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New Holley 80577 950HP Supercharger carb question

General engine tech -- Drag Racing to Circle Track

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ChevelleNut
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New Holley 80577 950HP Supercharger carb question

Post by ChevelleNut »

As the title reads, I've got a brand new 950HP Supercharger carburetor. I know it has different power valves than a standard 950HP, but what else is different? What would have to be changed to convert it to a standard, non boost referenced carburetor?
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thedynoguy
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Re: New Holley 80577 950HP Supercharger carb question

Post by thedynoguy »

to simply change back to a non boost referenced mode, plug the external boost fittings and open a vacuum port from the power valve cavity through the baseplate so it sees full manifold vacuum.
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Re: New Holley 80577 950HP Supercharger carb question

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thedynoguy wrote: Fri Apr 30, 2021 5:39 am to simply change back to a non boost referenced mode, plug the external boost fittings and open a vacuum port from the power valve cavity through the baseplate so it sees full manifold vacuum.
This ^^ or connect a hose from the external PV nipple in the main body to the nipple in the base under the primary float bowl. The nipple below the bowl is hot manifold vacuum below the throttle. The PV will function as in a normal carb when the two nipples are connected.
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Re: New Holley 80577 950HP Supercharger carb question

Post by F-BIRD'88 »

The PVCR size may be different +/- relative to the PVCR size used in a N/A carb application.. Main emulsion jets sizes and main AB's sizes may be different..
Depending if the blower carb is intended for 2x4 use on a blower or as a single carb the idle circuit fuel metering sizes might be different.
You'd have to strip it down and measure stuff on this carb to know how its set up.
Draw thru or blow thru type will be set up differently.
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Re: New Holley 80577 950HP Supercharger carb question

Post by MELWAY »

Tuner wrote: Fri Apr 30, 2021 4:10 pm
thedynoguy wrote: Fri Apr 30, 2021 5:39 am to simply change back to a non boost referenced mode, plug the external boost fittings and open a vacuum port from the power valve cavity through the baseplate so it sees full manifold vacuum.
This ^^ or connect a hose from the external PV nipple in the main body to the nipple in the base under the primary float bowl. The nipple below the bowl is hot manifold vacuum below the throttle. The PV will function as in a normal carb when the two nipples are connected.
Tuner
When converting a single carb to use on 2x4 blower engine
Do you reduce the IFR due to 8 holes feeding engine over 4
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Re: New Holley 80577 950HP Supercharger carb question

Post by Tuner »

MELWAY wrote: Mon May 03, 2021 6:06 pm
Tuner wrote: Fri Apr 30, 2021 4:10 pm
thedynoguy wrote: Fri Apr 30, 2021 5:39 am to simply change back to a non boost referenced mode, plug the external boost fittings and open a vacuum port from the power valve cavity through the baseplate so it sees full manifold vacuum.
This ^^ or connect a hose from the external PV nipple in the main body to the nipple in the base under the primary float bowl. The nipple below the bowl is hot manifold vacuum below the throttle. The PV will function as in a normal carb when the two nipples are connected.
Tuner
When converting a single carb to use on 2x4 blower engine
Do you reduce the IFR due to 8 holes feeding engine over 4
Usually a 2x4, blower or NA, needs a smaller IJ than a single carb. It also seems a smaller IJ is less likely to have "blower roll" idle issues. Smaller IJ with correspondingly smaller IAB so the T-slot is rich enough, and perhaps a T-slot jet to keep it from going too rich if the valve timing is such that there is a large increase of vacuum from curb idle RPM to cruise RPM, is usually the best solution to have good drivability manners with a Roots blower, and for that matter with a 2X4 tunnel ram too. Idle jet in the .026" to .031" range is usually the sweet spot. I wish I could predict exactly, but no two engines are the same and changing mufflers or tail pipes on the same engine probably will need a revisit through tuning the idle/T-slot drivability.
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Re: New Holley 80577 950HP Supercharger carb question

Post by MELWAY »

Tuner wrote: Mon May 03, 2021 7:05 pm
MELWAY wrote: Mon May 03, 2021 6:06 pm
Tuner wrote: Fri Apr 30, 2021 4:10 pm

This ^^ or connect a hose from the external PV nipple in the main body to the nipple in the base under the primary float bowl. The nipple below the bowl is hot manifold vacuum below the throttle. The PV will function as in a normal carb when the two nipples are connected.
Tuner
When converting a single carb to use on 2x4 blower engine
Do you reduce the IFR due to 8 holes feeding engine over 4
Usually a 2x4, blower or NA, needs a smaller IJ than a single carb. It also seems a smaller IJ is less likely to have "blower roll" idle issues. Smaller IJ with correspondingly smaller IAB so the T-slot is rich enough, and perhaps a T-slot jet to keep it from going too rich if the valve timing is such that there is a large increase of vacuum from curb idle RPM to cruise RPM, is usually the best solution to have good drivability manners with a Roots blower, and for that matter with a 2X4 tunnel ram too. Idle jet in the .026" to .031" range is usually the sweet spot. I wish I could predict exactly, but no two engines are the same and changing mufflers or tail pipes on the same engine probably will need a revisit through tuning the idle/T-slot drivability.
Tuner
Thankyou sir
I have seen some big idle jets and air bleeds on blown engine make for hard tuning and not responsive on idle screws
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Re: New Holley 80577 950HP Supercharger carb question

Post by Tuner »

It is particularly important the the idle jet is located below float level.
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Re: New Holley 80577 950HP Supercharger carb question

Post by ChevelleNut »

F-BIRD'88 wrote: Fri Apr 30, 2021 7:05 pm The PVCR size may be different +/- relative to the PVCR size used in a N/A carb application.. Main emulsion jets sizes and main AB's sizes may be different..
Depending if the blower carb is intended for 2x4 use on a blower or as a single carb the idle circuit fuel metering sizes might be different.
You'd have to strip it down and measure stuff on this carb to know how its set up.
Draw thru or blow thru type will be set up differently.
I know the power valves are different along with the primary and secondary jets. Air bleeds I'm not sure of, but probably a good chance.
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