Mongo

What does the black bird sound like on the 928? The lengthened intake pipes should improve the torque, just like the dyno says.

Louie928

I've explained the mods before, but basically raise the air filter, and air filter box top, about 3/4" or as much as space allows. Make an insert that goes in the bottom of the air box to give a larger radius turn into the MAF. The raised air filter helps the top end by about 6 hp and the larger radius into the MAF helps the bottom end by about 6 lb ft. We tried it on Heinrichs S4 and it did about the same, Mike Schmidt made one and I think about the same gain on his. It worked on my 5.0L GT and my S4. Mark Kibort tried somethng like it, or at least the larger radius to the MAF and saw no gain, maybe a slight loss. I don't know if he raised his filter and air box top though. Mark has holes cut in his air box top to admit extra air but with the big radius insert would still need to be raised because it puts the filter too close to the radius insert. I tried no air filter raising along with a K&N filter and it was pretty horrible. You have to have both. Here is some pics. The grey air box insert is one I made. It has a carved balsa wood core covered with bondo and primer sanded smooth. The pink styrofoam air filter spacer is a crude one I made for testing only. It worked so I made another from 1/4" x 1" wood strips bonded to the air box with RTV. It's a little less crude and I don't have pictures of it. The nice phenolic air filter spacer is one Mike Schmid made. Mike's air box insert is made from glass fiber cloth in a mold.

https://rennlist.com/forums/attachme...d=210801&stc=1
AirBoxInsert01.jpghttps://rennlist.com/forums/attachment.php?attachmentid=210781&stc=1
Flow3.jpghttps://rennlist.com/forums/attachment.php?attachmentid=210780&stc=1
Flow5.jpghttps://rennlist.com/forums/attachment.php?attachmentid=210806&stc=1
Spacer2.jpghttps://rennlist.com/forums/attachment.php?attachmentid=210808&stc=1
Spacer1.jpghttps://rennlist.com/forums/attachment.php?attachmentid=210804&stc=1
AirBox1.JPGhttps://rennlist.com/forums/attachment.php?attachmentid=210805&stc=1
AirBox2.JPGhttps://rennlist.com/forums/attachment.php?attachmentid=210802&stc=1
AirBoxSpecer1.JPGhttps://rennlist.com/forums/attachment.php?attachmentid=210803&stc=1
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AO

I think it's the orange tubes that provide the power... Everyone knows orange molecules are more slippery.

Louie928

Dyno testing shows no improvement with the orange tubes vs the stock black venturi tubes. The rationale is that Black + Venturi = Orange.

ew928

Been wondering why the 928 air filter is assymetric. This explains it. A properly installed paper 928 filter has it hunchback over the air inlet placing it further away from the inlet.
A K&N oily filter is flat. That thing sits a lot closer to the 928 air drain than the paper filter.
So where's the HP gain in that???

Thanks Doc Ott. 1 less thing that baffles me.

So when's someone going to mold out a bunch of air filter spacers/inlet radii smoother and airbox strap extensions for sale?
So if one adjusts the hood to sit a little 'high' at the back end one can jam the air filter a little higher.
My hood sat at little tilted for a while and people were wondering if I had a forward hinged hood like them Jaguars.

John Speake

I'm fairly sure that my S2 airfilter box is deeper than the S4 and later ones, with more of a space between MAF and bottom of the airfilter element.....

Louie928

1. There is no gain for a K&N on a 928 over the stock paper filter. The proximity of the filter as well as the very coarse screen pleats mess up the air flow into the MAF.
2. Anyone who wants to get really rich very quickly can supply the air box mod products.
3. I think DR's Blackbird filter setup accomplishes the same sort of improvements to get the air directed down into the MAF smoothly.

Louie928

Yes, the pre S4 filter boxes are deeper and should work better. The '85/'86 air boxes are good too and may fit on an S4/GT/GTS with some modification. They already have the larger radius opening to the MAF.

worf928

Thanks Louie. What made you decide to use the reader on the dampener as opposed to the spark pickup? Anecdotes from others in 'the dyno-know?' Or your own observations of the spark pickup?

