Why do the intake manifolds look like this?
 

I was changing the spark plug wires, and decided to take off the UIM to see what they look like after ~4k miles. I ported and (somewhat) polished them when I put my motor back together the last time.

Could just be my stupidity, but why are the 2 inside runners still squeaky clean and the outside 2 look like ass? And it's kinda wet around there. My hands were so dirty I couldn't tell if it's oil or gas. The elbow is clean with no oil residue, so I'm guessing that it's gas on the gasket.

https://www.rx7club.com/attachment.p...postid=2578499

Close up

https://www.rx7club.com/attachment.p...postid=2578517

i have no idea but did you port the engine or the manifold?

One thing to consider is that the main airflow hitting those runners is regulated by the secondary plates in the throttle body. I suggest you head further up the chain and start examining. Find out where it *starts* and/or *ends*.

Just had a discussion about the secondary throttle plates which may be influencing this, as well...

https://www.rx7club.com/showthread.p...hreadid=262918

Steve Kan ported the engine. I ported the upper and lower manifolds.

I'll check that out tomorrow clayne, right now it's bed time.

There's no way that could be gas. Could be oil tho, might be time to rebuild the twins.

They're brand new BNR stage 2's. I put them in less than 3 months and 5k miles ago.

Replacements for the crappy stage 3's.

But if it was oil, wouldn't the intake, IC piping, and elbow be coated as well?

Been awhile since I've looked at it but the crank vent breather from oil filler neck comes into the manifold not long before that. I'd have to guess based on your picture that it enters the runners that split to the outside edges but unfortunately I think it actually feeds into the lower runner which is the two middle ones. It's almost like your lower runner is blocked or something and nothing is getting through the two inner runners. That's really strange though, way too clean compared to the outside runners. I don't remember seeing that. Does the car run reasonably well? As much power as you'd expect?

Kevin T. Wyum

I had some issues with fuel for the past couple weeks. Took off the relay going to my pump.

It starts, but it's like its flooding every time I shut the car off. I can't start it normally, I have to floor it, then start. It coughs a bit at first, then runs ok.

On WOT, I get power, although maybe not as much as I'd expect. However during cruising and very slow deceleration it kinda pops and is rough. Not really a surging, but it doesn't feel right. If I give it gas during that time, it hesitates for a split second, kinda jumping forward, then back, then strong. But if I floor it from a gentle acceleration, its perfectly fine.

Perplexing.

The seconday plates/runners are usually open during WOT acceleration or above 3K rpm. So it stands to reason that your turbos are spewing oil into the systems and that would explain only the secondaries beeing dirty, allthough as said the elbow and IC piping would be full of oil resedue as well.....

I didn't check the IC piping on the turbo side yet, but on the elbow and the IC pipe connected to it, there isn't one single drop. I ran my finger in it and it was completely clean.

So the secondary runners are the 2 outside, and the primaries are the inner 2?

On other cars, do the insides stay pretty clean, as in mine, or is there somewhat of a residue on all the runners?

these were my intake runners from a 67K stock motor. Same distribution of gunk (the outside runners), but less overall fouling. I'm voting that it's blowby/PVC action, but what the hell do I know?

If the ic piping is not overly oily than it has to be from the pcv valve.

Yea I was gonna say: Check your PCV, also check the check-valve that is supposed to be present.

Pull your PCV and try to blow through both sides... after wiping it off of course! :D

If it is the PCV, you think that buildup is what's causing the hard starting and partially flooded behavior?

Check things out first, then we'll speculate.

That is totally freaky looking....like NOTHING has ever flowed into the center runners.....
Strange, to say the least.

Just to make sure, the PCV connects to the neck of the oil filler inlet, then on the other side to near the bottom of the uim?

I can blow through fairly easily one way, but it doesn't seem like a super clear path. The other way sometimes the air was completely blocked, but some times a little air would get through.

Pull intake elbow off and verify all throttle plates are opening.

It's almost as if the key to your primary throttle plate shaft is missing.

My second gen intake always looked like that. Im thinking its the fuel injectors are higher up in the secondary runners so those runners are basically a "wet"intake like a carb. When the rotor closes the port the wet charge bounces back up the runner leaving residue. Its also possible all your injectors are leaking and since the outside runners dont get airflow all the time the excess fuel pools. If im totally off my rocker just ignore this/call me stupid-whatever.

hey cavell, you can bypass the pcv by using an oil catch can....just look @ my car next time you are @ gotham.....the red one that has been there forever....it is really simple and will get rid of the gas smell in your oil as well...

the secondaries have a ping pong effect, where when one rotor ends its intake stroke the incoming air will bounce off of the closed port and bounce back and around to the other rotor and be just in time to go into the motor. we actually see positive manifold pressure on out na because of this.

the reason its nasty is because the secondary injecotors are not on all the time, fuel is an excellent cleaner. if the secondary injectors were on all the time, the runners would be clean