Right now I just have a mild 74' 350. It has an edelbrock 600 cfm carb, mild cam, and aluminum intake with stock heads.

I have heard many say where a good place to start for timing is, but still how do you know thats ideal for the engine? I drove the car and advanced the timing by hand until I got pinging, then I backed it off until the pinging was gone. Isnt this the best spot for the engine? Dont you want it to be as advanced as possible as long as it doesnt ping? Wont this give me the best power and mileage? So how do you guys know your dead on? Thanks, Brett

A nice place to start is with the vacuum advance disconnected set your initial timing at 6* BTDC. You cannot go wrong there. Anything after that is experimentation.

I ran mine on a chassis dyno to see what was best. Mine ran best at 36 total. I have 20 initial because of the big solid cam I run. It will not run below 16 initial so I have the dist setup this way. I run no vacuum advance. It makes 409 RWHP out of a 385 SB motor. Every car will be slightly different but 36 is a good starting point. You want to see where your total advance is without the vacuum advance connected. Set up your total advance to 34 to 36 all in by 2500 rpm. Let the initial advance fall where it is. The total is more important than initial. Most SB Chevys will make the most power at 34 to 36 total. Some cylinder heads will need slightly less and if you get into nitrous and blowers that is a whole different story.

AN AFTERMARKET NON GM STOCK PERF CAM MILD OR HOT NEED APPROX 18 DEG INITIAL ON AVG.

Running stock GM initial ign timing settings like approx 4-6 deg btdc with a mild perf cam with more duration then stock is too retarded so crank the initial up to 18 deg.

A good place to start the ign timing curve for most mild to fairly hot SBC/BBC is 18 deg initial,18-20 mechanical(all in by 2800-3k rpms) for a 36-38 total . You should also go with a vac advance to give you approx 50-54 deg while at part throttle/low load situation like when crusing at a steady 55-60mph.

Scott

It is really best to set your final timing (without vac advance) and then make adjustments if necessary to the mechanical advance to change the initial.

It is really best to set your final timing (without vac advance) and then make adjustments if necessary to the mechanical advance to change the initial.

This brings up more questions though. How do I know that that much total is what it likes? So say I set the total advance to whatever, still how do I know the motor likes it? Sounds like the only way to really get it perfect is a chassis dyno. Right?

Brett,
This is one of the best books I have ever read on the subject. If you are serious about tuning your ignition, buy it .... you wont be disappointed.

http://www.amazon.com/Doctors-Step-Guide-Optimizing-Ignition/dp/0965085600/sr=1-1/qid=1169422659/ref=sr_1_1/102-9502813-1971361?ie=UTF8&s=books

This is how you set your timing:

Disconnect and plug vac advance line. Rev motor till you see the advance stop advancing - and rev it hard to make sure, as some advancing don't come in till ~5000rpms (especially stock GM dizzy's). From a performance standpoint, you want all your advance to be in by ~3000 roms. Set the total timing to 36* (a good if not perfect base line), and leave it. You have no choice, that's it. That should give you approx 14*-16* intial timing. If you want to have more initial, you must have the dizzy modified.

IMHO you should NOT set the timing using the Final method with your mild non stock perf cam.

What often happens is when you set timing as final/just total to lets say 36 you can then end up with the initial way too retartded like approx 8-10 deg which is too retarded.

This depends on just how much mechanical advance you have to begin with but you just about always end up with a retartded initial going this route.

Getting the mech advance dialed in correctly is very improtant because if for example the mech adv has 25-30 deg (which some stock dist have) then when you set the final/total to 36 deg you only have approx 6-11 initial which is running anywhere from 7-12 deg retartded for the initial in that case.

Running 7-12 deg retarded on initial timing gets you a soggy bottom end & poor throttle responce,lost power,wasted fuel,and a hotter running motor.

The CORRECT WAY to do it is have the mech adv recurved/limited to approx 20 deg (all in my 3k rpms)to run with 16-18 initial for a 36-38 total along with a vac adv with your setup. But you may have to tweak the initial a deg or so adv/ret depnding on your setup but this setup will get you very close for a starting point.

It's a little more time consuming to do this dialing in process then setting the timing the final way as was suggested above which is a quick & dirty way to do it. Its up to you how you want your motor to run,like a slug due to retartded initial timing or run well due to the initial & mechanical timing being dialed in correctly along with running a vacuum advance.

