taurran

iTrader: (18)

I just stumbled upon this post today, and I'm looking forward to results. Someone brought this up locally a little while back and we were discussing the results of polishing the upper/lower plenum. I'd love to see the results, especially on an FI'd Z.

Make sure to keep us updated (unlike many of the other posters on this forum).

bilinghm

iTrader: (3)

A quick update:
I have found a shop that is not too far away that will do a baseline pull on my car prior to the install of the DIY plenum. Hopefully I will have it done soon.

Bill

DaveO

Bill,

I'm looking forward to seeing your results. You lowered ports 1 & 2 much more than I did. That may change the results.

My modified collector is working great. My G35 AT's torque off idle to 4500rpm is up noticably. There doesn't seem to be any change on the upper end--the engine still pulls as strong as ever to redline.

One day I may dyno the car again.


DaveO

ATL_Red_G35

iTrader: (8)

I was quoted $50 for 3 pulls. LMK if you need more info.

However, my friend will try to find and lend me his Gtech Pro RR unit where we can do street dynoes and average out the graphs. It's pretty acurate, from what I heard.

bilinghm

iTrader: (3)

DaveO, Just beautiful work! Polishing aluminum sure is a filthy job, eh?

bilinghm

iTrader: (3)

ATL_Red_G35,
What dyno shop are you using? $50 is a good price. Allspeed in Peachtree City would do three pulls for $50, but the Dynojet is out of service while they move to a new location.

3hree5ive0ero

iTrader: (95)

this is pretty interesting.. subscribing

ATL_Red_G35

iTrader: (8)

It's Mainstream Performance. I'll PM u with more info. They'll have a special Dyno day on june 11, 35 for 3 pulls.

sq40

iTrader: (4)

Would you make power at a lower RPM by extending the Velocity Stacks to 8-10" ??

first350

iTrader: (24)

So why not shave off some from the top of all 6 runners and just take a little extra from the front 2? I'm wondering if the runner wall thicknesses are that thick b/c of the casting process...it doesn't need to be that thick for strenght...if you were carfeul, couldn't the runner thicknesses be taken down to an 1/8"? Wouldn't this effectively give you a thicker plenum spacer? [end result being rear 4 runner with thickness of 1/4" and front 2 runners with 1/8" thickness]

explanation: I don't think this has been said directly...but one reason to have intake runners (and not have the intake/exhuast ports from the cylinder head open to a wide open space of air) is to cause a higher velocity of air flow directed at each cylinder; the smaller the cross-section of the runners, the higher the velocity (you're passing the same amount of air through a smaller area, so the speed needs to increase). When air moves at a higher velocity, it has a higher momentum...so when the intake valve opens, and the piston moves down (intake stroke), there's a point where the pistons slows dow and begins to go upwards (start of compression stroke), around this point - the piston is no longer 'pulling' the air in - so if the air just outside of the cylinder has a high momentum towards the cylinder, a little more air will make it into the cylinder prior to the intake valve closeing...more air, more fuel, more power.

The downside to intake runners is that higher air velocties also cause higher resistances...the higher the RPM's go, the higher the velocities go....so in theory that's why shortening or enlarging the intake runners will take power from the lower part of the RPM range, but will free up power up top.

In the end, it's a balance to produce the power and you'll usually have to sacrifice low/mid power for high rpm power...the general idea also applies to exhaust. (I forget the motorcycle, but one has a chamber that effectvlye changes the exhaust velocities for different RPM ranges...I thinK it was a Honda)


btw: after reading this post, I'm thinking of trying some of this too...anyone have an upper/lower plenum that I can have/buy?

-Peter

bilinghm

iTrader: (3)

First 350:

You make some excellent points. Certainly the manifold was designed using CAD, and extensive computer analysis /modeling was was done in it's development. However, it has already been demonstrated that there is some hidden power lurking in this casting. The puzzle is to figure out where it is. Certainly the bell mouths of each runner have vast anounts of material ready for experimentation. BTW, most of the plenum is quite thin, less that 1/4 inch thick, so you cannot really do much to most of the casting without the risk of breaking through.

ACEMAN

iTrader: (29)

Been doing alot of reading today, bored at work

And to build apon what first350 was saying

Visualize the intake cycle of the engine as air flowing through the intake manifold runner, past the intake valve, and into the cylinder. Everything is fine and dandy until the intake valve shuts.

