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why would a stock street hemi have only 5in vacuum ? #1533306
11/14/13 02:19 AM
11/14/13 02:19 AM
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ogopogo Offline OP
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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.

Re: why would a stock street hemi have only 5in vacuum ? [Re: ogopogo] #1533307
11/14/13 02:50 AM
11/14/13 02:50 AM
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Mt. Vernon, Ohio
dartman366 Offline
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where is the ignition timing set at and have you tried to increase the initial and re check the vac.?


Light travels faster than the speed of sound,,,this is why some people seem bright untill you hear them speak.
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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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)
Re: why would a stock street hemi have only 5in vacuum ? [Re: ogopogo] #1533309
11/14/13 10:33 AM
11/14/13 10:33 AM
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Taxes & Virus's R-US, NY
Dragula Offline
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Low initial timing...


'70 Cuda,...605 EFI Hemi Street Car (6.20 best pass, 1.33 60ft)
https://www.youtube.com/watch?v=WYw6RA-k5Bk (6.25 at 108.75mph from inside car)
https://www.youtube.com/watch?v=3zQEb9uxFng (6.25 at 108mph from outside car)
https://www.youtube.com/watch?v=JCvfzsC4NgM (9.9)

'66 Barracuda AWB Stretched nose Blown 440 Car in build stage

'71 Duster Drag Car 400 Low Deck 512 best 6.002 at 115.44mph
https://www.youtube.com/watch?v=Znuo3jMUXTk
Re: why would a stock street hemi have only 5in vacuum ? [Re: ogopogo] #1533310
11/14/13 12:43 PM
11/14/13 12:43 PM
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Crizila Offline
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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.


1. VACUUM LEAK. 2. timing retarded. 3. cam in wrong.


Fastest 300
Re: why would a stock street hemi have only 5in vacuum ? [Re: Crizila] #1533311
11/14/13 12:45 PM
11/14/13 12:45 PM
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Give it 18 initial with 34 total, works good on this gas Dean. Then take it for a rip.

Sheldon

Re: why would a stock street hemi have only 5in vacuum ? [Re: RUNCHARGER] #1533312
11/14/13 01:06 PM
11/14/13 01:06 PM
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ogopogo Offline OP
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Timing is set at 18deg initial and 36 total.Spark plugs are always completely black and sooty,dry,but sooty.
No indication of any vac leaks.while engine is running i can pull the hose off of the brake booster and the RPM's climb,it wants more air.
the cam being in wrong would not surprise me just because the the engine builder had exhaust pushrods in the motor that were .210 too long (sloppy workmanship)

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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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.
Re: why would a stock street hemi have only 5in vacuum ? [Re: dartman366] #1533314
11/14/13 02:29 PM
11/14/13 02:29 PM
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Spokane Washington
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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.

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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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

Re: why would a stock street hemi have only 5in vacuum ? [Re: DodgeCharger] #1533316
11/14/13 02:58 PM
11/14/13 02:58 PM
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ogopogo Offline OP
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If its an intake vacuum leak wouldnt the engine be smoking and wouldnt the plugs be oil fouled and wet? i will post a pic or 2 of the plugs later today.
i have not had excessive valve lash at any time to indicate a bad cam but that could have occured before i owned the engine.
Sounds like i will be pulling the intake next.......

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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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.
Re: why would a stock street hemi have only 5in vacuum ? [Re: DodgeCharger] #1533318
11/14/13 05:44 PM
11/14/13 05:44 PM
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Taxes & Virus's R-US, NY
Dragula Offline
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Intake leak is also a strong possiblity with the stock intake pattern, we always glue ours in place first.


'70 Cuda,...605 EFI Hemi Street Car (6.20 best pass, 1.33 60ft)
https://www.youtube.com/watch?v=WYw6RA-k5Bk (6.25 at 108.75mph from inside car)
https://www.youtube.com/watch?v=3zQEb9uxFng (6.25 at 108mph from outside car)
https://www.youtube.com/watch?v=JCvfzsC4NgM (9.9)

'66 Barracuda AWB Stretched nose Blown 440 Car in build stage

'71 Duster Drag Car 400 Low Deck 512 best 6.002 at 115.44mph
https://www.youtube.com/watch?v=Znuo3jMUXTk
Re: why would a stock street hemi have only 5in vacuum ? [Re: ogopogo] #1533319
11/14/13 06:42 PM
11/14/13 06:42 PM
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If none of the plugs are shiny black you don't have oil on them dull black = dry, shiny black = oil on them, been there, done that, especially on Hemiroid motors with no spark plug tube seals 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


Mr.Cab Racing and winning with Mopars since 1964. (Old F--t, Huh)
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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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.

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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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?

Re: why would a stock street hemi have only 5in vacuum ? [Re: WO23Coronet] #1533322
11/14/13 07:29 PM
11/14/13 07:29 PM
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Cincinnati, Ohio
Challenger 1 Offline
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Quote:

Quote:

Low initial timing...




Why would low initial timing affect vacuum if the idle RPM is set proper? Isn't vacuum dependent on the mechanical specs of the cam? What does it matter to vacuum where the plug fires?




OH yea it matters big time.

I have to question the if it really has 18 degrees of timing at 900-1000rpms? Are you sure?

140 psi on the compression test would make want to check the cam also, to see if it's in right, unless it has really low compression pistons in it.

Last edited by Challenger 1; 11/14/13 07:34 PM.
Re: why would a stock street hemi have only 5in vacuum ? [Re: Challenger 1] #1533323
11/14/13 08:08 PM
11/14/13 08:08 PM
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ogopogo Offline OP
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ive pulled the intake and dont see any indication of oil being sucked in,ports are wet from fuel but not oily.
if anyone has a completly stock street hemi they dont mind throwing a vac gauge on i am curious what the reading should be.
i wasnt impressed with 140 psi comp reading until i checked the service manual and it says 110 psi is the acceptable minimum.cam lobes appear fine at a glance. i think i will pull the timing cover next.

Re: why would a stock street hemi have only 5in vacuum ? [Re: ogopogo] #1533324
11/14/13 08:12 PM
11/14/13 08:12 PM
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fredericksburg,va
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Sounds like you have carter carbs yes? If so the low vac. is not keeping the needles in the seats, thus very rich. I would check how big that cam is and where it's degree in at, sounds like a 110• or lower centerline.

Re: why would a stock street hemi have only 5in vacuum ? [Re: cudaman1969] #1533325
11/14/13 08:27 PM
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ogopogo Offline OP
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i was just thinking that exact thought,its super rich because the metering rods arent being sucked down in the carters.

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