pappy92651

Hello Rob,

Yes, a change in the fan configuration would help. I don't think that bigger fans are required, instead a fan switch that triggers the fans at a lower temp. I have not been able to find anything that fits in the system. Any ideas?

The other factors are better cooling at speed and more air pressure to the air box. The diverter increases smooth air flow through the radiator at speed. My temp gauge is now reading below 1/2 at cruising speeds and is down around 3/8 at 100 MPH. The pressure gains from the hoses are however minimal. They serve better as a source for cold air. Without the diverter the turbulent air rolls around against the hood / radiator, picks up heat, and then enters the air tubes.

Yes, It's all about keeping it cool at all speeds.

Tony

I have the GTECH RR with PASS software. A bit $$$ but well worth it. It has a great feature where you can email the GTECH files to one another and with the software be compared to your own car or others...Ive run mine agaisnt Ferraris..Vipers etc etc on the software.
Im not slamming you at all, but remember, a stop watch is only as accurate as the reaction time on the finger running it and the eyes scanning the rapidly rising speedo across 60mph. A least the GTECH is hands free and records everythign for you.

rob rossitto

pappy, you've done some really incredible research - automotive OEM quality stuff IMHO...

I picked up the devek aluminum "sale" shroud, dual 1300cfm spals, might put some extra vents w/rubber flaps in "dead" spots for extra flow/cooling at speed... was hoping they'd push more air than the mech stuff through the compartment at idle and keep air moving through the front too...not a lot of room for much else as you know/thought about louvers in the fender wells as a last resort, but your diverter seems like a clever way to further isolate the intakes...also did jet hot on the headers to keep temps down, but was advised NOT to use header wrap/although I suspect it would help a bit too...

funny thing about gtech vs dyno - my race bike wrench sold his dyno (al holley) cause it never seemed to be accurate when bikes were run in the 'real world'... something about varying loads and wind, rates of accel, etc... suspect there's a place for both, but I'd probably trust gtech type stuff more for a real world measurement on most airflow type mods...

have you experimented w/the ott velocity stack and his airbox mods (larger bottom section)? I've got one coming, so if you want to "borrow"/experiment/ck it out/etc till I need it, I can leave it at greg's for you... claims of 8hp and better throttle response on a stock (+/-) GT were made by PO who now runs a FI system...might be interesting w/your other mods...

AO

Just thinking here... all very interesting stuff by the way... I certainly see the benefits for ducting cool/cold air. No problems there. Where I'm having difficulty is understanding how this will generate ANY positive air pressure (a la super charging). Somewhat akin to Wally post regarding stalled air after the radiator, wouldn't the same be true for the air filter? The only way you'd be able to ram-air the 928 is to completely seal the intake tubes, filter box, etc. If there were any holes or leaks in the system, you'd lose all the pressure benefits.

Am I wrong?

Since I don't see any attempt to seal the system, I think your goal should be going after cool air alone. This may give you some design freedom. Good luck.

drnick

steve, i asked mark k about his airbox mod and you can see pics of it on his website. they have simply ducted air directly from the base of the windshield through the stock cavity there (with wiper motor etc) and into the airbox. i can remember a concern expressed about water ingestion but when i asked mark he admitted to having driven in the rain with no ill effect on at least one occasion when it was raining very heavily. this strikes me as the most striking method of improving the intake system.

pappy92651

Tony, I agree. I need the means to log results and spread sheet them. I'm getting consumed by consulting work again. So much new equipment to buy. Too bad I can't spend all my time on 928 designs. That would be fun, but no money in it, at least not enough to live on.

Rob, Thank you. I think that we are all of the same opinion. Try it if the theory is sound. Many designs that we think will increase performance in fact do not. Only one way to find out after the math is done, try it.

Ceramic coatings work very well on exhaust systems. Wraps work until they leak minutely. As small openings allow air to contact the header a temperature differential occurs. If the delta becomes great enough we get cold spots on the tubing. Micro cracks begin to appear. These eventually result in leaks and even complete fractures. On cars which have disposable racing headers this is not important.

Louie provided the plans to create his stack. If you have one I would love to try it. I will be at Greg's on the 10th. Perhaps you could lend it to me. I would love to give it a go and provide a report.

Andrew, I think your on target. I am measuring a slight pressure increase over the stock system, from 1.2 PSI to 1.5 PSI. This is not a large increase in pressure at 100 MPH. The new induction circuit is bringing in colder air. If you were to attempt a complete seal the entire system would have to undergo a massive change. The air box would require an outer seal, the EGR would have to be blocked, the cam covers would be bypassed, etc. It is not a simple undertaking. The gains would probably not be worth the effort. In fact I suspect that the wind shield duct / scoop probably adds cold air to the air box in the same way but adds very little positive pressure increase because you still have a leaky system. I have noticed two very strong peaks in my torque curve from 2000 to 4000 RPM and from 4500 to 6500 RPM that are only interrupted for a few milliseconds as the resonance valve opens. The car pulls like a freight train up to red line. I still have not had time to alter fuel and timing on the dyno. The car runs so well that I'm afraid to fool with it.

