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

[Bleyseng]

Ah, but the question here is- Is the carbonfiber manifold for a upright type4 or for a 914?

Geoff (IMG:http://www.914world.com/bbs2/html/emoticons/biggrin.gif)

[Katmanken]

Ya know you can tune your intake runner length in two ways....

One is to cut it to length. As the pulse is reflected up the intake runner, it hits the cut end and reverses direction...

Now iffin you were, clever you could reverse the pulse where ever you wanted (in a system) by adding an anti-reversionary feature (cone) in the manifold- say below the MAF or MAP sensor. That sucka would act as a one-way valve and allow air to be sucked in and would reverse the pulse once it hit the AR feature...(See Feuling patents on AR exhaust) (IMG:http://www.914world.com/bbs2/html/emoticons/huh.gif)

Now iffin you were brilliant, mebbe by taking a thin wall tube and placing it into the manifold near the ideal tuning point with the AR feaure on the trailing end would allow you to move the AR feature to locate the tuning point..... (IMG:http://www.914world.com/bbs2/html/emoticons/ohmy.gif)

Since that tunes it for one RPM, moving it back and forth with a mechanism would tune your intake over the RPM range........ (IMG:http://www.914world.com/bbs2/html/emoticons/idea.gif) (IMG:http://www.914world.com/bbs2/html/emoticons/happy11.gif)

Kenny needs math! Quit hoardin it Ahndie........

Ken

[TimT]

QUOTE

moving it back and forth with a mechanism would tune your intake over the RPM range.

kinda like varioram on the 3.8's?

Mike, there are no baffles or runners GT3RS plenum. However, the small restrictor has a cone that goes into the plenum.. I dont have a small restrictor so no pics

[Qarl]

I don't think the carbon fiber plenum needs to be strong at all. Only strength is for the connection points for the throttle body or afm.

[Mueller]

QUOTE (Qarl @ Dec 21 2004, 02:37 PM)

I don't think the carbon fiber plenum needs to be strong at all. Only strength is for the connection points for the throttle body or afm.

I was thinking about that statement (for a few weeks it appears, LOL)
and I got to wondering about what happens if you have backfire and what are the chances of spliting the plenum wide open???

I know for some of the 911's they had a pop-off valve that could be added to help prevent damage in case of backfire, maybe it would be a good idea to add one to a newly design plenum if going with a composite material ???

[Britain Smith]

The backfire issue was the reason that Brad and I decide against an aluminum intake plenum on my turbo motor and had it made in steel.

-Britain

[Mark Henry]

I can't believe I didn't see this thread before... (IMG:http://www.914world.com/bbs2/html/emoticons/wacko.gif)

Anyways...I'm also debating a IR or plenum system for my 2.7/4.

A Honda Accord 2.0 FI TB....at 64mm it's huge compared to a 914 TB. Not too much crap on it, has an idle bleed screw, but it does rotate opposite from a 914 TB, so I'd have to get a new TPS.

(IMG:http://www.914world.com/bbs2/html/emoticons/idea.gif)

[Mark Henry]

If I was going to do an upright, like a DTM, I would consider something of this flavor...

[Mueller]

QUOTE

A Honda Accord 2.0 FI TB....at 64mm it's huge compared to a 914 TB. Not too much crap on it, has an idle bleed screw, but it does rotate opposite from a 914 TB so I'd have to get a new TPS.

it's interesting how large some TB for the size of the motor they come off of....I have a Mustang 5.0 TB that looks to be about 2/3 of the size of the TB that belongs on my 2.8 VR6 engine

i bought an oxy-acetelene welding setup last night, so I'll be welding/burning up a new plenum for the car pretty soon (IMG:http://www.914world.com/bbs2/html/emoticons/smash.gif) (IMG:http://www.914world.com/bbs2/html/emoticons/welder.gif)

[Mueller]

more plenum ramblings.....

okay....let's say we take a stock 2.0 plenum, cut it in half and widen it to do 2 things...1st would be to increase the volume for a larger motor and the 2nd thing it would accomplish is allowing one to cut down the overall length of the intake runners.

