timing with vacuum gauge

Jon B
Jon B Administrator
edited November -1 in HUDSON
A recent technical article in the New England Chapter newsletter sets forth the method of adjusting timing by using a vacuum gauge, not a timing light. It says to turn the distributor until the highest vacuum reading is obtained, then back off about 1" on the gauge. Using this method, the markings on the flywheel, and use of any timing light, is not employed.



I was curious to know if anyone has tried this on their late-30's Hudson products (without vacuum advance). If so, were the results better, worse, or the same as when you used a timing light?

Comments

  • Geoff
    Geoff Senior Contributor
    The problem is the nebulous "about 1" on the gauge". I prefer to use the light myself, but if you have a vacuum gauge it is a handy tool for adjusting the idling mixture and timing. Personally I think the earomoter is just as good!

    Geoff.
  • Unknown
    Unknown
    Give it a shot Jon and let the rest of us know the results. I've had my best luck with the light. What you are talking about is some real old school stuff.
  • EssexAdv
    EssexAdv Expert Adviser, Member
    I have used this method for years altho I set it at max vac and do not pull it back. This method eliminates concerns over inproper cam timing due to chain slack or gear lash. Used to use it all the time on slightly older cars when I was in the repair business. Never had a problem with ping or under preformance
  • J Spencer
    J Spencer Expert Adviser
    'back in the good old days' I used to use a vacuum gauge alot to set timing and adjust carb. always worked well for me. Into the seventies the timing light was usually a better method due to emission controls, lean carburetors etc. Some of the seventies stuff was hard to advance even a couple of degrees from factory specs.



    Im had a 1972 chevy Impala 350 2 brl carb. 15 MPG was about tops for mileage. I put a stock 4brl Q-jet carb on it, put advance weights/ springs from a 1970 350 and I was able to run 4 degrees mare advance than factory. all tha and a special torque converter and I was getting 19 miles per gallon-- highway.



    Didn't work for all chevys though



    JSpencer
  • Unknown
    Unknown
    :) I agree with Lew ... the following has been on my website for sometime.

    Optimizing your timing to the operating altitude

    From the Hudson Chat Page: Brad Gentner '70 Uncut and Bone Stock

    Someone also asked about this tonight, but I deleted it before I thought to respond. I will describe how I timed my engine w/ a vacuum gauge. First, attach vacuum gauge to a source of manifold vacuum. With engine at operating temperature, idle set to specs. and vacuum advance line disconnected and plugged, advance timing by rotating distributor clockwise. Your vacuum reading should increase. You'll get to a point where further timing advances have no effect on vacuum reading. This is the timing that develops max. Vacuum. Now retard the timing until the gauge reads 1/2 in. Hg. lower than this max. Level. Tighten down Distributors hold down, and, voila, this should be the optimal timing for your altitude.


    I know that this method has been used by may experienced Hudson mechanics... it assures, as Lew points out, that you optmize the engine for the operating enviornment. This method will assure you properly adjust the carburator too. Word to those who traverse this path... YOU MUST set the point gap correctly first. Then you are able to maximize your engine preformance.
  • [Deleted User]
    [Deleted User]
    If this method works, it is pure luck. DEFINATELY not recommended.
  • tigermoth
    tigermoth Expert Adviser
    rod, you seem to be dismissing, pretty quickly, a lot of experienced mechanics. could you please elaborate a little more the reasons for your statement. thanks. tom
  • SuperDave
    SuperDave Senior Contributor
    This method surely cant be used on computer controlled cars. They are entirely different. However, Setting the timing on older cars not only can be done this way, It should. Using the factory supplied timing on every engine under all condidtions is not useing your brain! Many OEM manuals tell you that those timing specs are for general use. "A starting point". Different air temperatures, different fuel, different altitude, different compression due to carbon build up, and different combustion chamber temperatures all have some bearing on the timing that needs to be in the engine for optimum performance.. Many if not all older car manuals tell you to set the timing and then adjust it until you are on the threshhold of pre ignition. Using the vacuum method along with a test drive will net a smoother running, cooler running, more economical operating and stronger engine. For example, My 262 super six with 80,000 miles at sea level, 85 degrees ambiant temperature on regular gas is not going to need the same timing as someones rebuilt Hornet 308 in Wisconsin in February! Set it by the book and not read the next paragraph will work. Just won't be optimized.
  • Jon B
    Jon B Administrator
    I wonder if the following statement by Park W., (published in this forum last July) would have any bearing here:



    'I'd been troubled by the low mileage on our Twin-H '51 Hornet (that's why I was rechecking the timing), so I advanced the basic setting to 6 degrees before TDC. No ping yet, so pushed it up to 8 degrees. Then drove to Front Royal for Doc's Meet (1,000 miles round trip). Mileage went up 6 mpg from what I'd been getting!'



    Would using the "vacuum method" automatically give you the same result as advancing the timing as far as possible (via the timing light), and optimize gasoline mileage in the process? I'm a rank amateur when it comes to timing engines so I'm curious.
  • [Deleted User]
    [Deleted User]
    I use both the timing light and the vacuum guage, always have. I have a snap-on scope so I hook up both the timing light and vacuum guage its just standard op for tuning an older engine. You can tell a heck of a lot about an engine using a good vaccum guage. And it isn't luck its based on solid principles of engine design. Setting your timing based on your location and elevation is part of a proper tune up and I guess is the reason some of us get good gas mileage and some of us complain about poor milage. I grew up in a garage and saw my Dad tune a lot of cars with a light and Vacuum guage. The light gets you to the factory spec the vacuum guage gets you precisely tuned for your location.
  • hudsontech
    hudsontech Senior Contributor
    Jon B wrote:
    A recent technical article in the New England Chapter newsletter sets forth the method of adjusting timing by using a vacuum gauge, not a timing light. It says to turn the distributor until the highest vacuum reading is obtained, then back off about 1" on the gauge. Using this method, the markings on the flywheel, and use of any timing light, is not employed.



    I was curious to know if anyone has tried this on their late-30's Hudson products (without vacuum advance). If so, were the results better, worse, or the same as when you used a timing light?



    While we at the New England Chapter newsletter staff attempt to verify all material that we use, we will admit that some stuff is a shot in the dark.

    As I recall we purloined that article from a WTN that came out about 15 or 20 years ago.

    We erred, in this case, by neglecting to post a source note.



    Hudsonly,

    Alex Burr

    Editor, Nor' by NorEast
  • terraplane8
    terraplane8 Senior Contributor
    There should be no side-play in the distributor bushings to avoid erratic timing which can be significant. Also, a rolling road dyno would be an interesting exercise to find the optimum ignition advance at all speeds using today's fuel, and then recalibrate the distributor advance curve accordingly.
  • 464Saloon
    464Saloon Senior Contributor
    My experience is that setting timing for maximum vacuum will give great throttle response but generally will ping under any kind of load. This has all been with cars with vacuum and centrifugal advance for the most part. My 51 Ford flathead V8 I tried this with and its is vacuum advance only and it would rattle (ping)under load. With cars that had both vacuum and centrifugal advance, timing by this method generally made them overadvanced at high rpm, which they not only rattled, but the engine did not rev freely. In my 2 cents timing by vacuum would be good for low rpm, peak response ,peak fuel mileage. Other than that, it depends on your motor and type of distributor you have.
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