When looking at the 3.4LDOHC engine without its runners attached... makes me wonder if anyone has ever tried to use box steel, a steel plate, and tubular steel, to create a short runner, medium sized plenum intake for a 3.4LDOHC in an attempt to increase upper RPM HP? Just a thought that came to mind. Could also do a dual TB version, dual plenums, angled box steel, to try a more direct path to the intake ports.

Also on a side note, True Dual 180 degree equal length headers for a 3.4L, any real benifit in upper RPM ranges vs just tubular long tube headers? I was thinking if I did a 3.4L DOHC, I could run my true dual design out the middle of the tail lights, with a very short exhaust system.

PS: I know I do a lot of thinking and not a lot of action, I never can make up my mind!

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Graduate of Wyoming Technical Institute
Currently a technician at Amoskeag European Automotive
NH State Inspection Certified

Furry and proud of it!

A while back, someone here constructed a large (about the size of a shoebox, IIRC) plenum that sat on top of six very short runners.
I'm thinking about 4" between the plenum and the lower intake. This on a 3.4 DOHC.
Seems like I remember that the top end was amazing (around 300 HP) but that the bottom end TQ suffered.

I'm sure that someone else here has a better recollection.

quote Originally posted by Raydar: A while back, someone here constructed a large (about the size of a shoebox, IIRC) plenum that sat on top of six very short runners. I'm thinking about 4" between the plenum and the lower intake. This on a 3.4 DOHC. Seems like I remember that the top end was amazing (around 300 HP) but that the bottom end TQ suffered. I'm sure that someone else here has a better recollection.

Thanks! if anyone has links or anything to that I would appreciate it.

That HP number sounds about right for the decreased runner size. I was looking at the 3.4L DOHC runner length and they are massive! I was looking for an increase in upper end HP for high acceleration, without worrying too much about lower end torque for streetability. I actually love the feeling of low streetability engines, when you mat the gas in low RPMs, and you feel it bog for a few seconds, then get kicked in the chest as it catches up with itself, and doesn't stop pulling. With the "Drive it like you stole it" way I drive, my engines generally see high RPMs on a daily basis (my recently rebuilt 2.8L V6 sees 5500RPMs every day, the engine is loving it, the transmission is hating it), so high HP in the upper RPM range is what I aim for, to make it fun. At some point too, I would want a supercharger pushing ~5-10PSI of boost, added on top of the short runner intake. I appear to be growing more in love with the 3.4L DOHC potential every day...

3.4 don't need 180 degree headers it's already evenly spaced 120 degree exhaust pulses just like the 2.8.
There are several members that have made a custom short runner intake for the dohc
I just elimate the neck on the 96-97 intake and mount the throttlebody directly to the plenum which moves the power band up yet no noticeable loss of torque down low

http://fiero.cc/fiero-tdc/m...ws/intake/index.html

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1988 GT, 5-speed, white, beechwood leather, 3.4 DOHC crate motor with Getrag 5-speed. 6-speed installation is next.

I have a few pics from over the years, but the one im missing it the Red fiberglass/carbon fiber one that is real cool.

Here are a few pics. I also ran a "search" using "DOHC intake" (select all active and archive forums) I got back pages of data on this subject. Lots of threads to read up on.







Also, I have two sets of 96-97 upper/lower intakes/TB arms and misc parts for sale if anyone wants to cut one up.

Rob

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88 Coupe, CJB T-TOP, 1996 3.4 DOHC and a GT clip

quote Originally posted by qwikgta:

I really like this one, if it was on a 3.4L DOHC not PR engine. it is one of my ideas to do something similar but with smaller plenums. Thanks for all the info guys, I should have just searched, hehe. One more + to add to the 3.4L DOHC swap tally, I am trying to figure out what engine would be the best bang for buck, so far the DOHC one is it, since I can fabricate a new intake and get some decent HP to the wheels.

This one?

[This message has been edited by Sourmug (edited 10-07-2010).]

quote Originally posted by Sourmug: This one?

That looks pretty well made!


Another question regarding intakes, with the dual throttle body, if you use 2 GM 2.8L Throttle bodies, instead of 1 3.4L DOHC throttle body, would the combined surface area of the dual 2.8L throttle bodies allow more airflow? And, connecting the two together, a threaded rod between the two and a single throttle cable, and use a Unisync to sync the throttle blades (generally used on multi carbs)? then comes the issue of IAC valves, which if I switched the ECM from a 3.4L DOHC ECM, which would be dated, to a MegasquirtII system, with SFI and maybe even pencil coils with Direct Ignition instead of Waste Spark... all of these ideas might work right? in theory at least? I mean, the removal of IAC valves would make the engine horrible for the street, since it wont control its idle automatically, basically at that point it would be a race engine.

For even more upper end HP, a 6/6 advance on the camshafts...? I am very intrigued on the N/A HP potential of a 3.4L DOHC, without messing with internals like pistons, compression ratio, and valve lift and duration. 300-320 Flywheel HP possible? and can a 4T65E-HD support all of that? (I would have to make or buy a trans controller for that transmission because of the megasquirt)

[This message has been edited by Racing_Master (edited 10-08-2010).]

I was really looking into making my own intake, or having one cut down. I found that a 3.5L DOHC motor has the same TB and even has a small 1/2 inch plate that attach's it to the plastic intake manifold. The design is differant than ours and cannot work, but the TB is the same. Here is a pic.






My idea was to have the plate welded onto a piece of 3" alumium tube and have it welded to a cut down upper intake manifold.

Rob