veedubbed

After searching for days for a vacuum leak, I thought of another possibility. my engine pulls 12 inHg at idle, but runs completely fine. I am doing a compression test tomorrow to make sure it's not a seal issue (I can almost guarantee it's not, this motor made very strong compression on the pallet). Anyway, on decel, it pulls 25 inHg, which is pretty damn good in my opinion. That's when I thought of another option - maybe my engine is ported a little. I have no idea what the history of this engine is, I bought it off a member here when I blew up the original motor in the car. The engine that I have now has obviously been rebuilt at some point in it's life - it was painted, missing the exhaust sleeves (yeah... someone's a retard), and had "RK Racing" engraved into the middle iron.

Does this sound like a ported motor? Is there any real way to tell? If the compression test shows up good, would it be safe to assume the motor is ported?

Jpk3200

Sounds a little low to be stock, unless you have a vacuum leak. To be 100% sure, you may have to open the engine up and look.

RotaryResurrection

iTrader: (8)

Ported motors, depending on how much porting, usually pull anywhere from 14-10inHG at idle below 1k. Stockers, depending on how tight they are, usually pull 18-14. Raising the idle also artificially raises the vacuum reading.

However, if you build a stock port engine with really worn housings and compression is weak, your vacuum will also be weak. Vacuum is just a reflection of compression. In fact mazda dealers do not usually do compression tests on rx8s to check for engine wear, they do vacuum tests. Vacuum is not as an accurate an indicator, but it gives you an idea where you stand (assuming stock ports). It is also much easier to do than a compression test.

veedubbed

So.... if I do the test, and it shows 100 PSI on both rotors, would it be a safe assumption to say it has had some porting done?

mmmjesse

depends on your idle. Where does your car idle? Like he just said, if you have a raised idle, then youll have less vacuum.

veedubbed

Compression test showed 3 even bounces of 60 PSI on each rotor and 90 PSI when the check valve was left closed. That was with only the leading plugs removed.

My car idles at 750-800 fairly smooth.

Turbo II Rotor

iTrader: (2)

Higher idle, higher vacuum.

RotaryResurrection

iTrader: (8)

With 90psi, the low vacuum could simply be weak sealing/compression.

veedubbed

I kind of thought that too.

Guess I should start thinking about rebuilding or selling before I blow it and tear everything up inside motor like last time.

RotaryResurrection

iTrader: (8)

Well, there's a misconception. 90psi on a rebuild is not the same as 90psi on an old motor. IF you use worn housings in a rebuild, your new seals will have a hard time forming a perfect seal against them, and thus you get low compression. But you still have new seals that arent going to wear out or break for a LONG time (unless you do it by force, aka overboost/ping). Whereas with an old original engine, the low compression is caused by the worn housing AND the worn apex seals, and those worn seals can break at any time.

veedubbed

That makes sense. This engine was extremely clean when I received it, it surely hasn't been ran too very long after it was pulled apart. I will rock it for a while and see what happens.


The only thing that concerns me is that it has a flooding problem. It is really points towards the injectors (stock 550's that have 115,xxx miles, and I get 12 MPG keeping my foot out of it). I should probably try replacing them before making any conclusions.

veedubbed

Also, I am having a problem both when it is running cold and at high-RPM.

When I start it cold, it will enrich itself and idle at 1500 RPM. This is even when I start it in gear, and with all of the cold start B.S. removed except the BAC. When it's doing this, it has a ton of misfires, won't even attempt to idle smooth. It will run at 1200-1500 for a minute, then come down to 1100, where it will run smoothly, and slowly work it's way down to 750 as it warms up. Now, this is all fine and dandy, but it just misfires so bad above 1100 RPM's, there has to be something wrong. It will also misfire really bad anywhere from 1100-2000 RPM's if I hold it there with the throttle, even when fully warmed up.

The car also stalls when I clutch-in at a stop light until it is warmed up a little. If it hasn't been running for more than 10 minutes, I have to keep it running at every stop with the gas peddle.

I searched, and found someone with a similar problem, they said faulty injectors could be causing it. This also leads me to believe my primary injectors have hit the *******.


Now, at high RPM's I am having a similar problem. At 5500 RPM, my shift buzzer goes off. At 5800 RPM, it starts with a small misfire, and if I keep in it 'till 6000, it will misfire like crazy.

That sounds more like an ignition problem to me, but I don't know.

If I can get these problems sorted out, the car will be 100% good to go, but it's been driving me crazy the last month or two trying to figure out what is wrong.

Delicious

Check ur pulsation damper and make sure its not pouring fuel all over ur exhaust.... also sounds like a bad ground

RotaryResurrection

iTrader: (8)

With regard to his last post, what does the pulsation damper have to do with the price of rice in china?

Sure, it's a good idea to check it, but...

Your reply was about equivalent to me making a post about how to set the TPS and you replying about checking your tire pressure.

You could be right about the grounding issue, but then that could be said of most every rx7 on the road today so that's not exactly ground breaking information either.

84stock

iTrader: (5)

If you "really" want to know if it is ported you could pull the intake off and feel inside. If it feels like your girlfriend in high school it is stock and showing some wear due to the vac loss. If it feels like the hooker looking chick you picked up at the bar with a extra little crack (bridge) , then you've got some porting.