Ported vacuum advance or manifold. Let's debate!
- Thread starter Kern Dog
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Dragon Slayer
Well-Known Member
Go read my post in the correct hemi carb discussion, I explain it there. It doesn't matter what you measure, it is how the current manufactures describe it. Bores for actual 3/4" or 13/16" pumps are larger.
Thank you all for the great info. on this subject. You gave us all alot to think about with the vacuum advance system. I feel like I have a better understanding of how it all works now. I look forward to trying some different things out in the future.
I did make a short try with it. I think the vacuum can has a bit two much advance to work with it on this car. With 15 deg base timing I had 36 to 37 degrees advance running at 1100 rpm idle. This 66 Hemi car has the air valve idle speed adjustments and I closed them down to about 1/8 turn open and wasn’t getting the idle down so I discontinued after a short drive. The car drove fine, just didn’t like the hanging idle.
The next time I have the distributor out I’ll look at it to see if a limiter can be made to cut down on the amount of advance. I think the adjustable cans just change the amount of vacuum pull they start responding to if I remember right.
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And to continue to stir up the controversial subject pot, several additional talking points to ponder......best spark plugs, best oil brand and viscosity, cam, ported vacuum advance vs manifold vacuum, best beer to drink or whiskey or pizza or the basic fundamental understanding of Thermodynamics relating to vehicle cooling sydtems OR the real pot stirrer.....Green rear axle bearings vs Timken tapered axle bearings.......now......let the word wars begin......and the "the way I do things is better than your way".......
BOB RENTON
Hemirunner
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We’ll need a few Krekel burgers and a custard to get through all those subjects!!
Wietse
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Like the current conversation is not bad enough yet.....
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Geoff 2
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DS,
Post #82. I take your point about 'current' manufacturers. Jon Hardgrove, owner of the Carb Shop, bought all of Carters old stuff including blueprints etc. He lists 4 sizes of pumps for WCFB, AFB, AVS; 23/32" is not one of them. So the sizes I quote are based on Carter sizes.
There was an AVS used here on 245 in line six by Chry Australia that had a 46XX number & I no longer have one but I am pretty sure it had the 13/16" pump.
Post #82. I take your point about 'current' manufacturers. Jon Hardgrove, owner of the Carb Shop, bought all of Carters old stuff including blueprints etc. He lists 4 sizes of pumps for WCFB, AFB, AVS; 23/32" is not one of them. So the sizes I quote are based on Carter sizes.
There was an AVS used here on 245 in line six by Chry Australia that had a 46XX number & I no longer have one but I am pretty sure it had the 13/16" pump.
Dragon Slayer
Well-Known Member
Yep but he does not show pumps separate or discuss measurements other than generic. He also does not make his own parts. Maybe gaskets but not hard parts. He is really only into selling kits now a days. So Walker, ACE and maybe someone else are the manufacturer that all the parts houses are using. Walker catalog is good, Mike and Quadrajet have good sites with documented spec. But again, we are down to about 8 Accelerator pumps to cover about a 150 + different carter part numbers. Mopar AFB used only 3 and 1 was only in early carbs. So either 212 with anti perc, or the 279 performance with no perc head. AVS did introduce more part numbers in 69 models.
I have documents on early pumps and carter would specify the shaft part number, type of spring, spring dimension, even down to the type of plating on the spring, but they never gave a specific diameter dimension. Only overall length of the pump. That is why I measured part dimensions, length, collapse length etc... of original carter pumps. So at least I can do an apple to apple comparison on the new stuff.
I have documents on early pumps and carter would specify the shaft part number, type of spring, spring dimension, even down to the type of plating on the spring, but they never gave a specific diameter dimension. Only overall length of the pump. That is why I measured part dimensions, length, collapse length etc... of original carter pumps. So at least I can do an apple to apple comparison on the new stuff.
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Krekel burgers are excellent as are Culvers offerings......although I own MCD as well as AAPL....all provide a satisfying experience....."food" for thought......
BOB RENTON
71scgc
Member
Run what you're comfortable with.
I do find the big shift from manifold to ported occured when people were looking for fuel economy and manufacturers were looking for better emissions numbers.
My Savoy has no vac advance. That's a new wrinkle for me, but it'll give me something new to study. Any increase in knowledge is beneficial, sometimes even fun.
I come mostly a sport car and Corvette background. One of the tuning gods in the old Corvette world, Lars Grimsrud says to go manifold vacuum 99% of the time in these old cars we love. And let's face it, the engine doesn't know if it's in a Corvette, a Yugo, or a kikass Max Wedge Plymouth. I tend to agree with Mr. Lars.
I'm running 52* total advance in my 1965 396 Corvette. I define total advance as Initial (on the balancer), centrifugal (from the distributer weights), and vacuum (from the can on the distributer). I know y'all are knowledgeable enough to not need that, but many folks refer to total as just initial and centrifugal. Never saw much sense in that, as it leaves a significant variable out.
