I have a 385 sbc with 300deg of adv duration hydraulic roller cam, aluminum heads, single plane int. A friend gave me a 850 demon he couldnt tame. I had it on a healthy 383 with a similar cam but it was mechanical solid lifter and old iron 462 2.02/1.60 heads that had been cleaned up extensively. It took a 5.5 to get it right. This new engine has a 2.5 in it now. It may get a 3.5 if it acts lean on the launch. This weekend I'm going to install an air fuel ratio gauge. I really want one on each side.
So what your saying Holley is that my engine makes a vacuum reading on my gauge of 15 the stock 6.5 power valve is okay for my Holley 600 carburetor or do I step up to a 7.5 power valve?
@@michaelphelps5064 I think you got it backwards. I'm no pro tho. If an engine makes 15 inches of vacuum at an idle, and you slowly open or stab the throttle, it'll go to 14 inches, then 13, then 12"......... So, an 8.5 would open faster (more rich sooner) than a stock 6.5 I think that is what I learnt. Correct me if I'm wrong.
Just a heads up to everyone... The vaccum they list here on selecting the correct power valve just gives you a starting point. The lower # will bring in fuel slower and the bigger # faster. This chart called for a 2.5 power valve on my carb and we had to go to a 8.5. So trust your AFR not this video.....
This is a GREAT POINT. Mine had a 6.5 on both sides. I followed the instructions here base on my manifold vacuum and put in 4.5s. It's VERY lean now and way too slow to receive fuel no matter the combination of jets, squirters, and pump cams. I'm going back to a higher PV. Maybe even higher than 6.5
Yes, very combo-specific. Huge difference, for example, between single plane and dual planes, as the dual plane will pull more vacuum, and also have higher velocity (which makes the carb run a little richer). This is why we need accelerator pumps: when you crack WOT, instantaneous flow velocity in the manifold drops to near zero, and no fuel is pulled.
you have to watch your AFR with RPM (under a load) i have seen a big difference with accelerator pump/ squirter combo... however the PVRC jet (the little jet behind the power valve). made the biggest change for me between lean and rich at my trouble rpm. i ended up with a 4.5 front 2.5 rear with bigger PVRC in the secondary block. but i had about 8.5 mmhg at idle.
TPV Productions you are correct! My car called for a 6.5 based on this video but it was open at idle! It was running extremely rich and had a symptom of a blown power valve. I went to a 10.5 and now it's better.
so I can run my screws (just have 2) all the way in and it does not phase my 350 at all itcontinues to idle so im assuming my power valve is blown and is the culprit of my hesitation/boggin under load? or getting into it half throttle or maybe just before half
That's what he said. IF the car doesn't stumble of stall with idle screws all the way in, the power valve is not working properly. Think about it, if the idle screws aren't allowing fuel in, what is the car running on?It means it is running on the open throttle circuit. When I say that it occurs to me that it is possible if the float level is too high then fuel could be making its' way into the system too early. But a carb expert might disagree.
Very likely. Also Google "transfer slot adjustment". When things are right you can literally adjust your idle speed with your idle mixture screws. Your primary throttle plate must be set correctly and have the correct pv installed for your idle mixture screws to richen or lean out your idle. It's a balance. Also make certain your secondary throttle plates are barely, and I mean barely off their seat. There is an Allen screw to adjust them. To perform these adjustments the carb must be removed, set up and installed. Then fine tuned with the mixture screws. Its a balancing act. Like a ballet between Fuel and Air.
If you have 4 corner idle you will have to shut them all down, be gentle on those metering needles, vacume is holding the power valve closed, unless that diaphragm is blown.
Surprisingly informative even 15 years later...
I have a 385 sbc with 300deg of adv duration hydraulic roller cam, aluminum heads, single plane int. A friend gave me a 850 demon he couldnt tame. I had it on a healthy 383 with a similar cam but it was mechanical solid lifter and old iron 462 2.02/1.60 heads that had been cleaned up extensively. It took a 5.5 to get it right. This new engine has a 2.5 in it now. It may get a 3.5 if it acts lean on the launch. This weekend I'm going to install an air fuel ratio gauge. I really want one on each side.
So what your saying Holley is that my engine makes a vacuum reading on my gauge of 15 the stock 6.5 power valve is okay for my Holley 600 carburetor or do I step up to a 7.5 power valve?
