Lower plenum modification

[bruce]

Well, the disclaimer at this stage it would be too expensive, and time consuming, to mess with, but it does work.

What you say?.

Increasing the plenums volume.

There are all kinds of *cures* for evening out the air distribution, but there are several factors involved.

First is considering what the manifold was designed to do and then what we're asking it to do.

One of the concerns of GM engineering is the EPA. Most all the testing is done at low speeds, and fuel mileage is a big issue. So they want to min accleration enrichments. A dry manifold is a great way to do that, and keeping the plenum small is another way. The Dry manifold is a done deal and it's pretty close as delivered. But, in my opinion the plenum is too small. After investigating what could be done with the upper, I decided on redoing the lower. Well what was 42 CID is now 72, on my car. It's taken 8% more fuel at WOT and it's still a little lean, and it's taken a whole lot of Accleration Enrichment, to get it right.
Yes, it works, and works well.

I have another manifold now, and am going to take it to the max with this principal. As thrilled as I am with this first effort, got some neat ideas to try on the next one.

Just a share, and some food to think about.

 

[Dan Thompson]

Are you saying you ported the lower plenum?

 

[FJM568]

Hey Bruce, how much bigger of a plenum volume do I have with a CAS V2 FM and about 6 ft of 2.5" alum. mandrel bent tubing??? I have a stock 87 lower intake, but running a TA51 turbo in the stock 85 location...TB is mounted on the turbo...So I have basically increased my plenum volume by a CAS V2 FM IC and about 6 ft of 2.5" alum. tubing...Any tuning tips you could give me???

BTW, do you know if there are still any parts kits available for the DIY-WB O2 setup??? I'm still waiting to hear back from the guy who was handling it about my request for a couple(need 3 kits), but haven't heard anything...Been a long time

Thanks...

 

[John Larkin]

Back to the old hotrodding days, an open plenum has lower air velocity than say a dual-plane; runner size and length also affects velocity. Even though ours are open style stock, in your opinion what do you think your enlargement process as done to the airflow velocity and what RPM range do you feel you gained efficiency in? What's the seat-of-the-pants meter say?

 

[bruce]

Originally posted by Dan Thompson
Are you saying you ported the lower plenum?

Not even related to porting, other then grinding some walls out.

 

[bruce]

Originally posted by FJM568
Hey Bruce, how much bigger of a plenum volume do I have with a CAS V2 FM and about 6 ft of 2.5" alum. mandrel bent tubing??? I have a stock 87 lower intake, but running a TA51 turbo in the stock 85 location...TB is mounted on the turbo...So I have basically increased my plenum volume by a CAS V2 FM IC and about 6 ft of 2.5" alum. tubing...Any tuning tips you could give me???

BTW, do you know if there are still any parts kits available for the DIY-WB O2 setup??? I'm still waiting to hear back from the guy who was handling it about my request for a couple(need 3 kits), but haven't heard anything...Been a long time

Thanks...

If you're really wanting to figure the volume of what you have out, I'd suggest removing it all, capping off the carious bits, and then use a 1 liter pop bottle to measure how much fluid it takes to fill up all the pieces. Then knowing a liter equals about 60 CID (feel free to look up the exact amount), then you can figure all the volumes out accurately.

Last I heard he still had kits available.

 

[bruce]

Originally posted by John Larkin
Back to the old hotrodding days, an open plenum has lower air velocity than say a dual-plane; runner size and length also affects velocity. Even though ours are open style stock, in your opinion what do you think your enlargement process as done to the airflow velocity and what RPM range do you feel you gained efficiency in? What's the seat-of-the-pants meter say?

Geesh, just mix a bunch of topics together why don't ya....

Runner velocity is primarily a function of cross sectional area, all other things being equal.

In a N/A engine, the plenum works as a function of various wave motions, and everything effects that. On a turbo motor all this stuff still matters, but only when in N/A, mode.

When you start talking turbo or super charged engines, then the plenum, is basically a capacitor. It's just a large reserve of air available to feed the cylinders. The large the volume, and higher of pressure it has, means that the instant the valve cracks open the air will try and fill the void, and actually start to push the piston down. This pushing of the piton down, is what gets the non N/A engines for far into the incredible range VE wise.

The air as it enters the manifold is moving fast, and has alot of inertia due to this speed. It's this air with so much enertia that when it hits the floor in the rear of the manifold that the path of least resistance is filling 3+6. Twist the boost up, and it makes the problem worse. By removing the floor and changing the rear wall of the manifold you can avoid this. In looking at various manifolds, it just seems like more is better to a large degree. As for my theories about what the correct volume is, I'm not ready to say until I do some more testing with what I have, and run the next generation manifold.

As far as the buttometer,
well,
I hate guesing, but here are a few points to ponder. I've added 8% more fuel. HP is .5 BMFC. Sooo, this 8% increase in fuel MIGHT, and I say MIGHT be reflecting a 16% increase in HP. There is going to be alot of that potential gain lost in cylinder cooling. But, the difference is dramatic. And, again this is in my case, I do have the ignition to really fire things, and I don't know if a stock DIS system begins to have enough reserve to light the mixture like this.

With the larger Plenum all the Accleration Enrichment stuff gets involved, and that in it's self is headache. And that's going to vary by ecm used. While you might think an aftermarket ecm can cover this easily, at first glance, I'd say, maybe yes and maybe no.
The oem ecm has alot of AE stuff in it, and the aftermarkets are trying to keep things simple, and I don't know if they have the sophistication to pull this off.

For rpm ranges, well,
below 2,200 has taken alot of work to get the drivibility correct and that's been an AE thing. And I've had to add alot of fuel at 2,400 rpm in PE mode. So it seems that below 2,200 has taken a hit in performance, while WOT from about 2,400 rpm has really improved. And I even added more, and more fuel starting at 3,200.

Again, this ain't some easy bolt-on, but, hopefully that will change.

The fun part is that this is almost invisible when installed.........

 

[charlief1]

We miss you Bruce but this is worth bumping.

 

[trixdout]

Now I was thinking because this motor is a turbo'd motor and some people that have high power and go well into the low 9's and have the issue of leaning out cylinders 1+2, really don't know if anyone has tried this and what kind of results they had, but what if they rotated the manifold horizontally 180 degrees. That way the turbo keeps pushing the air towards the front of the car into the manifold because it is rotated that it does not lean out cylinders 1+2?