mark kibort

Yes, i still have this (probably more correctly called a vent) to the TB covers. remember, air only move to differential pressure. no pressure change, no flow. if you get some ram effect (at 160mph or something) then yes, there is probably some flow . because air is moving over this port, it does create a vacuum, like what is seen in the Throttle body to run vacuum advance, and fuel pressure regualtor relief. more than likely, you are getting a very small flow amount either in or out of these vent tubes to the TB covers.
yes, the dyno is the only way. but remember, if you dyno and test, be sure to seal the front and air box attachment points because there is serious leaking there under vaccum (and you WILL get vacuum with the stock tubes because thats what venturis do! by definition)

mK

Sharks

Mark, can you post a pic of the vented air box that you are speeking of, thanks.

JKelly

I'm more interested in the differences between idle temp (sitting at a stop light) and moving temp that Pappy measured. Heatsoaked components have little to do with heat transfer when all you have is hot air to breath (sitting at a stop light, not under WOT). If the car is breathing 150 degree air when you mash the throttle, the horsepower is not going to be delivered to the rear wheels as fast as if the car were breathing 70 degree air, right? If the car is breathing 150 degree air for several minutes or more, then all of the inline components would heat up even more from the 150 degree air being breathed in. The "significantly quicker" sounds like it comes from having a constant supply of cool air; with or without the car in motion. Therefore, I think this data has a great deal of meaning.

Also, from what I gather, I think Pappy has or will have quite a bit more than 240rwhp when he is through with his engine.

pappy92651

Hi folks,

This thread really started to run while I was gone. Good discussions. Thanks for all the input.

Mark, will you post pictures of your air box vent so that we might understand it better?

You used the phrase WOT at least three times. I would love to run the car at WOT on the street all of the time but I would be in jail by now . Now, I also agree with almost everything your saying, but we are talking about two separate issues, launch after sitting and continuous high speed running. These are two very different dynamics. Lets separate the two and recombine them later on.

A track car will see very little time at idle. A nicely insulated air system could be a waste of time because at WOT very little heat is transferred to the air charge. Increasing available air volume makes more sense. The only time a race car might benefit from insulation is during a standing start. I have seen a few races where an early lead developed because a car was quick off the line. A stock warmed up 928 is not going to be quick off the line. A 928 with a cool intake system will be quick (see Mr John Speake's earlier post).

A street driven 928 in LA California will be lucky to spend 50% of it's life above 60 MPH. We have very few opportunities to run at WOT for more than a few miles. Most of the driving is stop light to stop light. Here a well insulated intake system would be a major benefit (I mean the entire system, tubes, air box, and intake manifold).

The best possible configuration would provide higher available air volume ahead of the MAF and a well insulated intake system. Thats what I'm trying to accomplish. The testing is not complete. I have a project that Mr Ott wants me to try (ceramic).

pappy92651

Jim,

I found a new scoop that has a lower, wider profile. I will send pics when I start playing with it.

John,

The car currently dynos at 306 RWHP. It made more when we retarded the cam timing and The CATs were off, but it was so LOUD.

I will post my test results before and after the intake manifolds are swapped. WOT air charge temps will not be taken for the very same reason Mark Kibort stated, probably the same as ambient. With the car at speed the temperatures might even drop below ambient inside the intake plenum.

As you stated I'm more interested in preventing the associated intake systems from adding heat to an engine which is operated at idle, low speed, or at partial throttle. Porsche powder coated the intake manifold for more than one reason.

pappy92651

Thanks Tony. I got one!

GlenL

Yeah, sounds like a bit of "talking past" one another.

Maybe we've hit on why the later engines (GTS?) had those insulated tubes: so there'd be more power off the line after sitting.

To Mark's point, if you're not a WOT, then open it up more. As a minor track junkie, I'm also not really interested in stoplight issues. I want power out of the corner where I'm already doing 30-60mph.

The dyno test I ran (open airbox vs. tubes) confirmed the negative effect of underhood heat.A 5hp gain with tubes indicates the air was 11F cooler with the tubes, ignoring any theoretical volumetric efficiency gain! Now I'll be first to say the conditions were not perfect, especially not having a jumbo fan in front, but the results were impressive.

Couple of things:

The engine should run fine even with hotter air being drawn in. A bit of stumbling on launch indicates some other problem.

Ducting through the firewall is not a good option for street cars. The set-ups I've seen don't adequately prevent rain water from getting to the engine. Also, while I plan to have the car forever, cutting the firewall would reduce the value.

mark kibort

dont confuse hot air with restricted air. density is the discussion, and open air box vs with tubes is not heat related, especially if you saw 5hp diff, it is pressure drop related due to restriction.
mk

pappy92651

Also if you look at the GTS tubes they do not have the venturis / restrictors! They are straight through.

Tony

Good. You may have to order extension leads for it to reach the cabin though. I ordered 4 6ft'ers. Wires run through the gap in the fender/windshield area and in through door post.