Yup. Those charts look really good. The ~1 - 3 hp difference at various points in the otherwise identical curves are what I would expect (and hope) to see.

You mentioned previously...

Have you seen these 'squiggly' S4 curves on your dyno when using your optical pickup?

I agree that the derivation of engine output data is unaffected by any inaccuracy in the engine speed derivation. The question in my mind is how the engine speed values and engine output values are correlated to produce the final RPM vs. output graphs we commonly discuss. In the case of both measurement streams, the actual values can be nothing other than the times at which pulses were recorded. All values are calculated based upon the periods between series of pulses.

I do not know the method of correlation. However, at the most fundamental level the only common factor between the two data streams is time. (Absolute knowledge of overall gearing would allow for one rotation speed to be calculated from the other, but, gearing is usually calculated by the dyno software. The method you describe previously wherein the gearing is 'calibrated' isn't going to be very accurate as you yourself write.)

What I'm really trying to get at is: are the "squiggly lines" seen on lots of dyno charts real? Or are they measurement artifacts? I've seen charts where torque oscillates up and down through the whole chart by 10% or more with a period of a few 100 rpm. I have difficulty believing that the motor is actually doing that. Especially when I can produce a chart with similar oscillations from a smooth power curve by adding a few percent of noise to the rpm calculation. But, without getting my hands on the software code, all I can do is ask 'black box' questions of folks that have access to the 'black box'

mark kibort

louis and i talked about this design of his for some time. it was EXACTLY what i was thinking about, to make a more "bell mouthed inlet for the MAF. even, right down to the spacer. So, i did fabricate a .5" spacer but was not talented enough in fiberglass to attempt the inlet, so Louis graciously gave me one of his prototypes, which i modified to fit. For all the reasons we talk about, it made perfect sense that it would improve the air flow and reduce pressure drops at the inlet. HOWEVER, for some unknown reason, I saw a loss. I didnt want to beleive it, so we kept testing it, but it continued to show a loss. Thats also when i put on the large cone filter with a unique bell mouthed inlet, internal to the filter and it showed the same loss. (picture a big cone filter sticking straight up in the air going about a foot up above where the hood would be.)

Air flow dynamics are not intuitive, and many variables need to be addressed to predict the outcomes of any changes to the already proven stock air box. Also, part of the reason that many see gains with the venting of the holes in the rear of the airbox, is to provide less restriction, which have measured with some of the most advanced pressure measuring devices. (industrial control type equipment) we saw an even bigger pressure drop on the S4 air box when we sealed the airbox up around the filter area.. the only way we got the pressure back, was to vent the rear of the air box and add an eRAM positive pressure device on the rear of the air box. (most S4 and pre s4 air boxes are pretty leaky, so it could be the reason that you see a 0 gain with a KN vs a stock paper air filter.

another interesting observation was the increased air flow through an eRAM by use of a filter. (we could measure lbs of thrust) with a filter vs a bell mouthed inlet, showed near the same output, basically proving that the filter does reduce turbulence through a large diameter inlet. we verified this on a flow bench as well. something to think about. sometimes, the flow without a filter could be more turbulent than with a filter, unless you have a nice bell mouthed inlet. maybe the inlet i created with louis' help, needed less filtration to be more effective. I dont doubt that he saw the gains he did with his tests, but there are some other subtle vairables that are somehow different.

I do like the blackbird design and should probably consider testing it out. however, i would think that a 3rd vent in the rear might be a good modification to it, since there is a sourse of cold air, without having to traverse a lengthly tubular contraption.

looking forward to hearing about other tests to confirm its hp gains.

mk

mark kibort

i dont have screens. that could be the difference! (i just though of this)
maybe with the screens , this kind of "riser" and "bell mouthed " inlet brings back the efficiency lost with the MAF screens. Louis, did you have both screens still???

Do you know that the Harrier jump jet, couldnt even get off the ground with screens to prevent ship-hands from being sucked into the jet inlets? screens are murder on inlet efficiency, so they were removed and only a few sailors got sucked into the Harrier's inlet over the years.

Now thats a pressure drop!

mk

Louie928

Hi Mark,
No screens for me. They are supposed to promote laminar air flow into the MAF, but I always get a bit better results without them.

