Cold Air Handling, an Hypothesis....

[TurboDave]

Originally posted by bruce


Now, you've changed things to suit your point.
If you look back I said increasing the volume was a good thing, and didn't limit it to JUST using a spacer.
With some work you can about double the oem plenum's volume, and that does work. Which gets back to the original statement that you disagreed with. A large plenum will even out the distribution, and you don't need to be running 9s to notice it. And a simple glance at a how HAC ducting is done will clarify what the real problem is.

While a spacer alone might not make a huge difference, things add up. Rework the plenum, add a spacer, and you can make a difference. Not to confuse things, but I increased my plenum 30 CID, and then had to add 8% more fuel to get back to a given AFR. To me that would indicate, the engine was flowing more air, and needed an increase in fuel. And again, to me, I think increasing the airflow, and amount of fuel an engine consumes, maintaining a specifc AFR, would be a good thing.
YMMV

Well, I'm not going to continue argueing with you. My point was that plenum spacers in turbo charged applications haven't been proven to work (as they're sold for our mostly stock type manifolds). You then moved the thread in the direction of "distribution". OK, fine, but they certainly don't help distribution, not an open spacer anyway, as was first brought up.
OK, then you moved it back toward the "volume change" making more power. I guess we'll have to agree to disagree.

What ET and MPH gains did you make with the spacer. And please don't throw a lot of "high brow" theory at me about having to change "this or that" because of "whatever". Show me results and you'll have a convert.

 

[The Radius Kid]

Originally posted by bruce


While a spacer alone might not make a huge difference, things add up. Rework the plenum, add a spacer, and you can make a difference. Not to confuse things, but I increased my plenum 30 CID, and then had to add 8% more fuel to get back to a given AFR. To me that would indicate, the engine was flowing more air, and needed an increase in fuel. And again, to me, I think increasing the airflow, and amount of fuel an engine consumes, maintaining a specifc AFR, would be a good thing.
YMMV

I'm with Bruce on this one.Plenum volume and resonant effects are not just limited to normally apirated engines.Take a look at the Buick Indy manifolds[Big Joe Horvith has one on his car,I believe],fixed plenum volume and variable length runners.You can change the length of the manifold runners in relation to the plenum to work in conjunction with the head runners,changing the point that the runners become resonant in relation to the rpm's.
A plenum has a point at which it becomes resonant or augmentive in conjunction with the intake runners.Need an example,look at all the bandpass boxes kids use for there car stereos.They tune their boxes and their woofers responses by varying the internal volumes in relation to the port sizes and it works.What they're playing with is Helmholtz tuning.that effect comes into play in intake manifolds as well.
I've played with different spacers and they do even out the airflow distribution to no small extent[check the plugs before and after,you'll see it].You can hear it in the tone of the engine under power and off.You can see it in the gas mileage and in the way the car responds to throttle.
I found the 1/2" spacer to be about the best compromise,3/4"-1" was too much[power dropped off in the bottom end even though it came on big in the top end],1/4" was not that noticable.No spacer had snappy off idle response,but didn't seem to "have it" in the top end like the 1/2" spacer did.
These are just some observations I've found through empirical testing and trying,and have found them to hold true as have many stock and race engine designers around the world including F1 and Cart.

 

[salvageV6]

Thank the Lord I saved my Kenne-Bell Indy plenum spacer. 1/2" too.

 

[bruce]

Originally posted by The Radius Kid


I'm with Bruce on this one.Plenum volume and resonant effects are not just limited to normally apirated engines.Take a look at the Buick Indy manifolds[Big Joe Horvith has one on his car,I believe],fixed plenum volume and variable length runners.You can change the length of the manifold runners in relation to the plenum to work in conjunction with the head runners,changing the point that the runners become resonant in relation to the rpm's.
A plenum has a point at which it becomes resonant or augmentive in conjunction with the intake runners.Need an example,look at all the bandpass boxes kids use for there car stereos.They tune their boxes and their woofers responses by varying the internal volumes in relation to the port sizes and it works.What they're playing with is Helmholtz tuning.that effect comes into play in intake manifolds as well.
I've played with different spacers and they do even out the airflow distribution to no small extent[check the plugs before and after,you'll see it].You can hear it in the tone of the engine under power and off.You can see it in the gas mileage and in the way the car responds to throttle.
I found the 1/2" spacer to be about the best compromise,3/4"-1" was too much[power dropped off in the bottom end even though it came on big in the top end],1/4" was not that noticable.No spacer had snappy off idle response,but didn't seem to "have it" in the top end like the 1/2" spacer did.
These are just some observations I've found through empirical testing and trying,and have found them to hold true as have many stock and race engine designers around the world including F1 and Cart.

With any plenum change to really capitialize on it you'll want to tweak the Delta LV8 AE a little, and in the case of bigger changes the PE vs RPM. With the real big plenum I added alot of AE, then split the 8% PE between the PE vs RPM, and PE vs TPS.
And yes, the plugs get more evenly colored.
In some forms of racing they are reaching 1.5 to 2x the engine displacement in plenum volume. But the GN manifold is really tiny compared to those. BTW, some of the Australian Turbo Drag cars fall into that large plenum catagory.

 

[The Radius Kid]

Oh sure,go talking all technical like!
Salvage,if that spacer is the one that dooesn't overhang the inside of the plenum,it should work pretty well.
I should also add that my doghouse and T-body[stock size at the time of testing]were "Jacksonized"[about 7 years ago before I ever heard of the Jackson treatment or this board.It just made sense.].
I also have been using the cold air inlet,dropped behind the headlight for about five years now,before they became popular.
Surprisingly,my setup looks a lot like the ones avaialable now.Go figure,I guess we were on the same page.
If you run the standard PV/T formula in S.I. units,you'll find that using 75 degrees for coldair and 200 degrees for underhood[converted to S.I.],you'll see a density increase of ~ 8-10%.
Of course,underhood heating of the air inlet,reduces the temp difference at that plenum.that suggests to me that some heat insulating of the inlet and I/C pipes is in order.
However,even taking that into account,I had to raise my F/P 8 lbs to make the car run right again.Something had to have happened to cause this need.