intake duration
Mar 14, 2005 | 06:30 PM
#11
I'd like to hear whitt1s explanation on that as well. -EDIT- I was going to type up a rebuttal, but after re-reading his statement, I'm going to hold off until I see a reply. I think the wording is deceptive.
Mar 15, 2005 | 12:34 AM
#13
Originally Posted by BigTex
I'd like to hear whitt1s explanation on that as well. -EDIT- I was going to type up a rebuttal, but after re-reading his statement, I'm going to hold off until I see a reply. I think the wording is deceptive.
Mar 15, 2005 | 12:52 AM
#14
TECH Junkie
Joined: Mar 2002
Posts: 3,019
Likes: 1
From: memphis tn
Intake duration is just part of the equation the opening point of the exhaust valve will have a greater effect on powerband than anything other variable as it determines lobe separation and valve overlap.Sorry for not answering sooner I had to go out of town saturday.If you look at the exhaust duration and lobe separation you can compare cams from the same manufacturer to predict which one will produce power at a lower rpm.
Mar 15, 2005 | 01:35 PM
#17
Originally Posted by whitt1
Intake duration is just part of the equation the opening point of the exhaust valve will have a greater effect on powerband than anything other variable as it determines lobe separation and valve overlap.
The intake side dictates powerband. Choosing the correct combo of intake vs exhaust will net you the most power in that range. An effective exhaust as a whole will hold your power curve out further past peak.
I can't see how the exhaust lobe dictates powerband. If so, then the powerband would change with a swap of exhaust primary lengths. I don't recall gaining rpm peak w/ my long tubes. However, intake manifold runner lengths can change your peak. That's why these 3.62 stroked ls1's seem to all reach a 6200-6400 rpm peak. 15'' manifold.
If you look at the exhaust duration and lobe separation you can compare cams from the same manufacturer to predict which one will produce power at a lower rpm.
With the same exhaust system, excluding the lobe.
x-e
intake lobe-220 on a 112 - 6000rpm
intake lobe-224 on a 112 - 6200rpm
If the exhaust lobe is paired correctly, you will make more power within that range.
Mar 15, 2005 | 03:11 PM
#18
TECH Junkie
Joined: Mar 2002
Posts: 3,019
Likes: 1
From: memphis tn
Moving the exhaust openings determines the point that the combustion chamber is most efficently scavenged.Savenging is a product of exhaust pulses combining to suck the unburned mixtures from the chambers a kind of back side supercharging effect.
Mar 15, 2005 | 03:44 PM
#20
Geoff @ Thunder
I underlined that one piece, because he was talking about reverse splits. How does this relate? The underlined part shows that given the same intake lobes but different exhaust lobes, the power range does not change, but the curve does.
I'm still not catching on, to how the exhaust lobe determines rpm range.
To let everyone in on a big secret about reverse splits: As soon as you open the exhaust valve on the power stroke of a 4-cycle engine you aren't going to get any more useful force to push the piston down with. The catch to all of this is that there is a balancing act between taking energy to push the piston down and taking that same energy to push the exhaust out of the pipes to scavange the cylinder. A reverse split does not make torque or horsepower in a different RPM spot than a conventional cam assuming all other valve events besides exhaust opening, such as intake opening, intake closing, exhaust closing, overlap stay the same. The only affect of the reverse split if all of the other valve events are optimized is that you will have a later exhaust opening point which will delay blowing the cylinder pressure out of the exhaust pipes. Will this make more power? Again it depends if the exhaust system is up to the task of properly scavanging. We have tested all of this and know it works.
I'm still not catching on, to how the exhaust lobe determines rpm range.