Cruise Seems Lean

-
Chrysler used a useless technique because their engines were efficient at idle.
Nobody else back then could figure out how to do that.
Yep. That must be it.

Sorry, there's no magic in using manifold vacuum. The magic is in lighting the mixture so pressure maxes out around 20 deg ATDC. Its pretty much as simple as that.
 
71GSSDemon said:
Thanks and I will work towards that after these current changes are done. I may have a couple 1850s laying around to possibly steal the blocks out of but not until after the radiator and water pump pulley fix.

Side question. There seems to be debate as to manifold vacuum or port vacuum for vacuum advance. Books say port vacuum was only a change due to emissions and it will run cooler with manifold vacuum adding timing at idle. This is how my hot rod is because the 950 Holley 3 barrel has no ports. Works well in that.
Click to expand...
I love all the posts, great stuff.
To port or not to port the vacuum advance really boils down to how much initial timing your engine can tolerate. Remembering that you will need to curve the mechanical advance match.
I do run my current 340 setup, ported, initial timing @ 18*
All in @ 2400 rpm 34* total
Cruz speed timing with vacuum advance is 44*, I would like more but the vacuum advance is adjusted out to the max.
 
Mattax said:
This isn't true it all. Any book that states that is wrong.
All you have to do is look at various pre-emissions shop manuals and cars, especially Chrysler products.
For example, from 1959 (Session 136) of the Chrysler MTSC.
View attachment 1715749843

While some car companies, on some engines, did use manifold vacuum, they did so to get the best timing at idle they could with the distributors they were using.
But you can see in the manuals, on the cars, and in the information to the techs, Chrysler did not need to add vacuum advance at idle. Another example here.
View attachment 1715749844
from Ignition System Analysis (Session 259) from the Master Technician's Service Conference

However its interesting to note that on some early Clean Air Packages (CAP) Chrysler did use a manifold vacuum connection to the vacuum advance. This manifold connection was made to the vacuum advance through a special valve which operated during engine braking. This was to insure the leaner closed throttle mixtures were given enough advance to burn thoroughly for reduced emissions. See 1967 Chrysler CAP System: Master Technicians Service Conference (Session 241) for more details.
This later was dropped as unneccessary for automatic equiped cars.

It is true that retarded timing can put too much heat into the cylinder walls. And it is true that retarding the timing at idle was a technique used to better consume HC, especially early in the emmissions era. Further into the emissions era some vehicles used manifold vacuum that connected when coolant temperatures become excessive. But again this was to offset the retarded initial timing. Sometimes, when stuck with using an emissions era distributor advance curve, using manifold vacuum at idle may be a fine solution. It all depends on the specific situation.

Ten years ago I too thought ported vacuum was an emissions related development. See "Carb Issues", scroll down to #11, 17 (me), and responses #13, and #19-22 where Shrinker et al set me straight.
edit: Also very much worth reading is Shrinker's post 10 where he explains what is going on at idle with timing and fueling.
Click to expand...

All this reading of Shrinker's.....just fascinating. Need to take breaks to try and absorb even a fraction of what is being said. Read through all of "Carb Issues" today. WOW.
Thank you
Eric
 
Shrinker sure didn't spoon feed!
Tuner's posts are in general easier to apply directly to whatever issue or setup is being worked on.
Shrinker gets us thinking about what is happening and why. In the long run, that's really helpful. The fact he was willing to share what he was learning with the 4 gas and dyno, along with distilling or highlighting papers he'd read is just incredible. Tuner does some of that too, and because he's worked on such a variety of street cars and been in the business so long, and a great learner himself, he has priceless insight.
 
Last edited:
Just for the record.
1965 Cheverolet L-78 with 4150 list 3124
65l78_9_4cb76915662fccb81e408f6ad568bf5e10224fb9.jpg


This appears to be an original 4150 Holley List 2818
47682672d1319133625-numbers-for-an-original-holley-2818-choke-housing-2818rh3.jpg


As shown in this diagram
B-ENGINE-IGN-05-vacuum-advance-lines.gif
 
So, for anyone with specific 660 holley carb experience, in the below picture (just a pic from Google), #1 is where my vacuum port nipple is. #2 is tapped but doesn't appear to go anywhere. One of my carbs has a plug screwed in, the other is empty. Does anyone know if there is both ported and manifold vacuum ports on these? or can #2 be opened up somehow to have ported vacuum?

upload_2021-6-10_12-52-6.png
 
71GSSDemon said:
So, for anyone with specific 660 holley carb experience, in the below picture (just a pic from Google), #1 is where my vacuum port nipple is. #2 is tapped but doesn't appear to go anywhere. One of my carbs has a plug screwed in, the other is empty. Does anyone know if there is both ported and manifold vacuum ports on these? or can #2 be opened up somehow to have ported vacuum?

