What are folks using for initial timing on 67 GT500's with the stock distributor? Book says 8 -- which is what I have marked in chalk and am still using.
Quote from: Brandon on August 24, 2025, 09:12:48 PMWhat are folks using for initial timing on 67 GT500's with the stock distributor? Book says 8 -- which is what I have marked in chalk and am still using.
That's good. Octane of fuel is a big consideration if you go higher. Others may have a different opinion.
Always use 91, with some percentage of ethanol nowadays.
Quote from: Brandon on August 25, 2025, 02:02:01 AMAlways use 91, with some percentage of ethanol nowadays.
If you go more then 8 on 91 octane I suspect you will get pre ignition/ping when you get on it.
do your timing by ear
warm up the engine, loosen the distributor: just enough so it can be turned by hand
retard the timing first, then advance the timing by slowly rotating the distributor
listen for detonation: or "spark knock" and then back off the distributor slightly until the sound disappears.
secure the distributor, then take the car for a test drive.
listen for pinging under load or hesitation on when you start it.
make further adjustments the timing if needed.
retune your carb after setting the timing.
best of luck in your endeavors
Quote from: FL SAAC on August 25, 2025, 07:24:00 AMdo your timing by ear
listen for detonation: or "spark knock" and then back off the distributor slightly
Well, I agree with this in theory it definitely needs to be driven under load. As Bob mentioned there are many factors such as resurfacing of cylinder head in deck, combustion chamber, piston, size, etc., as well as the octane used.
I don't think you're gonna be able to hear that nation on an engine that's idling and not underload to a point where were really matter. I suggest you start with an initial around 10 to 12° and drive it and see if it does pain. If it does under a heavy load and back it off 2° and check again. I think you'll find you probably can get up getting around 12 if you go up to 93 pump gas.
The other thing that's a big factor is your harmonic balancer. Has it been rebuilt or checked? A lot of these balancers actually can shift a little bit overtime and spend which will make the factory timing Marks non-Reliable.
I wonder why someone decided to invent a timing light :o
Quote from: TLea on August 25, 2025, 06:28:25 PMQuote from: FL SAAC on August 25, 2025, 07:24:00 AMdo your timing by ear
listen for detonation: or "spark knock" and then back off the distributor slightly
Well, I agree with this in theory it definitely needs to be driven under load. As Bob mentioned there are many factors such as resurfacing of cylinder head in deck, combustion chamber, piston, size, etc., as well as the octane used.
I don't think you're gonna be able to hear that nation on an engine that's idling and not underload to a point where were really matter. I suggest you start with an initial around 10 to 12° and drive it and see if it does pain. If it does under a heavy load and back it off 2° and check again. I think you'll find you probably can get up getting around 12 if you go up to 93 pump gas.
I'm not sure where I'd find 93 pump gas.
QuoteThe other thing that's a big factor is your harmonic balancer. Has it been rebuilt or checked? A lot of these balancers actually can shift a little bit overtime and spend which will make the factory timing Marks non-Reliable.
No, I haven't done that. Are these easy to rebuild or is there someone folks use?
Quote from: Lincoln tech on August 25, 2025, 06:35:12 PMI wonder why someone decided to invent a timing light :o
+1! ::)
Scott.
Quote from: Lincoln tech on August 25, 2025, 06:35:12 PMI wonder why someone decided to invent a timing light :o
Too true - I've done it by ear since the 60s. If it pings back off a couple degrees.
He said, stock distributor but how about the cam? If it's not stock and has more overlap, you can run a little more timing. More overlap will bleed off a little bit of compression on the bottom end and build it as the rpms build up. Also have you checked to make sure your distributor is up to snuff?
Roy
I use Octane Supreme http://www.wildbillscorvette.com/octanesupreme01.htm to doctor the 91 octane available around me so that I can run a little more timing (better performance) without the pinging problem.
So true in a perfect world or just after a total rebuild a timing light and sometimes even then it's a NO....why?
On older engines with vacuum advance the timing more than likely will not be right with a timing light...close but not right.
Usually these engine have enough wear to have lower vacuum levels.
On mechanical advance if anything is worn, timing chain, springs, weights or pivot pins you are not going to get it right with a light.
Best cheap way to time them is hook up a vac gauge, advance the timimg until max vacuum is achieved.
Or use your PRO timing light
Wow.
So no one here adjusts the curve on their mechanical advance.
Quote from: Drew Pojedinec on August 26, 2025, 07:18:03 AMWow.
So no one here adjusts the curve on their mechanical advance.
I would say 2/3 of the time it needs help. Maybe because it is all gummed up inside or maybe (more likely) it has been monkeyed with in the past by someone who just sticks a different spring inside. I would plug the vacuum advance, set an adjustable timing light at around 35-36 degrees and set it to that at full advance (whatever engine speed that is) and see what you have.
Quote from: Drew Pojedinec on August 26, 2025, 07:18:03 AMWow.
