Common plenum or individual runners???, for gas milage and drivability Options

[Mueller]

for my 2316 it seems that the stock plenum might be reaching it's limits as far as volume goes.....so, I either fabricate a larger common plenum, or go with individual throttle bodies such as TWM or Jenvey*

single plenum would be easiest, but the individual throttle bodies look better (IMG:style_emoticons/default/smile.gif)

has anyone switched from one to the other on the same motor with everything else being the same???



*Jake Raby is the U.S. distributor of these....

[lapuwali]

Biggest problem with IR throttles is getting a good MAP signal for the EFI. You need to fab up a plenum just for the MAP signal. You never need to balance a single throttle body, either. No linkage worries. Fabbing up a bigger plenum that used the stock runners shouldn't be too big a deal. Use a bigger throttle body off some other EFI car.

[ottox914]

Here is another place to check for FI throttle bodies, manifolds, and injectors: http://redlineweber.com/Redline1.htm
I have been interested in the same question for a while- general answers I get are that the longer runners/larger single plenum can be designed to boost low/mid range torque, while the I/R throttle bodies will help the top end. Might be a "package" sort of decision, thinking about valve sizes, cam, redline, etc. Jake had a thread awhile back about testing intake velocity stacks, and found 2.5" to be the best overall size, so if you go I/R this might be worth keeping in mind.
As far as real world experience, got none to share, only opinions at this time. I'm not the smartest nut on the workbench, but am working my way thru "Scientific Design of exhaust and intake systems" third edition, by smith and morrison. It'll take a while for it to all sink in, but interesting none the less.

[Bleyseng]

for my 2316 it seems that the stock plenum might be reaching it's limits as far as volume goes.....

Based on what? Have you done the math? Brad ever built something like that and it didn't work??

DaveHunt's 2270 is supposed to be running tonight and he should get it tuned soon sooo we'll all know if a 2.0l setup can work well.
Charles from L/N told it should work but maybe suffer alittle at high rpms. So, how high you gonna rev this thing??

Geoff (looks like I am heading down this slippery slope also) (IMG:style_emoticons/default/wacko.gif)

[914werke]

Im not smart enough to follow this ... (IMG:style_emoticons/default/wacko.gif)
Why would the collection of intake air in a larger common cavity enhance mid & torq as compared individualm properly sized TB's?

[Bleyseng]

air velocity I think. Under lite vacuum at cruising the plenum is a large supply of air already past the TB. Duals is great for WOT.
Thats why the throttle response it so great with a Djet set up vs Dual carbs.
or I am talking out my ass...........

[eeyore]

The general gist is short intake runners for high RPM, long runners for low RPM. It isn't just the piston downstroke that moves air into the cylinders, it is the masses of air moving through the engine as well. At low RPM, with low piston velocity and intake pulses stretched out, lengthening an intake runner creates a reservior of high(er) momentum air to help fill the cylinder.

I think that valve overlap is another thing that assists in cylinder filling, where both valves are open at the same time so that the outgoing air charge is creating a vacuum on the incoming charge.

Dual carbs with IRs probably have poor low RPM response due to low intake velocity, hence poor fuel atomization. (Now I'm talking out of my ass too)

Dual-length runners systems are what made the Corvette ZR-1 and the SHO Taurus great (if it wasn't sales hype)

[Mueller]

Geoff,

Based on another thread in which Jake mentions it on Dave’s motor, mine will be larger and if his is already on the brink, then mine would reach the limit even sooner

Just 'cause Dave’s car runs, it does not mean the plenum is sufficient in volume, he won't know for sure until he cranks up the RPMs.....one way to know whether it works fine is how well the car responds at WOT, too much vac. at WOT and it could indicate too small of a plenum (the throttle body could do this as well, but I know he has a larger throttle body to help)

[Bleyseng]

The difference between a 2270 and a 2316 isn't that much is it? You can always add a bigger TB onto the 2.0l plenum for better WOT flow, say a 55mm one. Just ream out the hole some.
I spoke with Jake and Charles the other night and they feel they can come up with a cam that will work with my new setup (103x71 using Nikkies and Djet intake, 45mm TB)

[ottox914]

My very basic understanding of plenum and runners VS throttle bodies: when the intake valve closes, the incoming air charge is still on its way, hits the closed valve, and bounces backwards thru the intake runner and into the plenum. By doing the math (not my strong suit) you could take in to account the speed of the "bounce back", the volume and shape of the runner, size of the plenum, and calculate lengths for runners, and capasity of plenum, such that when the incoming air charge bounces off the plenum, and rushes back down the intake runner, that it gets back to the valve as it is opening again, resulting in better cylinder filling, sort of a "super chargeing" of the intake charge. Down side to this is that is is pretty rpm dependent, based on length of runners and timing of valves opening/closing, hence some cars w/variable length "tuned" intake runners. The individual throttle bodies, if run open topped, have nothing for the charge to bounce back off of, but do offer lots of air flow and a more direct path at higher rpms. If they are run w/air cleaners, again, the overall length of the intake, from the top of the air cleaner (or thorttle plate?) to the valve is likely to be less than the stock T4 system, and the bounce back effect happens faster, and therefore provided more benefit at higher rpms, when the valves are open/closeing faster.

