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First time doing a compression test so I definitely may have done this wrong. I performed the test while the car was cold and I didn't run the test at WOT either. I'm now reading that would be the correct way to run the test. Results are in order of cylinders from front of the car to back.
Seems kind of all over the place. I'll try re running the test warm at WOT. Should I be concerned about these results?
It's been a long while since I've run a compression test and honestly I can't recall if I did it at WOT or not. Ultimately looks like the results aren't great but not horrible.. you could also rerun the results with a warm engine (unless this was warm) and see if the results improve. Ultimately not something to probably worry too much about if the car feels fine. Other things to keep in mind have you done a valve adjustment in a while? Definitely something to do if some are out of spec that will affect a compression test. If you really cared you could run a leakdown test as well but not sure if it's worth it to you.
Nice build thread. This probably isn't a bad idea for me to do as well as a baseline for my 120k mile engine. The list of stuff keeps growing.
Ultimately looks like the results aren't great but not horrible.. you could also rerun the results with a warm engine (unless this was warm) and see if the results improve. Ultimately not something to probably worry too much about if the car feels fine. Other things to keep in mind have you done a valve adjustment in a while? Definitely something to do if some are out of spec that will affect a compression test.
Nice build thread. This probably isn't a bad idea for me to do as well as a baseline for my 120k mile engine. The list of stuff keeps growing.
Hmm. Not familiar with valve adjustments. I should look into that. Thanks for the suggestion. I ran the test warm and at WOT. Results below. Car is running fine and the motor sounds good. Mostly just checking to see if I should plan on pulling the motor during the off season if needed.
Thanks!
Originally Posted by emilio700
Not familiar with those. In the B series engine we like the NGK BKREIX
Went with NGK BKR5E-11 (aka 5464) Iridiums. Thanks for the suggestion.
Compression test done while motor was hot and at WOT.
I noticed the tester came out wet after testing the fourth cylinder. Looking at the spark plug from the same cylinder you can see that the threads are wet. I'm not sure what this means. Will have to look into it.
4th cylinder spark plug shown on the right. The threads are wet. Seems to be oil. Couldn't be anything else, right? Didn't smell like fuel.
New plugs gapped to 0.044 per Treasure Coast Miata suggestion.
Out with the old in with the new at 102,105 miles.
You've got something going on in cylinder 4. Plug and compression test shows it. Whatever it is, it might be happening in 2 as well, plug isn't showing it yet though.
Next do a warm leak down test to see if its rings or valves. Intake valves will leak out the throttle body, exhaust out the tail pipe, and rings can be heard/felt through the oil cap.
Just looked through your thread to see if you have a reroute, I noticed you didn't. IMO, hot side superchargers are the reason miata's got the reputation for melting #4 pistons. If you have an aftermarket ECU that's capable of it, you can enable individual cylinder correction, and add a percent or two of fuel to #4 to help it out.
But if you were to ask me, I'd be taking the winter to pull the engine, re-ring it, add a Supermiata reroute, send your ID1050x injectors out for cleaning, or buy them if you don't have them, and pull the supercharger for a turbo.
A few things. The -11 on the end of the plug part number is the gap. They are pre-gapped to 1.1mm, which is .043.
Stock NB1 coils aren't strong and may have trouble jumping that gap at 7,000rpm and 10psi. If, after rebuilding the engine and adding a reroute as Josh suggested, you get an intermittent misfire from spark blowout, don't reduce the gap. Do a Toyota or better yet, Audi R8 COP conversion and open the gap to like .05 or .06. Much better combustion with a fat consistent spark.
You've got something going on in cylinder 4. Plug and compression test shows it. Whatever it is, it might be happening in 2 as well, plug isn't showing it yet though.
Next do a warm leak down test to see if its rings or valves. Intake valves will leak out the throttle body, exhaust out the tail pipe, and rings can be heard/felt through the oil cap.
Just looked through your thread to see if you have a reroute, I noticed you didn't. IMO, hot side superchargers are the reason miata's got the reputation for melting #4 pistons. If you have an aftermarket ECU that's capable of it, you can enable individual cylinder correction, and add a percent or two of fuel to #4 to help it out.
But if you were to ask me, I'd be taking the winter to pull the engine, re-ring it, add a Supermiata reroute, send your ID1050x injectors out for cleaning, or buy them if you don't have them, and pull the supercharger for a turbo.
