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Localy made front facing plenum for a RB - thoughts?

Gradenko

By Gradenko,
in Engines & Forced Induction

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Gradenko Mentor

Gradenko

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Does this look the part?

http://board.performanceforums.com/forums/...30&pagenumber=1

Fairly cheap and the build quality looks good. Not sure about the box shape design though, shouldn't these things taper back so that air speed increases towards the last couple of cylinders (furthest from throttle body)?

Not sure about everyday driveability with it either. So, who wants to be the guinnea pig and get one first? :)

Gradenko Mentor

Gradenko

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Oh, haven't got one yet. You'll know when I do, I'll be the git running around with an ear-to-ear grin :lol: Besides, can't get one without a bit of fuel control, the stock ecu would get pretty confused with something like that bolted on. Hell, the stock ecu is pretty confused even on a stock car.

Cutting the end off the stock plenum is one way to go, but I don't think its going to be healthy for anyone. Factory plenum is designed from the ground up to distribute airflow evenly between the cylinders with air entering from the center. Its not going to do its job too well (if at all) when the entry point is changed like that. But I think you were jking, so no problems :wink:

BOOSTMEISTER Mentor

BOOSTMEISTER

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R34

Thats right and wrong.....That plenum would be OK if you were to run more than 20psi but under that you would definately cause some of the sylinders to run lean and some to run rich. It should also be tig welded on the inside as well or it will just blow apart at the welds after a while at around 15psi.....A plenum with square sides is not the best for air flow, just take a look at about every other plenum on the market for a better idea.......At the end of the day if you buy this you will have a $650 plenum that is worth $650 and will deliver $650's worth of benefit. The standard plenums on rb 20 and 25 are actually quite good for performance and flow well to all cylinders. I tested this when I had mine off and the cylinders all flowed the same volume at the same speed.

There is a lot of r&d that is needed when designing a plenum thats why they cost so much.

Cam

JiIMb0, the plenum basically acts as a resouvour for air til the engine calls for it. The engine sucks a lot of air and if you just had a small pipe the engine would stall as it couldn't suck in the volume of air that it needs.

Gradenko Mentor

Gradenko

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It should also be tig welded on the inside as well or it will just blow apart at the welds after a while at around 15psi.

There is a lot of r&d that is needed when designing a plenum thats why they cost so much.

[/quote:8c2559842b]

This plenum [b:8c2559842b]is[/b:8c2559842b] tig welded, also uses tuned length ram tubes and, importantly, accepts all std air bypass valves. While I agree that square sides are not best for air flow, I don't belive we'll see any cylinders run lean under pressure.

I'm sure most of us here would give our left nut for a Greddy or Jun plenum, but since we aren't all chasing after that 1/10th of a hp and we all have street cars that need idle control, this plenum doesn't look like a bad choice. I'm certain its better than the stock plenum, I have no faith at all in Nissans design choices in this area. Everything about the RB25det was designed to meet a price point, theres nothing on the engine (except the turbo) that makes it easy for us to get power out of it.

So yeah, its only $650 worth of engineering and manufacture but its still heads and shouders above the stock plenum. If anyone is up to the task, buy one and put it on a flowbench. I'd love to see the results :)

BOOSTMEISTER Mentor

BOOSTMEISTER

Posted
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You really have to know how air flows before you realise that some designs work and some don't. I am not saying I know everything I was only saying that from what [b:04433b2acc]I have actually tested [/b:04433b2acc] the rb plenum works much better than most people realise. I too am looking for a new plenum and will either build my own using short runners or use a rb25 GReddy item and modify it to fit. Regardless of cost if you are going to the expense of doing a mod it had better be worth while. Unless you run more than 20psi there is no need (other than better intercooler piping route) to change the plenum. Remember that for $700 there are many better mods to perform.

I am a HUGE fan of bang for your buck....cam gears @ $350 for 10-15% increase in power is what I am talking about as an example.

If anyone does buy one of these please get it flow tested prior to fitment at the SAME boost level you are intending to push through it.

Perhaps Gradenko will buy one first and prove me wrong.....I will be happy to know that a simple cost effective design actually works.

Cam

Gradenko Mentor

Gradenko

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Thanks meggala, had a bit of a hunt around SDU and found a pic of dans plenum. Still has right angle corners but its a fair bit curvier than one for sale. Wonder what the insides are like? Maybe dan dooorift could let us know...

Looks good tho, and has factory idle control bolted up too.

Heres a link, http://www.geocities.com/medved_skyline/car/ click on Dcp_0005.jpg.

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