Thats all I think I know, if someone knows more feel free to correct me.

[Jake Raby]

Bleyseng,
I have never had ANY engine that I could not design a proper cam for! The D jet that you are using is much more tricky and that cam will have split centers, split lift and split duration, so it won't be cheap! I do have 4 different masters we can work with and some data from Djet tests in the past to compare. Using the Djet SAFELY will sacrifice duration which will boost vacuum (atleast on the intake side) this will cost you drastic power of the potential of the combination using something else_Kit Carlson or Carbs... But If you really wanna use it, go for it- but its uncharted territory!

Getting a proper vac signal for the IR runners is easy. I have already found in the Kit Carlson testing the size of the vac ports needed as well as the hose and small collector that works best as well. One of the test engines that made the best power was an IR set up that actually idled and fired up with low speed operation better than the plenum based version in my 912E.

BUT you need the correct cam designed to make this easier- Yet again no problem because I'm a cam specialist on these suckers! Its just come from trial and error!

All the guessing and planning in the world and trying your heart out to get it perfect ain't gonna cut it! Unless you use a 100% proven arrangement that has all the bugs worked out and has EVERY part that was used in that arrangement installed- You can make a goof....

Don't be afraid of making goofs- If you are don't try it and pay someone else that is. Its impossible to build it perfect! It can ALWAYS be better! Take it from me, the guy that has torn a particular engine down 18 times making nothing but a cam change to find out the heads were the limiting factor because the ports and valves were too big! The issue looked cam related, but it wasn't.

Build it, drive it, and if you don't like it tear down and change it- OR get a full set up 100% designed to work and you better not complain about the friggin price, because all guesswork is removed and thats worth DOUBLE the cost alone!

BTW, I'm the only US based dealer for Jenvey TBs. I have exclusive rights to thier goodies and they are being added to our line up as we speak.

Take this seriously guys, but understand its never gonna be perfect-

[Bleyseng]

Jake, I am going with the Megasquirt setup but retain the djet intake set up. If it doesnt work, well I have a set of Dells sitting on the shelf.
If Dave Hunt can't get his to run right I will be changing my direction.
Geoff

[Jake Raby]

I'm sure he can make it run right, but the question is will the engines VE have to be sacrificed to do so???? If it needs weird VE numbers to be drivable and stay cool it will suffer in the performance arena.

That VE table will tell the tale.

The plenum that Charles and I have been working on will be sized for 2250-2320CC engines specifically.

[Bleyseng]

Ok, 'bout how much more Volume do you think it will take.(so I can imagine this in my head). Double? 50%? 60mm TB?
Geoff

[Jake Raby]

(IMG:style_emoticons/default/lol2.gif)

[Mueller]

Build it, drive it, and if you don't like it tear down and change it- OR get a full set up 100% designed to work and you better not complain about the friggin price, because all guesswork is removed and thats worth DOUBLE the cost alone!

I like that additude (IMG:style_emoticons/default/smile.gif)

Guess I'll be going the IR route....like you said, if it does not suit me, replace it with something else till it does (IMG:style_emoticons/default/smash.gif)

[jwalters]

Im not smart enough to follow this ... (IMG:style_emoticons/default/wacko.gif)
Why would the collection of intake air in a larger common cavity enhance mid & torq as compared individualm properly sized TB's?

(IMG:style_emoticons/default/wink.gif) This si the same technology all the japanese bike makers use to squeeze every last iota of power from the tiny engines...point:

Testing has showed and confirmed that having the largest Airbox possible slows down the intake velocity and turns it into pressure-----

Further testing has shown and confirmed that the use of a decent sized airbox coupled with a large plenum has the same effect--

On these engines as well as any other high rpm / high power engine the speed of the air being "sucked" into the carbs are approaching or exceeding the speed of sound--this is not good--high velocity means low pressure, think of it as a carb venturi--by being in the transonic range ( just prior to going supersonic) and pushing thru S/S, negative pressure waves develope which can in the right instance actually stop and restart the flow of air up to 100k times per second.

Which gives very poor performance and causes aircraft jet engines to " flame out" i.e.-...not run at all.

Too much velocity is bad juju----- (IMG:style_emoticons/default/wink.gif)

[Jake Raby]

The only true test is in the driver's seat....

100% of what I have developed has been proven this way...

Most of what I have was developed was done before I ever owned a dyno.... Including the camshafts- Thats why they are so damn effective in the driver's seat..

[SirAndy]

single plenum ...

use a 3.2 upper intake and cut off 2 of the runners.

the dia. of the runners is a bit bigger than the 2.0 runners, perfect for anything from 2056 to 2316 (according to my pre-school math).
the 3.2 plenum has much more volume over the 2.0 plenum, which is gud.
also, the runners are much longer, promoting low/mid range torque.

all you need to do is find a set of short dual carb runners and mate the 3.2 intake to them. they're only about 3 mm off.

i went through this whole setup for my 2056, did all the math/research.
just haven't deceided yet if i'm actually going to use it ...
(IMG:style_emoticons/default/wink.gif) Andy

[nebreitling]

that's a brilliant idea, andy.