Steve Dallas

Sure. We have Miata specialty shops in the Dallas area that can rebuild my block and/or head for just a few hundred more than it would cost me to do it, or sell me a rebuilt block for around the same price as Treasure Coast, so those are also options.

Back to the value in a JDM engine, assuming it is a good one. For less than $1500 you get:

1. Flat top IM, worth $400
2. High compression block with forged rods
3. Additional VVT head worth ~$400
4. All the dressing bits
5. A deal on a 6 speed trans on the cheap

That seams like a good deal to me, again assuming the engine is good.

Reading your build thread now. Good stuff.

concealer404

iTrader: (3)

The rods aren't any different, and the 10.5:1 pistons seem to be pretty hit or miss.

That said.... cheap 6spd, flat top, and more vvt is nice.

turbofan

iTrader: (1)

I also don't know about cheap. But if you're getting a JDM VVT engine and 6-speed trans for $1500 you're doing damn good.

Steve Dallas

Parade. Rained upon. Sadness.

sonofthehill

iTrader: (1)

I was going to say, I have not heard about VVT rods being special. I have a good set that I was planning to use as legs for a little dog sculpture, I let you have for cheap.

concealer404

iTrader: (3)

Nah the dropouts are still good value. Pretty much any Jay DEE M y0 6spd drop out for $1500 is a good buy if the motor is healthy.

Steve Dallas

I thought I read somewhere that VVT rods and pistons are forged. Maybe my member berries are acting up again.

[EDIT: That bastion of perfectly accurate information we call Wikipedia agrees with my member berries, for what that's worth, which probably isn't much:

[/EDIT]

A JDM engine does not necessarily include a transmission for $1500. But, both of the importers I spoke with mentioned they would make a great deal on the transmission, if they don't have to pull it off the engine. "I'll sell you the transmission cheap, if I can just drop the whole thing in the bed of your truck." I don't know what "cheap" or "great deal" looks like yet, and the engines are a few weeks out still.

concealer404

iTrader: (3)

BP4W isn't VVT, though. And wiki is still wrong.

Steve Dallas

Hey, I'm working off several absolutely possibly valid assumptions here! 1. Wikipedia is always totally right. 2. The supposed forged thingies of the great Wiki carried forward into the BP6D.

This is the Internet, where everything and nothing can be true. My personal reality is just as valid as yours, and I like mine better! Wait. I'm not a Millenial. Never mind.

Back to sadness.

dcamp2

iTrader: (4)

The JDM engine sounds like a good buy if it does come with a squaretop and can get you a deal on the transmission. 6 speed is always good for track use- especially when you have 114whp. (sorry haha).


Also someone above said 10:1 compression is good for rotrex. it is not. mine melted.

turbofan

iTrader: (1)

Well, better for Rotrex than turbo AIUI. Several people have had good luck with a stock VVT and <10psi rotrex.

dcamp2

iTrader: (4)

Yeah. If I could do it all over again (with the rotrex) I'd have kept my original pulley setup (8 psi) and gotten another 9.0 CR block from a 94-97 car. That combo made decent power and lasted a long time.

I ran into problems with higher compression, more boost and running long sessions.

codrus

AIUI, all stock Miata cranks and rods are forged, all stock pistons are cast. I think this (rods and crank) is pretty much required for a gas engine with a 7K redline because of the tension loads.

--Ian

concealer404

iTrader: (3)

I'm not sure if the rods are actually forged or not, but they're weak, either way. VVT rods aren't stronger than earlier ones.

I'm honestly not sure why the cranks are forged. I think all the Mazda B-series engines with a 7k+ redline are forged so that's true. Mazda has other motors with cast cranks with higher redlines, though. Maybe they're more inherently balanced or better, though? Interesting thing i never thought about.

sonofthehill

iTrader: (1)

My forged BP4W rod

Chilicharger665

iTrader: (2)

Rods aren't different. No strength advantage.

Steve Dallas

I just finished reading your thread. Much sadness. My parade is officially rained out vis-a-vis the JDM idea, unless I decide to keep it simple and stay N/A, which is looking better and better.

Track day this past Saturday. One turbo Miata lasted half the first session, and it was 35 degrees ambient. Not sure what happened, but it went home on a tow truck. MP62 supercharger ate its needle valves or something in the 2nd session, and owner had to drive home with his SC belt between his legs. Naturally aspirated Miatas never opened their hoods.

The shop that was supposed to give me a 2nd opinion on my engine and have the car back to me by lunch time kept it all day and never looked at it, so I didn't drive Saturday. Not thrilled about that. The weather and track conditions were perfect in the afternoon, and there were a lot of Miatas to play with in the instructor group. I really wanted to drive.

I worked on the tune some Sunday, after seeing some odd AFR readings on the way to and from the track. It was very rich at cruise (~13.5) at 4K RPM and would go lean (~15.5) at 4.5K, when I would speed up to pass. I also noticed the manifold air temp rose steadily, and was always at least 30* above ambient, sometimes as high as 60*. That's not normal, considering I have an NB2 with a cold air duct and an airbox for the K&N. I suspect the sensor is heat soaking, since it is located right behind the radiator, so I need to figure out how to deal with that. Before spending too much time on it, I may put the OE intake back on and do some pulls for Virtual Dyno to see how much I lose. If it isn't much, the K&N might find itself in a very lonely place.

Steve Dallas

Played with the IAT sensor situation a bit last night. If I let the car idle for a while, the MAT will rise to 150*. It takes about 10 miles of highway driving for it to drop to 90*, which is still 20* above ambient. Next test was to heat it up again, pull it out, tape it to the prop rod, and put a fan on it. It took 20 minutes to reach 70* ambient. The OE sensor is closed element and encased in plastic, and is sloooooooow to respond to changes. So, I pulled an open element GM sensor out of the parts box, wired it up, ghetto installed it, and changed the MS calibration to use it. I didn't have time to drive the car with it installed, but I re-ran the fan test. That sensor is about twice as fast as the OE one, but is still surprisingly slow.

What's the point in all of this? If I start driving the car after minimal warm-up and get on the highway, it runs rich for a long time. Like at least 2 hours that I know of. If I allow it to heat soak by sitting in traffic or city driving through lots of stop lights and stop signs, it follows the AFR table closely. If I allow it to idle long enough to heat soak the sensor, idle AFR climbs at least into the 17s. Time to hit the Mega Manual again and see if there is some temperature compensation happening and if it can be controlled. I imagine the car heat soaked on the dyno, and it was tuned hot, therefore the AFR table matches when hot.

Might as well continue learning the MS, while I endlessly debate what to do about the engine...

aidandj

iTrader: (5)

Don't use the mega manual. Its outdated.

Megasquirt Manual Index - Megasquirt EFI

Steve Dallas

By "Mega Manual," I mean the 16MB manual included on the thumb drive that came with my MS, that is specific to its firmware. It's pretty Mega.

Unless I'm missing something, there is no way to adjust the effect of air temperature / density on fuel calculations, except perhaps in MAF mode, without adjusting the Air Density Table itself, which should be normative in my beer addled mind.

What I find curious about this car's behavior is, IAT seems to be having the opposite effect of what I expect to see. Shouldn't I see leaner AFRs at lower IATs and richer AFRs at higher IATs?