foreigneRS,

Mate, I totally agree that we are all entitled to our own opinions . I am in no way trying to “make” you agree with me as that would be childish and very anti productive of me I and am happy to continue the discussion on this topic in an adult manner not only for “our” benefit but also all the other cossie enthusiast that put in the time to read this topic.

Ok, getting back to it, I can’t see how I am contradicting myself . In fact this comment of yours made it clear to me that you may not be 100% clear on the two separate points we are discussing. In fact I feel that you may be considering the two separate points as one and I believe that this is the reason for your confusion.

Point 1 being, the power increase from the fitment of the plenum spacer.
Basically the increased distance from the trumpet to the inner wall of the plenum (10mm becomes 26mm) is the sole reason for the power increase.

Point 2 (I think this is where you’re getting confused) is the fact that the spacer plate does not aid/feed MORE air flow to Cyl’s 1 and 2 ONLY. It improves air flow to ALL 4 Cyl’s by the same amount meaning that what ever the problem was with the stock Int manifold is still present as it has not been rectified. For it to be fixed would mean that the spacer plate would have to DIRECT more air towards Cyl’s 1 and 2 ONLY and NOT Cyl’s 3 and 4 to balance out the air flow to ALL Cyl’s cos as it is Cyl’s 3 and 4 are being feed more air than Cyl’s 1 and 2.

To cover it once more. Let’s say Cyl’s 1 and 2 receive 100cfm of air and Cyl’s 3 and 4 receive 110cfm of air WITH a stock Int manifold. Meaning Cyl’s 3 and 4 flow 10% more than Cyl’s 1 and 2.

Once a spacer plate is fitted Cyl’s 1 and 2 NOW receive 110cfm of air BUT Cyl’s 3 and 4 NOW receive 121cfm of air. So this would mean that Cyl’s 3 and 4 are STILL receiving 10% more airflow indicating that the spacer does not “balance the flow” to all Cyl’s. It only increases the flow to all Cyl’s with a linier result.

To answer your own question that you asked………. ”if the airflow was increased by fitting the plenum spacer, why did it not need a remap? And how could it gain 16 bhp?”


Would be the same as asking you………..By fitting a 3” big bore Exh system you gain power but the ecu did not need a remap, Why?

The reason a remap is not required is simple because the power increase on a % basis is so small that the difference in fueling/Ign timing is minimally affected.

The reason the power increased is because the engine can now inhale/exhale more air hence make more power. Again the increase of airflow thru the engine is a small % gain compared to the TOTAL amount of flow the engine had prior to the mods.

This is my explanation to how I have seen/tested the effects of the plenum spacer. I don’t expect you to agree or disagree. I am interested in your thorough explanation to better understand what your opinion is. Thanks.

Cossie604,

That’s a good question . I had actually fitted/tested two spacer plates to see what the results would be and there was no difference in power/torque by fitting the second spacer plate.

I should also add that another “myth” is that a spacer plate adds more lag due to the increased volume of the plenum area. This is also NOT true. To prove the point is simple.

When your driving along a flat bit of road your Vac/boost gauge is obviously reading in the vacuum area, as soon as you put your foot down the gauge swings to 0psi or a few psi (depends on the rpm your driving at) basically the time it takes your gauge to go from vacuum to 0psi is the time it took to fill all the intercooler pluming, the ‘cooler and the plenum. Not a lot of time at all really