View attachment 1715750024
Click to expand...
#1 is a blank hole that holley did not drill and tap for an idle mixture screw
#2 may have been for ported vacuum but I am not sure?
Normally ported or timed vacuum are drilled in above the butterflies and non ported full manifold vacuum are drilled in below the butterflies.
 
512Stroker said:
#1 is a blank hole that holley did not drill and tap for an idle mixture screw
#2 may have been for ported vacuum but I am not sure?
Normally ported or timed vacuum are drilled in above the butterflies and non ported full manifold vacuum are drilled in below the butterflies.
Click to expand...

#1 is definitely drilled in both carbs and has a vacuum hose nipple screwed in mine (pic above was NOT my carb/s)

#2 is tapped to a depth of ~ 0.5-0.625" but it appears is deadheaded at the end.

These are my actual carbs.

Resized952021061095143536.jpg


Resized952021061095143546.jpg
 
Last edited:
This is the passage for the timing vacuum on your block. See if the passage is drilled through.
upload_2021-6-10_16-37-2.png

Then check the face of the main body opposite the white arrow. There should be a drilling there.
Shoot some carb cleaner or blow some air through to see if it goes through.
Holley's website says it should.
Holley 0-4224 660 CFM Center Squirter Carburetor
then click specs

Good illustrations identifying all of the passages and basic concepts in Urich and Fisher. If you find a used copy cheap, I think its one of the better books to start with. It does have some self promotion but still good a reference. https://www.amazon.com/dp/0895864339/?tag=fabo03-20
 
71GSSDemon said:
#1 is definitely drilled in both carbs and has a vacuum hose nipple screwed in mine (pic above was NOT my carb/s)

#2 is tapped to a depth of ~ 0.5-0.625" but it appears is deadheaded at the end.

These are my actual carbs.

View attachment 1715750064

View attachment 1715750065
Click to expand...
Interesting your carbs have no secondary metering block, cant say I have ever seen that before.
How the hell does that work?
 
They're Model 4160. Metering plate is sandwiched in there.

This one is originally from a list 3310-3
upload_2021-6-10_16-53-54.png


Fuel enters at the bottom where the larger drill bit is.
upload_2021-6-10_16-55-2.png
 
512Stroker said:
Well
#2 i am not sure but that looks to high up on the cab to be for timed vacuum, but I have wrong before
#1 I definitely the full manifold vacuum port. I hope you have not been running them uncapped as shown, that would cause a huge vacuum leak.
Click to expand...

512Stroker said:
Interesting your carbs have no secondary metering block, cant say I have ever seen that before.
How the hell does that work?
Click to expand...

The one port is uncapped in the front carb as that is where my vacuum advance is normally connected, but I have to replace that hose. The rear carb has that port capped.

As for metering block for the secondaries, these run metering plates like many do.
 
71GSSDemon said:
The one port is uncapped in the front carb as that is where my vacuum advance is normally connected, but I have to replace that hose. The rear carb has that port capped.

As for metering block for the secondaries, these run metering plates like many do.
Click to expand...
That clear up one question, you are currently running full manifold vacuum to your vacuum advance.
With it disconnected and the port capped with is your initial timing?
 
512Stroker said:
That clear up one question, you are currently running full manifold vacuum to your vacuum advance.
With it disconnected and the port capped with is your initial timing?
Click to expand...

IIRC, it is 20 deg initial and 38 deg all in
 
71GSSDemon said:
IIRC, it is 20 deg initial and 38 deg all in
Click to expand...
It's going to get higher than 20* when connect it to full manifold vacuum.
Are you sure your transition issue is not caused by to much initial timing?
Something is wrong
 
Last edited:
Mattax,

Sorry your post #101 on vac adv is totally incorrect. Set any Chrysler 6 or V8 engine to the factory initial 6-12* timing. With the engine idling, turn the dist slowly to advance the timing. Idle rpm will increase [ more hp ] & vacuum will increase [ increased efficiency ]. To do this, one could use more init timing....or use vac adv connected to man vacuum to get the reqd amount of timing for best idle.
The exh dilution of the mixture at idle & low rpms [ even worse with increased cam duration, the rough idle ] requires more time to burn as efficiently as possible, & that includes Chrysler engines, & this is achieved by more timing at idle.
 
