solid lifter adj vs vacuum
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Instructor
Joined: Jun 2013
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From: Ontario
solid lifter adj vs vacuum
I adjusted my 30 30 cam 365 to .26 intake and exhaust as recommended cold . Re checked in between .24 and .26. My vacuum is 11 at 1000 rpm I believe it used to be 14 to 15. This will seem to affect the mechanical vacuum on my distributor. Should I reset the valves to .27 degrees. Thanks for any suggestions
Team Owner
Joined: Mar 2003
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From: Greenville, Indiana
I adjusted my 30 30 cam 365 to .26 intake and exhaust as recommended cold . Re checked in between .24 and .26. My vacuum is 11 at 1000 rpm I believe it used to be 14 to 15. This will seem to affect the mechanical vacuum on my distributor. Should I reset the valves to .27 degrees. Thanks for any suggestions
The vacuum cannister used with that cam should be fully deployed at 8" vacuum. It starts to deploy somewhere around 3" vacuum.
Advanced
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It is called the 30-30 Duntov for a reason. These cams have very soft clearance ramps, adjusting the valves tighter than 0.030" puts the lifter on the ramp too soon. Idle vacuum does not have too much to do with the function of vacuum advance, as long as the engine idles.
Drifting
Joined: Jul 2005
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From: Putnam Valley, New York. Amateur Radio Operator K2NS
Low vacuum
That engine IS NOT known for making much vacuum at idle. The tighter you go on the valve adjustment the less vacuum you will have. The vacuum advance can that should be on that engine should pull in all the way at 8 inches of vacuum. If yours doesn't, then you probably have the wrong one. I think the proper one will have either 236 or B28 stamped in the arm right behind the can. If it says anything else, it's the wrong one.
RON
Last edited by rongold; Jul 8, 2013 at 05:17 PM.
Advanced
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Yes, that is pretty much what I intended to say, although a bit too brief, perhaps. What I meant about function is that, as we were taught in auto shop, vacuum advance is designed to enhance efficiency at cruising speeds. There is a big fat spring in the chamber that provides retard under low vacuum (engine accelerating) conditions. I have found that, in the case of high-performance smallblocks, the best vacuum curve is no vacuum curve. Lock the plate and tune the mechanical advance curve. High-performance smallblocks generally are mated to higher (numerically) rear-ends so vacuum advance becomes redundant.
Le Mans Master
Joined: Nov 2008
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From: columbus oh
Yes, that is pretty much what I intended to say, although a bit too brief, perhaps. What I meant about function is that, as we were taught in auto shop, vacuum advance is designed to enhance efficiency at cruising speeds. There is a big fat spring in the chamber that provides retard under low vacuum (engine accelerating) conditions. I have found that, in the case of high-performance smallblocks, the best vacuum curve is no vacuum curve. Lock the plate and tune the mechanical advance curve. High-performance smallblocks generally are mated to higher (numerically) rear-ends so vacuum advance becomes redundant.
Melting Slicks
Joined: Oct 2002
Posts: 2,317
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From: St Louis MO
I adjusted my 30 30 cam 365 to .26 intake and exhaust as recommended cold . Re checked in between .24 and .26. My vacuum is 11 at 1000 rpm I believe it used to be 14 to 15. This will seem to affect the mechanical vacuum on my distributor. Should I reset the valves to .27 degrees. Thanks for any suggestions
) Usage of tighter lash such as .025", advocated by several on this forum, will reduce idle vacuum a bit and boost upper rpm performance a tiny bit - it's your choice, but I've followed the Chevy spec of .030-.030.
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Team Owner
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From: Washington Michigan
Yes, that is pretty much what I intended to say, although a bit too brief, perhaps. What I meant about function is that, as we were taught in auto shop, vacuum advance is designed to enhance efficiency at cruising speeds. There is a big fat spring in the chamber that provides retard under low vacuum (engine accelerating) conditions. I have found that, in the case of high-performance smallblocks, the best vacuum curve is no vacuum curve. Lock the plate and tune the mechanical advance curve. High-performance smallblocks generally are mated to higher (numerically) rear-ends so vacuum advance becomes redundant.
http://www.camaros.org/pdf/timing101.pdf
Team Owner
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From: Washington Michigan
I adjusted my 30 30 cam 365 to .26 intake and exhaust as recommended cold . Re checked in between .24 and .26. My vacuum is 11 at 1000 rpm I believe it used to be 14 to 15. This will seem to affect the mechanical vacuum on my distributor. Should I reset the valves to .27 degrees. Thanks for any suggestions
Racer
Joined: May 2006
Posts: 364
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From: Fairfield County Connecticut
It is called the 30-30 Duntov for a reason. These cams have very soft clearance ramps, adjusting the valves tighter than 0.030" puts the lifter on the ramp too soon. Idle vacuum does not have too much to do with the function of vacuum advance, as long as the engine idles.
Also I went on the same journey adjusting the valves in my 64 L76 mill a whole back - you can read about it here:
http://forums.corvetteforum.com/c1-a...nt-method.html
or you can save yourself some time and I'll tell you the 30-30 setting improved my low end torque and general driveability. The previous owner of my car had it set much tighter and it was a kitten as far as low end power and takeoff pickup.