Nick, I'm sure that the windsheild scoop works well. Several people are running it. I think the reason that it works well is due to cold air induction (see previous to Andrew). The pressure gains in a system that is not fully sealed would not be that great.

I'm moving on to another phase of the experiment. Rob had an idea that I am following:
So if we turn the fans on earlier, we keep the water temp lower and reduce heat rising off the front of the radiator. This can be accomplished by adding a second switch in parallel with the aux fan switch on top of the intake (since we are also trying to keep it cool). Or an NTC thermistor can be installed in parallel with the switch that will reach 850 Ohms at 65C (150F) turning on the fans until the temperature drops to 60C (140F). Realize that this is during a stopped idle condition. The fans will be running while stopped, at low speeds, or on extremely hot days (as though the AC were ON).

rob rossitto

just don't tell anybody where you got it, or you'll be in the padded cell next to mine...

airbox w/stack shipped yesterday, I'll let you know when it's here/get it to greg asap for you...

guess I'll settle w/jet hot, although maybe a compartment diverter/heat shield could seperate the exhaust heat from the top 1/2?... just what we need, another shield to mess with...

math 1st? tried that on my pistons and got into a real mess... I'll just follow anyone's lead that works - and it sounds like y'all are onto a thing or two for sure (sorry, superbowl drawl/hangover)...

blau928

You could also put in a larger capacity rad that would hold a bit more water to give you a bigger reserve/absorbtive capacity for those hot days.. That coupled with the fans would be interesting to monitor..

I like the thermistor or aux fan switch in parallel to the temp switch...

Oh, cold water and warm oil makes a happy motor happier...

my .02,

pappy92651

Rob, Thank you. I will give it a go. Just let me know when Greg gets it.

The diverter (as it is today) might not be required if the thermistor solution works. The cooling effect is great. With a thermistor in parallel with the aux fan switch a half diverter (like the one Louie designed) might be effective. That would eliminate the hoses to the nose. My water temp on the freeway is down near 1/3 on the gauge. It never, ever, ran that cool before.

Richard, Agreed. I ordered a selection of thermistors for the test. I am using a Devek radiator which will alter the cooling result (more efficient and higher capacity). I expect to see a different fan duty cycle than stock, but with more on time at low or 0 speed. The goal will be to keep the water temp between 1/2 and 1/3 under all conditions.

bcdavis

It would be interesting to research what the new Subaru uses, to keep water out of their hood scoop.
Assuming it is functional...
If so, a *really* low-profile version, over the airbox, might do the trick...

rob rossitto

not sure on "correct' temp limits, but w/my forged stuff if I ran too cold it might be an issue... any idea what 1/3 on the pcar gauge relates to in the C or F scales?

pappy92651

bc, I have a WRX hood scoop and tried it on my cut up hood right over the air box. The top of the air box was cut in 2 places and foam seals connected the openings. I got very strange results. The MAF voltage was all over the place and the car would not idle. In order to make this work the stock MAF would have to be tossed or shielded from turbulent air. Many of the race cars tossed the MAF long ago. Try running the car with the top of the air box off and you get similar results. For those who are just tuning in this applies to LH cars (86.5 and up). I gave up before I got to the water problem.

Louie and I have been discussing the induction system. Several people have tried similar experiments and the results were not good. If the stock MAF is retained the air must enter from the sides. The hood of the car is also a negative pressure zone which creates additional issues. The areas that have positive pressure are the base of the windshield and the nose. I am tempted to reinstall my nose snout, install a fully closed diverter, and measure the air box pressure again. I have not tried a closed diverter yet. All of the air would come off the top of the nose from between the headlights. Any water entering the nose snout would utilize the stock Porsche hood drains (4 traps in the side cross members).

Rob, 1/3 on the gauge is roughly equivalent to 78C or 173F.

pappy92651

BTW: Speed Channel has been doing an Acura RSX build up (track car). Guess what? The same principals are being applied. Low temp thermostats, fan switches, radiator, insulated intake tube, air box blanket, etc. And for nay sayers, this is a track car, not a street car, and they are posting significant dyno gains (also reduced lap times).

Tony

I cant recall the numbers but i can find out exactly again next time i drive.. My guess is it will vary a bit from car to car. Ive found the stock gauge very slow to react compared to my Autometer gauge whose sensor is about 2 inches away from the stock pickup.

pappy92651

As measured with a type K at L2, my car: 1/3 on the gauge is roughly equivalent to 78C or 173F