02GF74
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| posted on 3/4/09 at 09:33 AM |
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confirmation - effect of inlet manifold length and tuning
... probably been asked a trillion times before but what is effect of inlet manifold length?
I seem to recall that shorter lengths are will be more effective at high rpm and longer ones at lower rpm.
no doubt cam timing has an effect too.
so a simple summary anyone?
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omega0684
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| posted on 3/4/09 at 09:55 AM |
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AFAIK its best to have the butterflies as close to the inlet port as possible for the best throttle response
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dinosaurjuice
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| posted on 3/4/09 at 09:58 AM |
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for throttle response: as close as possible.
for more torque at lower rpm: longer is better (usually)
i think saab came up with the idea of a variable volume design which gave best of both worlds.
bmw have a system where the valve lift is varaiable - wont get much closer than that!
[Edited on 3/4/09 by dinosaurjuice]
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l0rd
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| posted on 3/4/09 at 10:18 AM |
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Is that why my laguna is so slow and the throttle responce is awful but have plenty of torque at low rpm?
The manifold runs from the back of the engine to the front.
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Phil.J
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| posted on 3/4/09 at 10:28 AM |
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Have a look at the FAQ section on the Jenvey site here:
http://www.jenvey.co.uk/
It answers most of the questions people have about induction systems.
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smart51
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| posted on 3/4/09 at 10:30 AM |
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Longer inlets resonate at lower frequencies so contribute to better cylinder filling at lower RPM but may restrict airflow a bit at high RPM.
Shorter inlets resonate at higher frequency as there's less volume of air in there. This gives better filling at higher RPM so better torque
and power up the RPM band.
Resonance in a system of a cavity (cylinder) and neck (inlet tract) can give a cylinder volumetric efficiency of over 100%. That is the air and fuel
are rushing towards the cylinder at the moment the valve opens and just piles in to the cylinder. When the cylinder is full, the momentum of the air
in the column squeezes just a bit more in, giving you just over 100% filling. The inlet valve closes and you've got a peak in your torque
curve.
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02GF74
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| posted on 3/4/09 at 10:41 AM |
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cheers, 's how I understood it.
Now dare I ask effect of trumpet length? 
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dinosaurjuice
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| posted on 3/4/09 at 10:42 AM |
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quote:
Originally posted by l0rd
Is that why my laguna is so slow and the throttle responce is awful but have plenty of torque at low rpm?
The manifold runs from the back of the engine to the front.
theres a few other factors, but yeah thats why.
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iank
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| posted on 3/4/09 at 10:43 AM |
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quote:
Originally posted by l0rd
Is that why my laguna is so slow and the throttle responce is awful but have plenty of torque at low rpm?
The manifold runs from the back of the engine to the front.
Or it's a diesel 
If you want to see a wacky manifold designed to package maximum length into a small space have a look at a nissan micra.
 
micra inlet
--
Never argue with an idiot. They drag you down to their level, then beat you with experience.
Anonymous
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smart51
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| posted on 3/4/09 at 11:12 AM |
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quote:
Originally posted by 02GF74
cheers, 's how I understood it.
Now dare I ask effect of trumpet length?
The trumpet is part of the inlet. It is the whole length from trumpet mouth to valve seat that affects the tuned frequency. Look at the 2008 R1
engine. It has variable length trumpets that are adjusted according to RPM.
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yellow melos
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| posted on 3/4/09 at 11:23 AM |
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So is there a best length for both tourqe and responce ???
also what would happen if you had say a throttle body nearer to cylinder no 1 ???
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l0rd
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| posted on 3/4/09 at 11:25 AM |
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quote:
Originally posted by dinosaurjuice
theres a few other factors, but yeah thats why.
Apart from the fact that it's 1300+ kilos?
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Phil.J
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| posted on 3/4/09 at 03:46 PM |
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quote:
Originally posted by yellow melos
So is there a best length for both tourqe and responce ???
also what would happen if you had say a throttle body nearer to cylinder no 1 ???
I refer to my posts of a few post ago! There's not much point in asking questions if you don't look at the answers!
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yellow melos
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| posted on 3/4/09 at 04:04 PM |
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quote:
Originally posted by yellow melos
So is there a best length for both tourqe and responce ???
also what would happen if you had say a throttle body nearer to cylinder no 1 ???
I refer to my posts of a few post ago! There's not much point in asking questions if you don't look at the answers!
Look i have had an hour less sleep this week due to the stupid clocks going forward.... give me a chance. 
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