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Discussion Starter #1 (Edited)
I am cross posting this from the PY forums for some additional eyes, please excuse my rambling... I tend to default to more info when I don't know exactly what could be relevant. :)

I finally got the '69 GTO home and have started researching whats been done to her over the years, while attempting to learn the basics as I go... looking for a little clarification on the current setup. (I have only driven the car on my test drive, and home to my garage... had clean dry and COLD roads up here in Alaska, just good enough to park her for the season)

I have confirmed that the engine is indeed the original 400 with what appear to be the original exhaust and intake manifolds. The transmission has been replaced (in 2011) with a th700r4 (receipt details pic) and a Hughes Performance 2000 stall torque converter. The previous owner also installed a Eaton limited slip (details) and a line lock (details). I believe it still has a 3.55 gear ratio (about 3k rpm at 60mph, which seems to check out with online calculators I have run).

OK, lots of information for a semi-simple question (bear with me I am learning)... researching the basics of a stall converter most of the information I read generally relate to higher stall ratings (2500-3500 range). What is the benefit of a lower stall converter when its down closer to the idle range? From what my limited understanding tells me, a higher rating wont engage the rear end until the engine hits near the rated stall speed... but in this case idle is much closer (I have to double check what she is idling at but it feels high and will try to jump when put in gear... another thing i need to lean about Mech.Adv... and I believe its set at 23 degrees mechanical advance from a random note on the distributor paperwork (picture))

So, is the 2000 stall just there as protection? or is it there and related to the line lock + posi install to help with breaking the tires loose and staging in general?... or is there more benefit that i am just not understanding.

Thanks for reading my rambling... I am in the "i don't know what i don't know" stage so any pointers would be greatly appreciated!
 

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The 2000 RPM converter is close to a stock converter which the car would have had with the TH400 automatic. I think it is actually more like 1800 RPM's.

The RPM rating is not the RPM's that the car moves at. The engine idles at 650 RPM's for example, you drop it in gear, and it will move forward. You don't have to put your foot on the gas and rev it up to 2000 RPM's before it will move forward. However....

If you had a "loose" race converter, this might be the case as your friend has said. There are "tight" converters and "loose" converters.

The stall speed is typically the RPM at which the engine will over power the brakes. Put your foot on the brake, bring your RPM's up, and the converter "grips" so to speak and the engine is going to over power the brakes and want to either move the car or spin tires providing the front brakes hold -thus the purpose and use of the line-lock, to hold the front brakes on.

The line-lock holds the front brakes. It can be used to apply engine power to the rear tires to "torque" up the driveline. If you have skinny tires out back, your tires might start spinning/break loose in the lower RPM range. Wider tires of course grip more, so they would most likely spin/break loose at a higher RPM. So, with a line lock, you are setting the front brakes without having to foot brake all 4 wheels just to lock up your front brakes. You are allowing your rear brakes to be free which will let your tires spin at a given RPM. You see this at the drags, it is how they heat up the rear tires to make them "sticky" so they grip better on launch. So that is one use for the line-lock It can also make for a good smoke show, so it can be used to show off at the local cruise-in until you get caught and ticketed by a cop.:yesnod:

OK, we covered stall & line-lock. Now, why else do we have different converter stalls? You want to match your converter stall to your camshaft selection. If you start looking at camshaft options, you will note that they have a specific RPM that they are suggested to be used within.

If you selected a cam that went from idle to 4500RPM, you want a stock (or even an RV towing converter which has a lower stall than stock) because you don't want the converter to have much slip when you hit the gas pedal. Using your 2000RPM converter, let's say I either mash the gas from a stop OR I am pulling a hill. I don't want my converter to begin working at 2000RPM's when I want it to work much lower down in my RPM range. 2000RPM's puts me just about in the middle of my power band and that means I basically skip/slip right over the useable lower RPM's my engine was built for. So a 2000RPM converter would most likely be too much stall for my engine.

