Front Facing Stock Plenum

[GeeTR]

I believe i covered most of this in my "pack of snow dogs, lowest common denominator analogy" in post # 9 - Haha LOL

Edited April 21, 2008 by GeeTR

[Adriano]

Just wondering michael, whether you believe the EGT's are soley effected by the A/F ratio. I would be very interested, as i thought there would be other factors?

[GeeTR]

Well, from my / mates experience they are, but only when in fairly constant / normal operating scenarios (10:1 - 17:1) PULP, piston motor accelerating.

But your correct other factors like super rich / lean, big cams, decel, ignition misses, too retarded ignition can make things very uncomparable Iv seen super retarded ignition increase EGT's instead of lowering Ie.

Thermocouple per cyl and a decent A-D box is just so much cheaper then 6 LC1's. If only we could warrant the cash :\

[sonoramicommando]

if there are no flow figures are available, all we are doing is speculating.

one assumes that because nissan is a large automobile manufacturer, the stock plenum is going to be good.

same goes for GReddy plenum.

if one says a cut-and-shut front facing plenum has terrible air flow distribution judging solely from its shape, it is equally valid to say that the stock plenum flow distribution is far from ideal either.

to me, this flow business is one of the least intuitive things in the world and so-called common sense doesn't necessarily work out, but for the life of me, i can't go along with the people saying that stock plenum is fine when all you can see through throttle body is #3 & 4 cylinder runners while the same people maintain homemade front facing plenum will kill engines.

the thread with some flow figures on front facing plenum was interesting because #3 & #6 flowed most, with 1&2 the least, which doesn't seem to follow any logic as far as i can tell.

im curious to know how different are honda & silvia front facing plenum design internally, because they have single throttle body unlike GTR/GTIR ones.

some honda ones look like a log type design, with a huge tube hooked up to a throttle body with four short branches coming out the side to each cylinder.

Edited April 16, 2008 by sonoramicommando

[**RB2530**]

if there are no flow figures are available, all we are doing is speculating.

one assumes that because nissan is a large automobile manufacturer, the stock plenum is going to be good.

same goes for GReddy plenum.

Nissan provides 100,000km warranty based on their design!! Greddy plenum resembles shape of GTR plenum...And at WOT the TB position is largely irrelevant...So in my mind the Greddy shape is valid...

I am more than happy that people use the modified rb25 plenums but I never will...And I dont believe they produce reasonable results either...

And as I have said many times before, dont quote me figures of cars using the modded rb25 plenums that make x rwkW (and stating they work well) unless you have data from the same car with a Greddy plenum and associated data that shows the Greddy is worse, the same or better...

[**RB2530**]

I believe i covered most of this in my "pack of snow dogs, lower common denominator analogy" in post # 9 - Haha LOL

Sorry...maybe you did cover it...I dont think snow dogs would have a very high RON though:blink:

[GeeTR]

lol

[**RB2530**]

me, i can't go along with the people saying that stock plenum is fine when all you can see through throttle body is #3 & 4 cylinder runners while the same people maintain homemade front facing plenum will kill engines.

That only means the stock plenum would be crap if its job was transferring light...But its not...I can't see my exhaust valves from my muffler so does that mean my exhaust is crap??

Plus I dont believe I am saying that home made plenums kill engines...please read carefully...I am saying that you may lose horsepower (in comparison to a well designed plenum) due to unequal cylinder performance...

[sonoramicommando]

Nissan provides 100,000km warranty based on their design!! Greddy plenum resembles shape of GTR plenum...And at WOT the TB position is largely irrelevant...So in my mind the Greddy shape is valid...

this only means nissan was fairly confident in their design in its bone stock form (you know warranty is void as soon as you modify something - and i doubt there are hardly any of us who didn't modify our cars at all, obviously some push it far beyond its stock from than others). In your ideal world, no one would have a faulty car because nearly all passenger cars come with some kind of factory warranty.

And I'm not quite sure how you came to a conclusion that at WOT TB position is largely irrelevant.

That only means the stock plenum would be crap if its job was transferring light...But its not...I can't see my exhaust valves from my muffler so does that mean my exhaust is crap??

ok, obviously you can't quite visualise #3 & 4 runners would be forcefed with more air under boost given the stock location of throttle body.

Plus I dont believe I am saying that home made plenums kill engines...please read carefully...I am saying that you may lose horsepower (in comparison to a well designed plenum) due to unequal cylinder performance...

never singled out you or anyone said this or that.

maybe not from this thread but there are peope who think that homemade front facing plenums are responsible for detonation due to leaning out on some cylinders and excessive bore wear on other cylinders due to rich mixture.

others, like you, think uneven air distribution merely causes loss of performance, without affecting reliability of engine.

to me, you are basing your judgement on reputation of Nissan and GReddy than anything else - that's fine but that still doesn't prove or disprove anything at the end of the day.

Edited April 17, 2008 by sonoramicommando

[**RB2530**]

No!! I am basing my opinion on my knowledge of 'Fluid Mechanics'!!

[**RB2530**]

And I'm not quite sure how you came to a conclusion that at WOT TB position is largely irrelevant.

At WOT pressure on both sides of the butterfly are close to being equal..Therefore difference between GTR 6 TB setup is very similar to single TB set up...ie

at WOT for GTR plenum inlet is not restricted (no TB to begin with) and at plenum outlets all TBs fully open so no restriction.

With GReddy plenum at WOT TB is fully open and no restriction at outlets...So in my mind they are very similar flow conditions..

PS I appreciate that the a 100% open butterfly will present a small restriction but I dont think it is all that significant...