Scott

OK, Thanks for all the info guys. Appreciate you chevelle dudes more than you realize. I got the next round. :beers:

If he doesn't want to modify his distributor, he has no choice - he has to run 36* total.

If he just sets it to 18 initial as you suggest, and his dizzy has more that 20* mechanical, which many do, he will run 40* + and risk damage. then what?

Most dizzy's have 20-22* mechanical, so he should be at least OK w/36* total, although I agree that more intial would be nice, it is what it is.

Vince,your right that total would go too high if you set initial to 18 deg with a stock 25-30 deg mech adv setting which i had covered. Thats why i said he had to get the mech adv limited to 20 deg so the total would end up 36-38 deg with the 16-18 initial.

I suggested this because he was likely leaving 8-10 deg initial timing on the table by just setting timing to a total or 36-38 if he in fact has a stock 25-30 deg mech adv setting in the dist. I just wanted him to be aware of what he was doing and how it would affect the motors perf running with the initial timing being retartded if he didnt want to get his dist recurved,not trying to ruffle any feathers.

Scott

Scott, I doubt he's leaving that much timing on the table. Most HEI's in my experience have 20-22* mechanical, so if he sets it to 36* he probably end up with 16* (maybe 14*) - that should be enough to get it to run good, and not warrant a dizzy make over. What he needs to do is set it to the 36*, and see where his initial ends up, I bet it wil be at 16*.

If you really feel like getting invloved and want to shorten the curve, all you have to do is this - I run a 16* curve (little trial and error howver to get it perfect):
http://www.chevelles.com/showroom/data/500/medium/hei_advance.JPG (javascript:;)

I have a 350 with an intake, carb, and possibly a slightly larger cam.

I bought the Mr. Gasket weights and springs (all brands do the same thing) and put in the lightest springs...all in by 3k with 20° of mechanical advance. With total timing at 36° @3k RPM, initial falls at 16°.

My engine loves it, but my starter hates it (that's another story). I won't go back to the stock settings which was initial @0° and total at ~22° @5k. The throttle is crisper, more power, and better mileage.

Anyway, buy the weight kit at Jeg's or summit and throw the lighest springs in, and see what happens. The kits runs under $10.

Vince,you could be right,i dont know if he is running a stock older point type or an HEI dist (i may have missed that in original post). But i would think the same theory applies & there may be a little less initial timing lost with the HEI vs the stock dist as you pointed out. Thats all i wanted to get across the person that posted timing question so he would be aware.

Scott

I am running an HEI ignition.

Brett Go back and look at my first post. I said 6* was a "nice" place to start. With 6* you'll be very close to what the factory origionally wanted the initial timing to be at in your SBC.

Now all of the hot rodders have chimed in and told you to do all sorts of stuff that you probably aren't going to be able to do. I noted in your post that you were setting your timing by hand. If you don't have a timing light GO GET ONE!

You cannot time an engine by ear. Lack of pinging doesn't mean you have the timing set optimally. It only means that you have the timing below the ping threshold.

I really don't care what kind of camshaft you have. 6* is a STARTING POINT. If I thought 18* was a GOOD STARTING POINT I would have said so. I DO NOT.

To make blanket statements like that does not serve the Team Chevelle community at large at all well. There are too many people reading this stuff that take stuff like 18* to heart and go out and time their engines to that spec and then come back here with problems hoping we can help them.

6* will get you running very well and then as I said in my first post you can "experiment". When you do it that way you LEARN. Thats what this site is all about, "learning".

Get a light, do what I said and then get comfortable with various timing setting until you are happy with how your car runs.

Dont dive into modifying your distributor UNTIL you learn what you are doing and what the effect of what you're doing is on your car.

You'll note in another post that one felllow said that his engine liked that way advanced timing but his starter didn't. Thats a very telling point. When his engine is hot the engine preignites while he's cranking the starter and then the engine bucks back against the starter. Thats pretty hard on the starter. 6* won't cause that kind of problem. 6* will be gentle on your engine and you can work from there to find your optimal initial timing setting.


FWIW 18* would kill my engine. My compression is way too high to tolerate that much initial timing.

I have a timing light, and the engine runs great. My first post and even the title though is about how you know its right. The engine runs well, I have good power, good fuel economy, but could it be better? Noone here yet has said of one way to know that you are perfect except for on a dyno. Everyone is just saying it runs "well" at this setting, well yes it runs well, but is it perfect?

