Number 6 Lean On Rb26

[Scooby]

Guys;

I've read on here that no 6 (rear) cylinder can run lean on RB26s due to the design of the intake plenum.

Does anyone know under what circumstances this becomes a real problem?

Can this be rectified by extrude honing or some other method?

Cheers

[tang0]

its the same on the rb25 as well, not sure about rb20, but lots of boost and injectors reaching their max duty will cause #6 to lean out first, get hot, and melt ..

ways to fix - get your injectors flow tested (and cleaned) and put the highest flowing in #6

i just bought some new injectors for my rb25, billed as 550cc, when i got them the flow test report shows one of them flowing upto 576cc this one will go into #6 !

i've thought about various methods of providing extra cooling to the side of the block as well via ducted air from the front of the car, cant hurt ..

just my 2c

[Sydneykid]

Lots of boost and very high airflow required, I haven't seen the problem until well over 2 bar and 60 lbs of air per minute (700bhp). The problem exists in all log style plenums with an entry at one end and outlets along the log. It is due to air wave pressure build up at the end of the log (the end opposite the inlet). The rear cylinders (5 and 6) get too much air, so honing (enlarging) makes it worse. That's why Nissan tapered the plenum around #5 and #6, this works quite well until the boost gets way outside the design parameters.

The simplest way to over come any minor issue is (when you get your injectors flow tested) to simply put the highest flowing one in #6, the next highest flowing in #5 etc. The 1-2% variation in flow is usually more than enough. You can also adjust the individual injector trim with most aftermarket ECUs (Power FC, Motec, Autronic etc). If you have trim adjustments over 3% then its time to think about changing to a large volume plenum, at least double the capacity of the engine (5.2 litres+).

Hope that helps:cheers:

[smok74]

Well said.