Instead of the stock t/b, pretty much any t/b could be mounted on top or how about 2 throttle bodies of smaller size???

hmmmm???

[lapuwali]

QUOTE (Mueller @ Jan 20 2005, 02:21 PM)

more plenum ramblings..... okay....let's say we take a stock 2.0 plenum, cut it in half and widen it to do 2 things...1st would be to increase the volume for a larger motor and the 2nd thing it would accomplish is allowing one to cut down the overall length of the intake runners. Instead of the stock t/b, pretty much any t/b could be mounted on top or how about 2 throttle bodies of smaller size??? hmmmm???

Now you've killed one advantage of a single TB: no throttle synchronization required. The only advantage I can see to a smaller TB on a large plenum is less throttle sensitivity at small throttle openings. Intake velocity across the TB seems to be completely unimportant unless there's a lot of other resonance tuning going on, but this is all black magic to me. Velocity in the runners I see as being much more important. Shortening them is going to raise the power curve higher in the rev band (according to the usual theories, anyway), and you're building a big, torquey engine. So, it seems that's to cross-purposes to me.

64mm is bloody huge. Compare this to the 2x28mm restrictors required on all DTM cars. That's a total area of 200 sq.mm for the Honda v. 176 sq.mm for the 475hp V8s used in the DTM. The Accord certainly doesn't need that big a TB for flow, so they must be using it for some other reason.

[Bleyseng]

Think progressive TB Mike. Lots of them out there to pull off junkyard cars. Small opening for low rev throttle response and the big secondary for WOT. Woohoo!
The more I read and check stuff out, I think DaveHunt is gonna have to go to this to be able to tune that sucker.

Geoff

[Mark Henry]

James on a T4 with the DTM, that woud be 4 X 28mm on dual/dual Webers.
On Jakes/Kit Carson's test engine the were running Jenvey TB's and I forget the size off hand, but it was 4 X 45mm - 48mm or something like that.

64mm is big for a single TB but I'm going to have a 2.7 type 4 (IMG:http://www.914world.com/bbs2/html/emoticons/blink.gif) (IMG:http://www.914world.com/bbs2/html/emoticons/biggrin.gif)

[dinomium]

I got this from the 2004 GT3 cup car manual... pretty kewl stuff INDEED!

[lapuwali]

Somewhat apples and oranges, though. With individual throttles, you need to look at peak flow for each cylinder with that relatively tiny manifold volume providing no real "buffer", so each throttle has to flow enough for that cylinder at peak. While that one cylinder is sucking as hard as it can, the other three are basically idle. With one TB feeding a sufficiently large plenum (at least the combined size of the number of cylinders drawing air at once, or 500cc for a 2.0 four), then the air for one charge is being drawn from the plenum, and the TB only has to flow enough to keep one cylinder full (on a four, 1.5 on a 6, 2 on an 8).

...I'm hand-waving here, not operating off actual theory, but this sounds close to correct. I have NO data, this is me just thinking out loud. I'm sure Jake will pound me into the ground with actual data...

So, if a 28mm venturi works with a pair of dual Webers on the target engine, then a single 28mm TB with a plenum one cylinder in size should also work. Probably upping the size of the plenum and the TB some to account for inertia effects and cam overlap is a good idea, hence the 45mm TB on the 2.0 (which is probably bigger than actually required for flow). Note that many a 2056 is out there making more power than a stock 2.0, and each cylinder is being fed by a 32mm venturi or thereabouts. A 150hp 2270 is using, what, 36mm vents on 44IDFs?

[Bleyseng]

Well, you are mixing apples and oranges since carb vents and TB's have little in common. The venturi is where the fuel is mixed and you must achieve proper atomization. The TB is a air metering device sized by the air charge needs.
Dual TB's suffer from poor driveablity and tuning but a great for drag racing where they are tuned for one basic rpm (WOT).

