Power valve selection 670 Holley Street Avenger

Theron

Theron

Member
The literature says that the 670 comes with a 6.5 Hg power valve. My engine pulls 7.5 in Hg at 900 rpm. Is the stock power valve correct for my engine or should I order a different one right off the bat.

1969 Chevy C10, sm465 manual, 383 stroker, Dart Pro comp 215cc heads, edelbrock 7501 air gap intake, comp cams XE284h-10 12-250-3, 450hp, 450 lb/ft.
 
why would you start ordering new parts,
to replace the original components before you have even seen how the parts work,
in your particular application?
If your running 7.5" of plenum vacuum at idle Id suspect a 3.5- to-4.5 power valve in this application, or possibility a 5.5 power valve would be closer to the ideal power valve than the 6.5 but ID sure test it before swapping parts just because I'm a firm believer in not assuming a darn thing, about how an engine responds to a carb selection, and dealing in tested and verifiable facts rather than guessing

years ago I purchased two of these assortment packs when they cost about 1/2 the current price , Ive tried hard to keep 4 jets in each size in inventory as I use those, 72 jets in assorted sizes for $52 is still a good deal , and it gets better if you buy the pack or two of them, when summit posts a discount code
http://www.summitracing.com/parts/hly-36-181
hly-36-181.jpg


IF you can read spark plugs , USE A TIMING LIGHT, and use an INFRARED TEMP GUN AND VACUUM GAUGE
http://www.harborfreight.com/cpi/ctaf/d ... mber=93547
A MULTI METER AND TIMING LIGHT WILL BE USEFUL
image_12926.jpg

http://www.harborfreight.com/5-in-1-dig ... 98674.html

http://www.summitracing.com/parts/MSD-8991/
timinglite6.jpg



vgauge.gif

TUNING A HOLLEY IS DAMN SIMPLE
chevfireor.gif

infrared thermometers are a very useful tool to track down issues with tuning, or mal functioning sensors
T504-4254_product.jpg

viewtopic.php?f=50&t=138&p=168&hilit=infrared#p168
http://garage.grumpysperformance.com/index.php?threads/holley-carb-power-valves.1639/

http://garage.grumpysperformance.com/index.php?threads/carb-tuning-info-and-links.109/

http://garage.grumpysperformance.com/index.php?threads/holley-accelerator-pumps-cams.1790/

http://garage.grumpysperformance.com/index.php?threads/holley-annular-vs-down-leg-boosters.5229/

http://garage.grumpysperformance.com/index.php?threads/differences-between-the-holley-4150-and-4160-series-carbs.10736/

http://garage.grumpysperformance.com/index.php?threads/holley-carb-tune-info.264/
 
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I live in the middle of nowhere. Our local parts suppliers carry almost no performance parts. I am also one of those people who like to have the things on hand that I might need so that I don't have to waste time ordering parts every other day. I have the jet assortment that you listed above. If I could find an assortment of power valves, shooters, etc... I would buy it. I always test and try things before I make changes, but I like to know what the expected combination should be... whether or not it ends up being correct. If the 'math' says that a 4.5 or a 5.5 PV is the best likely combo for the engine, I will have one on hand in case I need to switch it out. Now, back to reading the threads that you posted above.
 
Ok. New 670 is on. Idles with much less throttle plate opening. Doesn't have as much of the same dieseling issue.
Set the floats. Set the 4 point idle to maximum vacuum.
Problem: Hesitates at part throttle while driving.
Next: Going to check spark plugs to determine lean/rich condition.
Question: What affect would reducing the power valve size from 6.5 to 4.5 have?
 
it will tend to help noticeably to reduce the hesitation, by adding additional fuel flow during the transition from idle too WOT
http://garage.grumpysperformance.com/index.php?threads/holley-carb-power-valves.1639/
or put a different way, swapping will change the transitional fuel/air ratio for better or worse and youll notice the difference, giving you a feeling of what direction changing the power valve number has effected your engine response

http://www.onallcylinders.com/2013/03/07/how-to-tune-the-power-valves-on-a-holley-carburetor/
 
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Dropping to a 5.5 PV helped a lot with dieseling, but I am still having to come up 10 jets from stock. I'm at 75 right now and I think that the plugs look good.
-I STILL have a bit of a surge when driving.
-Changing the idle mixture screws really makes no noticeable difference on the idle or vacuum. I can bottom one out and the truck does not stall. From what I have read, that means that I am not on the idle circuit??
Idle is currently a lumpy 750-800 rpm.
(I stared on your basic carb tuning 831 thread and I am at the "get the jets correct" part of it. I set the base idle, set the float levels, set the power valve to "in the ballpark" -2 from idle vacuum, I think that the jets are in range, now I am at "tweak your idle mixture screws" and I have issues because nothing is happening).
 