Does it bog down when you stab the throttle? If so it could be a tad rich due to the pv opening a bit too soon. If not, leave it.
@@michaelphelps5064 I think you got it backwards. I'm no pro tho.
If an engine makes 15 inches of vacuum at an idle, and you slowly open or stab the throttle, it'll go to 14 inches, then 13, then 12"......... So, an 8.5 would open faster (more rich sooner) than a stock 6.5
I think that is what I learnt.
Correct me if I'm wrong.
Just a heads up to everyone... The vaccum they list here on selecting the correct power valve just gives you a starting point. The lower # will bring in fuel slower and the bigger # faster. This chart called for a 2.5 power valve on my carb and we had to go to a 8.5. So trust your AFR not this video.....
This is a GREAT POINT. Mine had a 6.5 on both sides. I followed the instructions here base on my manifold vacuum and put in 4.5s. It's VERY lean now and way too slow to receive fuel no matter the combination of jets, squirters, and pump cams. I'm going back to a higher PV. Maybe even higher than 6.5
Yes, very combo-specific. Huge difference, for example, between single plane and dual planes, as the dual plane will pull more vacuum, and also have higher velocity (which makes the carb run a little richer). This is why we need accelerator pumps: when you crack WOT, instantaneous flow velocity in the manifold drops to near zero, and no fuel is pulled.
you have to watch your AFR with RPM (under a load) i have seen a big difference with accelerator pump/ squirter combo... however the PVRC jet (the little jet behind the power valve). made the biggest change for me between lean and rich at my trouble rpm. i ended up with a 4.5 front 2.5 rear with bigger PVRC in the secondary block. but i had about 8.5 mmhg at idle.
i have not had to mess with the air bleeds on top yet i think i would feel better doing that on the dyno first.
TPV Productions you are correct! My car called for a 6.5 based on this video but it was open at idle! It was running extremely rich and had a symptom of a blown power valve. I went to a 10.5 and now it's better.
What about 4 corner idle screws? do i need to close them too to check if the power valve is blown?
Yes,, awl the Woolworths
so I can run my screws (just have 2) all the way in and it does not phase my 350 at all itcontinues to idle so im assuming my power valve is blown and is the culprit of my hesitation/boggin under load? or getting into it half throttle or maybe just before half
That's what he said. IF the car doesn't stumble of stall with idle screws all the way in, the power valve is not working properly. Think about it, if the idle screws aren't allowing fuel in, what is the car running on?It means it is running on the open throttle circuit. When I say that it occurs to me that it is possible if the float level is too high then fuel could be making its' way into the system too early. But a carb expert might disagree.
Very likely. Also Google "transfer slot adjustment". When things are right you can literally adjust your idle speed with your idle mixture screws. Your primary throttle plate must be set correctly and have the correct pv installed for your idle mixture screws to richen or lean out your idle. It's a balance. Also make certain your secondary throttle plates are barely, and I mean barely off their seat. There is an Allen screw to adjust them. To perform these adjustments the carb must be removed, set up and installed. Then fine tuned with the mixture screws. Its a balancing act. Like a ballet between Fuel and Air.
1:42 If the formula results in an even number, go higher not lower. Safer to be a little rich than lean.
Do you turn in all of the idle screws to check the power valve? or just the one shown in the video? thanks
Are we kicked out of awl the Woolworths or just this one?
If you have 4 corner idle you will have to shut them all down, be gentle on those metering needles, vacume is holding the power valve closed, unless that diaphragm is blown.
@@DANTHETUBEMAN Already have it sorted. Thank you for the reply though. Appreciate you bro.
yes you have gave some Mechanics A great refreshment of how calibraiton should be
I have a 500 cfm 4412 on my 390 going to need to do this test good vid .
What power valve should i use on a Amc 258? Do not own a vaccum gauge but heard that the vacuum reading is between 15” and 20”
what is the number of the stock power valve?---im running 18 in of vacuum so im wondering which one i need. any help ??
Stock power valve is usually 6.5. Your 18 would suggest an 8.5 would be the best place to start on yours.
8.5 should be right on
18 in gear or idle?
@@ghtrcp7554 mine is 22 at idle
Yes at 18 vacume you desperately need a BIGGER CAMSHAFT!!! it will never haul ass with that Much vacume , you engine literally sucks to much
Great vid...
That's what he said, right? I would replace PV.