Dokii

Hello! I need some help deciding on connecting rods. After hearing some feedback from people, and low end torque killing multiple peoples connecting rods, I'm looking to upgrade. I'm aiming at 220 rwhp and possibly more on e85 in the future. This is on my MSMs stock turbo and bolt ons/ecu. I'm planning on staying on stock pistons, but I need some help deciding rings as I believe I should be replacing them with the pistons out, also I believe I'm supposed to replace bearings while I'm at it. I would love recommendations on what rods to get, and if there is anything else I should do like stud upgrade on block or rod caps. Also I have another question, I currently installed a supermiata reroute, and im wondering, do I get a NB1 or NB2 HG? I mainly think NB1 but I saw some person with a msm engine swap saying to do NB2, so I'm lost on what to pick. Literally any help will be appreciated, thanks in advance!

shuiend

iTrader: (24)

Any forged rods will be more then good enough. I have used ebay rods for over a decade without issue. You want ARP rod bolts.

Honestly if you are going inside the motor and doing rods. Spending an extra $500 on forged pistons is probably worth it.

Z_WAAAAAZ

At 220whp, you are likely not going to kill the rods. However, doing a forged bottom end build for peace of mind is well worth it in itself. Also, you may likely want to up the power in the future. It's generally accepted that stock pistons are ok up into the high-200whp range, but like shuiend said, if you're already going to open up the motor, there's worthwhile value in dropping the additional coin for forged pistons. You'll want to do rings too, obviously, while you're at it. Wiseco XX rings are probably the most popular around here. Lots of threads on this site regarding what gap to go with. Basically just follow manufacturer recommendations that come with the rings.

ARP rod bolts are going to come with most all forged connecting rods out there. I'm not sure but I believe most if not all eBay connecting rods come with them (someone please correct me on that if I'm wrong).

You want a 94-00 head gasket, which is a direct bolt on to any 1.8 motor and will give you better cooling system performance with the reroute.

https://www.949racing.com/supermiata...-engine-build/

Lots of good information from SM regarding BP engine builds in this post.

SimBa

I would echo what Z said. If your current goal is around 220 WHP you might consider just running the engine as is until you really get the desire to turn the power up. I'm personally running Eagle rods.

I did a pretty good amount of research last fall prepping for my engine build and most of what I heard was that stock pistons are good upwards of to 300 WHP with a solid tune. Most people said that if you have a tuning "hiccup" around/over 300hp, then stock pistons will fail. I found a lot less evidence of piston failure than rod failure. I figure that's because the rods fail first and most people probably up their power goals at that point and do forged pistons as well. I had planned on doing a rods only build, but got a great deal on some pistons, so I snagged them as well.

The way I look at it, if you're shooting for around 250 or under, don't open the engine. Run a bit less power (maybe 220 like you mentioned) to protect your rods.
If you're shooting for over 250, then you might as well get pistons too. Otherwise (based completely on internet research) you're putting in a lot of work and not gaining a ton of ceiling power wise. Again, I have no personal experience with rod or piston failure, this is just based on my research.

Also, I went back and reread your posts. It sounds like you have a bit of research to do, mostly based on "I believe I'm supposed to replace bearings while I'm at it". Yes, yes you would absolutely replace your bearings.

I would highly recommend Napp Motorsports engine build video (2+ hours long), as he covers every step of the process. TheCarPassion channels video (~30 minutes long) is another good one, but there's no narration in that one, just visuals. Bofi Racing also has a webpage that outlines the general failure points of the Miata platform, which might give you a better idea of what you do/don't need to replace.

Dokii

I've done more research since posting, I already have it down to the bare block to just clean everything up because I have all the time and its fun. Anyways I dont think Id ever go to 300hp, maybe 275 but thatd be in the way future. Im not sure I want to spend the 500-600 bucks on pistons, and instead just get rods. So Im really not sure.

SimBa

Sounds like we might have gone down a similar path then. I went all in with the engine build and then came to the realization that my trans, clutch, turbo, fuel pump, exhaust, would limit out before or around 300. I have a lot of headroom as far as the engine goes now, but I'd have to change a lot about the car to really utilize it. I don't regret building the engine, but my time and money might have been better spent elsewhere. The engine was a really rewarding project.

I'm still working on getting my power output turned up, but I've driven a ~270 WHP Miata before and it was rapid. I think the 250-300 WHP is a good range to aim for.

I assume you would reuse the stock MSM pistons in that case? I have no idea if those are stronger than other generations. Do the pistons look good to reuse?
I'd say go for it on the stock pistons just to see what happens. I doubt you'd break them under 300 assuming your tune is good.

Dokii

See this is where I am not sure, I want a reliable build for a fun car, maybe everyother weekend or so. I really dont wanna drop money on the pistons but on the other hand I feel like I should

Z_WAAAAAZ

If you're doing a full rebuild already, I'd throw a set of forged pistons in it.

Additional tidbit: NB2 pistons are the highest compression ratio of any stock Miata piston (10:1). If you're planning on running pump gas and not e85, lower compression pistons will be better suited to the application (more ignition timing for a given boost level before running into detonation).

SimBa

Z, he's got an MSM, so his pistons would be 9.5:1 I believe.

Dokii

So Considering I do plan on going E85 in the future, but for now on pump gas, what compression pistons would I want to get? Im not sure if I should bore the cylinders because to be honest Im not sure exactly on honing/boring and stuff like that. So I got a lot to still try to figure out

der_vierte

Compression is highly overrated. Just go for 8.8-9.5 and you're good to go.

