that went into this swap, but it's such a better car for what Dylan is looking for in this setup, and it's a driving experience like no other. Obviously if you want to be different for the clout or any reason that isn't personal enjoyment, then maybe reconsider, but if you have a dream build that might be crazy, but it'll make you love driving your car even more, don't listen to other peoples opinion. If everyone did the same thing, cars would be boring.
This blog post has gone on wayyyy longer than I expected, but if you want to watch the build series itself, there's a whole Playlist on YouTube! I'll just link it here. https://www.youtube.com/playlist?list=PLs9NdPzSO8kuBIWMEjP4o73u48FyxIzVa
Thanks for reading, I'll probably do more of these in the future for the other builds I tackle! The K swap should probably get its own entire saga.