RB26 AFRs at cruise speed.

Hi All.

I’ve an RB26 running step 2 Vcam and an EFR turbo,

at cruise speeds around 70mph Its fluctuating around 12.5-13 AFR.

this is at approx 20-25% TP, MAP 100-110KPA. 3500-4000 rpm

now I know the ITBS and turbo don’t give a great representation of MAP at partial throttle.

Not having an EGT sensor would it be safe to try and target around 14.0 ?

I know itl never be great on fuel but I have a few more long journeys coming up to take it to events and worried about oil dilution more than anything.

What manifold vacuum is it pulling at that cruise?

Under light throttle, I'd normally be expecting an AFR of 15-16.5:1, and you may find you can add timing for better efficiency.

Hello Jack,

On the RB26 with the ITBs I target 14.7 at 100kpa MAP and have not experienced knock.

Hi Gord, showing 100-110 KPA however because of the ITBS and turbocharging it’s not a great representation of what the manifold pressure actually is.

Frank - What kind of EGTs are you seeing (if sensor installed)?

I don't have an EGT sensor installed, sorry.

Good point, Frank - many manufacturers will target stoich' of 14.7 for best cat' efficiency and exhaust emissions.

Jack, you DO realise that there is no possible justification for running rich at light loads, especially where charge cooling, detonation resistance, and exhaust temp's aren't a concern?

Stoich until component protection demands something richer. At steady state cruise with an unloaded car at reasonable speed of 70 MPH I'd expect to be at stoich.

Since you mentioned EGT is a concern, having a sensor and knowing for sure is ideal.