hei pros

[76bonanza]

I am running a msd hei with the silver heaviest and blue second heaviest springs in the mechanical advance.

My intial advance is 10 degs it sounds like I am still getting detonation at the very high end of my throttle.

Is this possible? with that late of a curve and low of intial settings?

It is a daily driver and hardly sees those high revs what damage could this do to engine if I leave it?

Also could an exahust leak or something like that be what I am hearing only very high rpms right before the shifts?

Thanks

[swervin ervin]

There is a lot of stuff that can cause it. First one that comes to mind is the easiest. What port do you have your vacuum advance hooked to? Hook it to a vacuum at idle port and see how it does. This will only work if you now have it on a ported source, or vacuum above idle. If you have it on manifold vacuum now, switch it to a ported source, although I don't recommend ported vacuum. No way you should be having any pinging with a heavy spring. I'm running a light silver and blue in mine with 15 degrees initial. Of course compression ratio, gas quality, carbon buildup (which raises compression and also forms hot spots), and a lot of other stuff causes it. A lean condition does it too.

The MSD HEI vacuum canister has a built in 16 degrees and it's not adjustable. This works fine with my engine since I have a EGR. 16 degrees is a tad too much without a EGR. Without a EGR 12 degrees work best. One thing you can try is unhook the vacuum advance canister and plug the hose. Test it without it hooked up and see if the pinging goes away. It's not good to run a engine with any pinging. If it's only at high rpm, you can live with it but if you are like me, I like things to work right.

[76bonanza]

I am lost As it has always been explained to me the vaccum advance does not raise the total timing any. the total timing is my intial of 10 plus my mechanical which is 23 with the stock stop on the msd. Changing the port will only advance it at idle not at higher rpms is that not right? I know you are in favor of hooking the advance up to full vaccum but msd told me that was not a good idea and the way he explained it at WOT both ported and full ports have the same vaccum reading. so it does not matter but at low throttle or part throttle it keeps the timing down? When I hook it up to full vaccum my engine races and my advance goes way up at idle. I dont see how the ports will matter at 4000 rpm at WOT can you elaberate to me.

Also I think I have an exhaust leak in my heat riser or manifold could it be that getting really loud and crackle at high rpms?

[swervin ervin]

You will not have any vacuum advance at WOT no matter where you hook it. Yes, full manifold vacuum is at idle and cruise, right where it needs to be for fuel economy and normal driving. If you have too much vacuum advance, it will cause pinging in the cruise/off idle range. This is where most folks have trouble, especially with the crappy 305's, which I know you don't have. I have found ported will increase the chance of pinging in the higher ranges.

Switch it around and see what happens. It's not hard to do. If nothing changes, remove it and then test it. Rule out the vacuum advance and go from there.

[76bonanza]

I will and I am not trying to say you are wrong. I just like to understand why things do what they do and I only have pinging at WOT under load like up hill or something. being 4x4 I have more load working aganist me already. When I run it with both heavy silvers it seems ok but with any others ping. With the setup you run in yours (that is how I set it up to begin with it pinged like crazy. Also I am running NGK 6630 at .045 gab could they be to hot or gap not right? And I have never heard pinging before so not sure what I am hearing is pinging. How would you describe it.

I will try your suggestion if I leave to heaviest springs in will the only thing I be sacraficing is power?

Also if I go with full vaccum do I have to slow the idle down?

[swervin ervin]

Yes, you will have to adjust the curb idle.

Pinging sounds like marbles in a tin can. Once you ever hear it and know what it is, you'll never forget the sound. If you hear it under load and going up hill, it's more than likely pinging. There is no set curve that will work with every vehicle. Weight, engine, tranny and just about everything else must be considered. No way I could sit here and tell you do this or do that. You will have to try different settings and combos to find what will work with your truck. You just have to rule out things one at a time. If you start doing too much at a time with timing, you will be lost as to what done what when you change things. It's pretty easy once you get the hang of it, but can be nerving at the start.

[76bonanza]

hey swervin what about my plug gap is .45 ok. Also I move my advance hose to full vac did not have to adjust the idle much it smoothed it out really well. Have not had a chance to get for pinging yet or try lower springs. When I hear pinging it is very faint can only hear with windows up and everything else quiet is that right?

Also if I run with two heavy springs to be safe will I just be losing power or will it harm the engine?

It is my daily driver I dont race it or anything (lets face it its a beast) so 10 or 15 ponys in exchange for drivablity and peace of mind is a good trade.

[swervin ervin]

Yes, .045 plug gap is what you want for HEI. Running full vacuum at idle makes the engine run much better. How easy it is to hear pinging depends on how bad it is. If it's just a tiny bit, yes, it will be hard to hear. The two heavy springs are close to a stock setup. No, it won't harm the engine one bit. All the springs are for is to control how fast/easy the mechanical advance comes in. I suspect with the heavy 4x4, a fast advance is not needed as much anyway. It will loose a little bit of power but if it's pinging the other way, you are loosing power also and could do damage to the engine in the process, although very light detonation won't do much anyway. But IMO, any is not a good thing.

I do know for a fact the lighter a vehicle is, the faster and sooner you want the advance to be full in. This is where trying different things with it comes into play. Like I said, no way I could sit here and tell you what springs and amount of advance you would need for your truck. If your truck was identical to mine in every way, maybe I could say set it up exactly like mine and it would be fine. Although after saying this, in every aspect it is better for the advance come in as soon as it will let it. But you have to work with what you have. I say try the two heavy springs and not worry about it too much. This stuff will drive you crazy if you let it. It took me a long time and much trial and error to figure out what goes on with timing and how it really works. I had a lot of folks tell me years ago to do this and that and never really knew what it did. I finally decided to gain as much knowledge as I could about it. I don't like doing things because someone tells me too. I want to know why I'm doing it. Knowledge is the king.

