Printable View
Hiyall,
I'm wanting to re adress my centrifugal advance on my Chevy HEI distributor.
Does anone know the optimum curve? When they should start advancing? How far should it advance? I been just changing springs around and testing it out but i'm tired of guessing, I guess.
Static advance is 12 degrees BTDC. Stock cam n crank timing. Stock vaccum advance. Car is red :D
Ooops yeah,
It's the 76 Monte, 350 4bbl THM 350 tranny with a stage 1 shift kit.
I recently did the same thing on my '76 Monte. I got the best results from this combo: 16 deg base timing, 20 degrees mechanical starting around 1000 rpm, all in by 2800, and 15 degrees vacuum advance.
Try to shoot for 52 degrees of total timing (base + cent. + vacuum advance)
The trick is to get all your timing in at an RPM that is reasonable to you, and not advanced to the point that you have pinging and hot-start problems. I spent an entire weekend tuning and tweaking to get my car where I wanted it. Somewhere I have a link that gave me all the information I needed. I will look for it. I don't think I can post it here since it is from another forum. (I think this violates forum rules, someone correct me if I am wrong) If I dig it up, I will send you a PM
Making these changes made a HUGE difference.
Dang! 52 degrees total timing? I think i'm sitting at 45 now and it makes people cringe.
However, i'm gonna try it and let them try to stop me.
Thanks for the link!
52 degrees on an sbc????? Better recheck that. I would think 8-12 degrees base timing, then all the advance in somewhere around 2800. If you check it with a light that has the advance knob on the back I think you'll discover it's around 32 to 36 degrees total...
Base timing is set with a light with the vacuum unhooked, then reconnect the vacuum and the vacuum advance and the mechanical advance combined will pull around 24 to 26 degrees for a total of 32 to 36 degrees. At 52 degrees of timing as measured with a light, don't think you'd even be able to keep it running, but if it did it wouldn't run for long.......
Do you mean "TOTAL" total? Or just "initial and mech" total?Quote:
Originally Posted by DennyW
I dont think that sounds unreasonable (52 deg). I think what he is alluding to is cruise/no load timing such as the highway where he might be running @ 2900rpm or so, initial + mechanical +vac adv puts you right in that ballpark wouldnt it?
Case in point, and tell me where this goes wrong....
'69 350cid, 255hp (extracted from a MOTOR's Manual)
Initial timing is 4deg BTDC
Mech is 32deg @4400rpm (crank degrees, advance starts around 1000)
Vacuum advance is 24deg at 13" vacuum
So at 4400rpm cruise, it would be 4+32+24 = 60 degrees assuming 13" of vacuum
Backing down to 3000rpm...you have 4+18+24 = 46 degrees total timing.
Okay, not quite 52 degrees :rolleyes: , but more than 36 degrees. Point being, if the car is tuned to run lean and clean, should it not be able to handle the extra timing at cruise?
Just to clarify what you said Denny,
Trying to clarify where you are talking crank degrees and where you are talking distributor degrees...thanksQuote:
Originally Posted by DennyW
The mechanical and vacuum advance was given in distributor degrees which I doubled to give the "as seen at the damper" degrees.Quote:
Originally Posted by DennyW
4 + (16x2) + (12x2) = 60 (assuming at 13" of vacuum is present)
BTW: thanks for the clarification in your second post. I think maybe the gorilla in the picture typed the first post? :rolleyes: kidding...:LOL:
Dang, I think i'm getting it now. Well, at least i'm not going to yank the stinking cap off again for a while.
Now, I got my crank timing set at 12 degrees BTDC with the vaccum advance unplugged. The weakest springs I got will start the centrifigual advance a 900 rpm and advance 20 degrees to 8000 rpm.
I'm using one of those.
The next spring starts at 1600 rpm and advances 15 degrees total at 6000 rpm.
I'm supposing my real advance is somewhere in between then.
I donnou if I even see 6000 much less 8000 rpm.
So, ballpark advance on the weights would be 16 degrees starting at 1100 rpm? With the springs I got right now?
Sooo, mine would be 12+16+15= 43 degrees? Am I right?
Quit the math games and either put a timing tape on your balancer or borrow somebody's light that has the timing advance knob on the back.... I seriously doubt your springs are advancing near that much. You will find that the springs advance simultaneously, not separately. Read your real timing at the balancer and the timing mark to see what the actual advance is....
Yes, one spring starts advancing at 900 rpm at 20 degrees at 8000 rpm and the other starts advancing at 1600 rpm at 15 degrees at 6000 rpm. I'm just splitting the difference. At least this chart I got says so.
All I could find this week was a single action point and shoot timing light as my other one is in Ireland.
Tape won't do me good cause I got one of them fully illuminated genuine chromium plated accessory timing plates that cover the whole dang harmonic balancer surface right to the very end an all you see is a teeny speck of the timing mark.
Now, I know i'm just making excuses and of course, Mr Severson is elevated and correct and of course would end all the guesswork out of total timing.
