Thread: th 400 modulator and a holley hp carb

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Put my brand new MTS intake and hp holley carb on my car yesterday( waiting for it to finally start to warm up here and get rid of all the snow)
started to figure things out found a vacume port on the front of the carb which i can use for the vacume advance( i am running full manifold vacume advance ) found a big port on the rear of the carb for the pvc but nothing for the trans modulator at all.
any other way to get manifold vacume to the modulator short of drilling the intake and tapping a port. I dont thnk I can tie into the PVC line as that wont show a proper vacume signal. any other place on a hp holley carb that i can get a manifold vacume signal.
I think i may be taking some of this apart again

I would think you should be able to run a tee at the big rear port and take the vacuum off for your mod valve.

i was worried that having the pvc and the modulator on the same vacume line may mess with the shifting as the pvc vacum is not as strong. will give it a try once running.

I would just tee into the vacuum advance hose.

Nothing worked good with this intake a t looked like crap no where to hide it , drilled and tapped the pass side rear runner and put a 1/8 npt 90 in it looks a lot better. greased it all up before i tappped it and only drilled a 1/8 hole right through the intake and then the big hole only enough to get theads in it looks good. Just afraid to put a hole in a perfectly good piece of aluminum

I think the vacuum port down low on the holly gets' it source below the throttle blades (ie, same as tapping the intake runner) and isn't there a vacuum port up on the side of the metering block for vacuum advance?

there is a capped port there but i think that is the port where vacume increases when the throttle is opened up , wont work with how my advance is set up.

Originally Posted by canadianal

there is a capped port there but i think that is the port where vacume increases when the throttle is opened up , wont work with how my advance is set up.

Aacch! That is the "ported vacuum" source which is to be avoided at all cost.