So no one here adjusts the curve on their mechanical advance.
cant believe the "experts" did not bring ,this up previously
excellent point you bring up and how about retinkering with the carb after the adjustments
Quote from: FL SAAC on August 26, 2025, 07:57:23 AMcant believe the "experts" did not bring ,this up previously
I think if one were to utilize a "timing light", versus just twisting the distributor about and attempting to listen for 'ping' not having any real idea of what they are actually doing, this subject would lets' say . . . . "come to light"! ::)
Scott.
So much for chat gpt responses
;D
Quote from: rockhouse66 on August 26, 2025, 07:28:09 AMQuote from: Drew Pojedinec on August 26, 2025, 07:18:03 AMWow.
So no one here adjusts the curve on their mechanical advance.
I would say 2/3 of the time it needs help. Maybe because it is all gummed up inside or maybe (more likely) it has been monkeyed with in the past by someone who just sticks a different spring inside. I would plug the vacuum advance, set an adjustable timing light at around 35-36 degrees and set it to that at full advance (whatever engine speed that is) and see what you have.
Just to remind Jim of who I have mucho respect for of ability is that a stock 67GT500 does not have a vacuum advance.
Listening for ping while at idle , retinkering with the carb ???????? Good thing we are not talking about airplanes here :) :) :)
[/quote]Just to remind Jim of who I have mucho respect for of ability is that a stock 67GT500 does not have a vacuum advance.
[/quote]
Y'all gota realize that a bunch of these old cars don't have their original components in it
So that explains vaccum advances appearing that should not be there.
Or in my case you look at our cars and they have the vacumm advances in place.
But you can't see the B.B. inside the vacuum control hose plugging it up.
Plus our cars are fully advanced and of course by EAR
Quote from: Lincoln tech on August 26, 2025, 12:08:40 PMListening for ping while at idle , retinkering with the carb ???????? Good thing we are not talking about airplanes here :) :) :)
Well . . . . with my Lycoming 540, 260 H.P. "strait-valve", the O.E.M. ignition timing value is 25 degrees (B.T.D.C.), though with testing I established that "best performance" was had by advancing to 28 degrees, but not more; and don't ask me how I know that! :o And I also swapped out the MA-4-5 carburetor for a MA-6 which presents a larger venturi bore and the example being a helicopter application carb also richer fuel settings. 8)
O.K., it isn't my fault! Somebody else injected "airplanes" into the conversation, I'm just following their lead! ::)
Scott.
Quote from: pbf777 on August 26, 2025, 02:46:09 PMQuote from: Lincoln tech on August 26, 2025, 12:08:40 PMListening for ping while at idle , retinkering with the carb ???????? Good thing we are not talking about airplanes here :) :) :)
Well . . . . with my Lycoming 540, 260 H.P. "strait-valve", the O.E.M. ignition timing value is 25 degrees (B.T.D.C.), though with testing I established that "best performance" was had by advancing to 28 degrees, but not more; and don't ask me how I know that! :o And I also swapped out the MA-4-5 carburetor for a MA-6 which presents a larger venturi bore and the example being a helicopter application carb also richer fuel settings. 8)
O.K., it isn't my fault! Somebody else injected "airplanes" into the conversation, I'm just following their lead! ::)
Scott.
And yet I resisted
Quote from: JohnSlack on August 26, 2025, 02:50:46 PMAnd yet I resisted
Such control, . . . . but then, that's what comes with being a "Sr. Member"! ;D
Scott.
Quote from: pbf777 on August 26, 2025, 02:46:09 PMQuote from: Lincoln tech on August 26, 2025, 12:08:40 PMListening for ping while at idle , retinkering with the carb ???????? Good thing we are not talking about airplanes here :) :) :)
Well . . . . with my Lycoming 540, 260 H.P. "strait-valve", the O.E.M. ignition timing value is 25 degrees (B.T.D.C.), though with testing I established that "best performance" was had by advancing to 28 degrees, but not more; and don't ask me how I know that! :o And I also swapped out the MA-4-5 carburetor for a MA-6 which presents a larger venturi bore and the example being a helicopter application carb also richer fuel settings. 8)
O.K., it isn't my fault! Somebody else injected "airplanes" into the conversation, I'm just following their lead! ::)
Scott.
At least it sounds like you know what you're talking about , unlike ,,,,, ;)
Quote from: pbf777 on August 26, 2025, 03:03:10 PMQuote from: JohnSlack on August 26, 2025, 02:50:46 PMAnd yet I resisted
Such control, . . . . but then, that's what comes with being a "Sr. Member"! ;D
Scott.
On the Rare Bear the ignition system actually had a circuit that allowed you to retard the timing as you got into Cruise, not that we ever "cruised", however the airlines and the military DID use the cruise circuit. There were two sets of points in the distributor one set, the standard set was the advanced set that were normally used for ignition. The retard circuit would select the retarded points which if I remember correctly were 5° retarded. The ultimate feature that we were going to use this system for was that a pressure switch would be in circuit with the nitrous oxide that when the switch sensed pressure it would be automatically retarded 5°. Of course there would have been a manual override switch so that the retard circuit could be overridden at speed if needed.