Louie928

Dave,
The optical sensor is what the dyno company recommends. They said there would be too much noise with attendant spikes and holes in the dyno curve using a spark wire inductive pickup. Also engines using coil-on-plug setup isn't possible to use the inductive pickup. I tried the spark pickup because it is easy to connect, but it gave poor results. Some runs ok, some runs were very rough. Sometimes there'd be so much garbage in the data, the dyno program would freeze so I gave up on it and went to the optical. The dyno curve with the ignition pickup would have sharp spikes, not the wavy curves you see on some 928 charts. I've spent a lot of time trying to get those waves out of the 928 dyno runs. Most of the waves are due to poor tuning. Some waves will occur above about 5500 rpm and can't be eliminated by any amount of tuning. The preeminant authority on LH 2.3s told me that was because the processor just couldn't keep up with all the tasks it has to do at elevated RPMs. Some tasks are skipped until the next time around so it all gets a little shaky. Careful Sharktuning can really minimize even the upper waves as you can see on my dyno graph of my S4. I suppose some of the waves could be generated in the dyno equipment too but the wave period is often too regular to be random noise. I think it is from slight surging in the engine as the LH/EZ-K is fighting to get the mixture right. Possibly an inop WOT switch where the LH may stay in closed loop under full power. Here is a file of my GT showing it in stock configuration and with X pipe exhaust, piggyback computer tuned on mixture and timing, and the air box mods. These were all done on the same (very long) day on the same Dynojet dyno. Note how wiggly the stock curve is and how much smoother the modded curve is. It went from a struggling engine to a happy engine.
https://rennlist.com/forums/attachme...d=210931&stc=1
MyCar_Stock&Mods.JPG

mark kibort

Oh well, there goes that theory.

i dont think the screen will promote laminar flow, but i can make fore better distribution of the air around the MAF sensor. (in theory) However, i saw better fuel and more hp as by removing the screens and all the the other air box mods.

by the way, what were the mods that took those graphs from 290 to 325rwhp?

mk

Louie928

Hi Mark,
This is sort of OT so sorry, and if it continues in this direction maybe move another thread. However it is related to getting better air flow into the MAF and exploring why the dyno curves were so wiggly both before and after the BB install.

I was thinking after I wrote about the laminar flow screens that I was probably wrong. I'm trying to remember what the screen purpose was and I thought it was to restore laminar flow. However, just looking at the MAF will show that laminar flow through it is not possible. It's just to rough and crudely made. Besides it takes several pipe diameters in length to restore laminar flow in a pipe after a disturbance. I could go along with the idea that the screen help to smooth out turbulence and rapid changes to air flow that would otherwise exist at the MAF inlet. Other experiments I made indicated to me that without the screens, you do need to pay more attention to keeping smooth air flow into the MAF or you get a real lumpy/wavy dyno curve. Have you looked at the MAF output with an O'scope? It's really a noisy signal and not what you'd expect at all. Must be a lot of turbulatin' going on.

The mods to my GT were not a lot. X pipe, dual 2.5" rear exhaust, the intake mods I mentioned, piggy back (Dastek brand) tuning of the LH/EZ-K for hopefully optimum WOT mixture and spark timing. It did have Autothority chips so the optimization was on top of those. They could even have been worse than stock chips, but the 290 stock power is about normal for a GT. The chips did give me about 6800 rev limit which likely contributed to my rod bearing failure. Chalk up another win for chips.

I'll insert a pic of three dyno runs showing the result of tuning. The bottom one is with just the exhaust changes. From 290 to 310 with the exhaust. The middle one is with mixture tuning which brought it up to 321. The last one was the effect of timing optimization. I was able to advance quite a bit at the lower end, about 6 - 8 deg IIRC, for good torque gain but not so much at the top, maybe 2 degrees for 3 or 4 more peak hp. Notice how much smoother the curve is when the tuning is better than when first started. Most of the smoothing is due to timing being better. The Sharktuner results should be better due to the ability to get more exact optimization not to mention less dyno time. Checking the dyno run numbers it took 42 runs to get this done and most of the runs were to do the timing.

https://rennlist.com/forums/attachme...d=211008&stc=1
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