Have driven my 3.4 pushrod conversion for a couple of days now and wanted to give my impressions. After having heard that you shouldn't expect much over the 2.8 without major mods, I wasn't sure what to expect. I don't consider head and manifold porting, or cleaning up the exaust restrictions, major mods. I did put the sprint headers on it and an Engle cam with specs between the 260 and 272 cams. It also has Comp 1.52 roller tip rockers, a Darrell Morse TB, and I "throated" the upper plenum. That's it, stock bore, stroke and compression. Stock exaust with a cat. It's a rocket! I have new GoodYear Assurance tires on it and, even with an automatic, I have to be careful if I want to keep them stuck to the pavement. I can't imagine what it must be like to drive a Fiero with one of the higher hp conversions. Anyway, anyone considering a 3.4 pushrod conversion but wondering if it's worth it, it is. I don't think I would want my wife driving it if had any more hp. Hope to get it dynoed by the end of the month and will post the numbers.
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08:59 PM
PFF
System Bot
carnut122 Member
Posts: 9122 From: Waleska, GA, USA Registered: Jan 2004
Wasn't it you who added the extra section to the bottom of the upper plenum inlet pipe, to increase the diameter? I'm looking forward to seeing your dyno results.
What injectors, chip, fuel pressure regulator are you using?
------------------ Raydar 88 3.4 coupe........... Coming soon... 88 Formula, presently under the knife. Read Nealz Nuze!
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09:37 PM
triker Member
Posts: 454 From: Yreka, Ca. USA Registered: Apr 2000
Yes, I'm the one, I'm calling it "throating" the stock manifold. I'm using the stock chip and the 17# , 3.4 injectors (cleaned and tested). I did a data scan with the stock chip and the numbers don't look too bad. I'll run them by darthfiero as soon as I get my adjustable fuel reg installed. Anyway, it pulls hard to 6 grand and I'm happy!
I cut open the neck or "throat of an upper plenum and found that the cross sectional area at the narrowest part is only about 18 square cm's whereas the bored TB has an area of 25 square cm's (stock is 21). So, using a piece of 2" id aluminum tubing, I've increased the neck to about 27 cm's. I have more pictures of the steps but here is a pic of the finished product.
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11:42 AM
lou_dias Member
Posts: 5258 From: Warwick, RI Registered: Jun 2000
I cut open the neck or "throat of an upper plenum and found that the cross sectional area at the narrowest part is only about 18 square cm's whereas the bored TB has an area of 25 square cm's (stock is 21). So, using a piece of 2" id aluminum tubing, I've increased the neck to about 27 cm's. I have more pictures of the steps but here is a pic of the finished product.
You nailed it right on. I have a plenum that I cut out the Fiero logo and I have some access to that area. It is the most pinched section of it. I took some rough measurements of it and came more or less to a 1 1/4" X 2 7/16" at that point for an area of +/- 3.0468 sq-inch. Stock TB measured a diameter of 2 1/16" for an area of 3.3393 sq-inch. That is about 9% restriction. Now for my Darrel bored TB the diameter is 2 3/16 for an area of 3.7563 sq-in. For that one it is about a 19% restriction. I think your idea is just great
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03:34 PM
triker Member
Posts: 454 From: Yreka, Ca. USA Registered: Apr 2000
It's even more restricted than that if you measure diagonally accross the neck instead of staight across the front of the plenum where it widens out. Anyway, other than porting out the runners where they turn down into the middle manifold (you can remove at least 1/4 inch of the outer radius there) I didn't do anything else to them. They look stock (I did two of them) and I'm happy with them.
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05:26 PM
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Nov 27th, 2005
1MohrFiero Member
Posts: 4363 From: Paducah, Ky Registered: Apr 2003
