# 1968 GTO set base timing and total timing??



## rob40999 (May 18, 2018)

Hello All: New member. I got a 68 GTO 400 engine. Just bought. Not stock. Got Elderbrock mandifold with Elderbrock cfm 600 4 barrel. Hooker headers. No cam. A MSD 6200A electronic ignition. No points or vaccum line going to distruibutor. A matching number 68. Flow master exhaust system. I've read alot of your post on setting the timing??? I'm asking what I did is ok for the engine. I started out with my total timing at 36 degrees pulling in at around 2700 RPM's. Base timing is set at 15 degrees. What I did was subtract 36 degrees from 15 degrees, and got 21 degrees. With engine running at around 2700 RPM's the engine tab at zero matched the balancer BTDC (0) perfect. My timing light is the one you can preset the dwell. So I set it on 21 degrees, and both zero's hit perfect. I did have my base timing at 12 degrees BTDC, but the engine runs smoother at 15 degrees, and excellerates much better. No back fire which I had with Manufacture base timing at 9 degrees BTDC. Wondering if what I did is OK???? Question one: Is my base timing to far advanced? Don't want to burn a cyclinder head. No pinging. Also I hooked up a fance vaccum gage, and that was in the Green at Idle, and stade in the green at 3000 RPM's. I'm a old 66 years old disable Vet, and had one of these in high School. Back then we use to take out the termostate, and just ran her that way. Took off the Air cleaner. And just ran the shit out of her. Now at 66 years old I wash, and wax her. Vaccum the car every other day. This is the last thing on my Bucket list. LOL LOL So I hope the engine isn't going to blow up. The car is a His, and Her automatic.

Thank you, Bob


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## PontiacJim (Dec 29, 2012)

Each engine combo can be different with regards to timing. The factory settings were just that, for the factory engine. Often the initial can be set higher and run better. You also no longer have the vacuum advance, so your initial setting wants to be higher without it. Vacuum advance adds to better fuel mileage when cruising under light load/high engine vacuum.

The key is not to have too much total timing, as that is where you destroy the engine - ie burn a piston or hammer the bearings away. Personally, 36 degrees total in my book is about the limit and I would feel safer with 34, but from what I read, the ethanol in the gas will allow for slightly more timing advance - so IF you are not hearing any "pinging" then I suspect you are OK. A stop limiter could be added to the mechanical advance in the distributor if you like your distributor's initial timing and it's curve, but find some pinging due to too high total advance. 

The problem arises when you don't here the audible detonation. Outside temps & under hood temps can rise and this can create a problem that leads to detonation. Modern cars have knock sensors and can automatically adjust timing to compensate. Our older cars don't have this feature.

If your car starts well at 15 degrees initial, then that is also fine for your application. It is when you have starting problems, the engine struggles to turn over, that it may be too far advanced for the initial. So if it starts good and runs better as you stated, then leave it.

If you can lug the engine and it does not ping/detonate, then it should be OK - old school way of timing for maximum advance, right? :thumbsup:


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## rob40999 (May 18, 2018)

*1968 GTO intial, and Total timing.*

Hello PontiacJim: I first would like to Thank you for your reply. Very Good.
Have a Question Jim: Would you like if I turned back my Total Timing to 34 degrees, and Intial Timing at 13 degrees???? Would this be a safer adjustment??? The car is running great. No hessitation on acceleration. Starts right up in the mourning with the choke on. It takes the gas right off the bat.
Runs very fast. I believe if I had some pinging I could hear it at Idel?? It is Ideling at 850 RPMS. As you can tell I'm a little nervous.. :-( Engine was rebuilt 20,000 miles ago. I put a Vaccum gage on it, and it read in the green at Idel, and in the green at 3000 RPMS. Does that mean any thing. Well again I Thank you for the good advice. Have a great Weekend.

