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Role of ITB's in making BIG power

Gabriel, Pete and myself have been disucussing the the role of ITB's in achieving power, throttle response, etc. for some time now. I have always considered what the factory, and teams like Kremer did, as the gold standards for making power. All used ITB's

Recently, Pat Williams racing has been dominating the the PCA GT1 and R classes with these two cars:

2.6 liter tt making nearly 500hp, and set a lap record at Sebring last month


vid of this car at Sebring couple months ago:YouTube - Pat Williams Racing - Porsche New Lap Record - Part 1 This car just smoked the field.

3.4 liter making over 700whp that last month won the PCA overall at Daytona last month:


At daytona... that ***er's fast! YouTube - Pat Williams Racing - Porsche Daytona Win!

Both of these cars are using motors based on the TT layout of the PWR 2.1 that dominated in PCA several years ago


All of these PWR motors are using ITB's, intake manifolds and a rear TT setup nearly identical to the factory's 935 TT set-ups




So, I guess my question this: Should any build looking to optimize power and throttle response and minimize lag at least consider ITB's? Based on what the factory did, and what PWR is achieving in PCA right now, this would seem to be the case.

(And no, i don't work for, or have any affiliation with PWR... i just think that the fact that these cars are dominating, and winning ahead of their classes, just like the 935's did, is REALLY cool!)
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Last edited by juicersr; 11-17-2009 at 12:44 PM..
Old 11-17-2009, 12:21 PM
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ITBs are $$$$ more than a single TB and set-up is a little difficult initially. That's the only negatives I can think of.
The factory 965 Le Mans car used ITBs too.
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Old 11-17-2009, 03:24 PM
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I think TimT and Bill R at Rudtners (sp?) have built more than one turbo motor with ITB's maybe they will chime in.

I have considered lowering my CR and going turbo with my ITB's.....

Cheers
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Old 11-17-2009, 03:40 PM
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For N/A motors, its mandatory for maximum power. Take a look at the area of the individual throttle body bores and imagine one throttle plate with the same area. It would be the size of a saucer plate, so the restriction is definitely less, which means more power

For racing turbo's it is pretty much the same story, but it is hard to get a nice, progressive throttle with that much throttle area being exposed every time you blip the throttle. Doable, but it takes some effort.

The Pat Williams car is nice, but they definitely exploit the rules. The governing body has no idea how much weight to add when you show up with a 2.0L engine that is boosted hard, but hey that's what racing is about too.
Old 11-17-2009, 03:46 PM
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ITBs have their strengths especially under load but are not to good at feathering under normal driving conditions with the tune so far with my experience. Still looking for the Guru that can dial it in a little better. If you are going for all the HP with the hugh injectors, cams don't expect too much driveability off the track, at least that is my experience so far if you need 700+HP to get around.
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Old 11-17-2009, 04:38 PM
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On my NA motor, the ITB's offer just fine driveability. I can idle through pitt lane, cruise around under yellow or cruise on the freeway with no issues what so ever...... it is all in the tuning.

Cheers
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Old 11-17-2009, 05:15 PM
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Thanks guys.

Goran? GJF? Juan?

One more question, if ITB's are the way to go, does the ever versatile Carrera manifold thus become limiting when aiming for higher HP?

$$$ aside, are there any disadvantages to using an ITB/dual bank manifold set-up? Gabe was told by a Rennlister that his mid-range response would suffer if he went to ITBs, but i call BS as it really has to depend on the tuning and turbo selection.
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Old 11-17-2009, 06:23 PM
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Quote:
Originally Posted by Jeff Alton View Post
On my NA motor, the ITB's offer just fine driveability. I can idle through pitt lane, cruise around under yellow or cruise on the freeway with no issues what so ever...... it is all in the tuning.

