My current setup is 4 degrees BTDC. I'm running a 350 with a 600CFM Edelbrock and Holley Contender manifold and lake headers. It's a fairly fresh rebuild with a mild cam. She runs good, but I'm bored today. What could I do timing wise to make things a little more interesting? A little advance? Being bored on a Saturday sucks.
I knew a kid in high school that would pull his car up against a telephone pole with the front bumper, pop the hood and with it running in gear ( obviously an auto trans) he would move the dizzy while accelerating until the tires started spinning. Lock down the dizzy & call it timed! I don't agree with his method but do find myself messing with initial and total advance for better performance/ driveability. I say go for it, try 6 or 8 initial and see how it starts & runs.
It's been my experience that SMC's like about 12 degrees initial timing. Just as long as you have NO ping, or excessive starter drag..
I remember the label on my 68 327-350hp saying in red "8" degress before top dead center and it came with an air pump. It does just fine on pump HT gas at 10 btc....with AC 44's...I only have a set of 45's now waiting in the wings but afraid it will ping with 11:15 compression with the 45's. Not many R44's left in the world. I have had two 305 street rod engines and ran 8 degrees in both of them. My old mechanic had a hot 350 like a LT1 engine....about 4 is all he could ever set his at....go figure.
I was running 8* in my Tbucket at first but found it liked to be a 10* after driving it and tuning it awhile. Now that motor just sits on an engine stand as the car is gone.
Timing is based on your camshaft.... Find out what your cam profile is. If its stock its installed straight up. Get your timing curve..... Set initial, bring to rpm where its all in, set timing there, then re-check at idle.... intake carb ect don't matter with timing, its all in the cam.
I like the way Hoop98 thinks. And again, one of the shortest answers is one of the best. It won't hurt to experiment a bit with your initial timing, but remember that it's only one part of the equation. Not all distributors have the same amount or rate of mechanical advance. Not all distributors have the same amount or rate of vacuum advance. Not all engine combos "like" the same amount or rate of advance. Just remember that you're trying to balance a few different things here between initial, mechanical, possibly vacuum, and total spark advance. Changing initial timing is going to also change the total timing, but not necessarily for the best.
That's why you set initial first, then check total.... Other wise if you cant get it then you have to change weights and springs..... to high of initial you will be eating starters, to much total, your gonna detonate....
Exactly. No such thing as one size fits all. My dizzy is locked out. I'm running about 36* btdc with no issues.
Definitely. Advance the timing 2 degrees and drive it to a deserted stretch of road. Boot it till redline in each gear. Repeat the process till it starts to ping and then back it off to the previous setting. Best done on a hot day for your climate or if it pings later when the weathers hot just remove 2 degrees till it stops pinging.
Roger on that... If you can afford chassis dyno time, you power time it for maximum hp, back up 2 degrees and go drive it. If you leave it at maximum for street driving it will usually ping a bit with a stock type ignition.
so many variables that decide what the engine wants, cam, compression, aluminum or iron heads. I have seen SBC that will ping on 10* initial and 32* max timing on premium gas and I have built 9.5 compression SBC that like 22* initial and 38* max on low octane gas. I find that usually 12* initial and 36* total plus vacuum advance of about 15* is a good base to start with. My current one runs great on 16* initial and 36* max plus 15* in the vacuum can. About 36* total works great on most SBC, initial is worth messing with for throttle response, low end torque and fuel economy.
Initial means little - bumping the initial moves total. total is where the power is found. However you can run into trouble with this and that's why distributors get recurred.
ClayMart is right on the money here, from my experience. I had a '73 Chevy PU, that had an initial setting of 12 degrees, if my fading memory is correct. Might have been 14. It was a starter eating SOB too. I think, but, I'm not sure, that you would want to set your initial timing based on what engine your distributor came from, if you don't know what it has for mechanical and vacuum advance. And it never hurts to experiment from there Good Luck
X2 Quickie cheat on total advance. Set your damper at 0 on the timing tab. now rotate the balancer UP so your balancer line is at 10. Make a new line at 0. Do this till you have 4 marks (0, 10, 20, 30) on your balancer. Set your initial at what you want. Fire it up, bring the RPMs up, with a timing light watching the marks your total will be where that last mark lines up I too am in the 34-38 total advance camp. (mind you this is for the folks like me who never had the fancy shmancy timing light with the total advance dial on the back) When I run 38 on my stuff its usually for cool weather, premium gas, new plugs and as much power as I can get out....oh and a good battery and starter just for insurance purposes.