Think about that with your R-3350 powered swamp boat. I do still have the manuals and part numbers.
John
Quote from: Lincoln tech on August 26, 2025, 03:11:30 PMAt least it sounds like you know what you're talking about ,,,,, ;)
Mannn . . . . Maybe, I should go into politics! ::)
Scott.
Quote from: JohnSlack on August 26, 2025, 03:45:50 PMOn the Rare Bear the ignition system actually had a circuit that allowed you to retard the timing as you got into Cruise, . . . .
Now see, us here Red Neck's, for those who'd bin think-in' they'd be needed it, we dun' have dee-vised our own "add-justable" timing capable ignition system on these little "Piper-Popper" motors; this here by utilizing spring-clamp loading on the magnetos (2 ea.) hold-down/retention fixturing, preset stops against the housings, and cable-pull attachments. Shazam! 8)
But then, most dun figured there rarely is a "cruise" scenario pushing that there boat hull through the water (after all water is thicker than air ::) ) or over the ground (as takes more pushin' when you's ain't got no wheels! :o ), but still might prove useful with N2O! But then most of even the dumbest of us here Red Neck's dun have heard of "MSD" (available with "adjustable timing retard")
And speaking of "cruising", and how it really isn't relevant in this venue either, this is another reason for utilizing the "helicopter" carburetor, as it doesn't have the fuel "economizer valve" as common in the others for fixed-wing aircraft, which just causes lean instances as mounted to the airboats. ;)
QuoteThink about that with your R-3350 powered swamp boat. I do still have the manuals and part numbers.
Yeah, . . . . . I do still have my R3350 ("A" series"), but I kinda gave up on trying to put it on a boat. This actually because by the time I came up with a boat hull and a prop(s), I realized that too many of the road and highway bridges that we encounter wouldn't have the clearance for it to go under! At least not when the water is high! :(
So I decided to be a "bit" more realistic, . . . . . I have reduced the size of things by changing direction and going with the R1820 (-82WA @ 1525 H.P.); which ought to have enough "push", and which I just happen to have a couple of! ::)
O.K., I know, maaaan . . . .have we ever gotten lost! But again, I was just following someone else's lead; but this time that of even a "Sr. Member"! Ya' can't blame me! ;D
Scott.
Wait...are you calling me, "an adjustable timing retard"? I resemble that remark.
Quote from: pbf777 on August 26, 2025, 06:45:13 PMThink about that with your R-3350 powered swamp boat. I do still have the manuals and part numbers.
O.K., I know, maaaan . . . .have we ever gotten lost! But again, I was just following someone else's lead; but this time that of even a "Sr. Member"! Ya' can't blame me! ;D
Scott.
Got s friend that has a swamp air boat, they call him tater
Scott, Scotty, Scotto, listen to buddha
neva eva follow a Senior Señor
"No one saves us but ourselves. No one can and no one may. We ourselves must walk the path."
Buddha
Walk alone and make your own path. Be yourself.
Him
Continuing on this interesting thread, I would still do it by ear...
Just buy one of those new fangled distributors that you control by bluetooth with your smartphone and you can adjust it on the fly.😉
Roy
Quote from: TA Coupe on August 30, 2025, 05:01:18 PMJust buy one of those new fangled distributors that you control by bluetooth with your smartphone . . .
You know the idiom of "I wouldn't trust that any farther than I could throw it" seems to come to mind! :o But then, I'm sure could throw my smartphone at lot farther than I actually would trust it! ::)
Scott.
Quote from: TA Coupe on August 30, 2025, 05:01:18 PMJust buy one of those new fangled distributors that you control by bluetooth with your smartphone and you can adjust it on the fly.😉
Roy
Interesting concept we must say...
Quote from: FL SAAC on September 02, 2025, 01:42:04 PMQuote from: TA Coupe on August 30, 2025, 05:01:18 PMJust buy one of those new fangled distributors that you control by bluetooth with your smartphone and you can adjust it on the fly.😉
Roy
Interesting concept we must say...
Here you go:
Progression Ignition - Ignition Distributor, Ignition Timing https://share.google/hHqYTD3mO2RlSiMvy
Roy
Quote from: TA Coupe on September 02, 2025, 04:16:36 PMQuote from: FL SAAC on September 02, 2025, 01:42:04 PMQuote from: TA Coupe on August 30, 2025, 05:01:18 PMJust buy one of those new fangled distributors that you control by bluetooth with your smartphone and you can adjust it on the fly.😉
Roy
Interesting concept we must say...
Here you go:
Progression Ignition - Ignition Distributor, Ignition Timing https://share.google/hHqYTD3mO2RlSiMvy
Roy
The future is now
Quote from: FL SAAC on September 02, 2025, 07:05:43 PMThe future is now
Yeah, like "Self-Driving Cars"! ::)
Scott.