intake manifold modification

[tassie wombat]

gday looking at modifying the intake manifold on my 4.2 tdi any ideas?hopefully this is where oldmav will step in!!

[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.

[Robo]

Nice info there buddy.
It's great that someone who obviously loves his job is willing to spend the time to share.
Thankyou.

This upgrade improves both non and intercooled equally.
A 50mm alloy spacer, or some exotic material (for other gains if any) .
Is a spacer available or needs to be custom made.
Will fuel settings need to be tweaked or left as is?.

[OldMav]

Makes no difference intercooler or not. You don't have to change fuel settings but from experience a lot more fuel can be added in the spool area so compensator adjustments are required to get the best results. What happens is you basically gain 2 afr in the spool area for example on a 2860 setup before manifold gave 16 afr lowest after manifold was 18 afr lowest but this did reflect about a 2 to 3 AFR gain through out the rev range. So there is a lot of room for extra fuel.

The modification is quite simple and doesn't have to be anything flash something like this pic is fine..

IMG_0593_zps995561fc.jpg

Another test I did was on a std manifold to see what was going on inside using the bench in reverse with all the intake valves cycling, with this much volume required I could only obtain a bit under 4 psi pressure in the manifold. I used a very fine dust material magnetite. This stuff deposits where turbulence or flow is distorted or limited flow areas are.

P1040588.jpg

You can see the very large deposits around 1 and 6 cylinders hence the huge problems with distribution. I did the same thing with a 50mm raised lid like the previous pic but for some reason I cannot find those images. Any way the difference is very different as their is no deposits on any of the dividers just like 3 and 4 dividers in the image.

Now I didn't know this at the time but much later testing suggested a very different reason why there is so much black deposited magnetite in the bottom of the runners the deposits are all the same on all runners right in the angle bit of the runner bottom. I had always thought this was due to the sharp angle there causing a change of direction. later testing as suggested in the above post has nothing to do with the bend but this is caused by that vacuum lock caused by the valve opening. As pressure is raised this deposits moves further into the runner but not quite into the head runner. What is happening here is as the valve opens the valve sucks in some air but not enough air can accelerate fast enough to fill the void hence we get a flow lock at this point so very little air can enter the combustion chamber as you would expect. but once the valve reaches about max stroke the boost pressure does over come the disturbance hole. But we have significantly reduces the time boosted air can flow into the cylinder through the valves. Now all the is not perfect as my bench is sort of set in reverse as suggested so I do have a closed system other wise the bench doesn't work so we do have some vacuum under the head just like the real operating engine but obviously I cannot simulate the exact vacuum the cylinder can produce so you can see this is a serious limitation to our manifold. Also I have opened many std manifolds, and have seen this sort of carbon deposits in the same places, this just gives more weight to my theory.

I have built plastic models of a 3 cylinder manifold using the centre runner on the head for testing to try and reduce this issue. Basically we need to have vertical dividers and not horizontal dividers. I haven't built and tested a real life example but I have passed this idea on to a another fellow other forum member who has built a real example. First impressions look very good but dyno testing etc needs to be done to prove the idea..

[tassie wombat]

Thanks oldmav,so basically as long as the inlet pipe is at least 50mm higher than a standard manifold that's all that is needed,all the new chamber does is increase the volume of air that the manifold holds.doesn't need any special baffles or diverter plates.?

[OldMav]

Yes mate that's about it. But I really have no idea except good guesses at what point this plenum volume needs to get bigger to accommodate higher boosts levels and at what point do we need to consider direction turbulence issues. But I do know at about 150ish rwkw volume does make improvements.

You don't need baffles or dividers or any such things just a open chamber.

[tassie wombat]

thanks again mate,just have to find a spare manifold now so the cars not off the road,and do some homework on how to adjust the fuel pump!

[mudski]

Thanks also as i just picked up my td42t to start the rebuild and was wondering about this mod.

[tassie wombat]

do you know if an intake of a tb42(petrol) would be the same as the diesel one oldmav??

[BigRAWesty]

do you know if an intake of a tb42(petrol) would be the same as the diesel one oldmav??

I'm pretty sure both diesel and tb42 carby are the same, the efi is different.

I'm watching this with interest guys as I'm a fan for NA power. Imo more reliable.

Im looking at modding the front airbox for more flow.
I also like the idea of the manifold increase. Did you trial any different designs or just that square increase??