fast idle for Vintage Air AC
06-15-2017, 11:50 AM
#1
Melting Slicks
Thread Starter
fast idle for Vintage Air AC
I have the VA in my 64 and it's working great. However, when the compressor kicks in, idle drops dangerously. I need to set the idle above 900rpm to stay out of the stall zone.
One way out is installing a high-idle solenoid as described here http://www.corvetteforum.com/forums/...-solenoid.html , but these have not enough power to push the carburator arm by themselves. So you have to 'blip' the throttle each time the compressors starts, not very handy when waiting for a traffic light or when stuck in traffic.
I am experimenting a different method, using a vacuum advance canister. That should be strong enough to overcome the carb springs (I hope...).
I build a bracket and a 90° arm with adjustable end (much the same way the idle adjusting screw works).
The vacuum to the canister will be fed through an electric vacuum switch valve (from a BMW), itself connected to the clutch power feed of the compressor. When the compressor goes on, the switch passes the vacuum and the fast idle sets in.
Still need to test it though, waiting for the vacuum switch.
One way out is installing a high-idle solenoid as described here http://www.corvetteforum.com/forums/...-solenoid.html , but these have not enough power to push the carburator arm by themselves. So you have to 'blip' the throttle each time the compressors starts, not very handy when waiting for a traffic light or when stuck in traffic.
I am experimenting a different method, using a vacuum advance canister. That should be strong enough to overcome the carb springs (I hope...).
I build a bracket and a 90° arm with adjustable end (much the same way the idle adjusting screw works).
The vacuum to the canister will be fed through an electric vacuum switch valve (from a BMW), itself connected to the clutch power feed of the compressor. When the compressor goes on, the switch passes the vacuum and the fast idle sets in.
Still need to test it though, waiting for the vacuum switch.
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carl3989 (06-04-2023)
06-15-2017, 12:29 PM
#2
Melting Slicks
Interesting idea. I just posted on my lack of success with installing a conventional idle speed solenoid and hadn't considered the downside as you mentions. I may look at a similar solution myself now that my original plan isn't going to work without some customization.
06-15-2017, 01:18 PM
#3
Team Owner
I had toyed with modifying a cruise control setup for this task. But it turned out to be a non-issue on my 63. I set the idle up 50 RPM in the summer and that works.
06-15-2017, 04:16 PM
#4
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Mine idles a little fast anyway, so it's okay with the compressor on. It will die in a panic stop, however, so I try to keep those to a minimum.😕
Last edited by 59BlueSilver; 06-15-2017 at 04:18 PM.
06-15-2017, 06:48 PM
#5
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St. Jude Donor '07
lol.... EFI will take care of that...; maintains the idle speed no matter what...
BUT, a VERY clever solution; I hope it works for you as the accelerator 'tapping' is a PIA...
Bill
BUT, a VERY clever solution; I hope it works for you as the accelerator 'tapping' is a PIA...
Bill
06-23-2017, 04:17 PM
#6
Melting Slicks
Thread Starter
did final install and first test ride today, and system works as expected. Although the vacuum advance force is way higher than from a solenoid, it still does no have 100% full authority over the carb springs (I do have the dual concentric springs) . But I can drive now without worries for an engine stall. I did order a canister for a HEI that kicks in at the lowest Hg I could find, assuming these have a softer internal spring so more of the vacuum is translated into pull force. It will take 2 week to get it here, I'll let know how that works.
Last edited by alexandervdr; 06-23-2017 at 04:21 PM.
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carl3989 (06-04-2023)
06-23-2017, 04:25 PM
#7
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St. Jude Donor '07
did final install and first test ride today, and system works as expected. Although the vacuum advance force is way higher than from a solenoid, it still does no have 100% full authority over the carb springs (I do have the dual concentric springs) . But I can drive now without worries for an engine stall. I did order a canister for a HEI that kicks in at the lowest Hg I could find, assuming these have a softer internal spring so more of the vacuum is translated into pull force. It will take 2 week to get it here, I'll let know how that works.
Bill
Last edited by wmf62; 06-23-2017 at 04:27 PM.
06-26-2017, 10:48 AM
#10
Melting Slicks
Thread Starter
update: I had ordered a HEI vacuum can and a B28 can (used for a standard distributor SBC, the B28 is for high performance so low vacuum engines like EFI ). The B28 came in today. It opens up at way lower Hg 3-5 compared to 7-9 of the B22 I had used. The effect was as hoped: when the compressor kicks in, the vacuum pulls the rod to it's full retraction. And it has more than enough power to control the carburator arm without getting stuck halfway. I now have the set screw on my DIY system calibrated, and the difference with or without compressor load is zero rpm, it actually goes unnoticed. No right foot tapping needed at all
PS: for those interested, this is an excellent article about vacuum advance cans outintheshop.com/faq/Vac%20Adv%20Spec.pdf
PS: for those interested, this is an excellent article about vacuum advance cans outintheshop.com/faq/Vac%20Adv%20Spec.pdf
Last edited by alexandervdr; 06-26-2017 at 11:54 AM.
