Ok, here's some specs on different cubic inch/res freq/pk tq . It's an approximation, of course. Hank L gave me the formulas, I did the measurements....
Cubic Inch Resonant Frequency Peak TQ
318 stock 3200-3600rpm 4400rpm
cut runners 3400-4000rpm 4400rpm
cut/ported 3400-4000rpm 6200rpm
360 stock 3200-3600rpm 3900rpm
cut runners 3400-4000rpm 3900rpm
ported 3200-3600rpm 5500rpm
cut/ported 3400-4000rpm 5500rpm
408 stock 3200-3600rpm 3450rpm
cut runners 3400-4000rpm 3450rpm
cut/ported 3400-4000rpm 4800rpm
ported 3200-3600rpm 4800 rpm
so you can see that cutting and porting a manifold for the 318 puts the resfreq and pktq way out of phase. So for the 318, I recommend a mild cut on the runners ONLY. The best bet for matched up performance on a 360 is to just cut the runners all the way down...on a 408, you could get away with cutting and porting since it has huge CI, and stroke to make up for the mis-matched resfreq and pktq. So, Hank, if you want to check my math...
318 =39.75 CI per cyl
360 =45 CI per cyl
408 =51 CI per cyl
manifold plenum vol is approx 425 CI
stock runner vol is approx 31 CI
cut runner vol is approx 25 CI
res freq is where the pulses of intake air takes on "inertial supercharging" effect
Peak TQ is where the manifold vol, and runner vol/length fill the cyl the best...depending on CI of the cyl.
1. Longer runners provide better low-rpm power because the cyl fills better.
2. the huge plenum provides excellent throttle response in smaller C.I. engines (along with a bigger TB) because there is more available air at that moment(before it has to pull it through the TB)
3. 318's tend to have a higher powerband with the kegger anyway simply due to runner volume vs. cyl volume, so an M1 would basically put the powerband so high it becomes nearly un-useable for good low-end TQ.
4. Auto-tranny trucks like fully- modded kegger. (dont know why...)
:blahblah:
