Need More Vacuum

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7

72DartSwingerV8

Well-Known Member
Joined
Jan 10, 2010
Messages
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Location
San Diego
Here's my build:
318LA
.030 inch overbore
1.88 and 1.60 intake and exhaust valves put on stock head
Purple Shaft 340 specs cam
4 barrel spreadbore Eddy intake manifold
Rebuilt Holley 650 4175 spreadbore carb
Hedman headers

Currently I'm getting 7inchlbs of vacuum off of my manifold. I need at least 14 in order for my power brake booster to work. How do I increase my manifold vacuum?

Thanks
 
check for a vacuum leak and or how was the cam installed, retarded?

was it degree'd in?

fwiw what kind of cylinder psi do you have when dong a cranking compression test?
the bandaid or trick when all else fails is a vac canister, they store built up vacuum.

Im also in SD, north SD...so if you continue to have this problem, let me know.
 
No vacuum leaks. I used a smoker and found no leaks. Cam was installed advanced. Haven't checked the compression but I hope to god its good. The engine has been completely rebuilt. I wouldn't mind trying the vacuum canister but it seems like the engine should be able to make 14 easily. I have a PCV and a breather through the air cleaner. Should I cap them or something?
 
Thats too lil timing.imo

If you want, bring it by and ill fix it or at least find the problem and can do watch you want after that.

let me know, Im in vista
 
What woul;d u recommend for timing? I can't drive it because I don't have any brakes cuz I don't have enough vacuum haha.
 
10 before should get you in the ballpark with a stock distributor.
 
Fire it up & let it get to operating temperature. Connect a vacuum gauge to the manifold.

At idle, advance the distributor while watching the vacuum gauge. The highest vacuum reading is the maximum spark advance for that rpm. If the idle speed climbs out of range, adjust the idle, and twist the distributor for max vacuum again.

Check the timing, and write it down. If it is more than 15 degrees it will probably ping under load. Test drive it. If it pings, back off 3 to 5 degrees and test again.


B.
 
No doubt about it. Retarded ignition timing will cause low manifold vacuum. Once you get the timing right, I bet it will haul ***, too. I would start at 10* BTDC as mentioned. Might need more. Of course, you might need to step up to some better grade fuel, too.
 
Alright, so I set the timing at about 14 BTDC but my vacuum is only at 12. Therefore, I still have to push the brake pedal to the floor to get it to stop. I tried giving it more advancement but it didn't change the vacuum. I used the smoker again and no vacuum leaks. I need a few more inchlbs of vacuum.
 
I take it this is an automatic. You might try adjusting the idle mixture. Use a vacuum gauge to get it to the highest reading.
 
Do you know the correct procedure? If not, I'll let you know....if you do, just ignore this. lol Block the drive wheels really good. Set the parking brake hard. Find the small angled vacuum outled in front of the carb on the base plate. That's manifold vacuum. Hook your gauge there. Strat the engine and bring it up to temp. Drop it in drive. Adjust the idle mixture screws until you acheive the highest reading on the vacuum gauge. I usually go a half turn leaner and call it done. You're bout runnin outta tuning things that can cause this. Rockers having the lifters pinned down with too much preload would be in the back of my mind.....but try the carb and see what happens.
 
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