Any thoughts on the heating issue on the IM? Ive been looking into phenolic spacers as I have had good experiences with them on 16v engines before. I see the potential of even more gains on this motor under certain circumstances, though the application will be a little more difficult to construct.

-Sean

You can use Glyptal as an insulator: <a href="http://edsaudi12v.com/audi/imworkshop/27.htm">http://edsaudi12v.com/audi/imworkshop/27.htm</a>

Also, use headshield under the IM: <a href="http://edsaudi12v.com/audi/imworkshop/28.htm">http://edsaudi12v.com/audi/imworkshop/28.htm</a>

Mance, I have been wondering lately, why not use Glyptal on the IM upper half as well? (All this area between the secondary runner inlets)...
<img src="http://edsaudi12v.com/audi/imworkshop/intake39.jpg">

slows and insulates migratory heat from getting to the top of the manifold where the IM is VERY much a heat-sink.

More related info above as I answer the original question in this thread.

...I also think that is a very interesting idea.

Even though the manifold does cool with the car moving forward, that heat is taken back into the engine with the intake air. That may be good for economy but bad for power, correct? My water temp gauge really only peaks when I'm not moving, perhaps these would help for exactly then?

Would longer bolts be required? Could the upper be isolated from the lower as well as the I/M from the heads? There looks as though there would be room under the hood.

If the I/M plenum &amp; runners are made larger &amp; longer, would the area under the power curves be shifted to a lower rpm?

Carving these spacers would be a big job.

Firstly because no matter how thin it is it alters the mating face geometry between intake manifold and heads "diagonal" mating surfaces. Any time you add "any" thickness to the IM-to-head gaskets you also must raise the IM by half as much as the additional spacer thickness. That is to say if you add a 1/8" thick phenolic spacer then you must also now use 2 gaskets (1 on each side of the phenolic spacer). Now when the IM bolts to the heads it WILL be raised higher by 50% of the phenolic spacer thickness plus 50% of the extra gasket thickness. Once you do that your IM runner mating flanges and head runner mating flanges no longer line up. You can gain some back by "gasket-matching" but that task now is not just "grinding" alone but also "filling" with an epoxy or similar filler to eliminate the "step" created by raising the IM but not the head. On the 12V head that risks grinding into the water and oil passages when trying to gasket-match. And "most" phenolic spacers are twice as thick as 1/8" in order to be more efficient. With "any" spacer material between IM and head your IM intake runners will ALWAYS mount higher than the head intake ports! And as IM goes higher on any V-engine so does the horizontal gap grow between IM outlet mating flanges and cylinder head inlet mating flanges, again because of "diagonal" mating surfaces. It becomes a Catch-22 situation ad infinitum. This is only the case on V-engines and not single head/single deck engines tho in the case of those engines IM's do move further away from heads by the thickness of the phenolic spacer but that isn't necessarily a bad thing as it does increase velocity. With inline engines it's a single, usually 90 degree single plane issue. With V-eninges it becomes a compound issue between two diagonal mating surfaces, ie; every time something goes vertically it has to grow a proportionate amount horizontally. If you make phenolics for a V-engine (yes, it can be done but fretfully spendy because they are "wedge" profiles rather than flat) then ever overheat/warp a head on that engine and you have that head or both heads milled flat any phenolic spacer just became a paper-weight and ya start over. On non-V engines you simply re-use the spacer after milling.

Secondly phenolic is only meagerly successful in keeping heat down in enclosed areas. Works great on motorcycle engines due to the engine being out in the airflow. On car engines it's good for about 20-30 minutes of slowing heat from migrating back into the part your trying to keep cool via fastener migration and phenolic transference. The thinner a phenolic spacer is the less efficient it is. But that's a double-sided dagger because the thicker it is the slower it is to cool. Heat migrates into the part you want to keep cool via the bolts running through the phenolic and phenolic heat saturation and subsequent contact surface transference from the phenolic into the part you're trying to cool. Phenolic, while a decent, not great insulator is terrible at shedding heat. It's FAR slower to cool than either steel or aluminum. Once hot phenolic wants to STAY hot unlike the metal parts it's sandwiched between which would otherwise cool much faster if phenolic were not there. Phenolic also works better on 2, 4, 5 and 6 cylinder engines when machined as individual runner spacer-insulators rather than one single giant spacer with 2-6 runner ports machined into it. Reason being is the smaller, individual spacer rings will absorb and transfer less heat than a single, larger mass single spacer-insulator with 2, 4, 5 or 6 ports in it which is absorbing heat over 100% of it's cylinder head contact surface area instead of just around the small area of an individual runner port.

Thirdly the IM on the 12V is a VERY cool-running IM indeed! Only time the top surface is really "hot" is in summer months while parked at a red light, idling with the AC on. Any time you're moving forward the IM starts to cool very rapidly, least if you're running a stock airbox and not some cone setup. On commuter streets the IM is only slightly warm to the touch, even cooler at highway cruising speeds and on track during 100+F days the IM is actually "cold" to the touch after running at WOT. Try pulling into the paddock sometime after a track run and immediately place your hand on the IM top. It's surprisingly COLD!! I mean probably 25-30*F colder than your hand in spite of it being over 100*F outside!

