G'day Peter,Quote:
Originally Posted by OldMav
Hi Tassie basically the biggest single improvement to the std runner system is to raze the top 50mm. This has the effect to allow the centre entry air to enter the plenum more effectively or more so to allow the plenum to have a chance to have equal pressure across all runners. This is not a KW gain as such but does allow a few point of extra AFR hence more fuel can be added to gain the benefit. More to the point it allows The air to enter the plenum so it can slow down a bit so basically a accumulator more so than a distribution plenum. This has the effect of allowing the air to enter the runners at a much more straighter angle hence will allow more air to enter the runners and promote better cylinder filling through the valves. This usually shows up on the dyno as a quicker torque rise and a few more Nm of torque the stuff we should be concerned about. This sort of thing you can feel in the seat of your pants and the stuff that makes a 4x4 diesel fun to drive.
Now I must add you can over come all this by just adding a lot more boost but by the nature of turbo's we just don't have a turbo big enough with a small enough turbine to allow the pressures required to do this effectively as a simple top lift. Sure it is possible to get 200rwkw from this std manifold I did this nearly 24 years ago, with my first turbo. But you couldn't drive the beast it was just madness. So with a lot of trial and error and a bit of logic I spent more hours driving my flow bench than I did driving my Mav. But I did learn how to make our TD a more effective high output engine. Now much of what I have done is to improve the effectiveness of a above 150rwkw TD system but much of this stuff does work for the lower tune values like the 50mm lid lift.
To note the std runner system after a lid lift now becomes the main restriction factor to cylinder filling ability. To explain a bit here and to try and put this in a way that can be understood. I have modified my flow bench to reverse flow so it blows into the manifold just like a real turbo engine unlike a std bench which works on pulling air from the combustion chamber through the valves and runner. Sure I have to sacrifice some of the measuring equipment like the calibration plate ( the main thing you set your measurement criteria and gauges from) in the measuring plenum boxes but it still gave me a good indication of what was improved. I did all testing on a std head single cylinder as I had stuffed the other runners and valves through failed experiments. Anyway with hand held measurement probes I discovered when I cycled the valves with an electric motor set up to depress the valve just like a real engine at a simulated 200orpm or 1000rpm cam revs I found when the valves open in those short millisecond points there was vacuum holes in the std runners. This is what locks out any ability to approach cylinder filling ability of the head without the manifold and the limiting factor to outright power and torque rise. Hence my suggested statement that porting the head runners is a very small marginal gain in torque and outright KW. And in my experience and very expensive fails is usually a reduction in torque and kw. But a slightly bigger intake valve does seem to reduce the vacuum hole as the valve cycles, hence a bit more cylinder filling ability which reflect better torque rise the stuff we want.
So as you can see there is a limit to what we can achieve with the std runners and just about all other modifications to the manifold past lifting the lid top 50mm is only very marginal increases hence my common reference to 1%ers. Sure as cool effective boost is increased or more effective turbo's are used we can do things to achieve better results. I can point these out if needed if above 150rwkw is your goal.
Now to explain the whys here and how it effects spool or torque rise, If we improve cylinder filling we can effectively get better combustion for a better fuel ratio hence a better volumetric ratio this in turn produces a higher velocity of exhaust gas which in turn spins our turbine wheel faster with more force inturn our compressor accelerates quicker and faster to produce more volume/pressure earlier in the rev range hence more torque on a flatter curve. Our intake manifold is only one item in this chain that can be improved to get better usable torque/power where it is needed most. Unlike my first 200rwkw effort.
Ok until next time or more question to spark more info locked away in my silly head.
Thanks again for your in-depth and quality information, i always look forward to reading your posts, has i always continue to learn something new!
Regards,
Paul
