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ignition on a 77 Blazer

Discussion in 'The Garage' started by bigoltrux77, Jul 3, 2002.

  1. bigoltrux77

    bigoltrux77 1/2 ton status

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    im thinking about changing out my old ignition. I just got the truck and dont know much about it. Its a 77 Blazer with 350. I dont know what type of ignition it is..I dont think i have points. What type of performance ignition should i get? How much will it cost me nad can i do it myself? Im good with trucks. ALso im looking into buying a new cam. What should i look for in those too.? On more..Hooker Headers or Flowtech?
     
  2. barbastard

    barbastard 1/2 ton status

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    I've got a 77 also....you don't have points you've got a HEI ignition which has the coil in the top of the cap. I recommend replacing the cap and rotor and getting a high output coil. I've got an MSD that puts out around 42,000 volts but they make 'em as high as @50,000. You do that and you'll be styling!! /forums/images/icons/cool.gif
    Might as well do new wires and plugs while you're at it too!!!

    Take care and good luck...

    Nate

    AKA "BARBASTARD"
     
  3. bigoltrux77

    bigoltrux77 1/2 ton status

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    about how much will all this run me? What all parts will i need?
     
  4. Greenblazer-AZ

    Greenblazer-AZ 1/2 ton status

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    If I'm not mistaken, you should have HEI ignition. If so most people will tell you that is an excellent stock set up, and changing it will not give you a whole lot for the amount of money you'll spend.

    There are aftermarket add-on ignition boxes that use the stock distributer. The ones designed for off-road applications may be helpful.

    The one from: http://www.jacobselectronics.com/products/energypaks/energypaks.htm
    personally appeals to me, but I don't know anyone that's tried one.
    The one from: http://www.msdignition.com/
    might be easier to find someone that's tried it.

    MSD products are very popular, but most of their stuff is geared towards hotrodding and high RPM applications, which are not really useful for rock crawling or trail running, mud bogging yeah you can use high RPM stuff, but there ain't hardly any mud round these here parts(Arizona).

    There are lots of other things you could spend money on that will make much more useful differences in the way your truck performs. One of the most overlooked mods by people new to wheeling is lockers, for offroading that is probably the most important mod you can make. With lockers a stock rig on stock tires could go places someone with 35" tires and open differentials couldn't go.
     
  5. HarryH3

    HarryH3 1 ton status Author

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  6. Greenblazer-AZ

    Greenblazer-AZ 1/2 ton status

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    Thanks Harry! That thread was enough to convince me to scrap the idea of getting the Jacobs system. It's things like this that make my membership worth every penny!
     
  7. Blazer_Boy

    Blazer_Boy 1/2 ton status

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    Leave that "stock" junk alone! /forums/images/icons/laugh.gif Ever try sticking a match in a fire thats already lit? Not gonna do much, why try to ignite a mixture thats already burning. MSD boxes fire several times instead of once below 3,000 RPM. All of your big power figures are made above 3,000 RPM. Those boxes are really only useful in racing because of the RPM potential and all of the add-ons they accept (rev limiter, retard controls).

    Now there are three schools of though on the HEI.

    1)Its fine, keep your damn hands off it.
    2)A little help can make a great setup even better
    3)Oh lord, the sky is falling , get an external coil, big ignition box, etc.

    #3 isn't wrong by any means, but definitely not necessary if your still going to keep the HEI. Why modify it when you can just buy an MSD distributor thats meant for an external coil, is smaller, and will directly hook up to the box.

    I tend to fall in with the #2 statement. David Vizard's Small Blocks on a Budget book has several tests on HEI componets. A stock coil can charge 2.5 amps per millisecond, an MSD HEI coil can do 3 amp per millisecond. The stock coil in the test began to mis-fire at around 4750 while the MSD hit great till around 6,100.

    Module testing showed that a stock module will deliver around 5.5, while an MSD unit pumps out around 7.5 amps. The test again showed that the stock module ran out of pep at around 4750, while the MSD module went off the scale!

    Next would be plug wires. Buy those super low resistance wires. MSD ones have 50 ohms per foot. Boy, I'm starting to sound like a commercial. Get the wires first, coil, then module. All this will probably set you back $200. You've got a complete HEI setup for price of just the 6AL box.

    Forgive me if I go into to detail, but I don't know your level of skill. Take off your distributor cap and rotor. There should be two funny shape weights and a plate in the center. Holding things up will be two springs. What happens in there is that when the distributor begins to pick up speed, those weights start to come out. This makes the plate the rotor attachs to move, and changes the timing. The springs in there adjust how fast this happens. Chaging to lighter springs in there makes the advance come in sooner and can improve performance. This system will provide 20 degrees of advance on top of where your initial timing is set.

    So, lets say you've got your timing set at 8 degrees BTDC. With the vac advance disconnected, you rev this thing up. 20 degrees mechanical advances happens, plus the 8 you have from the initial timing. So typically you'd have 28 degrees of mechanical advance occuring at around 4,000 rpm. Literally too little too late /forums/images/icons/frown.gif .

