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Old 06-21-2022, 02:17 PM   #1
shoestring
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Join Date: Jun 2009
Location: Swampscott, 01907
Post Cam and I built one of these David Vizard budget flow benches

So the way these benches work is that you hook up a shop vac (the nuttiest one you have) to a "cylinder" that the head sits on, and there's a capillary tube that feeds a manometer. Ours has 80 inches of water in it. You run the vac, open the valve to say 0.300" and read the number. Say it pulls the water to the 30" mark. We started at 40" (80" in a U-shape is 40" per leg), so it's pulling 10" of water times 2 (there's 2 legs of the manometer) for a total of 20". You do some mods and remeasure. Well this time it only pulls say 9" for a total of 18. There's an obvious improvement here because the capillary tube which is located in the cylinder is seeing less vacuum (more air is cruising past the valve). It's not 10% in this example because there's some square roots involves and stuff but that's not really important and not a good idea to focus on.

And while I can't tell you exact flow numbers (because we don't know them), I can tell you that for a fact the B21F intake outflows the B230F intake by a fair margin. The head used was the one off of our LeMons car which has some bowl and valve/valve seat work but is a stock 44mm valve. There is ZERO chamber work on this head, but it is cut about 2.25mm below stock 146.1mm spec and they measure between 44 and 44.5cc.

So here's the real flow result of the head off of our LeMons race car that has the standard 44mm intake valve with a multi-angle valve job and bowl work, and a 38mm exhaust valve, also with multi-angle valve job and bowl work, some of which includes filling the long side turn. As measured at 28" on a Superflow at R&L Engines, Dover, NH:

LIFT--------INTAKE CFM---------INTAKE W/MANIFOLD & TB-------EXHAUST
0.050..............24.1........................... ...23.5.............................23.8
0.100..............52.5........................... ...49.0.............................48.5
0.150..............77.0........................... ...76.5.............................67.2
0.200............102.9............................ ..97.0.............................82.5
0.250............125.2............................ 113.8.............................91.2
0.300............148.8............................ 125.7............................100.2
0.350............163.9............................ 134.0............................107.1
0.400............168.2............................ 141.0............................111.3
0.450............171.9............................ 144.0............................114.5
0.500............173.9............................ 142.0............................116.7
0.550............175.2............................ 142.0............................117.8
0.600............175.6............................ 141.9............................118.2


As I've posted a million times before, we make 144 whp with this head and a K cam. This is not the EXACT intake and throttle body we use, but they are all stock, unmodified pieces.

Also note that this head has a 38mm exhaust valve with a strong amount of bowl work but doesn't flow a lick more than a stock valve on a stock port! Why? Valve shrouding. Again, I can't tell you exactly how much of a gain in flow it is, but I can tell you it's a LOT.

Ask away, I just wanted to get this put up, I've been sitting on the info for a little bit. the only thing I've been able to do with the intake that's worth a crap is grind out the throttle body stud bosses that get in the way of the #1 and #2 runners in the plenum. You've got to take them all the way off, like on the opposite side, and it's going to expose the studs, so you may need to pull the studs and do some vacuum-leak prevention with some sealer or something. Those bosses make a bunch of turbulence at higher (>0.300") valve lifts and removing them helps alleviate this.

This flow test also answers the question I've had as to why Volvo cams are ground either single pattern or with a little more intake lobe: they need it. There's a 75% "rule" (let's call it a guideline) for exhaust-to-intake relationship. This is lobe-to-lobe, not just a single lift point, so hopefully you have a calculus person in your house like I do. If you've got less than 75% exhaust flow compared to the intake, you need more exhaust lift/timing. The opposite is true if you have more than 75%: you need to crutch the intake. BMW S54 is a good example.

DON"T CRUCIFY ME OVER THE PREVIOUS STATEMENTS, obviously it's not necessarily that simple. It's merely meant as a conversation starter.

DISCUSS.
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Last edited by shoestring; 06-24-2022 at 04:54 PM..
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