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Discussion Starter · #1 ·
Our (plastic) intake manifolds have a bit of a grid on the inside just after the throttle body, in the plenum before the intake runners. Anyone have any idea if it's a restriction? My oppinion is that it's either just there as a result of the moulding process, or for structural support under high vacuum. Oppinions? It HAS to be a restriction at high RPM. But these motors were designed for low end torque, every design feature about them indicates this.

When experimenting with cold air intake designs (ABS pipe, easy and cheap to play around with), when using a large diameter (3" ID) pipe, i lost pretty much all low end grunt. To the point where airflow seems to stall until about 2500RPM, it's less pronounced in the lower gears obviously, but if you're in 5th lets say, and you mash it, it will bog a little before the revs climb. Top end power and response improved greatly. My oppinion is that the stock intake system is good, it already gets ambient air from the gap between the hood and core support. It also has resonance chambers to pack in air at low RPM.

It would be nice to see how Dynatek made high RPM gains but kept all the stock low end. From pictures it looks like their intake has a larger plenum/chamber/tank feeding the runners.
 

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Discussion Starter · #3 ·
That's what i'm thinking. Tomorrow i'll pull the intake off. Good time to see how the plugs look as well.
 

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Sucks its plastic... Aluminum manifolds you can cut open, smooth out the inside and weld back together. People do it all the time as cheaper alternative to custom made manifolds.
 

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Discussion Starter · #5 · (Edited)
Well i removed the grid, it bolts up just fine without it, there's a rubber ring that seals the throttle body. I think the grid is only there to cover the EVAP purge port to mix those fuel vapors better when it purges so #1 cylinder doesn't get a rich spike. I also smoothed out the runners and removed what moulding flaws i could.

Definite small gain. More power across entire range. Pulled harder, climbed inclines with less bogging.

Unfortunately, the runners become squished where they bend to mate with the head ports, i think this is just to clear the fuel rail or block, but could be there to increase velocity. Seeing as these were designed for more low RPM torque than usual 4 cylinders. The runners are actually quite long. Cheap gain and a half hour job... I noticed a deffinite gain.

Quick tip for people removing the intake for something, don't unplug the throttle body, just let it hang aside. It's completely unecessary to remove the intake. Nissan wants you to remove it but there is no reason to. Also you will need an idle air relearn from a scan tool if you unplug it, at least i did. I had surging that wouldn't go away, it won't adapt itself if it's been unplugged.
 

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Discussion Starter · #7 · (Edited)
I can't take pics because my iPod has a fucked up screen that won't register touch anymore.

It was pretty simple. The grid was actually not part of the manifold, i had thought it was based on when i had to pull it last, but that was a while ago. It is just a simple insert that is clocked to go in one way, it helps hold the throttle body sealing ring in position when you install the throttle body. But in fact it reduces the diameter and is a choke point strictly speaking, plus that little grid might possibily starve cylinder #1, or cause excessive turbulence like you said.

Then what i did was feel for the moulding lines in the runners, a couple runners had significant raised lips where the curve meets the straight part of the runner. Sandpaper will work but takes a long time, X-Acto knife with a chisel style blade worked to get the bulk of it. Not much to do at the top by the plenum, if you look inside, all runners have nice bell mouths on them already. All you can really do is sand the runners making them smooth as much as you can, and take out that grid. I think most of the gain is attributed to the grid.

Port matching could be done, but this intake fits really well as it is, and port matching involves taking the head off. I may do that when i get more into this. I do know that whenever airflow meets an edge/lip that runs perpendicular to airflow, it does affect it measurably. And like i said, i think the portion of the runners where they are squished, either intentionally, or to clear the fuel rail/block, is a constriction, but i can't fix that.
 

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Decided to pull the manifold today and try this out.

Here is the grid behind the TB, you can take it out without removing the whole intake. I did notice it would be better to cut out the grid and sand the ring smooth because it does leave a lip when you take it out.





Inside the manifold



The mold lines are just inside the runners, I smoothed them out pretty quick with my dremel.



Cleaned out a good amount of junk from the head too.. nothing excessive but I've only had my catch can on for 10k of my 65k miles.



As for the results I do feel a slight gain.

It feels smoother between shifts and less boggy when you mash the gas at low rpm.

Pulled nicely from 2k to 6k :D

Oh and thanks for the tip on the TB, had no issues keeping it plugged.
 

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Discussion Starter · #9 ·
Sweet, that's exactly what i did. Thanks for posting pics. I may go back in there and smooth the transition from throttle body to intake. Be curious to know if these motors also starve for air at high end from the throttle body, it's pretty small. Who knows.
 

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I can't think of any reason for this being in there. I'm sure it was designed that way with a reason in mind. I wonder if the 1.6 engines also have this behind the throttle body.
 

