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By kansas - 15 Years Ago
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Just put a set of Mr gasket d250 springs in my stock 292 with 4v/ I also have their timing tape on damper with initial advance set at 10 degrees / total adavnce at 2000rpm is 48 degrees , when I ran it up to 3000rpm Im over 60 degrees / car runs great but Im worry that thats to much advance for old eng./ Not sure if I should try adj vacum advance can /or just put the old springs back in/ Im not sure if thats to much advance or not /any ideals?
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By oldcarmark - 15 Years Ago
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How much advance is the vacuum can giving you?Hook up direct vacuum source at idle and see how much it advances timing.60 is too much.Did you have a look at the cam assembly and see which advance stop is engaged-13L or 18L perhaps.This will limit the amount of centrifugal advance available and should be the 13L stop engaged.Easy to change-there a small clip inside the top of the cam which holds it in place.This may be why you have such a high # total advace.The springs control the rate of advance not the total timing available.You should be aiming for total available advance of about 42-44.Initial+centrifugal+vacuum.If you have the advance slot on 18L that will give you 36 at the crank +10 initial=46.If the vacuum advance is set for 12-14 that would give you 58-60 available which is too much.If the cam is on the 13L slot and you adjusted the vacuum can to give 8 maximum that would put you at 44 available which is where you want to be.The light springs should allow maximum advance by 2600-2800 RPM.If you want to fine tune the rate of centrifugal advance you could reinstall one regular spring and see how that changes rate of advance or working through the breaker plate you can slightly bend the anchor posts to tighten the springs so it does not advance as quickly.Or you could find someone with an old Sun distributor machine to really set it up for you.
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By joey - 15 Years Ago
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kansas (12/25/2010)
initial advance set at 10 degrees / total adavnce at 2000rpm is 48 degrees , when I ran it up to 3000rpm Im over 60 degrees / car runs great but Im worry that thats to much advance for old eng.If you are truly getting 60 degrees of advance, wow. That is too much timing for a stock 292.
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By Pete 55Tbird - 15 Years Ago
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Kansas How much total mechanical advance ( with the vacuum advanced disconnected and plugged) do you have now? This is more important than the total combined mechanical plus vacuum advance because as you accelerate the manifold vacuum drops and that advance is reduced. The chance of detonation and preignition engine damage is based on compression ratio ( your engine has a low compression ratio and mechanical advance ) For a lot of years I drove a Cutlass with a SBC and it had a total advance of around 60 degrees but since the compression ratio was just under 8 to 1 it was fine and the gas milage was good too.
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By oldcarmark - 15 Years Ago
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It is true that vacuum advance drops as engine vacuum drops under acceleration,Vacuum advance comes back into the total timing advance equation at cruising speed. Engine vacuum peaks again at cruising speed as engine load decreases.If the true advance at 3000 RPM is 60 its too much.You are almost firing the cylinder before in the firing order.Engine surging will occur as full total available advance kicks in at high engine vacuum.I suspect the 18L stop is in use in this distributor and the vacuum advance can needs to be adjusted limiting the amount of vacuum advance available. Its not difficult to diagnose or fix the total advance available and limit it to 42-44 BTDC.
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By LordMrFord - 15 Years Ago
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I had over 40 degrees (total)at 3000 RPM cruising load with no worries.
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By Don Woodruff - 15 Years Ago
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You cannot trust a timing tape unless you have absolutely positively verified tdc. There are two types of advance, centrifigual, controlled bu the weighs and springs in the distributor, and vacuum controlled by the diaphram and its internal springs. Vacuum has two subcatagories, manifold and carb port. Optimal Y block timing (like all others) depends on the heads used, compression ratio, and cam shaft. The old Hipo FE engines liked 18 initial, 38-40 total all centrifiugal and all in a little over 2000 rpm. This is safe at wide open throttle with good fuel. Add a vacuum advance for part throttle cruise and you might easily see annother 20 degrees of advance and 11/2 to 2 mpg better mileage. Looking at total advance with the engine unloaded is a waste of time. If you want to really get into it use a vacuum gague to determine engine at either the carb or the manifold at various cruise speeds, up and down hills etc. Then use a hand vacuum pump attached to the distributor to determine what your setup is doing. make adjustments on your cars needs and the componets on the car. Bottom line. You say your car runs great. Why worry if it is not pinging or detonating. It is fine. Could better advance curves be developed? Quite possibly. Is it worth the effort? That is up to you. There are guys around that specialize in distibutor work. It is both an art and science. It has been my experience Ford was really fumbling around (badly) with Y ignition curves. I completely redid my Tbird ignition, limiting the centrifigual advance and modifying the vacuum advance.
