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FE Ford: Ported on non ported Vacume advance

Discussion in 'The Hokey Ass Message Board' started by Beep, Sep 21, 2009.

  1. I have a freshly rebuilt 390 FE engine. It is basically stock with the exception of a Comp Cams 270H hydraulic cam, an Edelbrock Performer intake and edelbrock 650 cfm carb. The inginition is stock Ford electronic.

    With 6 degrees initial advance (set by vacume line unhooked and plugged) and the vacume advance hooked to the ported vacume line, she idles sloppy and is sluggish at low speeds. Things improve with 12 degrees initial advance, but she tends to want to kick back on the starter some and tends to pings when put under load at slow speed.

    My question, should I hook the vacume line to the unported vacume or the ported vacume line? Ford says the ported one I think?

    How about it Ford guys?
  2. What does the Edelbrock Carb manual say??? I have never used an Edelborck Carb, but every Holley I have ever used on my Ford engines stated very clearly where to hook the vacuum advance.
  3. Bruce Lancaster
    Joined: Oct 9, 2001
    Posts: 21,205

    Bruce Lancaster

    Ummmm...trying it both ways would cost....taptaptap on calculator...$0.00 dollars, rounded off, and a few minutes...
    Only real work is dialing idle back down a bit when you go to manifold. Road test, feel, listen...
  4. I think it has more to do with the distributor than the carb. I know the older FE's with Ford carbs used a non ported vacume system. Ported ones weren't invented yet i don't think. I just thought some smart FE guy could tell me....................
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  5. BigChief
    Joined: Jan 14, 2003
    Posts: 1,953


    Ported vacuum source for FE's with single diaphram advance units.....and Duraspark.

    Set the initial timing at 8-10 degrees and shoot for about 34 total with today's "premium" fuel (all of this done with the vacuum advance unhooked). Make sure you always run premium in the old girl. You may be able to use more than 34 degrees total depending on cooling capacity, local fuel quality, jetting, etc, etc.... If its still lazy down low you may need to have the distributor recurved. Get all of the advance in by 2500-2800 crank RPM. If you run into spark knock with the vacuum advance hooked up you may have to pull some out of the advance unit. Luckily many FOMOCO vaccum advance units are adjustable (use an appropriately sized allen wrench in the port).....use a hand held vacuum pump and a timing light to check your progress....I had good luck with 8-10 degrees initial, 5-7 degrees in the vacuum advance unit, 24ish crank degrees in the dizzy with my 428CJ....unhooked you'll have 34ish total and hooked up you'll have a little over 40. Adjust as necessary.

  6. BigChief
    Joined: Jan 14, 2003
    Posts: 1,953


    ....remember, the car based FE's usually weren't lacking for compression. You don't have a big cam in there either so your not going to be bleeding much cylinder pressure off at low engine speeds like you would with a bigger cam. Premium fuel and quite possibly good octane booster may very well be required. You also want to keep operating temps down to 180 or less when possible with these pressure cookers.

  7. Big Chief,
    Thanks for the help. The temp is one of the issues I am having. With 6 BTDC initial timing and the vacume hooked to the ported line (not sure of the total), she tries to run around 195. In heavy traffic she builds to around 205 quickly. On the road she will go to around 180. I do have a choice between distributors. Currently I am using the stock 75 Ford electronic distributor, but do have a Mallory vacume distributor as well. Is one better than the other? I understand about the compression. Not sure of the total static ratio, but doing a compression test brings 225 pounds on every cylinder within three turns of the crank so it is fairly high don't you think?

    So, reviewing what you said. Using the Ford distribtuor (vacume line disconnected)set the inital timing, at slow idle, at 8-10 BTDC. With increased the rpm (vacume line still disconnected), the timing should move up to about 34 BTDC? I assume that this means that the distributor has a mechanical advance method built in. Then when hooking up the caume line the total moves out to 40 BTDC?

    Sorry for sounding ignorant, but I am used to using magneto's with either locked in advance or mechanical advance (no vacume). I don't do much door slammer stuff.

