Folks,
I'm finally to the point to where I'm ready to start fine tuning my PMO carbs.
Engine Background
Link to my engine rebuild
Gordo's 3.2L Engine Rebuild - Ready to Reassemble
And a photo to catch the interest of those who don't like to read
Rebuilt 3.2L Engine Specs include:
Dougherty Racing GT2-102 cams (
Dougherty Racing Cams)
JE 9.5:1 pistons (measured CR came to 9.3:1)
Electromotive XDi Ignition (Initial @ 10º, 3000 RPM @ 24º, Rev limit @ ~ 5700 for break in)
B&B exhaust - 1 & 3/4" headers
Stock 3.2L heads - reconditioned
ARP rod bolts and head studs
46mm PMO Carb Specs (as purchased - used; previously on a 3.0L engine)
38mm venturi
F16 emulsion tubes
160 main jets
55 idle jets
190 air correction jets
To assist with the carb set up and tuning I installed the Innovate LM-2 Wideband meter (will post graphs as I proceed...).
Carb Set Up for First Start / Engine Break In
For the initial carb set up to get the car running good enough for the cam break in and break in drive, I simply adjusted the idle mixture screws 2 turns out and I was off and running (rather rich - but good enough for a 20 min RPM yoyo ride).
Based on my research I found most recommend very basic adjustments be made to the carbs when you are working with a newly rebuilt motor. Sync'ing the carbs and getting a better mixture adjustment takes time and can wait until after you have the critical break in done (assuming the car runs good enough to drive without stalling or experincing excessive popping).
Post Break In First Adjustments
Once the initial break in run was done, I synchronized the carbs (STE syncrometer) and adjusted the idle mixture a bit better.
I followed the PMO instructions for carb tuning:
PMO Porsche 911 Carburetion - Installation. Another good / similar bit of instruction can be found here:
Weber Carbs Technical. And yet another great reference:
Tuning Webers
One item regarding the instructions was (and is) a bit confusing - do you lean best each throttle/cylinder, or adjust one and then adjust the rest of the idle mixture screws the same # of turns?
I opted to lean best each throttle/cylinder.
I've made a few short runs since tuning - the engine's a beast, but definitely in need of some additional tuning.
Based on my LM-2 feedback, I think I have some more idle mixture adjustments to make before I consider what's happening at higher RPM's and load - my idle is at 11.1 AFR...
Based on my initial run's it appears I'm rich at idle and constant mid-range RPM's, and quite lean on hard acceleration - however I will hold off on firm assessments until I'm sure I have the basic settings right.
I'm ultimately planning to dyno it with these guys
Dyno Tune Virginia Fuel Injection TEC3 Performance (about an hr away) once I think I have the AFM's and ignition settings as good as I can them.
Will update as I progress...
Gordo