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Honestly the only reason I can think of is what 07vesa said about the EVAP port.

You can see the port is right behind the grid in the first pic. The grid is also tapered so that it increases air velocity right before the port. I think its purpose is to push the EVAP gases back and share it with the other cylinders.

But I feel like that would only be needed at idle, higher rpms would have enough air velocity and the grid just becomes a choke point.

I'm curious to know when our port actually purges.. but lets say it does at idle, then maybe C1 now ends up with excess fuel vapors causing a slight rich condition.. Consequence being a little more emissions? Some unburnt fuel?

:shrug:
 

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Discussion Starter · #13 · (Edited)
That's my theory. It's PWM controlled (pulse width modulation) based on load, RPM, MAF signals. Could be another intake resonance thing to boost low end torque, they really tried to make these engines torquey. Long ass skinny runners, all the resonance boxes. I lost pretty much all my low end with a cold air intake, i'm going to try keeping diameter the same soon, and see how it shifts the power band. I'm sure if i could calibrate the MAF to the larger diameter piping it would be different, but right now i'm having to use a reducer for proper MAF signal, so it defeats the purpose of using larger diameter piping.

I bet the scale of returns goes way up with increased displacement, this has got to be even more of a restriction at high RPM on an MR20. Even though it flows fine, calculate the area that thing frees up when removed. Although this grid probably only truly starves the motor at high RPM, and the runners are probably the next bottleneck, i've noticed a difference. Bit more response and power. The diameter of the narrowest part of the plenum/whatever you want to call it that feeds the runners in actuality flows just enough or quite a bit more than this motor needs. Still a cheap easy thing to do, i thought it was worth it.

You know, i wonder if you were to do ITB's on this, whether you could use the stock actuator itself to work the linkage for all of them. Probably could.
 

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I tried a cold air too and lost a lot of torque. A short ram seems to work a lot better on these engines.

But I agree the runners are prob the next choke point. ITB's would be awesome but very hard to make it work, especially with our lack of engine management.

ITB's, built internals, bigger cams, high compression, and 9k revs on E85 :reddevil:

Now where did I put my disposable income..
 

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Discussion Starter · #15 · (Edited)
I think an MR20 swap with a 2.5" exhaust is probably the best bang for buck with these cars at this stage. Few years will probably elevate these to more like Civics or Fit's, Versa's are really in a grey area right now. I have a high mileage 07, so i can afford to do whatever the hell i want without worrying about reversability or depreciation, but most others here can't.

Oh and as far as cams go, Ben from JWT (Jim Wolf Technology, a Nissan specialist) emailed me back and basically i took from what he said that it's the same old problem, too much talk not enough commitment from people. Not enough interest, it's the same thing that's happened with every other custom project, like that Dynatek manifold.
 

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Yeah I feel its gonna be a long time before the aftermarket takes off..

I've got the same mentality on my 09 tho. Paid for it in full when I bought it and have no plans on selling it. I'd love to throw in an mr20 but the 18 is still going strong.. I'm not particularly nice to it either lol.

Thought about doing a custom turbo/supercharger or even an electric supercharger but I keep telling myself "That's about 5 more grand I could put towards my next car (Subaru STi)" Which undoubtedly will be much more fun and mod friendly. I'll always keep the V around tho, as long as I can keep it alive. :driving:
 

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Discussion Starter · #17 ·
I plan to go with a rear mount turbo soon. I could do it for a $1000, i have a turbo just sitting around that needed rebuilt.
 

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Oh and as far as cams go, Ben from JWT (Jim Wolf Technology, a Nissan specialist) emailed me back and basically i took from what he said that it's the same old problem, too much talk not enough commitment from people. Not enough interest, it's the same thing that's happened with every other custom project, like that Dynatek manifold.
I would be interested in some cams, I got JWT S4 cams in my B14 SE-R, they are great cams, highest lift and duration without needing springs and retainers & they cost $595, you can get used for around $300-400.

But then, you got your typical cheap Nissan owners! If it cost more than $20 and takes more than 20 minutes to install, they think it isnt worth doing. They wanna build a street car for less than $100.
 

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Discussion Starter · #19 · (Edited)
I was wondering if the cams are similar enough between the MR an SR motors that they could swap, but if they were JWT would probably advertise that they work in MR motors too. I'm wondering how conservative MR cams are, probably alot.

I think honestly they'd need probably 100 truly willing buyers before they consider it. On Rennlist, the Porsche forum i'm always on, i asked a guy there that developed tri-flow cams for the 928, and he said development was about $60 000... Mind you that was for a brand new cast cam custom machined to profile, it wasn't a good OEM core with a regrind. So the costs of casting them and grinding them, plus research into what works.
 
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