  8. BigChief
    Joined: Jan 14, 2003
    Posts: 1,953


    Your temps seem normal for an FE is a warmer climate. You could improve the fan/fan shrouding to help with low speed cooling problems. Bigger radiator may help too if the shouding isn't helping. Water-wetter will help but its effects seem to fade as it ages.

    There's nothing wrong with either dizzy. I like electronic over points, especially on FE's. they seem to start and idle much better. Either distributor may need to be recurved (or at least checked) so its your choice. Your correct on you thinking about the advance(s) in/on the distributors.

    Thats plenty of cranking compression....225psi is PLENTY for pump premium/iron heads/small cam combination, actually. Either you have more mechanical compression than you think or possibly something is "making" compression.....namely the cam. Did you degree the cam in before installation? We've had a couple CompCams come through lately ground wrong or stamped incorrectly.

    You may need to degree/double check the cam timing. Make sure you (or your builder) installed the correct cam (verified by using degree wheel before final installation) and that it is installed "straight up" - as opposed to advanced several degrees. If you've got a multi-position timing set double check that its installed so that the cam is straight up and not advanced. We've also had a couple timing sets come through that were incorrectly marked as you really need to make sure where the cam timing is on this one.

    If the cam and and its installation pan out then you've probably got more mechanical compression than you thought. More/better fuel and/or mixing with race gas is an option if you can afford it. Otherwise you can try retarding the cam 3-4 degrees, maybe install a larger camshaft with more duration to bleed off low speed cylinder pressure or finally reduce your mechanical compression ratio with different heads and/or pistons.

  9. BigChief,
    Thanks for all the information. As to actual static compression ratio or cam timing, I have no idea. I bought this engine complete and running from a guy having $$$ issues due to the economy. It had less than 2000 miles on it. Here is what I know. 1975 390 from a pick-up. Bored +40 w/flat top pistons (no dish or pop up) Heads are from a car (don't know the year or type) and they have had larger intakes installed (don't know what size), steel seats and SS valves. The Comp Cams cam I told you about (270H) with Comp Cams springs & retainers and Sharp adjustable roller rockers with Comp Cams pushrods, Edelbrock fuel pump, Performer RPM manifold and Edelborck 650 cfm carb. Timing chain is a double roller.

    The Mallory distributor is electronic vacuum advance (model 4755301H). The vacuum module is broken (thats why I am using the stock Ford one) so I orderd a new one yesterday. When I get it in, I think I'll switch over. I assume that setting the timing with it is the same method (line disconnected, set at 8 to 10 initial, connect to the ported line),,right?

    Again, Thanks for the all the help. I have been working on race cars since 1957, but always used magneto's with locked set ups. Everything is set initial. No changes once she starts. Very different. My nostalgia AA Fuel Coupe runs at 40 initial..locked in.
  10. Truckedup
    Joined: Jul 25, 2006
    Posts: 3,785


    [​IMG]I'll tell you what works on Chevy small blocks,and being a V-8 is a V-8...
    Run full manifold vacuum to the advance unit.Limit the total vacuum advance to about 12 crankshaft degrees with a stop of some kind,a little trial and error might be necessary.Then run the total mechanical advance as usual.The photo is a Chevy HEI,but you can see how easy an advance stop is made,
    My self and several others have done this and noticed an improvement in part throttle response and improved idle quality especially when a hotter cam is used.This does work better than ported vacuum advance,try it and see.
    In some situations,the ported vacuum will see a false vacuum signal at wide open throttle when you do not want the vaqcuum advance to operate
    Last edited: Sep 23, 2009
  11. BigChief
    Joined: Jan 14, 2003
    Posts: 1,953


    FE flat tops typically have about 5cc volume due to the eyebrows.....the lowest you'd be for a static compression ratio is about 9.7:1 if the pistons are .020" down the hole and you have the later 76cc smog heads and they were not decked. Since you've got 390 car heads (the most common chamber sizes are in the 68-74cc range) that could bring the compression ratio up to as high as the 11:1 range depending on actual chamber volume, gasket thickness and deck height.

