So plenty of people seem to be ripping off manifolds and putting on ITBs with stacks, but what's the average approx gains from their usage? Assuming your plenum wasn't originally oddly sized and your single throttle wasn't undersized so you see vac at WOT, surely there's no gain other than noise?

My understanding was because most people can't fit the original injection/carb in.

Also a lot of oem inlets are not tuned for power.

Plus bike ITBs are much cheaper than using the car alternatives.

Plus I'd expect to gain 10/15bhp by swapping

[Edited on 13/4/11 by Ben_Copeland]

One might assume then that for a performance engine from a car, with access to the ECU etc, the gains would be minimal, if any at all, for the extra faff.

Your restriction to the airflow is MASSIVELY reduced as your inlet tract effectively becomes a couple of inches long.

You also have no issues with interference from the other cylinders (admitadly on a high performance OEM engine, the inlet would most likely be tuned aroudn this any way)

Plus you ensure even fuel flow to each cylinder

Bit of a silly statement if you don't state exactly what engine your talking about. Every engine will gain different amounts. A performance engine could gain the most on itb's or the least.

speedstar - On a performance, transplanted engine you'd have virtually no intake anyway - after the plenum you'd likely be straight into a filter and that's it? (I'd actually consider no filter depending on location and accept accelerated engine wear as part of the fun, especially with a locost engine option).

Even fuel to each cyl only different if you have a single point injection or a single carb'd intake as standard, any modern port injected car should be pretty much identical AFR on each cyl even with a stock intake?

(In consideration is a 6A12).

[Edited on 13/4/11 by coyoteboy]

[Edited on 13/4/11 by coyoteboy]

Why not just turbo charge it instead. The mitsubishi engine is pretty solid and would benefit greater from turbos. No point in ITBs then.

The problem is nobody ever seems to have definitive answers to this.
The only test would be to test an engine with std induction, then swap to itb's and restest after a proper mapping session. All very expensive research. Even then it isn't fair testing, as you really need a mappable ecu with the std induction, and tune it in the same way as the itbs.

In which case I doubt there is very much in it.

For simplicity and reliability I like the idea of using the std ECU and adapting the induction, using an original single TB. Gets round loads of problems and faff, with a few BHP sacrificed but very possibly a better overall drive (too much effort goes into the max power thing, with little thought to drivability across the rev range)

Saying that, I have a ITB setup etc for my engine, but in many ways would rather have the std setup. I think. If it would fit.

i ran a 2 litre zetec with basic standard inlet mainifold, 2 litre MAF and RS1800 throttle body on standard ford ECU was from memmory 136bhp, then fitted ITB's a plenum and still 2 litre MAF and standard ford ECU went up to approx 150 bhp mainly with increased rev band on assumption lot lest restriction through 4 38mm ITB's than a single believe 60mm ish one

standard 2.0 zetec goes from 128bhp (standard injection/ecu) upto 160-170 bhp with just the throttle bodies and decent exhaust, plus remapped ecu of course
more there if you change cams too so imo best gains available when tuning normally aspirated engines

With respect to turbocharging it - yes, that is an option I'd consider, though I believe they're only good for 5-6psi of boost, which isn't a great gain (70hp on a decent motor) for the difficulty involved in modding the exhaust for it, and losing some of that lovely wail. The ITBs would make it lighter and more responsive, where as the turbo would do the opposite. I'm used to the turbo route, forgot how bloody hard it is to extract more power without a compressor! That said, I've been told the non-mivec 6a12 (170-180hp) is a better bed to turbo from as the added mivec (200hp) complexity is basically obliterated by the turbo gains.

Some of those later gains seem pretty large but as mentioned, how much of that is from different mapping and would have occurred without the ITBs with a good rolling road session?

There is something to be said for standard installations, standard ECUs and no major faffs.

[Edited on 13/4/11 by coyoteboy]

My point exactly. Of course an engine will do better if you change induction, exhaust and ecu.

The better example was the plenium to ITB example, but I suspect that is comparing book figures with rolling road results. And rolling roads are notoriously unreliable fot figures as it is easy to fiddle results. Brilliant for setting a car up though.

And the other thing is that peak power figures are not what it is about. You really need to compare torque and power curves.

which an accoustically tuned stock intake probably does better.