Mechanical Advance Timing
The engine I purchased online (350 sbc) has a mechanical 4 degree advance (in the timing chain) which I verified manually.
So, next step is to do the timing and I need some assistance.
For a stock chevy engine advance is 6 degrees, so, for this engine do I:
1. add the 6 degrees to the mechanical 4 degrees for a total of 10 degrees.
2. put it at 2 degrees with the thought being that it is 4 degrees below zero (retard) so plus 6 is 2 degrees
3. other thoughts are appreciated.
Mechanical Advance Timing
Here is an a good article to read before you begin to fine tune your 350 Chevy. http://www.crankshaftcoalition.com/w...EI_distributor
We need info. Are you talking about degreeing in your cam or setting up your ignition timing?
Even though changing the cam timing (or "phasing") also changes the ignition timing (if the distributor were installed when the cam timing was changed), cam timing is a separate issue from the ignition timing.
So in your case, you can ignore the amount of cam timing change you made w/the timing gears when it comes to setting the ignition timing. In other words, nothing needs to be added or subtracted from the ignition timing, regardless of where the cam timing is set.
In most cases, the cam manufacturers design the cam w/some amount of advance already "built in". The cam card specs will show this. This means in most cases, installing the cam straight up (no advance or retard) is the best way to go.
For the ignition timing, you can use more than 6 degrees BTDC in almost every case. The page cdminter59 linked to has info on setting up the distributor w/an advance curve suitable for how the vehicle will be used and the other things that need to be considered.
What cam is in the engine? Do you have the engine specs?
Hello and Thanks for the information sofar.
Greg T; I am looking at Ignition timing.
I am new at this so bear with me. With the help of some friends we got the engine working about 6 months ago and it has been running ever since but it has been bothering me that it just does not seem to be running totally ok. I.e. I get lots of pinging at WOT. So I decided this week, since I'm off, to redo the timing from scratch and educate myself on how that works. I was using another article but I will review the one provided as well. (http://www.crankshaftcoalition.com/w...op_dead_center).
The first thing I did was pull the plugs and took them to the engine building shop for this engine to have them take a look at them. They said they were fine and when I explained the pinging at WOT they indicated it was likely a distributor problem and to look at that next. Since the distributor I used came from questionable origins (i.e. it came out of an older chevy truck sitting around for years but I did update the modules inside) I decided to purchase a new MSD one (should arrive in a couple of hours). I then also decided I may as well refresh the wires and plugs. The plugs I used before are R45TS and, for now, I will stick with the same ones. (although I am working on figuring out if the stock Gap is correct - 0.40).
Late last night I used a stop piston tool to set my TDC acurately and it showed on the timing tab that it is set at 4 degrees advance. I then recalled the guy who sold me the engine telling me that it has 2 advances in the timing chain built into the engine. (which I read equates to 4 degrees). No information was provided by the fella on why he did that (as I read this is now typically done through the cam's) and I don't know where he is anymore to follow up so it is what it is and I'll work with that.
So, that's is where I am at right now. In discussing this with the boys over drinks last night as to the next steps we came up with the question I posed; which is, how do I do my initial timing after the new distributor is in and how does the built in advance affect that.
I should also mention that when I look at how the current distributor is installed it looks like it may be off by a tooth or two towards the 8 cylinder.
The plan following, after initial timing was done, was to then run the engine and start working on the next steps to fine tune the timing (lots of reading for me to understand it I'm not in a rush on this).
Here are the engine specs that I received from the guy:
rebuilt V8-350 4 bolt main.
Stock bottom end but rebalanced and new seals/bearings.
Heads: high output 416 heads unshrouded with large valves
Cam: 450 lift, 224 duration, 206 lobe centre.
Ignition - standard HEI
Intake - edelbrock performance intake
Holley 600 street carburator - pn 0-80457S
I use 94 octane Sunoco fuel.
Thanks Again for your assistance!
Ok, did lots of reading up and it's all figured out now.
1. ignored the advanced timing in the chain
2. Installed new MSD distributor as per proper distributor setup (i.e figure out TDC and point rotor to #1 cylinder)
3. Changed springs in distributor to ones that will give me full timing at around 3000
4. Removed and plugged vaccum advance
5. started engine and set BTDC at 12. (made sure idle was below 800)
6. rev'd to 3500 (timing was not increasing around 3000) and adjusted timing to 36.
7. back down to idle and noted idle timing is now 18.
8. took her out for a run and she had lots of power and no pinging.
Next steps is for me to figure out what the weights do to the setup that came in the advance timing kit from MSD p/n 8428 and whether I even need them. (springs are already in)
I then also need to figure out if I need to adjust the stock vacuum advance settings and whether I need to put in the vacuum advance stop or not. Any help is appreciated.
With the vacuum advance connected and the engine speed high enough that the mechanical advance is all in, the amount of timing you see should be in the area of 46-50 degrees. This usually requires using the stop plate to keep the vacuum advance from adding too much timing. The page cdminter59 linked to below has info on setting up the distributor w/an advance curve suitable for how the vehicle will be used- including the vacuum advance.;)
Vaccum and mechanical advance
Thank You cobalt327 and f-bird'88; I'll read the details and work on that next weekend. Cheers.
Advance travel stop
F-BIRD'88, I have confirmed out total timing is 36 BTDC on the timing tape and idle timing is at 18.
