78 Pace Car l-82
Le Mans Master
Joined: Oct 2010
Posts: 6,938
Likes: 848
From: melbourne florida
2023 C3 of the Year Finalist - Modified
there is improvement to be made almost everywhere. but with what you describe it likely won't be worth the effort or money.
set the curve up in the distributor e mail lars for his distributor papers on that and setting up the quadrajet and you should be very pleased.
set the curve up in the distributor e mail lars for his distributor papers on that and setting up the quadrajet and you should be very pleased.
Last edited by 7t9l82; Jan 1, 2014 at 10:41 PM.
Tech Contributor
Joined: Aug 1999
Posts: 14,380
Likes: 6,391
From: At my Bar drinking and wrenching in Lafayette Colorado
Lars’s Tuning Secrets: The Common Tuning Tour Observations and Fixes
During the Tuning for Beer World Tour Event Series, I run across some common themes and problems during the tuning. Thought I’d share the most common performance tuning and upgrade issues that we typically see during the Tours. Here are some comments, tips, and things to look at to help you in your tuning and setup:
First trick to any tuning, and I emphasize this constantly during the Seminars, is to tackle the ignition system first. Never, ever, try tuning a carb without first having tuned the timing curve. 90% of all carb problems are ignition problems.
Get a good dial-back timing light and learn how to use it. This is the most valuable and indispensable tool you will ever own. Sears has them for $69.95, or you can get a nice digital one with built in tach through Summit for around $110. Invest in good tools, and get a timing light.
Unless your distributor has recently been rebuilt and set up by someone competent, your distributor is messed up. I guarantee it. Whether you have a 200,000-mile tach drive points unit, an HEI, or a brand new MSD ProBillet, the distributor does not have a good advance curve in it. Yank it out, shim out the endplay (setting shaft end play to .005 - .007” for cast iron units and .010 - .015” for aluminum housings), clean it up, and make sure the advance system is working right.
Most point-style distributors are missing the advance stop bushing (little rubber bushing on a pin under the cam advance plate). You can get a brass replacement bushing in Mr. Gasket kit part number 928G. Smack the bushing with a hammer before installing it to make it fits very snug on the pin. This kit also has springs that you can use for your advance curve. For HEI distributors, use the 2 gold springs in the kit. For points systems and MSD distributors, use one black and one silver spring as a starting point.
Set up your timing to 36 degrees total advance, and install a set of advance springs that make the total timing come in around 2500-2800 rpm (faster if your engine can handle it without detonation). The resulting initial timing is not real important as long as it’s in a general acceptable range. For a performance engine, I like to see initial timing in the 16 – 18 degree range. Mild-cammed engines can get by with a little less. Big-cammed engines like 20 to 24 degrees initial. But set total to 36 as a starting point.
Use a vacuum advance control unit that does not pull in any more than 16 degrees of vacuum advance, and make sure it is “soft” enough to pull its full advance in at the vacuum reading you get at idle. You can run off of either ported or manifold vacuum, depending on what your engine wants for best quality idle, but most engines will respond best (and run cooler) with the vacuum advance attached to manifold vacuum. See my timing papers for more on this subject.
Set your carb up to the stock specs for the carb number you are using and make intelligent jetting choices from there. If you are running headers, free-flowing exhaust, good intake, etc., you can bump the carb jetting up about 2 jet sizes as a starting point for your tuning. See my Q-Jet Setup paper for some specific instructions on how to set this up.
On Holley and BG carbs without secondary power valves, secondary jet size should be 8 sizes larger than primary jet size. The Holley Street Avenger carbs are jetted extremely lean, and respond well to this type of jetting mod.
On vacuum secondary carbs, run the softest spring you can find for the secondary. This is the short white spring in the Holley spring kit. If this produces a stumble going into the secondaries, tighten it up one notch by running the yellow spring.
Beware of commercially rebuilt Q-Jets: These carbs are seriously messed up. Typically, we find that the common screw-ups are: Incorrect floats; cut/modified power pistons; incorrect jetting; and plugged idle air bleed holes. These issues must be corrected before the carb can be made to run right.
Make sure your Q-Jet secondary throttle blades do not open over-center. The secondary throttles should only open to the point that the top edge of the blades points directly at the lower edge of the air baffle. This is short of vertical.
On Q-Jet-equipped C3 Vettes, the most common performance issue is that the throttle linkage does not allow enough travel to open the secondaries. Check throttle travel on any C3. Remove the floor mat to correct it in most cases. If this does not do enough, grab the gas pedal and bend it upwards until you can get WOT at the carb.
Holley and BG carbs flow idle fuel on the secondary side. Therefore, you must also have air flow on the secondary side at idle. All Holley and BG carbs have secondary idle speed screws. Use this screw to make the secondary side throttle opening identical to the primary side opening at idle, and make all idle speed adjustments equally to both primary and secondary sides.
Set Holley and BG float levels to the bottom of the sight hole with the engine hot.
Initial bench setting for Holley and BG idle mixture screws is 1 turn out from lightly seated. Make all idle mixture adjustments in small increments, adjusting all mixture screws evenly for best quality idle.