[sonoramicommando]

No!! I am basing my opinion on my knowledge of 'Fluid Mechanics'!!

if you can satisfy yourself with your fluid mechanics knowledge on this matter, that's good for you.

but if it is your intention to convince me, you are still not coming up with any proof that stock manifold is far superior to cut & shut front facing plenum - you will note from my posts that im only interested in stock manifold vs cut & shut job.

and i don't appreciate being misquoted.

ps. i will go along with your explanation of WOT situtation btw.

[**RB2530**]

if you can satisfy yourself with your fluid mechanics knowledge on this matter, that's good for you.

but if it is your intention to convince me, you are still not coming up with any proof that stock manifold is far superior to cut & shut front facing plenum - you will note from my posts that im only interested in stock manifold vs cut & shut job.

and i don't appreciate being misquoted.

ps. i will go along with your explanation of WOT situtation btw.

Mate I haven't highjacked 'your' thread!! Read back a bit...My comments are on topic..I make no apology to you...

Also I cant convince you because you are not thinking about it!! This is evidenced by the fact that you are not giving any alternative explanations or reasons or questioning anything...You are just accussing me of commercial bias...

Now I am asking myself how have i mis-quoted this guy because he doesn't appreciate it?? Maybe you could point out where I have...instead of just mentioning it without detail or facts......

anyway I hope others got something out of my posts...I have spent a fair amount of time thinking about it..cheers

[sonoramicommando]

1. mOrt wanted to know what would happen when he puts his TB at front of stock plenum.

2. Later on, he also said that he wondered why there are no stories of lean cylinders at 1& 6 due to stock TB position.

3. I said that I have my RB20 one out and said there are no fins, ribs or baffles to stop uneven air distribution (3 & 4 vs 1 & 6 cylinders).

4. Later, I replied in general (note I did not quote anyone) that we are only speculating without flow figures and once again raised the issue of stock plenum air distribution.

5. You replied, quoting my post, that nissan has 100,000km warranty based on their design

"Mate", here are your problems:

Also I cant convince you because you are not thinking about it!! This is evidenced by the fact that you are not giving any alternative explanations or reasons or questioning anything...You are just accussing me of commercial bias...

Where are the alternative explanations or reasons? How can I take you seriously when your reply is that Nissan gives warranty???

Mate I haven't highjacked 'your' thread!! Read back a bit...My comments are on topic..I make no apology to you...

sure it is not my thread, you are not jacking my thread, but if you are gonna quote and pick apart my posts, you might as well stick to my main point.

never in any of your posts, you addressed my original point of air distribution of stock vs modified stock with TB at front.

don't dwell on side issue - and was I wrong to say we are speculating without any figures? I don't think so.

Now I am asking myself how have i mis-quoted this guy because he doesn't appreciate it?? Maybe you could point out where I have...instead of just mentioning it without detail or facts......

Plus I dont believe I am saying that home made plenums kill engines...please read carefully...I am saying that you may lose horsepower (in comparison to a well designed plenum) due to unequal cylinder performance...

I'm assuming this response was for me...

Now, you tell me where I said that YOU are saying that home made plenums kill engines.

YOU read carefully. I said "people" in general, never quoted you.

I'm done in this thread.

[**RB2530**]

..how about we stick to the technical stuff..

Anyway I have been thinking about the stock plenum some more have some more comments on the factory plenum...

Fluid flow is terribly non-linear...From this it follows that any balancing of air flow between cylinders by design would most likely change once the factory air flows are exceeded...So variations between cylinders at factory airflow may be ok but at twice the airflow the variation may be unacceptable...

[GeeTR]

Sweet, back on topic (Sam is pwning u atm btw)

You raise a good point. Best mate who's a mechatronics engineer, was talking how non linear air can act in certain violent circumstances. Sposedly some FEA plugins for popular CAD apps dont take into these effects... (which i thought was odd)

you'd like to think Nissan thought about customers wanting to flow more air (powaah) then factory, when designing the m.fold.. but to what extent? ... ?

I must admit, being able to run the sims through some speccy FAE, taking into account all conceivable factors, air heat, boundary effects, mass, inlet stroke pulses, car movement? lol - would be great.

I vote, we find a some bored uni student to LIDAR a stock manifold, mod it, and run it through some sims.

... but that could just be my nerd gland talking...

PS: Theres a dood on SAU atm, talking bout multi e.manifold metering, via temp or 02... watching that keeenly

Edited April 21, 2008 by GeeTR

[**RB2530**]

(Sam is pwning u atm btw)

Sorry buddy I come from the generation that uses English to communicate...maybe you could translate this for me....

[**RB2530**]

Ok just looked it up...Ummm if thats what you reckon so be it....The arguments presented to me were very technically inert. ...I must have the wrong idea about this forum I think...I hoped for intelligent discussion regarding this topic.... dont think I'm gonna find it...

regards....

[GTScotT]

ok, dont do foward facing cut n shut stock plenums, as rb2530 has stated about flow velocity and the disign on the manifolds from factory (with nissan spending millions on flow testing components and what not......) if u look at the rb20 manifold u will notice it is larger in the middle were the tb is located, and its acutaly not a good size at the end to put a throttle body, i looked at this last week as i wanted to do the same thing, a better idea i would think would be cut n shut the stock manifold to be directly opposite where it is now and put a 90 degree bend and plum it from there, as this wouldnt affect the flow in the manifold so much, nissan knows what there doing when they build a car, theres a reason reputable companys release things designed they way they are, and its not so someone can build a better designed peice in there backyard in 10 min, or even expect them to work half as good

[craked]

my 2 cent ive done it to four cars in the past 2 years with out a problem drop the inlet temps so that has got to help also if anyone remembers that yellow s15 from power crusie with the rb25 it has a forward facing mainfoild go to youtube and see the skids it does