Mike

[76bonanza]

Thanks for all your help mike you have always been a big help. One other thing someone told me was I may not be losing all my vaccum at WOT and still be advance with the vaccum ontop of the total advance. To check they said just unhook the vac advance completely then run if it does not ping it is prolly still holding enuf vac at WOT to pull in more advance. If this is the case then maybe an adjustable cannister will help.

[ocbaud]

Originally Posted by 76bonanza

Thanks for all your help mike you have always been a big help. One other thing someone told me was I may not be losing all my vaccum at WOT and still be advance with the vaccum ontop of the total advance. To check they said just unhook the vac advance completely then run if it does not ping it is prolly still holding enuf vac at WOT to pull in more advance. If this is the case then maybe an adjustable cannister will help.

the msd distributors wont accept an adjustable aftermarket canister

[76bonanza]

No? The msd tech told me to try one from moroso or accell.

Thanks for the heads up ocbaud

[ocbaud]

Originally Posted by 76bonanza

No? The msd tech told me to try one from moroso or accell.

Thanks for the heads up ocbaud

mike has said that they wont accept the crane unit, but i'm assuming it will be the same

[ocbaud]

i just unhooked and capped my vacuum advance on my engine, and took it for a drive. it stopped the pinging at high to full throttle i had it hooked up to manifold vacuum but i tried ported and it didnt help any. until i can find an adjustable one, i'm just gonna use the block-off plate that came with my dizzy and remove the vacuum advance. oh and i've been running 93 octane on it only. i have my plugs gapped at .045, should it be more?

[76bonanza]

I have thought about doing that but I have heard it will not do your engine any good. Carbon up plugs and valves and stuff? But dont know that for sure just what I heard. Also I would think you would lose some low RPM advance? But I dont know that for sure either.

[GMC Jim]

GM 1971-80 Tune-Up Specifications ( Manual SD-100) lists the following engine configurations for the 1976 light truck models. Light Duty Emissions:- 350 2 Bbl & 350 4 Bbl. Heavy duty Emissions:- 350 4 Bbl and 350 4 BBl. California Emissions. The advance curves are somewhat different for these engines.....The 350 4Bbl light duty emissions; auto trans are :- 8 degrees advance @ 600 idle RPM. 12-16 degrees centrifigal advance ( vac advance disconected & plugged) @ 2000 RPM. Total advance ( centrifigal & vacuum) 28-36 degrees @ 2000 RPM.
The heavy duty emissions engines have considerable less advance ...... If you would want the specs for the other 1976 engine/emissions combo...... will post them ; no problem...........Jim

Note: This manual states to set idle speed with distributor vacuum advance disconnected and plugged.

[86-C10-V6]

I am trying to set up my 4.3 with an Crane Cams ajustable vacuum advance and 1 silver and 1 blue spring.
Please tell me what the curve should look like.
The emissions decal calls for 0 degrees at 500 RPM with no vacuum.
Just curious where I can find the documention for this ignition curve. I have the Helms service manuals, I have not seen this listed in them.

Thanks

[swervin ervin]

Back when I had the stock HEI with the Crane kit, a light silver and blue gave me a curve of around 800 start and full in at 2800. I never could get this to work right. I done a lot of thinking on this along with reading different things. I found it best to use both blue springs with a curve of 800 and 3200. One thing I found out from a lot of trial and error, a light vehicle can use a quicker curve over a heavy vehicle, like a truck. If it comes in too quick, the extra weight will cause pinging.

With my MSD distributor, not being able to use a Crane canister, I used the springs that MSD supplied. A light silver and blue gives me a curve of 1100 and 3000. This seems to work quite well.

[GMC Jim]

Dave M---The SD-100 manual I refered to cover vehicles 1971 to 1980... There is another manual available ( from GM Dealers? ) that covers later models. The specs for Distributors is listed in the back of my 1971 Chevrolet Truck Chassis Service Manual...Specs, Section 15.. Complete specs are given for the engines used in the 1971 model year. Not to argue with anyone about setting advance curves; I feel the only proper way is to use a distributor machine...Distributor rebuild shops have these machines... For instance the centrifugal advance curve for a 1971 402 engine is ( degrees @ RPM) 0 @ 930; 2 @ 1260; 16 @ 2400 and 30 @ 4400. I feel it would be next to impossible to set the 4400 RPM specs with any degree of accuracy with the didtributor on the engine! One could plot the curve on a sheet of graph paper to determine the advance for RPM ranges between 2400 and 4400. Even so, setting the curve at 2400 RPM would take some trial and error. About 12 years ago, I had a local firm that specializes in automotive ignition, set the curves to the proper specs for my engine ( 402 BB).....I set the plugs to .045 , installed new spark plug wiring , installed the distributor and set the required 8 degrees adavance at idle RPM of 600 RPM....Have been very satisfied and have had no problems . Philbin Mfg Co., here in Portland set the advance curves to factory specs (Phone 1-800-869-7301)....I have talked to them recently and they stated they would need to know any engine modifications that have been done.. such as higher compression, hi-lift cam shaft, etc....in order to properly set the ignition curve.....

[greg0380]

I installed the crane kit (like Mike used on his stock HEI) a couple of weeks ago. I wound up with the same results as him, both blue springs. I started with replacing one stock spring with the blue and worked my way down until I got pinging. I found it best to disconnect and plug vac. advance so you can isolate mechanical and initial. Then you can set up the springs and not get confused by having the vac advance thrown into the equation.