Jetting Help
Thread Starter
Staging Lane
Joined: Oct 2014
Posts: 82
Likes: 0
From: Highland Village Texas
Jetting Help Howdy
I put a stock 5.3 in my fox and I need some help or some guidance on the jetting size to get started. I opened up the carb to replace the gaskets and to get a peak at the jets and power valve. I am not new to carbs and have had several but I am new to these lsx motors.
Current Setup
Mighty Demon 750
74/84
Primary Power Valve is a 55
Rear Power Valve is a block
Also, the jets are stuck or really in there. Any tricks to removing them with out breaking them? Not sure if those tools are worth the money.
Thanks again.
I put a stock 5.3 in my fox and I need some help or some guidance on the jetting size to get started. I opened up the carb to replace the gaskets and to get a peak at the jets and power valve. I am not new to carbs and have had several but I am new to these lsx motors.
Current Setup
Mighty Demon 750
74/84
Primary Power Valve is a 55
Rear Power Valve is a block
Also, the jets are stuck or really in there. Any tricks to removing them with out breaking them? Not sure if those tools are worth the money.
Thanks again.
On The Tree
Joined: May 2013
Posts: 143
Likes: 1
The jets shouldnt be that tight, unless someone cranked them down. I use a flat screwdriver with a thick tip and have never had a problem. There are a handful of jet-removal tools available for under $20 though.
What is causing you to want to change the jets, are the plugs rich/lean, is it not running right?
Do you have a vacuum gauge? Its a very valuable tool that can help you set your idle mixture, and you can use it to determine what type of power valve best suits your setup.
As far as choosing jets, you will need to either use a air/fuel gauge or read the spark plugs to see whats going on inside the engine.
Videos below are from Holley but its the same process with a Demon
Hot to set idle mixture
How to choose power valve
What is causing you to want to change the jets, are the plugs rich/lean, is it not running right?
Do you have a vacuum gauge? Its a very valuable tool that can help you set your idle mixture, and you can use it to determine what type of power valve best suits your setup.
As far as choosing jets, you will need to either use a air/fuel gauge or read the spark plugs to see whats going on inside the engine.
Videos below are from Holley but its the same process with a Demon
Hot to set idle mixture
How to choose power valve
Last edited by LQ4BU; Oct 24, 2016 at 10:33 AM.
Thread Starter
Staging Lane
Joined: Oct 2014
Posts: 82
Likes: 0
From: Highland Village Texas
5.3 is bone stock out side of the intake. Its a Holley single plane.
I haven't fired or started the car yet but will by weeks end. 74 / 84 seemed pretty stout compared to what I have had in the past. Never had to get that high on a sbf with heads and cam. I searched around here first and a 750 with those jet sizes are 6.0 with a cam.
I have had to change the jets many times in the past on several cars and have never had them to were I can get them to budge. Ended up chipping on off... Thats what i get for a CL deal.
I haven't fired or started the car yet but will by weeks end. 74 / 84 seemed pretty stout compared to what I have had in the past. Never had to get that high on a sbf with heads and cam. I searched around here first and a 750 with those jet sizes are 6.0 with a cam.
I have had to change the jets many times in the past on several cars and have never had them to were I can get them to budge. Ended up chipping on off... Thats what i get for a CL deal.
On The Tree
Joined: Jul 2015
Posts: 149
Likes: 0
I would invest in a vacuum gauge and a wideband A/F meter. They will make precise tuning 1,000,000 times easier.
With a stock cam 5.3, that power valve is only going to open at WOT. I would use a 10.5 minimum (it's the heaviest one they sell) if you are going to keep that cam, or something similar in there. I have a 650 DP on my stock 5.3 and it pulls 23" Hg at idle; I made a custom 16" power valve for it, Could probably do better with 18.
I assume you are changing the cam, hence the 750 and the single plane manifold? Are you tuning for best mileage/driveability/performance or is this a track only car?
With a stock cam 5.3, that power valve is only going to open at WOT. I would use a 10.5 minimum (it's the heaviest one they sell) if you are going to keep that cam, or something similar in there. I have a 650 DP on my stock 5.3 and it pulls 23" Hg at idle; I made a custom 16" power valve for it, Could probably do better with 18.
I assume you are changing the cam, hence the 750 and the single plane manifold? Are you tuning for best mileage/driveability/performance or is this a track only car?
Thread Starter
Staging Lane
Joined: Oct 2014
Posts: 82
Likes: 0
From: Highland Village Texas
Thanks Greg for that info. I have been looking at Innovations wide band setup to get it dialed in for the long run.
This is a track only car and a cam & nitrous are coming soon. Left it stock for now just to get the swap going and work some bugs out.
Ran across these jets and thought they were large for this motor. I am mostly curious what others are running on their stock 5.3's.
This is a track only car and a cam & nitrous are coming soon. Left it stock for now just to get the swap going and work some bugs out.
Ran across these jets and thought they were large for this motor. I am mostly curious what others are running on their stock 5.3's.
I would invest in a vacuum gauge and a wideband A/F meter. They will make precise tuning 1,000,000 times easier.
With a stock cam 5.3, that power valve is only going to open at WOT. I would use a 10.5 minimum (it's the heaviest one they sell) if you are going to keep that cam, or something similar in there. I have a 650 DP on my stock 5.3 and it pulls 23" Hg at idle; I made a custom 16" power valve for it, Could probably do better with 18.
I assume you are changing the cam, hence the 750 and the single plane manifold? Are you tuning for best mileage/driveability/performance or is this a track only car?
With a stock cam 5.3, that power valve is only going to open at WOT. I would use a 10.5 minimum (it's the heaviest one they sell) if you are going to keep that cam, or something similar in there. I have a 650 DP on my stock 5.3 and it pulls 23" Hg at idle; I made a custom 16" power valve for it, Could probably do better with 18.
I assume you are changing the cam, hence the 750 and the single plane manifold? Are you tuning for best mileage/driveability/performance or is this a track only car?
