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Plenum Modification?


Tricky-Ricky

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Sure i saw something about it a while back but I'm dammed if i can find it.

Anyway i thought i would remove my plenum today for a clean, polish or paint, and was pleasantly surprised to find virtually no oil residue and not particularly dirty, so thats a plus, anyway now i have it off the car i thought if i could turn up any info on doing a little grinding/filling that may gain me a few ft lb it would be worth doing, so if anyone knows the best way or has some links i would appreciate it :)

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I believe there was a topic regarding Plenum polishing that the the printed/cast standard had been ground down. Search! ;)

 

Not looking for a guide to polishing, thats no problem, its modifying the lower plenum runners that I'm looking for, thanks anyway.

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There are a few sharp edges from casting inaccuracies and identification marks on both upper and lower sections that can be smoothed out.

 

On the lower section, if you wanted to shorten the longer runners to equalise the lengths you would probably gain a little peak power - the shortest runner is tuned around 6000 rpm, although the experience on the rev-up lower section suggests that the power loss lower down probably makes for a net loss in overall performance.

 

Personally I would only be altering runners if I had a cam change. The standard runners/cams appear quite well matched.

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I have done a little more research, and found that my 350GT plenum is a revision 2 item, which equates to the modified front runner already lower in profile and the rest are all of practically equal length, also they are somewhat longer than the early types that i have managed to find pics of, interesting, i have no idea what difference this will make? didn't the revision engines have other mods? i don't mean the VR series though.

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As you guys keep linking my thread I thought I would comment :)

 

Steve is correct that the runner lengths are very well matched to the stock cams so this is something I haven't modified. The challenge that has been advertised through multiple vendors and threads. The front two cylinders get starved of air. Plenum spacer will help to an extent but i thought I'd have a go.

 

On a thread on my350z.com on a stock 276bhp car they put a modified plenum on and gained 5/6bhp. On the rev up cars the runners are alot shorter which looses alot of TQ but gains topend grunt. This is why just bolting on an older design 276 on a 296 without modification would significantly increase midrange TQ. the shaving of the front two cylinders only adds a little, but if it helps its better than not having it in my opinion.

 

For reference this isn't a scientific experience I shaved from 15.6mm down to 12mm on the front two cylinders and removed the MR1 and MR2 logos out of the lower collectors.

 

Not sure how much power it gained but I do know Im 274bhp @ the hubs with stock airbox, plenum spacer and exhaust with Uprev tune.

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Some pics for clarification,

photo4-1.jpg

 

My plenum is like the one on the right,and has the first two runners reduced in hight, so is the one on the left the early version, and what does the revision 3 plenum look like?

 

Thought some might like to see how the VQ engine should look like if it has to stay N/A ;)

 

g35_stroker_itb_engine_angle.jpg

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Tricky, unfortunately you are wrong.

 

The plenum on the left is a 296 (rev up) the one on the right is the 276 that has been modified with lowering the front runners.

 

you have only referenced one standard plenum (the 296) with the shorter runners with the modified 276 (Mrev) i.e two completely different parts which doesnt show the modification.

 

Here is the 276 vs the Mrev

 

realmrev2-1.jpg

 

313 engine is completely different Plastic for a start and square runners!

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This is a pic of my lower plenum as you can see its already cast with a lower front two runners, so this is obviously not a first generation plenum, but you say its not a rev 2, so what is it?

DSCF3215.jpg

DSCF3214.jpg

 

There is obviously a lot of misinformation around as you are saying that the previous pics are labelled wrongly, but i also found other pics that are labelled the same as those, it would be good to see all the relevant plenum's side by side.

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is there a difference in the G35 versus Z33?

 

In theory the engines are to all intent's identical, the only thing i can think of is that being a JDM only car

they where deliberately fitted with the updated plenum's, perhaps to offset the extra weight.

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is there a difference in the G35 versus Z33?

 

In theory the engines are to all intent's identical, the only thing i can think of is that being a JDM only car

they where deliberately fitted with the updated plenum's, perhaps to offset the extra weight.

its a 03? so is mine.... could go look at my plenum and see its up the attic somewhere

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is there a difference in the G35 versus Z33?

 

In theory the engines are to all intent's identical, the only thing i can think of is that being a JDM only car

they where deliberately fitted with the updated plenum's, perhaps to offset the extra weight.

its a 03? so is mine.... could go look at my plenum and see its up the attic somewhere

 

 

Mine is an 04 plate, be interesting to see if there is any difference.

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Tricky Im not aware of any official revisions of the de lower collectors other than the change for the revup - from your pics that is a standard de lower collector, exactly the same as mine. The mrev2 is a machined aftermarket version of that same lower collector that many people do a diy copy of. The rev up version show in the previous pics is the only other design supplied by nissan that I am aware of.

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Tricky Im not aware of any official revisions of the de lower collectors other than the change for the revup - from your pics that is a standard de lower collector, exactly the same as mine. The mrev2 is a machined aftermarket version of that same lower collector that many people do a diy copy of. The rev up version show in the previous pics is the only other design supplied by nissan that I am aware of.

 

 

If that is the case then why do people bother to modify the two front runners by reducing there hight by 3-5MM, mine is already that much lower on the front two runners? i was under the impression that the runners where all the same hight, which is why the spacer mod or the machining works?

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Ive had the standard lower collector in and out of the car and also a genuine motordyne mrev2. The mrev2 doesnt do anything on a non revup with a spacer.

 

Trust me your is standard, the runners are not equal heights. The mrev2 is basically yours with the tops of the front runners shaved.

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This is all becoming increasingly confusing, so you're saying the a std no rev runners are not all the same hight? (not talking length)

and that in order to make it comparable to the mrev2 the two front runners need to have the hight shaved further? is this correct?

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This is all becoming increasingly confusing, so you're saying the a std no rev runners are not all the same hight? (not talking length)

and that in order to make it comparable to the mrev2 the two front runners need to have the hight shaved further? is this correct?

 

It's confusing the hell out of me.

 

I'm going to be purchasing a lower plenum mod soon, was planning on the Mrev2. Are we saying this is bad? This mod will be complimented by a 5/18 plenum spacer and UpRev flash on my 2004 UK. I hope this is not gonna be a waste!

 

This thread has kinda thrown me...

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