Z_WAAAAAZ

Derp. Thanks for the assist.

Dokii

What do you mean by highly overrated? Surely one has to have its benefits over the other?

LeoNA

Higher static compression will increase off boost torque. Max power is largely due to the increased air from the FI. It is less difficult to tune with a lower CR especially on gas. I recommend forged pistons with aftermarket rods. The cast pistons wear out faster with boost. The reason is not always to prevent catastrophic failure. Forged pistons will also be more tolerant to minor tuning mistakes and will make more power.

Dokii

Considering the MSM came stock with the turbos, wouldnt the pistons be more in favor of boost? Or are the indentical to NB1 Pistons?

Fireindc

iTrader: (13)

I'll chime in here, just because I went through all of this about 5 years ago when I rebuilt my motor.

I ended up going with stock pistions (bp4w 99-00, IIRC 9.5:1), stock OEM VVT oil pump, ebay rods, NPR rings, and ARP everything. It was a budget build with the intent to not go much over 300whp on e85.

The car made 308whp on e85 (2860rs) and has been dead reliable, including lots of track use. I also DD'd it for a winter and didn't feel as bad about sub-freezing cold starts, short drives to/from work, etc. I think this is the benefit of a stock piston setup, you can still use it like a stock car.

If I were to do it again, now that I'm making more money, I'd probably just go fully forged. But like I said I have no regrets of going the way I did. IIRC I had less than $1500 (parts + labor, including having the machine shop actually assemble the bottom end and head) into this motor and it's been a beast. I don't remember the tolerances, but I told the shop (a well known spec miata shop in the area) that it would be a turbo motor targeting 300+whp, and told them to build it to the "loose end of OEM specs".

My reasoning was that I didn't want to go down the rabbit hole that comes with >300whp miatas. The whole drivetrain swap thing, the idea was to keep it on a 6 speed. I.E. ~250whp track, 300+ street type of car. And it has done exactly that for the last few years (and 30k+ miles) reliably.

Dokii

That shows a huge relief on my end, I now don't think Ill be getting forged pistons, I've already spent a lot of money on the suspension/wheels/ecu and I just really did not want to drop so much on the engine build, It'll be nice to keep the stock oil pump, because 300 for the engineering one is insane to me. Would you recommend replacing the water pump? How much did it cost to get it machined? Did you get it cleaned? Ill most likely be assembling the bottom end myself, do you have any tips on clearances and stuff? Im still personally researching it but I just cant seem to grasp it. I don't think Ill be going above 300. How much were the ebay rods? I was looking at the Manley ones from GWR, but if ebay are no different, then I might go with that. If I keep the tune down I'd hope it'd be even more reliable. What seals did you replace? I'm thinking of replacing most seals but not sure all of them, really just confusing. Currently attempting to work on a spreadsheet to figure out everything to order and what parts Im needing.

Fireindc

iTrader: (13)

I'd go with a new OEM oil pump, and definitely not re-use the stock one. I skipped the BE gears, but went with a Fluidampr on my car, which does help with the oil pump gear issue in a different way. I also set my rev limit at 7200 and left it there.

Definitely replace the water pump, all gaksets, and accessories and use all OEM stuff.

Yes I had my block hot tanked, my crank polished, and the whole thing profesionally measured and assembled. It was less expensive than I thought, I think it was an additional $350 for the assembly which was money well spent to me.

Ebay rods I got second hand off this forum for $200. They were unused and new in box. I'm sure they've gone up since. I certainly wouldn't say that ebay are "no different", but as others have said they are plenty strong. The big deal about ebay rods are having the small end honed properly, and measuring the big end for roundness, etc. Again, I had the machine shop do this part.

Sounds like you are on the right path, but I will admit some of the questions you just asked make me think maybe you shouldn't be doing the bottom end assembly yourself. And I mean no offense at all, I'm sure you can figure it out, but if the whole thing grenades you'll be in the hole a lot more than just having a shop do the assembly for you.

rjacobs

Pay to have the bottom end assembled... its usually pretty cheap in the grand scheme. Have the machine shop set all clearances. They have the tools to do this, you most likely dont. Thats another 2-300 bucks in tools. And what happens if something is off, you have no way to remedy that. The machine shop does.

I have Eagle rods in my engine, but had bought a set of the ebay MaxPeeding rods which the machine shop didnt want to use since they didnt supply them. They looked to be 100% the same as the Eagle rods...

Get an ATI or Fluidamper damper on the engine. If I was bumping the HP I would ALSO do at least the Boundary Gears in an OEM housing.

NB1 head gasket with a reroute. But I think the MSM head is already basically an NB1 head anyway right? so...

I would stud the bottom and top end, again if I was bumping the power, as you are. I didnt but I am just a "stock-ish" VVT motor.

Dokii

is the damper necessary? I dont seem to understand why they cost so much? Yea Ill probably just have the shop do the bottom end. Also question, how do I decide bushings? Will they have to like hone or bore the rods? Im still really confused when it comes to the pistons, do I just get the size I want, have them bore it to that size and get rings for that size which theyll set the clearance too? How would I decide bottom end bushings unless they tell me what size I need? Ill get the BG gears in the OEM housing. Thank you guys so much for your help!