Oil is very similar to phenolic and a basic understanding of how phenolic is made goes a long way in understanding why that is. They both started life as the same product. Oil/Phenolic are both VERY good at absorbing heat and VERY bad at shedding it. But if they are absorbing heat from one surface and in constant contact with another surface they will transfer that heat to the next surface in sequence... and so on... and so on. Phenolic can only "slow" heat migration but NOT reduce migratory temperatures or prevent it. It's the law!

How much heat would it really be blocking? Wouldn't most of the heat be migrating from the lower IM and conducting though where the top/bottom meet? (Not doubting/contradicting what you just said, but trying to understand it). I can see the Glyptal blocking radient heat coming from "inside" the IM, but wouldn't that be quickly cooled by intake air?

So, if we shouldn't use Glyptal there, is there any alternative for smoothing the surface/removing "dead air" spots?

our manifolds are legend for accumulating. It's the same reason I've used Glyptal in over 30 years of engine building in engine blocks, sumps and crankcases, ie; to allow engine liquids to flow easier, with less friction down into the sump via gravity or ancillary pumping device than the sand cast/rough textured block walls and/or passages/ports and gallies. It's a "slicker/slippier" surface for oil solids to run off of and gives them no surface which they can adhere to. It's a "glass-to-cinder block" analogy. Stack a pane of glass and a cinder block vertically or horizontally side-by-side. Place a drop of oil on both near their top and see which one runs down and hits the surface below either first. On the horizontal see which you can blow off the glass or cinder block with "breath-power" first and easiest.

Then compare the amount of blowby soilds on the tops of a disassembled IM compared to the bottom. It becomes a case of diminished need on the top.

Bottom line at least for me these days is the Glyptal stays only on bottoms of IM and ONLY to prevent the buildup and tenacious grip of blowby accumulation. I doubt having it on the top harms anything. I couldn't even discern a 1 degree variance when using it on the bottoms via a temp probe an an oscilliscope. But I struggle with seeing any "need" for it on the IM celing.

in that area. Which I suppose leads to my ultimate question, is there really any room for improvement in this area? Specifically the valleys between secondary runner inlets?

is that I built 2 identical IMs using the exact same techniques in both. If I thought "anything" would've or could've made them flow better ya GOTTA know, after the excrutiatingly LABORIOUS hours spent on each one that I would've implemented it in at least one of them.

Now with that said I don't see any negative to what you're proposing... just no inherent benefit. But I'll remain agnostic and say "it might, but I don't believe it will."

"If it aint broke, fix it til it is!"

;-)

I don't see how these "dead air spots" are any less significant than the ones in the lower IM which you filled with QS.

I'm not even sure that they're dead air spots, but by looking at it, it appears that way to me.

I think the low side dramatically more affected by those spots and that the high RPM runners could suck the icing off a birthday cake from across the room (figuratively speaking of course).

Much of that thought process comes from taking low negative boost vac readings of the intake tract with the Dwyer Digital Manometer during high/low switchover runs which those findings are posted hereabouts somewhere with the air filter comparisons.

But isn't the low rpm air crossing the path of the valleys, esp. the air moving to the primary inlets furthest from the TB?

What I was thinking, is to fill the valley area between the secondary inlets with epoxy, bringing that surface up to the level of the secondary inlet lips, and hitting it with a coat of Glyptal. It would be a lot of epoxy, but wouldn't decreasing the internal volume of the IM potentially increase the velocity of air moving through it?

I'm trying to understand the air flow patterns inside the IM. If the primary inlets are sucking air, does the air slide along the bottom half "grid" surface exclusively, or does it fill the entire top-to-bottom (grid to secondary inlets) cavity? (In which case it would collide with the valleys...)

kick in. You could easily deplete all reserve air of that reservoir VERY rapidly. And no increase in intake tract diameters can make up for it without a HUGE throttle body. Capable of even more flow than my RSXTB's are capable of. It can only fill so quickly and in that situation could easily deplete it's reserve volume faster than it could replenish it.

Problem is even in verifying this I'd risk ruining an IM. And I'm MUCH more interested in limiting my future intake mods to ITB's than trying to get any more out of the same intake manifold. But if you build it, I'll flow it!

once I finish. Are both your IM's installed on cars? If not, I could just send the completed top half?

mis-leading as both my modified IM tops and bottoms are CC'd to within 1 drop liquid volume across all 6 primary and secondary runners (tho my secondaries won't be used in the flow results). My hunch is it will flow less once modified and definately create a moderate intake tract negative boost (vacuum) and DEFINATELY be harder to cool due to the thick blanket of epoxy.

I just can't help but think there's some room for improvement in that area...

and I considered this very early on but it was frought with pitfalls. That was building a half-inch thick or so spacer block to sandwich between upper/lower manifold halves. It would also have a better cooling affect due to greater surface area as well as increased volume. But the reasons "against" were staggering from both a logistical, design and cost standpoint.

But packing "mud" 1/2" to 1" thick in the IM ceiling is not gonna make cooling be anything but difficult if not outright impossible. I think it's a waste but I'm willing to waste flowing it if you're willing to waste making it. Every mod I've ever done has filled dumpsters every step of the way before paying off.

"when omellette's on the menu there's gonna be some broken eggs"