I was wondering if there is anyway I could switch the TB from my 2.8 plenum onto the 3.4 plenum.. Would It be better or the same.. I have a 3.4 in it now... So I was wondering about air restictions, etc.

 

For ME the 3.4 intake is a VERY ATTRACTIVE intake, it's certainly eye candy!
BUT
The 2.8 is MOST EFFICENT
WHY
ya can take apart the 2.8 three piece set up & "open" to your hearts content.
That cannot be accomplished on the 3.4 intake, at all.
PLUS
The 2.8 Throttle body FITS perfectly on the 2.8 WHICH SAVES YA the effort to Mickey Mouse the 3.4 Throttle body for operation
PLUS ADDED BONUS!
The 3.4 TB OPENING IS EXACTLY THE SAME SIZE as the good ol 2.8 tb!
What that means is the 2.8 intake set up is EXACTLY AND AS EFFICENT AS THE 3.4 intake!
The 2.8 MPFI intake unit is a very efficent & adaptable intake. I noticed NO REDUCTION in power due to using the 2.8 on top of my 3.4 mill. Make MORE COOLER OUTSIDE AIR ENTER the 2.8 Intake on the 3.4 mill & that is the hot ticket!
In this case the Math reads 3.4 Bottom + 2.8 Top=MORE RUBBER ON THE ROAD!

 

So, because you can take the intake apart in more pieces, you believe it is more efficiant? Also that the opening where the TB happens to be the same size makes it as efficiant?

All this time I thought efficiancy was more of a CFM, RPM, cylinder fill deal, I guess not.

 

I like the way the 3.4 intake looks.. I'm not planning on porting or polishing anything yet. So I just was wondering if I could just swap over the TB. and use the plenum... So my actual question is can I switch the TB's over and use the original 2.8 sensors when I switch the TB over.....

 

The 2.8 intake has longer runners, which should help with the high end power.

But the effects would be minimal unless your camshaft was also tuned in regards to the intake runner lenght.

 

I have not had a 3.4 intake in hand, at least not in a way I could check, but is distributer cleance an issue, I know the 3.4s when they are installed in the 4th gens use DIS, and I have seen very few people actually use the 3.4 intake, and the DIS is used on every swap I have seen that uses the 3.4 intake.

 

Uhh.. Lee.. long runners tend to aid port velocity.. i.e. low end, not high end... not that the 2.8/3.1 intake's sharp turns between the upper and middle plenum are going to help velocity in any manner..

 

LOL, so true.

 

yeah, sorry bout that. I was busy reading up on Hemi technology when i posted that.

 

Techsmurf beat me to it. Yep - long runners tend to increase low rpm velocity = more cylinder fill at lower rpm = better low end torque.

I don't believe the 3.4 intake will clear the 2.8 distributor. You'd have to check that out.

Even so, I don't see these engines actually pulling enough air to really have a big difference between the two - other than looks.

 

I certainly didn't design and build a new plenum for low end. The 2.8 actually draws better into the runners because it can draw from the center chamber into each runner. The 3.4 splits after the TB into two separate chambers that fight back and forth for air from the TB. The 3.4 had to be designed that way because of the DIS coil packs. It doesn't hurt flow because the stock motors don't draw much. Put some umph to it and it will starve unless force fed.

 

What does DIS have to do with intake design? I also can't see each plenum "fighting" each other.

 

The back of the 3.4 intake won't clear the distributor - you'd need DIS. I think it can clear, if you do some grinding on it, though...

 

The DIS coil packs were mountedup in the center valley- thus the intake design was altered to allow room.

As for "fighting"- when a runner draws air, it draws from the plenum chamber. The plenum chamber is feed by the TB of course. If the runners can draw off of the same larger capacity plenum, the airflow volume is more in abundance to each runner. The way the air is split after coming in through the TB on the 3.4 cuts the volume in half to each side and causes a velocity increase due to a sooner starvation of feed. At higher rpm's, this effect only increases. This 3.4 intake lacks flow volume feed to all runners at lower speed that the 2.8 intake- in other words, the 2.8 and 3.4 are about equal up to a certain CFM & velocity and then the 3.4 intake drops off because plenum volume.

I know its hard to grasp- most would consider that if it splits and the two separate plenums are smaller, then thats still fine because each side only feeds 3 runners where as the one center plenum on the 2.8 feeds 6 (thus the same right? Wrong!). But this is where demand allows each runner to draw access from one larger volume and will pull from the center, more direct feed of the single plenum just after the TB.

You ideally want the plenum velocity as low as possible with as large of volume of resourcefull air to feed each runner/cylinder. When that feed velocity is high before the runners can draw it, then it will restrict sooner at higher rpms. We are going for volume, not speed. Speed is determined by the runner path (straightness of flow to the head)

 

Have you looked at a 3.4 installed in a 4th gen? The coil packs are mounted no where near the intake, but attached to a bracket that supports the coil pack and power steering pump which is bolted to the head.