Bewy said:
Mattax,

Sorry your post #101 on vac adv is totally incorrect. Set any Chrysler 6 or V8 engine to the factory initial 6-12* timing. With the engine idling, turn the dist slowly to advance the timing. Idle rpm will increase [ more hp ] & vacuum will increase [ increased efficiency ]. To do this, one could use more init timing....or use vac adv connected to man vacuum to get the reqd amount of timing for best idle.
The exh dilution of the mixture at idle & low rpms [ even worse with increased cam duration, the rough idle ] requires more time to burn as efficiently as possible, & that includes Chrysler engines, & this is achieved by more timing at idle.
Click to expand...

Question on this statement, and just a question. If initial timing with vacuum advance disconnected, is set at 18-20 (already well above factory settings) this additional timing is there. Then if connecting to ported vacuum, it is as set. If connected to manifold vacuum, it will be considerably higher but only until the throttle is opened - same as ported vacuum as it is equal to manifold vacuum once the throttle is open. So, with a more aggressive initial timing and the mechanical timing limited due to this, are we talking the same thing to some degree (pun intended)?@mattax your thoughts on this statement?
 
Last edited:
Been there. Done that.
A long time ago.
Some of us learned the hard way that test doesn't show what you think it shows.
Shrinker explained why.
 
@Mattax your thoughts on my statement in #121? Am I way off base? From above to the comments about your timing theory being incorrect:

Question on this statement, and just a question. If initial timing with vacuum advance disconnected, is set at 18-20 (already well above factory settings) this additional timing is there. Then if connecting to ported vacuum, it is as set. If connected to manifold vacuum, it will be considerably higher but only until the throttle is opened - same as ported vacuum as it is equal to manifold vacuum once the throttle is open. So, with a more aggressive initial timing and the mechanical timing limited due to this, are we talking the same thing to some degree (pun intended)?
 
Mattax said:
Been there. Done that.
A long time ago.
Some of us learned the hard way that test doesn't show what you think it shows.
Shrinker explained why.
Click to expand...

Maybe you could post a link to Shrinker’s discussion on that just as a refresher. When the distributor has a decent curve in it, running manifold vacuum isn’t a good idea. And if you do use manifold vacuum and the engine is happier you then need to figure out why.
 
71GSSDemon said:
If initial timing with vacuum advance disconnected, is set at 18-20 (already well above factory settings) this additional timing is there. Then if connecting to ported vacuum, it is as set. If connected to manifold vacuum, it will be considerably higher but only until the throttle is opened - same as ported vacuum as it is equal to manifold vacuum once the throttle is open.
Click to expand...
This is correct

71GSSDemon said:
So, with a more aggressive initial timing and the mechanical timing limited due to this, are we talking the same thing to some degree (pun intended)?
Click to expand...
To some degree yes if you look at it in the way you just did.
In general no, because its fixated on a belief that extremely early timing and lean burns produce power.

@yellowrose
Sorry, My post was referencing
Sorry your post #101 on vac adv is totally incorrect. Set any Chrysler 6 or V8 engine to the factory initial 6-12* timing. With the engine idling, turn the dist slowly to advance the timing. Idle rpm will increase [ more hp ] & vacuum will increase [ increased efficiency ].

@71GSSDemon mentioned he had read Shrinker's posts, in particular the paragraph from post #10. Bewy obviously chose not to, or did but choses to believe the current magazine writers are more knowledgable. The two big points from Shrinker in those two paragraphs is that early timing goes with lean burns and there has to be enough later burn to push the exhaust out. Elsewhere he explains why lean burns are foolish at idle, but the bottom line is they don't make power. Maybe I can dig that out later and post it up. Tests in neutral do not indictate power.

@71GSSDemon following upo on 512stroker's question. Remind us. Was the vacuum advance connected during this last drive? and if so where?
 
You must log in or register to reply here.
-

Back
Top