    SBC chevys like around 32-38 degrees of mechanical. 32 degrees would be fine for very efficent aluminum fastburn heads from GM, or similar. Production heads are going to like around 34-38. 38 being the high figure for a very inefficent combustion chamber.

    So we need more advance and at a faster right. Buy the crane advance kit for the HEI, it comes with new springs and adjustable vacuum advance. The kit has some guidlines as to how fast their springs will bring in the advance. GM used different weights over the years and it would be foolish to say that those figures are set in stone. What you want is advance that will happen just off idle (not during) and is all in by about 3,000 rpm.

    With that redone, go for a ride. Make sure the thing is warm and its hot out. If you're wise, you'll have the stock air cleaner hooked up instead of the open element design. This setup actually has brains! /forums/images/icons/laugh.gif . It has a tube that will suck heat off the exhaust manifold when cold and has a flap that opens to suck COLD air from the outside. The problem with your '77 is though that it doesn't have the tube to suck cold air. This happened in '81. Look at later models to get the idea. Your front clip will have a round hole next to battery with a plate tacked over it. I guess they thought about it but never got around to it. Pop that out and run a tube to your air cleaner. An 80's air cleaner would be ideal because of the bigger snorkel. This helps to give consisent performance and less variables.

    Now set your intial timing at 12 and plug off the vacuum advance. Look for good throttle repsonse when driving. Check for how it feels comming off a stop sign, or even when you get after it a bit. Find a BIG hill and start pulling up. You're listening for detonation/pinging. We've made the engine spark earlier with the mods done. Now we've got a ball of combustion flame happening while the piston is traveling up. It this happens too late, turbulence and pressure go wack and you'll hear a knocking noise. Its almost unmistakeable when you hear. I usually hear it comming from around the shifter hump. It doesn't sound like engine noise, but more like something rattling around. It is an engine noise and we don't want it.

    If things are good, turn it off. Start the engine up? Did it struggle? Keep going up as much as you can. 14, or 16 if you can and it works better. 18 is not recommended by me, but it is the end of the 32-38 generic total advance recommendation.

    If you have a knock with 12 degrees, or starter drag. There are some things you can do. Premium fuel for starters. I don't understand some people's fear of it. Its like $.10 more per gallon. If you spend all your money on performance parts, yet can't cough of the extra for the appropriate gas, then so be it.

    Next would be a cooler thermostat. This is a good idea anyways, it keeps the intake cooler and that equates into denser air and better peformace. 180, should do the job. GM even used that in some vehicles. 160 degrees or no thermostat is not recommended. 160 won't keep the heat up enough to ensure good atomization of the fuel or boil off any water vapor. No T-stat won't slow the water down enough to allow it too pickup heat and will make for a slow warm-up.

    With everything in order, we now must adress vacuum advance. This is not for performance, if things don't run good without it, we need to do more work up above. The idea behind this is just to throw in a little more advance under lighter loads to keep the plugs clean and mileage up.

    With the engine running and warm, check the line for the vac advance. It should have no vacuum at idle and will begin to suck when you open the throttle. That is called ported vacuum. GM did it that way to keep the initial timing down and to decrease emissions. Emissions or not, the way the Quadrajet does ported vac is perfect for what we want. It will offer no vac advance at idle, yet will give it when you're crusing. If you really open it up or load it down, engine vacuum will fall, along with vac advance. Thats why I say don't rely on vac advance for performance, its only there for a little bit more mileage, clean plugs, and throttle repsonse. It is a LOAD sensitive system.

    Anyways to get back on track here with your vac advance now hooked up to ported vacuum. All you have to do with the adjustable vac advance is stick an allen wrench in there and crank it to the left to reduce the amount. One turn usually drops off 2 degrees. Run as much of it as you can. If you go for a ride and the thing sounds kinda chuggy, doesn't feel as good, or does that knock/rattle, back it off. Keep the wrench in the truck for a while. One turn back at a time when you adjust.

    My setup goes something as follows. 16 initial + 20 Mechanical (in at 3,000) + 8 vacuum. I have a 180 T-Stat, 91 octane gas, 9.2:1 compression with a stick shift. If you add the numbers up, its 44 degrees total. Sound like I monkeyed things up? The stock settings were 4 degrees intial, 20 degrees mechanical, and 20 degrees vacuum, for a grand total of 44 degrees. Sound familiar?

    Save the cam for a new motor. Why? Well stock motors have super lower 8.5:1 compression. Performance cams are made to work with higher compression. You can get ones for lower compression, but why not have more? You could get more compression with better heads (vortecs), but then you have new stuff on top of a tired old 350.

    Doug Thorley seems to be the choice on here for headers. Hedman has some heavy-duty headers that look prettty sweet. Personally I have some pretty sweet tubular stainless steel manifolds that GM used for a time. They are rather rare because I'm sure stainless isn't cheap. My uncle Kirk got them off some GM military stuff he bought at an auction out at Fort Carson in Colorado.
     

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