(Every bit of the following is IMHO -- YMMV - street only advice.)
Well, the general idea is leave the intake side alone for STREET use.
Increasing the size of the intake valves or anything else (carbs, ports) will
will reduce the velosity of the mixture through the intake tract at low RPM--
this costs low end torque. And unless you increase the useable RPM range of the
engine, you can't take advantage of the increased top end flow capability.
Increasing the exhaust flow through the valves, ports, and exhaust system
is the first step for a street engine. This just reduces pumping losses. Less
torque pushing exhaust through the system = more torque at the wheels. Exhaust
"tuning" really isn't an issue if you run any mufflers at all... (except for
Tri-Y headers- Tri-Y = good)
I'd go:
1. Revised exhaust manifold/free flow exhaust system (+ bigger ex valves)
2. More Spark! Timing is everything...
3. Increased Compression Ratio
4. New cam (greater overlap/dwell/LIFT -- this can also differ
intake/exhaust - go mild not wild- new wave street cams have more
lift/duration on the exhaust side)
5. Carburation
6. Bigger inlet valves/port and polish
7. MORE SPARK!
One through three are basically "free" torque throughout the rev range. No
bottom end penalty if done properly.
4-7 will push the torque/HP peak further up the RPM scale. You could wind up
with less torque than you started with stock at low (street) rpm's. Especially
if you failed to do 1-3.....
Once again IMHO.... Just gleaned from Grassroots Motorsport over the years.
Have fun. Good luck.
Chris Lillja
Spit MKIV
Norton Commando
TR4A
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