Give the car what it wants: Listen, feel and smell. The car will “talk” to you as you make changes, and you need to listen.
Happy tuning!!
Lars
Last edited by lars; Jan 1, 2014 at 11:00 PM.
Le Mans Master
Joined: Apr 2006
Posts: 5,403
Likes: 95
Lars probably just forgot to mention it. After tuning the Q-jet if your still not happy with the performance buy the 1406 edelbrock carb its a square flange carb so you will also need the edelbrock performer manifold to bolt it on. The good news then you can use either carb on the manifold for comparison tests. You do have deep pockets with money to waste ?
Thread Starter
Racer
Joined: Jan 2013
Posts: 300
Likes: 10
You're not going to make any noticeable power gains by replacing components. The Edelbrock "Performer" intake manifold is actually modeled after the intake you currently have on your car, so swapping one for the other is pointless. The best improvement you can make is to optimize what you have and set it up right: During the "Tuning for Beer World Tour" seminar series, we documented 20 to 70 hp improvements in these cars just by setting them up right. Here is the short summary sheet from the Tuning Tour - do this to your car before anything else: These tuning tricks are worth more hp than any single component swap you can make. You can also e-mail me for my Q-Jet Setup paper, which will allow you to gain a significant edge on your existing carb:
Lars’s Tuning Secrets: The Common Tuning Tour Observations and Fixes
During the Tuning for Beer World Tour Event Series, I run across some common themes and problems during the tuning. Thought I’d share the most common performance tuning and upgrade issues that we typically see during the Tours. Here are some comments, tips, and things to look at to help you in your tuning and setup:
First trick to any tuning, and I emphasize this constantly during the Seminars, is to tackle the ignition system first. Never, ever, try tuning a carb without first having tuned the timing curve. 90% of all carb problems are ignition problems.
Get a good dial-back timing light and learn how to use it. This is the most valuable and indispensable tool you will ever own. Sears has them for $69.95, or you can get a nice digital one with built in tach through Summit for around $110. Invest in good tools, and get a timing light.
Unless your distributor has recently been rebuilt and set up by someone competent, your distributor is messed up. I guarantee it. Whether you have a 200,000-mile tach drive points unit, an HEI, or a brand new MSD ProBillet, the distributor does not have a good advance curve in it. Yank it out, shim out the endplay (setting shaft end play to .005 - .007” for cast iron units and .010 - .015” for aluminum housings), clean it up, and make sure the advance system is working right.
Most point-style distributors are missing the advance stop bushing (little rubber bushing on a pin under the cam advance plate). You can get a brass replacement bushing in Mr. Gasket kit part number 928G. Smack the bushing with a hammer before installing it to make it fits very snug on the pin. This kit also has springs that you can use for your advance curve. For HEI distributors, use the 2 gold springs in the kit. For points systems and MSD distributors, use one black and one silver spring as a starting point.
Set up your timing to 36 degrees total advance, and install a set of advance springs that make the total timing come in around 2500-2800 rpm (faster if your engine can handle it without detonation). The resulting initial timing is not real important as long as it’s in a general acceptable range. For a performance engine, I like to see initial timing in the 16 – 18 degree range. Mild-cammed engines can get by with a little less. Big-cammed engines like 20 to 24 degrees initial. But set total to 36 as a starting point.
Use a vacuum advance control unit that does not pull in any more than 16 degrees of vacuum advance, and make sure it is “soft” enough to pull its full advance in at the vacuum reading you get at idle. You can run off of either ported or manifold vacuum, depending on what your engine wants for best quality idle, but most engines will respond best (and run cooler) with the vacuum advance attached to manifold vacuum. See my timing papers for more on this subject.
Set your carb up to the stock specs for the carb number you are using and make intelligent jetting choices from there. If you are running headers, free-flowing exhaust, good intake, etc., you can bump the carb jetting up about 2 jet sizes as a starting point for your tuning. See my Q-Jet Setup paper for some specific instructions on how to set this up.
On Holley and BG carbs without secondary power valves, secondary jet size should be 8 sizes larger than primary jet size. The Holley Street Avenger carbs are jetted extremely lean, and respond well to this type of jetting mod.
On vacuum secondary carbs, run the softest spring you can find for the secondary. This is the short white spring in the Holley spring kit. If this produces a stumble going into the secondaries, tighten it up one notch by running the yellow spring.
Beware of commercially rebuilt Q-Jets: These carbs are seriously messed up. Typically, we find that the common screw-ups are: Incorrect floats; cut/modified power pistons; incorrect jetting; and plugged idle air bleed holes. These issues must be corrected before the carb can be made to run right.
Make sure your Q-Jet secondary throttle blades do not open over-center. The secondary throttles should only open to the point that the top edge of the blades points directly at the lower edge of the air baffle. This is short of vertical.
On Q-Jet-equipped C3 Vettes, the most common performance issue is that the throttle linkage does not allow enough travel to open the secondaries. Check throttle travel on any C3. Remove the floor mat to correct it in most cases. If this does not do enough, grab the gas pedal and bend it upwards until you can get WOT at the carb.
