LocostUSA.com

I don't think ITB's fit in well in todays world. This is an old technique that inspires wet dreams among the unwashed.
ITB's popularity comes from some romanticized concepts carried over from vintage Leman's and GP cars.
When ITB's were what was available and could be built reasonably AT THE TIME.

I have done extensive flow bench research on different intake setups.
We were specifically looking for an advantage on a 360" sprint car, as their rules limit the stack size.
Builders were using 410" injector stacks with a restrictor in the stack to satisfy the rules.
This creates a venturi in the stack but then the air slows down at the end of the restrictor.
Airflow is further screwed up by the butterfly and shaft bisecting the port.
So the energy from the stack flow was lost and little gain was realized.

Working on the flow bench we found that there was up 20% flow loss due to the shaft and butterfly in the airstream.
A half shaft reduced the loss but the butterfly is the big issue.
Our theory was to eliminate the shaft and butterfly from the airflow and have a consistently sized runner from top of the stack to the valve.
This would maintain the flow velocity and provide VE gains due to enhanced ram effect.

Dr Frankenstein wanted to make a variable length runner to tune the intake,
but I figured out that that you could change the effective length of the runner by changing the weight of the air.
Installing a second (third) injector at the top of the stack you could change the weight of the air by adding fuel.

We had been using slide throttles on 4 banger Midget motors but the ports on a SBC are right next to each other.
John came up with a roller design for throttle control that opened like an iris and presented a smooth bore at WFO.
He received a patent for the design but could not market it.

The gist of all this blather is that ITB's suck for the street (at anything less than WFO).
Runner length is only effective in a limited (narrow) RPM range.
For the street balancing the idle and blade opening on multiple cylinders is difficult and you get wonky results that change from thermal expansion and shaft flex.
ITB's violate intake design theory at many levels, theoretical gains are lost when the throttle shaft is in the air flow.
Butterfly throttles admit huge amounts of air in the first few degrees of opening and THAT "throttle response" is misinterpreted as a power gain.
This can also cause drivability issues in a light car and be herky jerky (difficult to smoothly modulate)
When in fact torque and peak power are lower than with a smooth bore tract.
So this proves that unobstructed intake tracts are an advantage and a plenum with a single TB are a further advantage. Look at all the newest generation OEM intake designs.
This can be taken a step farther by using multiple TBs on the plenum staged to linearize the throttle, a small primary butterfly and a large secondary (remember spread bore carbs?). (This was also used on FI VW Rabbits) OEM's have now solved that issue with FBW throttles and the algorithm adjusts the servo travel for linearity. There are also linkage tricks you can use to linearize the throttle.

With AlphaN and MegaSquirt idle air speed control is not effective as it bypasses the TPS which is what adjusts fueling when using AlphaN.
I don't think O2 correction works well enough to fully compensate for this.
So for effective ISC you have to have a servo to bump the throttle so AlphaN can track the throttle position and correct fueling as needed.

_________________
Honey anyone?

That's a hellofa post Bent.

I wanted to talk about Skinny's TBI sbc swift, hence the pm

I did think about converting a late model v6-60 to diy slide throttle and removing the upper plenum to improve the hood clearance but quickly found it would not be worth the trouble and the air filters would negate any benefit for me.

If it were really only about numbers, there would be no Morgan trikes. Touch the patina! Smell the leather!

_________________
Miata UBJ: ES-2074R('70s maz pickup)
Ford IFS viewtopic.php?f=5&t=13225&p=134742
Simple Spring select viewtopic.php?f=5&t=11815
LxWxHt
360LA 442E: 134.5x46x15
Lotus7:115x39x7.25
Tiger Avon:114x40x13.3-12.6
Champion/Book:114x42x11
Gibbs/Haynes:122x42x14
VoDou:113x44x14
McSorley 442:122x46x14
Collins 241:127x46x12

I stopped wearing underpants for the exact same reasons.

_________________
The Lethal Locost
The Lethal Locost 2 - Even More Lethalerer

So, some counter point to Bent's post specific to non-race cars:

1. Sound - this is not trivial for a car like this. We have no rule book so if you are after stupid power just put a stupid engine in the car. I'm after a great driving experience which, for most people, is focused on sound. ITB's sound like nothing else and rival the sound power of a good exhaust.

