78mm too much?
08-20-2009, 12:38 PM
#1
Thread Starter
Join Date: Jun 2009
Location: ohio
Posts: 24
78mm too much?
i was looking into buying the bbk 78mm throttle intake, and CAI this weekend but i wasn't sure if 78mm is too much air flow going into a stock engine, i read some of your signatures and most of you have 70, 75mm throttle bodies. my local advance auto parts told me 80mm should be the highest to go on a stock engine, the reviews on the product is great, but it suggests to use on a heavily modified engine. if anyone has this product on their stock engine let me know please.
08-20-2009, 12:50 PM
#2
Go Texas!!!
Join Date: Jul 2009
Location: Lincoln, NE
Posts: 4,613
I think 78mm is bigger than you need especially with a stock engine. I would go with 70 or 75mm. 70mm is plenty without f/i but many people have gone with 75mm and been happy. Don't expect much from it, just better throttle response.
08-20-2009, 01:33 PM
#4
6th Gear Member
Join Date: Jan 2007
Location: MI
Posts: 5,884
When i threw on my 75mm i had no problems, and it seemed to have better throttle response. I can't see 3mm making much of a difference. I would imagine it'll work fine for now, and even better if you do a HCI combo, nitrous, of a centrifigual supercharger.
08-20-2009, 01:45 PM
#5
TECH SAVANT
Join Date: Dec 2006
Location: Saint Augustine, FL
Posts: 10,938
A larger TB will not cause "too much" air flow into the engine, the engine can only suck in so much air, about 475 cfm for a 2V 4.6L at 6500 rpm. What a larger TB does do is make it easier for the engine to suck in that air.
This means that manifold vacuum decreases at WOT, and the density of the "sucked in" air is higher, which equals more oxygen (measured by the MAF) and more fuel (because the MAF tells the ECU there's more O2), which equals more power...
However at some point the manifold vacuum, relative to atmospheric pressure, drops to such that the velocity of the air being drawn in (the charge velocity) is reduced and perfomance suffers. This is because at that critical point the ram effect, created by the mass and velocity of the intake air column (which actually stuffs more air/fuel into the cylinder near and after BDC and while the intake valve is still open) falls below optimum and power loss occurs.
Short answer--75mm is too big for and n/a 2V 4.6L (70mm is the sweet point), but not so bad as to matter in the real world, and 78 (9% larger area than a 75) is too large. You can read more about all this here, and here...
In an f/i application these concerns go away mostly, and within limits as big a hole as you can get is the best way to go.
This means that manifold vacuum decreases at WOT, and the density of the "sucked in" air is higher, which equals more oxygen (measured by the MAF) and more fuel (because the MAF tells the ECU there's more O2), which equals more power...
However at some point the manifold vacuum, relative to atmospheric pressure, drops to such that the velocity of the air being drawn in (the charge velocity) is reduced and perfomance suffers. This is because at that critical point the ram effect, created by the mass and velocity of the intake air column (which actually stuffs more air/fuel into the cylinder near and after BDC and while the intake valve is still open) falls below optimum and power loss occurs.
Short answer--75mm is too big for and n/a 2V 4.6L (70mm is the sweet point), but not so bad as to matter in the real world, and 78 (9% larger area than a 75) is too large. You can read more about all this here, and here...
In an f/i application these concerns go away mostly, and within limits as big a hole as you can get is the best way to go.
08-20-2009, 08:19 PM
#6
1st Gear Member
Join Date: Feb 2009
Location: Texas
Posts: 138
A larger TB will not cause "too much" air flow into the engine, the engine can only suck in so much air, about 475 cfm for a 2V 4.6L at 6500 rpm. What a larger TB does do is make it easier for the engine to suck in that air.
This means that manifold vacuum decreases at WOT, and the density of the "sucked in" air is higher, which equals more oxygen (measured by the MAF) and more fuel (because the MAF tells the ECU there's more O2), which equals more power...
However at some point the manifold vacuum, relative to atmospheric pressure, drops to such that the velocity of the air being drawn in (the charge velocity) is reduced and perfomance suffers. This is because at that critical point the ram effect, created by the mass and velocity of the intake air column (which actually stuffs more air/fuel into the cylinder near and after BDC and while the intake valve is still open) falls below optimum and power loss occurs.
Short answer--75mm is too big for and n/a 2V 4.6L (70mm is the sweet point), but not so bad as to matter in the real world, and 78 (9% larger area than a 75) is too large. You can read more about all this here, and here...
In an f/i application these concerns go away mostly, and within limits as big a hole as you can get is the best way to go.
This means that manifold vacuum decreases at WOT, and the density of the "sucked in" air is higher, which equals more oxygen (measured by the MAF) and more fuel (because the MAF tells the ECU there's more O2), which equals more power...
However at some point the manifold vacuum, relative to atmospheric pressure, drops to such that the velocity of the air being drawn in (the charge velocity) is reduced and perfomance suffers. This is because at that critical point the ram effect, created by the mass and velocity of the intake air column (which actually stuffs more air/fuel into the cylinder near and after BDC and while the intake valve is still open) falls below optimum and power loss occurs.
Short answer--75mm is too big for and n/a 2V 4.6L (70mm is the sweet point), but not so bad as to matter in the real world, and 78 (9% larger area than a 75) is too large. You can read more about all this here, and here...
In an f/i application these concerns go away mostly, and within limits as big a hole as you can get is the best way to go.
For a heavily modified motor in n/a form...a 75mm will be ok.
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