With a factory GM cam 6 deg btdc initial is fine like was suggested but with any kind of aftermarket perf cam like you stated your running 6 deg initial is too retarded.

This is because even the mild perf cams have a fair amount more duration then most all stock gm cams had unless it was an
l78/L88/DZ302 or something like that. You need to run approx 16-18 deg initial with that non stock aftermarket cam.

So you go ahead and try the 6 deg initial to see how it feels/runs with that (will likely be soggy/sluggesh),then try 16-18 deg initial to see how the motor responds to that. You will have to idle it down some after advancing the initial from 6 deg to 16-18 deg so keep that in mind too.

Which ever setting the motor runs best/most responsive at is where you want to be but listen for ping with initial increased. This is because if there is enough mech adv in the dist your total could go over 40 and cause ping if you have enough cyl pressure.

If that happens you can either back off the initial a couple deg and loose a smidge of power/bottom end umph or you can pull the dist to have it recruved for only 18-20 deg mechnical to run with 18 deg initial for a 36-38 total which is the way to go for best perf.

Many people with aftermarket perf cams here in team chevelle find they need to run approx 16-18 deg initial timing with aftermarket mild to hot perf cams. The only time running 16-18 deg initial with an aftermarket perf cam is a problem is when for example your runnig too much comp on todays low quality pump gas (unlike the high octane/high quality sunoco 260 i used to run in the late 60's-early 70's) or if your running high comp along with a mild cam too short on duration/overlap for the compression in the motor which builds too much cyl pressure resulting in detonation.

Good luck & let us know what works out the best for your setup.

Scott

6* intial means ~26-28* total...no good.

6* intial motor probably wont even run.

I have a timing light, and the engine runs great. My first post and even the title though is about how you know its right. The engine runs well, I have good power, good fuel economy, but could it be better? Noone here yet has said of one way to know that you are perfect except for on a dyno. Everyone is just saying it runs "well" at this setting, well yes it runs well, but is it perfect?

Yes, it would take a dyno to determine what is the absolute best setting. The reason that so many people recommend 36º total is because most engines perform best at or near that (sb's with Vortec/fastburn heads like closer to 32º).

Advance has to be a compromise. Unless you're in detonation, it takes awhile for the fuel to burn and the goal is to have most of the energy developed at the point that it makes the most power. If you start the process too soon more energy is wasted trying to push the piston back down on the compression stroke, leaving less to push it down on the power stroke. If you start the process too late power is lost because less of the fuel was burned before the exhaust valve opened.

With a factory GM cam 6 deg btdc initial is fine like was suggested but with any kind of aftermarket perf cam like you stated your running 6 deg initial is too retarded.

This is because even the mild perf cams have a fair amount more duration then most all stock gm cams had unless it was an
l78/L88/DZ302 or something like that. You need to run approx 16-18 deg initial with that non stock aftermarket cam.

So you go ahead and try the 6 deg initial to see how it feels/runs with that (will likely be soggy/sluggesh),then try 16-18 deg initial to see how the motor responds to that. You will have to idle it down some after advancing the initial from 6 deg to 16-18 deg so keep that in mind too.

Which ever setting the motor runs best/most responsive at is where you want to be but listen for ping with initial increased. This is because if there is enough mech adv in the dist your total could go over 40 and cause ping if you have enough cyl pressure.

If that happens you can either back off the initial a couple deg and loose a smidge of power/bottom end umph or you can pull the dist to have it recruved for only 18-20 deg mechnical to run with 18 deg initial for a 36-38 total which is the way to go for best perf.

Many people with aftermarket perf cams here in team chevelle find they need to run approx 16-18 deg initial timing with aftermarket mild to hot perf cams. The only time running 16-18 deg initial with an aftermarket perf cam is a problem is when for example your runnig too much comp on todays low quality pump gas (unlike the high octane/high quality sunoco 260 i used to run in the late 60's-early 70's) or if your running high comp along with a mild cam too short on duration/overlap for the compression in the motor which builds too much cyl pressure resulting in detonation.

Good luck & let us know what works out the best for your setup.

Scott


Scott if you think 6* initial is too little you should go for a ride in my Chevelle. It ain't a dog. I'll try 18* some day and see how much it pings. Like I said earlier I have a lot of compression.