Fins on back of Valve & Fins pre TB

[festy]

Lots of difference in the plenum shape. Do you think this is for packaging or are they looking for different effects? What the most important feature of the plenum? Volume or shape?

Shape has a lot to do with it - here's a simulation of a plenum that was being built for an Alfa inline 4.
[youtube]https://www.youtube.com/watch?v=0ft7W_2PbYI[/youtube]

edit: Meh, I lost at youtube embedding roulette again so here's a link instead: http://onemanracing.com/en/uncategorize ... simulation
mod edit: you need to use a /watch? link .... ive fixed it for you

[vlad01]

While on a visit to Biggvl's shop today I we gave another shot at tuning the gemini after custom extractors.

we did the unthinkable, proving/disproving the function of the bellmouth in the VN-VR engines with real test results.


This VN s1 worked engine didn't have one to begin with so we decided to install one as see what it did.









After we tuned it.




Now to install one

















We lost about 10hp and around 20-30Nm by the looks of it with bellmouth installed.

[immortality]

Awesome. That's another definite result for the doubters.

[vlad01]

I never would of thought that would be the case, I always thought it was the other way around and that it was just a myth that removing it would increase performance.

My speculations were completely wrong. But its good! as it means there is more power and torque to be had from my VR and that we all can learn something for it.

So what is the function of it? Its incredible interesting now such a small change can have such larger real effects on how a manifold works.

[vlad01]

Awesome. That's another definite result for the doubters.

that's the thing, In the nearly 10 years of tinkering with the V6 and lots and lots of reading and searching on the net, no one had ever come though with data and results to prove claims.

I think we maybe the first ever to document it for everyone to see.

[Gareth]

That was a surprise, goes against a lot of theory i've been reading lately...

So why was it put there to begin with???

Forgot to take photos of the 'dual plenum ecotec manifold' that we sat together today, ill go back up to the shop tomorrow and take some and post then, sorry vlad.

[VL400]

Air distribution to the rear cylinders?

Otherwise it probably works like a restrictor plate! Did you happen to get a log of the two runs? Likely pulling some vacuum with it installed.

[vlad01]

On Tueday when we run your ecotec VH, can we take the plenum lid off and post a pic of that as well?

I'd love to see what makes this engine special.

[vlad01]

Air distribution to the rear cylinders?

Otherwise it probably works like a restrictor plate! Did you happen to get a log of the two runs? Likely pulling some vacuum with it installed.

I didn't log it as I saw no change in the new VEs in the history table from a quick look , it was unchanged with AFR and vac too. The MAP is connected tot he TB so its before the bellmouth anyway.

Same thing happen with my VR stock air box and mace CAI, the fueling stayed the same despite a larger difference in airflow.

[yoda69]

Can be a lot of strange things from the OEM's, but there is normally a reason.
The only one I can imagine for this is that maybe at cruise or mid load there was some uneven cylinder filling and this helped to balance it out a bit and was a reasonable compromise across the entire rev and load range.
WOT runs are only one a small snapshot of a vehicles running conditions, OEM's spend a lot of time working on driveability, especially in the areas a "typical" driver is expected to spend a lot of their time.