350 timing with HEI

[LONGHAIR]

You really should have started a new post, rather than hi-jacking a 5 year old one.....but at this point, I guess it doesn't matter.

The main thing to note here is that the statement "I just installed an GM HEI distributor", means very little. There are at least a dozen different variations of calibration. Just because they all "look" the same and they all "fit", does not mean that they will "act" the same.....because they will not.
You really need to know where the advance curve is tuned to....and be willing to adjust it. For some reason, many guys think that they can pull out the points distributor, drop in the HEI, and they get all of the advantages "automatically".
It's just not that easy, unless you go to the trouble to have your "new" distributor calibrated to match the old one before you install it.
Most of the stock HEIs are set-up to run with ported vacuum...and you don't want that.

[slowboy]

Thanks for your information on HEI's. I did not know any of this.


Also...sorry to upset you by "highjacking a 5 yr. old post".
I didn't look at how old post was.

I still have not figured out how to start a new post, and since
this post was pertaining to some of my problems, I don't see
how my replying on it could possibly upset/hurt anyone.

If you will, please tell me how to start a new post, [per section XIII
of guidelines and rules] and I promise that this kind of
"highjacking" will not happen again.

Thank-you.

[LONGHAIR]

It's not about being up-set (it takes a lot more than that) it's about following the rules.

To start a new thread,

[Keller]

I can see his point... sometimes new posts get flamed for "not doing your research and searching previous posts on the forum." I probably would have done the same and just responded to a thread that already existed.

[slowboy]

To me, it's just nit-picky. I've read guidelines and rules, have seen nothing about 'not' replying to old posts.

Whatever...not here for pissing contest...here to learn and ask questions.

So...my last word on this is God Bless Longhair, and thanks for advice.

Now...time to go back through guidelines and rules, and hopefully I'll be able to avoid this kind of stuff in the future.

[mwmeador38]

Your vacuum advance is ruptured.

[cherokeejohn]

ok I've been reading thru this thread and soaking up all posts in hopes that I will finally get my timing adjusted right, but the last post about the vacuum advance being ruptured really just threw me for a loop. If you would, please explain this or an example. mine is a stock 350 with a remanned Qjet on it. the HEI is a Maliroy that runs off a ported vac. I've set the plug gaps correct, capped off the vac ports and set it at +8 and still it isn't running correctly. I'm almost ready to kick it to the curb and buy a good new points dist set. any suggestions, advise, or thoughts are welcomed

[geezer#99]

If the vac can has a hole in it, you get no vacuum advance.
That's what he means.
Also if there's a hole in it then you have a vacuum leak.
Easy to check your vac can.
Draw a vacuum on the hose. Use your lung power.
Or just switch the hose to manifold vac port while the motor is idling. If the rpm increases then it's working.
And 8 degrees isn't anywhere near enough.
Try 14 initial.

[slikside]

Old thread, but good info! Sub'd.
Posted via Mobile Device

[diggerbob]

I put an accel HEI in my new engine that I put in my 70 truck back in 1992. It ran good until I started doing other mods (particularly adding a 700r overdrive transmission). With the overdrive, I became aware of pinging on partial acceleration under load (like climbing a hill). I never heard it with my old 3 speed trans because the engine was revving so high at cruise speed, I couldn't hear the pinging. Gasoline changed too with the addition of corn fuel (methanol) to good old fashioned fossil fuel. The overdrive slowed down my engine rpm's so I could hear what the motor was doing under load at cruise speed.

Distributors (or their later day counterparts, which everyone calls HEI's) are pretty much the same from the standpoint of engine timing. Ignition timing on an old fashioned 70's motor is controlled by 3 things:

1. Initial timing (which you set at a low idle rpm before dynamic timing kicks in-meaning no. 2 and 3 that come next);

2: Mechanical advance (which involves a couple of little springs and curved weights located under the rotor-they advance the timing after you go past an idle speed of 800 rpm's or so);

3: Vacuum advance which is determined by the little vacuum can on your HEI/Distributor that has a hose connecting to engine vacuum. (tip-don't call a distributor a "dizzy" on this board...that pisses some folks off)

A lot of the off-the-shelf HEI's that you can buy at autozone or other parts stores have vacuum advance units that give 24 degrees or more timing advance, which you don't want because that lifts your total advance timing way higher than you want it. You need to limit the vacuum advance to something more in the range of 6 to 12 degrees of maximum advance or you will get detonation/pinging. You can get adjustable vacuum advance cans, but they are a pain for a novice engine tuner to work with.

Once you get the correct vacuum can, set your initial timing at 12 degrees. If it is hard to start or it tries to keep running after you turn the ignition key to off, back timing down by 2 degrees. You shouldn't have to go less than 8 degrees before-top-dead-center to eliminate dieseling (running after the key is turned off) or pinging/knocking under load or acceleration.

Someone can chime in with a suggestion and a part number for the man or even tell me that I am dumb (heard it before).

[71CHEVYSHORTBED402]

I have a 400 and haven't timed my HEI in over a decade. Don't drive it much, but will reset with restore. Wish I could remember exactly, and was foolish not to make note, but I believe retard 8 is a guide. Pretty sure elevation matters. I do seem to remember the spark plug gap should be a pinch wider than original.

[joewell80]

I installed a new GM performance HEI (proform) on my 350 with Edelbrock carb and Holley aluminum intake. I'm using CR43ts plugs gaped to .045, initial timing set to 14* at 700 rpm's and at 3000rpm's mechanical advance jumps it to 36*. When I hook up the vacuum (ported) it jumps to 48* at 3000 rpm's. It seems to run ok but I'm wondering if the vacuum is advancing total timing to much?

[Big Kev-O]

Wow, old thread alive again.

joewell80

I don't want to start the old ported vs. full manifold arguement but for educational purposes you may want to read the link below. I would personally never run a non emmissions controlled engine on ported vacuum advance. The first section is about camshaft timing and is of noconcern to you, breeze through it and you will get to the part about using a ported vs. fulll manifold for vacuum timing crankshaft advance.


http://www.jalopyjournal.com/forum/t...ot-time.54221/

[toolboxchev]

Originally Posted by Big Kev-O

Wow, old thread alive again.

joewell80

I don't want to start the old ported vs. full manifold arguement but for educational purposes you may want to read the link below. I would personally never run a non emmissions controlled engine on ported vacuum advance. The first section is about camshaft timing and is of noconcern to you, breeze through it and you will get to the part about using a ported vs. fulll manifold for vacuum timing crankshaft advance.


http://www.jalopyjournal.com/forum/t...ot-time.54221/

The jalopy journal read is EXCELLENT! A very wise man says you are never to old to learn something.

[mredd]

Originally Posted by bluedog

Just installed an GM HEI distributor. Plug gap set at .045. What are you guys setting the timing at? I have a stock engine with a Edlebrook 4 bbl. and mainifold. Stock exhaust.

Thanks,

Scott

Timing is timing. Doesn't matter if it's an HEI system or standard breaker points and a coil. Gap is a bit different, though due to the current in the spark. Open them up from what you use for a system with points to 0.038-0.045.