With my MEVI I have been trying to think of different ways I could modify it to see if I could gain a little more power out of it.

So i have 3 ideas, they may have been said before so if this is a repost I'm sorry. But I was hoping to get some input. Obviously no one will know for sure but I'm just looking for your thoughts on the ideas.

1. cut open the area where the butterfly plates are and make it one big plate.
2. lower the butterfly plate to be closer to the runners.
3. add a spacer to the chamber area to allow a greater volume of air in.

Now I have no idea if these would help in anyway. I would like to do them to find out for sure but I don't know how much that will cost. But i don't want to spend the money if I would be completely wasting my time and money and come out with no gain whatsoever. So again I'm just looking for your thoughts on the matter.

 

I thought of the spacer idea but Stephen seemed to think it would lower low end TQ IIRC. It should be a good test though if you can get a spacer made.

 

IMO number two is the only thing that would be worthwhile. I think that would actually boost mid-range torque since the airflow would be more laminar.

 

Funny, I've been eyeballing my MEVI lately.. I kinda recall that the MEVI works on a resonance effect when the butterflies open, giving a column of air above each intake port that returns a pulse of manifold air back into the individual port for extra cylinder filling. Messing with the butterfly plates might just destroy the whole extra-pulse timing. I tried a 1/2 inch spacer under the top cover, but I saw no difference at the strip. Of course, this was before I got the Jbars installed to eliminate torque-steer and wheel hop. Hum - maybe time for another test.....

I don't care what happens below 3,000 RPM, and my MEVI is set to switch at 4,800 and the stock ECU just has time to 1-2 shift the automatic before fuel-cut about 6,500, at 6,100 after that. If there is anything really wrong with the MEVI, it could be the long intake runners and restricted log manifold that feeds the runners.

Anything that can actually improve air flow through the log and the long runners will provide even more air pressure to the intake ports when the butterflies open. We know the MEVI works as-is, but what can be done to get more air into the manifold before the butterflies?

 

The main flaw with the MEVI is the space between the runners and the butterfly valves. The runner length has nothing to do with it's short-comings, since the 00VI has longer runners yet outperforms it.

 

Is this correct? ( and skipping the 00VI subject for now)

With the butterflies closed, nothing happens in the column down to the intake port. When the butterflies open, there is a resonance-effect is each column that pushes extra air into the intake at higher RPMs.

Are you thinking that the butterfly location is affecting air flow through the manifold? Just trying to understand what you're saying...

 

The butterflies aren't flush with the runners. This creates turbulent air and is what causes the mid-range torque loss.

 

The only problem I see with moving the butterfly plates down is that when it opens part of the plate would stick down into the runner and I think that would have a negative effect on the air flow. So inline with moving it down I also think you would have to either move it forward and remount the plates so that they only open up into the direction of the chamber and not into the runners.

 

Stephen is getting me a quote on a spacer as we speak. i pmed him a couple weeks ago on this. I will dyno once i get it installed.

-grey99max any pics of you spacer? how much did it cost you to make it ? If you wanna loan it to my i will dyno it on my car. i have before dynos. Since i haven't done any mods since the dyno i could get a direct comparison.

 

I agree, number two seems like the best idea.

 

After doing some research and getting a little better understanding of how resonance works, I'm going to guess that on your dyno with adding a spacer to the chamber will lower the RPM of where you make your peak power. for example if you made peak power at 5600 RPM, with the spacer it might drop where you make your peak power to 5400 RPM. So we'll wait to see what happens. As for the rest of the powerband I'm not sure what will happen.

 

I had made it from two layers of Kydex ABS plastic 1/4" thick each. I used the top cover to make a paper template, marked both sections and cut with a jigsaw. Clamped and drilled both together, and put between the main body and the top cover.

Of course, I threw the whole thing away after zero measurable results....

 

OK - I see what you mean, because the "resonance-runners" open downwards into the airstream right above each intake port, and they are open upwards to the butterfly. This is what creates turbulence that messes with mid-range torque?