The "Z" Man


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## BearGFR (Aug 25, 2008)

If it's not pinging/detonating, don't worry. Put it under some load at low rpm, like pulling up a long hill in high gear for instance with the engine nice and warm. If it's going to detonate, you're most likely to hear it under those conditions. Pull a couple of spark plugs and examine them really closely with a magnifying glass. If you don't see any shiny specs - sort of like bits of glitter - on your plugs, that's more evidence that you're not getting into detonation and more confidence on your part that things are ok. Every engine, every build is a little different. Rules of thumb are exactly that - rules of thumb. That doesn't mean that a specific engine won't be happy with a little more timing than usual. It's the total and how fast it comes in that matters. The initial setting is nothing more than a way to 'get to' what you want for the total. As long as the engine isn't running so much initial that it's hard to start, and it's not detonating, you're good.

Bear


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## rob40999 (May 18, 2018)

*1968 GTO intial, and Total timing.*

Hello Mr. Bear: Great information... I pulled 3 spark plugs, and looked at them with my magnifier glass, and everything looks OK...  Your right I should be
OK with the way I have it set up. My spark plugs are ACDELCO R45S... Gap is .045 inch. In fact I still had the Spark Plug Gap tool from back from 1965... LOL LOL
Is this spark plug ok for this car????? What would be a better spark plug????
The old days back in 1969 we use to use a cold plug. I believe it could of been
a CHAMPION R16 ???????? Does this bring back the old days???? I've been adjusting this timing for a month. Manual says. 9 DBTD.. Then I went to 12 DBTD... Engine ran better. Now I went to 15 DBTD, and engine runs great....
Your question about a Hill to put a load on the GTO would be hard to do in Florida... LOL The biggest hill in town is my driveway... I got this car just like the day it came off the assembly line. If you can think of anything else I should do or check let me know... You have been a great help.

Thank you, The "Z" Man (Bob)


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## BearGFR (Aug 25, 2008)

Hey Bob (my name is also Robert) -- As long as the plug is getting the fire lit (and it sounds like yours are fine in that regard), the other considerations on choice are that you want a plug that will stay hot enough to keep itself clean, yet not so hot that it becomes a 'hot spot' that can lead to detonation and/or have a shortened life. If your plugs fit all three of those concerns, they're fine.

My 69 likes lots of initial too. I'm running a Davis HEI that has 20 degrees centrifugal in it, and my heads (Edelbrock RPM 72cc round ports) seem to like 36 total, so I set my initial at 16. I might need to retest after I finish the current build because I'm making a significant cam change, also an intake/carb change.

Bear


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## PontiacJim (Dec 29, 2012)

rob40999 said:


> Hello Mr. Bear: Great information... I pulled 3 spark plugs, and looked at them with my magnifier glass, and everything looks OK...  Your right I should be
> OK with the way I have it set up. My spark plugs are ACDELCO R45S... Gap is .045 inch. In fact I still had the Spark Plug Gap tool from back from 1965... LOL LOL
> Is this spark plug ok for this car????? What would be a better spark plug????
> The old days back in 1969 we use to use a cold plug. I believe it could of been
> ...



The factory plugs for the 1969 400 ('cause I have the specs handy) is AC R44S. A colder plug may be right for Florida weather. So you may want to try the R44S and see how that works. As long as you don't experience plug fouling - then you have gone too cold.

You will not hear pinging at idle, only under load, whether it be light load or heavy load. An engine will ping under light load if it is way too advanced. Heavy load testing is done under Wide Open Throttle. As Bear stated, a hill can be best, but Florida is indeed flat for the most part. If you have an automatic, His/Hers trans, you should be able to manually keep it in second gear. If so, accelerate from about 10 MPH under WOT for a short blast and listen. If a 4-speed, same deal, but try 3rd gear to lug the engine. This should produce the same results. So that is the key, WOT under load is where you want to listen for the pinging


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## rob40999 (May 18, 2018)

*1968 GTO intial, and Total timing.*

Hello Mr Bear (Robert): You sound like you know what your doing. I being a retired Military Aircraft mechanic have some Idea what's going on. Plus having one of these car's (1968 gto) Back in High School. I was Hot back then. Now at 66 years old I just think about what's for Dinner. LOL LOL 

About the spark plugs. The plugs where really clean, and looked like there fairly new. I've only owned this car since March. It's starting to come back to me. Back in 1969 I spent more time adjusting the points, and playing with timing than I wish to do now. Use to race the car. It was a 4 speed, and I blew that clutch a few times. Changing it in the street. Driving it up on the curb, and getting under there, and doing the work. Back then we did this stuff our selves.. Now I wash and wax the car, and call the Mechanic...

