OK, so why do the IDF Throttle Bodies work so good?

[jrandy]

IDF style throttle bodies have no plenum, the runners (manifolds) are short, there are 4 throttle plates, one TPS and no air boxes.
So, why do they work so well?

[Paul H]

Because each cylinder has it's very own induction system with no interference from the other pots.
You have garanteed success with individual runner regardless of which cam, heads, exhausts you have

[raygreenwood]

Because each cylinder has it's very own induction system with no interference from the other pots.
You have garanteed success with individual runner regardless of which cam, heads, exhausts you have

Success is a relative thing. And...you do not have guaranteed "sucess" with any cam heads exhausts etc.
But...what you can have....easier..... is an engine that runs quite well....and from a ground up standpoint....is simpler to tune to a good running condition.
It will however have a whole slew of issues related to the cam, heads and exhausts....that may keep the system from reaching the best HP and torque potential for that engine size and configuration. For instance...few if any properly sized runner and plenum systems will ever experience fuel and air reversion that reach or exit the TB.
However almost all individual runner and TB systems will have some reversion at the TB. The manifold is simply too short to dissipate the TB turbulence and there are no adjacent "push" phases from the other cylinders connected to the runner to keep reversion from the valve slamming shut.... damped down.
Does this mean it will run badly? Yes sometimes....and no...not at all at aother times. It will probably get less milage and may not make as much hp in as wide of an rpm range as a plenum system. But it will be easier to set it up to run smoothly when making a system from scratch....as compared to getting a similar engine set up with a plenum and runners.

This also depends upon what you want to do with the car. For street driving, fully independent runner and TB systems are not always as flexible. For the track....where its WOT most of the time....the ITB's....will be able to push more air and volume through the engine....and probably produce the best HP and torque in a narrower band.
The term "interference"...from the other cylinders is imprecise. On a properly tuned plenum manifold.....there is no intereference from the other cylinders. The pulses from the other cylinders actually help each other in a cyclic manner.

Too many people are dealing in black and white visions when they state that one system works better than another. ITB's retain all of the airflow issues of carburettors. However...by injecting at the port and metering with fuel injection....they more than cut the limitations of fuel mixing that carbs have...in half.
There is a reason why virtually every vehicle built on this planet now uses a tuned plenum and runner system....and it its not because it cheaper (its actually more expensive)...and its not just for good gas milage (many times it can produce worse gas milage if you are tuning for sport or power in odd ranges). Its because the plenum and runner systems are very efficient in making power in a wide band.
They are also very expensive and time consuming to tune in for every application. Not tuning the system individually to very application can many times leave you with an engine that just does not run well.
This is the difference with ITB's and plenums. There aree definate and significant advantages to plenums over ITB's....but they are not simple to tune.
Yes...there are a "few" combination plenum and ITB set-ups out there. Very few. And they will have probbaly even more testing and tuning time behind them. You can only tuned so far around airflow with the electronics of the system. Youcan tune more around ITB's....than you can around a poorly desigend plenum system...with the electronics. Ray

[Paul H]

Good theory Ray but in the real world there is no runner/plenum system available and if there was
it would only be applicable to efi motors as we all know what happens to centre mount carbs.
To take advantages of the runner/plenum intake it would have to be designed around certain
engine capacity and specs and would take a lot of testing and development especially trying
to fit it neatly into the engine bay around the alternator stand etc and a badly designed system
would be way worse than any ITB except 51.5 idas on a 1600(or just 51.5 idas period )
The only system I know of readily available is the progressive weber for the type 4 and type 3
and I know from running a VW garage for 10 years that these run like crap compared to the original injection
or standard dual carbs or 40 idfs. The VW mexico injection set up is certainly an improvement but soon
falls flat when you try and flow any power through it.
The individual runner intake will rule the aircooled world forever until the oil runs out

[raygreenwood]

