Better take off when I'm not flooring it?
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Joined: Apr 2002
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Better take off when I'm not flooring it?
I'm trying to explain to myself how this works: It seems like I get more take off from a dead stop when I give steady acceleration rather than pushing the pedal to the floor. I wonder if this sounds right:
I know our cars run rich out of the factory. I have cai, new cam and bbtb... Perhaps the sensor on the tb is telling the ecu to give it x amount of fuel, but now that I have the tb bored there's more air coming in. So now the fuel to air ratio is better and there's more power. Ah yes; now I see I'm confusing myself and I think I'll end this right here.
Sound right, or just confusing?
I know our cars run rich out of the factory. I have cai, new cam and bbtb... Perhaps the sensor on the tb is telling the ecu to give it x amount of fuel, but now that I have the tb bored there's more air coming in. So now the fuel to air ratio is better and there's more power. Ah yes; now I see I'm confusing myself and I think I'll end this right here.
Sound right, or just confusing?
Senior Member
Joined: May 2001
Posts: 1,436
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Sounds like volumetric flow versus velocity. Big words huh? smile.gif Check it out...
Engines work best when air is flowing at specific speeds. If the air is moving too slowly, then your engine isn't able to suck it all down and as such it makes less power. At the OTHER end of things, if the air is moving too fast, it "backs up" and causes high pressure in that area -- high pressure that your engine has to push against. A proper header ensures the exhaust gas isn't moving TOO slowly at idle and low speeds, but doesn't "back up" at high speed when it's all trying to move so fast.
Ok, so now we know that air should be moving at an "ideal" velocity for best power.
When you floor the car at 1000 RPM's, there is too much "open hole" for the air to move quickly. Think about it like a garden hose: with the water just running out, it kinda makes a fat stream that rolls out to the ground. But stuff your thumb in the end, and the water "speeds up" and sprays like a mofo.
By NOT opening the throttle to full, you're doing the same thing as putting your thumb in the hose: the air is forced to speed up to get around the throttle plate. Air velocity is what you're looking for, and that's why your engine responds better when only partially applying throttle at low speed.
NOTE!
Velocity is VERY important. If you port your head to huge proportions, port your intake manifold the same, and also run a 70mm throttle body, your car is going to SUCK at low speed because you simply have too much "opening" to get any good velocity at low RPM's.
This is why bigger is not necessarily better, and also why "flow bench" numbers rarely equate to performance...
Engines work best when air is flowing at specific speeds. If the air is moving too slowly, then your engine isn't able to suck it all down and as such it makes less power. At the OTHER end of things, if the air is moving too fast, it "backs up" and causes high pressure in that area -- high pressure that your engine has to push against. A proper header ensures the exhaust gas isn't moving TOO slowly at idle and low speeds, but doesn't "back up" at high speed when it's all trying to move so fast.
Ok, so now we know that air should be moving at an "ideal" velocity for best power.
When you floor the car at 1000 RPM's, there is too much "open hole" for the air to move quickly. Think about it like a garden hose: with the water just running out, it kinda makes a fat stream that rolls out to the ground. But stuff your thumb in the end, and the water "speeds up" and sprays like a mofo.
By NOT opening the throttle to full, you're doing the same thing as putting your thumb in the hose: the air is forced to speed up to get around the throttle plate. Air velocity is what you're looking for, and that's why your engine responds better when only partially applying throttle at low speed.
NOTE!
Velocity is VERY important. If you port your head to huge proportions, port your intake manifold the same, and also run a 70mm throttle body, your car is going to SUCK at low speed because you simply have too much "opening" to get any good velocity at low RPM's.
This is why bigger is not necessarily better, and also why "flow bench" numbers rarely equate to performance...
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Joined: May 2001
Posts: 11,851
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From: Rancho Palos Verdes, CA
Vehicle: 2008 Toyota Prius 2006 Suzuki SV650S
QUOTE
Red:
This is why bigger is not necessarily better, and also why "flow bench" numbers rarely equate to performance...
Exactly the point I was trying to make here.This is why bigger is not necessarily better, and also why "flow bench" numbers rarely equate to performance...
http://www.teamsr.org/cgi-bin/ultimatebb.c...c;f=16;t=001816