But I can't help feeling deflated like a total failure so if you'll excuse me I will now go ask my wife to beat me senseless with my new useless timing light. I will return if I survive.
Not putting you down, just hate to see someone get stuck on the math and book stuff instead of the "real" stuff....
I would say have all your advance out by 2,800 rpm's.
I would try total timing of 33-36 degree's
Some days your reading comprehension is really off....New Meds????Quote:
Originally Posted by DennyW
MEDICATION TIME!!!:LOL:Quote:
Originally Posted by Dave Severson
Aww don't mind me i'm just pouting cause I gotta go buy another timing light and spend $100.
Bout the only way to know really.
Thanks.
I meant for me.:LOL:Quote:
Originally Posted by DennyW
I painted it silver an it still shows up. Just a sliver of it though. That stupid aftermarket pointer about covers it up.
PS, My wife had a different suggestion on what to do with my new timing light. Personally, I think it's anatomically impossible.
Am i gonna have to seperate you two again?
Im sure there is a website out there where this has been done!! :CRY: But i would not recommend trying it at home:LOL: :LOL: !!!!Quote:
Originally Posted by Good Wrench
TRASH Reply's Like this one ! Is the # one reason so many Members have to go to other Forums to get there info . Dave you really need to Clean it up ( NOW ) :mad: NOT COOL / SB Chevy TangoQuote:
Originally Posted by Dave Severson
What I said was don't get stuck on the book stuff, then of course you took that to be no more book stuff...... See the difference???? Just a comprehension deal, or reading things in to what I wrote..... whichever..... My complaint is that people can't take things the way they're wrote..... It seems Good Wrench understood and it's his thread so I guess that's all that counts,..,,,,,Quote:
Originally Posted by DennyW
Quote:
Originally Posted by DennyW
The link is from another forum. I was trying to avoid any mud-slinging. But...here is the link. I found it to be VERY helpful.
http://www.chevelles.com/forums/show...t=ignition+101
I'm not going to argue with anyone, I can't say that I know as much or more as some others here, but I know how I set my timing, and it is working for me. I was a little surprised with the results too.
Bingo. We are on the same page.Quote:
Originally Posted by 65cayne
And BTW: I used a timing tape.....no guesswork.
HIya Denny if your still on.....
OK Got the $^#$% timing light...
12 degrees initial...
19.3 @3000 RPM no vaccum advance
36.6 @ 3000 RPM with vaccum advance.
Changed springs in centrifigul advance to play out at 23 degrees @ 3000 RPM
Once again I mixed springs, one medium, one light.
Total advance now is 39.9
Too much?
Yeah, thanks!
Now if I may ask a real stupid question. In college I set my timing by the book and it was usually 8 BTDC on Chevy motors. But I personally have always kept it on 12 BTDC.
I never really got this down.
Is there an optimum setting? I know it depends on everything else but just general?
It was mentioned to set initial timing at 16 BTDC but it tends to fire through my carb on occasion. In cold weather.
Ohh not to get off subject but what temprature range should the engine run warm at?
160? 180?
Mines usually 130.
Thermostat works too.
Ahhh, OK. Yeah, You see the car kinda stumbles in cold weather. Choke works fine,
When I put the engine together I did everything i could think of to keep it as cool as possible. I got a Milodon deep sump oil pan that holds 12 quarts of oil, a high volume oil pump to move it around. One of them fat desert cooler radiators with all the fins in. A flex fan with the stock shroud still in, a transmission cooler and I painted the engine black. Best I got was 145 temprature at the radiator. Ususally the under dash mechanical gauge barely lifts off the peg at freeway speed. Most I seen it rise was 130.
Thats probably whats throwing me off then.
All these years I just had only the stock dash idiot light. Now I know.
Now, do I try to make it run hotter or do something else?
Hiya Denny w,
I got 2 temp gauges on the car and both say average 130 degrees. Goes up to 140 if I keep revvin the engine but cools back down. My lovely wife checked as well on one while I did the other. Thermostat is recent.
Well, I redid initial timing to 8 degrees an got 35.6 total timing. Gonna try that an see wot it does.
Here's another wrinkle, I hooked my vaccum gauge to the carb and i'm only pulling 16.2 inches of vaccum at idle. I pulled off all the leeches on the vaccum and it remains unchanged. I reset the idle mixture screws, no change. I changed around the timing. No change.
The heads have been recently rebuilt and the car usually runs as smooth as a cats back. So, no lope. Just developed an off idle stumble, or mini surge. But yesterday morning the car ran as smooth as silk. Got the stumble early in the morning with outside temprature at 25 degrees. Had the heater on. No reading on the uderdash gauge.
A surly fellow at the speed shop said to configure my 1406 carb to 1405 specs. This I have done as close as I can.
.98 jets .075x.042 needles, orange 5 kg springs.
I tell ya, i'm getting kinda confused now.
Will test it out though. See what it does.
Wish I was rich enough to run the Holly again. Dumping huge amounts of gas down that engine makes it run lika scalded chicken. An no problems.