Custom Plenums

[WHITER33GTS-T]

I have the standard throttle body and plenum on my 33 and that makes 300rwkw. I will see how it goes with my new turbo setup.

[Fitzpatrick Speed Works]

nothing stops the power its just like anything, once you start doing good numbers, you can design something that will suit the purpose better. As an example back in the 90's every hi-po vl was pushing 400rwkw from a 68mm ford throttle body. As another example at 10inches of water a 50mm round hole can flow 250cfm, a 65mm hole can flow 450cfm. Your intercooler will be a resriction well before a plenum or throttle body will; a good 300x600 core flows around 300cfm!!!

However this said once you are doing the numbers, it can be improved on, mainly the fact the standard item is so heavy on the middle cylinders in airflow.... I have not seen any strong evidence to this day that will suggest the standard plenum has a limit on how much power it will support....but as I mentioned you can always improve on things so if you have built the motor, got a top notch management system, big turbo and the right auxillary's then look at some plenum upgrades.. Probably a waste of time till then

Cheers

Edited October 11, 2006 by Fitzpatrick Speed Works

[croat]

if someone is keen on doing this i have the upper half of the RB25det plenum perfect condition. it has also been sand blasted so is 100% clean. PM me if interested.

[gts-4 dreamer]

so how bad is the heat soak in the piping crossing the engine? Has anyone ever tested the standard piping route to see just how much it heats the intake charge ?

That and the lesser lag would motivate me to go for a front facing plenum.

Would the effects be negligable considering after a good bit of hot running I can still quite comfortably leave a hand on that intake piping just infront of the throttle.

[Abo Bob]

This subject has been covered so many times. Sydneykid once laid out all the calculations of the speed of the air as it goes through you piping and the air is in the hot pipe for such a tiny amount of time that it doesn't have time to take on any of the heat.

For some reason I don't understand the length of the runners has an effect on torque, particularly, the longer the better for low down torque and I suppose the shorter the better up high. Can anyone confirm this?

There are engines, I think some ford 6's, that have variable length runners for this reason.

[Dahtone Racing]

waste of money.

When you can make over 300rwkw on the stock one

why change it? Doesnt pose a restriction or hinder the car at all

standard reply once again aye

to you, yes its a waste of money

to others, no its not

some people actually like their engine bays to look good and like to have easier access to spark plugs, injectors, etc

im not going for over 300kw and im getting a front facing plenum made i think its the best mod i could make to my engine bay cause the stock one looke like absoloute shit

believe it or not some people are after a bit more than "bang for your buck" perfomance

[R31Nismoid]

Of course its a standard reply, funnny that i tested the standard item and proved it to work quite fine, as have many others

So i'll use my standard response as much as i like, i did the R&D with RPM, i'll use the results from a performance perspective.

Do your rocker covers you have nicely coated give a performance gain?

No, they just look good, and thats fine for you if thats what you want.

Same as the plenum.

You have money to burn, so your buying one for looks. Thats your choice.

Im not interested in looks, and im not made of money, and when performance beats rice in my version of paper, scrissors, rock... performance gets the focus.

Hence if the stock one does the job it gets the vote from me.

People appreciate information (generally) thats all im providing, is there an issue with that?

Also remember, most people on this forum are from a certain demographic. 18-24.

Not all have a fortune, so the majority wanna see bang for buck for thier 5-7k they have worked hard for.

[NV N01]

Have you considered the fact that if you just change the position of the Throttle body you are risking blowing your engine, through it leaning out in Cylinder 6?

They're designed to be fed from the side and as such have all the airflow paths made to suit, ensuring that all cylinders get enough air..

If you just simply cut and weld the throttle body to to front you will lack are in some cylinders..

[Bass Junky]

Doesn't more air = leaner and less air = richer?

so having less air at cylinder 6 would mean more fuel to air ratio.....

Using that example, there is much more air going into 3 and 4 on the stock plenum?

[Fitzpatrick Speed Works]

A standard plenum provides significantly more air to the cylinders 3 and 4 thus they will be more likely to run lean. In a front facing plenum design believe it or not number 6 will receive the most airflow even though it is furthest away it is the most inline with the incoming air, cylinders one and 2 for example must draw the air to change its incoming path whereas 6 get it shoved down its throat figuratively speeking. standard plenum modified to be front facing will be a lot more of performance disadvantage and riskier at over 300rwkw than a standard item.

Cheers

[Silent]

Have you considered the fact that if you just change the position of the Throttle body you are risking blowing your engine, through it leaning out in Cylinder 6?

They're designed to be fed from the side and as such have all the airflow paths made to suit, ensuring that all cylinders get enough air..

If you just simply cut and weld the throttle body to to front you will lack are in some cylinders..

Is that tru?

[2BNVS]

agreeing with Fitzies post about the cylinders...when my mate made up the custom plenum he was very particular with how cylinder 1 and 2 would get air flow, this is why alot of flow testing was done etc to make sure the cylinders were recieving almost equal ( negligable difference between all 6) air flow...

also with his post about the numbers can always be improved, if ur chasing the best possible figure for ur aplication then go for it, thats what i did. no point spending big money on a great motor, only to skimp out on something that can give u even more gains...

modifying the stock one is not an option i wanted to do or would recommend...

i have no doubt in my mind that in my application the intake plenum has helped with response, flow..eliminated an ugly engine bay.

ben...

[Abo Bob]

When I blew my engine by accidentally putting way too much boost into it, 3 and 5 pistons were stuffed and 4 was in pretty bad nick. I suppose this is partially due to the middle ones getting more air, thus being leaner at the time.

If you have a PFC you can put more fuel in particular cylinders but I'm not sure what the potential side effects of this is. Can anyone answer that?

Eg, if you did a dodgy cut and shut with the stocker, could you add fuel to 5 and 6 to compensate for extra air?

[Bass Junky]

Yep, there is individual cylinder trim on the PFC.

Mine is set to give a little more fuel to cylinder 6 as it's a problem even on stock plenums.

I have a 2% variance between 1 and 6 and a nice slope in between.

[Silent]

so its a bad idea then?

[D-limo]

Have you considered the fact that if you just change the position of the Throttle body you are risking blowing your engine, through it leaning out in Cylinder 6?

They're designed to be fed from the side and as such have all the airflow paths made to suit, ensuring that all cylinders get enough air..

If you just simply cut and weld the throttle body to to front you will lack are in some cylinders..

This is almost common sense imo.. Would be interested to see some sort of flow test results for confirmation though.

Nissan spent big $$$ on these plenums getting the flow characteristcs right. Is it not ignorant to think that completly changing the direction and angle of incoming air will not effect how the plenum feeds the cylinders?

Edited October 18, 2006 by Drift_Limo

[Spook's_Skyline]

im sure nissan spend big money on their plenum

for stock applications

perhaps when modifying your engine, there are advantages to be had

[Silent]

So modfying a standard item to a front facing plenum is a no go?