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Old 08-27-2005, 12:50 PM   #1
FalconRS
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Default ITB's: Ever been tried?

At a recent car show here there was a K-series swapped 95 Civic with Individual Throttlebodies on each cylinder. Has something like this ever been tried on a subaru?

I'm not considering trying this on my year-old, still-on-warranty car or anything, I was just reading a lot of threads that agree that there's not a lot of options if you're looking to shoot for the stars, like 200+ whp on these cars, just wondering if this has been tried in a race application or something. Would get rid of the restrictive giant spider on top of the engine anyways.

EDIT: I had intended for this to go in the Naturally Aspirated Forum. My morning coffee hasn't sunk in yet.
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Last edited by FalconRS; 08-27-2005 at 01:05 PM.
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Old 08-27-2005, 03:12 PM   #2
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you would still need some kinda 4 legged spider connected to the ITB's to supply air, unless someone planned on running them open. I would also imagine the cable setup would get slightly complicated on a suby. with an inline engine you get all TB's lined up, with our boxer engine you would have 2 lined up on each side but then somehow you would need to split the cable to both side of the engine.
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Old 08-27-2005, 05:29 PM   #3
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It's complicated but totally possible for the dilligent.

One concern is that you'd have to convert to MAP reading so you can easilly reference airflow without impeding it. Stand alone would do that. Just as well because that's what it would take to reall tune it.The trottle bodies can be sourced from a street bike.

It would be unique, but this is generally an option only for fairly hi-rpm applications. Im still a newb, but my understandling is that the intake runnerson Soob heads are a limiting factor in high rpm application.

It's totally doable, and genuinly exotic, but alot of money for the performance yeild. If you would like to find out more about about itb, search for Toyota 4age. Use search terms "5 valve" and "itb" to dig deeper.
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Old 08-27-2005, 06:16 PM   #4
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there have been threads on it...I'll see if I can load my pictures of itb setups onto my server then post them
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Old 08-27-2005, 06:45 PM   #5
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Quote:
Originally Posted by Dead Man Sliding
It's complicated but totally possible for the dilligent.

One concern is that you'd have to convert to MAP reading so you can easilly reference airflow without impeding it. Stand alone would do that. Just as well because that's what it would take to reall tune it.The trottle bodies can be sourced from a street bike.

It would be unique, but this is generally an option only for fairly hi-rpm applications. Im still a newb, but my understandling is that the intake runnerson Soob heads are a limiting factor in high rpm application.

It's totally doable, and genuinly exotic, but alot of money for the performance yeild. If you would like to find out more about about itb, search for Toyota 4age. Use search terms "5 valve" and "itb" to dig deeper.
This guy's on the right track. I was kind of thinking an '04 MAP engine converted to the '05's throttle-by-wire system, throttle cables cease to become an issue, it's now an electronics/wiring situation.
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Old 08-27-2005, 06:49 PM   #6
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It's in the making on my car. My project for the winter. But there is going to be something on top of them. I have the designs for them.

The bonus is instead of air jamming up in a manifold it is going on a straight, direct path into the head. For racing, this is awesome because it keeps the air cool when your on the throttle all the time.

On an everyday driver....ummmm... unless you have 4 filters and a solid hood so no water gets in, go for it.
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Old 08-27-2005, 09:25 PM   #7
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ITBs on a EJ25 would sound very mean. ITBs already sound mean on hondas with sub 2.0 liter displacement. Someone above hit the nail on the head, as ITBs are generally found on higher reving engines, which contrasts many subaru engines that generally lose power past 5k and usually dont have redlines over 7k. I would still love to see it done. If theres a sound clip out there please post it in here.

I've read up on the idea alil bit on the miata forum. Its pretty much standard to run a standalone with ITBs. You wouldnt need a common plentium to connect all 4 TBs, just put air horns on each TB with a foam cover filter at the end. The main problem with ITBs is the cost, after the project is said and done youd likely have spent enough for JDM engine swap (that would proably put out more power too).
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Old 08-28-2005, 12:33 AM   #8
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I think the reason high-revving and subaru don't really go together is because of intake manifold design. Long runners make for great low-end torque but choke high-rpm horsepower. I've learned this from close to 10 years dealing with turbo- and supercharged 3.8L domestic V6's. When a long runner (4" tops on a 3.8) is swapped for just a big "boost box" style intake with short ports into the heads, they go from running out of breath at 6-grand (like our n/a EJ series) to pulling hard to and past 8-grand (if the valvetrain and balancing is in place to support it of course).

ITB's would be a similar result, I think it would take the torque curve and toss it way up because you've got such a short run before the air enters the combustion chamber. With balancing and valvetrain, there's no reason an ITB setup couldn't put down power past 8-grand I don't think.

Another interesting thing to try would be a sheetmetal intake manifold with a larger central plenum and shorter runners. Make for a similar effect, reduce the run, increase top end (at the expense of low end torque). Would be fun to try if I had a local AWD dyno and a bottomless bank account.
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Old 08-28-2005, 02:07 AM   #9
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yes, intake manifold design is the short coming of subaru high revving power...still kinda amazed the JDM EJ20's revving to 8000+ make decent power up there...
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Old 08-28-2005, 03:03 AM   #10
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imagine this....the USDM STi motor with ITBs....yeeouch
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Old 08-28-2005, 03:05 AM   #11
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Quote:
Originally Posted by The Stig
imagine this....the USDM STi motor with ITBs....yeeouch
ROFL...well ITB's in a plenum could work...gives crisp throttle response...but otherwise it would definately suck
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Old 08-29-2005, 01:57 AM   #12
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If i can find a good set of itb i will make the manifold and dyno it on my 2.5 turbo engine
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Old 08-29-2005, 02:58 AM   #13
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I was thinking dual tb might be a good option. Just throwing ideas out here....

Imagine the stock spider manifold. You could cut out the little plenum in the center, and 2-3 inches off each runner along with it. Then make a larger plenum out of mild steel with two seperate chambers and two rear-facing tb's. Each chamber could have two little velocity stacks inside, which would potrude from the plenum about 1 inch. Then these could be mated the the truncated stock runners with short sections of rubber hose and clamps. That would take care of the problem of attaching aluminum to steel, and give the whole assembly a bit of flex for easier fitment.

The idea here is an intermediate step.

1.The flowbench data on Cobb's site suggest that the stock tb/manifold assembly flows about as much as the intake ports on the heads. I think this dual itb design would bump up the flow and shorted the runner to yeild a shift in the powerband that would be useable with a mild set of cams. At least moreso than a wild quad tb setup with really short strait runners.

2. By using the lowers of the existing runners, you can sidestep the effort of exact fitment, fabbing flanges, and trying to get injector bosses in just so.

3. Now the whole unit is modular and easy to dissasemble, for when you come up with the inevitable version 2.0.
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Old 08-29-2005, 02:10 PM   #14
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Josh at Cobb had been working on a set for his own car, and then he wrecked the car, and the project was shelved.

Syms actually makes an ITB kit. If you google around a bit or search here on NASIOC, you can find the pics...
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