Now on the other side of the coin, lets say I build this engine to make gobs of power and I choose a cam that works between 3000-7000RPM's. I now want to choose a converter that is going to bring my engine RPM's up real quick to the lower power range of my cam, 3000RPM's. The 2000RPM converter is now too small. I nail the gas and it grabs at 2000RPM's which is 1000RPM's below where my engine power band begins to work. It'll probably bog the engine out or stumble like a bad carb on it. So what I want is a converter that will slip up to or even a little past my 3000RPM lower power band. I want to get my engine to rev up to near 3000RPM or more before my engine overpowers the converter and it moves.

Now here is the other use for a line-lock. I would apply my line-lock, be able to rev the engine to the point where my tires are just about overpowered by my big engine, which should be 3000RPM's, which is also at the bottom end of my power band based on my camshaft selection, and then, when the light turns green, nail the gas and release my line-lock simultaneously and take off like a rocket because my launch is right at the RPM where my engine begins to make big power!:bannana:

I should also mention that a higher stall means more slip from the converter which creates more heat......and heat is bad for transmissions and fluid without adding a good cooler as a minimum.

All righty. How's that for an explanation that you won't get at PY?:biggrinjester:
 

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Discussion Starter #3
Awesome reply and exactly what I needed... I really appreciate the time for the response.

A stack of receipts from prior owners is great for trying to figure out whats been done, but I have a lot of learning before I can get to the "why it was done". Honestly it hadnt even crossed my mind to look up what the original th400 would have had as a stock converter... so that makes much more sense.

Overall it looks like the previous owner kept it in great shape and nothing is jumping out as needing to be fixed to have a good driver come spring. Again, thanks a ton for the reply!
 

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Twist, good luck with that car, and a clear post by PontiacJim. Let me add on your timing advance. There are 3 parts to it. The base timing which is where you turn and set the dizzy to. vacumn advance timing which comes from the vacumn can at the bottom of the dizzy and connected by rubber hose to the intake vacumn. third mechanical advance or centrifugal advance which is advance by weights and springs under the distributor cap.

Base setting you do with a wrench and timing light it is fixed. vacumn advance is load sensitive or sensitive to the demand of your foot.

Centrifigal or Mechanical is RPM sensitive ONLY. It is not effected by vacumn or other factors just RPM.

So what you want is 34 to 36 Total advance. total advance is base & centrifigal together. vacumn advance is not calculated there asit has no effect at wide open throttle. If your centrifigal is actually 23 than add 11 to 13 at base for your 34 to 36 total.

Vacumn advance and a good vac can are very important on a street car and make it fly when set up right. But get you toal advance right first. If it pings at 13 or 11 retard it two degrees until it does not ping.
Of course sometime you will want to verify your centrifigal number. But it is marked so give it a try:willy:
 

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:agree 'Zactly. Every engine is going to have a total timing (base+centrigual) setting that it's going to "like" the best for full power, wide open throttle operation. "Best" in this case meaning where it makes the most torque/power. What you're trying to accomplish is "timing" the lighting of the fuel/air mixture in the cylinder so as to maximize the work you get out of the resulting pressure rise. Light it too early, and the forces of the expanding gasses actually work against you and resist the action of the piston as it's still rising in the cylinder. Light it too late, and the piston is already so far down the cylinder that you get little benefit from the pressure increase. What matters then is how long it takes the mixture to light, how well and thoroughly the mixture burns, and how quickly the burning gasses expand. These rates will vary from engine to engine and are greatly influenced by all kinds of things, such as temperature of the surrounding metal surfaces, combustion chamber shape, how well the air/fuel is mixed, even the direction that the spark plug is "pointing". Case in point. 1967 '670 heads make good power, but their "closed" chamber shape has characteristics that cause them to "like" more ignition timing (earlier lighting) than say 1960 '62 heads (which probably came on your car) that are going to be their "happiest" with less (later lighting). Aluminum aftermarket heads also tend to like "more" (earlier) timing because aluminum runs cooler than cast iron.

What also matters is the "rate" at which the mechanical/centrifugal advance comes in and at what rpm it reaches maximum. This rate (also known as 'advance curve') is determined by a pair of weights and the springs that hold them that both live underneath the rotor in the factory distributor (also in HEI's). If advance comes in "too fast", it has the same effect as having "too much" timing (the engine has more advance than it needs at a particular rpm). And I bet you can see that advance that comes in "too slowly" has the opposite effect.