I also run 52* total on a 400ci small-block Chevy engine I built. It's about 500-550 horse and torque. Runs great at that level of advance. Still, I'd love to have an extensive dyno session to really dial it in (in all aspects).
Right now, my Savoy needs that worse.
So, run it how you're comfortable, and satisfied with the performance, whether you measure that by power, fuel economy, emissions or any other metric.
Most importantly, enjoy your car. Enjoy every part of it. Driving. Wrenching. Racing. Cruising. Showing. All of it.
Carter
I do find the big shift from manifold to ported occured when people were looking for fuel economy and manufacturers were looking for better emissions numbers.
My Savoy has no vac advance. That's a new wrinkle for me, but it'll give me something new to study. Any increase in knowledge is beneficial, sometimes even fun.
I come mostly a sport car and Corvette background. One of the tuning gods in the old Corvette world, Lars Grimsrud says to go manifold vacuum 99% of the time in these old cars we love. And let's face it, the engine doesn't know if it's in a Corvette, a Yugo, or a kikass Max Wedge Plymouth. I tend to agree with Mr. Lars.
I'm running 52* total advance in my 1965 396 Corvette. I define total advance as Initial (on the balancer), centrifugal (from the distributer weights), and vacuum (from the can on the distributer). I know y'all are knowledgeable enough to not need that, but many folks refer to total as just initial and centrifugal. Never saw much sense in that, as it leaves a significant variable out.
I also run 52* total on a 400ci small-block Chevy engine I built. It's about 500-550 horse and torque. Runs great at that level of advance. Still, I'd love to have an extensive dyno session to really dial it in (in all aspects).
Right now, my Savoy needs that worse.
So, run it how you're comfortable, and satisfied with the performance, whether you measure that by power, fuel economy, emissions or any other metric.
Most importantly, enjoy your car. Enjoy every part of it. Driving. Wrenching. Racing. Cruising. Showing. All of it.
Carter
Geoff 2
Well-Known Member
Carter [ Great name! ].
52* at cruise [ Init + VA + part/all centri ] is not that high. Comp ratio, cam size, chamber shape etc all have an impact on total cruise timing.
Take a low comp ratio engine with a cam that has a lot of duration/overlap; although the cam is probably a poor choice, the owner might want to stick with it & up to 60* at cruise might be reqd.
52* at cruise [ Init + VA + part/all centri ] is not that high. Comp ratio, cam size, chamber shape etc all have an impact on total cruise timing.
Take a low comp ratio engine with a cam that has a lot of duration/overlap; although the cam is probably a poor choice, the owner might want to stick with it & up to 60* at cruise might be reqd.
Dragon Slayer
Well-Known Member
Words and definitions matter. Total is considered to be max timing at high rpm, without vacuum. Vacuum would normally be off at that point in the rpm range. So some folks would raise an eyebrow with that number in a normal carb engine. Because if you actually had 52 total at max rpm chances are your damaging your motor. At Mid rpm cruise, a whole different thing, but folks don't normally call that total timing.
Now it is getting confusing again. How could the timing be higher at mid RPM than at max RPM? Centrifugal is all in around 3000 and it doesn't go down. It must be the vacuum can pulling it progressively more as RPM increases, then dropping off at WOT. Does manifold vacuum drop after a certain point?
Wietse
Well-Known Member
Your initial and mech advance are only applicable at WOT, the mech advance curve will increase timing until it is all in.
Say at 3000 rpm it is all in, it stays the same from there on.
Things change at partial throttle, then the v-can comes in to play and provided additional advance depending on manifold vacuum (engine load) and could result in higher advance than the WOT timing.
Dragon Slayer
Well-Known Member
Yes. At WOT you have very little to no vacuum so vacuum advance is 0. So your total timing is initial and mechanical, which is all in. At mid throttle and cruising which is low load on motor, you have motor vacuum and you have vacuum timing added. So you now have Initial, mechanical, and vacuum timing which is usually greater than total timing of 35-37. Which is what the motor wants for cruise. You need more timing.
Mechanical timing makes adjustment based on motor speed. (RPM)
Vacuum timing makes adjustments based on motor load. (Vacuum)
Those two factors determine what the best timing is for the motor.
Go find the Chrysler training documents on google. I think the Imperial site still have them listed. They have a great training document/video on motor timing based on operating condition and why.
Mechanical timing makes adjustment based on motor speed. (RPM)
Vacuum timing makes adjustments based on motor load. (Vacuum)
Those two factors determine what the best timing is for the motor.
Go find the Chrysler training documents on google. I think the Imperial site still have them listed. They have a great training document/video on motor timing based on operating condition and why.
Dragon Slayer
Well-Known Member
Hemirunner
Well-Known Member
Total timing is simply the total timing seen by the engine at a given time under a given set of conditions. It doesn’t specifically refer to WOT and doesn’t dismiss vacuum advance. If manifold vacuum is zero at WOT, then it obviously wouldn’t contribute to the number calculated as total timing. Most would probably be surprised at what their manifold vacuum is at WOT throttle as the assumption of zero is not always correct.
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