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Inlet trumpet dyno testing


kpr

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Just watching that video again, I wonder how much effect there is from the silicon joiners effectively dampening out the resonance.

So here's something I'd be interested to see. 

Lots of people use a balance chamber between all four cylinders for sake of idle speed and having a map signal etc. 

However when you have your cylinders nearly completely isolated, the actual pressure fluctuates depending on where in the cycle it is. 

Generally what you're trying to acheive is maximizing pressure right as the valves close. 

So I wonder if there's a case where, using a common chamber between them means you've built in a pressure relief point where not only are you lowering the pressure of the port at the critical time when it's above atmospheric and the valves are juts closing. But you've also got another cylinder at its lowest vacuum point chugging on the chamber as well, increasing the pressure differential between the chamber and the high pressure point making it even worse.

At steady state (cruising not full throttle admittedly) with a MAP sensor connected to just a single cylinder there's variations of 20-25kpa through the cycle

Capture.PNG.1dd90fabadc183354621b747f644f0d0.PNG

TL;DR:

Would be interesting to test with and without cylinders linked together
Like it might only be the tiniest smidge of difference, but the tiniest smidge x 8000rpm adds up

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Interesting point. Smooth out the power curve whist taking a bit of a hit in the peaks? 
The setup on there,  runners are 100% isolated from each other, no idle or map circuit.
Hilux has the same same itb's   but are linked via a chamber under the throttles.  which has an 8 or 10mm port from each throttle to the chamber. much the same as what the bmw ran that the throttles came from.  kinda like a mini plenum.  likely too small to have much effect at wot.
Could make a setup linking the runners pre throttle plate  easy enough welding some pipes between the shiny pipes. 

Also  re silicone  joiners i made this vid a few days ago as a follow up to the above one.   To calm down the angry youtube scientists in the comments.       isn't no perfect comparison as to what effect the silicone actually does,   but rules out they were the cause of the massive power loss.  which i assumed they wern't before retesting.

 

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Just now, Yowzer said:

I was wondering if the tubes themselves vibrating was causing an issue and if adding some mass or dampening them somehow would have a noticeable effect.

Starlet manifold vibrates like a bastard around peak torque rpm if it doesn't have supporting braces on it. No idea if that has any effect on the power though

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Thats because no one can harness the full power of a 4k, 

 

 

This is how i needed mine to work. change positions as quick as possible.  so isn't effected by rpm rate.   getting the friction down to almost nothing would be key. so can use a fast actuating system  that doesn't require alot of energy.   linear bearings or something. 
from memory it needed to switch between long and short a few times across the rev range.

If got the mechanical side of it sliding nicely. probably not a whole lot more drama to go full variable

15 minutes ago, Spencer said:

Someone build this, OS engineering challenge.

 

 

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That one looks like it is just an air cylinder so you would only have two positions? Still better than nothing, but I'm sure a system could be developed with more precise control. / combine it with vvt for all the funs

 

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There is a video of that running, it is the real deal, there is another vid of it at idle and it moves though the range super quicl. AS KPR said on normal engines you need a big sweep so packaging, control, friction etc etc are all pretty decent engineering problems. That F1 solution earlier is super slick but only moves like 2 inches I guess due to the RPM and small operating range of the engine etc. 2 step design seems much easier, there are a lots of examples from manufactures.  Thread hijack but hey.

 

 

 

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Thats pretty  sweet.    not what most people would think.     "short hi rpm long low rpm"

Even that one with a fairly big range looks like they are running out of travel

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I think its they are riding the harmonic wave to stretch out the peak, then they quickly skip the "dip" and get to the next peak range again for the next reflection 

Which is why its not just a slow progression

I've seen the same thing on other intakes like that but less severe.
But in the other case it was more like it was shortening fast, then slowed down,, then quickly jumped a distance then progressively travelled further inwards again. Never seen one go in and out like that. And their yoyo of the runners at idle is hilarious. I wonder if its just vacuum operated or something.

I quite like the designs some bikes have, where they sit one trumpet on top of the other, then pull the top one up to let air flow in the sides of the lower one. 


 

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Yeah now i watch it again  it doesn't make much sense.  slowly extending the runner length would get you out of the negative pressure faster than a fixed trumpet.  but doesn't seem ideal.

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It could be that the video was some derp posting it up when they just first got it together and had barely tuned it. 

No self respecting ECU geek would leave it yoyo-ing like that when off the gas. 

Or maybe there's more weird shit going on when you've got an inlet restrictor and and 14,000rpm

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Made  some basic shapes.  Plan is to start with  the straight pvc 51mm id.   no bellmouth at 205mm long,  cut it down  20mm at a time till end up with nothing.   Then move back to current 185mm trumpet length and start to try different diameters and  bellmouths.      
big diameter shiny pipe 57.5mm id. - no bell
silicone bend
solid bend
horrible 90 cast bend     
will probably have to mess with length a bit on the bends to get the harmonic the same
pvc with sharp half bell
pvc  with bigger half bell -  will reshape after testing above
pvc  basic cone  - same as above
pvc  with full plastic bell 

Would like to test  some smaller tubes also,  if anyone has some 2" tube (should have 47 -48mm id)  to donate to the cause or cheap keen to grab it.   material doesn't matter, exhaust tube fine long as isn't rusty.  4x 185mm long

After the basic stuff  will move onto other stuff. 

Thoughts?

 

20200510_130506.jpg.23f87e7b32d522f012eeca9c8357898c.jpg

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