need more stopping power. vacuum issue?

[smokedat]

not a big deal on carbd engines u can throw the most agressive cams on carb engines and they are easily tuned to run try that on EFI good luck computers eaven after being retuned will not run appropietly. I am referin in particular to choppy as F@k idles wich are vaccum robin, but sick as f@k

[baclay9]

Originally Posted by smokedat

valve lift is on the high side. what is youre LCA Lobe Center Angle the lower it is the less vaccum thus choppier idle, this is a good thing defenite sound and performance of having a cam, minus the breakin issues

The LCA is 110

Here is the cam card of the one I will be running.

http://www.compcams.com/Company/CC/c...?csid=396&sb=2

[454HO]

Originally Posted by 3r!c84

yea that little ball !! haha damn there went that idea. the other idea was on my stock 305 it had like a check valve looking thing on the line from the carb to the booster. do i need that? im just running a rubber line to carb to booster

There absolutely needs to be a one-way check valve somewhere... either in the hose between the intake manifold and the brake booster, or sometimes they are built into the inlet of the brake booster itself.

A quick test:
1 - start engine and let idle
2 - press brake pedal sharply and listen for a 'hiss' sound. That sound indicates you have some vacuum
3 - release brake and let engine continue to idle for a few seconds
4 - shut off engine and wait 10 seconds or so
5 - repeat step 2. If the system is working properly, you should still hear the same hiss sound. If you do not, then the system is not holding vacuum. Either the check valve is bad or missing, or the diaphram in the booster is ruptured or leaking. You should get at least 2 or 3 brake pedal pushes with vacuum boost assist before all the vacuum is blead away with the engine not running.

Back to the earlier discussion on the vacuum can. If you are going to add one, it would need to be on the booster side of the one-way check valve. The vacuum can only adds extra 'capacity' to the vacuum system. It does not in any way generate more vacuum. All it can do is hold highest vacuum the engine can generate.

[blackbeaSSt]

wow, lots going on in this thread since yesterday! im not 100% sure of the cam that is in there. i might be able to get in touch with the previous owner but for right now i have no clue!

and im also not the most mechanically inclined person but i don't wanna throw money out the door for someone to check basic stuff

[LONGHAIR]

Originally Posted by 454HO

Even if the initial timing were set to something more appropriate for a performance cam, say 14 degrees, the engine still may not run smoothly with ported vacuum advance. If this were the case, moving to manifold vacuum advance could provide the additional timing the engine wants and result in a smoother idle with higher vacuum for the power brakes.

Does this mean the distrubutor might need some work? Of course. And that is why I was asking the questions. But since the original poster has not provided any details on the engine or how it is tuned, all we can do is speculate...

You can't "just move the vacuum line connection" w/o recalibrating the distributor. Even if that move would increase your vacuum at idle, you would probably get into a pinging situation because of it. If the vacuum really is that low, the advance cannister my not be functioning properly. That will get you an erratic idle, which compounds the problem.

The whole thing seems to me like "too much cam" w/o having the surrounding systems "adjusted" to compensate for it. This could also include the torque convertor. If it is too tight, other issues get involved. He also may be lacking the compression needed to make the cam function too...

My point about switching the vacuum line was more about the fact that it will not "use up" the available vacuum than the technicalities that get over many people's heads.