Holley and BG carbs flow idle fuel on the secondary side. Therefore, you must also have air flow on the secondary side at idle. All Holley and BG carbs have secondary idle speed screws. Use this screw to make the secondary side throttle opening identical to the primary side opening at idle, and make all idle speed adjustments equally to both primary and secondary sides.
Set Holley and BG float levels to the bottom of the sight hole with the engine hot.
Initial bench setting for Holley and BG idle mixture screws is 1 turn out from lightly seated. Make all idle mixture adjustments in small increments, adjusting all mixture screws evenly for best quality idle.
Give the car what it wants: Listen, feel and smell. The car will “talk” to you as you make changes, and you need to listen.
Happy tuning!!
Lars
Lars’s Tuning Secrets: The Common Tuning Tour Observations and Fixes
During the Tuning for Beer World Tour Event Series, I run across some common themes and problems during the tuning. Thought I’d share the most common performance tuning and upgrade issues that we typically see during the Tours. Here are some comments, tips, and things to look at to help you in your tuning and setup:
First trick to any tuning, and I emphasize this constantly during the Seminars, is to tackle the ignition system first. Never, ever, try tuning a carb without first having tuned the timing curve. 90% of all carb problems are ignition problems.
Get a good dial-back timing light and learn how to use it. This is the most valuable and indispensable tool you will ever own. Sears has them for $69.95, or you can get a nice digital one with built in tach through Summit for around $110. Invest in good tools, and get a timing light.
Unless your distributor has recently been rebuilt and set up by someone competent, your distributor is messed up. I guarantee it. Whether you have a 200,000-mile tach drive points unit, an HEI, or a brand new MSD ProBillet, the distributor does not have a good advance curve in it. Yank it out, shim out the endplay (setting shaft end play to .005 - .007” for cast iron units and .010 - .015” for aluminum housings), clean it up, and make sure the advance system is working right.
Most point-style distributors are missing the advance stop bushing (little rubber bushing on a pin under the cam advance plate). You can get a brass replacement bushing in Mr. Gasket kit part number 928G. Smack the bushing with a hammer before installing it to make it fits very snug on the pin. This kit also has springs that you can use for your advance curve. For HEI distributors, use the 2 gold springs in the kit. For points systems and MSD distributors, use one black and one silver spring as a starting point.
Set up your timing to 36 degrees total advance, and install a set of advance springs that make the total timing come in around 2500-2800 rpm (faster if your engine can handle it without detonation). The resulting initial timing is not real important as long as it’s in a general acceptable range. For a performance engine, I like to see initial timing in the 16 – 18 degree range. Mild-cammed engines can get by with a little less. Big-cammed engines like 20 to 24 degrees initial. But set total to 36 as a starting point.
Use a vacuum advance control unit that does not pull in any more than 16 degrees of vacuum advance, and make sure it is “soft” enough to pull its full advance in at the vacuum reading you get at idle. You can run off of either ported or manifold vacuum, depending on what your engine wants for best quality idle, but most engines will respond best (and run cooler) with the vacuum advance attached to manifold vacuum. See my timing papers for more on this subject.
Set your carb up to the stock specs for the carb number you are using and make intelligent jetting choices from there. If you are running headers, free-flowing exhaust, good intake, etc., you can bump the carb jetting up about 2 jet sizes as a starting point for your tuning. See my Q-Jet Setup paper for some specific instructions on how to set this up.
On Holley and BG carbs without secondary power valves, secondary jet size should be 8 sizes larger than primary jet size. The Holley Street Avenger carbs are jetted extremely lean, and respond well to this type of jetting mod.
On vacuum secondary carbs, run the softest spring you can find for the secondary. This is the short white spring in the Holley spring kit. If this produces a stumble going into the secondaries, tighten it up one notch by running the yellow spring.
Beware of commercially rebuilt Q-Jets: These carbs are seriously messed up. Typically, we find that the common screw-ups are: Incorrect floats; cut/modified power pistons; incorrect jetting; and plugged idle air bleed holes. These issues must be corrected before the carb can be made to run right.
Make sure your Q-Jet secondary throttle blades do not open over-center. The secondary throttles should only open to the point that the top edge of the blades points directly at the lower edge of the air baffle. This is short of vertical.
On Q-Jet-equipped C3 Vettes, the most common performance issue is that the throttle linkage does not allow enough travel to open the secondaries. Check throttle travel on any C3. Remove the floor mat to correct it in most cases. If this does not do enough, grab the gas pedal and bend it upwards until you can get WOT at the carb.
Holley and BG carbs flow idle fuel on the secondary side. Therefore, you must also have air flow on the secondary side at idle. All Holley and BG carbs have secondary idle speed screws. Use this screw to make the secondary side throttle opening identical to the primary side opening at idle, and make all idle speed adjustments equally to both primary and secondary sides.
Set Holley and BG float levels to the bottom of the sight hole with the engine hot.
Initial bench setting for Holley and BG idle mixture screws is 1 turn out from lightly seated. Make all idle mixture adjustments in small increments, adjusting all mixture screws evenly for best quality idle.
Give the car what it wants: Listen, feel and smell. The car will “talk” to you as you make changes, and you need to listen.
Happy tuning!!
Lars
