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To do that right (and in our case it needs to be done right since both ends connect to two round 3.5" pipes), I think one needs steel dies. Those are very expensive to have made.
If one just wants to flatten a single pipe for some section, press with plates is probably just fine.
not really, you just crush as much of it as needs to be flatter and leave the ends round and the tube has its own natural transition.
sorry i was saying that for a one-off or even small production run i don't see dies as necessary, the tubes i've done still have perfect round ends for attachment points to other tubes/couplers just flatter/elliptical in the middle where they need to be.
sorry i was saying that for a one-off or even small production run i don't see dies as necessary, the tubes i've done still have perfect round ends for attachment points to other tubes/couplers just flatter/elliptical in the middle where they need to be.
Sure I can see how that can work out and if there's risk then just wooden inserts in both ends can get the job done. However, I'm talking about our situation of potentially squeezing something into a shape such that both ends have perfect 3.5/2 inch radius semicircle on both sides such that the four pipes can be welded on cleanly.
The new exhaust manifold fits and so do the new, dual 3.5" downpipes. John still has to weld in the sensor bungs and cuts some threads. After that, the manifold and downpipes are shipped to thermal barrier coating.
They look good, don't they? In any case, despite of being made from stainless, those pipes will go to thermal barrier coating. Then they'll look the same as the older, mild steel pipes. The reason why they will be thermal barrier coated is twofold. First, to better protect components, although we'll also add some heat shields to protect wires, gaskets, and hoses. Second, to light up the cats better. Thermal barrier coated thin-wall stainless steel pipes will light up the cats real quick.
While John's finishing the exhaust, I've been thinking about what improvements one could make on the intake side of the system. The focus is on the throttle body element. I see real diversity of opinion on how much restriction the stock-sized 75mm throttle blade causes in the S4 intake manifold. Also, many opinions on how much restriction the casting shape causes, especially the up-chute turn on the driver side. Ake Jonsson is performing some science experiments on the S4 throttle body element for me, while I'm trying to figure out a measurement strategy that would help pin down the extent of restriction between the plenum box (in the place of stock air filter box in my system) and each of the two intake manifold plenums feeding the runners.
While John is working on the exhaust, Ake is testing some throttle plate sizes for me. Tooling to make arbitrary size throttle plate for the S4 throttle body:
I'm trying to figure out a measurement strategy that would help pin down the extent of restriction between the plenum box (in the place of stock air filter box in my system) and each of the two intake manifold plenums feeding the runners.
Did you have the whole inlet tract (with throttle fully open) measured on a flow bench, and how did it compare with how much the heads flow?
Did you have the whole inlet tract (with throttle fully open) measured on a flow bench, and how did it compare with how much the heads flow?
No, not really. I don't even know how I'd design such an experiment in a way that it would fit on a flow bench and the results would make sense.
When bare, the throttle body with 75mm plate in the casting flows about 800-900 CFM at 28" with the throttle fully open (S4 fully open angle, GTS fully open angle is a little different). Theoretically maximum flow thru a 75mm bore at 28" is about 1000 CFM. So it's not like the element is ridiculously inefficient, and if one wants to get it to flow more one probably needs a bigger throttle plate. After a bigger throttle plate has been installed, then it may be that welding more material to the casting and porting the up-chute turns to flow better is necessary for further gains. That's one part of the problem, how to feed the main casting plenums efficiently.
The heads flow almost 300 CFM at 28", but that's at very high lifts. At lower lifts, it'll of course flow less. The intake runners of the main casting that are on the engine now flow about the same, but I don't know the exact numbers. Some people say that the intake manifold runners should flow about 15% more bare than the head and you're safe, but obviously that's no substitute for integrated testing. That's a separate part of the problem.
And to a point, that's off topic. What this little experiment at hand is about is the first part of the problem, that is, whether the throttle body element flow well enough to not cause a pressure drop in the side plenums that feed the runners.
One option is to measure this on a running engine. I've got some measurements of the pressure drop from the plenum box past the throttle inside the bottom of the throttle body element. At high 17 psi, it's almost 1 psi, but I might remember wrong. It's also that the velocity is different at the measurement points because the cross-sectional area and flow direction is different and that's not really the relevant spot to measure it anyway. So those data are not reliable for many reasons.
The next time we get this car to run, we'll try to take a more relevant measure. That is, measure the pressure differential from the plenum box widest part to the intake manifold plenum cover side plate. That will include the restrictions from MAF housing, throttle plate, and the up-chute turns. If there's a big pressure drop, then it's worth seeing if a bigger throttle plate and ported throttle housing help.
The whole engine bay is so packed now that the down pipes need to be test fitted with a fixture that keeps them exactly parallel in the right spot. The boost pipes out of the compressor need to hit exact center of the wheel well holes.
The reason why we can't just use two parallel 3.5" pipes is that they don't fit, and even if they'd fit in the center they wouldn't fit with a well flowing and gentle turn. So John has to fabricate the "infinity pipe" for the center and then divorce it into legs that go to the rear axle muffler:
09-18-2017, 05:22 PM