'Some folks' try to address a problem engine that tends to get into detonation (which is very bad for the engine) by "taking timing out of it" (reducing both the amount of total advance and the rate it comes in) - which sometimes can work, but also kills performance.

The best way to find your engine's happy value is to take it to the track (where there are very accurate clocks) and start making passes. Make sure you have a way to set TOTAL (not just initial) timing. This usually means having a 'dial back' timing light (or an accurate timing tape on your balancer), disconnecting and plugging the vacuum line to the vacuum advance mechanism, holding rpm steady at the point where you can tell the advance is "all in" (usually 2500 rpm or so), and setting the total (I'd start out at say 33 degrees) while the engine is held steady at that rpm. Doing this can be a little unnerving, so be careful and have some help. Make small adjustments until you find the setting that produces the best e.t.'s, and you've got it. When you find the best setting THEN use your timing light to "read" what that setting is at idle (vacuum disconnected and plugged) so that you'll be able to return to that setting in the future without having to set it with the engine at rpm.

Bear
 

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Discussion Starter #6
Much appreciated guys, I was having difficulty wrapping my brain around the multiple type of timing adjustments and both of the above posts helped clarify things greatly. Basically its turned into poking around the car in the garage and a file full of receipts to find things that don't understand and researching Google for the basics.

I am planning on ordering the Service, Assembly, and the Fisher Body Manuals here shortly... anything else i should look into or will those be a good start?

Off topic question: (this is my first car in 15 years with a carb) Any input on some residue ?gas? would he appreciated... {Carb Pic 1} {Carb Pic 2} <-- those pictures make it look a little more pronounced than it is due to the flash. Is this something I should address before spring? I was planning to do a quick cleanup before running her again to see if it shows back up but at the moment i don't know if its new from the last drive or just old residue of some type.

p.s. Bear: Before seeing you on this forum I came across your video on Youtube and your website with all the rebuild photos. They have been a great learning tool just to see things pulled apart and put back together, quite a journey you had there! With beautiful results!
 

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"Off topic question: (this is my first car in 15 years with a carb) Any input on some residue ?gas? would he appreciated... {Carb Pic 1} {Carb Pic 2} <-- those pictures make it look a little more pronounced than it is due to the flash. Is this something I should address before spring? I was planning to do a quick cleanup before running her again to see if it shows back up but at the moment i don't know if its new from the last drive or just old residue of some type."


The 2 pics of your carb/manifold look like my experience. Your carb is flooding over/leaking which appears to be seeping past your carb/manifold gasket and then over the intake manifold and that's where the staining is coming from.

There are a number of causes that can do this, incorrect float level (check level), the factory float (styrofoam like material) which can get saturated by gas becomes "heavy" and does not have the bouyancy needed to apply pressure to the needle and seat so any gas line pressure in the fuel system when you shut the car off can overcome the needle & seat and gas seeps past them under pressure to overfill the fuel bowl -which trickles out into the carb and can show up as seepage at the gasket(replace with brass float), a bad/worn needle and seat(replace), too much fuel pressure going into the carb(check fuel pressure), warped carb base, top, main body, or the famous plug at the base of the main body which needs a little gas resistant epoxy sealant.

In any case, I would personally look into the cause and correct it and not risk a gasoline fire which usually is too late once you see the smoke as your going down the road. So, at a minimum, you probably want to rebuild the carb or replace it with another rebuilt carb. Stick with the Q-jet, don't go Holley.

SUGGESTION: with any old car, get a small fire extinguisher rated for gas/electrical fires and keep it in the car. I also suggest a battery disconnect at your positive batter post just in case you have an electrical fire/meltdown as the only way to sometimes stop these is to disconnect the battery. Nothing more frantic than watching wires burn and you can't put them out as the wires short/heat up like the elements of a toaster because they are grounding out and you can't find a wrench to undo your battery cable. Most autoparts stores sell these cheap -and its cheap insurance to boot.:thumbsup:
 

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Discussion Starter #8
Thanks Jim, I went and bought a fire extinguisher before I drove it home :) but will look into a disconnect as well sounds like easy insurance for sure...

As for the carb issue, I appreciate the heads up... I will dig into it a little and see what's up, sounds like I've found my first couple issues to tackle.
 
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