Is this just a theory, or has someone demonstrated that power is better below butterfly-switching if the vertical runners are blocked or filled in???? Have there been other MEVI mods that reshape the power curve at the upper end?

If the vertical runners add power above the butterfly-switch point, I'm still OK with that, since I launch at 3,000 and never drop below ~4,500 after that.... It's the upper-range power I crave.

 

I was thinking more like some sort of modification to the upper part of the mevi, where that cover bolts on, but sold my car and don't need to anymore

 

Keep me updated on the spacer!

I saw this done to a 350Z and they gained 10 hp off it.

 

I'm sure the spacer you are thinking of is a very different kind of spacer than what is being discussed here.

 

+1. A spacer in this context won't add HP, it'll just change the resonance sweet spot (RPM).

 

Now that I understand resonance a little more, with how the MEVI is situated the only mod to it that I stated that would help would be the lowering of the butterflies. Thus regaining some lower end torque.

I think other than turbulent air being created, it messes with the resonance effect because some of the resonance air gets caught up in the open area rather than traveling all the way back to the end of the ports thus making us lose low end torque because the resonance effect isn't fully happening correctly with the butterflies closed. Some of it is being stalled from traveling at the correct distance it is supposed to. So I do think the lowering of the BF's would make the MEVI perform much more like the USIM down low.

the only other thing I could think of would be to bore out the ports of the BF plates to allow more resonant air to flow through while it's open. however I think that might be more of a hassle than it's worth since you'd have to have bigger plates made to match the ports.

 

They unbolted the lid off the variable intake on the Z and laid down a spacer and bolted the lid back on adding more area inside of there. I'm pretty sure thats what Zack was talking about doing here.

 

... ... ...

 

A friend of mine has a MEVI and I've messed around with in the past. So, I kind of know how it's put together.
So, I was thinking about modifying the butterfly plate...
Like it has been said in this thread, the turbulence underneath the closed butterfly plate has to be hurting low end.(picture 1) But if you move the pivot point of the butterfly plate down, it puts the plate in the way of the incoming air when it's open.(picture 2)
But what if you move the pivot point down and forward and have the plate open up, you can have the butterfly plate flush with the intake runner and out of the way when open. (picture 3)
The only problem with moving the pivot point like that it will have to be away from the wall of the runner unless you D-shape the port.
I ignored the fact that turbulence will happen with the plate open regardless.
The pics: (crappy paint pic)


And as far as the plenum spacer goes, if I have my hemholtz resonance stuff right, the larger the spacer - the lower the rpm at which resonance occurs when open.

 

10 frijoles

 

Great friggin graphic. That's exactly what we've been thinking. The 3rd picture seems like the best option yet. And +1 for a n00b with a useful first post.

Yup yup...

 

I'm glad we're all falling upon the same understanding.

So really what we need is someone to shave down the mounting face of the cover to see if that will help in raising the RPM sweet spot. I think it would, I just wonder if the lack of available space/volume would hinder performance. Although that would be tough because you'd still need the surface to come out as flat as possible. And I'm sure you could only get like 1/4" off, how much would that really help?

 

Daymn - that's good work for a newbie! Spill it, you've stuck your hands inside of cars before this, right?

That is a clear and concise theory - but is the turbulence power-loss part of your proposal backed up by dyno graphs showing a power loss that disappears when the BFs flip up??? For instance, the air flow in the runner only moves when the intake valve is open - then air is pulled into the intake port. Outherwise, the air is more or less still.

Hummm, I wonder if the dyno curves of a standard IM looks just like the curves of a MEVI - before switchover? Turbulence would show as the difference of the curves, perhaps? Something else to think about....

 

he's been reading this site for a while. yes he has worked on cars before i have pictures that show him bare foot on top of his engine. I guess this summer we'll mess with my mevi. Don't strip bolts this time!!