Good theory Ray but in the real world there is no runner/plenum system available and if there was
it would only be applicable to efi motors as we all know what happens to centre mount carbs.
To take advantages of the runner/plenum intake it would have to be designed around certain
engine capacity and specs and would take a lot of testing and development especially trying
to fit it neatly into the engine bay around the alternator stand etc and a badly designed system
would be way worse than any ITB except 51.5 idas on a 1600(or just 51.5 idas period )
The only system I know of readily available is the progressive weber for the type 4 and type 3
and I know from running a VW garage for 10 years that these run like crap compared to the original injection
or standard dual carbs or 40 idfs. The VW mexico injection set up is certainly an improvement but soon
falls flat when you try and flow any power through it.
The individual runner intake will rule the aircooled world forever until the oil runs out

No theory involved at all....its fact.
Also...you just said ....is pretty much what I said.
For ACVW's....other than stock EFI plenum and runner systems....no one is making them for ACVW's. The stock plenum and runner system...spanks any ITB system out there ....for....the size range of engine it was designed for. Thats the key. The problem here is not that the plenu mand runner system is not better....its just that is very difficult to make one that fits around type 1 cooling. Thats the fault of the design....not of the plenum and runner system.

Also...the aftermarket and runner system for the tow barrel proggressive....is NOT a plenum and runner system. It has no plenum, the runner diameters and volumes are not tuned for any engine and neither is the space under the TB....plus they do not have any manifold heat (another nifty feature of carbed systems in general). They do run like crap. Who ever stated they didn't?
The original fuel injected type 1 system does not count....was poorly designed because it had to be assymettrical to fit the cooling system and alternator. Thats not the fault of the "type" of system....its the fault of the manufacturer for putting a poorly tuned assymmetrical plenum system on an engine without optimizing the cooling system to fit it properly.

Twin TB's are simpler to tune for adequate running. that does not make them better. Twin TB's will rule...because the manufacturers of aftermarket equipment see no profit in manufacturing 30 different sizes of plenum and runners for a very small market. Thats a ton of money.
Also...most ACVW tuners are far too lazy to bother to do the testing and tuning it requires even if you did have the proper volumetric sized plenum and runners to start with.

Personally...I work with type 4. I don't have the issue of the por assymettrical cooling system in my way. Ray

[drmiller101]

a 2180 with dual carbs or with fuel injection, it seems entirely reasonable to expect 150 to 160 horsepower.

The same motor with single carb, or any plenum with a single throttle body, it seems like the limit, at best, is 125 horsepower.

I'm not understanding why a plenum costs manufacturers more then individual TB's for each cylinder. It seems like a bunch of TB's would cost a lot more then some cast aluminum or plastic tubes.

[raygreenwood]

a 2180 with dual carbs or with fuel injection, it seems entirely reasonable to expect 150 to 160 horsepower.

The same motor with single carb, or any plenum with a single throttle body, it seems like the limit, at best, is 125 horsepower.


I'm not understanding why a plenum costs manufacturers more then individual TB's for each cylinder. It seems like a bunch of TB's would cost a lot more then some cast aluminum or plastic tubes.

The same motor with single carb, or any plenum with a single throttle body, it seems like the limit, at best, is 125 horsepower.

ANY PLENUM?....like you have tried ....thousands of them? Not true at all. Where do you find this information? Virtually every engine made today is single TB plenum injection....making hp undreamed of WITH fuel economy unheard of.....in carburetted "streetable" vehicles...from 20 years ago.


The plenum systems costs FAR more than ITB's. TB's are not that expensive. There is nothing to really designing a TB. Its a TB. Been a jillion before it whose design will work fine. They are investment cast...in mass....and CNC milled. The plenum casting is a FAR more complex casting than the ITB runner assembly. Just think about it the shapes involved. And...then internal polishing and machining (if needed). But all of that is fairly automated now.

No the real cost for a plenum system is that...in order for it to work at its best....and not just work in general......which is what far too many people do with ITB's...."hey look at me! ...twin TB's and it runs like a champ (but does it run as good as the engine has poetential for?)......in order for a plenum system to run at optimum, it has to be tuned to the engine and cam, and exhaust system....with the gearing weight and drag in mind of a specific vehicle.
Yes...in vehicles of like weight a gearing, many minor changes can be done in fuel curve and inlet porting....but major changes take dyno time, development...and test track work....tons of it.