The plenum and runners FI is a different concept than dual carbs. Since the intake air doesnt have to hold fuel in it and the fuel is delivered smack on the valve, its more tuneable. The runners are sized to hold atleast one chambers volume for an intake stroke. The plenum holds the recharge air plus additional as there is overlap from other cylinders. How the engineers calculate this with math is beyond me. I am hoping out resident math wiz has figured it out!

Geoff

[lapuwali]

QUOTE (Bleyseng @ Jan 20 2005, 05:35 PM)

Well, you are mixing apples and oranges since carb vents and TB's have little in common. The venturi is where the fuel is mixed and you must achieve proper atomization. The TB is a air metering device sized by the air charge needs. Dual TB's suffer from poor driveablity and tuning but a great for drag racing where they are tuned for one basic rpm (WOT). The plenum and runners FI is a different concept than dual carbs. Since the intake air doesnt have to hold fuel in it and the fuel is delivered smack on the valve, its more tuneable. The runners are sized to hold atleast one chambers volume for an intake stroke. The plenum holds the recharge air plus additional as there is overlap from other cylinders. How the engineers calculate this with math is beyond me. I am hoping out resident math wiz has figured it out! Geoff

The sizing of carbs has the additon of fuel metering, true, but pure airflow is all I'm discussing here.

The venturi is going to limit the amount of airflow into the engine, regardless of whether there's fuel getting sucked through a jet or pumped through an injector. The max. power of the engine is basically limited by how much air it can ingest. If an engine can make 150hp with 36mm carb venturis (one per cylinder), then it's also going to be able to make 150hp with a sufficiently large plenum fed by a 36mm TB, since the TB will flow as much air as the venturi in the each carb.

The exact reasons why a 36mm venturi would be chosen in a carb are clear, given the need for good intake velocity past the jets. Why TB sizes are chosen as they are is, frankly, still a mystery to me. They all seem to be too big, even the 45mm unit on the stock 2.0.

[Jake Raby]

Its all in the combo!

[lapuwali]

QUOTE (Jake Raby @ Jan 20 2005, 06:25 PM)

Its all in the combo!

Y'know, that's probably the politest correction Jake's ever given. (IMG:http://www.914world.com/bbs2/html/emoticons/biggrin.gif)

[Bleyseng]

QUOTE (lapuwali @ Jan 20 2005, 06:21 PM)

The sizing of carbs has the additon of fuel metering, true, but pure airflow is all I'm discussing here. The venturi is going to limit the amount of airflow into the engine, regardless of whether there's fuel getting sucked through a jet or pumped through an injector. The max. power of the engine is basically limited by how much air it can ingest. If an engine can make 150hp with 36mm carb venturis (one per cylinder), then it's also going to be able to make 150hp with a sufficiently large plenum fed by a 36mm TB, since the TB will flow as much air as the venturi in the each carb. The exact reasons why a 36mm venturi would be chosen in a carb are clear, given the need for good intake velocity past the jets. Why TB sizes are chosen as they are is, frankly, still a mystery to me. They all seem to be too big, even the 45mm unit on the stock 2.0.

The runner and plenum store the intake air charge until the valve opens then its sucked in.The valve closes and the moving air is bounced back up the runner (reversion). The air is bouncing around the plenum, helping to fill up the runners, with the valves closed. The reversion helps fill the runners too ready for the next time the open.
The plenum and runners are part of the whole system as it the cam and cam timing, as Jake is saying "Its all in the combo".
In dual carbs the air bounces back up the throat disturbing the incoming air/fuel charge Velocity. But there is no plenum to buffer the reversion or use to help fill the other runners.
The TB is sized accordingly to control the fill rate of the plenum volume not the runners. Thats the difference between the two systems. Of course too large of a TB can cause problems with tuning.

Geoff (I am not the greatest at explaining this stuff, hell I am General Contractor not a Automotive Engineer)