can't decide which pistons
 

I'm in the middle of waiting for parts to come in for an engine rebuild, but I'm having problems deciding which route to go

Planning on semi daily driving the car when it's nice, plus autox and maybe a track day or two. turbo obviously

Route 1: 8:6 supertechs .020 overbore with forged rods and go all out with balancing, etc. at a machine shop spending da monies....

Route 2: Topline standard pistons with forged rods. Engine cylinder walls are in good shape, but will obviously get a hone and a good cleaning if I go this route. Would be trying my hand at balancing pistons and rods myself with a digital scale/belt sander. Budget build

Obviously money is a factor, but I want something that will last. Do I go all out with the supertechs? Thing is, I actually ordered the pistons already. Rods are on their way to me too. Worried about DDing the car and having to warm up the thing carefully every time I drive it with the forged pistons, or do I go Topline and worry about it on the track? ugh, can't decide

OPtion 1. forget the balancing, just check the piston weights yourself.
Cranks are generally well balanced from the factory.

NO need to warm up car, Supertechs use lower expansion alloy which run tighter clearances. Just drive extra gently til the coolant is hot.

On either build, at a minumin, do a half balance, Rods and pistons.

As Jason said, most cranks are fairly close from the factory.

Pay close attention to your ring gaps, and Piston to wall clearance.

Going an extra .0005-.001 clearance on the PTW clearance, will not give piston slap, but will give you a tad more when you go hammer it for extended periods of time.

Adding an extra .001-.003 on the first and seconed ring gaps, will also allow the rings to "grow" a tad without the end butting and flexing during hard runs, or a miss calculation in the tune that would give you a lean condition.

I just posted about the Supertech piston that you are thinking of.
https://www.miataturbo.net/engine-performance-56/first-look-supertech-pistons-1-8l-dohc-65235/

welp, looks like the store I bought the pistons from said the supertechs are on a nationwide backorder from supertech until....... mid june. Anyone know of someone with them in stock?

Wait for them? Or try to find a comparable piston? I like the pricepoint of the supertechs, but not sure if I can wait that long

A quick check of some net catalogs, shows 9:1 cr forged pistons made by both Cp and JE

I have no data to share, but I have both in diffrent builds over the years.

I have no Idea on price.

After holding a JE piston in my hand from a Miata motor, go CP.

looks like I'll be doing both options :P

getting some topline for the current engine so it's going to be the budget build with a hone first

got my extra engine sitting in the garage, so that will get the supertechs and forged rods once they come in stock.

just want to get this thing back on the road, way too many sunny days being missed :(

Can I ask why topline? Not NPR?

forgot if it was on miataturbo or somewhere else comparing the topline pistons to another brand and the quality was a bit better on the topline. most people that i've seen have been recommending topline for cast. other than that, not much of a reason?

Ok, I can go with that.

Reason I asked is NPR is an OE supplier to some of the Japaneese car makers.

hmmm, I'll keep that in mind next time I have to buy pistons :) learn something new everyday, thanks!

i picked up some wiseco's after contemplating literally everything...
why?
cause they were new, but they were 2nd hand. i'm ok with that.

Wow, I think I just picked the time that everyone else is doing engine rebuilding.

Topline pistons are out of stock.
Npr pistons on Ebay don't exist for a 1994.

I've had my orders for pistons canceled on me 3 times now lol

However the supertechs actually came into stock early and are shipping to me, but I've decided that's for the other engine now

The supertechs came in early? When I spoke to ST they told me they were expecting 10 sets of the 8.6:1 cr pistions in 8 weeks.

Well, I guess they had one or something. It's already on it's way to me technically. The place I ordered from said supertech told them it was backordered, got a refund, but during the lag in communication, they then said supertech had shipped out my order even though I was issued a refund. Then I paid again.

Funny thing is, the package, according to tracking, was already in my city, and supertech issued a package intercept as I had originally been refunded. Now the intercepted package has to go all the way back, and then shipped to me again.....

stupid communication problems

awwwww yeah :) finally. took about 3 weeks, but I guess better than waiting until June. thanks guys for the info and help. funny thing is, everywhere I tried to order cast pistons for the other engine, they're all out of stock too... topline, npr, etc. :(

https://www.miataturbo.net/attachmen...1&d=1335895550
https://www.miataturbo.net/attachmen...1&d=1335895550
https://www.miataturbo.net/attachmen...1&d=1335895550

Now scale them and see how close your box is.

will do. got myself a digital scale :) still gotta balance my rods too, but I'm just happy they actually got here. I've been in limbo for almost 2 weeks waiting on these things

pistons weigh in at 297, 297, 298, and 299 grams each. I need to get a smaller scale that measures in 10ths of a gram

What are the wrist pin weights?