Im tossing the cats and smog stuff back on mine today. I have to smog by the 17th. Im also pulling all the SC stuff off to give it a once over after 1000 some odd miles to see if any thing is rubbing, coming loose, leaked, cracked etc etc.
Im also tossing in the 24lbs injectors. Im not happy with the 30s at this point.
Also gives me a chance to use my new fender covers from Specialists courtesy of Santa this year.

mark kibort

Let me shoot a few holes in the points made so far. First, if you are at a stoplight and have 150degree heat soaked air and tubes, do you know what the volume in the entire intake system is? put it this way, it wouldnt take more than a 1/10 second at 4,000rpm (launch rpm) to clear the hot air. then, as we have already agreed, the heat transfer from the hot components will be less than negligible. at 300cfm (aprox the air flow at 4000rpm ) thats 5 cubic feet of air in a second. thats a cube 5 feet tall 5 feet wide and 5 feet deep.

So, there is NO real reason to try and cool the air, if the source of the air comes from a clean one. most cars , have intakes right in the engine bay, our 928, has a HUGE inlet and two duct inlets above the radiator that are fed by the big nose inlet. this is one of the best designs around. very hard to improve on this.

NEXT, is the biggest hole Ill shoot. if you are concerned with city driving and think that only on the race track, are you at WOT, because you dont want any tickets, then why are we having a maximizing power discussion??? if you want to have more power, push the gas pedal to the floor!!!!! anytime you are at part throttle , you are reducing mass flow to the engine via the throttle body (by definition, it means " CHOKE") so , it doesnt matter whether you have a pressure drop across a throttle body or have heated air , the result is less mass flow. there is no chance of the engine running rough wiith hot air. hot air is less dense . you want to have more power off the light, push the pedal down farther. if you are not running WOT, then this discussion is meaningless. want more throttle response (if you think you are preceiving less power off a stop light) then, try setting up the throttle cable to open farther for a given push of the gas pedal.

The point is, there is very little hot air volume at any time in the system. as soon as you floor the 928, in a fraction of a second, the air is burned and you are now just absorbing the heat soaked components much of which are in the plennum area anyway. brake ducts do a great job of keeping heat transfer. those fabric tubes quickly are cooled at WOT. where as the other components take minutes at wOT to disappate their heat. (also proof that there is not much heat transfer to the intake air. If they cooled over 10 seconds, then, i would buy your guys theory and goals. but in actually, there is not much heat transfer, due to lack of resident time of the air molecules near the surfaces as it moves toward the intake valves!

as a note , a problem of inuslating the intake plenum on the s4 is that they still will become heat soaked. (it will just take longer) now, where does the heat all go under WOT?? now, almost all of it has to transfer to the intake air and little is able to escape out. probably doing exactly what you dont want it to do!!!! something to discusss. anyway, it looks good, and that is the major benefit.



Mk

heinrich

yes. good points.

mark kibort

on the dyno, we have not seen any change with hot intake to cold intake ((cooler after several back to back dyno runs) with regards to mixture. the maf does an excellent job of metering mass flow. (regardless of temp) temp sensors are their for fine tuning only. O2 sensors are out of the loop at near full throttle as well. If the cool intake was worth pursuing, wouldnt we see much more hp when the intakes were cold on back to back dyno runs where the intake plenum goes from hot to the touch to almost cool? usually, we dont see much difference at all.

however, removing the air box cover /venting the air box to the rear of the car, sure has shown more than 5hp on numerous occasions.



MK

Tony

Before i got the fancy K thermocouple set up i used a basic Indoor outdoor thermometer from radio shack to get some basic starting point temps. It worked but it didnt really update quick enough to be of any real value for me.

However, i do know that in the middle of the summer here, the temp at the srceen of my MAF would be in excess of 155'f after idling at a stop light. It would climb IMMEDIATLEY upon stopping and in the length of a typical "red light" would reach that 155'F+ point . The starting point was usually appx 13'f above ambient which is where it seemed to run cruising around normally before coming to a stop. . My car did not stumble "off the line" but it sure is a pig in the summer. With those temps and 91 oct, your foot to the floor, i guarentee your knock sensors are sensing knock or very close to it.

Now with my blower i can get airtemps BELOW ambient at my filter due to the velocity of the air being sucked in. It drops the pressure and thus the temp.

Just my experience with temps.
Every little bit does help especially when you start dealing with some extreme temps like i do out here in Vegas.

pappy92651

Mark,

This is what I'm talking about. If your particular 928 does not drop power off idle when the intake is hot then you have modified something to compensate for it. If you remove the hood or bring cold air to the intake tubes the car launches like a rabbit. All stock S4 / GTS models behave the same. The computer is leaning the mixture because sensors are telling it to. With a very lean mixture at launch power is reduced and the engine is likely to ping causing the computer to retard timing.

Cooler intake charges do increase HP. It does show up during dyno testing.

Home work: What is an intercooler used for?


Tony,

You have experienced the same thing. This is true of every S4 that I have driven. They lack power from a standing start until they cool off.