LannyL81

Have an oil leak at the rear of the intake and was wondering if this could also be a vacuum leak?

Well I hope it is just a leak in the RTV and not something cracked.....will find out when I get it apart.

Thanks

gerry72

If you mean an oil leak at the bulkhead (Chinawall) where the base of the intake meets the engine block, then no it would not indicate a corresponding vacuum leak. It wouldn't preclude it either, though. They are mutually exclusive.

Timsride

I don't think that it could leak vacum off the rear seal of the manifold without it leaking coolant first as it is the next thing in line before the intake runners.

snoopykissedlucy

Technically, your PCV system has a vacuum and that's connected to your rocker arm area which is connected to the oil valley which extends to both china walls, front and rear.

LannyL81

I am measuring 12" to 13" of manifold vacuum at idle; searching for vacuum leak...not sure I actually have one...but this sure seems low compared to what others are measuring.

Taking the vacuum measurement at the port behind the carb where the hose for the headlights attach.

Any particular spots I need to check? Engine has always had this vacuum reading since rebuild two years ago.

The engine is a 355, zero decked, Chevy 882 heads with 2.02/1.60, 1.6 roller tip rockers, 2 valve relief pistons, comp cams 268H, computer controlled E4ME carb and stock intake, Hooker side exhaust/headers.

Timsride

Thats probably all the vacum Your going to get out of that combo. If its running good I wouldn't worry about it. Is there a problem other than oil leaking from back of manifold?

LannyL81

Runs okay other than being a bit rich...but still working on carb settings.

I just thought I would be able to feel more power than I do. Thinking it is time for a better set of heads but not able to go with a 64cc head with the zero decked block. Only ones I have found so far are the World Products Sportsman II at 72cc, or S/R Torquer at 76cc. But at $1000+for these....I doubt I will do either.

Others have told me that the vacuum is to low so I am searching for leaks right now. I did find that I can increase vacuum a little by advancing the timing a bit....but I feel that I am at the upper limit now at about 12 degrees BTDC at idle.

sakins.02vert

Did you ever figure this one out? I have a sb350 in my 76 L-82 that was rebuilt. I'm only pulling 7 lbs at idle, think this is really low. My mechanic said he thinks it's due to a too my cam being too heavy. I didnt rebuild this but I have a slip that said "melling high performance cam .480 lift" . My car is back firing and bogs on acceleration at times.

I think I need to check timing and vacuum leaks but just wondering how this turned out.

Rikoshay

If your cam is extremely aggressive then the engine would have to be set at a higher RPM just to idle. Have you tried rotating the distributor to see if vacuum changes? Sounds like something is way off, possibly the distributor is off by 1 tooth and the engine is just barely running.

sakins.02vert

Thanks. I took it to my mechanic, this hot rod guy I met at a car show. He turned it while trying to get the best settings. Problem is he's an hour drive away. I may try a few things my self if I know what to do.

vettes4evr

I'm also pulling 12-14 inch lbs of vacuum on my LT-1. So I pulled the distributor last night and reclocked it. It ran better immediately. I'm also at 12 BTDC @900 rpm (distib vacuum line plugged). But there is an occasional carb pop (back fire).

I've consulted with some others, who say that the valve lash may be too tight. It makes sense,since the engine is a giant vacuum pump and if valves aren't opening all the way, vacuum will be affected. So I'm going to have these adjusted asap and see how it affects vacuum. I also took the AIR pump belt off, which stopped exhaust popping. I was told by another LT-1 forum member to put my hand over the carb while it's running. If it stalls, thats good. Otherwise, its sucking air in through a vacuum leak if it continues to run.