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46mm ITBs big enough?

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So I'm thinking about going itb on my engine for better response. My engine is 4.2 litres. I was thinking about using two sets of 46 mm ITBs off a GSXR1300. my engine redlines at 8k max hp is at 7850. Would these throttle bodies be sufficient?

Here are the engines specs. I'm still looking for reliable specs on the ITBs, but from my searches it says it's 42mm at the flange and tapered to 46 at the trumpet flange. 42 sounds small but if it was bored completely to 46 ???

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I'd say there is a very good chance you could go backwards in performance on an engine so well developed by the manufacturer. I would be looking at if there are throttle delay timers or similar on the current ecu package that can be adjusted first.

Well I'm swapping this engine into an e36 drift car. I'm planing on either going MS3PRO or Haltec. And some of my inquiries about 46mm ITBs say I'm good others say too small. But what about 49??

Unfortunately there's usually a little trial and error in selecting the best size throttle for an N/A engine. A ITB that's too large will kill air velocity and can destroy bottom end torque while going too small can pick up the bottom end torque at the expense of high rpm power. Given that essentially you're at 530 cc/cylinder then this is relatively comparable to a 2-2.2 litre 4 cylinder. 45 mm throttles are a pretty common option for this sort of engine and should be sufficient unless you're aiming to run the engine to 9-10,000 rpm.

Thank you Andre, I don't plan on going to 9-10k rpm but it is my drift car so I will be in high rpms to redline.