quote Originally posted by Will: I would think you'd need more plenum volume than that would provide...

+1

The plenum servers a purpose, and should be designed to the specs of the engine, not the size of the TB being used.

In that case, and since there isn't much of a plenum on these setups, would that just mean use bigger diameter piping to give some more volume?

Just some ideas, but when I built mine, I didn't use tubing. I welded a piece of 3/16" thick aluminum plate to the cut-off runners to make the "floor" of the plenum. This allowed me to clean up the port transition from the plenum into the runner, and add a nice smooth bellmouth. Once this was complete, I used some 0.090 aluminum sheet that I carefully bent to a u-shape by hand using a 2" piece of pipe. This was then welded to the plate to complete the plenum shape.

This technique will let you make the plenum to whatever dimensions you want, and not be limited to off-the-shelf tubing sizes. It also makes the transition from the plenum to runner easier than it would be with a round tube plenum. The biggest advantage to me is it allowed for a much better transition form the plenum to runner, without the need to cut an access hole in the tube/box plenum that would somehow need to be sealed later. The downside is it requires more fabrication time and some more welding, which may be less desireable if you are hiring the welding out.

Marty

I really like the overall look of the round tubing. However I do like the method you used as it allows you to bevel the runners to the plate. I would imagine that you could weld a plate to each side, bevel the runners, and then take the pieces of tubing and cut off the equivalent of the plate from the tubing and then weld that on. Pretty much the same except instad of sheet metal you just use round tubing. Btw how did this intake setup work out for the car you had it on?

quote Originally posted by goatnipples2002:

quote Originally posted by RacerX11: That is the intake I built for my 3.4L X-11 back in 1999-2000, before all of the forum discussions on the topic became popular. If you look at the picture again, you should be able to see that the middle intake portion was shortened considerably versus stock, so avoiding “overkill” was not a factor. ...For mine, I cut the middle intake perpendicular to the runners at the point where the port shape and curve upward begins....The end result is a straight shot from the plenums down into the intake ports....

Thanks for clearing things up for me with your response. I see now what you did, eliminate some of those nasty, sharp turns that airflow otherwise would be forced to take with an unmodified Fiero V6 intake manifold. The "striaght shot" of air with your set-up became especially apparent to me after I located a different picture, that of your intake manifold turned upside down:

quote Originally posted by goatnipples2002:

In contrast, I thought this picture nicely illiustrates the tortuous bends of a stock V6 Fiero intake manifold:



Source: A photo by triker on page 3 of his thread, Porting the Fiero intake ( https://www.fiero.nl/forum/A...0811-2-066086-3.html ).

Not my auction, but I built this manifold: http://cgi.ebay.com/ebaymot...em&item=270709324671

quote Originally posted by Jennings03: I would think that any extra space in the intake would just mean that it takes longer for the air to travel through the intake, and the closer to the same size as the TB would create more vacuum. However I have absolutely no experience here so anyone with ideas or knowledge on this would be great. I probably won't actually order any tubing until this weekend and that link you posted project34 looks like the best option for the tubing.

If it makes you feel more comfortable about the plenum diameter sizing issue, be aware that PFF member, TT Slick, who I believe created that shiny dual plenum intake manifold I posted a picture of before, used aluminum pipe with an inside diameter similar to the 52mm we discussed earlier, although from its outside appearance, it might seem much wider than that:


The illusiopn of wide plenums on TT Slick's set-up occurs because the outside diameter (OD) of his plenums is much wider than that of the pipe I mentioned to you in an earlier post, but the inside diameter (ID) is not. How can that be? As you've probably guessed, he simply used pipe with much thicker walls (1/2 or .500-inch, instead of the thinner, .154-inch thick walls of the pipe I mentioned earlier) in order to get, as TT Slick stated, an ID of 2" from a pipe with an OD of 3":

quote Originally posted by TT Slick: My tubes are 2" ID x 3" OD extruded aluminum, one side is milled flat just wide enough to bolt to the middle intake. These are then bolted in place, mounted to a milling machine bed and the fronts are milled square and parallel. The flanges are 3/4" thick and weleded to the front of the tubes....

Source: See page 2 of the archived thread, How to build a dual TB intake ( https://www.fiero.nl/forum/A...100421-2-077346.html )

quote Originally posted by Jennings03: I really like the overall look of the round tubing.

If you're interested in installing cylindrical dual plenums similar to the way TT Slick did his, it looks like you can easily order aluminum pipe having the dimensions he used, an OD of 3" and an ID of 2" (which is 51mm, versus the stock throttle body's 52mm), from a different page of the website I mentioned earlier, namely, http://www.speedymetals.cal...061-t6-aluminum.aspx .

Incidentally, Jennings03, you may be interested to know that within the same post of his that I cited earlier, TT Slick stated of his set-up:

quote Originally posted by TT Slick: With twin throttle bodies it never stops pulling, I don't think I've had it to max RPM yet.

Ok so its been a few months delay on the intake I've been making but I finally bought the aluminum tubing for the intake. It has an inside diameter of 52.5mm as some of you have suggested. My question now before I cut the tubing is how long each pipe should be? Which is better longer or shorter? Or somewhere inbetween?

You call 5 months a few?

I already made one for a 3.4, but I sold it to Xanth here on the forum after I rid of my headache POS 3.4. It was a learning experience, and it was also a total money waster.

Picture updates of progress.



The tubes are 14 inches long and are shaved down on the bottom with a flat plate that gets welded to the top of the runners. This way I can match the ports and bevel the top of the runners instead of it being a sharp transition.

quote Originally posted by project34: I'd hoped that somebody would have been manufacturing these for sale by now. However, the short answer to my question about that in the aforementioned thread was "No" in 2009, and unfortunately, it still is.

Actually someone is making a dual throttle body intake for the Fiero:

This is the company that makes them: http://www.yourstreetsoluti...rticle&id=7&Itemid=9

Here's where you can buy them: http://www.tlg-store.com/Hi...nifold_p/4010104.htm

They're not cheap, but small volume handmade items never are.

Before you weld the plenums to the middle intake, port the hell out of that middle intake. The runners in the stock intake are pretty thin. Plus, there are casting flaws and irregularities that will hamper airflow.

Yea if you look on the first page I have already ported the lower intake. Now I just have to drill and match the aluminum plate on the bottom of the tubes to the middle intake and Im also going to bevel the plate to make for a smother transition.

I know this is an old thread but was just wondering if this manifold design was ever completed. From the offset plenum tubes (rear one towards pass side, front towards drive side) it looks like a TT setup might be in the works. Nice job by the way!