For instance...you can go look at the watercooled golf, jetta and sirroccos over any 3 year period. You will generally find about 5 different manifolds...subtley...but significantly different, a half dozen TB sizes and at least 4 exhaust systems. These all used basically the same 1.8 or 2.0 engine.

There are plenty of 2.0, 2.2 etc. out there (albeit most are watercooled)...that get closer to 200 hp with a plenum system and sngle TB.

I've been able to make a factory-esque 1.7L type 4 with D-jet (heavily tweaked of course with lots of mods)....get 102 hp using the stock plenum with a different TB (among other things). Very few carbed twin TB 1.7L's actually make much more than that. Could the plenum have made more...certainly!....but not THAT plenum and TB. That was stretching it as it was.
With a better plenum and runner design......a corrrect plenum and runner design for the heads, displacemnet, compression and exhaust can make 125 hp+ on virtually any 1.7 or 1.8L.

The single TB design can limit ultimate HP capability.....but then again no one ever said you have to have a single TB on a plenum system . Do not confuse having twin or muliple TB's and NOT a possibility with a plenum and runner system.
If you want to see what is possible look at some of the variable volume plenum systems out there (few...but they work well)....like Porsche used. ITB's ...would do no better in HP and torque than that....and would certainly be less flexible.

Is something like that practical?....of course not if you are building only 1000 vehicles per year. But if a company was making 100,000 units year....it would be totally practical.

That puts it into the same boat as ACVW's....and explains exactly why there are no bolt on plenum systems out there for us. There is not enough market to cover the design and casting/forming cost. Its not that ITB's are better at all.....its just that we have a unique engine configuration that is expensive to do the R&D on to make a system that is correct for. Not to mention an unending range of exact engine specifications.

If we as a market segment...whittled it down to a handful of common displacemnt and stroke combinations...regardless of cam, valves etc..... (on one cooling system platform)....someone might be able to affordably produce runners in say.... three main volumes with plenums in say 2-3 main volumes....with a universal TB mount so that you could then use most any TB size for tuning. Coupled with programmable injection, several plenum and runner sizes to choose from and a huge range of TB's from any source on earth.....you would see a LARGE surge in usage and much better results with plenum systems on ACVW.

As it is right now...for example....we get people taking plenum and runners from a 1.6L type 3 (with no swappable TB) and slapping them on a 1776 or 1906...and wondering why it doesn't even seem to run as well as carbs. Why would you even expect a plenum manifold optimized for one engine size work well on another totally different sized engine? You can't even do that WELL with twin ITB's!

Just within the STOCK type 4 injection systems...there are 4 totally different plenums, three different runner sizes and no less than 6 differnt TB's.....not to mention a huge variation of ancillary equipment. You get a half dozen wildly differing engines based around pretty much the same parts.

Ray

[Paul H]

There are quite a few reasons why major car manufacturers use plenum/runner manifolds
nothing to do with power,economy,driveability
1 Noise-they are quieter for sure
2 Packaging - getting it all neatly into the engine compartment
3 Assemblability- bolting a sub assembly to the engine in a production line
4 Less moving parts with 1 throttle and no fancy linkages or couplings
to deal with
5 Throttle resolution better at low speeds
6 Easier intake air routing and filtration
7 One peice combined manifold single TB is very cheap to produce once tooling is paid
It's all about the strict emmision control-multi throttles are a nightmare
These will be first and foremost in the manufacturers minds after which they can tweak it to give
best results in the power department.If they weren't bound by these contraints and they put the same
amount of R+D into a ITB system there would be big improvements in the power department
Back on to VW and the P/R they produced-it's all about packaging
Type 4 engine lid,vanagon engine lid,type 3 engine lid-didn't have much choice really did they
ITB's are way way more tunable than any plenum system and can be tuned anyway you want
either maximum top end power,maximum torque,maximum mpg or a compromise of all.Tune them
just the same with runner length,runner volume,throttle size,throttle plate position,ram pipe length etc
the sky is the limit and the sky is your plenum
The only thing holding you back is same as the PR system which is lack of variety in the parts availabilty
as the generic IDF pattern 48mm manifolds is about your lot-you got a choice of straight or offset

[drmiller101]

ok.

has ANYONE built a 2180 with 150 plus horsepower with a single TB using ANY plenum?????