On your sentence
Also, F-BIRD'88 and COBALT327, on the vacuum advance, I read the part in the article below but have not yet tackled that. Adding what you said makes total sense; I just now need to figure out how to read what my vacuum is before I install the vacuum advance stop plate (if needed) and setting the appropriate curve.
I am thinking of attaching a vacuum gauge to the port and then going through some driving scenarios and recording the numbers to see where I'm at - does that sound reasonable or is there a way to do it in the driveway (i.e. does the engine need to be under load?).
btw, I am using the ported vacuum port on the holley.
I have included a copy/picture of the vacuum advance settings for my HEI distributor; does the degree column correspond to initial timing? (in which case my row would be the 18 degree row). It doesn't say how many turns the canister has when you buy it though but it looks like the max is 15 degrees so at least I won't be over the max.
Hmm, sparkplugs is another whole research I'm working on. I currently run AC Delco R45TS's gapped at 0.45 because, well, I had to start somewhere and that seemed to be the consensus out there for non-boosted chevy's but I now need to understand why. Why such a cold plug F-BIRD'88? every article I have read says at most a R43 for a chevy and down from that only if you have boosting.
I did read that you can check your plug to see if it is fouling (too cold) or melting (too hot) and the old ones I pulled out were perfect so I stuck with the same one. Once I have the engine timing perfected (which is looking really soon!!) then I plan on playing with that.
I found the following method to determine gap:
A 750 holley is in the works as budget permits :D
As always, thanks for the help! it is much appreciated. :thumbup:
LOL :D, Thanks for that, I needed it. Your absolutely right, my current career (in computers) requires me to read manuals all the time as technology changes daily so I tend to think the same about cars; read all you can about it, make a decision and then try it out. Unfortunately the information out there is sometimes contradictory or, worse for me, accurate for different reasons not clear to me yet.
I just noticed one other item; what you indicated is not an 'extended' plug. Any particular reason?
Also, F-Bird'88, can you answer my question re: Vacuum advance and my confirmation request on the timing below please. If I can get that completed during the holiday weekend it will be a very productive one indeed.
DRive with a vacuum gauge taped to the windshield. That lets you know what cruise vacuum is. The vacuum cans are rated, and are avalible to match the driving conditions you have and ammount to correct the curve. Or use the crane adjustable one and that has a adjustment chart.
Mecahnical timing is rpm dependant. No chassis roller is needed.
Thge timing , reading, and plug addvice is spot on. Fbird knows.
I taped the vacuum gauge to the windshield and went for a drive in a number of conditions (fast, slow, slowing down from fast, up a hill, down a hill, cruising at 60mph on a highway, etc) and my trusty sidekick (da wife) noted that the highest the vacuum went was 18.
I looked into the vacuum can that came with my new MSD 8362 and they are no longer adjustable but MSD provides a stop plate that, depending on how you install it, will limit your vacuum advance.
There are 4 positons it can be installed in, A=14 to 17 degrees, B=11 to 14, C=8 to 11 and D=5 to 8. I'm going to install it as B as that will ensure it does not go over 15.
That should then complete my timing setup and now next steps are the Holley finetuning... Idle Mixture, secondary kickin, verify power valve, verify transfer slot is not too much, off-idle setup, etc. Lots of reading to do..
BTW, ordered the Champion RV8C spark plugs, will be in later today.
There is no need to redo any timing type work is there when you change plugs that have a different gap?
Nope. Just plug and play. I don't know about anyone else, but i always put a drop of anti-seize on the threads when installing plugs. Makes them much easier to get out later on.
Hi, I need some help with the timing, it is too high and I'm not sure why.
Before working on the vacuum advance setup I went and verified the total timing set last week and at 3000 rpm it was 36 degrees but when I went up to 4500 it went to 45 degrees! does that mean I didn't have it yet at 'all-in'? I used the MSD medium springs that are supposed to have all-in by 3000 rpm.
I don't recall how high we went last week but I do remember watching the timing and it stopped increasing between 3000 and 3500 so I assumed I was good.
Does timing increase again when you get into the high, close to WOT, range?
I then did an experiment and removed the springs in the distributor; the thought being that it will go 'all-in' to maximum timing at a lower RPM (4500 is awefully loud in a garage) and it immediately went to 55 degrees (at 1500 rpm), increasing to 2500 rpm still kept it at 55. That's crazy and does not make sense; the MSD 8362 is supposed to have a maximum mechanical advance of 21 degrees which should have made my total of 18 idle plus 21 be no more than 39 so where do the 55 come from.
I did ensure that the vacuum advance was closed off at the can and at the Carb so as not to affect this.
Any help is appreciated.
Ps. it idles at 18 degrees fine, no stumbling or anything. 18 is what it ended up with after my initial setting of 12 when we did our total timing setup last week and thought we had it at 36.
I confirmed my TDC at that time (using the piston stop tool method) to be correct and I have a timing tape installed on the balancer.
|All times are GMT -6. The time now is 10:16 PM.|
Powered by vBulletin® Version 3.8.7
Copyright ©2000 - 2015, vBulletin Solutions, Inc.
Search Engine Optimization by vBSEO 3.6.0 PL2
Copyright Hotrodders.com 1999 - 2012. All Rights Reserved.