position for ITB vacuum reading

position for ITB vacuum reading

Author
Discussion

Inline__engine

Original Poster:

195 posts

135 months

Wednesday 12th October 2016
quotequote all
I'm going to add some nipples into an intake manifold for purposes of using a carb sync tool for balancing throttles using vacuum signal. Is there any guideline on where to put them? i have 6 " of length between blade and head.

i presume you dont want them to be too close to the throttles, but maybe im wrong and it doesnt matter ?

cheers

KiaDiseasel

83 posts

90 months

Wednesday 12th October 2016
quotequote all
Close to the butterfly is best to get the largest pressure drop readings and best accuracy. What's more important is they all be at exactly the same distance from the butterfly.

spyder dryver

1,329 posts

215 months

Wednesday 12th October 2016
quotequote all
^^^^^This. The vacuum take off ports on superbike throttle bodies are almost right on the edge of the butterflies.

Inline__engine

Original Poster:

195 posts

135 months

Wednesday 12th October 2016
quotequote all
i was just worried that if they were close to the butterflies then unless they were each exactly positioned in the same position around the circumference and distance from the blade that it was more likely to introduce variation, as looks quite chaotic just down stream of the throttle in CFD ive seen

i can get it about 5/8"-->3/4" downstream from throttles, presumably on the bottom is ok to as the injectors and connections are sort of in the way on top unless i put them in at a slight angle

https://i.ytimg.com/vi/m2IzJlaEu9Q/hqdefault.jpg

thanks

99hjhm

426 posts

185 months

Wednesday 12th October 2016
quotequote all
That should work fine still for the point of balancing.

PeterBurgess

775 posts

145 months

Thursday 13th October 2016
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If you have them downstream the depression will collapse as soon as you open the throttle as it will be max vac reading with throttles closed, the idea is to get a 'good' signal by having it slightly upstream of the throttle disc/butterfly so it comes into play as the disc opens and presents higher speed air flow to the take off.
Unless for some reason you require max vac only at idle?
Peter

Edited by PeterBurgess on Thursday 13th October 08:46

KiaDiseasel

83 posts

90 months

Thursday 13th October 2016
quotequote all
PeterBurgess said:
If you have them downstream the depression will collapse as soon as you open the throttle as it will be max vac reading with throttles closed, the idea is to get a 'good' signal by having it slightly upstream of the throttle disc/butterfly so it comes into play as the disc opens and presents higher speed air flow to the take off.
Unless for some reason you require max vac only at idle?
Peter

Edited by PeterBurgess on Thursday 13th October 08:46
Say what? How do you propose the OP balances his TBs at idle if he puts the take off point upstream of the butterfly?


Edited by KiaDiseasel on Thursday 13th October 15:02

KiaDiseasel

83 posts

90 months

Thursday 13th October 2016
quotequote all
Inline__engine said:
i can get it about 5/8"-->3/4" downstream from throttles, presumably on the bottom is ok to as the injectors and connections are sort of in the way on top unless i put them in at a slight angle. thanks
I wouldn't fret too much about them being a little way down the manifold from the butterflies. You get some pressure recovery as you go further away from a restriction so the signal will be a bit weaker but anywhere up near the TB end of the manifold will do.


Edited by KiaDiseasel on Thursday 13th October 15:01

PeterBurgess

775 posts

145 months

Thursday 13th October 2016
quotequote all
If it is only for balancing then it is covered by my...Unless for some reason you require max vac only at idle?

Peter

KiaDiseasel

83 posts

90 months

Thursday 13th October 2016
quotequote all
PeterBurgess said:
If it is only for balancing then it is covered by my...Unless for some reason you require max vac only at idle?

Peter
Well I guess it's an understandable mistake given how unclear the original post was. If only the OP had said something like "for purposes of using a carb sync tool for balancing throttles".

Oh...... rolleyes

PeterBurgess

775 posts

145 months

Thursday 13th October 2016
quotequote all
Mea Culpa , good job I backed it both wayssmile
Peter

Inline__engine

Original Poster:

195 posts

135 months

Monday 17th October 2016
quotequote all
ok thanks everyone, i normally sync with the syncrometer but its handy to be able to get a reading without disassembling airbox and everything.

do people have a preference for syncing by vacuum or syncrometer?

PeterBurgess

775 posts

145 months

Monday 17th October 2016
quotequote all
I use a single vacuum gauge and have an adjustable clamp on the hose so I can damp out the pressure oscillations to an acceptable level for obtaining repeatable readings. I used to yearn for those multiple manometers you could buy for setting up bike carbs many years ago! I would be wary of using multiple Bourdon vac gauges as they may not give like for like readings due to manufacturing/calibrating differences.
Peter

Inline__engine

Original Poster:

195 posts

135 months

Monday 17th October 2016
quotequote all
i have a gauge http://www.carbtune.com/ for each cylinder, has a small pin sized orifice piece that goes in the hose to filter fluctuations

rev-erend

21,404 posts

283 months

Monday 17th October 2016
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I use one of there meters .. cant remember who makes them.