Intake air velocity
04-26-2002, 09:10 AM
#1
Senior Member
Thread Starter
Join Date: Aug 2001
Posts: 921
Likes: 0
Received 0 Likes
on
0 Posts
Intake air velocity
Instead of hijack Kemper's post, I'll repost here:
Is there some problem I'm not thinking of?(Aside from simply making the unit of course) I could see some benefits to it, even though they wouldn't be as large as for the big-block engines.
QUOTE
Red:
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...
I was actually pondering the merits of a progressive dual-barrel TB setup just the other day, couldn't find any examples of it for 4-bangers.(I did for motorcycles though)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...
Is there some problem I'm not thinking of?(Aside from simply making the unit of course) I could see some benefits to it, even though they wouldn't be as large as for the big-block engines.
04-26-2002, 01:36 PM
#2
Super Moderator
Aside from double the potential airflow, no not much merit at all.
Oh, wait, that was the point. Plus, if you want to use the hose-thumb analogy, you've got your thumbs on two hoses now, with a tighter squeeze on both...do you have faster airflow thru them? I guess...
Oh, wait, that was the point. Plus, if you want to use the hose-thumb analogy, you've got your thumbs on two hoses now, with a tighter squeeze on both...do you have faster airflow thru them? I guess...
04-26-2002, 01:46 PM
#3
Senior Member
Thread Starter
Join Date: Aug 2001
Posts: 921
Likes: 0
Received 0 Likes
on
0 Posts
Nah, man the point of what Red was saying is that if your intake area is too big, you get terrible throttle response at the low end because the large throttle plate opens too fast.
I'm thinking of a setup like the 4-barrel progressive throttle bodies & carbeurators on big blocks--each side has a smaller 'trim' barrel that opened first, allowing for good control of airflow at the low end, then a big-ass barrel that would let the air rush in when you need it. They have these things for turbocharged setups too, and like I mentioned on motorbikes.
I'm just curious if it has any merit here--it would probably require a completely different intake manifold. It could potentially provide a lot better throttle response than something like a quad-TB direct intake, providing similar airflow but with easier tuning. In my mind at least.
Please feel free to shoot down the idea though. smile.gif
I'm thinking of a setup like the 4-barrel progressive throttle bodies & carbeurators on big blocks--each side has a smaller 'trim' barrel that opened first, allowing for good control of airflow at the low end, then a big-ass barrel that would let the air rush in when you need it. They have these things for turbocharged setups too, and like I mentioned on motorbikes.
I'm just curious if it has any merit here--it would probably require a completely different intake manifold. It could potentially provide a lot better throttle response than something like a quad-TB direct intake, providing similar airflow but with easier tuning. In my mind at least.
Please feel free to shoot down the idea though. smile.gif
04-27-2002, 03:34 AM
#4
Super Moderator
Join Date: May 2001
Location: Rancho Palos Verdes, CA
Posts: 11,851
Likes: 0
Received 2 Likes
on
2 Posts
Vehicle: 2008 Toyota Prius 2006 Suzuki SV650S
HVE or RPW (think it's RPW) does offer a dual TB arrangement. The 2 TB's are progressive. They are both smaller than the stock TB, but combined they are larger. They are mounted side by side in the stock TB location.
The first one opens as you step on the throttle, once the first one opens past 50 or 75%, the second one opens.
In my opinion, I'm not sure if this setup would actually show any gains because of our large intake plenum volume, and the angle/curve of the intake runners. The only place the air would really speed up, is through the small TB restriction, it would then slow back down as it entered the large intake manifold plenum, and was forced to take a 90 degree right turn into the intake runners, then do the 180 degree arc back down to the intake ports.
If the intake manifold plenum was smaller (like it is on the V6 motor), then the air speed would stay high, and show a benefit, but I'm not sure the air speed would stay up in the I4.
[ April 28, 2002, 12:51 AM: Message edited by: Random ]
The first one opens as you step on the throttle, once the first one opens past 50 or 75%, the second one opens.
In my opinion, I'm not sure if this setup would actually show any gains because of our large intake plenum volume, and the angle/curve of the intake runners. The only place the air would really speed up, is through the small TB restriction, it would then slow back down as it entered the large intake manifold plenum, and was forced to take a 90 degree right turn into the intake runners, then do the 180 degree arc back down to the intake ports.
If the intake manifold plenum was smaller (like it is on the V6 motor), then the air speed would stay high, and show a benefit, but I'm not sure the air speed would stay up in the I4.
[ April 28, 2002, 12:51 AM: Message edited by: Random ]