ITB's vs. Intake manifold in an N/A application

[olie05]

Why choose an intake manifold over ITB's?

 

I am pretty much set on ITB's for the future with my car, simply for the looks, and the sound, and obviously the performance (getting rid of the stock manifold), but why do some people choose to build an intake manifold (sheet metal box, or log style) rather than just slapping on a set of throttle bodies?

 

This discussion should be limited to N/A engines, although it might be interesting to hear why turbo guys rarely choose to use independent throttle bodies.

[Mack]

the only reason I can think of is the fact that ITBs are harder to set up and tune. Although, once properly adjusted and tuned, they beat a plenum set-up hands down, i think.

 

There is a reason why most motorcycles utilize ITBs.

[Roostmonkey]

Cost is a big factor. Us turbo guys need a plenum either way.

[Careless]

for some reason I've been reading that in most cases, a plenum design will make more power than an individual runner style throttle design with no plenum.

 

I'm not sure if that is at full cruise or on a dyno, as it was never indicated. And it would surely have an effect on how much air is being directed into the front intake pipe in regards to the plenum design.

 

However, It's probably because the people had trouble balancing them out and tuning them properly. I'd assume there are some precautions that wouldn't hurt but are not always neccessary in ITB or IRTB setup that cost a lot of time. Things like cleaning the throttle chambers and plates, as well as the throttle shaft seals, and making sure that they aren't gunky or anything. and measuring the movement of each plate and adjusting them if you have to, or if you can.

 

Considering every mm of air space counts both in the runners and at the valves, no?

[JMortensen]

I think it's possible for a plenum style intake to outperform an ITB setup, but the plenum has to be properly designed to do so. "Properly designed" seems to be the tough part. There have been several attempts made at this. Tough to argue with Coffeys 280whp NA Z which had a plenum. Ron Tyler also built a very nice one, but the end result on the dyno wasn't very spectacular. I don't know if that was the plenum's fault or the rest of the engine or what.

 

I think the advantage of the plenum is that it can draw cold air vs engine compartment heated air (although I think people make more out of this than it really is worth) and the 6 cylinders can all combine to get the air velocity up as it goes into the plenum, which if done properly should increase hp vs 6 ITBs just pulling randomly from the engine compartment.

[RTz]

Plenum style manifolds have the potential to be...

 

Less expensive.

Lighter.

Use the plenum as a tuned spring (resonance chamber).

Easier to get 'clean' air.

 

 

ITB's have the potential to be...

 

More responsive.

Easier to 'get right' (less variables).

Sound GREAT

 

 

 

Ron Tyler also built a very nice one, but the end result on the dyno wasn't very spectacular. I don't know if that was the plenum's fault or the rest of the engine or what.

 

Jon may very well be right about my plenum. I suspect part of it is the combination... aggressive manifold and head, mated to a low comp. engine with a very mild cam and mild exhaust. The peak number isn't there. In defense, I will say its one of the sweetest running engines to come out of the shop. The dyno isn't telling the whole story... and never does.

[proxlamus©]

what about ITB's with a nice plenum such as for a turbo application?!

 

seems like a winning combo.. just costs alot lol

[mannyvig]

what about ITB's with a nice plenum such as for a turbo application?!

 

seems like a winning combo.. just costs alot lol

 

 

Thats the factory rb26 intake

[NZeder]

ITB's with a good cold airbox = as stated the best of both. If the air is designed right then you can run nice long trumpets in it too.

 

***Please admin's edit this post if this is inappropriate***

 

I have some triple throttle bodies for sale currently. I have sold my 280zx project car so these are no longer required (I have a second set for my 260z).

Below is a copy of the ad I have running on our ebay type website.

 

"Brand New - never used.

 

Here we have some Brand New never used Triple DCOE throttle bodies. These are 45mm with the pro series trumpets as shown in the pic. These come fuel rails for Jap 11mm O-ring top feed injectors. One TB has the D shaft mod for the included TPS switch/sensor. Also includes all balance joiner and a cable pull arm/linkage.

 

These retail here in NZ for close to $3000NZD. My loss is your gain.

 

Selling as I have had a project change and these are no longer required.

 

### I have also have these advertised else where and reserve the right to withdraw at any time ###

 

Suit any DCOE intake manifold - great for your Datsun Z car, Triumph with inline 6, Valiant, Torana, Falcon etc.

 

These are still wrapped up as I received them - but I will take some photos in the weekend - however they look just like the sample pic currently shown.

 

Info about the TB's from manufacture.

