Need ignition upgrade help/advice.

[5Tractorguy]

I'm looking to do some mild ignition upgrades to the 351 in my GMC 5000. Mainly trying to get a hotter spark in hopes that it will improve power....

Does anyone know of a good hot 12V coil? I have a NAPA replacement in there now (cylindrical style) and would like to replace with the same style.

And has anyone upgraded to an electronic ignition module and did away with points/condenser? If so, was there a difference?

[TJ's GMC]

I put the pertronix flamethrower in mine and the first thing I noticed was easier cold starts. Starts better hot and the engine runs smoother. The pertronix is fairly cheap and an easy bolt in unit, only beware is they can die without warning....like all modules.

Other option would be to build the Buick v6 dizzy that's explained here:
www.6066gmcguy.com/hei.html

Another option is to get a dizzy from HEIDIZZY on Ebay. Currently I don't see any on there.

I ran stock points with a 45K pertronix coil and it didn't take long for that hot coil to fry those points.

[5Tractorguy]

Thanks TJ.

So it looks like if I want to go with a hotter coil, I will have to upgrade to electronic ignition or I'll burn my points.

Do you have a link to the ignition module?

Now I have to figure if it's worth doing the swap....

[AZKen]

When there is a "normal "spark, the fuel ignites. The words "Hotter Spark" were invented by ignition parts manufacturers. You won't get anything out of a "Hotter Spark" except the same combustion.
If you mean a "hotter plug", that has nothing to do with "power", as you say you want.

A "hotter" plug is one that is of a higher heat range than another. Once you understand the heat range, you'll see why there's no such thing as a "hotter" plug.

The spark plug acts as a heat sink for the combustion chamber. The plug's heat range needs to be matched to the chamber temperature, not the general engine temperature.

Running a higher heat range plug accomplishes nothing positive, same as running a colder heat range plug.

I advise good timing with good fresh distributor components, wires, plugs, fuel filters, air filters, carb rebuild, tire pressure. In other words, a tune up. Best you can do to get "power". The max power is already built into the motor when running per factory specs. The motor has a max RPM, max torque.

You can get more speed thru the drivetrain gearing or more pulling power thru the drivetrain gearing, all the way to the tire size. Not the motor. Not the spark. If you want to redesign the internals of the motor, then you may get more power. But "more power" means different things to different people. Not sure what exactly is wrong with the performance of your motor or what you need more of. You must access the overall condition of the motor if you feel it is weak. Compression test first. Oil consumption thru exhaust. Exhaust system. Carburetor. Fuel pump, clogged fuel filters, clogged air filters, bad gas, bad clutch, brakes dragging, loads too heavy....all depending on exactly what you think is missing regarding "power".

You see the trouble others are having screwing around with ignition. The only thing HEI gives is no points wear, reliability and no adjustment. Not power. Points have served well for many years. I would run away from Pertronix. The only HEI to consider is the one explained on our pages under "performance upgrades".


Contact member WE7X Rod Johnson. He has the parts and instructions for the mod.

[5Tractorguy]

Originally Posted by AZKen

When there is a "normal "spark, the fuel ignites. The words "Hotter Spark" were invented by ignition parts manufacturers. You won't get anything out of a "Hotter Spark" except the same combustion.
If you mean a "hotter plug", that has nothing to do with "power", as you say you want.

A "hotter" plug is one that is of a higher heat range than another. Once you understand the heat range, you'll see why there's no such thing as a "hotter" plug.

The spark plug acts as a heat sink for the combustion chamber. The plug's heat range needs to be matched to the chamber temperature, not the general engine temperature.

Running a higher heat range plug accomplishes nothing positive, same as running a colder heat range plug.

I advise good timing with good fresh distributor components, wires, plugs, fuel filters, air filters, carb rebuild, tire pressure. In other words, a tune up. Best you can do to get "power". The max power is already built into the motor when running per factory specs. The motor has a max RPM, max torque.

You can get more speed thru the drivetrain gearing or more pulling power thru the drivetrain gearing, all the way to the tire size. Not the motor. Not the spark. If you want to redesign the internals of the motor, then you may get more power. But "more power" means different things to different people. Not sure what exactly is wrong with the performance of your motor or what you need more of. You must access the overall condition of the motor if you feel it is weak. Compression test first. Oil consumption thru exhaust. Exhaust system. Carburetor. Fuel pump, clogged fuel filters, clogged air filters, bad gas, bad clutch, brakes dragging, loads too heavy....all depending on exactly what you think is missing regarding "power".

You see the trouble others are having screwing around with ignition. The only thing HEI gives is no points wear, reliability and no adjustment. Not power. Points have served well for many years. I would run away from Pertronix. The only HEI to consider is the one explained on our pages by Jolly.


Contact member WE7X Ron Johnson. He has the parts and instructions for converting.

Some good things to consider and think about Ken.

I've been down this road once on here so I didn't want to sound like a broken record, but the back story is...

