chevy 350 with 272/282 dur cam ignition timing ??
help i dont know how to set/figure out ignition timing that my engine needs/wants, especially at idle and lower RPM
it is a bone stock 350 stamping suffix CMJ, untouched all original parts other than the summit cam k1103 i just put in it,
i am running a stock 1981 truck th350C and stock converter that was originally behind the 2 bbl 305 that was in the truck
i have long length headers with 3" collectors and 3 foot pipes
and stock 80-86 aluminum spreadbore intake with edelbrock 600 1406 on it
horrible axle ratio of 2.73 right now so it is hard to kick up the RPM to get going, until i find a higher stall converter and deper axle... its really bad til i do,
it seeems to want ALOT of base/initial advance at idle and such but not alot in higher rpm, as it pings in higher rpm
would this be correct ?
i am used to stock 350 cams where it only needs 4 to 6 degrees advanced initial timing
but wow, this one needs/wants WAY more than that
so how do i figure it all out ? how do i find/set my low speed/idle ign timing ?
Last edited by fast68; 11-12-2005 at 11:07 AM.
With more duration comes the need for more initial timing. Its going to be a matter of what idles/runs best from now on for your engine. With that combo, i'd start at about 12 to 16 degrees of base idle timing. You will also need a decent adjustable timing light to check your combined base and mechanical numbers too. Try to get your base+mechanical to read 34 degrees total by around 2000 rpm. The vacume advance really doesn't need to be used at this point until you get those 2 figured out.
Are you fellas using factory HEI distributors?
The mechanical advance in those things can run very high without a proper rotor in them. Most aftermarket rotors do not stop the advance weights at a decent point. I've seen it as high as 32 degrees mechanical, not counting initial timing. Add that to the initial timing number and you can see that you have a problem.
Get a GM/AC Delco rotor in it first or verify the amount of mechanical advance doesn't exceed 24-26 degrees with the parts house brand. Set initial timing at 10-12 degrees, rev it up until it quits advancing and make a note of the amount. If it exceeds 36-38 degrees total you'll need to make further changes to limit the amount of total timing.
You should be fine after that.
this is so complicated
thaks for info, i need to re-read it all
first i must reiterate that i think that my first and biggest problem is that im running a stock th350 and converter and 2.73 gears and all in a heavy truck 4100lbs
so therefore i cannot get very much rpm out of the truck at all until waaaay high into each gear and i mean WAAAY high, it takes forever to get up into higher RPM, but whern it finally does then that where its making good power big time
i was having alot of pinging under load/accelerating so that means too much advance too soon, or in general,
so i backed the distrib off, i finally figured that one out too.. and to have the vacuum advance connected to full manifold so it idles alot better,
the stock HEI springs are too weak i was told by a local racer guy, and that i need to get stronger ones,
what do you think ?
should i put stronger weights on the distrib ?
yes i am runnign stock untouched HEI out of a 1 ton 350 1981 non emissions non EST/ESC
i dont know what to do for sure?
-no i dont have an adjustable timing light, i have a normal everyday craftsman one
how much advance does this cam really need and what RPM ? or is it all dependent on axle ratio and slippage of the converter ?
if so then theres not gonna be a very god answer/value here
-also, i cannot check with stock timing tab it only goes up to around 10 BTDC on it
i am also having problem with pop ups through carb sitting still in gear, everyonce in while a little cough up the carb, like a popcorn pop, but it doesnt do any of that under load or anywhere else past idle
is it because the engine can spin free with the crappy stock converter ?
should i jut quit til i put in the th400 and higher stall converter ?
and deeper axle ratio ?
it has no pick up and go at all, until WAYYY up into the rpm's
otherwise it is very doggy and crappy, way worse than the stock cam was, by FAR and hardly any decent rpm until its moving top of each gear,
or should i just quit now and de-cam it and wait for a lighter body and also better axle ratio ? i am really thinking now that i am not gonna get much more out of this with my axle and converter and weight, and that i need to make some major changes in order fro the engine to get into power band quicker, so that its not doggy until it can finally get into its powerband,
also what does the rotor brand have to do with the weights and how and when they advance ??
the weights contact the inside of the rotor ??
how much advance do the stock weights and springs actually give out ?? and how much rpm does it take ?
vey curious here, i need to find this out, big time
thanks for further i appreciate alot
Last edited by fast68; 11-12-2005 at 01:36 PM.
Thats a whole lot of questions in one post! LOL
First off, the rotor has NOTHING to do with stopping the mechanical weights from over advancing. The weights are curved different for different advance curves and the slots under the spring plate limit the amount of mechanical advance. GM used thousands of different combo's depending on the engine, car weight and gears, plus lots more I don't even remember.
