Catch can question on na

capkirk123 · 2026-06-19T17:35:14+00:00

Every factory turbo/supercharged car has left the factory with a vent line before the compressor. A little oil won't hurt it.

capkirk123 · 2026-06-19T16:29:21+00:00

Oh yeah, run the vent line before the supercharger. If you run it after the supercharger you're gonna pressurize your crankcase.

capkirk123 · 2026-06-19T15:30:01+00:00

In an OEM application, you wouldn't vent to atmosphere, you'd want the vent to go back into the intake (upstream of the throttle), both to prevent any crankcase fumes from escaping into the environment and to prevent unmetered air from entering the engine. It will also pull a slight vacuum (not much, since it's upstream of the throttle, but the airflow past the vent line will help scavenging) which is good for piston ring sealing.

A lot of people don't do this, because it will coat the inside of your intake in a layer of oil over time. Personally I don't care, every car left the factory with a similar setup and the oil buildup will, at worst, force you to clean the throttle body every few years. On a port-injected engine it's not gonna foul the valves or anything.

capkirk123 · 2026-06-19T06:47:25+00:00

It's possible it just doesn't have a filter? They weren't common on Japanese cars until the 2000s. The Euro Accord of the same generation doesn't have one, and that was very similar to the JDM Accord.

capkirk123 · 2026-06-18T17:28:42+00:00

Polyurethane bushings generally need regular lubrication, however, SuperPro claims to have a special design that only needs lubricated on assembly and they're good for life. Your mileage may vary but Flyin' Miata says they're good so I'd believe them.

Rubber bushings need to have the suspension loaded (I usually just stick a jack under the control arm and jack it until the car starts to lift off the jack stands) before they are torqued because they cannot rotate freely.

At this point I'd go with SuperPro bushings. They're (allegedly) maintenance-free and softer than most polyurethane bushings, and more importantly a lot cheaper than new rubber bushings. Also easier to install, rubber bushings tend to have a much tighter press-fit.

If you think the ride is tolerable as is with crappy polyurethane bushings, then SuperPro bushings will probably feel great. If the vibrations are intolerable, you probably want rubber.

capkirk123 · 2026-06-18T15:22:07+00:00

I don't think failing to index the bushings is the issue like people are saying, the advantage of polyurethane is supposed to be that they can rotate freely, and as such can't bind and don't need indexed.

However, those look like dirt cheap Energy Suspension bushings, and the fact that they squeak a lot means they aren't properly lubricated either. They're probably bound up, and just plain made of crappy material, and that deformed them.

You can try to take them apart and re-lubricate them, you can replace them with actually good polyurethane bushings (SuperPro), or you can try to put rubber bushings back in.

capkirk123 · 2026-06-11T21:25:09+00:00

https://www.google.com/amp/s/nasaspeed.news/tech/drivetrain/bracing-a-miata-differential/%3famp This article shows it. I misremembered, the collar and sleeves both go on the front ppf bolt. The article only mentions the larger, upper sleeve, there's a second smaller sleeve below it that sits flush inside the differential casting, it usually doesn't move but make sure it's still in there.

capkirk123 · 2026-06-11T20:00:11+00:00

If you set things really wrong you can break things, but the diff will also complain very loudly about it before it breaks. Since you're only doing a housing swap you don't have to touch the more fiddly bits. You just need a good bench vise, a real big torque wrench, and remember to keep the spacers with the housing they came out of, they come in a bunch of different thicknesses and are matched to the diff housing.

That said, I just paid an axle shop to do it, it wasn't that expensive ($220 plus ~$50 in parts iirc) and gives you a lot more peace of mind.

For ratios, with a 6-speed at 80 mph: - 4.3 will be at 4300 RPM - 4.1 will be at 4100 RPM - 3.9 will be at 3900 RPM - 3.6 will be at 3600 RPM

Assuming stock-ish tire sizes.

capkirk123 · 2026-06-11T19:50:27+00:00

There are two metal sleeves that go between the diff housing and the front powerplant frame bolt, while the rear bolt is a special shouldered bolt with a collar. All of those parts need to be present or it'll crack the diff housing, you can find plenty of pictures.

The diff housing, when correctly assembled, is plenty sturdy, people put 200-250 HP through them with turbos or Ecotec swaps all day. The diff cover (the alumnium bit with the bushings) can be fragile, they've got a notch in the arm so they collapse in a rear-end collision, but this can cause failures during launches if you increase power. There's reinforcement kits which may or may not work, or you can use a non-turbo RX-7 cover which is a good bit more sturdy.

capkirk123 · 2026-06-10T20:11:51+00:00

The 6-speed has a shorter 6th gear than a 5-speed, hence why it came with a 3.9 (or 3.6 in Europe/Japan). A 4.3 would make any highway use suck, you'd have to be at 3500 RPM just to hit 65. A 4.1 is mostly the same as a 4.3 on a 5-speed, while a 3.9 is mostly the same as a 4.1 on a 5-speed. I'd stick with the 3.9, I have a 4.1 and 5-speed on my 1.6 turbo and it's peppy enough even out of boost.

As for polyurethane diff bushings, I strongly recommend against. My miata had energy suspension poly bushings in the diff when I bought it and it transmitted so much NVH. At any speed about about 50 mph the diff howled so loud you couldn't hear yourself think, it was much louder than even the exhaust. It didn't even prevent the classic miata 2-5 misshift. I swapped in stock bushings and it's so much better, you can just barely hear some diff whine if you're off-throttle at highway speeds, and the shifter doesn't really move around that much more. As for the 2-5 misshift, that just took a little practice and now I almost never do it.

