|
Re: Nice article on Vacuum Advance from reknowned tech
#126394
09/27/08 01:42 PM
09/27/08 01:42 PM
|
Joined: Apr 2007
Posts: 871
WA 98043
thecarfarmer
super stock
|
super stock
Joined: Apr 2007
Posts: 871
WA 98043
|
Quote:
JUST LIKE CUCU I HAVE 10 LBS VAC AND MY SIX PACK IDLED DECENT BUT WHEN I REV IT THE THING DOESN'T ALWAYS COME BACK TO THE 900 RPM THAT IT IS SET AT AND WHEN I PULL IT IN GEAR THE RPM DROPS TO THE POINT WHERE SOMETIMES IT WANTS TO STALL WITHOUT PEDALING THE GAS. SO DOES THE THE MOPAR PERFORMANCE DIST. HAVE ANYTHING TO DO WITH IT?
THANKS MOPARTS
Quote:
PATRICK
I TRIED NOT RUNNING THE VAC ADVANCE AND IT DOES THE SAME THING. I WILL CERTAINTY TRY WHAT YOU SAY SOUNDS LIKE YOU KNOW MORE THEN I DO. SO WHERE IS THE BEST PLACE TO CONNECT TO A PORTED VACUMN PLACE ON A SIX PACK?
THANKS HAROLD
Sounds like weak/lightweight advance springs.
Been there - done that.
Oh, and the cap lock can be found on the left side of the keyboard...  
About the 'ported vs. manifold' debate... I set my stuff up to run manifold vacuum.
Ported advance is largely an emissions thing. Period. Changing the advance has some effect on HC and CO readings (and if you don't believe me, just hook your car up to a 4 or 5 gas analyzer and fiddle the timing), and a real effect on NOX emissions. The EPA was on car makers in the early to mid sixties, long before we started seeing a whole lot of emissions changes (1970-73 model years).
As far as it being a "Chevy guy" who came up with something... I'll take a look at tech from anywhere I can. Who knows, I might learn something. I mean, look at the amount of aftermarket performance development that the SBC has enjoyed for fifty-three years. Nope, nothing whatsoever could be learned there... maybe I shouldn't listen to Monte Smith either - he sets up nitrous tunes for GMs. 
And Supercuda beat me to the other point I wanted to get to... just 'cause it's the way it was done doesn't mean it's the way it should be done.
One more thing... OE mopar vacuum cans (at least some of 'em) have a small allen (3/16"?) which can be turned to adjust the tension on the spring inside... I've been known to set 'em pretty loose on cars with big cams. Oh yeah, and that's running manifold vacuum.
But I was able to get good driveability out of a '72 318 with a 228 deg @ .050 cam with stock small-bowl convertor and 3.23's in a '66 B-body.
</rant>
-bill
Seduce the attractive, and charm the rest.
******
489 C.I.D., roller cam, aftermarket heads, tunnel ram, stock '54 Dodge rear axle assembly: which of these doesn't belong?
|
|
|
Re: Nice article on Vacuum Advance from reknowned tech
[Re: thecarfarmer]
#126395
09/27/08 04:38 PM
09/27/08 04:38 PM
|
Anonymous
Unregistered
|
Anonymous
Unregistered
|
ONE THING I LEARNED FOR CERTAIN IS THAT I'M CONFUSED AND DON'T KNOW IF I SHOULD PUT VANUMN ON A PORT,ON THE MANIFOLD OR LET IT UNHOOKED AND PLUGED OR PUT LIGHT SPRINGS OR PUT STONGER SPRINGS IN THE DIST. OR JUST NEVER KICK THE OUTBOARD CARBS IN THAT WAY IT SHOULD ALWAYS COME BACK TO IDLE.
HAROLD
|
|
|
Re: Nice article on Vacuum Advance from reknowned tech
[Re: stumpy]
#126397
09/27/08 04:45 PM
09/27/08 04:45 PM
|
Anonymous
Unregistered
|
Anonymous
Unregistered
|
how is this . now i have to put reading glasses on to read this thing
|
|
|
Re: Nice article on Vacuum Advance from reknowned tech
[Re: dave571]
#126399
09/27/08 09:03 PM
09/27/08 09:03 PM
|
Joined: Jan 2003
Posts: 1,066
California
70SportSatellite
super street
|
super street
Joined: Jan 2003
Posts: 1,066
California
|
Quote:
If your vacuum advance is affecting your idle, it's set up wrong.
There should be no vac advance at idle.
70 383 manual trans
Hughes cam lobe lift .326 .349
valve lift .489 .524
duration @ .050 219 228
Initial timing set 20 degrees. 12 inches vacuum. runs hot and rich. pings. new stock dist. ported vacuum.
