Thanks for the explanation. When you say loose down low, are you referring to stock factory exhaust manifolds or over Pacemaker header with 1.5 primary?
Cheers
Over the pacemakers.
Stock manifolds are bad for back pressure and flow. Any short or long tubular extractor will be an improvement.
The stock exhaust port is... Around 38mm from memory... 36mm?
Anyway, if you match the exhaust port diameter exactly with your exhaust primaries and run the primaries about 2 foot or so long before they hit the 3 into 1 merge collector, the exhaust pulses maintain as much velocity as possible when they hit the collector, which is fantastic for scavenging! And great for engine efficiency. This is what the pacemakers are designed for.
But, I you have a stock valve, stock exhaust ports and (let's say a big) 1 3/4" primary, there's such a space/volume increase as the exhaust pulse moves into the primary that it expands, looses energy and slows down. Making for an ever so slightly more lethargic exhaust flow. (Big valves and head porting will fix this and make the car want to live up in the 5000+ RPM range)
You'll gain performance with basically every different extractor on the market tho.
1 1/2" pacemakers are great for cars with minimal mods and still work well on cars with a few bigger upgrades like mild cams etc.
1 5/8" primaries will have ever so slightly less low end torque than those pacemakers. But there's some top end HP potential there as the slightly large primary will work better with higher volumes of exhaust gas.
