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Re: why would a stock street hemi have only 5in vacuum ? [Re: ogopogo] #1533326
11/14/13 08:56 PM
11/14/13 08:56 PM
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Niles , Ohio
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therocks Offline
oh wait.but hey.lets see.oh yeah.
therocks  Offline
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With pushrods being almost 1/4 inch too long the valves might be bent a bit.It dosent take much to have them not seating completley.That compression is low also.Thats a lot of extra lift.Rocky


Chrysler Firepower
Re: why would a stock street hemi have only 5in vacuum ? [Re: ogopogo] #1533327
11/14/13 11:26 PM
11/14/13 11:26 PM
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N.E.Ohio
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pacifica Offline
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Quote:

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.




I just did a compression check beginning of October on a stock hemi, standard bore, resto cam, ect.

It reads 160# - 175# all 8 cylinders.


Last edited by pacifica; 11/14/13 11:29 PM.
Re: why would a stock street hemi have only 5in vacuum ? [Re: pacifica] #1533328
11/15/13 12:22 AM
11/15/13 12:22 AM
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Spokane Washington
ScottSmith_Harms Offline
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Quote:

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




I agree, just be sure to use an INCH LB wrench, I believe the spec is only 12 inch lbs? It isn't much that's for sure! You don't want to break off a chunk of cylinder head by over torqueing the intake bolts.

I also agree on the low vacuum failing to pull down the metering rods, no vacuum will = pig rich with those carbs.

Re: why would a stock street hemi have only 5in vacuum ? [Re: ScottSmith_Harms] #1533329
11/15/13 12:54 AM
11/15/13 12:54 AM
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Bend,OR USA
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Quote:

Quote:

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




I agree, just be sure to use an INCH LB wrench, I believe the spec is only 12 inch lbs? It isn't much that's for sure! You don't want to break off a chunk of cylinder head by over torqueing the intake bolts.

I also agree on the low vacuum failing to pull down the metering rods, no vacuum will = pig rich with those carbs.


The FSM calls for 72 inch lbs(6 ft. lbs) on the center four intake bolts on both sides and 48 inch lbs(4 ft. lbs.) on the rest of the outer bolts and studs


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: Cab_Burge] #1533330
11/15/13 01:23 AM
11/15/13 01:23 AM
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Spokane Washington
ScottSmith_Harms Offline
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Thanks Burge, I couldn't remember for sure, I just recalled it wasn't much!

Re: why would a stock street hemi have only 5in vacuum ? [Re: cudaman1969] #1533331
11/15/13 02:13 AM
11/15/13 02:13 AM
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A Red State
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Quote:

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.




I just went through changing the springs on the metering rods on the edelbrock's/afb's (750's) on mine.
It took changing to the blue springs (weakest) on mine to get them to stay closed at idle.

It will now idles fine in gear at 700 rpm and it quit gas fouling the plugs. Installing an MSD-6 AL2 helped alot with the idle too.


Kayse can't keep up at all now. lol
Re: why would a stock street hemi have only 5in vacuum ? [Re: SNK-EYZ] #1533332
11/15/13 12:51 PM
11/15/13 12:51 PM
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Posts: 9,910
Eighty Four, PA
B G Racing Offline
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Don't over think the situation,start with the obivious things that can cause the problem.
a.check all carb areas for vacume leaks and mixture settings.
b.check intake for the same(tighten by hand,side to side and repeat till the bolts refuse to turn) use a small 1/4 ratch and socket.
c.Check all electrical for voltage and strong spark and firing order.
d.Check distributer for solid timing results.Set timing at 35* at 3000 RPM and no fluctuation at lower RPMs.
e.Check valve settings
f.If everything checks out,look to cam timing.
We have seen bad fuel cause issues also.Cam design,cam timing,distributer timing,valve timing and compression can all effect engine vacume.If you can idle the engine at low RPMs then it is usually not a vacume leak unless the intake is pulling air from the crankcase and then you should see oil foul and smoke.If it shuts off at low idle the leak is above the manifold(carbs).Occasionally if you have a leak and adjust the blades open too far and uncover the idle slots the engine will siphon from the main jet wells and cause an overrich condition.

Re: why would a stock street hemi have only 5in vacuum ? [Re: B G Racing] #1533333
11/16/13 10:20 PM
11/16/13 10:20 PM
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BC Canada
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ogopogo Offline OP
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so i spent the afternoon measuring lobe lift and duration,and checked degreeing of the cam and have determined I have a comp 292 in here,it appears to be out 2 degrees as well (timing events are 2 deg late) ,,specs:

http://www.compcams.com/Company/CC/cam-specs/Details.aspx?csid=754&sb=0

Last edited by ogopogo; 11/16/13 10:40 PM.
Re: why would a stock street hemi have only 5in vacuum ? [Re: ogopogo] #1533334
11/17/13 01:22 AM
11/17/13 01:22 AM
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Chilliwack B.C. Canada
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RUNCHARGER Offline
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Decent cam and 2 degrees late shouldn't be terrible. You're welcome to try my carbs if you want, they work terrific.

Sheldon

Re: why would a stock street hemi have only 5in vacuum ? [Re: RUNCHARGER] #1533335
11/17/13 04:49 AM
11/17/13 04:49 AM
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BC Canada
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ogopogo Offline OP
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thanks Sheldon,I actually have 3,yes 3, pairs of restored hemi carbs right now and I have tried all three on the car with no difference.I think im going to install a smaller cam (comp 278) and im going to carefully check the intake manifold fitment tomorrow.i have to assume the intake must have been leaking to cause the low vacuum.

im thinking the comp 292 is too big for a 100% completely stock car with auto trans,stock converter and 3:23 gearing

Re: why would a stock street hemi have only 5in vacuum ? [Re: ogopogo] #1533336
11/17/13 01:48 PM
11/17/13 01:48 PM
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Chilliwack B.C. Canada
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It is a shiver big but should come on strong around 4000. Obviously you checked for cracks in the intake and the old gaskets showed nice imprints from the castings, puzzling. I wonder if the head studs into the ports are leaking, but I've never seen them create this problem.