Switch to manifold, 15 inches vacuum, temperature comes down, idles smoother and cleaner, no pinging. runs strong.
stock build except cam which was degreed during installation. no vacuum leaks. carb rebuilt.
What's wrong with my setup? I will provide more info if needed. thanks
|
|
|
Re: Nice article on Vacuum Advance from reknowned tech
[Re: 70SportSatellite]
#126403
09/28/08 12:51 AM
09/28/08 12:51 AM
|
Joined: Apr 2007
Posts: 871
WA 98043
thecarfarmer
super stock
|
super stock
Joined: Apr 2007
Posts: 871
WA 98043
|
There's nothing being 'masked', just corrected. More cam likes more initial advance, because the cylinders don't fill as well at low speed (which is why you lose low end w/ a big cam). BTW, did you check the balancer for the TDC mark being correct? Just asking - oftentimes 20 deg initial will make the engine kick back against the starter a little when hot. If it ain't doing that, then I wouldn't change the initial. I would, however, limit down the mechanical advance so that the total mechanical + initial comes in around 36 or so in by maybe 2000-2500 (with vac advance unhooked). Manifold vacuum should work just fine; as you've already found out. Now back to the  -bill
Seduce the attractive, and charm the rest.
******
489 C.I.D., roller cam, aftermarket heads, tunnel ram, stock '54 Dodge rear axle assembly: which of these doesn't belong?
|
|
|
Re: Nice article on Vacuum Advance from reknowned tech
[Re: Y3 70 BEE]
#126404
09/28/08 01:14 AM
09/28/08 01:14 AM
|
Joined: Jan 2003
Posts: 5,275
near Harrisburg, Pa
440trk
master
|
master
Joined: Jan 2003
Posts: 5,275
near Harrisburg, Pa
|
Quote:
At WOT there is little manifold vacuum so what happens to all the advance you are getting from the vacuum advance? You could tune it for manifold vacuum but to me you should set the mechanical for 36 degrees or so by 2500 rpm and then run the vacuum to ported and fine tune from there. I use to run no vacuum advance but recently started running it and will run it from now on.
Vacuum advance will (or at least should) drop to 0 at WOT, regardless of where the vacuum advance is hooked to.
Ported vacuum only adds advance under part throttle conditions. Once the primary throttle blades completely uncover the "ported vacuum" port in the venturi, the ported advance will start to drop, until it equals manifold vacuum.
IMHO, Use ported vacuum on anything you drive on the street more than you drive on the track.
If you're only running on the track, don't even bother hooking up the Vacuum advance, as it will do practically nothing in a racecar.
|
|
|
Re: Nice article on Vacuum Advance from reknowned tech
[Re: 440trk]
#126405
09/28/08 07:06 AM
09/28/08 07:06 AM
|
Anonymous
Unregistered
|
Anonymous
Unregistered
|
Well I know one thing with my 440 six pack with 484 cam 915 heads 30 over mopar performance dist. every time i try to set the timing above 14 or 15 deg. with or without the vacumn advance hooked up the thing pings. Still have the problem with it not returning back to idle after i rev it.Running 100 oct. gas so it can't be oct. problem. Have 10 lbs vac. 5.5 power valve and 66 jets in center carb. Really don't know what to do.
Thanks Moparts
|
|
|
Re: Nice article on Vacuum Advance from reknowned tech
#126406
09/28/08 07:59 AM
09/28/08 07:59 AM
|
Joined: May 2005
Posts: 6,446
NJ-USA
HPMike
master
|
master
Joined: May 2005
Posts: 6,446
NJ-USA
|
Quote:
Well I know one thing with my 440 six pack with 484 cam 915 heads 30 over mopar performance dist. every time i try to set the timing above 14 or 15 deg. with or without the vacumn advance hooked up the thing pings. Still have the problem with it not returning back to idle after i rev it.Running 100 oct. gas so it can't be oct. problem. Have 10 lbs vac. 5.5 power valve and 66 jets in center carb. Really don't know what to do.
Thanks Moparts
Forget about the initial timing for a minute.. What is the total timing and at what engine rpm does it come in?? That is more important than what you see initially. The MP distributor comes with very light springs and, if unmodified, quite a bit of a centrifugal advance "window". Judging from what you wrote, I am willing to be that you are WAY overadvanced, if you are setting it up at 15 and you havent "closed" the window. You would be wise to have someone put your distributor on a Sun machine and set the advance curve. The six pack performance engines I build I usually set the initial around 18-24 and heve the total around 35-37 and try to get it(total advance) in at no higher than 1800-2200 RPM. I DO NOT run the vacuum advance. With all due respect to the aforementioned article, the reality is that the article makes NO mention of quality of fuel and it's effect on detonation resistance. In short, the inefficient cylinder heads of the older stuff, along with large swept volume, make it very difficult to tolerate the extra timing that the vacuum advance gives with the junk that's pumped from the local filling station.
