projectresto83

So how much vacuum shouldI be pulling at idle to run normal. carbed 306 with the stuff in my sig. the previous owner had vacuum problems before but with a stock single plane intake and a holley carb. I have the performer intake and carb. ill be testing tomorrow to see what i am pulling at idle and while revving. i dont seem to have enough for my brakes (stock 83 v6 setup).

99mustanggt

normal is 17-22,yours may be a little lower if your cam has alot of lift.

projectresto83

Yea I know the cam could be the problem. idk what the previous owner was pulling but like i said ill find out tomorrow.

92hatchLX

With my trick flow stage 1 cam and the other mods (.499/.510 lift .273/.279 duration) AND the fact that I'm damn near 6000 ft. elevation I'm pulling 12-13 in. at idle.

projectresto83

so what is it in a cam's specs that give it low or high vacuum? and on my brake booster whaich place would be better to hook it up? I eliminated the plastic tree on the firewall and just have a tree in my intake. but would that be better or the port in on the back of the carb designed for power brakes. both should be pulling the same vacuum since it is under the butterfly's on the carb correct???

mattdel

so your running a big vac hose from the booster all the way to the intake?
partial reason for the secondary tree is to create a bit more vacuum in the lines, by using a small hose up to the tree.

CrazyCobraSpeed

yes vacuum is effected by area, its very understandable if you like physics but a lotta ppl hate it.... newayz they tree was put there for a reason like mattdel stated... if they owner had this done to the car i wouldnt be surprised if this what his problem... granted there could be other things and i dont know the whole story but i would change it back... i should have 16.1in hg at idle but i dont... but that is becuase i dont have a s/c yet so my cam sheet is off slitly... as for a carb setup im not sure... i would think it would be similar but i dunno how much similar... ull need to talk to some1 with a great deal of knowledge about carbed engines i think

projectresto83

I'm running the same size hose from the manifold to my booster, its just a little longer. the motor is the only thing the previous owner had. my brother and i eliminated the plastic tree to help clean up the firewall a little. didnt think it would affect the vacuum much. and it thats the case should i just run one smaller hose from the manifold to the plastic tree and the split the lines to where they need to go????

mattdel

yah that would be an excellent start to this fix you are seeking.

its a tad late right now, but in the morning when i wakeup(10am, day off!!!) i'll measure the hoses for you.

projectresto83

when you do go do the measuring mattdel draw up a diagram of where the lines on you tree go. all i really need is the intake into the tree, the brake booster, and the hvac line.
Thanks