    Its safe to say you've probably got at least 10:1....most likely closer to 10.5:1. If you had aluminum heads you might be able to get away with this kind of squeeze but with iron heads and these motor's tendency to run warm its likely you'll need to do something about it.

    Here are some or more of the following should help get you dialed in.

    Race fuel and/or a race fuel/pump gas mix. Verifying that air fuel mixture is correct and running it a bit rich may help with the detonation.

    Water-Methanol injection.

    Cooling system upgrade.....probably could use more, bigger, badder regardless.

    Replace the cam with a larger one with more duration (verify piston to valve clearance) may bandaid things a bit by retarding this cam 3-4 degrees....maybe. If your on a budget then this may help.

    Replace pistons with dished pistons and/or swap to an aluminum heads with larger chambers.

    Good luck with it!

  12. OK, a final report on this. But first, thanks guys, thanks to everyone for all the help.

    * I replaced the vacuum advance module because I found out it was not working very well.
    * I then set the timing an 8 BTC with the vacuum disconnected and engine at a low idle.
    * I Then hooked up the vacuum to the ported side of the carb. It ran good and I even had to adjust the idle down to a lower speed as it jump up some.
    * I tested it out on the street and all the hesitation and most of the sluggishness was gone.
    * I then changed the vacuum to the non ported side and wow!!, the idle went way up. I had to reset it again downward and took it back out on the street.
    * Holy shit,,she screams now. She idles beautiful in gear w/AC on, has incredible throttle response and she runs fantastic.

    She does not kick back on the starter, does not ping under load a low speeds anymore and the best part, she does not tend to overheat anymore. Even in heavy traffic w/AC on. Now, the weather is a lot cooler than it was the other day, so we will have to see how it does when it is Texas hot outside. But tonight she ran around 165 to 170 at highway speed for over an hour. In traffic it jumped to 185 and stayed there.

    I'm a happy camper... :)

    Thanks guys..................
    Last edited: Sep 24, 2009
  13. Sounds like you are good to go, I run my 390 at 10 degrees and ported signal, but I have a petronix in my stock distributor. Just more food for thought I guess

  14. tommy
    Joined: Mar 3, 2001
    Posts: 14,763

    Member Emeritus

    Thanks for responding with your results. I was pretty sure that Ford went to manifold vacuum in 57 with a big improvement. All of those problems corrected by simply hooking up the vac adv to the correct port for the distributor that you are using.

    GM often tied the vac advance into the side of the carb with it internally routed below the butterflies...therefore manifold vac. leading people to believe that it was ported vac when in fact it was not. It sill can be manifold vac but not connected directly to the manifold which leads to lots of confusion.
  15. BigChief
    Joined: Jan 14, 2003
    Posts: 1,953


    Ford went from the God-aweful "Load-o-Matic" distributors to more conventional centrifical + a single diaphram vacuum advance in 1957. Both distributors were vacuum advanced equipped...the Load-O-Matic was all vacuum (manifold and ported) advance with no mechanical advance.

    On the many of the FE's in the 60's Ford used a series of thermostatically controlled valves (sometimes located on the thermostat housing) and dual diaphram advance (advanced and retarded the timing) units (along with normal mechanical advance) to dial things in. Oh joy....

  16. BigChief
    Joined: Jan 14, 2003
    Posts: 1,953


    Sweet! Make sure you keep any eye out for detonation and don't cheat on the gas and you should be good to go.
  17. Relic Stew
    Joined: Apr 17, 2005
    Posts: 1,043

    Relic Stew
    from Wisconsin

    I prefer manifold vacuum. As you noted, it gives better idle quality and throttle response.

    Ported vacuum tends to be for emissions purposes. Reduced idle timing increases exhaust temps (and engine temps) so AIR and catalytic converters work better.

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