Leak down tester ordered. I should have some results this weekend. Ironically enough, I do have the SuperMiata reroute sitting in my garage. I was waiting for a convenient time to install it - I guess now works. Stock ECU at the moment but I am shopping for a MS3Pro. Original injectors as well. I'm not entirely against pulling the motor to rebuild it - although it would be my first time. Would you rebuild it to OEM spec? Is there a standard recipe to follow for a reliable motor at ~250WHP? Lots of things to consider I suppose.
I can see a turbo in this cars future at some point but I don't think I'm ready for that. There's so much information to consider for a good reliable turbo build. I don't want to rush into that yet.
Originally Posted by emilio700
A few things. The -11 on the end of the plug part number is the gap. They are pre-gapped to 1.1mm, which is .043.
Stock NB1 coils aren't strong and may have trouble jumping that gap at 7,000rpm and 10psi. If, after rebuilding the engine and adding a reroute as Josh suggested, you get an intermittent misfire from spark blowout, don't reduce the gap. Do a Toyota or better yet, Audi R8 COP conversion and open the gap to like .05 or .06. Much better combustion with a fat consistent spark.
Oh I didn't know that about the numbering. Thanks. Once I get an MS3Pro a COP will follow. At least that is the plan.
I would rebuild to OE spec, yes. more than likely you have an eroded piston you can see on a really good borescope, or the rings just got too hot and lost tension. You typically build for torque, not hp, but whatever you do I'd suggest forged rods, and if you want to go over 280-300ft/lbs, I'd suggest doing forged pistons as well, personally I like Wisecos.
If you want a really good, cost effective, yet capable engine, buy a ball hone. Dump ATF on it, put it in a drill on speed 1, 1/2 to full throttle, and go up and down 12 times, fairly quickly. That'll give you a decent cross hatch for new rings. Buy OE, STD rings, OE STD rod bearings, and OE STD main bearings. One of those bearing sets is expensive, like $125, I think it's the mains, rods are around $60. I've rain the Mahle mains, they're like $25/set on Rockauto. Throw this all together with some forged rods from Eagle, K1, Manley, etc. If you want to be extra careful, take the rods to a reputable machine shop and have them check the big end for roundness.
I would rebuild to OE spec, yes. more than likely you have an eroded piston you can see on a really good borescope, or the rings just got too hot and lost tension. You typically build for torque, not hp, but whatever you do I'd suggest forged rods, and if you want to go over 280-300ft/lbs, I'd suggest doing forged pistons as well, personally I like Wisecos.
If you want a really good, cost effective, yet capable engine, buy a ball hone. Dump ATF on it, put it in a drill on speed 1, 1/2 to full throttle, and go up and down 12 times, fairly quickly. That'll give you a decent cross hatch for new rings. Buy OE, STD rings, OE STD rod bearings, and OE STD main bearings. One of those bearing sets is expensive, like $125, I think it's the mains, rods are around $60. I've rain the Mahle mains, they're like $25/set on Rockauto. Throw this all together with some forged rods from Eagle, K1, Manley, etc. If you want to be extra careful, take the rods to a reputable machine shop and have them check the big end for roundness.
Boom, 300+ capable engine for about $1000.
That's pretty much exactly my motor and it's holding up fine. Even stock head gasket and bolts. I know I'm at the outer limit, but at that time I built the car, that was all I could spent and it's a pure street car
Thanks that's some really good info. Do the 5 speeds survive on track with low 200whp or do they not last?
The transmissions are more sensitive to torque and therefore it’s more a question of how much torque you are putting through it and how much mechanical empathy you have…
Since you are SC’d the overall torque at ~200whp and the torque delivery should be more liveable for a 5-spd.
That said, it’s a bit of a dice roll. I had a 5-spd survive thousands of track miles turbo’d at ~190-200hp (~200wtq in the mid range). I’ve seen other people lose the trans first time out with 150wtq.
If you plan on tracking your car with forced induction, you probably want a spare 5-spd around for the inevitable.
Definitely a spare transmission, 5-speed if replacing gearboxes is one of your more enjoyable pastimes, otherwise 6-speed. If you break it once, take the hint.
Last edited by Gee Emm; 12-05-2023 at 03:25 PM.
Reason: speln
Definitely a spare transmission, 5-speed if replacing gearboxes is one of your more enjoyable pastimes, otherwise 6-speed. If you break it once, take the hint.