 

**Throttle bodies are manufactured from heat treaded 601 Aluminum alloy and are CNC machined. The brass shafts run on bearings with the butterflies secured by split screws for ease of servicing and reliability. The butterflies have .0005" tolerance fit to ensure good balance and fit while the injector bose placement is positioned to ensure good fuel atomization.

 

**The Pro-series rum tubes have been designed using advanced computer modeling and a flow bench to obtain the best flow. They feature a full 270 degree return on the bell mouth for additional draw.

 

**Linkages are manufactured from 6061 aluminum and reamed finished where the shaft mounts to obtain a slip proof fit. They come anodized blue for a smart appearance."

 

 

I am after $1900 NZD which using a 0.75 USD to NZD (exchange rate from the other day) = $1425 USD. Shipping from NZ to US should not be too bad as they are light and will go into a smallish box. I also have some RB25DET injectors and for some extra I could include some 14mm o-ring fuel rail too so you will have a choice of what injectors you want to run.

 

Here are some pics of one of the units that I have unpacked - the others are still as I got them (wrapped in bubble wrap)

 

PM if interested.

[johnc]

The advantage a plenum has over ITBs is a broader, flatter torque curve. I had very specific goals for my 3L L6 and one of them was over 200 ft. lb. of torque in a 3,000 rpm band. Given the budget for that engine was $20K Jim Thompson could have used any intake method available - he went with a 1.5L plenum with internal velocity stacks and diverters, 7.5" tapered intake runners, and a 65mm TB. The engine developed over 200 ft. lbs. from 4,000 to 7,500 rpm and over 250 from 5,200 to 6,500.

[Careless]

what if one was to make a plate that encase the ITB stacks, but not completely as to consider it a plenum.

 

Sort of like a heat shield for an exhaust, but instead, one that feeds off vents in the hood or at the edge of the hood? Separating it from the other hot parts so that hot air moves around it?

 

now lets say I did do this, and it was on one side of the car. given the fact that it's an ITB setup, what are the chances of the engine starving a little under hard acceleration into a turn that is opposite of the hood vent? I don't think it'd be a bad idea, seeing as you can filter the hood vent to some extent as well.

what say yous?!

[johnc]

What you're describing is a cold air box and that's something that helps an ITB or triple Weber setup.

[Accurate Injection]

A little Biased here: A fact I would like to interject here, is how many "Hours" of Flow Simulations did Jeff go thru to design a Plenum based ITB system he designed and get it distribute the Air Evenily among the 6 cylinders?

 

It is one if not the "ONLY" Plenum based Manifold I have seen to balanced out the Cylinder to Cylinder air Distribution in the Plenum itself? Lots and lots of time went into it, along with needing the software to do the calculations. So my point is ............without access to the Fluid dynamics software like Jeff had, and hours of time in development then you are winging it at best.

 

With ITB's the engine is Balanced Cylinder to Cylinder from the Start! Also I know there's lots of input out there for Cold Air Induction and the benefits of it are proven, but then this potentially puts you back in the Cylinder to Cylinder distribution senerio, but then again THERE'S WATER/Methanol injection that cools the intake Air Charge and boosts Octane at the same time.

 

Now don't try to spend that $.02 cents worth cause it will not buy much!

 

Kevin

[johnc]

So my point is ............without access to the Fluid dynamics software like Jeff had, and hours of time in development then you are winging it at best.

 

Unless you have a flow bench that can simulate multiple intake ports and later a test engine with Lambda and EGTs on all cylinders within 2" of the exhaust valve. Then there's the really cool spark plugs that can sense combustion chamber vibrations, electrical resistance, and cylinder pressures and dump that to a Motec EMS.

 

CFD can get you close (sometimes real close) but you still need to be able to do mechanical tests to validate what the software tells you.

[Accurate Injection]

True very true!

 

We have a partner Company working on a way of using a TMAP sensor in #4 cylinder to tell the ECU when to sequency timing in #1 Cylinder. It also negates the need to sense all 4 cylinders MAP Vacuum Signal! Pretty neat stuff!

 

Kevin

[Tony D]

"Then there's the really cool spark plugs that can sense combustion chamber vibrations, electrical resistance, and cylinder pressures and dump that to a Motec EMS."

 

There are similars for the stationary engine realm that give realtime BMEP data to the operators to prevent overloading of generator sets when...er...'making up production during peak consumption periods'....

 

Neat to watch the curve develop on an O-Scope.

[Daeron]

With ITB's the engine is Balanced Cylinder to Cylinder from the Start!

