I'm always itching to do simple mods to my car, especially ones where I can use OEM or modified OEM part. IMO, that's always the way to go in terms of fitment and quality. I had always been intrigued by the Motordyne's MREV2 concept for the lower plenum. As most know, the MREV lower plenums are OEM cores modified by Motordyne. The main modification is milling of the two front runner horns and some grinding/polishing of portions horns, valleys, and maybe some other things not obvious to me (I've never seen one in person). Tony at Motordyne is pretty secretive about what exactly is done and rightly so. He charges $460 for the modified plenum which is expensive for a modified OEM plenum, but there is quite a bit of labor involved and also the R/D that went into it so I think the $460 price is justified for the MD part. I also think you get a credit if you send in your core.

I bought a used plenum for $70 on MY350.com and modified it myself with an angle grinder, random orbital, and some elbow grease. I've spent about 3 to 4 hours modifying mine. Modifications I made to the manifold where:

1) Shaved the front two air horns down with a 40 grit flapper disc. Horns milled down to about 0.440"-0.450".

2) Random orbital to knock down the casting grain a bit on the exterior surfaces of the six air horns. These surfaces were not polished completely smooth. Completely smooth is not a good idea when it comes to intake flow.

3) Polished out some of the rough casting edges around a few of the airhorns and cleaned up some casting flash on the inside of the runners.

After about 10 days of driving now I can post my experiences with this manifold. I usually wait at least 7 days to post my observations because it's my experience that it takes most any late model ECU about 40 or so starts to fully take advantage of intake/exhaust modifications. So far, I've driven in 25 to 70 degree conditions with DA conditions varying from just below sea level to around 3000'.

Here's what I've noted:

1) There's definitely a bit more throttle response from 1500rpm to 3000rpms. Everything seem snappier. This is great for around the town driving. Nothing earth shattering. It's like adding another HR y-pipe.

2) The engine feels more refined, flexible, and more willing to rev above 5500rpms and seek the 6600rpm limiter. Instead of feeling truck like in the high rpms, it's a bit smoother. It reminds me more of my sewing machine smooth VQ30 in my 96 Maxima.

3) There's no real change in induction noise.

4) No driveability quirks. MPG is the same.


If you're looking for a relatively easy modification and you've got the money (MREV2) or the experience and tools (mod one yourself) this is a decent mod. I would imagine the MD unit would perform even better since quite a bit of RD went into the design. From the dynos I've seen, the MD plenum is good for another 4 to 7 whp/wtq across the powerband on a non-revup motor with a 5/16" spacer.

Mods to my 03 5AT sedan:

Revup airbox
Enlarged Powerduct opening
G-tube with resonators removed
5/16" MD spacer
Modded lower plenum
HR Y-pipe
3.5 gear

 

Nice write-up Dave!

I can't believe no one posted a reply to your thread. It seems like the forum has been quite dead lately.

 

strong work. glad to see people continuing to be inventive on our platform.

 

Pictures by any chance? i like this idea

 

I am guessing you didnt do anything above and beyond whats in the diy section but if you did pic's please

do you have anything to tune with?

 

I didn't take pictures because there's not a whole lot to photograph. You can some pictures in this thread showing the general idea of what I did. The difference is I didn't polish mine up to the degree of the lower plenum depicted.

https://g35driver.com/forums/engine-...ctor-pics.html

 

No tuning. I have an 03 doggy door and Technosquare gave up tuning so my tuning options are basically nill. About my only saving grace is that the older ECUs tend to be a bit adaptive to mods compared to the later 04.5+ cars equipped with wideband 02 sensors. I also don't have many mods that would necessitate the need for tuning. I really wish I did have the option though.

 

Here are pics of mine:

 

lol, any plans to run a em, utec or aem unit like the maxima guys

 

Nope. There's really no more mods I want, therefore not much need for tuning. I'm also clueless to all the programming wizardry that would be needed to get the tuning just right. I'd also want it tuned a Mustang dyno or similiar to get the tune just right for all load situations. Seems a bit silly to me to spend $800+ on the ECM stuff and then another $300 for tuning on the dyno just to gain 5 to 10whp. I would have done the Technosquare ECU though. I'll probably focus a little more on the suspension and hopefully source a wingless trunk lid and be done with it.

 

I'm about to try this myself on my 06 350Z 6MT. Im going to install the 03 lower plenum dyno then do the machining dyno again then do the plenum spacer then dyno again. I physicaly compared MD's plenum with a stock one and only found that they milled down and polished the front two runners. I didnt see any other milling or polishing. If everything goes well I plan on posting up a DIY with pictures within the next month.

 

Nice. I don't know if dynoing really is necessary though because others have done before and after comparison dynos. It would be nice to see the differences on a Dynojet or Mustang vs Church's optimistic dyno.

 

Well I decided to give this a try. I have an 06 G35 6MT (revup engine). I picked up a non-revup lower plenum and started modifying it last night. I'm currently scouring the DIY thread on my350z and looking at MREV2 pictures to see what the optimum grinding/smoothing is. My main question is if grinding down all runners (instead of just front 2) would eliminate the need for a spacer. The dynos I find for a revup shows most of the gain coming from just the plenum, with a little bit at the top end gained with the spacer.

Here's what I've started with so far, picked up some new sanding disks today:

 

https://g35driver.com/forums/intake-...t=indepth+peek


there are many ways to do these modifications guys. However if you deck all the runners and remain with a stock top i think you will starve the front cylinders. The reason i shaved all the runners is because i run a huge sheet metal top. Talk soon mike

 

Worked on mine some more last night. Knocked down the 2 front runners about 7/32" which is about 5.5mm. Don't have a measuring caliper, so did it with a ruler and eyeball, tops were at 2" so I knocked 7/32" off that. Then I used a DA with 180 grit to smooth things out, smoothed out the other runners and smoothed out the nasty casting line along the front edge of the runners. I still have a bit of work to reshape the fronts a little better. Sounds like what the OP of this thread described in post #1.

I'm talking to a guy selling a spacer and the whole plenum, so I might have another one to play with soon. Don't have access to a dyno, so might just stick with the 'tested' method of grinding the front 2 plus a spacer.