1st verify that your timing mark is showing TDC at the zero mark on the timing tab. Do this using a positive piston stop. Rotate engine until the#1 piston is at the bottom or close. Loosen the two #1 valve rockers so the stop doesn,t hit the valves. Install a piston stop in the spark plug hole.Then Rotate engine until the piston hits the stop. Make a mark on the balancer. Rotate crank in the opposite direction. Make a mark on the balancer. TDC is halfway between these two marks, Then install a timing tape (available at most any parts store) so that 0 on the tape corresponds with the halfway mark you just made. Now you know that your timing marks are good and you have the degrees marked up to 50 or 60 depending on the tape you have. With this tape you don't need a fancy dial back timing light. Now you are able to set your timing right. Now unhook and plug the vacuum line and plug it (no vacuum leaks). Hook up timing light and start engine. Rev engine slowly. Watch the timing to see at what rpm the mechanical advance is all in. If you are getting advance after 3000 rpm you need to use lighter springs. Get an advance curve kit (cheap) and install one light spring and one medium spring. This should get you close, but keep working at it until all mech adv is in by 3000 rpm. Now rev engine untill all mech adv is in. Then set your timing at 34-36 degrees. Don't worry about the initial adv yet. Initial advance plus mechanical advance =34-36 degrees. Bigger cams need more initial. If your engine doesn't idle well at this setting, you may need to limit the amount of mechanical advance. Initial plus mechanical always equals 34-36. Most stock distributors have about 20 degrees of mechanical advance. My engine likes 18 initial plus 16 mech. I had to limit the amount of mech adv. (Big cam). Now hook up the vacuum. Your engine will run cooler at low speeds and you will get better mileage with vacuum adv. BUT, most distributors have too much vacuum adv built in (20 to 24 degrees stock), so vac adv usually needs to be limited to 10 to 14 degrees. Initial plus mechanical plus vac adv should equal 46-50 degrees at 3000 rpm. I had to limit my vac adv to 12. My timing is: 18 initial + 16 mech + 12 vac =46. It runs like Jack the Bear. Sorry about the long post, but timing is a very misunderstood subject.
I should note that total advance is initial plus mechanical. Vacuum adv has nothing to do with total timing advance. Vacuum adv is used as a tuning tool and shouldn't be messed with until total advance is set correctly. I always use 34 degrees total, just because it leaves a little safety factor in case you get a bad load of fuel.
These are the specs for my 355 (CR: 9.75:1, cam dur @ 050" 230 deg) Initial at 700 RPM: 17 deg (with vac advance disconnected) Total mech advance: 19 deg (curve starts at 700 RPM & in fully at 2900 RPM) Note: 17 deg initial = 36 total advance from 2900 & up RPM Once I have the initial set, I then hook up the vac advance to a full time port & adjust the idle down to 850-900 RPM. The vac can I'm using is an off a 65 fuelie vette. The OEM # is B28. This can is special as it pulls the advance in fully under low vac conditions & moves only 15 degrees. A regular vacuum advance can will only pull in with more vac & moves between 18-24 degress. Hooking up the vacuum advance this way really helps with a big cam & keeps the motor running cooler as stated above. On the highway, I'm pulling in around 51-52 degrees total advance with no pinging or "trailer hitching" Autozone sells this "B28" vacuum advance under part # DV1810
I've studied several Factory Repair manuals in regard to distributor mechanical (centrifugal) advance curves. Different displacements, cams, carbs, CR's, trannys and type of vehicle all require different distributor advance curves. These curves are derived from engineers spending countless hours in dyno tuning facilities and on actual real world driving on factory road courses. Just bumping the "initial" might give you the seat-of-your-pants jolt you are desiring, but does not really approach the potential available in your combination. It never ceases to amaze me that we spend large money to build the powerplant but balk at spending a little more at a chassis dyno facility (with a proven experienced racetrack/hot street technician) to bring it all together! BTW, an engine designed for a 4000# car can handle a quicker curve and more lead when installed in a 2000# roadster. "How much more" is always the crux of the matter!
I agree. The specs I posted above are on an aluminum head '70 corvette, 4-speed manual trans & 3.36 gears. A heavier car or auto trans may not like that curve
We can be reasonably sure it will like 34-38 total but without a dyno how sure can we be. We tuned our cars in the 70's with a stop watch and a tach. We called it power ranges. We would run the car in second or third gear on a know road through the power band, if we shifted at 6500 we would time it from 4500 to 6500. Floor it at 4 and click the watch at 4500 then 6500. Of course you need to know the weather etc but we were usually making changes in jetting, cam timing, collector length, ignition timing. A tenth on an 11 flat car is about 10 HP, on a 12.50 car it's more like 7. A tenth of a second there would be worth about the same at the track. You can actually get pretty good at this if you are very careful. A good way to spend a few bored hours and learn what your car likes. Or set it at 36 total mechanical, add about 16 crank degrees vacuum and cruise!
That's right but that's PLUS the manifold sourced vacuum advance of about 12º depending on your distributor which I didn't see ID'd in the posts.
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