Cheers
So far still a few hesitation areas under light throttle responce and not able to get idle smooth below 2K using 96lb injectors with a 3.5 liter. Was much better with the 83 lb previous ones but needed the 96lb ones to get the upper end right @ 20psi. What lb injectors are you using as the last tuner thought that was the trade off.
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Last edited by voitureltd; 11-17-2009 at 06:59 PM..
Old 11-17-2009, 06:54 PM
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For driveability would it be better to have such a large injector mounted above the butterfly in more of a shower configuration? Ducati went to shower injectors on their S and R models years ago to improve atomization of the fuel due to having to run larger injectors.
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Old 11-17-2009, 07:19 PM
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I am perplexed - Common convention everywhere is that ITBs are superior from a common plenum setup in both linearity and throttle response, regardless of application when well tuned. See the S2K, Evo and STi forums (and any NA forum on this site).

What am I missing?
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Old 11-17-2009, 07:42 PM
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mid-range response would suffer if he went to ITBs, but i call BS as it really has to depend on the tuning and turbo selection.[/QUOTE]

The only thing that suffers with mine is light driving and high idle and of course MPG. Thats the trade off so far as everything else is like on a wire.
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Last edited by voitureltd; 11-17-2009 at 07:47 PM..
Old 11-17-2009, 07:45 PM
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Quote:
Originally Posted by juicersr View Post
All of these PWR motors are using ITB's, intake manifolds and a rear TT setup nearly identical to the factory's 935 TT set-ups
But dude, it says clearly in the ad and in the ad's images it's a Carrera 3.2 Manifold? I also see the ITBs in the other pics though...

Tim has talked about them on another thread, they're pure porn and will be part of my when I get the time and $$ together dream engine build...

I'm sure Tim says he gets the engine tuned with them without boost, then adds it later...
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Old 11-17-2009, 07:51 PM
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Quote:
Originally Posted by pkracer21j View Post
For driveability would it be better to have such a large injector mounted above the butterfly in more of a shower configuration? Ducati went to shower injectors on their S and R models years ago to improve atomization of the fuel due to having to run larger injectors.
Would they be a second injecter to atomize only when the butterflys are wide open?
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Old 11-17-2009, 07:59 PM
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Quote:
Originally Posted by spence88mph View Post
But dude, it says clearly in the ad and in the ad's images it's a Carrera 3.2 Manifold? I also see the ITBs in the other pics though...

Tim has talked about them on another thread, they're pure porn and will be part of my when I get the time and $$ together dream engine build...

I'm sure Tim says he gets the engine tuned with them without boost, then adds it later...
My bad, i meant both of the current PCA cars, not the original 2.1
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Old 11-18-2009, 01:48 AM
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Quote:
Originally Posted by kenikh View Post
I am perplexed - Common convention everywhere is that ITBs are superior from a common plenum setup in both linearity and throttle response, regardless of application when well tuned. See the S2K, Evo and STi forums (and any NA forum on this site).

What am I missing?
So why even bother with running a carrera, 964 or whatever single plenum intake on these motors? Do most of us use them simply due to $$ when it's ultimately just a 'rate limiting step' or compromise when trying to build the best turbo motor possible?

Or, to put it another way Kenik, when u are looking to optimize all of the above factors, is the cost and complexity of setting up ITB's and individual manifolds so much greater that it warrants going with a single plenum intake which is ultimately a compromise?

Just trying to learn some more stuff here.
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Last edited by juicersr; 11-18-2009 at 05:55 AM..
Old 11-18-2009, 02:00 AM
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Quote:
Originally Posted by voitureltd View Post
Would they be a second injector to atomize only when the butterflies are wide open?
Ducati first had the traditional injectors below the butterflies. but when the motors got bigger and the injectors got bigger, the bikes lost some ride-ability when rolling on the gas and in mid range/part throttle situations. so Ducati went to the shower injector setup above the butterflies in the velocity stacks of the throttle bodies so the fuel would have more time in the turbulent air to smooth things out. Now I know Suzuki and Honda have gone with double injector setups, one below and one shower for the same reason. keep the ride-ability of the bike but pour in the fuel under WOT. they also are using variable length velocity stacks with double butterflies but thats another thread.
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Old 11-18-2009, 04:49 AM
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If you want drivability you need to stay around 9 gm/s. If you need more than that, it's time to consider additional injectors or hig idle speed (2000). Those blue lines going from the fuel block to the throttle bodies aren't squirting koolaid.
Old 11-18-2009, 05:43 AM
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First, let me clear up a few misconceptions.

