pics of the new intake manifold!

[JK]

84z31 wrote: i've been thinking about doing the same thing only different. ops:

how come you made the back portion so small. the larger the plenuim the better low end you are supposed to have. and the longer the runners the better top end.

i was actually trying to design something with a larger plenuim area and then making the runners longer.

the penis is interesting. NSFW warning is probably needed. :wink:

The main purpose of the plenum is to distribute air equally to all cyl. 1.5 times engine volumn for 6 cyl will work. Also, longer runners best for low end, short runners for top end. Runner diameter influences rev's at peak HP.

His design is correct in shape, smaller at blocked end, as the cylinder closest to the inlet can be down on airflow up to ~5%. While the cyl at the blocked off end will be up ~5%. Detuned engines no problem, it becomes an issue with increased HP

[SATAN]

[quote]JK wrote:

i've been thinking about doing the same thing only different. ops:

how come you made the back portion so small. the larger the plenuim the better low end you are supposed to have. and the longer the runners the better top end.

i was actually trying to design something with a larger plenuim area and then making the runners longer.

the penis is interesting. NSFW warning is probably needed. :wink:
The main purpose of the plenum is to distribute air equally to all cyl. 1.5 times engine volumn for 6 cyl will work. Also, longer runners best for low end, short runners for top end. Runner diameter influences rev's at peak HP.

His design is correct in shape, smaller at blocked end, as the cylinder closest to the inlet can be down on airflow up to ~5%. While the cyl at the blocked off end will be up ~5%. Detuned engines no problem, it becomes an issue with increased HP

Hmm, see I read that anywhere from 50% to a 70% is a good all around plenum size. Indeed there is a lot that goes into designing an intake mani. unfortunatly on the z it is hard to start from scratch due to water passages and what not. See I knew the back would see more flow if it was blocked and the front less but I didnt know how much % wise.

But yeah, port diameter, runner length, runner taper, plenum volume, throttle body size..... A LOT goes into such a simple looking thing that just sits on the top of the engine. Just by changing the runner length you can change where you engine makes most of its torque, up high or down low. Lots of cool stuff!!!!

[OR-Zman]

autoworks, JK, Satan or anyone else who has actual experience desiging or testing intake plenums:

Longer runners for low end, 1.5 x engine volume, I get that, very good discussion.

But...just out of curiosity, how does this info play into the idea of guys with mildly boosted or smallish turbo cars or dare I say NA applications? :shock:

I have a L&P that will be installed on my new NA car but I really don't hold out real high hopes for its individual addition to my NA power. Also, I wouldn't think it would add, buy its self, much real gain to a lightly or moderately boosted turbo.

Here is how I see this issue. Please correct me if I am wrong. On NA or lower boost Zs, the intake mods (filter to heads) ,will probably not add much individually to the overall power or performance of the car.

However... when air intake is unrestricted as much as possible and coupled with head porting, exhaust, ECU tuning and other such somewhat advanced stages of modification, the intake flow and volume will be optimized to their "flow potential" on that particular engine. Basically the intake modifications will have an indirect effect on overall performance. "Easy air in and easy air out is a good thing" concept. OK, assuming you can tune accordingly.
(fuel management aside for the sake of discussion)

So, with an educated opinion what type of plenum design do you think is a good choice for NA or lightly boosted turbo cars. Personally I have thought that the tapered log design would work great for no or lower boost applications but....the just aren't out there for sale. :shock:

[JK]

Air flow restrictions can't be overcome just by turning up the boost. The plenum will help your car breath at 5000 rev's and up. Which is just where there seems to be a noticable fall off between the NA's and Turbo's. It is a bit silly to modify the plenum and ignore the heads. For an NA, the real value would be ported heads. You will gain more HP across the board. Very important to keep dia of ports the same. Don't allow anyone to hog out the runners. The plenum styles that are available (gutted, pathfinder) deal with the issue. At this point the most optimum plenum style isn't going to improve that much to warrant the effort. Put your emphasis on the heads.

Satan, as for plenum volumn. Optimum volumn of 1.5 deals with intake charge temp, that is where your smaller plenum could come up short. Only tests will bear this out.

[craZed]

[quote]SATAN wrote: [quote=craZed]

I like how you rounded the top piece of the plenum. what did you use to do that?
He sliced a tube at an angle for that part.
See thats what I thought at first but the back side of it flattens out and the front is more round. Doesnt look like he beat it flat. Meh, maybe thats what he did.

It looks like that from the pics but it actually isn't.There is a
half circular flat peace at the back set on at ~ a 45* angle.
Thats where the vac fittings are.

[Jason84NA2T]

That is just plain awesome. I bet it works well!

Did you have a stock or gutted plenum before?

[Jason84NA2T]

JK wrote: Also, longer runners best for low end, short runners for top end. Runner diameter influences rev's at peak HP.

I was actually a little suprised at how much runner length there is from the radius on a gutted plenum to the actual valve. I believe the gutted plenum even with a small spacer makes good enough torque from air column it has. Building onto the lower intake will take ~1-1.5" off that length, but who knows how it really hurts the output torque until he tests it... Most people can see the longer runners being much more advantagous for an NA buildup; where their effect is always much more clearly shown on a dyno graph.

[MikeZ]

Thats pretty nice. You swapped the TB to the passenger side on your other plenum, right?

