Plenum Ponderings

[LGAFF]

I was reading up on the Helmholtz resonance effect from intake tuning, specifically does the LT-5 open plenum leave power on the floor. Helmholtz is about creating a denser charge in the intake; which cannot be done with an open plenum due to the # of pistons opening/closing....he is a interesting product from a 928 engine builder.

ftp://12.234.229.133/installpdf/32Vintakemanifoldarticle.pdf

Secondly as I siamese my intake I have to wonder if it would benefit from coating the intake runners to block heat. The injector is so far down the IH that heat is not playing role in fuel atomizing and we have wide swings in temp from runner to runner with some exposed to coolant and others not.

Anyway, lets hear some thoughts....

[LGAFF]

With regard to helmholtz I am saying we woul need to divide the plenum

[Blue Flame Restorations]

Intersting theory...

[mike100]

My feeling is that a large displacement over rules the sonic resonance as it is conventional wisdom that certain engines always ake more HP when the port volume is increased.

this also changes the resonance to different speeds and such. I think intake designers already took that into account when the picked the runner volumes and lengths.

The one thing I'm interested in modern engine technology that uses moving parts inside the intakes to complement variable cam timing etc to have such a broad powerband.

Lambos have velocity stacks that change length and I know many cars these days have variable plenum volume flaps/doors inside them. I think variable tuning is the way to go- your pretty much stuck with what you have on the LT5. you may loose resonance at a desired rpm, but gain back more in total airflow as experience shows with certain mods.

btw, the link wanted a password

[LGAFF]

While I try to find the link, check this out...

http://forums.pelicanparts.com/porsche-928-technical-forum/488692-640-whp-7-litre-928-a.html

[LGAFF]

http://www.928motorsports.com/parts/intake_runners.php

Click on read the whole story...its in dark lettering by the pics

interesting use of nylon runners

[LGAFF]

http://www.ferrarichat.com/forum/showthread.php?t=317052

"The air box is a helmholtz resonator tuned to a 1/2 multiple of the velocity stack resonance. This resonance spresses the peaks and enhances the valleys of the velocity stack, giving a broad wide torque powerband"

[mike100]

sprint cars and vintage racers still keep velocity stacks alive. I personally think the individual throttle plates affect it the most. Really these types of manifolds are for top end power- I thought M3 sixes had indivial throttles, but that is an 8000 rpm engine I think...Taurus SHO w Yamaha engine comes to mind for some reason too.

http://www.kinsler.com/page--GM--17.html

[Locobob]

The 928 guys are sure doing some neat custom stuff.

[A26B]

If I ever get my shop built, I've been toying with the idea of a new plenum/inj housing design with internal velocity stacks and twin T/B's as the stock T/B is maxed out at 64mm. My current thinking is each bank would be communicated to the other. The lid will be removable, so it would be simple to dyno with & without the dual plenum divider window open.

[LGAFF]

really considering a divider in the plenum:

http://www.stealth316.com/misc/grapeape-inductionsystems.pdf

http://www.sporttruck.com/techarticles/0909st_increasing_power_output_4_6l_modular_ford_m otor/intake_manifold.html