YEAH! I KNOW YOUR 100% SURE ITS ALL CORRECT.
CHECK IT AGAIN CAREFULLY
check carefully for a vacuum leak
http://garage.grumpysperformance.com/index.php?threads/locating-vacume-leaks.882/#post-45944
verify your float levels, and fuel pressure
verify TDC on the damper & timing tab
VERIFY
the ignition advance curve and firing order
http://garage.grumpysperformance.com/index.php?threads/verifying-your-real-advance-curve.4683/

HAVE YOU DONE A COMPRESSION TEST ON ALL CYLINDERS LATELY?
http://garage.grumpysperformance.com/index.php?threads/leakdown-compression-test.881/#post-56489
HOW DOES THE VACUUM GAUGE WORK?
http://garage.grumpysperformance.com/index.php?threads/leakdown-compression-test.881/#post-56489

RE-ADJUST THE VALVES
http://garage.grumpysperformance.com/index.php?threads/adjusting-valves.196/
I really wish I was on location, there to help
GET A FUEL PRESSURE GAUGE AND MEASURE DON,T GUESS
how can you possibly set up your fuel system unless you know the pressure and flow rates required and what currently exist's
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READ LINKS

http://garage.grumpysperformance.com/index.php?threads/setting-up-your-fuel-system.211/

http://garage.grumpysperformance.com/index.php?threads/fuel-pressure-regulators.635/

http://garage.grumpysperformance.com/index.php?threads/how-big-a-fuel-pump-do-you-need.1939/

http://garage.grumpysperformance.co...ss-fuel-pressure-regulators.12776/#post-65998
 
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I will check for a leak and check the transfer slot again.

Not much chance for a leak... No vacuum accessories.
 
There is not much idle vacuum present.
Camshaft X284 is not that Hot.
Something is Amiss..
I would expect 11-12 inches at 650-900 rpm idle speed from 383 ci & Dual plane intake RPM air gap.
Check for vacuum leaks as Grumpy said.
Verify timing and advance rate with a decent timing light.
Jetting is getting FAT.....
I am using 70 primary jets , 69 secondary jets, 6.5 power valve, 770 cfm Street Avenger on my 1965 Olds 425 ci engine.
 
Also verify Fuel pressure.
I think its a must to use a Fuel Pressure regulator with any Holley Carb.
At least the old school Blue Pump fuel pressure regulator.
 
Fuel pressure regulator is installed. Pressure is 6.5.
This engine was tuned on the dyno with the 770 SA at WOT. 73 jets on the 770. No issues, but they didn't set it to idle. It had poor drivability once installed in the truck. This prompted my troubleshooting and carb tuning. I am assuming that the advance curve and timing are set correctly from the dyno since that is what I paid them to do.

They backed off the idle to 33 degrees to stave off detonation and dieseling from the higher-than-average compression (10.2/1... I assume they were referring to static compression) and the 91 octane requirement.

The vacuum rating of 7.5 is what Comp told me to expect from this grind. I specified that I did not require a lot of idle vacuum because I have no vacuum accessories.

I will check again for vacuum leaks in the morning and remove the carb and check for excessive transfer slot exposure.
 
Grumpy and Me don't like Comp Cams.
He likes Crane Cams & Crower.
I like Isky & Crower.

Not an ideal cam grind my 2 cents.

You answered your own question ....
Chassis Dyno operator peformed Flash WOT Power numbers.
A Good Chassis Dyno operator will make 10-200 part throttle pulls from idle to 5,000 RPM. Finesse Fine Tune for street driveability.
Then 1-2 Hero pulls Top End to Redline.
Only Time you make WOT AND TUNE THERE ONLY IS ALL OUT DRAG RACE.
10-6 SECOND ET RACE CAR.
 
I did not "answer my own question". Having the engine broken in on the dyno and tuned on a WOT run does not mean that the engine cannot then be tuned on the street.

I agree that a chassis dyno tune would be more effective in the manner that you state, but I have no way of getting a poorly running vehicle 300+ miles to the nearest reputable chassis dyno.
 
4.5 power valve works well with the secondaries open enough that it idles on the actual idle circuit.
The dieseling is nearly eliminated. I am at the most fine tuning that I can do without an A/F reader.
 
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