I am putting a late 261 with 848 head into a frequent driver 47 car this winter/spring and looked at the McGurk 261 dyno numbers.
I was curious about the actual percentage gain from doing one upgrade to the next to find out what makes sense for my application.
This car will mostly run on freeways and streets between 2000-3000rpm.
So I crunched the numbers and got some interesting results:
Upgrades ........ 2000rpm ..... 3000rpm
Dual exhaust ..... 4 / 4 ........... 6 / 3
Dual Intake ..... 12 / 6 ......... 10 / 12
Head mods ........ 2 / 2 ........... 7 / 7
3/4 cam ............ 8 / 5 ........... 3 / 2.5
Numbers show % Hp / % Torque gains from stock to dual exhaust and then one upgrade to the next.
With stock tranny, 3:55 rear and stock tires we get 49mph @ 2000rpm and 73mph @ 3000rpm
Remember the gains are all without wind, drivetrain and tire/road resistance factors.
An easy intake and exhaust upgrade can be done by just about anybody with access to a muffler shop and gives 16% total Hp increase over stock.
The extra gains from expensive and time consuming head and cam upgrades may not be worth it for daily or frequent drivers with a running engine.
If building from scratch it seems however a good idea, especially plus boring the cylinders.
