Fixed that for you. :)

Putting in 9:1 NA pistons is going to involve machining the block for them. At that point you're $450 away from having Supertechs in there, which is cheap insurance IMHO.

--Ian

Been driving around with the 3.9 and 5 speed and I have to say that it's an awesome setup. Going 65 at 3k in fifth is really really nice.

As a pleasant surprise, swapping to the goodwin rear diff bushings seems to have fixed my transmission issue of having it try to shoot out of first. I guess the synchro is a bit worn because I tried to downshift into first, but with less moving around it appears to be totally happy. Score!


Hah! I guess I'll find out about that when I get a ride along!

Re: Pistons.
Why would things need to be re-machined when all the pistons are the same outside of the compression? I remember a thread where a few folks had said that you could just drop them in with new rings. I can dig it up when I get a chance.
Found it!
https://www.miataturbo.net/engine-pe...-thread-89553/

From what I've been told (I'm not an expert on this), you can put the *same* pistons back in with new rings, but if you're going to put different pistons in then you're supposed to rebore it. So rods-only with the pistons you have now is fine (which are, what, 9.5:1?) but dropping in 9:1 NA8 pistons is different.

--Ian

You're spending a lot of money and time building an engine to skimp on the pistons. All of this ancillary stuff like wheels and intake manifolds can be bought and sold and bolted on easily later. Build a solid foundation and build it once. Take advantage of the 8.4 or 8.6 pistons offering you the opportunity to use better ignition timing for power. With pump gas we are detonation limited and timing makes power.

As we've discussed in our pm's the forged pistons are more forgiving in the presence of detonation if you happened to get a lower quality fuel or if you have a tuning issue when initially setting up the car. It also helps if you're suddenly running more power on a particularly cold day. With the power levels you are discussing there will be very little room for error.

I have never reused a set of pistons. But then again I'm not an Okie trying to get my family to California during the Dust Bowl in a 40 horsepower Model A Ford. I understand why some people do it. I also understand that they have the ability to pull an engine and redo things at their leisure. I don't see you as being one who has an interest in tearing down engines replacing components or blocks regularly.

As stated, you don't just pull a set of rods out through the bottom. The rods and pistons come out through the top so the head's got to come off anyway.

I'm really puzzled by your resistance to spend a very small amount of money in the big picture for much added power and reliability when your are willing to spend the money in other directions that are not as critical.

Nothing happens in a vacuum. What happens when you crack a piston at 300 horsepower and 7,000 RPM? You often lose the block or the head or both and the turbine eats all the metal. Sometimes people get lucky and iron piston rings crack but don't come loose and just score up the block a little bit. Maybe you'll be lucky and it won't cost you a turbo and a head and maybe a block. You mentioned Pdexta so I should probably point out that I own a spare GTX ball bearing turbo that I purchased from him with significant turbine wheel damage. He is unsure when the damage occurred as he's been through several motors. Maybe you will be lucky.

Just wanted to share this glorious sound:

AFR's are a bit lean. I think it's due to the cold and the wastegate leak fix. I added fuel to the VE table after seeing the video. I think the boost oscillation has something to do with it as well. Don't freak out at the end. It's not actually seeing 13's. Forrest let his foot off. He's driving!

And yes, I'm embarrassed to show the values, but the sound was too good not to share.

Thanks forrest95m for driving! I figured it was fair since you let me drive your car like... last year!

I just want to give Todd @thirdgen kudos for putting this ish together.

https://www.miataturbo.net/diy-turbo...2/#post1103691

I doubt OE's are boring to exactly match piston dimensions. They're likely boring every hole to the same diameter and the piston diameter tolerance is held tight enough that it won't matter.

If the concern is that the pistons are wearing to the bore then you have bigger problems.

I looked over the 2 sets of NA8 stock pistons that I have and I'm honestly not all that happy with their condition. A friend has a set of NA8 pistons in good condition for 60 bucks that I might take a look at, but it looks like I might just end up buying forged because I don't want to fuck around with looking for used pistons and I'd rather not trust DNJ for non-stock power.

