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Benefits of ITB's with a boosted engine?

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So was just curious on how much of a benefit ITB's are on a boosted engine? is the main benefit throttle response?

Certainly adds abit of complication to the setup/tuning, has anyone done a comparison on a motor like a RB26 etc with and without ITB?

Hi there viper,

I noticed you have not received an answer on this yet so I figures I would respond with the best of my knowledge. From what I know ITB's are an N/A only application. This being due to the fact that ITB's are usually accompanied by intake "trumpets" which would not allow for a seal between the turbocharger compressor outlet and the intake ports of the engine. This would not allow you to build boost. Unless you meant maybe ITB's on each runner of a tubular intake manifold but I still fail to see a positive in this seeing as you want an equal flow of air across all cylinders at all times...so please elaborate do you mean intake trumpets when you say "ITB" or do you mean trottle bodies on each runner of a tubular intake manifold?

I had a lot of problems mapping a turbo car with itbs but it was a basic ecu and I was unable to set up the load like I wanted it ended up just putting a single t/b on it but I believe they have there advantages I look forward to seeing a few opinions

mnunez31 , The RB26DETT have ITB from factory and it's definitly NOT for N/A only.


-throttle response

-flow distribution

-less flow restriction*


-more complex

-harder to tune

-(very) expensive

*Here is an example of a Tibuc ITB for a rallycross engine:

They really aren't an ITB when there is a plenum that they all feed off before them are they?

All the turbo bikes I build are a multiple throttle body setup. Usually just one tps, other times one at each end. Just stick a plenum on it and run. The RB26 is a good example. I have built a few AE111 Blacktop engines for boost as well. Ludo hit the nail on the head for sure.

The marketing hype around itb's is that they will offer improved response to throttle inputs. My own experience suggests this is probably marginal or at least any improvement is probably difficult to really notice unless you're a professional driver. That being said it's very seldom that we get to do a direct back to back between an engine with itb's and a comparable size plenum with a single throttle.

Itb's and a turbo provide a unique tuning challenge though in that we can no longer rely solely on MAP as the load input for the fuel table and instead need to use both MAP and TPS in order to get good accurate control of the air fuel ratio. This adds a layer of complexity that some ECUs will struggle with (probably what @chrisccm was referencing).

For those interested we presented a webinar on multi throttle turbo tuning on an R32 GTR a while back which demonstrates the correct approach to configuring the fuel delivery. You can view it here - https://www.hpacademy.com/previous-webinars/4d-tuning-link-g4-plus/

@ludo that barrel throttle arrangement is a work of art! I guess it's worth mentioning that a barrel throttle in the wide open position will offer zero restriction to airflow, unlike a regular blade type throttle body, so you could expect some improvement in airflow from that addition alone irrespective of whether they are in itb or individual form.

Andre, Thank you so much for the itb tunning course. You are right, It really help to resolve the weird AFR and response for RB26 engine. The same car being tune on dyno but the tunner use MAP load axis which i really found weird driving on road....

Just finish few runs on road tune as your guide. Even it is running just on spring load boost at 0.7. Car drive so much different and afr target hit very close just only few runs. I think thats bcoz the LOAD=MAP so they are doing compensate in the background.

Attached Files

Before switching fm MAP TO TPS, something around 2000rmp, it always act delay no matter what we did

We usually reply within 12hrs (often sooner)

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