Quadrajet primary metering area tool - The 1947 - Present Chevrolet & GMC Truck Message Board Network

rpmerf · 12-13-2018, 07:48 AM

I made up a tool to compare jet and rod changes for the primaries on a Quadrajet. It compares the % change in the metering area for WOT and cruise.

Unzip the file. Open the HTML file. Enter your current jet and rods size and click calculate.

The top numbers are rods, the left numbers are jets. The second column is for WOT.

A good writeup on Q Jet tuning: http://www.corvettefaq.com/c3/QJetTuningPaper.doc

geezer#99 · 12-13-2018, 09:55 AM

Before I try to open it up I’ve got a question.

What calculation do you use for the apt?

rpmerf · 12-13-2018, 11:57 AM

It's calculating the total metering area. pi*r^2 to calculate the area. Calculate the area of the jet, then subtract the area of the rod. Measurements are in thousandths of an inch. This method was suggested in the linked paper on page 5. The numbers I calculate match the numbers in the reference on pages 23-33. The advantage here is being able to see the percentage change without having to calculate it. I am calculating everything on the fly, no lookup tables.

geezer#99 · 12-13-2018, 12:15 PM

Calculate area of the rod, but where on the rod?
Apt setting changes that.

rpmerf · 12-13-2018, 03:29 PM

It uses the diameter the rod is marked as. A 42B rod is said to be 0.042". I don't know where they measure it - thickest part of the cruise area?

geezer#99 · 12-13-2018, 04:57 PM

Actually it’s the power area.
It’s where to measure for cruise that is needed especially when the apt setting is factored in.

**mattfranklin** · 12-13-2018, 05:02 PM

Pretty cool. Excellent application of conditional formatting.

12-13-2018, 09:55 AM	#2
geezer#99 Registered User Join Date: Aug 2009 Location: Bowser Posts: 13,512	Re: Quadrajet primary metering area tool Before I try to open it up I’ve got a question. What calculation do you use for the apt?

12-13-2018, 11:57 AM	#3
rpmerf Registered User Join Date: Feb 2011 Location: Parkville, MD Posts: 1,024	Re: Quadrajet primary metering area tool It's calculating the total metering area. pi*r^2 to calculate the area. Calculate the area of the jet, then subtract the area of the rod. Measurements are in thousandths of an inch. This method was suggested in the linked paper on page 5. The numbers I calculate match the numbers in the reference on pages 23-33. The advantage here is being able to see the percentage change without having to calculate it. I am calculating everything on the fly, no lookup tables. __________________ 1970 C20 Custom Camper - 350, TH350 1997 GMC Suburban 1994 Acura Integra GSR 1987 Dodge Daytona Shelby Z

12-13-2018, 12:15 PM	#4
geezer#99 Registered User Join Date: Aug 2009 Location: Bowser Posts: 13,512	Re: Quadrajet primary metering area tool Calculate area of the rod, but where on the rod? Apt setting changes that.

12-13-2018, 03:29 PM	#5
rpmerf Registered User Join Date: Feb 2011 Location: Parkville, MD Posts: 1,024	Re: Quadrajet primary metering area tool It uses the diameter the rod is marked as. A 42B rod is said to be 0.042". I don't know where they measure it - thickest part of the cruise area? __________________ 1970 C20 Custom Camper - 350, TH350 1997 GMC Suburban 1994 Acura Integra GSR 1987 Dodge Daytona Shelby Z

12-13-2018, 04:57 PM	#6
geezer#99 Registered User Join Date: Aug 2009 Location: Bowser Posts: 13,512	Re: Quadrajet primary metering area tool Actually it’s the power area. It’s where to measure for cruise that is needed especially when the apt setting is factored in.

12-13-2018, 05:02 PM	#7
mattfranklin Senior Member Join Date: Dec 2011 Location: Moraga, CA Posts: 799	Re: Quadrajet primary metering area tool Pretty cool. Excellent application of conditional formatting. __________________ (Very) Slow-Going Build Thread: Stock 1970 Short Step with Stock 1970 LT-1 http://67-72chevytrucks.com/vboard/s...d.php?t=567340



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