If your idle problem still persists, I would be willing to bet that it can be trimmed in by the outboard idle screws.
MB
|
|
|
Re: Nice article on Vacuum Advance from reknowned tech
[Re: HPMike]
#126407
09/28/08 08:29 AM
09/28/08 08:29 AM
|
Joined: Jan 2003
Posts: 20,185
Park Forest, IL
slantzilla
Too Many Posts
|
Too Many Posts
Joined: Jan 2003
Posts: 20,185
Park Forest, IL
|
My little Slant has a .558"/300* camshaft in it. To get it to idle at all, especially when I back the total down to 25* to spray it I had to weld the advance slots about halfway shut. I run 15-20 initial and 25-30 total. Vacuum advance is not hooked up because if it doesn't pull off at WOT you can have "issues" with spray. I also run light springs. It will turn over and start, but as soon as it revs up much at all it is at full advance. That doesn't bother me though because I have a 3800 converter. 
"Everybody funny, now you funny too."
|
|
|
Re: Nice article on Vacuum Advance from reknowned tech
[Re: captaindodge]
#126409
09/28/08 11:42 AM
09/28/08 11:42 AM
|
Anonymous
Unregistered
|
Anonymous
Unregistered
|
The article points out a lot very good points that some of us have been pushing here for a long time. The biggest of those points is that EVERY ENGINE IS DIFFERENT and needs to have the vacuum advance turned just as you would a carb. The fact the he is talking GM probably makes it LESS important to him than most of us, because Chevy went to faster burning combustion chambers quite a bit ahead of MOPAR, if I remember right.
What it boils down to is to set your mechanical advance to match the burn rate of the engine. For instance, older MOPAR heads (like X heads) like the old standard 36* total. If youl use the newer style (like 302 heads) you will probably be closer to 30*. Once you get the mechanical done, you can do the vacuum. As the article said, get a can that is not on at your idle vacuum (if you use ported), but close to it. I haven't looked lately, but you used to be able to get a lot of different regular and adjustable cans. To set the vacuum advance amount, I have found exhaust temp to be a very good way. Pick a good speed (highway cruise is good) and vary the timing to get the highest EGT and then set the vacuum to give you 2-3 degree less than that. Usually this will be all you need to do to be where you need to be. You will find, I think, the faster your burn (tight quench, high velocity and swirl), the less of the vacuum advance you will need, because of the fast burn rate of the well agitated and mixed charge.
When I ran X heads/no quench I needed upwards of 45* (mech + vac), but with the 302's it is in the low 30's.
Personally, I like the ported setup, as it can be made to run well, and also makes the engine start easier with less load on the starter.
|
|
|
Re: Nice article on Vacuum Advance from reknowned tech
[Re: Supercuda]
#126410
09/29/08 12:27 PM
09/29/08 12:27 PM
|
Joined: Jan 2003
Posts: 4,153
Canada -- Posts: 4034 -Registe...
5thAve
Doesn't care what this says anyway
|
Doesn't care what this says anyway
Joined: Jan 2003
Posts: 4,153
Canada -- Posts: 4034 -Registe...
|
Quote:
Quote:
I was going to say it looks like a chevy guy wrote that and then someone said thats where it came from. So just ignore it and stick with ported vacum because thats how things were designed and thats what works.
careful, take this "logic" to it's full potential and we should run stock cams, carbs, etc because of this thinking.
It's all in the tune. I have had 30's and 40's Mopars and I don't remember if they were ported or manifld vacuum, I could look it up I guess.
I tried manifold vacuum on a mild 360 setup I had, only because I mishooked it, not on purpose. My idle speed stting was all over the place and nothing I did seemed to stabilise it. maybe that Echlin can wouuld be the ticket, but I found the problem, hooked the vacuum advance to ported vacuum and all was well.
We're talking about distributors and vacuum advance not cams carbs or anything else. If you want to throw your logic in there you can add a lot more to that list but this post isnt about any of that. And in the end ported vacum is what worked for you so the point of all that is????
|
|
|
Re: Nice article on Vacuum Advance from reknowned tech
[Re: stumpy]
#126412
09/29/08 04:31 PM
09/29/08 04:31 PM
|
Joined: Jan 2003
Posts: 1,359
Buzzard County, FL
IronWolf
pro stock
|
pro stock
Joined: Jan 2003
Posts: 1,359
Buzzard County, FL
|
Quote:
Back off the initial timing. Should be 12-15* with the vacuum advance disconnected. Then hook the advance back up.
This response is correct. Unless you do NOT care about fuel mileage. Listen to the man.
|
|
|
|
|
