K24 Test Engine Part 3
When we left our K24 last time, we had a basic K24 'Frank' with a few bolt-ons, and we demonstrated the importance of optimising the inlet manifold.
This time we will add some camshafts to make better use of the flow capabilities of the head, and introduce some more duration which should carry the power further up the rpm band.
Below you can see a graph showing where we left off last time vs cams added and tuned with the Hondata Kpro 4.
Now - this is a great jump in power and rpm but my experience tells me that something in this setup is holding us back.
We have shown previously how important the inlet manifold is, but we should never underestimate the importance of the cold air intake! A good cold air intake needs to flow enough air to supply the engine's demands, but also the cold air intake is responsible for resonance tuning along with the inlet manifold (albeit to a lesser degree).
Below you can see what happened when a 3.5” cold air intake was fitted, which I 'stole’ from my own EP3.
Cams added in red
3.5” cold air intake added in blue
The 3.5” cold air intake from my car tapers down to 3” at the throttle body, so I could not help but wonder whether a 3.5” intake without the reduction would be an improvement further still. I made a test piece as in the photo below which is a 3.5” tube with a radius adaptor (orange piece) fitted to the throttle body to provide a smooth transition for the air.
Boy was I wrong !
See graph below:
3.5” intake with taper in red
3.5” intake no taper plus radius piece at throttle body in blue
Without hesitation I switched back to the 3.5” intake with the taper at the throttle body. I have included a basic sketch showing the intake dimensions below for anyone who is interested, although it is likely that different cams and/or intake manifold dimensions will mean that this is not optimum for everyone.
In summary our best result to date is the K24 with bolt ons, an optimised intake manifold, some camshafts and a 3.5” intake as detailed above.
See graph below:
For reference, below is a flow test from a stock RBB cylinder head from our flowbench:
OK, that’s all for this time.
Next time we will change the RBB cylinder head for a PRB cylinder head. Please don't forget to like and share this article, and remember that the engine will be up for grabs when the project is complete!