1. Stock exhaust is better than a shorter side exhaust...might be a
venture effect,
2. Don't enlarge the exhaust ports, clean and polish only...might be
related to the exhaust above. I understand why you don't mess with the
intake ports, just surprised at the exhaust.
I would be interested if you or any members have comments on these two
items.
Paul:
1. The length exhaust system should be tuned to the engine components
and the style of driving. There is a math formula based on rpms that
describes the most efficient exhaust length.
The full length stock exhaust is most efficient in 2,000 to 3,000 rpm range.
The side exhaust is most efficient between 4,000 and 6,000 rpm. If you have
an aggressive cam and drive the car at high rpms, the side exhaust is the
correct configuration. If you enjoy a less aggressive use of your Healey,
the OEM exhaust is the ticket.
2. Exhaust port size is also related to cam selection, use of the car
and head flow rates. Old school theory was to keep the exhausts small to
help scavenge the cylinders by increasing the forced exhaust flow rate.
Ferrari proved a long time ago that large exhaust valves can help build a
lot more power, especially in high revving engines with significant
intake/exhaust valve overlap. Street cars today still maintain smaller
exhaust valves than intake valves but as the engine is modified to increase
horsepower and rev range, both exhaust and intake valves will increase in
size and the ratio between intake and exhaust valves will decrease.
As always, how you modify the engine depends on what your use of the engine
will be.
Best regards,
Jim Hockert
BJ8 Rallye
Dallas, TX
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