06-26-2017, 11:42 AM
#11
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St. Jude Donor '07
update: I had ordered a HEI vacuum can and a B28 can (used for a standard distributor SBC). The B28 came in today. It opens up at way lower Hg 3-5 compared to 7-9 of the B22 I had used. The effect was as hoped: when the compressor kicks in, the vacuum pulls the rod to it's full retraction. And it has more than enough power to control the carburator arm without getting stuck halfway. I now have the set screw on my DIY system calibrated, and the difference with or without compressor load is zero rpm, it actually goes unnoticed. No right foot tapping needed at all
PS: for those interested, this is an excellent article about vacuum advance cans outintheshop.com/faq/Vac%20Adv%20Spec.pdf
PS: for those interested, this is an excellent article about vacuum advance cans outintheshop.com/faq/Vac%20Adv%20Spec.pdf
Bill
06-26-2017, 11:52 AM
#12
Melting Slicks
Thread Starter
Thanks! I do think it should be possible to make a kit system with a 2 or 3 piece bracket that can be tuned to fit the majority of cases. Those with airco in a C1-C2 are probably the more conservative driver/cruisers, and may have the most 'standard' configurations in stead of exotic carb and manifold combinations. Although I am just guessing ...
06-26-2017, 12:28 PM
#13
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St. Jude Donor '07
please don't be offended if I refer to you as "Bubba at His Best", as necessity is the mother of invention and the impossible only takes a little longer, which is what has led me to do many things to 'improve' my car...
from one Bubba to another... GREAT JOB...
Bill
...and, there is a niche need for what you have designed and fabricated
from one Bubba to another... GREAT JOB...
Bill
...and, there is a niche need for what you have designed and fabricated
Last edited by wmf62; 06-26-2017 at 12:30 PM.
08-15-2020, 08:52 AM
#14
Classic Member
update: I had ordered a HEI vacuum can and a B28 can (used for a standard distributor SBC, the B28 is for high performance so low vacuum engines like EFI ). The B28 came in today. It opens up at way lower Hg 3-5 compared to 7-9 of the B22 I had used. The effect was as hoped: when the compressor kicks in, the vacuum pulls the rod to it's full retraction. And it has more than enough power to control the carburator arm without getting stuck halfway. I now have the set screw on my DIY system calibrated, and the difference with or without compressor load is zero rpm, it actually goes unnoticed. No right foot tapping needed at all
PS: for those interested, this is an excellent article about vacuum advance cans outintheshop.com/faq/Vac%20Adv%20Spec.pdf
PS: for those interested, this is an excellent article about vacuum advance cans outintheshop.com/faq/Vac%20Adv%20Spec.pdf
Thanks, Craig
08-15-2020, 09:08 AM
#15
Melting Slicks
Thread Starter
Wow, this thread goes back in time. I just re-read it again because my L76 and AC do not like each other and I'm looking for fixes. Do you still have this vacuum set-up you did working on your car to help the RPM drop? If so, can you offer the part numbers for pieces, I'd love to try in on mine. I have a stock original L76 with the original Holley 4 bbl and an awesome 500RPM drop when the compressor kicks in. Not good with the STV by-pass cycling system in place.
Thanks, Craig
Thanks, Craig
I since then swapped carbs (from edelbroek to Holley) and put in a camshaft that had much better low end torque. Result is that the rpm at idle merely drops from 650 to 550 when AC kicks in, keeps running smoothly, so I no longer need the device. But it work like a charm, and would use it again if I had substantial drop. I have no experience with L76, and I know it's better at high than at low rpm, but 500 rpm drop seems a lot, are you sure advance is set up right?
08-15-2020, 01:31 PM
#16
Classic Member
It's all made out of sheet metal , fabricated&welded myself.
I since then swapped carbs (from edelbroek to Holley) and put in a camshaft that had much better low end torque. Result is that the rpm at idle merely drops from 650 to 550 when AC kicks in, keeps running smoothly, so I no longer need the device. But it work like a charm, and would use it again if I had substantial drop. I have no experience with L76, and I know it's better at high than at low rpm, but 500 rpm drop seems a lot, are you sure advance is set up right?
I since then swapped carbs (from edelbroek to Holley) and put in a camshaft that had much better low end torque. Result is that the rpm at idle merely drops from 650 to 550 when AC kicks in, keeps running smoothly, so I no longer need the device. But it work like a charm, and would use it again if I had substantial drop. I have no experience with L76, and I know it's better at high than at low rpm, but 500 rpm drop seems a lot, are you sure advance is set up right?
Thanks, I understand that the brackets were custom made. I went back and re-read the thread and got the part numbers I needed for the Vacuum can and the switch. I am going to try this set up since you said it was seamless in RPM change when it worked for you. You have a creative mind, thanks for this idea.