Is a 20,000 mile '61 GMC 5000 12ft flat bed, used to be a fire truck. Ever since I got it home there has been an issue with it being able to pull the hills or loads (even a 2400lbs tractor). It has a bad tendency to slow down on the slight hills and I have to drop a gear. That's from 35mph without being in overdrive.

I've done just about everything to the engine except pull the heads and oil pan. Compression is 120+/-, ignition has all been done, carb rebuilt a couple times ETC... Maybe someone messed with the jets?

So at this point it either is what it is for a 56yro truck, or there's something I'm still overlooking.

[AZKen]

Fire trucks carry 1000 gal H20 @ 8.34= 8340 lbs. Yours may have had a larger tank than that!!! Maybe it's built special with heavy duty frame or something? 20K miles should run strong. Something big does seem to be wrong. Is it winding up OK? while climbing/hauling or is it bogging down? Ebrake stuck on? Something goofy like that could be happening. Two speed rear end? 5 speed trans? I'm no expert on hauling with big trucks but do you keep it wound to highish RPM using proper gear changes? Could it be you? or are you experienced?

It is made to haul and it should do a good job.

I would absolutely check all brake shoes and parts at each wheel if you have never looked.

Been reading your past posts. BBV6 mentioned 5 deg BTDC, you said 10. I think 5 means 5. If it won't run there, find out why, don't use 10.
Snazzypig questioned your jets, gasket arrangement, vacuum, etc. I think you need a new stock carb. I think you have tinkered it into a mish mosh. Start over, do it right, don't screw with Mother Nature. These motors are not made to customize and tweek around on. They are designed by engineers who perfected it already. It ain't no SBC. Leave the jets alone. Assemble carb carefully, ALL NEW parts, setting level and drop as necessary. You are only 450 ft above sea level unless you are on some big mountain. So that should not be the problem.

I am not slamming you, just cutting to the chase. Hope you understand. Don't want to blog it to death, want to fix it. Making sure you are out of the past box and into brainstorming. You have added many new parts. Double check your work and your points gap. Tune it all TO SPEC, not someone's BS ideas. You can play with timing a little. It's not what it sounds like, it's what it runs like. I think you may have said it "pops" at 5 deg? Make sure that is Before TDC and not after. If it backfires at spec then it's vacuum leak....big time. Even an exhaust leak will do that. Analyze some more and see what you get. Please state if it's a carb backfire (pop) or a tail pipe backfire....at 5 BTDC. We'll get there...me, Snazzy, BBV6, TJ and anyone else who can try.

[TJ's GMC]

Jake, did you ever get a chance to put those new intake gaskets on? Lightly buff the surfaces? Also did you reseal the valley pan?

351 power specs are: 180 hp @ 3400 and 312 pound ft @ 1800-2000 gross

351E power specs are: 220 hp @ 4000 and 320 pound ft @ 1600 gross

So not a Ton of power to begin with but plenty of torque to haul that thing at a decent speed. Specs are 4-6 degrees advanced so if you had to add an extra 5 degrees advance just to make it run decently I have to wonder if the timing jumped? The chains on these are not very tight so that could be a possibility. I haven't read of it happening yet, but there's always a first time.
Vacuum leak already mentioned.....check all gaskets and hoses.
When you did the carb rebuild did you check to see if the throttle shafts in the carb were all worn out? Vacuum leak through there will cause backfiring and power loss.

[5Tractorguy]

Originally Posted by AZKen

Fire trucks carry 1000 gal H20 @ 8.34= 8340 lbs. Yours may have had a larger tank than that!!! Maybe it's built special with heavy duty frame or something? 20K miles should run strong. Something big does seem to be wrong. Is it winding up OK? while climbing/hauling or is it bogging down? Ebrake stuck on? Something goofy like that could be happening. Two speed rear end? 5 speed trans? I'm no expert on hauling with big trucks but do you keep it wound to highish RPM using proper gear changes? Could it be you? or are you experienced?

It is made to haul and it should do a good job.

I would absolutely check all brake shoes and parts at each wheel if you have never looked.

Been reading your past posts. BBV6 mentioned 5 deg BTDC, you said 10. I think 5 means 5. If it won't run there, find out why, don't use 10.
Snazzypig questioned your jets, gasket arrangement, vacuum, etc. I think you need a new stock carb. I think you have tinkered it into a mish mosh. Start over, do it right, don't screw with Mother Nature. These motors are not made to customize and tweek around on. They are designed by engineers who perfected it already. It ain't no SBC. Leave the jets alone. Assemble carb carefully, ALL NEW parts, setting level and drop as necessary. You are only 450 ft above sea level unless you are on some big mountain. So that should not be the problem.

I am not slamming you, just cutting to the chase. Hope you understand. Don't want to blog it to death, want to fix it. Making sure you are out of the past box and into brainstorming. You have added many new parts. Double check your work and your points gap. Tune it all TO SPEC, not someone's BS ideas. You can play with timing a little. It's not what it sounds like, it's what it runs like. I think you may have said it "pops" at 5 deg? Make sure that is Before TDC and not after. If it backfires at spec then it's vacuum leak....big time. Even an exhaust leak will do that. Analyze some more and see what you get. Please state if it's a carb backfire (pop) or a tail pipe backfire....at 5 BTDC. We'll get there...me, Snazzy, BBV6, TJ and anyone else who can try.

