Throttle bodies for CVH?

[dtype38]

Originally Posted by graham bahr

when i arrived at the optimum inlet trumpet length after many hours on the rolling road, i meassured the total intake length from the back of the valve to the end of the trumpet, it was exactly the same length as the exhaust primaries.

Now that is interesting...

Maybe rather than looking at the intake to the turbo, it might be productive to look at a "branch manifold" between the turbo and the head... A mirror image of the exhaust manifold (in length) perhaps?

(I'm assuming multi-point injection just before the head)

[graham bahr]

Originally Posted by dtype38

Now that is interesting...

Maybe rather than looking at the intake to the turbo, it might be productive to look at a "branch manifold" between the turbo and the head...

already got one, well two in fact as i've just made a new one to suit the 16v engine.

actually i miss read your post i thought you were talking about exhaust manifolds, but as it happens the answers the same inlet or exhaust

[graham bahr]

Originally Posted by dtype38

They're pretty long intake trumpets you're using Graham. Just out of interest, have you ever tried a tuned length branched intake manifold (like the reverse of a tuned length branch exhaust manifold)?

that is basically what your doing with ram pipes on throttle bodies, without chokes, aux vents etc to interfear with the induction pulses the engine sees the whole induction system as the intake length.

those huge long intakes were obviously refeering to my engines before i started bolting turbos on, once you do turbo them as long as the manifolds can deliver enough air evenly all this intake tuning stuff goes out the window

[dtype38]

Originally Posted by graham bahr

once you do turbo them as long as the manifolds can deliver enough air evenly all this intake tuning stuff goes out the window

Is that a general principle, or does turbocharging just move the goal posts or change the rules a bit. I can see why it gives a massive power boost all by itself, but wouldn't tuning the intake manifold achieve the same charge density at a slightly lower boost, which would in turn produce less exhaust restriction in the turbine? Dunno. Is it just that the benefits are so minute as to be not worth bothering about?

[graham bahr]

it totally changes the rules,

the reason pulse and ram tuning work in atmo engines is that at certain lengths/ revs etc you get a slight supercharging effect, where you have actually created a positive pressure wave ramming the mixture in, although at certain points you can get the opposite a negative wave that will actualy increase the vacuum in that tract and get worse cylinder filling, obviously these effects only start to take place once you have a decent amount of air flowing into the cylinders, by which time a forced induction engine is pressurizing the system many times more than any ram or pulse tuned effect, rendering this type of tuning pointless.

[dtype38]

I'm familiar with the concept of standing waves in intake tracts. I was just curious as to if this effect isn't similar in turbocharged engines, but just much shortened in length due to the higher density of the air.

[graham bahr]

i see what your getting at, but it doesn't happen, as you cant get a pulse somewhere there is a much greater pressure present, and if the engines going slow enough not to have any boost then its also not going to produce in intake tuning pulse,

you also need to bare in mind that turbo engines use cams with quite mild timing and almost no overlap which effectively also stops induction tuning, its the same only the opposite way round why ram pipes etc only start to make BIG differences in atmo engines once they have some pretty radical cames fitted

[dtype38]

Ok, my comprehension is growing significantly here But you do manage to keep putting in little throw-away lines like:

Originally Posted by graham bahr

you also need to bare in mind that turbo engines use cams with quite mild timing and almost no overlap which effectively also stops induction tuning,

Doh!

Well, ok, I understand that with big overlap cams we're talking intake tract tuning with the aim of keeping the charge flowing in the right direction during the overlap period. We need momentum in the intake charge at just the right moment (not unlike two-stroke inlet design), coupled with exhaust exit velocity for extraction effect.

But! I thought that similar momentum principles could be applied to short duration cams to create "over-pressure" behind the inlet valve during its closed period. I understood that with enough length of intake tract, the momentum of the air flowing air in the earlier sections can be used to "compress" the air behind the valve when its shut, with a consequent gain in initial cylinder filling as it opens. Is that not the case?

[graham bahr]

Originally Posted by dtype38

Ok,

But! I thought that similar momentum principles could be applied to short duration cams to create "over-pressure" behind the inlet valve during its closed period. I understood that with enough length of intake tract, the momentum of the air flowing air in the earlier sections can be used to "compress" the air behind the valve when its shut, with a consequent gain in initial cylinder filling as it opens. Is that not the case?

yes sort of, infact ram tuning has more to do with the air mixture going into the cylinder through the open valve with such velocity and interia that despite the piston comming up and trying to push it out again it still piles into the cylinder effectively overfilling it, but that doesn't happen at low revs, or you wouldn't have a vacuum in the manifolding, my point is still that by the time you have enough revs to make any of this induction tuning work and maybe generate a few miilibars pressure round the back of the valve or into the cylinder the turbo is now generating maybe 0.25-0.5 bar boost.

[dtype38]

Ahaaa


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[graham bahr]

morning ken