Tim
p.s. = what John Z said - 9-10" of vac is right on the button at idle for a 30-30 cam - mine measured right at 10" - some knucklehead before me put a vac can in from a Belair that needed 16" to pull in fully and I could not get mine to idle right until I got the correct can that pulls in fully at around 8" - If memory serves me it's a B26 or B28 can
Last edited by climbabout; Jul 8, 2013 at 09:25 PM.
Team Owner
Joined: Mar 2003
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From: Greenville, Indiana
(Please don't use .27 lash - it's about 10 times too much, but is probably a typo.
) Usage of tighter lash such as .025", advocated by several on this forum, will reduce idle vacuum a bit and boost upper rpm performance a tiny bit - it's your choice, but I've followed the Chevy spec of .030-.030.or you can save yourself some time and I'll tell you the 30-30 setting improved my low end torque and general driveability. The previous owner of my car had it set much tighter and it was a kitten as far as low end power and takeoff pickup.
p.s. = what John Z said - 9-10" of vac is right on the button at idle for a 30-30 cam - mine measured right at 10" - some knucklehead before me put a vac can in from a Belair that needed 16" to pull in fully and I could not get mine to idle right until I got the correct can that pulls in fully at around 8" - If memory serves me it's a B26 or B28 can
Thread Starter
Instructor
Joined: Jun 2013
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From: Ontario
Thanks for all the input.
I am re checking the valve . ( seems a bit tight ) adjust to .027 cold
MSD Ignition 8572 - MSD Billet & Pro-Billet Distributor .
Edelbrock Performer 600 cfm carb
The problem I am having is that when I slow down the car dies.
To get it started I have to place the gas pedal to the floor and crank it over
A number of times. I have seen the mechanical vacuum drop off as the engine is running.
I have 2 Medium springs in the distributary. Maybe I should change one to a light spring ?
Re set base timing from 8 deg 600 rpm to 10 deg 800 rpm
Cam is a comp cam replica of the 30 30 .
I am re checking the valve . ( seems a bit tight ) adjust to .027 cold
MSD Ignition 8572 - MSD Billet & Pro-Billet Distributor .
Edelbrock Performer 600 cfm carb
The problem I am having is that when I slow down the car dies.
To get it started I have to place the gas pedal to the floor and crank it over
A number of times. I have seen the mechanical vacuum drop off as the engine is running.
I have 2 Medium springs in the distributary. Maybe I should change one to a light spring ?
Re set base timing from 8 deg 600 rpm to 10 deg 800 rpm
Cam is a comp cam replica of the 30 30 .
Melting Slicks
Joined: Oct 2002
Posts: 2,317
Likes: 111
From: St Louis MO
Thanks for all the input.
I am re checking the valve . ( seems a bit tight ) adjust to .027 cold
MSD Ignition 8572 - MSD Billet & Pro-Billet Distributor .
Edelbrock Performer 600 cfm carb
The problem I am having is that when I slow down the car dies.
To get it started I have to place the gas pedal to the floor and crank it over
A number of times. I have seen the mechanical vacuum drop off as the engine is running.
I have 2 Medium springs in the distributary. Maybe I should change one to a light spring ?
Re set base timing from 8 deg 600 rpm to 10 deg 800 rpm
Cam is a comp cam replica of the 30 30 .
I am re checking the valve . ( seems a bit tight ) adjust to .027 cold
MSD Ignition 8572 - MSD Billet & Pro-Billet Distributor .
Edelbrock Performer 600 cfm carb
The problem I am having is that when I slow down the car dies.
To get it started I have to place the gas pedal to the floor and crank it over
A number of times. I have seen the mechanical vacuum drop off as the engine is running.
I have 2 Medium springs in the distributary. Maybe I should change one to a light spring ?
Re set base timing from 8 deg 600 rpm to 10 deg 800 rpm
Cam is a comp cam replica of the 30 30 .
Thread Starter
Instructor
Joined: Jun 2013
Posts: 233
Likes: 0
From: Ontario
Thread Starter
Instructor
Joined: Jun 2013
Posts: 233
Likes: 0
From: Ontario
Turned the motor over until the intake starts to open and adjust the exhaust at that point as it would then be on its base circle-
adjusted cold to .028 . Engine works great vacuumed 15 deg now.
The car really pulls well in all gears. When I get a chance I will re adjust and try .027 see if it makes any difference.
The other method did not work for me by indexing the motor by 90 degrees and adjusting it. Ended up way to tight . I must be missing something.
Thanks for all the help.
adjusted cold to .028 . Engine works great vacuumed 15 deg now.
The car really pulls well in all gears. When I get a chance I will re adjust and try .027 see if it makes any difference.
The other method did not work for me by indexing the motor by 90 degrees and adjusting it. Ended up way to tight . I must be missing something.
Thanks for all the help.
Last edited by Wayne1964; Jul 18, 2013 at 06:08 AM. Reason: update