Thank you Ken! Reading through that widdled everything down that I've been thinking about.

Let's see... this was a tanker truck so I'm sure it had at least 2000gal tank on it, I would figure. Has the boxed frame with the ladder-work on the inside.
Seems to wind up okay when you are on flat ground, sometimes a little hesitation at first.
Sometimes when winding up going up a hill or pulling a hill, I can keep putting my foot into it and there is no RPM/power change, then when getting close to the floor it will start to pick up some..

Negetory on the E-brake, no problems there.

Yep, 2 speed rear, 5 speed main, and a 3 speed brownie for OD. I keep the rear in HI now that I have the brownie. When pulling hills I keep my foot into it, not over speed the engine but to keep the momentum in order to change gears. If it's flat, 2nd, 3rd, 4th, 5th then OD. Hill or hauling, starting with the Brownie in Direct (2nd)... 2ndD, 3rdD, 3rdOD, 4thD, 5thD, 4thOD, 5thOD. The gap between 3-4 is pretty significant and I have a working 4th.

Front brakes have been done, rears I haven't but they don't drag... should still check 'em.

Sounds good, I'll have to set the timing back to 5 and see what happens.

As for the carb, if I can find another that would be great, if not, I'll have to see about ordering another kit and 2 new jets, because I messed with these ones...

Exhaust pop at 5. And that was before I did manifold gaskets and a few other things this year. Need to check that again.

YES! Less write up and more progress. I have to haul tractors to a show next weekend with it so with any luck I can delve into it before hand and give you-all an update.

Originally Posted by TJ's GMC

Jake, did you ever get a chance to put those new intake gaskets on? Lightly buff the surfaces? Also did you reseal the valley pan?

351 power specs are: 180 hp @ 3400 and 312 pound ft @ 1800-2000 gross

351E power specs are: 220 hp @ 4000 and 320 pound ft @ 1600 gross

So not a Ton of power to begin with but plenty of torque to haul that thing at a decent speed. Specs are 4-6 degrees advanced so if you had to add an extra 5 degrees advance just to make it run decently I have to wonder if the timing jumped? The chains on these are not very tight so that could be a possibility. I haven't read of it happening yet, but there's always a first time.
Vacuum leak already mentioned.....check all gaskets and hoses.
When you did the carb rebuild did you check to see if the throttle shafts in the carb were all worn out? Vacuum leak through there will cause backfiring and power loss.

Yep, that I did TJ. Beginning of the year took care of everything...

Throttle shafts are good and tight.

Timing chain has been on my mind for a while now. I did the whole metal rod in #1 cylinder at TDC thing, distributor was where it should be, of course that might not tell me if the chain is off.

[George Bongert]

Originally Posted by TJ's GMC

Jake, did you ever get a chance to put those new intake gaskets on? Lightly buff the surfaces? Also did you reseal the valley pan?

351 power specs are: 180 hp @ 3400 and 312 pound ft @ 1800-2000 gross

351E power specs are: 220 hp @ 4000 and 320 pound ft @ 1600 gross

So not a Ton of power to begin with but plenty of torque to haul that thing at a decent speed. Specs are 4-6 degrees advanced so if you had to add an extra 5 degrees advance just to make it run decently I have to wonder if the timing jumped? The chains on these are not very tight so that could be a possibility. I haven't read of it happening yet, but there's always a first time.
Vacuum leak already mentioned.....check all gaskets and hoses.
When you did the carb rebuild did you check to see if the throttle shafts in the carb were all worn out? Vacuum leak through there will cause backfiring and power loss.

Greetings fellow members!

I agree with TJ. Although rare, timing chain "jumps" have been known to happen, and when they do, the engine runs really crappy, and you have to advance the ignition timing to even get the engine to start and run. I know. I had a '70 Buick Le Sabre in which the timing chain "jumped" causing the problems that I just described. If the chain has "jumped" and you have no (or known) vacuum leaks, you will have a very low vacuum reading on your vacuum guage indicating "late valve timing," and as I previously said, your engine will run really lousy and have no power.

[AZKen]

Did not get feedback on my post re: Backfire. Carb? Exhaust? or a pop somewhere? May or may not be a clue there. Hard start would be a clue. Slow or fast starter turning could be a clue. Hope you didn't put on a custom 3" Dia. air cleaner or some such item? Did we mentioned fuel pump, fuel filter clog, line clog, tank clog or gas cap not venting? Run without cap.

He said all cylinders have 120 psi. Jump timing would probably lower the psi. Compression would be uneven or low.

Low mileage, seems unlikely chain is stretched that much.

I think he will recon the situation as time allows. If it runs on flat land at 50MPH and slows on hills. Gravity may be acting on gas flow or debris flow somewhere. Bad fuel pumps always show up under load/hills.