 

IMO it is a matter of preference, for the most part. I think all of us would agree that a theoretical "ideal air intake" (given: limited to throttle plate type setup) would likely be ITBs with a Perfect version of Jeff's plenum on it. This ideal would likely cost arms and legs, thousands of arms and legs, so it will never come to Be...

 

However, one thing I wanted to point out is that the primary benefit in having a plenum (cold air aside) is the common resonance chamber and assisted velocity from running all six cylinders though one common orifice. I may be poorly stating it, but jmortensen said as much above and I don't think enough attention was brought to it.

 

This is one reason I am eager to build myself a dual TB bolted to SU EFI manifold, and start tinkering with an air plenum supplying them with fresh air. Once I get the bloody thing back together, that is. Obviously I will be fudging around in the dark, but in my mind it should be fairly easy to make it a "best of both worlds" scenario on a budget, if I can do it right. With such a pile of parts, it is hard to think of NOT using anything that I have already and buying something else instead.

[blackwidow]

As far as the plenum goes, I was under the impression that the extra velocity created by sound waves from the valves opening were only calculated from the valve to the end of the runner, not into the plenum. Doesnt the resonant wave reverse once it expands at the end of the runner or stack, whichever you may have. So why would having a common plenum be a benifit? I am intrested to know how multiple cylinder pulses benifit any other cylinder. Do you have diffrent length runners for each cylinder? How much of a benifit do you think your plenum intake made over a ITB setup? Sorry for the questions, very interested. thanks

[ozconnection]

Can we use the terms 'Helmholts resonance' and 'organ pipe tuning'? From here on in it gets pretty heavy so I'm going to let the 'scientific' types chime in and explain this to everyone, including me, please! .

 

It's for this reason why for any degree of accuracy in designing a 'good' plenum chamber, a computer software program is needed. But there are always going to be some compromises with a plenum type intake manifold. Why? Because the waves that are generated to assist with cylinder filling run in and out of tune as engine speed varies. Now you know the reasons why some manufacturers design and use variable intake manifolds, to keep this 'tune' in tune for more of the rev range. Couple this to variable cam timing and presto.....superb performance everywhere!!

 

If built for max power, theoretically a plenum intake will beat an ITB setup. Most are not and are built as compromises or worse, as 'educated' guesses.

 

A lot of written literature relates to the performance of Chev and Ford V8 engines. It's from this that the idea exists that ITB's can be restrictive. In these engines, cylinders are larger than 600 cu cms. Nissan cylinders are considerably smaller than this so there isn't the same flow restrictions placed on ITB's when used on our engines. In other words, there is minimal flow restriction as long as the runners and throttle body bores are of sufficient size and volume, which they often are, to feed the cylinder. Unfortunately, this style of intake cannot rely on plenum pressure wave tuning to assist in cylinder filling. However some tuning of ITB's can be achieved with altering manifold length, volume, taper and trumpet size and shape.

[Accurate Injection]

1 word here everyone seems to forget guys "velocity" What holds the Air Charge in the cylinder as the piston moves back up on the compression stroke, and the intake valve is still open? Air Velocity! Once the column of air is moving at a high rate of speed it also has a ramming/holding effect. Those Huge ports and large intake tracke flow numbers you can acheive with your porting tools and flow bench creates a intake track that flows just as good backwards as they do forwards! There's no one solution for any given engine combination, but unless you have access to very sofisticated software to analyse a plenum based manifold ITB's will always out perform hand made plenum based manifolds because the idiocrencies and wave cancellations of a plenum are simply not there.

 

Helmholts tuning only works in a very narrow rpm band, usually only a few hundred rpm, but if you time the resonanance to accure at a "DIP" in your torque curve you can use it to smooth out the curve to aid in "driveability" on a race track, this is why you see itb's more in road racing than drag racing. Using Helmholtz at peak Torque looks good on a dyno sheet, but has little benefit as it just makes the engine more "PEAKY" and harder to drive at the limits of handling! Imagine hitting a 5 to 10lb torque spike or dip in the middle of an off camber corner?

 

Variable intakes or dual runners do one thing, gives you another place in the RPM Band to fix a dip or bump the Torque Curve, or better said another part of the rpm range to tune, and "VELOCITY" plays a huge roll here. Now when somone figures out how to make a Variable intake Track that is computer controlled and based on or tracks with the RPM of the engine, (A RPM controlled Trombone if you will) then life will be grand! Do you think "extrusions" could be of use here?

 

Kevin