Realistically, I don't think that I'd really want to go over 300, but it is what it is. Like sixshooter stated correctly, I'm not someone that likes to constantly putz with this stuff, especially not motor stuff. I'd rather do it and move on with life and this seems like the best way to do it. I think I can afford to put another 1000 into the miata budget for the next year's worth of things and it should cover the pistons, machine work, and some odds and ends. Hopefully my torsen and a few other things sell soon.

i say do whatever provides you with the most piece of mind...you don’t want to pour money into your build and be worried about the components inside after you’re done

This is the only condition of stock low comp piston I would run. I reworked it by hand when I was bored and my wife was traveling. All the ring lands and bearing surfaces look decent. The scuffing on the skirt is not ideal but I will be fine. All the early pistons have jagged edges where the valve reliefs are cut from the crappy castings. Almost all the images I have seen of broken stock pistons, we're along the casting lines near the jagged edges of the valve reliefs, obviously not counting for ones with holes in the middle.
https://cimg2.ibsrv.net/gimg/www.mia...097485a560.jpg
https://cimg6.ibsrv.net/gimg/www.mia...36665a2b6e.jpg
https://cimg7.ibsrv.net/gimg/www.mia...d0f3997dcf.jpg
I don't think you actually want to put in the time for something like this, amirite?:eek5:

Yeah, mine look nothing like that haha. The ones I have for stockers look like this and there's no way I'm running them. I'm guessing your post wasn't an offer now, was it? :rofl:

Putting the pics in a spoilerrr:
I am slightly risk averse which is why I'm still at 200tq on my stock block. I know I can push it, but why go higher. That said, on a rods build, I'd be reticent to go over like 270-280 wheel torque. Can always get a bit more power by adding boost in the higher revs without causing the same amount of stress.

I honestly can't see myself going over 325 with this, probably closer to 300. I'm planning on holding onto my stock block so I guess I'll have a spare till I'm sure things work, forged or otherwise. Regardless, going higher than that would make me very anxious on stock pistons. And my injectors and pump would both need to be replaced past that (Mustang injectors with FF adapters and have a DW200 waiting to go in.)

That said, my turbo isn't getting swapped out for a bit anyway. And I really do love how I originally planned to do a rods only build so I could safely go to the limits of the 2560 without worrying about the rods in the stock block.
The peer pressure in this place tho! Y'all love spreading the boost gospel!

Are you coming to MATG next year? Any track days planned?

Thanks Sean. You dah real MVP.

MATG is soooo far away, not sure I'll be able to get away for that long during residency application time.
No track days planned. I want to do honey bunches of autocross to start. I think I'll need a lot more work to get the car to a point where it will survive a 15-20 min session on track. I'm hoping to do some of that over the winter and my next few rotations. I should actually have some time over the next few months.

Task list for the winter:
1) Figure out motor/build plans/goals... try not to live up to the new thread title. Again, thanks Sean lol.
-If goal is to stay with current setup and turbo (2560 equivalent), then do a rods only build because that's more than adequate. If plans are to ever upgrade turbo, then suck it up and go pistons.
-Install volvo springs on my NB1 head. Tempted to go to a VVT head, but don't want to lose money in the swap. Can possibly keep an eye out for a trade, but I honestly like the simplicity of the NB1 head unless something fun appears for the NB2...
2) NB2 headlight and front bumper swap.
-I really want better headlights. Need a bumper still. Might have scored a deal on headlights, but still working out details and fighting with the fuckers at UPS that broke all my shit.
3) Install undertray and work on some ducting.
-I'm an idiot and didn't run an undertray. Almost overheated a few times because of it. Need to work on undertray, ducting, and sealing air.
4) Opposite to 'sealing' things. Install hood vents.
-Won a set of R theory vents. I'm pretty stoked about this. Rajan has been fantastic to deal with and I'm honestly going to support his business in the future if they have other things that I'm interested in.
5) Install oil cooler.
-Bought an oil cooler from Sixshooter. I need to figure out if I should install it or not. With the R-theory vents, I should be able to set things up so it actually sees some air moving through it under the hood.
6) Install coolant reroute
-You should have done this with the turbo, you newb.

Timeline between tomorrow afternoon when I walk out of my final and march/april. Rotations next year should be more manageable.
Also in there: Help bytevenom and chris moarbewst whatever his name is with their respective miata things.

Oh, and that entire get things prepped to apply for residency in the fall thing.

Shoulda changed the title to, "retard the coated pistons"

Why's that?
You realize that ship sailed forever ago right?

Because you were asking about the coating on the pistons in another thread.. Guess you missed that ship as well.

Did you just assume his piston's gender(s)?

Fake news homie.
I sold the calico coated Pistons I had a while ago.

way too much hypothetical theory pondering bullcrap waste of time and not even 1% of real life application in here.

I'll check back in a year or two. maybe you'll actually do something then :giggle:

Don't hold your breath. In two years, I'll be in residency... bigger fish to fry.