I bought a bare '99 head and a '99 intake. The head is gonna get freshened up, and I'm going to run stock valves, stock cams, stock everything.
The intake is a different story.
I have been reading up on possible performance gains from gutting the VICS chamber, and unless I am looking at it wrong, I came up with this.
VICS is actuated at a set RPM. This opens valves and changes the runner length, allowing slightly more air into the engine. The goal of removing the crap in the upper plenum is to allow a lot of air into the engine, thus the more CFM's flowed, the more power will ultimately be made.
Here's my plan:
The first photo is the upper intake. The whole green area will be removed after I trace the outline of the gasket (and clean off the dog hair). The red part looks to be some factory port where the air flows through to the lower part of the intake. I want to snip off the part of the gasket that's in yellow, and also remove that chamber on the upper plenum (which will be part of the green colored removal task anyway.
The second photo is the lower intake. The red smiley face sort of drawing is the factory chamber where the air flows. I plan of leaving that right where it is, but where the red line is on the left; I plan on welding that shut. The yellow part on the right will be shaved down smooth against the face that the butterfly's meet, and the red port inside of it will also be welded shut.
Does anybody know the reasoning for this factory port? Why does it come from the center of the chamber on the upper plenum and flow to the front of the lower plenum? Is it for equilization purposes?

 

Pretty sure all the extra ports/holes/chambers are for EGR.

 

I forgot to mention, EGR is getting welded shut too. There will be nothing emissions related, PCV is also getting the same treatment. The only ports I am leaving on the intake are for vacuum to supply my brake booster, my BOV, and for my MS signal. I should actually say, "I am leaving all my factory vacuum ports right where they are."

 

Delete the EGR, that's no problem. But why get rid of the pcv? Or are you planning some sort of breather/air-oil seperator/fancy catch can system?

As for the rest: do you plan to do anything around/near the tb? Or touching the tb or replacing it? It seems kinda half *** to me when people port/gut manifolds but then leave tb and passage right past the tb bone stock. Seems like itd bottleneck

 

I've got a modified 1999 upper manifold sitting by my desk if you want to save yourself some effort.

There is a chamber in the manifold that's a vacuum reservoir for the VICS actuator.

 

I plan on running a similar crank evac as FaeFlora, single -12AN line with check valve.
As far as TB, I'm thinking stock. I currently run an SR20 turbo with 2" I/C plumbing into an FM I/C that has 2 1/2" ports. I want to ditch the Sr20 turbo for the same godspeed 3076 that you ran, Vlad; then upgrade to 2 1/2" plumbing. With a turbo of that size, I think I'll have no issues with moving a greater volume of air.

 

Right but that's not my point: if you're moving more air pre and post tb, wouldn't it be a good idea to address the tb and try to free up some flow there too?

Unless our tb's flow a ton of air that I didn't know about and its really not a bottleneck..I dunno

 

Please share your results with us, it still seems like we're lacking some good emperical data on gutted manifolds. I've got a friend who's gutting one for me now. I'm hoping to get some good before and after logs to compare, but I'd love to see some other results.

18psi makes a good point about the throttle body, but are there any inexpensive bolton options for us to upgrade to?

 

We've tested them on high-output naturally aspirated engines. There's no benefit. However, Gary at Track Dog says that they do show a benefit on boosted engines. We're going to do some before/after testing on an FI car shortly: stock VICS, gutted VICS, stock VTCS and flat-top.

 

I'll be looking forward to the results, please be sure to share with us!

 

+1 in for results

 

Boost is different though

Todd get rid of that stupid brass knickle ahit too. The volume of that is not negligible. About 2 cups of aliminum

 

I'd rather leave the VICS intact so that I have adjustable runner length. I just want to remove the restrictions that lead up to the VICS so when it opens I have a significant amount of flow.

 

VICS isn't adjustable runner length. It's adjustable plenum volume. Hollowing out the plenum actually gives you a short/long runner option.

 

That's what I meant, but I worded it poorly.
I'm so pumped to finally start doing something performance related on my engine that I think I may just start on this tonight when I get home.
Does it make sense that I'm keeping my '99 head stock?

 

Here's what I did with mine. I felt there was an advantage because now can use the extra plenum volume at a lower rpm. I can set this at say 65% throttle and up and open the VICS at whenever the throttle is floored. Seemed to help with spoolup/boost. Take out and smooth as much metal as you can in the area after the air goes through the TB and up over the hump into the plenum.

https://www.miataturbo.net/showthrea...highlight=VICS

 

My friend ported the top half for me, he's still working on the bottom half. I installed the gutted top half with the full bottom half to see how it would do. Based on back to back logs graphed in virtual dyno we can definitely add this to the "what not to do" list.

Blue is stock, Red is with the ported top. Both done at 15psi.

 

oh snap, that's terrible

 

By porting the bottom half, do you mean removing VICS? I can't believe just a gutted upper plenum would effect it in such a negative way. Thoughts on why?

 

The bottom half of the intake manifold was untouched with VICS active. I can only assume that the ported top disrupted flow enough to lose power. I'm putting it back to stock until the whole manifold is ported and I'll try again.

I'm doing some more comparisons today since I'm undoing it anyway, and it's difficult for me to believe it would be THIS bad. I'm doing a log at 19psi, and one with the wastegate disconnected (since my friend is running this setup on his NA car). I'll let you guys know how the numbers come out.