ITBs do improve throttle response in NA and boosted applications. For NA this is done by providing equal intake tract lengths and plenum volumes. Equalizing the distribution across each cylinder builds power and provides balance to the air-flow. In boosted applications the throttle response comes from the location of the thottle plate relative to the intake valve. Remember the throttle acts as a pressure regulator of sorts. If the throttle is far from the intake valve there is a time lag to pressureize the volume between the throttle and valve. For a common plenum this can be substantial. For ITBs it can be greatly reduced adding to throttle response.

The addition of a common plenum style tract to ITBs is a secret of tuning. Porsche has done wonderful engineering to optimize the resonance tuning. Think V-ram at this point. You can take advantage of the Helmholtz Resonator Calculations for intake tuning and then the throttle bodies help throttle response. It is not hard to cut the lower section off a Carrera manifold and mount them to ITBs. In fact, it is even easier to do this using a 3.6 manifold. To quote Steve Weiner, "truly impressive gains" can be had.

Some high HP motors do suffer from low speed drivability. Some of this is due to tuning but usually it is due to equipment limitations. Large HP numbers require large flow injectors. These injectors have a finite limited open/close time usually around 1mS. They just flow too much fuel during that time to run clean at low rpm. The solution is stacked injectors (duel fuel rails) or low impedance injectors that control the transient response better for faster open/close response.

Placing injectors at the top of the intake tract behind the butterfly can help higher rpm and WOT response. The fuel simply has more time to atomize before being sucked into the combustion chamber.

I absolutely 100% disagree that mid range throttle response suffers with ITBs. It is greatly improved save the tuning on the car. The issue is transient response on throttle tip-in. When one changes the throttle position there is a momentary lean condition and a huge rush of air reaches the combustion chamber. Unless someone monitors this and compensates with extra fuel (not too much) the engine will have a lean stumble. This happens on a 100mS time scale and can easily be overcome with enrichment parameters on an EFI system. CIS has no hope here.

The cost and complexity of these systems is due to making sure every component is properly matched for volume, volumetric flow, flow velocity (cross sectional area of heads and intake) as well as turbo and intercooler setup and finally fuel delivery (EFI, ECU, timing). You can't just have one piece of the puzzle. However, when you have all the pieces of the puzzle you get staggering performance. PWR is a testament of that.

Yes, I saw the PWR 996 car (2.1l built on a 76 targa?) during one of its inaugural races at TWS. Yeah, it was fast.
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Old 11-18-2009, 06:05 AM
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Before my 914 race car received the water cooled engine, I ran ITB's with a 3.6 twin turbo. In different states of tunes and configurations (turbos, intercoolers, etc.) we ranged from 630rwhp to 650 rwhp. Torque numbers were 100 less than the HP figure.

Tony is correct. The ITB's will make more power and part throttle is difficult to tune.

The biggest problem I had was with the manifold on top of the ITBs. I went through 3 setups to find a solution to busted parts. The final answer was a set of "962" type tanks I had hand formed.


Andy


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Old 11-18-2009, 06:15 AM
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Well basically, I was worried about losing torque low down on my 3.8tt that has every hot mod short of Ti rods and a flat fan...

I'm making 634 rw at 1 bar, going for a MOTEC retune here very shortly and just want to ensure that I'm not going to be losing out on power down low with ITBs (which I have in hand ready to go on). So I'm 99% going with them anyways just to see, and I can't imagine a sharper throttle response as is she rev's quicker than a sport bike.
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Old 11-18-2009, 06:59 AM
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