 

Yep been working on my 3.8l purshrod v6 boat for a little while. Spinning that thing up to 6400 currently. Check out my homepage if you want. I'm also a semester away from a mech. enigneering degree so I'm familiar with fluids, advanced thermo, basic engine theory, etc.
Been lurking on here ever since abci30 (tooled around in his whip before)told me about the mevi a couple years ago. I've been learing how nissian and other car companies use hemholtz resonance and eventually I would like to do use this theory in my pushrod v6. Just bought 'Scientific Design of Intake and Exhaust Systems' so I can really get into it..
You guys do tons of great stuff on here and I'm impressed as to how far your dohcs are taken.
Anyways, grey99max I'm not 100% on what your asking but I'll take a guess.
I definitely don't have any dynos to back up my theroy. But IIRC its pretty much accepted that you loose a noticible amount of low end going from the early vq30 upper intake to the mevi. And the only real noticible difference is the open area near the butterflies. That definitely reduces port velocity.
When the butterflies open, the air up behind the butterflies most likey dosen't
do much of anything? But now that the wall that the butterflies provide is gone, even more port velocity is lost. This is counter acted at a specific rpm range due to the resonance effect.
I'm defintely a noob to VQs since I don't have one but I'm just putting what I have out there..
I'd be more than happy to mess around with abc's mevi but I have little experience with stuff like this.

 

Not bay soo funny that your a semester away from your Mech Engineering Degree. I have mine and didn't remember that until you just presented it. i hated fluids anyway though. nice work.

 

n00B of the YEAR. I salute.

 

The air flow inside the runner is only still when the car is turned off. The reason being the engine is rotating so fast that there is no time for air to become still. That is where the resonance effect takes place. The intake valve pulls in air and then closes, the momentum of air is still causing the air to continue to move, but because the valve is closed the air has no other choice but to bounce back up (causing the resonance to take effect) while the valve is closed, it will continue to bounce back and forth. Since this is a continuous process the air will never become still.

As for turbulence, the reason this is messing things up is because it is not allowing the air to flow properly into the intake valve and thus we lose low end, because the it is messing with the resonance that is taking place before the butterflies are open. So in theory if you were to move the butterflies down it would reduce the turbulence effect and the lower part of the dyno curve would much more closely match the stock IM dyno curve down low.

 

Just for clarity the MEVI causes a low of mid-range torque, not low-end, which is even worse.

 

HA! I knew it - a real car guy in hiding here........ Glad to see you here.

 

I still would like to see dyno curves on stock IM and MEVI, and compare the actual changes in power at low, mid, and top-end RPMs. I know you don't have them available, but theories and facts are often different, and dyno curves could show what really happens....

Remember VQ35 installs and 350Z intake manifolds? They were impossible until people did them. Remember "exhaust back-pressure is required for higher performance"?

Well, enough about this subject... my MEVI, coupled with my custom electronic RPM switch and solenoid controller, works jest fine....

Thanks, and

 

Well from the 'Proof that 00vi owns MEVI' Sticky:


No rpm but there is a general idea.
Edit-
I'm guessing the tq loss of the MEVI would be worse without the spark advance of the aftermarket ecu though..

 

I like you - you're persistent.... But with 125-shot nitrous and stock ecu, I really don't want ignition advance....

I know about that sticky, but there are a lot of variables with intakes, not the least of which is the type of intake system before the throttle body. I have an Ingen modified to pull air from underneath the front of the car, and the long tube really seems to boost the low end - the car feels like it has more torque with this setup than stock intake or a short tube intake.

So have you bought a 4th gen Maxima yet?

 

Sorry to bring another thread back from the dead. I just have had time to think about my car again lately and there are all these questions I've had from before that I never asked but are coming back to mind.

Anyhow, I'm wanting to see if there is a way I could seal the opening for the butterfly plates when they are closed?

I know I'd need some type of gasket but I can't think of anything that will work. I've contemplated using RTV sealant but with friction involved with the plates opening and the vacuum pressure, I would fear that it would eventually pull the gasket off and into the engine.

I would really like it to be something similar to the rubber gasket the 3.5 IM has on the butterfly plate in the plenum, but I wouldn't know where to begin looking for something that would work.

Does anyone have any suggestions?