triple su's on a trimatic... hmm

Devilrod · Post by **Devilrod** » Wed Jul 16, 2008 10:04 pm

Is now the time to say I don't run any kickdown.....

Auto seems to work fine, drops down when necessary. I can't recall ever needing to manually kick it down. Is this good or bad? I'm new to playing with auto's as I had a mate who used to take care of that side of it for me.

bexterity · Post by **bexterity** » Wed Jul 16, 2008 10:09 pm

thanks to all for the info.. very helpful

sammy seemed to hit the nail on the head.. however with the redline manifold i am running all 3 pipes are joined so does that mean i only need the one brass fitting (which is already in there) ??

do i just run some rubber hose from the metal pipe to the fitting?

bexterity · Post by **bexterity** » Wed Jul 16, 2008 10:15 pm

this pic may be slightly helpful...

left red circle is the little pipe thingamajig in question... the 3 cirlces on the right... top one, drilled out with brass fitting, middle and bottom not drilled out....

the previous manifold that was on the su's when i bought them which were also running a trimatic, were using the same setup as i have below.

however... i have no idea what that looked like actually set up.. if that makes sense!

sloth · Post by **sloth** » Wed Jul 16, 2008 10:16 pm

get a manifold fitting from any holden that had vac modulator the hole is correct size if to large will cause auto to flare

Sammy · Post by **Sammy** » Thu Jul 17, 2008 1:24 pm

i don't know enough about SU's to know what the rubber hose connecting the carbys is but i would have a guess and say it could be for a brake booster .... which i can just see that you have one in the left of the pic....

if that rear hole is used for the vaccum to the modulator it might work alright, only thing you might find is that one cylinder might be leaner than the rest, thats why the recommendation for the three to be tapped and joined together to get even vaccum from each ...

having said that all the old 350 holley and stock manifolds i can think of usually had the port in the rear inlet ports only so maybe its fine to just connect to the rear one thats already setup.

karsten · Post by **karsten** » Thu Jul 17, 2008 6:22 pm

i dont think it would change the mixture sammy ,,once vacum is achived in the tiny line to the box it would not alter vacum to the cylinder,and the manifold has a bridgeing between the ports already to balanve itself

oldnek · Post by **oldnek** » Fri Jul 18, 2008 10:21 pm

If that!, what looks like Balance tube cast onto that Redline manifold is actually what it is. And does in fact have a hole running through the centre of it, That will be ok to tee it into the end with no effect of mixture change. But if it is only a support bridge to aid in fitment without 3 individual pieces, you definitely need a functioning balance pipe. It will change the balance if you run 1 vacuum feed, the SU will be lazy to lift the bell in order to get enrichment. Better off running 3 vacuum tees of the bosses in manifold, and tri- connecting your source as is and keep the balance in sinc.

John

HPaddict · Post by **HPaddict** » Mon Jul 28, 2008 8:53 pm

oldnek wrote:Bex, The vacuum modulator is there for upshifts only on the auto, and yes you do need a good vacuum source, but there is nothing stopping you from fiiting a balance pipe that runs along the manifold bridging the three manifolds together...........very similar to this simple diagram. If you get the gist!

I_____I_____I

I will draw it up for and post it if you like, so you can get a better idea.

Regards John

the vacume modulator is there for part throttle kick down also, it works in with the govenor in the box, if the speed is low enough the box will kick back at part throttle, if the speed is a bit too high the electronic kick down will overide at full throttle when the switch on the accelerator is utilised and the box will then kick back in the higher range of speeds up to a certain speed.

HPaddict · Post by **HPaddict** » Mon Jul 28, 2008 9:01 pm

with most triple manifolds the cast sections between the runners are almost always drilled right through to interconnect the three runners, so you can just run the vacume off the threaded boss provided on the rear runner. the other reason the three runners are also connected on street type triple manifolds is to balance out the vacume the so the three carbs run more evenly.