Craig
08-15-2020, 01:38 PM
#17
Classic Member
It's all made out of sheet metal , fabricated&welded myself.
I since then swapped carbs (from edelbroek to Holley) and put in a camshaft that had much better low end torque. Result is that the rpm at idle merely drops from 650 to 550 when AC kicks in, keeps running smoothly, so I no longer need the device. But it work like a charm, and would use it again if I had substantial drop. I have no experience with L76, and I know it's better at high than at low rpm, but 500 rpm drop seems a lot, are you sure advance is set up right?
I since then swapped carbs (from edelbroek to Holley) and put in a camshaft that had much better low end torque. Result is that the rpm at idle merely drops from 650 to 550 when AC kicks in, keeps running smoothly, so I no longer need the device. But it work like a charm, and would use it again if I had substantial drop. I have no experience with L76, and I know it's better at high than at low rpm, but 500 rpm drop seems a lot, are you sure advance is set up right?
08-15-2020, 09:11 PM
#18
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I have a similar issue with my 64 that has Vintage Air added to it. My car is an opriginal 300hp engine that has a factory 64 Rochester Fuel Injection in place of the carb.
I noticed a significant drop in RPMs (like maybe 300 RPM) when I switched the A/C on.
Right now my solution is to adjust the idle up a bit to compensate. And that does mean that me cars runs at about 1100 rpm at idle with the A/C off, and drops to about 800 rpm with the A/C on.
I thought about some sort of idle solenoid, but I am ultimately going to replace the Rochester FI with a Rochester EFI conversion system, so I'll just bump the idle in the summer for the time being.
I noticed a significant drop in RPMs (like maybe 300 RPM) when I switched the A/C on.
Right now my solution is to adjust the idle up a bit to compensate. And that does mean that me cars runs at about 1100 rpm at idle with the A/C off, and drops to about 800 rpm with the A/C on.
I thought about some sort of idle solenoid, but I am ultimately going to replace the Rochester FI with a Rochester EFI conversion system, so I'll just bump the idle in the summer for the time being.
08-16-2020, 07:42 AM
#19
Classic Member
I have a similar issue with my 64 that has Vintage Air added to it. My car is an opriginal 300hp engine that has a factory 64 Rochester Fuel Injection in place of the carb.
I noticed a significant drop in RPMs (like maybe 300 RPM) when I switched the A/C on.
Right now my solution is to adjust the idle up a bit to compensate. And that does mean that me cars runs at about 1100 rpm at idle with the A/C off, and drops to about 800 rpm with the A/C on.
I thought about some sort of idle solenoid, but I am ultimately going to replace the Rochester FI with a Rochester EFI conversion system, so I'll just bump the idle in the summer for the time being.
I noticed a significant drop in RPMs (like maybe 300 RPM) when I switched the A/C on.
Right now my solution is to adjust the idle up a bit to compensate. And that does mean that me cars runs at about 1100 rpm at idle with the A/C off, and drops to about 800 rpm with the A/C on.
I thought about some sort of idle solenoid, but I am ultimately going to replace the Rochester FI with a Rochester EFI conversion system, so I'll just bump the idle in the summer for the time being.
Craig
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Jacks64 (09-01-2023)
06-03-2023, 11:18 AM
#20
Classic Member
VA to increase idle when AC compressor goes on
I have the VA in my 64 and it's working great. However, when the compressor kicks in, idle drops dangerously. I need to set the idle above 900rpm to stay out of the stall zone.
One way out is installing a high-idle solenoid as described here http://www.corvetteforum.com/forums/...-solenoid.html , but these have not enough power to push the carburator arm by themselves. So you have to 'blip' the throttle each time the compressors starts, not very handy when waiting for a traffic light or when stuck in traffic.
I am experimenting a different method, using a vacuum advance canister. That should be strong enough to overcome the carb springs (I hope...).
I build a bracket and a 90° arm with adjustable end (much the same way the idle adjusting screw works).
The vacuum to the canister will be fed through an electric vacuum switch valve (from a BMW), itself connected to the clutch power feed of the compressor. When the compressor goes on, the switch passes the vacuum and the fast idle sets in.
Still need to test it though, waiting for the vacuum switch.
One way out is installing a high-idle solenoid as described here http://www.corvetteforum.com/forums/...-solenoid.html , but these have not enough power to push the carburator arm by themselves. So you have to 'blip' the throttle each time the compressors starts, not very handy when waiting for a traffic light or when stuck in traffic.
I am experimenting a different method, using a vacuum advance canister. That should be strong enough to overcome the carb springs (I hope...).
I build a bracket and a 90° arm with adjustable end (much the same way the idle adjusting screw works).
The vacuum to the canister will be fed through an electric vacuum switch valve (from a BMW), itself connected to the clutch power feed of the compressor. When the compressor goes on, the switch passes the vacuum and the fast idle sets in.
Still need to test it though, waiting for the vacuum switch.
Craig