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Aftermarket Rb26 Plenums

wogzilla

By wogzilla,
in Engines & Forced Induction

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manage13 Proficient

manage13

Posted
Posted
what if a good number high HP ones are still using the stock item?

I'm with you there!!!

Gary (Sydneykid) had a great post awhile back stating that changing to aftermarlet plenums have in most cases no gains and in some cases negative gains.

post-4055-1131577237.jpg

Mik Experienced

Mik

Posted
Posted
i see little point in changing either. there's nothing wrong with the factory one. i still wonder why nismo re-invented the wheel with their aftermarket jobbie.

d

The standard one may be okay for power, but with the standard plenum, more air is distributed to the rear cylinders which means an unbalanced engine and leaner mixtures on the rear cylinders (if you tune with one O2 sensor).

Hence why RB26's tend to always do ring lands on number 6, rather than one of the front cylinders.

Duncan Grand Master

Duncan

Posted
Posted

And the flow differences in injectors can be substantial, even after something like an hour of cleaning there was a variation of over 5% in the injector flow rates, which could result in a difference like 12:1 target but one cylinder running at 13:1

proengines Rising Star

proengines

Posted
Posted

It's not a terribly easy thing to flowbench test as it's impossible to accurately reproduce the conditions inside the plenum as they would be with the engine running. Pulsing and reversion will make a difference to the way the air is distributed.

You can test the percentage differences between the head with a bellmouth and the head with a plenum attached for each cylinder and gain some results from that.

The best way to test would be with an exhaust temp gauge on each manifold runner just out of the exhaust port. If you know that all the injectors flow the same and the rear cylinder runs hotter than the rest then you know that that cylinder is getting more air than the others.

Most decent computers let you trim each injector to compensate which can bandaid the problem.

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