I am talking about a type 1 engine, air cooled, no nitrous, no turbo, NA.

thanks.

[Paul H]

Closest I got to a P/R was a turbo motor using a 54mm TB on a handmade 1 5/8 centre section
and CB end castings pretty crude but it made 155 RWHP with the belt on-1745cc 76x 85.5
14 psi boost-thats about 210 at the flywheel with belt off, Compare that to a recent test of a 2017
cc motor with our quad 45mm ITBs same heads and cam almost exactly the same 155 RWHP but at only
7psi boost.The 1745 had a T3/60-1 turbo and the 2017cc has a Switzer so maybe this has an influence
but not much. The 2017 will make 220 RWHP by the time we finished tuning upto 14psi
Sorry no normally aspirated data

[1955cc66bug]

ok.

has ANYONE built a 2180 with 150 plus horsepower with a single TB using ANY plenum?????

I am talking about a type 1 engine, air cooled, no nitrous, no turbo, NA.

thanks.

I'm in the process. I have a 2109, W125, 9.3:1 40x35.5 ported 043's, 1 1/2" merged header. I'm using a Porsche 59mm TB, 2 1/2" center section down to 2" runners, ported CB end castings....30lb injectors. I had it running, but having ignition problems. So it should be back together this weekend. With 44 IDF's it dyno'd at 148 hp 160 tq to the wheels without the belt. So, we will see how it performs I will let you know.

[drmiller101]

I'm in the process. I have a 2109, W125, 9.3:1 40x35.5 ported 043's, 1 1/2" merged header. I'm using a Porsche 59mm TB, 2 1/2" center section down to 2" runners, ported CB end castings....30lb injectors. I had it running, but having ignition problems. So it should be back together this weekend. With 44 IDF's it dyno'd at 148 hp 160 tq to the wheels without the belt. So, we will see how it performs I will let you know.

that would be some really great information.

Thank you for offering, and I am really looking forward to hearing back from you!

My GUESS is 125 horsepower, and I really hope I am wrong!

[1955cc66bug]

Well, really it's just gonna be the "seat of the pants 'O' meter" lol. Don't see me getting it dyno'd soon. But I will be able to tell if it lost a considerable amount of power. Even if it did, and I'm happy with the low end torque and drivability, it will be worth it to me

[raygreenwood]

There are quite a few reasons why major car manufacturers use plenum/runner manifolds
nothing to do with power,economy,driveability
1 Noise-they are quieter for sure

that only depends on the application.

2 Packaging - getting it all neatly into the engine compartment

actually not true either. many of the runner systems purposely have to either (a) compromised in exact volumes and length and (b) made even more complex and expensive with S-patterns cast in to get proper operation. Twin banks of ITB's would be far cheaper and easier to stuff under the hood than a very complex plenum.
3 Assemblability- bolting a sub assembly to the engine in a production line

It makes no significant difference either way. A jig would be built...and the engiens are made on a sperate assembly line anyway.
4 Less moving parts with 1 throttle and no fancy linkages or couplings
to deal with
This is not even close to being true half the time. Typically TB's on plenum systems usually end up in very disadvantageous places due to having to stay out of the way of the runners and or becauuse of engine position. Not to mention, that TB's with plenum systems are usually more complex because of the need to plumb into them...IAC, many more vacuum ports than are necessary with multiple TB's and more ancillary systems. Spend some time in the junkyards looking at a vasy range of plenum system TB's and you will find that most are much more complex than what few ITB's are out there. Plus...most have an air straightner insert...almost are are tuned in size specifically to the engine application they go on. This many times also requires an adaptor piece or an insert to be pressed in if a universal TB body is to be used on a family of cars.