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By Ted - 15 Years Ago
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36°-38° total mechanical advance at the damper and another 10°-14° for the vacuum advance works in most instances for the stock configured Y engines. That works out to be in the neighborhood of 13° of mechanical distributor advance or 26° at the crankshaft before adding in the vacuum advance amounts if shooting for 10°-12° initial advance. Do all initial tuning with the vacuum advance disconnected and the vacuum port plugged off. Tune the vacuum advance last. Engine modifications such as increased compression, camshaft change, multiple or increased carburetion, etc. will usually require some tuning of the ignition curve.
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By kansas - 15 Years Ago
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mechanical advance with with both sets of springs is right at 32 at 2500 rpm, but total advance with the new 925D springs goes over 60 /with the old springs reinstalled total advance is right at 45 The new spring must be to weak/ Im going to stay with the old springs better safe than sorry (it was in the 13L slot)
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By pegleg - 15 Years Ago
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Kansas. The 13L slot means 26 degreees at the crank, Unless you had 19 dgrees initial you couldn't get to 45 (mechanical) The springs don't control the amount of total advance, the slot does. The springs only allow the weights to move sooner or later. Something else is screwy here.
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By GREENBIRD56 - 15 Years Ago
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kansas - you've got to have been checking this thing with the distributor vacuum line connected right? To accurately calibrate the initial and mechanical / centrifugal advance systems - it needs to be done separate from the vacuum advance. The vacuum pot should be installed - but the hose from the carb disconnected and plugged. Some of the vacuum canisters - unregulated - can provide as much as 15° distributor / 30° crank advance at 15 inches of vacuum (Hg). As you increase the mechanical advance at low rev's (for instance by installing the lighter springs) ....the engine vacuum will have risen, which is then increasing the travel of the vacuum can. Leaving this part of the system active can only confuse your efforts when trying to set up the mechanical advance. A good method to set this up - after installing the new springs - is to run the engine (with the vacuum canister disconnected / carb line plugged) and find the RPM where it stops advancing mechanically. Move the distributor so that the advance has stopped at the 36°-38° position and lock it down. Allow the engine to return to idle and recheck to see what the initial advance is at low engine speed. Assuming you are using the 13L slot - it should be around 10°-12°.
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By oldcarmark - 15 Years Ago
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Good explanation Steve!If the cam is on the 13L slot the most it can centrifugally advance is 26 crank degrees.If the initial timing is 10 that totals 36 at the crank.If the total advance is 60 the extra 24 HAS to be the vacuum advance can.The vacuum advance changes the position of the breaker plate.The centrifugal advance(mechanical) changes the position of the cam assembly.These 2 systems work independant of each other.The spring tension controls how quickly the mechanical advance works.They do not effect how much the mechanical advance works in degrees. That is controlled by the stops on the 13L cam slots.
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By kansas - 15 Years Ago
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vacuum line was disconnected and plug /initial timing was set at 12
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By GREENBIRD56 - 15 Years Ago
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Because the distributor's mechanical advance is not capable of doing what you describe (when in the 13L slot, it will only deliver close to 26° at the crank) - something else is the culprit....Be sure the advance mechnism is properly installed and the travel limiting pin is truly engaged in the 13L slot. This pin usually - as delivered from Ford - has a small bit of plastic tubing fit over it. If the tubing is gone - the slot will allow slightly more than 13° of (distributor) advance. Which part number/model number of timing tape did you install on the dampener wheel? It has to be one that properly matches the diameter or the increments will be incorrect. In order to "accelerate" the reading (show something larger than fact) it would have to be made for a smaller wheel. Is the cap properly seated on the top of the distributor body? - if a large phasing error is occuring, the spark could be "jumping ahead" of the rotor. Same goes for the rotor - if it is misplaced relative to the Pertronix trigger. This "phasing error" has to do with the position of the top rotor tip relative to the pins in the cap at the instant of spark generation. The cap pins are 45° apart - corresponding to 90° of crank rotation. As the advance system operates through say 26° of total crank rotation (the full centrifugal advance) - then the rotor will be steadily repositioning itself within a 13° sweep relative to the cap pins. If the initial ignition trigger point is "late" (this has to do with the poition of the Pertronix module) - then the advance system will be steadily moving the rotor tip towards the "next pin". If it is off enough, at a certain point the system will shift one pin - a sudden drastic change in advance. An effective "old-time" method of deterimining this "phasing" - and trying to do something about it - is to sacrifice an old distributor cap and cut a hole in it. The hole is a carefully placed "window" that allows looking at the position of the rotor relative to a cap pin, while the engine is running. By attaching a strobe/timing light to the spark lead of the pin seen through the window - the flash will reveal the relative positions of the parts as the spark occurs. You can then see the rotor tip advance in near to "real time" and make a judgemnt about whether something needs correction or not. This is an "advanced" tuner's trick - and usually employed by old guys who have struggled with badly installed (or badly manufactured) "dual point" conversions.
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