[DeTomaso] Intakes {rocker arms}.

[Daniel C Jones]

> Can you explain how the short ratio exhaust rocker arm improves the torque?

The reason the intake valve is larger (and port flow at a given
pressure drop is
greater) than the exhaust is because the intake is under atmospheric pressure
while the exhaust is under compression pressure.  Being under
pressure, the exhaust
blows down quickly in the lift cycle.  Dynamically, the exhaust side
is relatively
insensitive to valve acceleration but is sensitive to duration (how
long the valve
stays open).  The preceding is mainly a filling-emptying type of explanation.
Things are more complicated than this having to do with the unsteady
nature of gas
dynamics and the way finite amplitude waves travel within the exhaust
and I tend to
rely on wave action simulation to determine how any given engine may respond.
As a practical matter, Vizard suggests the best exhaust rocker ratio
is 0.1 to 0.2
lower than the intake ratio.  If you look at the cams used by most of
the competitors
in the EMC, they tended to have somewhat larger exhaust duration but
shorter lift
(either by the lobe chosen or a shorter rocker ratio).

We also found the exhaust port stuffers (MPG Stinger type) worked on
both long tube
headers and the Pantera GTS headers.

Port Plate Test
Same setup as pull number 10 with the Strip Dominator HVH intake setup and
Pantera header.  The Pantera header comes straight out from the cylinder head
whereas the Mustang Hooker header turns downward more quickly.  In both cases,
the Stingers helped.

Without Stingers
RPM     HP      Torque (ft-lb)
4000	278.7	362.9
4100	291.9	370.3
4200	294.8	369.3
4300	301.1	368.1
4400	308.9	369.0
4500	319.2	372.6
4600	331.7	378.5
4700	345.3	385.5
4800	356.9	390.1
4900	363.5	389.9
5000	372.8	390.4
5100	378.2	389.6
5200	382.4	386.5
5300	389.9	386.4
5400	396.7	385.9
5500	403.1	384.9
5600	407.6	382.3
5700	408.0	375.7
5800	405.9	367.4
5900	398.5	355.2
6000	395.4	346.2
6100	399.0	343.4
6200	404.4	343.6

With Stingers
RPM     HP      Torque (ft-lb)
4000	278.7	366.3
4100	286.2	367.0
4200	297.4	372.0
4300	310.4	378.8
4400	322.4	384.7
4500	333.8	389.6
4600	343.4	392.2
4700	353.6	395.0
4800	365.5	399.6
4900	372.6	399.7
5000	376.0	395.1
5100	385.4	396.4
5200	388.9	393.2
5300	395.0	391.3
5400	404.5	393.0
5500	411.0	392.4
5600	410.4	385.1
5700	404.9	373.3
5800	406.1	367.6
5900	407.6	362.5
6000	402.5	352.7
6100	400.9	345.8

Dan Jones