5 Throttle resolution better at low speeds
Very true....and its also true that throttle resolution is better at a wider range of rpm and power bands than ITBS. This also requires VAST amounts of tuning and testing to accomplish. It aint cheap.

6 Easier intake air routing and filtration

Not even remotely simpler. Take a closer look at a large number of plenum systems. What looks easier to the quick glance...usually requires several peices of injection molded ducting and a totally different sheet metal pressing to be welded into a car getting a plenum system. Not to mention the vacuum control devices for that ducting, clamp systems etc.
7 One peice combined manifold single TB is very cheap to produce once tooling is paid

Once you take a look at most plenums...and havee a bit of experience in the casting and molding industry....youwill find that to be 100% incorrect. Most complex multi-cylinder plenums require seriosuly complex multi-part casting molds. These can have in some cases ...almost as many parts as an engine block cast. Pick one up sometime...and I'll be happy to outline the seperate mold parts....both internal and external. every so many parts, the intire interior mold set of said master mold must be re-surfaced. Most ITB type most are a simple two part mold with finish CNC milling. Plenums cannot be done this way. The CNC systems cannot reach inside.

It's all about the strict emmision control-multi throttles are a nightmare


Agreed ...multi throttle systems are very hard to control. But plenum systems have been around...purposely......for performance reasons...long before a single person on this planet cared about emmission. They were used on aircraft to make HP long before cars. The fact that they can produce better emmissions (in specific cases)...is only part of the picture. Virtually every high HP luxury gas guzzler out there uses a plenum system....go figure!

These will be first and foremost in the manufacturers minds after which they can tweak it to give
best results in the power department.If they weren't bound by these contraints and they put the same
amount of R+D into a ITB system there would be big improvements in the power department
Back on to VW and the P/R they produced-it's all about packaging

Same goes for plenums systems on ACVW. There have been no factory R&D into flat engine plenum systems since 1976....save for Subaru...and the yare using a plenum system to GREAT effect!


Type 4 engine lid,vanagon engine lid,type 3 engine lid-didn't have much choice really did they

Totally untrue....in the 411/412/ two and four door....TWO entire upright type one systems could be used under either of their hoods. The same could have easily been done with a type 3....just like the type 4....which simply opted to ditch the back luggage area and make a storage behind the back seat.
They had room to use any intake system in the world on these cars and they opted for plenum type. The vanagon and busses are the same. There are no constraints for intake space on any of these vehicles...save for the type 3 and 4 station wagon variants.

ITB's are way way more tunable than any plenum system and can be tuned anyway you want
either maximum top end power,maximum torque,maximum mpg or a compromise of all.

They are NOT more tunable at all....they are just easier and cheaper to tune. Big difference. And still....everything uses plenums.

Tune them
just the same with runner length,runner volume,throttle size,throttle plate position,ram pipe length etc
the sky is the limit and the sky is your plenum

This is just as true with plenum systems as it is with ITB's....excpet there are effects and benefits from a properly designed plenum that you cannot get with ITB's....which is why ITB's are not as flexible over as wide of a range of RPM.

The only thing holding you back is same as the PR system which is lack of variety in the parts availabilty
as the generic IDF pattern 48mm manifolds is about your lot-you got a choice of straight or offset

And the same issues hold you back with availability of plenum systems for ACVW.
Ray

[raygreenwood]

ok.

has ANYONE built a 2180 with 150 plus horsepower with a single TB using ANY plenum?????

I am talking about a type 1 engine, air cooled, no nitrous, no turbo, NA.

thanks.

And if they did...what plenum are they using...and was enough testing done with enough different volumes of plenum to even ascertain if it had the right size and volume of plenums and runners? I'm not yring to discourage the use of ITB's.....I am trying to discourage the seat of the pants belief that plenum systems cannot be tuned to equal or surpass ITB's...when its being done every day. The issue here is that in not one case...not one.....where someone has stated that ITB's worked in a superior fashion on "X" engine as compared to a plenum and runner system.....di those persons EVER try multiple volumes of runners and plenum sets...or multiple TB's or both....nor did they possibly realize that cam and exhaust must also be optimized for a given P/R set. Ray