Here is where the law of inertia comes to play -- because the air was in motion, it wants to stay in motion. But the air can't go anywhere because the valve is shut so it piles up against the valve like a chain reaction accident on the freeway. With one piece of air piling up on the next piece of air on the next on the next, the air becomes compressed. This compressed air has to go somewhere so it turns around and flows back through the intake manifold runner in the form of a pressure wave.

This pressure wave bounces back and forth in the runner and if it arrives back at the intake valve when the valve opens, it is drawn into the engine. This bouncing pressure wave of air and the proper arrival time at the intake valve creates a form of supercharging.

In order to create this supercharging, all of the variables have to be aligned so the pressure wave arrives at the intake valve at the right time. This combination of synchronized events is known as 'resonant conditions'

http://www.chrysler300club.com/uniq/.../ramtheory.htm

http://en.wikipedia.org/wiki/Cylinder_head_porting

http://www.mne.psu.edu/me415/SPRING0...ke/intake.html

http://auto.howstuffworks.com/question517.htm

So depending on the length of the intake runners it effects when the pressure wave hits the open intake valve, by doing so more air can be sucked in. A shorter runner would flow earlier but also would die earlier and return the positive waves much too quickly and those waves would be weaker. With the Short runners low rpm torque is sacrificed for high rpm power

Longer runners would help boost the low rpm torque, by creating pressure pulses at the low end of the rev range. But with the longer runners higher rpm performance suffers because there are no high-pressure peaks in the runners at the higher engine speeds.

The goal of Intake runner tuning is to arrange the runners and valve timing so that there is a high-pressure wave in the port during the opening of the intake valve to get flow going quickly and then to have a second high pressure wave arrive just before valve closing in order to fill the cylinder as much as possible.

So i am curious to see how Jermey's Cut away runner inlets work for him. The more you cut away, the more it effects the pressure pulses and how far it has to travel up and down the runners. And by doing this it effects low RPM torque but should increase high RPM HP as Alberto was saying. But i would assume it would move peak HP to a higher RPM.

It now makes more sense to me why RevUp plenum differs from the 287hp Plenum. And why it makes more HP and less TQ. It does also have to do with the cams and a few other things im sure.

After reading all that i have today, it makes me want to try a few things with my lower plenum i have just laying around.

Also if i have anything above wrong please let me know trying to learn as much as possible and welcome any info or corrections .

And keep up the DIY stuff, i enjoy reading it.

Later
Aceman

bilinghm

iTrader: (3)

There are very exacting rules/formulas for tuning the length of runners to create a ram effect. Lengthing the runners would certainly lower the RPM of the tuning.

FOO_G

iTrader: (4)

someone needs to invent a variable geometry intake. Sort of like variable pitch props or the swing wing of the F14.

AudibleMayhem... your mission if you choose to accept it...

bilinghm

iTrader: (3)

It has been done. BMW has a central section in one of their intakes that rotates at variuos RPM's and changes the runner length.

atlsupdawg#2

Aceman,
Good read bro. I do believe the wave travels all the way up the intake tubing also, hence the deeper note you get when swapping over something like a CAI unit. Though I don't think the length is as important to intake tuning as what you mentioned, runner length, but it may play into the variables.

ACEMAN

iTrader: (29)

Thanks Atlsup,

I do believe the runner length is important. If it wasnt then why would the RevUp's runners on the plenum be shorter then the 287hp plenum. Also with the CAI units they do have more of a deeper note. I use to have the AEM installed. It rest in the fender infront of the driver side tire. Most of the reason it was louder is do to it being in the hollow area behind the bumber and in front of the tire.

But i dont know, i guess it all can come into play.

Later
Aceman

bilinghm

iTrader: (3)

Runner length is especially murky on the 287 because the runners are all different lengths one each side. This is undoubtedly a strategy to build a flatter torque curve. But it does complicate any efforts that DIY engineers may attempt to find that extra power. I think that the "laying back" of the port mouths may be a worthwhile strategy. The only way to find out is to do it. We are having a little meeting in my home machine shop over the weekend, and perhaps kick off more advanced mods.

Sleepy79

Someone has been doing their research.
If you can weld aluminum I would extend the lower part of the dividers between the ports. Whatever you do, do not knife edge the dividers when you are reshaping the ports.

bilinghm

iTrader: (3)

Thanks for your comments. I would be very intested in any advice or insights you can provide. The goal is a better plenum. All input is appreciated.