From Carbs to ITB's

[Europa88]

My engine is currently being rebuilt with a full steel bottom end at standard stroke. I have bought some cams with higher lift than my L14's and around 250 degrees duration at 1mm lift. The compression ratio will be about 11-1 and the idea is to use as a road and track car. More so road than track I guess.

My builder says I definitely need to go to 45mm induction as he will also port the head for me. I respect this guy as he has shown me the spec of the last TC he built and It made some where around 175-180BHP. He has worked with Paul Exon ex QED, Oselli Engineering and MED of mini fame.

So rather than buying 45mm Carbs, the idea is to go the ITB's probably Jenvey heritage. I already have a 3d ignition map and a base map installed for fuel injection set up by Richard Winter some many moons ago.
I'm just concerned the jump from 33mm chokes in DHLA 40's to a 45mm ITB is overkill and should i go with 40mmm ITB's?

[elanman999]

My understanding is that large ITB's do not suffer from the low speed running issues that large carbs will do as TB's don't need air speed to raise the fuel. You could also ask Jenvey or your ECU supplier.

Also from what you are saying you are increasing the BHP potential from the engine by quite a lot so you may need an increase in choke size. I assume the ECU that you have is for fuel and sparks? But it will obviously need re calibrating.
I am running (old style) 40mm Jenveys on my Elan and is very tractable, but that only makes 140 bhp.
Sounds a nice engine build you are having done.
Cheers
John.

[ill_will]

I faced a similar dilemma. Most of the sizing tables I could find suggested closer to 40 would be better unless raising the rpm limit and making peak power at higher rpm. A few knowledgeable people suggested that for a road engine using 45s would result in a lack of torque at typical street rpms. So it probably depends on what you want. Sadly I havent got mine together yet so can't say whether it was the right choice! Naury on this site made high HP with 40s from my understanding, albeit a 1700cc. HTH!

Will

[h20hamelan]

I have not completed it yet of course.

We are putting 630cc ITB’s on 2.1L Volvo from 1980, and that 700cc bike ITB’s are enough for the 2.3L RedBlock. MaxECU or…MS or….