I have no complaints about my low-comp Supertechs, but I haven't torn down the bottom end. I like 8.6:1 compression ratio more though. It typically makes significantly more output with a small compromise in throttle response that can be further minimized with spark angle.

alrighty, finally got another digital scale (thank you harbor freight) that measures in .1 g.

piston weights are: 296.4g 297.1g 297.7g 298.2g

wrist pin weights are: 97.2g 97.6g 98.2g 99.2g

wirelocks each weigh exactly .8 grams

Idea for funsies: weight the stock cast slugs and pins when you get them out of the old motor :bigtu:

Happy with my 8.6:1 supertechs as well.

I kind of wonder whether they "balance" like this before they box up the pistons. If you put the heaviest pin with the lightest piston and vice versa, you end at 395.6/395.3/395.3/395.4.

yeah, I was wondering that too. Works out pretty nice :)

Did you get the total weight out of the box with poston and wrist pin?

I had to swap around the wrist pins to get things closer in the bix I had.

https://www.miataturbo.net/showthread.php?t=65235

Seems the right wrist pins were in the box, but they mixed up the wrist pins during packaging.

Finally!
 

oops, should have responded to this thread earlier, but they didn't have the wrist pins matched to the pistons in the box, but I weighed them and after switching wrist pins around, they were matched almost perfectly.

Had everything machined and balanced, including the crankshaft and flywheel and pressure plate. Finally got the pistons in the block today :)

Some pics for your viewing pleasure. This is my very first engine build. First time putting pistons in, etc. taking it as slow as possible and having a great time

https://www.miataturbo.net/attachmen...1&d=1337826009

https://www.miataturbo.net/attachmen...1&d=1337826009

https://www.miataturbo.net/attachmen...1&d=1337826009

https://www.miataturbo.net/attachmen...1&d=1337826009

https://www.miataturbo.net/attachmen...1&d=1337826009

With a beam torque wrench, see how much force it takes to get it rotating. I like to see less than 20ft/lbs

I don't have a beam torque wrench, however it's quite a bit easier to turn than when I first tore down the motor. I'm sure it's less than 20 ft/lbs

Set your clicker style to 20 then and give it a spin!!

Looks good so far!!

with the clicker torque wrench, it won't click unless it's at 4 lbs or below :)

Sounds like everything is going together slick as teflon owl ---- then!

Got the motor in and she's back on the road :) So much smoother than before, and she keeps asking me to step on her more and more (can't as I've only just broken her in). Trying to avoid boost, but have done my 100 kpa runs to set the rings. So this is what it feels like to have a motor that's half built and balanced right :P Thanks again guys! especially BogusSVO, your threads are priceless

Get boost on the rings for break in!!

http://www.mototuneusa.com/break_in_secrets.htm

I've been trying to get it to full load for a good 2 or 3 gears up to 5500-6000 rpms, but avoiding too much boost. I think the most I've boosted is 5 psi. It's run it hard, but then other people have said to run it hard in respect to an N/A engine. I haven't had enough time in autotune to go into boost for extended periods and feel safe (connection issues with my laptop)

I'm finishing up a rebuild on a 1.6 motor with a JRSC kit on it. In the process I am also switching to a MS ECU. When I get the motor up and running, it probably won't be in a state of tune to handle boost. I'm not good at all at tuning.

The plan was to get the engine running, take it over to my tuner and get it setup from there. Only issue with this is how to I break in the rings if I can't really get the car into boost. From readying the Flyin' Miata how-to, seems as though I just need to get to 0 psi of boost with some accel/decel runs. But this Mototune link contradicts that.

Any words of advice to this issue? I would like to avoid doing a bunch of work self tuning if possible. Thanks.

Do Three 1/2 Throttle runs from
40% - 60% of your engine's max rpm

Do Three 3/4 Throttle runs from
40% - 80% of your engine's max rpm

Do Three Full Throttle runs from
30% - 100% of your engine's max rpm

Interesting.

I had that issue too of when I first started up the car to break in the engine. My tuning laptop was having connection issues as I was connected through bluetooth. I had to go back to my cable and then I think I raised all of my VE table cells by 5 just in case as it was running a tiny bit lean.

I also put in a new FM stage 1 clutch, so I didn't want to beat on it in the beginning (always a dilemma), but I was able to get the engine to 100 kpa (full N/A load) and then as my VEanalyze did its thing, I did some boost runs with probably about 3/4 throttle up to 5500-6000 rpms. Engine seems super strong, without any smoke. It had a bit of smoke on initial start up, but I'm attributing that to assembly lube burning off and the rings not seated yet. I've been varying the rpms constantly as I drive around, pissing more than a few people off on the hwy, lol. So far I think I've gotten my car up to 10 psi, from what my log shows