Ok confused on runner length...
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Ok confused on runner length...
Ok confused on runner length...
Need some help.
After reading the artcle put up by TequilaBoy (thanks bigtime man)
Iam confused on just how runner length effects the TPI system
Iam thinking logically that the longer the runners the more torque and hp down low in the RPM curve (below 4200) and that the shorter the runners the more torque and hp in the upper RPM band (above 5200).
So how come by porting the runners on an L98 motor (longer runners) do we get more hp in the upper RPM band? Wouldn't this be counter productive and just make more hp in the lower RPM band?
Longer = lowerband hp and torque but less in the upperband
Shorter = higherband hp and torque but less in the lowerband
Wouldn't we have to make the runners shorter to get more hp out of it?
hmmmmm
Need some help.
After reading the artcle put up by TequilaBoy (thanks bigtime man)
Iam confused on just how runner length effects the TPI system
Iam thinking logically that the longer the runners the more torque and hp down low in the RPM curve (below 4200) and that the shorter the runners the more torque and hp in the upper RPM band (above 5200).
So how come by porting the runners on an L98 motor (longer runners) do we get more hp in the upper RPM band? Wouldn't this be counter productive and just make more hp in the lower RPM band?
Longer = lowerband hp and torque but less in the upperband
Shorter = higherband hp and torque but less in the lowerband
Wouldn't we have to make the runners shorter to get more hp out of it?
hmmmmm
Race Director
Joined: Sep 2000
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From: The Top of Utah
Porting a runner doesn't change it's length. You are dealing with a different concept when you port existing length runners. When you port, you are changing the the cross section of the runners and their ability to accommodate a greater volume of air. Porting isn't (usually) tuning. It is just "hogging" it out for greater airflow. If you can handle more air, you can support combustion where more air is needed, higher rpms. Then (if you wish) you can take steps to tune for greater volumetric efficiency at a specific (higher?) rpm level.
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Its a slightly different concept. Larger ports decrease the port velocity in the runner at lower rpm and tends to raise the rpm where that peak port velocity occurs, which raises where the torque peak comes, which raises the HP.
High Port velocity=torque
Heads work the same way, they have a given length, but going with a head that is 170cc amplifies the lower end at the expense of the top, and a 190cc head amplifies the upper end more.
Race Director
Joined: Sep 2000
Posts: 17,298
Likes: 33
From: The Top of Utah
Kinda. Sorta. Yes. But, tuning has to do with more than simply velocity. Just like in your exhaust system, there are pulses of pressure and/or waves of sonic energy. When the pressure in the tube drops suddenly, as where it meets the combustion chamber, the plenum, or the collector in the headers, there is a reversion of negative (relatively) pressure that is reflected back up the tube. How long it takes for the pulse to reach the other end, depends on the distance it has to travel. Tuning with different length runners for both a TPI (or any intake system) and headers can change the rpms at which scavenging is maximized. Perhaps you recall the "Power Ram Inducted" 413 of the very early 1960s, as immortalized in the Beach Boys song, "Shut Down".
RACE ON!!!