Sheldon

Re: why would a stock street hemi have only 5in vacuum ? [Re: RUNCHARGER] #1533337
11/17/13 02:26 PM
11/17/13 02:26 PM
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BC Canada
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ogopogo Offline OP
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Intake is perfect I even pressure tested the exhaust crossover.head studs dont appear to have sealer on them and I plan to remove them one by one today and seal them up.Block may have been decked so I'm going to check intake fitment as well.
I dont think this trailer queen will ever see over 4000 rpm anyway unless the next owner actually drives it.I can use the comp 292 in the engine Im building for my challenger (4 speed car w 4:10's)

Re: why would a stock street hemi have only 5in vacuum ? [Re: ogopogo] #1533338
11/17/13 02:37 PM
11/17/13 02:37 PM
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Bend,OR USA
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Quote:

so i spent the afternoon measuring lobe lift and duration,and checked degreeing of the cam and have determined I have a comp 292 in here,it appears to be out 2 degrees as well (timing events are 2 deg late) ,,specs:

http://www.compcams.com/Company/CC/cam-specs/Details.aspx?csid=754&sb=0


When you say late cam timing are you referring to opening and closing or te lobe seperation angle? If the cam has the intake lobe installed at max lift at 110 degrees after top dead center move it so it is at 104 to 106 before top dead center In other words if the cam is opening the intake lifters two degree later(closer to top dead center) than on the cam card move it forward (away from top dead center) to open sooner 6 to 8 degrees to help it have more bottome end I've never had any type of Mopar V8 motor like having the cam timing late, on the dyno or at the track Having the cam retarded will kill the bottom end dramatically Try moving it before replacing it That grind is not that big, trust me on that Hemiroid motor need an love more air to make more power


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: RUNCHARGER] #1533339
11/17/13 02:46 PM
11/17/13 02:46 PM
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Downtown Roebuck Ont
Twostick Offline
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What does a "stock" factory street hemi cam spec at for duration and overlap and what does a "stock" Hemi have for idle vacuum? If the Comp 292 is anything close to the MP 292 cam, spec wise, I wouldn't expect idle vacuum to be much higher than you are at 426 cubes.

Probably an apples to oranges comparison but my 493 wedge has an MP509 that has 76 deg of overlap which is the same as the MP 292 Hemi cam. It idles at 7-8" at 1100 RPM.

As for 15% leakdown, my builder considers anything over 10% worn out on a competition build.

Kevin

Re: why would a stock street hemi have only 5in vacuum ? [Re: Twostick] #1533340
11/17/13 03:16 PM
11/17/13 03:16 PM
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Atlanta Indiana
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Dave Watt Offline
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Everything sounds good that you've checked.
I'm wondering if the carb base gaskets are causing a leak which in turn draws more fuel into the engine?

Re: why would a stock street hemi have only 5in vacuum ? [Re: Dave Watt] #1533341
11/17/13 04:21 PM
11/17/13 04:21 PM
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Eighty Four, PA
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The Comp 292 cam you show isn't much different than the Mopar Hemi 292,510/512 cam used in the 4 speed cars.They usually carry 12 to 15 inches of vacume.I have used the Comp Cam in many street applications and have all carried good vacume to operate vacume assist brakes.
You have an issue that needs to found and corrected.Did you remove the pan from the bottom of the intake and check for leaks at the core plug or for any cracks?Did you check for timing fluctuation?

Re: why would a stock street hemi have only 5in vacuum ? [Re: B G Racing] #1533342
11/17/13 04:36 PM
11/17/13 04:36 PM
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BC Canada
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ogopogo Offline OP
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Cab,
yes by late timing I mean the intake is opening at 35-36 btdc when it should be 38 btdc.
I have checked the plug on the bottom of the intake.Timing was a little erratic with the oem dual point but i replaced it and timing is good now.
How much of a vaccum loss would I see if the brake booster was bad?
what do you guys recommend to seal the head stud threads?

Re: why would a stock street hemi have only 5in vacuum ? [Re: ogopogo] #1533343
11/17/13 04:42 PM
11/17/13 04:42 PM
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Mt. Vernon, Ohio
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Quote:

Cab,
yes by late timing I mean the intake is opening at 35-36 btdc when it should be 38 btdc.
I have checked the plug on the bottom of the intake.Timing was a little erratic with the oem dual point but i replaced it and timing is good now.
How much of a vaccum loss would I see if the brake booster was bad?
what do you guys recommend to seal the head stud threads?


pull the hose to the booster and plug it. that will tell if it is .


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] #1533344
11/17/13 05:11 PM
11/17/13 05:11 PM
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Monrovia, So-Cal, USA
racerhog Offline
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I would move it one tooth and see how it reads....


Bob(Cowboy)Hogan
Monrovia So-Cal
Re: why would a stock street hemi have only 5in vacuum ? [Re: racerhog] #1533345
11/17/13 07:07 PM
11/17/13 07:07 PM
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Milwaukee WI
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TRENDZ Offline
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You say it's running rich, and you said the rpms climb with the booster vacuum line open.
It's to rich. the engine wont run well if its blackening the plugs. Find somone that knows how to tune these carbs ON THE CAR.
Everything you've stated tells that the engine wants more air.
Get the Air/Fuel ratio where it needs to be, change the engine oil, and maybe the leak down numbers will also improve. You are chasing a tuning problem, not a mechanical issue.


"use it 'till it breaks, replace as needed"
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