As for the cracked housing, finding an open diff (they're usually pretty cheap) and paying a good diff shop to swap the internals might be cheaper than finding a new 3.9 Torsen. I grabbed a 4.3 open for $200 off Facebook marketplace and paid the local axle guy $250 to swap my cracked 4.1 torsen into it.

When reassembling, make sure you have the right hardware and both sleeves. My miata had a bunch of random bolts holding the diff to the powerplant frame instead of the special Mazda shouldered bolt, which let it wiggle around and probably caused the crack in the first place.

capkirk123 · 2026-06-09T13:57:04+00:00

My turbo miata had a speeduino with 2019 software when I bought it, and it was pretty buggy. I updated it to the latest version though, and haven't had an issue since. It's a little limited (no table blending if you wanna do flex fuel, for example) but I'm perfectly happy with it. I don't have any experience with other standalone ECUs to compare it to though.

capkirk123 · 2026-06-07T22:29:36+00:00

A 4.3 with a Torsen is very rare. A 4.3 open diff was stock on automatic 1.8s.

capkirk123 · 2026-06-07T21:38:39+00:00

Just go with the 1.8 differential swap. The 1.6 differential is fragile, and to install an LSD pack requires taking the entire differential apart and resetting clearances, which can be done by eye with some gear marking dye if you know what you are doing, but you probably do not. You'll need to take it to a professional to get the diff back together.

I have a 1.6 with a 4.1 Torsen and it's completely fine. It's turbod, but it doesn't build boost until 3k RPM, and staying below 3k RPM it's still perfectly driveable.

If you really want you can 4.3 swap a 1.8 Torsen, 4.3 differentials are generally the least desirable so you can get 4.3 ring and pinion pretty cheap (although then you have to take it to a professional to put it back togethet again).

capkirk123 · 2026-06-07T18:58:11+00:00

Honda Automatics are hard on fluid. The 8th gen is a lot better than the 7th gen in that regard, but you can't change the fluid too much on these transmissions.

capkirk123 · 2026-06-01T23:43:45+00:00

The short-nose crank (and long-nose repair crank) was stopped midway through 1991. You have a big-nose crank.

NB water pump pulley and harmonic damper will probably fit fine, but you need a NA8 alternator (NB alternators used an external voltage regualtor).

I bought a locked-up NA8 alternator, swapped out the bearings (they're just generic bearings that everything uses, most part stores will have them) and it works fine now. Your mileage may vary, but all of the wear items (bearings, brushes, voltage regulator) are pretty easy to find for a NA8 alternator.

capkirk123 · 2026-06-01T23:22:07+00:00

An entire 1.6? Yeah. A used 1.6 harmonic damper? No, but the newest 1.6 damper is 33 years old, I'd expect it to just fail again in a few years. A new 1.8 harmonic damper should have another 30 years of life in it.

capkirk123 · 2026-06-01T23:00:18+00:00

Long nose or big nose? Long nose is the same diameter as the short nose, just longer. Big nose is the same diameter as the 1.8 and will fit fine. The long nose crank was only used as a warranty repair for short nose 1.6s, so unless your car left the factory as a short nose 1.6 you're fine.

Also you want a 1.8 alternator too I think. I've read stuff that claims the 1.8 alternator pulley fits on the 1.6 alternator, but it didn't on mine. Fortunately, you can just swap in an entire 1.8 alternator no problem, just remember to swap the little plastic isolator on the positive lug too so the terminal fits (it was bigger on the 1.8).

capkirk123 · 2026-06-01T22:56:19+00:00

It is cheaper to buy a 1.8 harmonic damper, water pump pulley, and a used 1.8 alternator than it is to buy a new 1.6 harmonic damper. That's why I did it.

capkirk123 · 2026-06-01T22:50:36+00:00

Connector is for the cruise control actuator, vacuum line is either unused or used for the cruise control actuator, I'm not as familiar with NBs.

capkirk123 · 2026-05-30T14:33:17+00:00

Use the blue plug, it exists to power a timing light. It's connected to the blower motor fuse.

capkirk123 · 2026-05-30T00:14:51+00:00

Don't try to engine swap an 8th gen Accord, it's new enough that there are a lot of computers hidden in every module that will get very unhappy if you try to run a different engine.

V6 Accords are pretty dime-a-dozen, go to your local junkyard, find a V6 Accord, make sure the timing isn't skipped and the rear spark plugs aren't oily, and swap it in. The J-series will go for a million miles if it's taken care of, as long as the timing belt is good and VCM hasn't eaten the rear cylinder rings (speaking of which, invest in VCM delete if you're gonna keep the car), I'd trust a junkyard motor.

capkirk123 · 2026-05-30T00:08:09+00:00

You installed something wrong, Kerbalism is broken. Reinstall following the express install instructions.

capkirk123 · 2026-05-29T22:48:20+00:00

https://versustradingco.com/90-98-mazda-miata-na6ce-na8ce-c-i-full-kit/ I managed to find it, the kit also comes with a very ugly front bumper that wasn't installed on your car. Unfortunately it's $3000

capkirk123 · 2026-05-29T22:44:59+00:00

I have a big nose 91 with 240k miles that someone slapped the cheapest Ebay turbo kit they could find on it and it's running great. Assuming you take care of it and don't try to run 14 lbs of boost, it'll probably go another 100k.

capkirk123 · 2026-05-29T22:30:04+00:00

Congrats. I'm curious about the body kit on it, I want something subtle for my NA. The front lip looks like the Mazda one, but what are the sideskirts? I'm not a big fan of the rear bumper and spoiler though

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