I think you have your theory a little off there. The fact that the plenums are connected to a common TB, has no effect on each bank "fighting each other". The reason the plenum is split, is a calculated volumn to feed each bank, under most circumstances AND provide a more direct (straighter) path from the plenum to the valve. If you look at the intake from the front or rear, you will see how the intake runners cross in the middle, although IIRC they do turn slightly, similar to the 2.8L base. There is also another factor here, the firing order is split evenly between both backs, fires a cylinder on one bank and then the other, the timing of intake pulses is also the same, if it was different, as in 2 cylinders on one bank fireing and then switch, maybe then it would be a fighting battle for the next cylinder on the other bank to get adiquate fill. It's not really that there are 2 plenums, as that would require 2 thottle bodies, but that the plenum is a long narrow one, that the throttle body happens to be in a area that makes the TB as equadistant to the cylinders as can be done with a single throttle body. If there was a fight between each bank to get air, then there would need to be 2 MAP sensors used (which is not the case) since in your theory intake pressure would change constantly.

 

Only 1 way to find out- try it. There's a reason why I built my own plenum

 

Notch the top of the tang on the 3.4 intake where the tb connects to let the 2.8/3.1 tb fit. Cut out the rear "crossover", seal it real good, tap & install the vacuum T in the rear. Make new EGR Tube, as the 3.4 has it connecting in a different place.

 

i've considered swapping to one of the 3.4 intakes. my motor needs A LOT of air on top end, i'd like to try it just to see what happens. i've also considered trying a v8 tb, one of the "2 barrels" to see if i'm starving my motor with the zig-zaggy intake plenum and tiny tb.

 

I would say if the 3.4 intake is any better in any way , it was an accident. GM didn't design it for looks or performance, it was a nice place to stick the coil pack and also keep them cool.

I am 100% postive that performance was a second/third thought in that design.

Matt

 

Though I love the coil pack. a mulity coil system is better. I tried running dual coils on my bird but it did not like it. Use to work great on a 68 ford I had, but it was points.

Matt

 

So, because you can take the intake apart in more pieces, you believe it is more efficiant?
Also that the opening where the TB happens to be the same size makes it as efficiant?

The 2.8 manifold can support the air drawn in using a 3.4 bottom end motor with no changes, which makes that original MPFI design very efficent.
The FACT that the opening of the TB of both 2.8/3.1 & the 3.4 is identical in size also supports my statement.
So MANY (not myself) want to open the MPFI runners for making more power, one cannot do that with a 3.4 intake, unless ya cut the 3.4 upper intake manifold.
The 3.4 intake will NOT clear the distributor used with a 2.8/3.1 MPFI.
The 3.4 multi coil packs are on the driver side of engine very close by the power steering pump area.
The best easiest way to make the MPFI set up more effective is to increase incoming of outside cooler air.
The 3.4 upper intake design was dictated by hood line of the 4th gen, with not much else influcing that newer design decision.
Drag part is no one YET has put their 3.4 with a 2.8/3.1 MPFI intake on a dyno (myself included), to prove many "power" statements offered/given/thrown out.
Having had both my 2.8 & my 3.4 intake assemblies in my hands for comparision, that is how I make/offer my statements.
In my driving of the 3.4 powered ride using the 2.8 MPFI, the car runs/performs great!
My BIGGEST power gain (after the 3.4 bottom end switch) was from getting more cold outside air into the engine, especially at freeway speeds. Around town, not much power felt gained (using more outside cold air fed to engine). Around town (slower road speeds) power gain was from the massive torque increase of the 3.4 mill.
The orginal 1985/1992 MPFI design is very efficent as is.

 

I agree. The stock 52mm Tb puts out Aprox 300cfm also where as the 62 puts out about 430cfm. At low end of course it doesn't matter (actually the larger may cause a slight hesitation if cracked open too fast on a stock motor), but on top end, velocity definately picks up and the plenum is restricted due to size and volume (lack of).

The motor I am designing and building will have a potential rpm of 8000 which the cam profile will max at 7200 obtainalble power. At the higher engine speed, the stock designs would kill me. Thats why I custom built a new plenum with a 62mm TB and inlarged the plenum size to 4+ liters instead of 1 1/2, and I shortened the runners for the broader torque curve.

Edit: Anyone (with is almost everyone; ex Redraif & AM91) running stock exhaust manifolds will not ever matter to run a larger TB or plenum- the exhaust will not allow for the extra intake flow. The is just too much restriction.

 

Edit: Anyone (with is almost everyone; ex Redraif & AM91) running stock exhaust manifolds will not ever matter to run a larger TB or plenum- the exhaust will not allow for the extra intake flow. The is just too much restriction.

WHICH is EXACTLY WHY, I'm heading off to Phoenix (where PaceSetter Exhaust is located) to have my car used for the making of Street Legal Headers for our 3rd Gen V6 rides.
To keep expressing interest in this product, send a kind short email to
fgerle@pacesetterexhaust.com

This dicussion is just like MANY older Corvette owners.
Corvettes from 1957 to 1962 use the EXACT SAME SIZED Fuel Injection units.
1957 283 FI HP ratings ranged from 250-283HP
1962 327 FI HP ratings up to 360HP.
EXACT same sized FI Unit.
The 1963-65 327 move the HP bar to 365 HP, which was made by slightly increasing the FI CFM rating.
Point Two.
Our V6 MPFI units designed & manufactured at the exact same facilities, Rochester designed & manufactured at the Winters Foundry.
Hertitage & history is under the lowly V6 hood!
The original V6 MPFI design is a very efficent & versital assembly.