DAzani

I can't figure out what the problem is so I'm giving as much detail around when it happened. So I was thinking of selling my 2001 FM turbo miata and went to get my compression test done at a family friend's shop. Compression was low (150/135/140/140) but all relatively close. The tech added automatic transmission fluid do a wet test and got upset when I said that he should be using 10w-30. Compression rose between 250-260 every cylinder. I'm no longer going to list the car, I'm going to have the engine rebuilt at rocky's miatamotive instead. Engine smoked for a while as it burned it off the copious amounts of ATF and I drove home about 35 minutes away. Earlier that day I noticed the thread for the hole used to bolt my heat shield and chassis grounding strap were barely holding on. Shortly after getting home from the shop I left to go see about throwing a helicoil in there and on my way home I was bombing up the massive hill to my house and I let off the throttle halfway up and the car just died... If I go to start it, it almost fires and then falls on its face and keeps turning over

What I've done:
-secured the ground
-checked for spark, it's there
-checked for fuel, I could smell it while I was checking for spark and my wideband read 13.3 after trying to start it. So I'm confident in saying that's good
-replaced the crankshaft sensor 2 weeks ago after I bumped it too close to the timing wheel during an AC reinstall and it got chewed.
-replaced the crankshaft sensor again 2 days later because the first replacement wasn't working correctly
-looked over all the fuses and wires and nothing seems brittle or like its failed/on its way out
-replaced the spark plugs because the others were covered in ATF
-sprayed carb cleaner in a vacuum line to double check fueling

Now I'm at a loss...

I don't think it jumped timing. It just seems really unlikely but that's what I'm checking after work tomorrow. There are no codes popping up on my ultragauge so I have no leads there either.

What else can I do?

bAsEDnancy

What are you using for management?

DAzani

I’m in CA and staying CARB legal so sadly just the stock ecu and voodoo box

DAzani

Somehow the adjustable timing wheel fully advanced timing. After all that work I just needed to check timing at TDC. Why didn’t I do that sooner *aggressive facepalm*

SpartanSV

FWIW incorrect cam timing will lower compression test results.

Unless you had issues that prompted the test I don't see a need for a rebuild.

DAzani

I fixed the timing and still got low compression. My rings are fried from consistently throwing 10 PSI at the stock NB2 higher compression pistons. Rocky at Rocky's miatamotive will be rebuilding it for me in the next few weeks. I've reached out to big name people all over the miata community and none of them have a machine shop that they trust in the LA area, go figure. I would have loved to rebuild myself but sadly I don't have the time or a trusty machine shop for resurfacing, boring and honing.

SpartanSV

Are you rebuilding based solely on the compression test results or do you have an actual issue with how the engine is running.

DAzani

Mostly based on compression results but I do want to run more boost reliably without worrying about anything. I want to run about 12 psi so nothing crazy. I have the money now but definitely won't when I hopefully start med school next year.
I went to test drive some new cars to try and find something as fun with a factory warranty and more practicality but nothing felt as good so I'm investing in my Miata instead. Do you think it's a waste to do it if the cars running fine? I'm just trying to plan long term and make sure I don't have to deal with any surprises down the road.

The chassis and engine only have 41k miles but it was mainly used as a track car until I bought it. It was clearly not babied with those compression numbers.

SpartanSV

IMO compression tests are really only good for identifying a cylinder with a problem. I have 2 testers that show a 50 PSI difference when used back to back on the same engine. Compression test results are also affected by things like elevation. Basically if you don't have extreme variation between cylinders then you probably don't have any major issues. I would absolutely not rebuild your engine based solely on your compression test results.

Saying "I want to run about 12 psi" tells me you should probably do a little more reading before choosing your path. You should never set a goal of a certain pressure because it's mostly meaningless. Set a power goal instead. Then determine if you need to change anything else to meet that goal.

One other piece of advice, don't daily a heavily modified 20 year old vehicle without a back up vehicle. If all you currently have is your miata then I would strongly recommend you use the engine build money on a second vehicle.

DAzani

I see your point and I said 12 psi because it’s relevant to the fact that the factory pistons were higher compression than all previous Miatas. They’re not great for adding boost. I’m also not running a stand alone. I have a voodoo box with adjustable fueling. Whatever i plan to do can’t exceed the ability of the stock injectors. I didn’t list a power number because I don’t know the current horsepower I’m making and therefore have no point of reference. It would be pointless anyways since I don’t have a stand alone to handle upgraded injectors, timing etc. I‘ll make whatever power I’m able to make within my limitations. I’m also not going to throw out an arbitrary target number if I don’t know how the car will drive at that number. I could say 300hp but that’d be dumb. I’ve never been in a 300hp Miata to say yes this is exactly how fast I want my car to be. What I do want is to push more boost through the engine and not worry about destroying my rings entirely and to also have some more longevity at a higher power level. I don’t consider a Flyin Miata turbo kit with a piggy back ecu highly modified seeing as how the engine is currently completely stock. I appreciate that everyone has their own opinions though and I’m thankful for your advice.

SpartanSV

That's highly subjective. IMO higher compression is actually better as long as you can reach MBT without detonation on the fuel you are using. I don't think people running under the limitations of stock rods are having issues reaching MBT on NB2 pistons.

That's one of the reasons I said you should do some more reading. If you're using a common setup like the FM2 you can do a quick google search and have a good idea of where you should be power wise. A 2560r which is the turbo used in the FM2 kit is probably around 200hp at 10psi on a NB2. I doubt there's much left at all in the voodoo management setup but I'll never run one so I'll let you do your own research from here.

To basically reiterate what I said above, do some legwork to educate yourself about what your current power level is so you can make an informed decision about how much more you want. You pretty much said you wanted to rebuild the engine so you could run 12 psi of boost. A little research may show that to be completely pointless if you're married to a voodoo box and that setup isn't capable of 12 psi anyway.

If you don't think making nearly double the factory horsepower constitutes highly modified then I'll just say that I totally and completely disagree and wish you luck.

EDIT to remind you that you started this thread because your highly modified car stopped running due to one of the modifications you made to it. LULZ

DAzani

I’ve done leg work believe me. Ive researched myself and spoken with FM and rocky extensively. At 10 psi FM stated about 225 hp, at 12 about 245hp was their estimate, right at the cusp of what they’ve found to be the limit of the stock internals. I’ve done a few pulls at 12 psi for ***** and giggs. I had a little more room for fueling on the voodoo. AFR was within FM’s recommended margins.They, like me, don’t think running that much boost with the stock NB2 pistons is a good idea. They, again like me, also don’t believe my compression should be anywhere near what it is with 41k miles. They are the ones who recommended a rebuild with lower compression pistons and they believe Rocky is a trustworthy person to build it well.

SpartanSV

Then why the hell did you say you had no idea how much power you were making at 10 psi????

The hole point of my original statement about your compression measurement is that you can't know that a 150 psi reading is actually 150 psi. The tester you used could consistently read 30 psi lower than the tester FM uses.

You've clearly made up your mind and I've wasted my time. I'll leave you to it.

DAzani

because they gave me an estimation and I’ve never personally dyno’d my car. They’re at a different elevation too. I don’t want to claim I know something I don’t.
I’ve used multiple testers since the original test. The original test actually gave the highest numbers. The others weren’t too far off though. Sorry you wasted your time. I appreciate you responding. Have a good night man.