Thread: Cfm

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Curious, what would be the flow capability of a 3" ID tube, smoothed on the inside and 4" long???? Working on a cold air system and don't want to end up with a restriction in the air intake system.......

Not enough! I took the plastic tube off the air cleaner on my '89 Merc 302, gained a couple MPG and noticeable power in lower gears.
I made a cold air induction setup for a 283 using two 3" flexpipes, the vacuum secondaries on the WCFB carb would never open! 4 grand was tops with it hooked up.

Well, the new EFI engines breathe on a whole lot less the two 3"tubes...... The TPI setup we just finished putting on a guy's '57 wagon gets all it's air through a 2.600" opening...... and it runs very nice.... What am I missing in this equation?????

What's missing is length, a small opening with a flared end will flow pretty good, where a long tube won't. Even then, something like a 460 EFI with the two small flared tubes picks up 25 horses or so with a few seconds work and a hacksaw. The factory stuff has a lot of things that aren't there for power, noise suppression and smog regs are tops on their list.
Lots of air cleaners had small openings, I never saw one that didn't benefit from cutting more holes or flipping the lid over.

Your friend's wagon runs good with a 2.6" opening. EFI can't tell if the intake is restricted, or if you aren't giving it the throttle, it won't flood like a carb. Up here in the frozen tundra, the air cleaner often plugs with snow, and the revs come down like you let your foot off. The engine runs fine, just won't rev up. Dig the snow out, or sit and let the engine heat melt it, and away you go. I bet if you opened the 2.6" up, you'd notice more power.

Then what does the MAF sensor do??? I just was wondering how many CFM a 3" tube flows.... I'm not running a stock type small snorkel air cleaner, but 2 3" tubes flowing air to a low restriction air filter element. The whole idea is to keep the hot underhood air out of the intake....

Dave, I talked to one of the racers at Firebird about this. He showed up with two 5" flex tubes into a very large filter. I asked him if he really needed that much tube. He said he dropped down to 4" tubes and the car slowed down. I still find it hard to believe, but this guy kept meticulous records.

Interesting, Richard... I know the old Thunderbolts did quite well with 2-4" tubes... I'd still like to know what the tubes actually flow on a flow bench....
Once I have that number, then add in a cushion, I'll know how much other external air I'll have to pull from the cowl area.... Love that low pressure air at the base of the windshield....

Now if someone could just explain how there are so many EFI cars producing 400+ horse with just a single 3"-4" tube....???????

I'm not saying anything is right or wrong, just wondering what the actual flow number is......

The MAF sensor senses air flow, but it doesn't know if the flow is being reduced by the throttle or by a restricted supply upwind of it. The throttle position sensor only reads idle and off-idle, so its no help either.

Dave,
What a MAF sense does.
Sorry I just copied it, I did feel like retyping it.

Pat

sorry to hijack this thread, techinspector1 I notice you said firebird raceway. And I would guess thats the track you tech at. This is a guy my dad ran around with and raced with in the early to mid 60's in Indiana. He ran an altered back then and moved to AZ in the 70's.

He visited my dad a few years back and said he was retiring from racing, I heard he was a staple at firebird raceway. He ran the fuel altered GORILLA. Anyway just curious if you knew him?