2. Megasquirt uses a blended table for ITB's, MAP at low throttle and RPM when the signal is good and Alpha N at high throttle openings when it's junk. This lets you use an ISC motor while it's on the MAP portion. Lots of examples of good running ITB's with MS online.

3. Sort of aligned with sound, I like to feel the car 'come on the cam' as the intake tuning band hits. You get a very guttural growl and a shove of torque for 500-800 RPM. Again, no rule book, you want more power/torque just put in a bigger motor, no need to worry about what you're losing with ITB's if you're using them for the more 'fun' reasons.

4. Throttle response and linearization can be handled with ETC very easily now. You can meter out that first few percent of throttle as slow as you like relative to the pedal.

In a classed race car with a strict rulebook I'd be right in line with ITB's not being the first choice for all the reasons mentioned (unless saddled with stupid SCCA intake rules). In our case of total free expression just do what you like, if that's the sound and character of ITB's just put enough displacement or RPM in the car to make your power goals.

Alex

When the first sentence of the first post states "3.4 DOHC Ford SHO V8", all discussions and arguments relating to maximum power potential can be thrown right out the window.

I also have read numerous times about how terrible driveability is on ITB cars, especially lightweight ones, yet when I drove benny_toe's MSII (no ITB mode) controlled 4AGE powered Locost I encountered no such issues. In fact, I found how smoothly and controllably it puttered through around town at low throttle/rpm to be the most unexpected part of it all.

Personally, I'll gladly trade a few hp every day of the week and twice on Sunday, if it gets me the right look, sound, and feel.

_________________
-Justin

"Orville Wright did not have a pilots license." - Gordon MacKenzie

I've been wanting to jump in here to voice an opinion. With software like Tuners Studio the ITBs were amazingly easy to tune. There is a learning curve of course. Once I got over that hurdle and to trust the MTs 'Analyze Live' feature things got a lot better. Also got a lot of help from smarter folk, JPSEurpoa for one. Thanks again Paul.

Mine is a factory set up, the Toyota AE101 20 valve JDM Corolla engine so not as tricky as some. Once going it is a pleasure.

And Justin, I don 't think you ever hit the rev limiter. It's performance changes respectfully above about 4,200 RPM. But the roads we were on with the traffic.was a big inhibitor. Still had a lot of fun!
PS - I have the rev limit set at 8,200.

Happy Easter all!

_________________
Larry in Seattle

"Lack of throttle response" is indicative of ITBs that are too large for the engine. You will experience the same thing with a traditional single throttle body on a manifold if the throttle body is too large. I suspect ITBs get a bad reputation since they are typically DIY upgrades and don't receive the same level of R&D as the factory setup - if sized correctly, they are as driveable as anything else.

_________________
-Andrew
Build Log
Youtube

We seem to be comparing wet flow and dry flow intakes. Wet flow is much more critical of port velocity to get the fuel to the chamber. Think of a traditional diesel. It is a dry flow intake with no throttle plate at all, just a convenient place to mount an air filter.

The limiting factor is the port area. I've not seen any ITB installation where the ITB bore was anywhere near as small as the port area. Diminishing returns with anything larger imho.

_________________
Miata UBJ: ES-2074R('70s maz pickup)
Ford IFS viewtopic.php?f=5&t=13225&p=134742
Simple Spring select viewtopic.php?f=5&t=11815
LxWxHt
360LA 442E: 134.5x46x15
Lotus7:115x39x7.25
Tiger Avon:114x40x13.3-12.6
Champion/Book:114x42x11
Gibbs/Haynes:122x42x14
VoDou:113x44x14
McSorley 442:122x46x14
Collins 241:127x46x12

The part number on the Hilborn system I have is 260-F-8B. I suspect it was designed for a 260 Ford. The butterflies are 1.81". Original 260 intake valves were 1.67", but 1.87" or 1.94" valves were normal for the kind of racing engines a Hilborn would normally be found on.

On the other hand, Crower manifolds for the small block Chevy came with 2.62" butterflies, far larger than any valve you could cram into an SBC, and there were even larger butterflies on some versions. I expect that was more an artefact of marketing than dyno testing.