All in all, you have a stock low hp, low compression, highway geared heavy truck with an aftermarket cam in it. Its NOT going to be a rocket even with a TH400 and better gearing. That tranny will actually make it take off slower as first gear is higher than the TH350.
My suggestion is to spend a few bucks and find someone to help set up the distributor better for your application. All things said, its not going to make a huge difference except maybe for the pinging problem. I think you are expecting way too much for what you have. You'd be better off to put the stock cam back in and start saving your money and build a complete hp engine.
ok cool thanks very good info here
yeah i realize that th400 gearing is taller than th350-
i very well know that 2.52 and 1.52 are the ratios of the 400
- and that the th350 ratio is deeper than this
-which means more rpm at take off with the 350 trans
- which is assumingly better for such duration of a cam(higher rpm band power producing cam)
i was just saying that installing a higher than stock stall T converter would presumably allow the engine to kick up so it can get going alot more -and at way lower vehicle speed- than it does now
no, i wasnt- and am not- expecing the truck to be a rocket after this cam swap by any means-
especially with the heavy weight and with the the 2.73 gears- and the stock T converter- im fully aware of this being a not very good combo at all, and knew it before installing the cam- but have found out first hand now- after completeing the said swap- so now i have some regrets about the cam in this particular vehicle
i am just looking for opinions on just what i need for sure, to help the truck- if even possible
deeper axle ratio?
+ stall converter ?
or should i just yank this cam and lifters out and swap in a truck low end torque producing cam ? RV >? towing ? which ?
i technically need low end torque performance- with this converter and axle ratio and vehicle weight- as this k1103 cam dos not produce any of that, at all, it only puts power out at way high RPM, in which is extremely difficult to get to in this vehicle, very slow achieving
and how would i possibly figure out what springs to put in this stock HEI to cut off the timing advance(pinging) under load and RPM
and why does it pop/cough occasionally at idle in gear
i cant get it to stop doing that- once in a while a little cough/pop in the intake
it wont go away no matter the timing adjustment
some adjustments make it worse or will kill the engine when put into gear
i really think it is due to the cam with the stock converter
please say it is or can be, or what else can it be that causes this to happen ?
and if you actually dont think that ive screwed up bad for putting in this much duration of a cam with this axle ratio and converter and vehicle weight then pelase tell me now-
thanks for your time!
yes it is alot of questions im sorry,
its better than 10 separate posts though lol
Last edited by fast68; 11-12-2005 at 03:22 PM.
your base timing ? or high RPM timing ?
so probably my coil then eh ?
never really thought of that
the engie is in fact sluggish to start up, takes some gas and stuff ot get it fired up every time, sorta difficult actually,
could be crappy spark causing issues
i did try anothr module though
but that changed nothing
so i dont think thats where any issue lies
should i also try heavier springs on mechnical ?
i have one i can try out
or do i not need to be supressing mech advance with such a cam ?
what is the truth here ?
i also wonder if maybe i have a valve or two adjusted too tight
i think better readjust them all
along with different a coil
Last edited by fast68; 11-12-2005 at 05:11 PM.
Popping out of the intake mean a lean mixture.
Popping out the exhaust means a rich mixture.
I don't understand how you could be getting detonation with a bigger than stock cam and very low stock compression. ???? Maybe the ignition curve is advancing a lot!! Or an intake lobe has gone flat.
Yes, you need to let us know base timing and total timing. That requires a degree'd balancer (timing tape) or a timing light with one of those degree wheels on the back.
And a compression test would be a good idea.
The K1103 has 214/224 duration at 0.050" and 0.422/0.465 lift. Not a huge cam but a cam that requires a 2000 stall and a 3.42 to 3.55 gear for best performance.
A th400 and th350 have about the same gear ratios (not enough to make any difference).
I reduce the length of the timing curve in my distributors my welding up some of the advance slots. A yes, a bigger cam needs more initial timing (like 15 or 16). And your engine with older style stock heads, needs about 40 degrees total timing.
A popping intake sound could also be a flat cam lobe. And there has been a rash of new cams wiping out lobes over the last few years.
Did you change valve springs? Popping intake sounds is also a sign of a broken valve spring. You should pull the valve covers and start the engine to watch each rocker arm at idle. A flat lobe will make the rocker arm move much less than the others. Then inspect the valve springs.
Most likely better just to go back to the stock cam or an RV torquer cam (less than 205 degrees at 0.050").
Next time make sure to use EOS oil additive for engine break in when you install a new cam.
I'm thinking your new cam has loss an intake lobe somewhere. No power, popping intake, and detonation in a low compression motor all point to that conclusion in my opinion.
And if you did eat a lobe. The engine bearings get messed up pretty badly from the metal in the oil then the rod knocking starts. I hope I'm wrong!!!!! But I have seen that first hand in some of my engines.
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