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Is having dual DCOE 48's equal to a 96/96 downdraft


norm

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Why do newer engines use 4 valves per cylinder, instead of just 2 giant valves? It's been tested. You get better fuel flow thru separate tubes instead of one giant one. I don't know the exact equation, though.

Bring a Welder

1974 2002, 1965 Datsun L320 truck, 1981 Yamaha XS400, 1983 Yamaha RX50, 1992 Miata Miata drivetrain waiting on a Locost frame, 1999 Toyota Land Cruiser

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Why do newer engines use 4 valves per cylinder, instead of just 2 giant valves? It's been tested. You get better fuel flow thru separate tubes instead of one giant one. I don't know the exact equation, though.

Not really. It's just geometry. You can get more valve area out of four holes rather than two.

CombChamber.jpg

More specifically, though, the separate intakes means there's no chance of two cylinders sucking air from the same hole at the same time, which equals better throttle response. Plenty of room to breathe!

Intakes do, however, seem to create more torque when they have long, specifically designed tube to each cylinder, like the runners on a tii manifold.

Is having dual DCOE 48's equal to a 96/96 downdraft?

I know the math does not work this way. 48+48/48+48 then 96/96

I just teach middle school algebra. Any of you "Air and Space" Engineers know the formula?

Norm

The formula is Area of a Circle = π • r².

So, doing the math, two 48mm openings are like having one opening that's almost 68mm. It's really more like a 68/68 carb, not a 96/96. Much better, though!

ClayW
1967 1600-2 - M42 - 1521145          Follow my project at www.TX02.blogspot.com          E30 DD Project Blog

 

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The dual 48's have the full port area available per cylinder at all times though, right? The 69/69 would be sequencing all ports through the same opening. So the dual 48's win again, right?

Yes and no. If you pair up companion cylinders, the intake pulls won't overlap and performance shouldn't suffer. It's been done for the single sidedraft manifold:

M086topsm.jpgM086bottomsm.jpg

Of course, having the sidedrafts negates the need to have such a manifold.

ClayW
1967 1600-2 - M42 - 1521145          Follow my project at www.TX02.blogspot.com          E30 DD Project Blog

 

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Why do newer engines use 4 valves per cylinder, instead of just 2 giant valves? It's been tested. You get better fuel flow thru separate tubes instead of one giant one. I don't know the exact equation, though.

Not really. It's just geometry. You can get more valve area out of four holes rather than two.

Thats true as well, but there are other benefits for flow. can't find the old article i'm looking for, which described the different 'donuts' of air flowing in, but unreliable wiki has this:

In addition, particularly as the valve begins to open, for equivalent valve/port areas multi-valve geometry allows for increased airflow.

http://en.wikipedia.org/wiki/Multi-valve

anyways, sorry to hijack, but it might relate.

Bring a Welder

1974 2002, 1965 Datsun L320 truck, 1981 Yamaha XS400, 1983 Yamaha RX50, 1992 Miata Miata drivetrain waiting on a Locost frame, 1999 Toyota Land Cruiser

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jeeze, I just did this math the other day. Search for 38/38....

48's are about the equivalent throttle plate area of a dual 38.

But the manifolding is what separates the turkeys from the buzzards.

THEORETICALLY, if airflow was the only restriction, you'd see no

improvement going from a 38/38 to a quad of 45's.

But that's not true, so there are other factors involved.

Happy smoking,

t

"I learn best through painful, expensive experience, so I feel like I've gotten my money's worth." MattL

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