IcemanG17

Has anyone upgraded thier air intake tubes to something bigger? Did it yield an dyno proven results? I've seen 3" straight intake tube kits for fairly inexpensive, but is it worth it? Any thoughts?

SteveG

Porsche claims these are aerodynamically designed with the venturi to eliminate some pressure/sound waves feeding back from the intake. I may not have expressed that correctly, but the point is they were designed with a purpose. Others may have a different opinion. Some feel they benefit from a straight tube with aluminum insulating. Like red paint they think it makes their car faster. I think Porsche took into condideration the rate at which the air passes through and saw insulation as negligible. God knows they are prone to over-engineering.

Greggles

It doesn't???

heinrich

removing the screens from the maf; and raising the airbox, and using a smooth air filter all make measurable differences on the dyno.

Shane

Of course it does, he is just sore because he has a slower black one!

SteveG

Black is faster at night.

mark kibort

the main gain is to get more of the cold air from the front of the car. as feable as the resonance sound reduction theory goes, if you look, the tubes were probably just designed to fit in the engine bay. straight tubes are definitely better, no noise is heard (trust me, porsche engineers were not worried about the intake tubes as far as performance) . we measured some vacuum in the air box at the inlet. if the tubes have any restriction , as they do, the air would leak in from the sides of the air box attachment. we found a lot of leaking around the filter with the stock clamps!!! .25Hg vacuum with the stock straps, vs .5mmHg with a sealed and clamped down air box. this much of the reason that the venting of the air box is probably the best bang for the buck. Anderson got as much as 10hp by just having a filter open vs the cover and tubes. we went from 295 to 335rwhp by removing screens, venting the air box and fixing the flappy.

we didnt see any gains with the raising of the air box with the spacer or rounded inlet over the MAF, but gains have been seen on lower powered S4 s. i wanted it to work, but it just lost us about 5hp on its own. Air flow optimization is a lot of work and experiementing. lots of things are counter intuitive.

there is no use for the plastic tubes, other than fit. anything you can fabricate will probably work better. venturis, neck downs, etc, on the intake, are used to reduce hp, not make any!

Mk

docmirror

I hate to sound like Dr Ruth, but 'bigger isn't necessarily better'. I've been looking at the intake stack setup, and I swear it looks like the worst design I could come up with. Not only do they have long tubes from the front to the back, but they also draw air from the little snorkel out of the cam belt covers(90 model). This seems like the inverse of an intercooler, maybe an interwarmer? If you are going to mess with the intake stack, ala, K&N, cold shot, etc style, it's gonna take a lot of fiddling. Like turn the MAF around so it faces forward, remove the cleaner asm, pull the tubes, install some kind of insulation barrier, air cleaner, and a straght shot into the intake manifold. All for the value of not preheating the incoming air charge. Lots of work. What result? Don't know....

Hey, how about a hole saw at the back of the hood, and a snorkel sticking up into the cold air steam. Well, maybe not. Brendan posted a fab link a few days ago about air flow that was kinda engineer-speak. So I just had to read it. It boiled down to: What we think would be logical in air flow dynamics, is usually exactly backwards in practice.

I remember a most important formula for cam height that defines the efficiency gains once the lift exceeds .25*vavle dia to be minimal. Soemtimes even detrimental. Area of the open column then exceeds the area of the valve head disk. I think we might experience a similar flow dynamic, although less critical in the intake tubes. Sub-sonic air flow in enclosed spaces is truely an art. One I'm not that familiar with, but like I said, everything that seems logical, might just make flow worse. The heat buildup on the other hand is clearly detrimental. More heat = lower density.

mark kibort

I think Dr Ruth would take anything she can get right now.