[JK]

Runner length of stock or gutted is ~11 inches (rough measurements)
Runner length of Pathfinder plenum is closer to 16 inches. This is bellmouth to valve seat. Interesting to note, small plenum chamber, large diameter runners on the pathfinder. Although the inside design seems much less restrictive. Its mad science. My choice is pathfinder for NA or slightly boosted engine, and the gutted plenum for the more modified engines.

[Gritt]

SATAN wrote: I went with smaller plenum for faster response. My plenum= 100 cubic "
smaller in the back also. seemed like the right thing to do since all of the intercooler end tanks taper like this. That and i'm sure it helps reduce swirl so airflow is not bias to certain cylinders. Oh and a q45 TB

Seems like that plenum is all right. curious about that long curved elbow after the TB though?

why the pipe after the tb. my engine sits a little higher due to the wastegate. my intake sits higher, allowing me to utilize the stock fuel rail. this though made the tb above the line of the hood.

i got the idea from some high end boosted car or another, seemed to make sence to me. the intake is 3" in the front to accomodate the tb. tall enough for the fuel rails (barely) and the back of the plenum is "sliced off" with a flat piece for the vacuum fittings. my heads are ported and polished and like i said earlier it feels like it revs lots quicker. i have an n/a block so that will help with the probable loss of torque. maybe a loss of torque will help my launches...? i`m hoping breathing a little easier will help me take advantage of the cams, schnieder springs and p&p.

this thing was designed and built on speculation and what seemed like it would work. it may end up smelling like a big shitty diaper or it may work well. dyno later this week and track on saturday. results to follow!

[SATAN]

JK wrote:
Satan, as for plenum volumn. Optimum volumn of 1.5 deals with intake charge temp, that is where your smaller plenum could come up short. Only tests will bear this out.

I guess I dont understand why intake charge temperature would have anything to do with plenum volume. I was under the impression that you run a larger plenum for untuned intake runners to act as an air capasitor of sorts.
From one of my books

"The rule for plenums without tuned runners and with airflow restrictors is to design an intake plenum with one to two times the engine displacement (this is your suggestion JK) in order to providea large amount of available reserve air. In this case, air volume acts as a low-pass filter (capacitor) between the engine and the restrictor, smoothing the flow through the restrictor. Without a plenum, the engine would choke the air through the the restrictor with each intake stroke of a piston.
The rules change when using a Helmoholtz resonator . The Helmoholtz plenum makes a dense charge by use of pressure waves, using the same physics as a tuned-port intake runner.
V-8's sharing one large plenum do not work well as far as resonation-effects tuning, but the optimal tuning size would be 40 to 50 percent of total cylinder displacement. For a four-cylinder, 50 to 60 percent of displacement works well. For three cylinders or a six with twin plenums, each plenum should be 65 to 80 percent of the displacement of the three cylinders being fed. for engines operating closer to 7000 to 7500 rpm, (this is me) reduce the plenum volume by 10 to 15 percent. For a power boost at 2500 to3000, the plenum should be 30 percent larger."

since I dont have restrictors(wich I would think is a NON gutted plunum?) BUT I am not using a tuned runner design I tried to "split the difference" if you will.

[SATAN]

[quote]autoworkZ wrote:

I went with smaller plenum for faster response. My plenum= 100 cubic "
smaller in the back also. seemed like the right thing to do since all of the intercooler end tanks taper like this. That and i'm sure it helps reduce swirl so airflow is not bias to certain cylinders. Oh and a q45 TB

Seems like that plenum is all right. curious about that long curved elbow after the TB though?


why the pipe after the tb. my engine sits a little higher due to the wastegate. my intake sits higher, allowing me to utilize the stock fuel rail. this though made the tb above the line of the hood.

i got the idea from some high end boosted car or another, seemed to make sence to me. the intake is 3" in the front to accomodate the tb. tall enough for the fuel rails (barely) and the back of the plenum is "sliced off" with a flat piece for the vacuum fittings. my heads are ported and polished and like i said earlier it feels like it revs lots quicker. i have an n/a block so that will help with the probable loss of torque. maybe a loss of torque will help my launches...? i`m hoping breathing a little easier will help me take advantage of the cams, schnieder springs and p&p.

this thing was designed and built on speculation and what seemed like it would work. it may end up smelling like a big shitty diaper or it may work well. dyno later this week and track on saturday. results to follow!

Im not saying it wont work good by any means. Believe me I'm no engineer! I'm just wondering what effect the pipe after the throttle body will have on performance, with the venturi being that far up stream from the plenum. I would assume the 3" pipe would be big enough too. Just most plenums have the TB right on the plenum itself. Just curious is all.

[Gritt]

don`t take what i said the wrong way. i understand what you were saying. i was just trying to answer everybody`s questions. i`m hoping the donkey cock after the tb doesnt adversly affect anything. the stock plenum had a long neck post tb and so does the z33, just maybe not quite as long.

jason to answer your question, my old plenum was not gutted. but if this is what a gutted plenum feels like, WOO HOO! for free reving!

[2+2turbo]

ohh wow , why didnt you guys post this crap earlier, ive been busting my ass porting my spare lower intake manifold by a couple of millimeters , now im thinking about not using it t all.. damm you!!!

maybe i'll bolt it on just to see the difference between stock and my modified junk.

[Stinky]

I can't wait for him to come back from a good night at the track and say "Damn, I love the donkey cock!"