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Re: why would a stock street hemi have only 5in vacuum ?
[Re: ogopogo]
#1533308
11/14/13 03:53 AM
11/14/13 03:53 AM
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Joined: Aug 2003
Posts: 43,335
Bend,OR USA
Cab_Burge
I Win
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I Win
Joined: Aug 2003
Posts: 43,335
Bend,OR USA
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Quote:
I have been fighting for a while now with a poor running stock rebuilt 426 hemi i have.it runs pig rich and has no power.it was rebuilt in 2005-06 to stock specs and the car has basicly sat most of the time since.i have switched out carbs,every single component of the ignition system as well as corrected an incorrect timing mark and replaced the exhaust pushrods that were too long,replaced the ebay rockers with OEM chryslers etc etc.I was working on it tonight and discovered it is only making 5-6 in of vacuum at idle which seems way too low.
Im starting to wonder if it could have an incorrectly degreed cam,an RB cam,or the cam has gone flat.
The engine leak tested perfect(under 15%) and compression is 140psi across the board.
Check the valve lash, if it has excessive lash on one or two lobes maybe the cam is going flat. More than likely whoever assemble the motor did not degree the cam, they stuck it in and aligned the dots  
Mr.Cab Racing and winning with Mopars since 1964. (Old F--t, Huh)
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Re: why would a stock street hemi have only 5in vacuum ?
[Re: ogopogo]
#1533313
11/14/13 01:57 PM
11/14/13 01:57 PM
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Joined: Jan 2004
Posts: 13,247
Mt. Vernon, Ohio
dartman366
I Live Here
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I Live Here
Joined: Jan 2004
Posts: 13,247
Mt. Vernon, Ohio
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I think that I would verify the cam setting first,then if that don't do the trick then I would go to the carb next and make sure it is in top notch shape with that said make sure the carb power valve is not blown if one is used in that carb also the it might be the idle air bleeds are not right for that motor, where are the idle air screws set at and do they make a difference when you screw them in or out there are a lot of little things that can cause it to not run right, is the motor rich at just idle or all the way thru the rpm range,i worked on a buddys 440 roadrunner for days, and he had the same problem but the car would die when you put it in gear only to find out that he had a cam with a lot of duration and was trying to use it with a stock torque converter 
Light travels faster than the speed of sound,,,this is why some people seem bright untill you hear them speak.
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Re: why would a stock street hemi have only 5in vacuum ?
[Re: ScottSmith_Harms]
#1533315
11/14/13 02:42 PM
11/14/13 02:42 PM
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Joined: Dec 2004
Posts: 2,703
Mohnton, Pa
DodgeCharger
master
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master
Joined: Dec 2004
Posts: 2,703
Mohnton, Pa
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Quote:
Trust me, the carbs are fine, I recently test ran them. That's the very last thing Id mess with on your setup. Just be sure there are no unplugged vacuum ports, carb gasket leaks, or any other possible installation mistakes. BTW its VERY common for Hemi intake gaskets to leak, usually due to some spec being wrong during a rebuild or just a sloppy installation. 
Maybe an intake leak and the black plugs are from pulling oil from the valve galley?
If the heads where trued up to make them flat it changes the angles one the surfaces where the intake manifold mates.
The intake can bottom out on the ends and not be sealed at the intake ports
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Re: why would a stock street hemi have only 5in vacuum ?
[Re: ScottSmith_Harms]
#1533317
11/14/13 03:03 PM
11/14/13 03:03 PM
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Joined: Jan 2004
Posts: 13,247
Mt. Vernon, Ohio
dartman366
I Live Here
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I Live Here
Joined: Jan 2004
Posts: 13,247
Mt. Vernon, Ohio
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Quote:
Trust me, the carbs are fine, I recently test ran them. That's the very last thing Id mess with on your setup. Just be sure there are no unplugged vacuum ports, carb gasket leaks, or any other possible installation mistakes. BTW its VERY common for Hemi intake gaskets to leak, usually due to some spec being wrong during a rebuild or just a sloppy installation.
gotcha', not knowing the history of them was my reasoning for my comments,,,now I know and can rule that out, at least we are eliminating possibilitys.
Light travels faster than the speed of sound,,,this is why some people seem bright untill you hear them speak.
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Re: why would a stock street hemi have only 5in vacuum ?
[Re: ogopogo]
#1533320
11/14/13 07:22 PM
11/14/13 07:22 PM
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Joined: Jan 2003
Posts: 15,439
Val-haul-ass... eventually
BradH
Taking time off to work on my car
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Taking time off to work on my car
Joined: Jan 2003
Posts: 15,439
Val-haul-ass... eventually
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Quote:
The engine leak tested perfect(under 15%) and compression is 140psi across the board.
Neither of those #s look good to me. IMO, a good leak test for a reasonbly fresh engine would have been 5%, and unless you've got some mongo-huge cam in their killing all the cranking pressure, 140 psi is what I'd expect out of a stock 383.
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Re: why would a stock street hemi have only 5in vacuum ?
[Re: Dragula]
#1533321
11/14/13 07:27 PM
11/14/13 07:27 PM
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Joined: Jan 2008
Posts: 4,258
Canada
WO23Coronet
master
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master
Joined: Jan 2008
Posts: 4,258
Canada
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Quote:
Low initial timing...
Why would low initial timing affect vacum if the idle RPM is set proper? Isn't vacum dependent on the mechanical specs of the cam? What does it matter to vacum where the plug fires?
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I do retighten the intake manifold bolts many times over( I wait twenty to 30 minutes between each time) and over until they don't take any more movement with a good inch lb. torque wrench, same thing after running the motor to warm it up, retighten those bolts many times until they stop tightening 
