Carb Vacuum Pressure

[censley]

Hey fellas,

So my engine and carb have about 3000k miles on it. Edelbrock 1411 performer carb and sbc 350 with a few performance upgrades when built. Supposed to produce 350 hp/380 torque.

Rebuilt 700r4 which I think the tv cable needs adjusted cause she ain't that quick!

Anyways, I was adjusting the ims on the carb with vacuum gauge attached. The max in hcg I can get is 10. That seems too low... Shouldn't I get at least 15 hcg? What's the issue? When water was on one of the intake bolts I noticed a few bubbles, nothing huge. That can be right...

1987 Olds 442.

Thanks!

 

[DRIVEN]

I would expect 15-18inHg depending on the cam. What's your base timing set at?

 

[pontiacgp]

Could any of your valves be adjusted too tight. Just a few of them too tight will give you low vacuum.

 

[censley]

I just read over my engine builders specs they did on the break in. Says that the timing without vacuum advance hooked up is at 10 degrees. With it hooked up, around 27 degrees. Could this be robbing me of hp and torque?

 

[DRIVEN]

10 degrees initial timing is a good place to start. Have you verified it? The total of 27 degrees seems a bit low but since I don't know anything about your combination I can't say that it isn't exactly what your engine likes.

 

[censley]

Around 1990 sbc 350 (vortec heads) rebuilt for performance at 355hp

Carb: edelbrock 1411 (750 cfm)
Jetting and rods are 73 x 42
Main jets are .113

My engine specs...
Bore: 4.030
Stroke: 3.48

Cam specs...
Int. Lift: 480
Exh. Lift: 480
Duration @ .50: 230-230
Lobe Seperation: 109

Head specs...
Int. Valve Size: 194
Exh. Valve Size: 1.50
Chamber size: 64cc

Spark plugs: R45TS

Engine builders break in sheet says that the timing should be set around 27 degrees with vacuum advance hooked up

 

[DRIVEN]

Looks like a Comp Magnum 280?

If so, 10-12inHg isn't too bad. The notes on that cam call for deeper gearing and more aggressive stall speed (probably 2200-2500). If those don't match that may explain the lack of power. Pontiacgp made a good point about valve adjustment too. Is the needle on the vacuum gauge steady or does it shake while you're testing?

 

[censley]

Cam is Speed Pro

Yes, had the vacuum pressure needle shaking when it read 10 hcg. Had my buddy retime the base idle at 15... I'll check vacuum again tomorrow.

 

[DRIVEN]

Shaking needle indicates valve issue. Possibly just need readjusting but could be a burnt valve or cam going flat.

 

[gbondo57]

Your edelbrock has 2 vacuum ports. The one on the passenger side should have zero vacuum at idle. That is the one for the distributor. The other is manifold vacuum. By this tread, the spark hose is on the wrong one. The spark vacuum port picks up vacuum on throttle up. And yes, a shaky needle indicates a burnt/bent/leaking valve. Oh yeah, that cable on the 200/700r4, needs an edelbrock specific "throttle/trans cable" bracket. We found this out from the trans shop. That cable increases pressure in the trans. My sons Elco seemed to slip till we corrected it. The correct bracket (eddy) mounts on both rear carb studs/blocking the brake booster port. (Engineered by a NONUSER) We cut the passenger side leg off the bracket, and pinned the inboard stud hole on the throttle side. Holley carbs too. Jegs defines them as such.