Ya for sure, I didn't realize they were made of glass. I guess it's best to just bite the bullet and plan for a 6 speed sooner than later. A good 5 speed is probably worth $300ish + a tow bill home + hassle and I shoulda just bought a 6 speed. Are the 6 speeds bulletproof <300whp?
Thanks for the advice guys. Was able to perform the leak down test today. The results are unfortunate but expected I suppose.
Cylinder 4:
Cylinder 1:
Cylinder 2:
Cylinder 3:
Cylinder 4 was the one with low compression. From my very limited understanding, the pressure drop isn't actually all that bad. About 15%. But it's definitely the rings because all the air was coming out of the oil fill cap.
Spark plug condition after about 60 miles for documentation:
1,2,3,4
4,3,2,1
I guess it's time to plan a rebuild. Is there a good guide out there? Video or written are fine. I found this video from Napp which looks to be detailed enough:
Yep between the air coming out of the oil cap and the condition of that spark plug, either rings are toast or cylinder wall is damaged, or a combination of the two. Good time to rebuild before catastrophic failure.
Also not sure if someone else mentioned it already but oil on the spark plug threads when you remove them but not on the tip is most likely a valve cover gasket leak.
Yep between the air coming out of the oil cap and the condition of that spark plug, either rings are toast or cylinder wall is damaged, or a combination of the two. Good time to rebuild before catastrophic failure.
I'm hoping cylinder walls are okay. I stuck a borescope down there to take a peak. It's not very detailed but I can see the reflection of the piston in the walls so I think that's a good sign.
I started putting together a couple of lists for parts and materials/tools needed for a rebuild. I leaned heavily on 929 Racings article called Planning Your BP Engine Build and Napp Motorsports video called Building a High HP Turbo Miata Engine - Full Build! (linked in post #34). Also the information given here by members like @curly above. Thanks guys.
The goal is to build a track reliable motor that can handle moderate boost from either a supercharger or turbo below 8K RPM (using that benchmark to match 929's guide). Hierarchy of objectives is: reliability, cost effective, best performance. I want to take advantage of “free mods” like porting and polishing that just require time.
Screengrabs of the lists below. Link to the Google Sheet can be found here for easier reference as well. Disclaimer for anyone who might come across these lists in the future. I have ZERO experience building motors. I'm just trying to learn. This is only based on some research in preparation. It's more of a public journal than anything else.
Am I on the right track? Am I missing anything or going overkill on anything? Getting the total for parts down below $2,500 would be really nice but I also don't want to save a penny to lose a dollar. Feedback is appreciated, thanks guys.
Pulled the engine and trans this weekend. First time to do this on any car so I'm happy it went smooth. I would say the most difficult part was removing the two bolts at the top of the bell housing that holds the slave cylinder line and wiring harness.
Before starting
End of first day
End of second day (PPF, driveshaft, and exhaust removed under the car)
Third day
Separated the trans
And just some overall shots for those of you with a keen and experienced eye. If you see anything of concern, please let me know ✌️
I didn't realize I needed to source bolts long enough to mount the engine on the stand and all the stores were closed. So this was as far as I could get. I was anticipating to just use some of the bolts from the bell housing but they're too short... Need to find some M12 x 1.5 x 110mm (or 100mm) along with some washers.
Last edited by HalalBuilt; 12-26-2023 at 10:53 AM.
A 1.5 hour round trip to and from McMaster Carr and I have bolts to mount the engine to the stand. First time going there for an in person pick up. Didn't even know it was an option. That's place is awesome. Anyway...
So the plan is to get down to the bare block, inspect the condition to determine if it needs to go to the machine shop, do some blueprinting (bought a set of feeler gauges and borrowed a set of micrometers, bore gauges, dial indicator, and a straight edge). Once either it's at the machine shop or we (hopefully with the help of you guys) determine no machine work is needed then I'll stop and give my garage a good cleaning/get it organized. Then I'll focus on getting ready for the rebuild.
Some photos of the eternal teardown:
Only a couple things stood out to me as mildly concerning. The intake manifold and ports were absolutely filthy. They had this shiny black crud build up. Is this normal?
And the second point of concern was some wear on the edges of the camshaft lobes. Normal?
Last edited by HalalBuilt; 12-29-2023 at 08:57 PM.
Reason: Speeling is hard
11-29-2023, 09:21 AM
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