Got a Question for you Mr. Robert: I got the Elderbrock Model 1460 which is 600cmf. Would It be OK for me to put on a bigger Carburator??? Say a 750cfm???? Or this should be just fine. When I hit the throttle, and she shift down to second, and the 4 barrell opens up??? Hang on.... My other car don't sound like that. LOL LOL

So Thank you, Robert, and have a great weekend.
The "Z" Man (BOB)


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## rob40999 (May 18, 2018)

*1968 GTO intial, and Total timing.*

Hello Again Mr. Jim: Your Idea about putting the car in 2nd gear is a good Idea. I have a Automatic, His and Her shifter. So I'll do that load test. This is going to be interesting. Maybe I'll do it with the Hood open so I can hear better???????? LOL LOL 

The spark plug that you suggested I'll give a try. Give me something to do... 

I guess it's a big deal changing the car from 12 degrees TDC to 15 degrees TDC??? I've been using 93 Octane, and adding a Octane booster with every fill up. Also some STA-BIL 360 Performance for the Ethanol in our Gas.. I've read here on this site that some people are using a Lead Substitute??? My mechanic was very puzzeled about adding a Lead Substitute??? The car runs great, and start's right up Cold or Hot. So as that worry wart that I am I'll do the load test Jim. I'll get back to you. It's raining today here in Florida. I'm waxing the GTO AGAIN in the garage. LOL
So I wish you a great weekend.
Thank you, The "Z" Man (Bob)


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## rob40999 (May 18, 2018)

*1968 GTO intial, and Total timing.*

To PontiacJim: Did load test on car. Put it in second gear at 10 mph, and gave her a lot of gas. You could hear the Engine trying very slowly trying to come up in RPM's. No Pinging at all... Just a smooth very slow upward RPM's. I guess I'm out of the weeds. I'll try those new spark plugs...

Have a great week,
Thank you, Bob


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## PontiacJim (Dec 29, 2012)

rob40999 said:


> To PontiacJim: Did load test on car. Put it in second gear at 10 mph, and gave her a lot of gas. You could hear the Engine trying very slowly trying to come up in RPM's. No Pinging at all... Just a smooth very slow upward RPM's. I guess I'm out of the weeds. I'll try those new spark plugs...
> 
> Have a great week,
> Thank you, Bob


Sounds like you are good to go. The weather in Florida is very similar to NC, maybe a little better as I have family in Florida and talk with them regularly. Rainy & hot here as well.

Jim


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## rob40999 (May 18, 2018)

*1968 GTO intial, and Total timing.*

Hello All: A funny thing happened to my GTO. I changed the base timing back to 13 degrees, and the Engine got hotter. It was up like 15 degrees. I set it back to 15 degrees base, and it now runs at 170 degrees going 40 mph. This is strange???????? It was at 185 degrees with base timing at 13 degrees.
Curious minds would like an answer???? LOL LOL

Bob


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## PontiacJim (Dec 29, 2012)

rob40999 said:


> Hello All: A funny thing happened to my GTO. I changed the base timing back to 13 degrees, and the Engine got hotter. It was up like 15 degrees. I set it back to 15 degrees base, and it now runs at 170 degrees going 40 mph. This is strange???????? It was at 185 degrees with base timing at 13 degrees.
> Curious minds would like an answer???? LOL LOL
> 
> Bob


Retarded timing will cause the engine to run hotter. Here is one of the best explanations I have read:

"Retarded will over heat it most quickly. The burn occurs over about 80 degrees of crank rotation, when started late, there isn't time for the the flame temps to be reduced by work against the crank. This combined with the reaction still occurring when the exhaust valve opens conspires to dump really hot gases into the exhaust passages. This greatly increases the valve temp and the amount of heat picked up by the cooling system thru the structure of the head and exhaust port. The exhaust manifold/headers also become very hot, enough to glow. With retarded timing, the temps come up very quickly.

