grumpyvette
Well-known member
lift by itself has very little effect on idle
duration can have a very pronounced effect but within limits its changes in the LSA that increases the overlap area that has the quickest effect as the duration increases , if your in the 220 @ .050 duration or lower range. its the overlap period when doth valves are open that in most cases causes the reversion in the intake ports that causes the rough idle,as the rpm levels increase the engines cylinder scavageing increases due to both inertia in the intake and exhaust tending to keep the airflow thru the cylinders going in the same direction, thats why the engine tends to smooth out as the engine rpms increase.
on a C-4 / TPI corvette your limited to about a 210@.050 duration and at least a 112 LSA to keep everything idleing fairly smooth, increase the LSA to 114 and things smooth out further, drop the LSA to 110 and the idle becomes noticably rougher
look at these two cams
http://dab7.cranecams.com/SpecCard/DisplayCatalogCard.asp?PN=114681&B1=Display+Card
.
http://dab7.cranecams.com/SpecCard/DisplayCatalogCard.asp?PN=110921&B1=Display+Card
.
they are the same cam EXCEPT FOR THE LSA
the first cam idles with a fairly rough idle
the second cam idles MUCH rougher
read this
.
http://www.newcovenant.com/speedcrafter/tech/camshaft/3.htm
http://www.newcovenant.com/speedcrafter/tech/camshaft/6.htm
other info
http://www.iskycams.com/techtips.html#2003
http://www.mercurycapri.com/technical/engine/cam/lca.html
http://www.victorylibrary.com/mopar/intake-tech-c.htm
http://tru-442.tripod.com/camselect.htm
duration can have a very pronounced effect but within limits its changes in the LSA that increases the overlap area that has the quickest effect as the duration increases , if your in the 220 @ .050 duration or lower range. its the overlap period when doth valves are open that in most cases causes the reversion in the intake ports that causes the rough idle,as the rpm levels increase the engines cylinder scavageing increases due to both inertia in the intake and exhaust tending to keep the airflow thru the cylinders going in the same direction, thats why the engine tends to smooth out as the engine rpms increase.
on a C-4 / TPI corvette your limited to about a 210@.050 duration and at least a 112 LSA to keep everything idleing fairly smooth, increase the LSA to 114 and things smooth out further, drop the LSA to 110 and the idle becomes noticably rougher
look at these two cams
http://dab7.cranecams.com/SpecCard/DisplayCatalogCard.asp?PN=114681&B1=Display+Card
.
http://dab7.cranecams.com/SpecCard/DisplayCatalogCard.asp?PN=110921&B1=Display+Card
.
they are the same cam EXCEPT FOR THE LSA
the first cam idles with a fairly rough idle
the second cam idles MUCH rougher
read this
.
http://www.newcovenant.com/speedcrafter/tech/camshaft/3.htm
http://www.newcovenant.com/speedcrafter/tech/camshaft/6.htm
other info
http://www.iskycams.com/techtips.html#2003
http://www.mercurycapri.com/technical/engine/cam/lca.html
http://www.victorylibrary.com/mopar/intake-tech-c.htm
http://tru-442.tripod.com/camselect.htm
