ITB balancing

[zaq123]

I 've been putting some miles on the car with new tune and dialing idle as best as I possibly can. Decided to take of ITB plenum to check if the balance is still ok from what I initially set it at. I actually forgot that when I initially was balancing it, cyl 3 and 4 were off from each other slightly. Obviously RHD ITB can only be balanced in pairs. The only way to adjust is to mess with a throttle plate. However I recall Rama's instruction not to mess with plates as they are set to account for the expansion etc etc.
Here is a video of it idling at 900rpm, my idle setting without AC (AC ON is 1000rpm). Cyl 2 and 3 TBs are off from each other by about 0.5-0.7 kgm or whatever this little tool shows? Should I leave it alone or mess with TB plate a little and hope it won't stick after?

https://www.dropbox.com/scl/fi/zqa09f7gc1z9mz6wswe3z/ITB-balance.MOV?rlkey=fccfjmg7x98zad9i151h5dpjb&st=ulziogbx&dl=0

[zaq123]

Post edits don't work again on this forum.. But just to add, my cam is Schrick 284...idles good enough for that cam?

[digger]

i only check balance with the ICV blocked off (and ideally cylinders unable to cross communicate via the small vacuum hoses), is the ICV operating in that video? Also presumably the valve lash has been done recent?

Its a moot point but the more expensive throttle have a little bypass to tune throttles on the same pair but properly isolated they should be quite a bit closer than as measured

[zaq123]

i only check balance with the ICV blocked off (and ideally cylinders unable to cross communicate via the small vacuum hoses), is the ICV operating in that video? Also presumably the valve lash has been done recent?

Its a moot point but the more expensive throttle have a little bypass to tune throttles on the same pair but properly isolated they should be quite a bit closer than as measured

valve lash was checked too many times due to me trying to stop that valve cover gasket seepage. It's not laking but sweats oil overtime just enough to annoy me. Originally syncd ITBs with ICV blocked of and at the throttle cable holding about 1000 rpm, ITBs idle screw is set to hold just over 800 rpm and ICV does the rest. This recheck was with ICV in the equation , just like in Ramas sync video.

https://youtu.be/1k0471HN5W8?si=CF59pjegXt_OReRP

[digger]

This whole thing is a rabbit hole

i saw values of

3.2
2.8
3.0
2.2
2.8
2.7

Your variation of 3 and 4 is quite off, with 4 running 27% less air than 3 which is not minor nor within normal tolerances. i dont think moving the blade will make up for this plus the screws can be a pita if locktited i always worry about stripping the little f...s

Starting from the beginning there are a couple of things that must be correct to get good results overall

1) The 3 manifolds needs to be perfectly co-planar (there is clearance to bolt holes so this is not a guarantee) ( a single manifold would have advantages here but a moot point and other issues.

2) The throttle 3 shafts must be coaxial (there is clearance to bolt holes so this is not a guarantee)

Any offset or angular misalignment of the shafts throws things off kinda like a universal joint. This is not likely the issue here but it is a good reminder

When i test without any influence of the ICV i would typically expect to see the same reading on the pair almost bang on except maybe half the width of the indicator line. The machining is fine on the TB even my 12year old one still does good it shouldn't be that far out

to me air is being ingested through the inlet valve this comes from both the throttle body and the vacuum tube from the ICV you are only measuring one path using that tool so not ideal. If you want to use the ICV then IMO you need to measure vacuum in runner to indicate total mass flow which presents its own issues and nuance i have been down there several times. i even retrofitted individual bleeds but waste of time just not worth the effort.

i test at 1,000 and say 1,500 rpm and 2000 rpm to help understand any rpm variation, if it changes alot with rpm then 1) and 2) might be the culprit (never will be perfect as the engine is 6 individual cylinders/engines that are slightly different) and i favor around say 1500 as at idle the engine will happily idle with quite some variation as there is no significant load but 1,500/2000 rpm is a real driving situation.

The same if i then hook the ICV up and it shifts/skews a bit because the hoses are different, the fittings are different or the little plenum is not big enough then i don't actually care as when the engine is doing some real work its more than likely going to be closer balanced geometrically at the throttle blades and the ICV air becomes a smaller % of the total ingested air.

This is all just IMO though and there is always more than 1 way to skin a cat