as far as intake tubes and intake design, bigger is usually better, but its really about flow effieciency. a bell mouthed inlet to a MAF can flow as much as a straight tube 50% larger. so, comparing apples to apples, flow theory is pretty straight forward on the pressure drop side of an intake system. this is why, you will see ALL race teams with larger air boxes, large inlets, large plennums to reduce the amount of pressure drop (hp loss, mass air loss, density loss, etc) along the way. Now, stop when you get to the intake runners and heads, as their tuning is much more of a science and thats where tough stuff begins. (this especially includes heads, port work and valves) Lots of flow work has proved that better designed smalller ports can flow more than larger ones. but again, thats after the plennum and air inlet areas. In the air inlet areas, larger will aways be better, especiallly from the throttle body out to the fresh air. no as far as heat, the air flow is moving much too fast for any resident time to elapse to transfer much heat. most of the flow is in the center of the tubes anyway. However, there is some losses there. venting to the rear of the engine compartment is one way many of the 928 racers can keep these losses down and utilize the higher pressure zone at the base of the windshield for far more gains than in the heat transfer area.

Again, look no farter than ANY pro team that has done much of this work and verification for you. even still, some are still misled in trying to get cold air, rather than high pressure air. all in all, that part of the equation is just shaving hairs. remember we are talking .36psi at 160mph and .08psi at 80mph in an amost perfect intake design (out of boundary layer, like a big dragster inlet). so even the high pressure zone will hardly be used /realized in most racing unless you are running only at Road America!! However, a venturi or neckdown/pressure drop in an intake will ALWAYS be there anytime you are at WOT.

Most of us that have been to the dyno often, can show the gains of opening up the air box to start

Mk

rob rossitto

heard about the other stuff, think mr ott has most of it on his web site, but
fixing the flappy? was it broken or did you fix it into a specific position?

very interesting... kinda wondering what to do w/my stroker's increased needs... good timing...

mark kibort

No, just fixed a flappy that wasnt working. all that should have done was boost up the 4k range torque.

I think there is a lot of things you can do with the stroker, the hard part is determining where to start. Between Andreson and M. Tomas, there is a lot of great information there. 485-500+hp on a 6.4 liter with intakes, manifolds, Motec, engine building details, etc.

mK

BC

I've been trying to figure out what I will do with the intake on the 78. The 89 is no issue, as it will have 14 or a bit less pis bring rammed down its throat, so....

There will be no MAF on the 78 or anything else between the intake valves and the filter except for the throttlebody. So I'm hoping for some gain there.

That filter location on the 928 is somewhat determined by the Water neck arrangement. Going out the front, I think, would mean moving the water fixture up there....

What about cutting into the fender like Tony in Vegas did? I'm not sure what side, but...

rob rossitto

that flappy is one slick item...

IIRC, M&M (mark&marc) noted the stock intake manifold is good to about 450rwhp or so w/stroker/valves/cams/motec/piggyback stuff.... manifold changes like the dual TB threshie CF/madge stuff put them into the 500+ NA range, IIRC...

I'm just using a stock gt intake, ecu -so I'm kinda limited to sub 425rwhp range.... did find a larger, custom air box w/ott velocity stack... but also kinda like the idea of going straight out the front instead of all the 90deg stuff in the stock config - assuming it's not a plumbing nightmare... IIRC, there's a bit of stuff in the front already... of course, the more stock it looks, the easier to pass smog too... lots of trade-offs to ponder... IMO, deciding cams/valves was easier


happy holidays!

Nicole

Retired Porsche Engineer Jörg Austen writes in his book "Porsche 928 - Die technische Dokumentation des Transaxle-Achtzylinders", in the chapter about model year 1981 (B Program):

"New intake mufflers between the vehicle front and the airbox prevent the noises that occur on acceleration, which add to the exhausst and mechanical noises during the measurements for legalization in certain countries. The tubes are designed as noise reflecting venturi [jets???] and do not obstruct the air flow."

Take it for what it's worth...

FlyingDog

Since most of our cars are louder than stock and higher HP than stock, I don't think we need to worry about air noise from the intake tubes. The tubes may not be a restriction on a 220HP 1981, but could be on the 300, 400, 500+ HP cars.