Too much advance will eventually result in overheating but it's much slower to build compared to retarded timing. Usually before anything bad happens one usually notices that the engine is hard to start, tends to explode thru the carb, and if it runs at all it's with no power and tends to detonate from the extreme pressures formed before TDC. So you usually head this problem off before the temps get very high."

And I also found this explanation:

"Late timing will allow the fuel/air mixture to continue to burn while the piston travels away from TDC. This causes a lot of heat to be absorbed into the cylinder wall that wouldn't ordinarily be there. If extreme enough, exhaust gasses will still be carrying a lot of heat w/it. This heats up the exhaust valve, seat, port and the surrounding water jacket has to try to absorb all this additional heat. The result of it all can be an overheating condition.

Over advanced timing will damage pistons due to detonation as well as increased heat. Detonation can pinch the rings in the lands so they won't be able to do their job. This can allow flame erosion to occur. At the worst, detonation can cause pistons to crack, scuff bores along w/bearing damage and if bad enough crank failure. At the least, power will be down. In any event, accelerated wear will happen."

Basically, your engine is telling where it likes to run. So as long as no pinging from detonation because it is too advanced (which you said it was not), then listen to your engine and set the initial where it wants to be.


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## rob40999 (May 18, 2018)

*1968 GTO intial, and Total timing.*

Hello Jim: I got my base timing now at 15 degrees. I'm getting a little back fire when I get off the gas at 3000rpm's, and just start coasting down to a red light. I didn't have that before. I've been taking out the Idle screw's on my Elderbrock carberator, and blow them out with some compress air, and then put them back in, and adjust them for my Idle at 850rmp's. Then the back fire goes away??? I've seen this in the Elderbrock Ytube if the Idle screws don't work. It seems to make the engine run more smoother. But after say 100 miles the engine start back firing again on coast down. Very confusing for me. Engine runs great. Just start getting that back fire after awhile. ?????? What's up????
I have a very strange 1968 GTO with a 400 engine????? 
Wishing everyone a great Holiday Weekend.
The "Z" Man (Bob)


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## PontiacJim (Dec 29, 2012)

rob40999 said:


> Hello Jim: I got my base timing now at 15 degrees. I'm getting a little back fire when I get off the gas at 3000rpm's, and just start coasting down to a red light. I didn't have that before. I've been taking out the Idle screw's on my Elderbrock carberator, and blow them out with some compress air, and then put them back in, and adjust them for my Idle at 850rmp's. Then the back fire goes away??? I've seen this in the Elderbrock Ytube if the Idle screws don't work. It seems to make the engine run more smoother. But after say 100 miles the engine start back firing again on coast down. Very confusing for me. Engine runs great. Just start getting that back fire after awhile. ?????? What's up????
> I have a very strange 1968 GTO with a 400 engine?????
> Wishing everyone a great Holiday Weekend.
> The "Z" Man (Bob)



Hard to say what the cause is. Could be a couple things. Why is your idle at 850? First guess might be that your primary throttle plates are still open enough to suck gas out of the idle mixture and dump it through the exhaust when decelerating. So my first "test" might be to see if I could get the idle RPM's lowered closer to stock which is 650 RPM's for an automatic in Drive. Now the RA engine shows timing at 15 degrees BTDC and an idle speed of 750 RPM's.

Make sure your choke is operating correctly and wide open when warmed up. You don't want it being sucked closed during high vacuum conditions.

Next I might try to pull the vacuum advance hose off and plug it. With the initial advance of 15, plus your mechanical advance, adding in the vacuum advance during deceleration might be pulling the timing way too much and it needs to be limited. So shut the vacuum advance off and see what happens. It does not affect full throttle blasts.

Make sure your PCV valve is working. According to my manual, the way to test is to pinch off the hose and RPM's should drop by about 60 while running.

I might also back the idle mixture screws out a little more. Used to be seat them then back them out 2 1/2 turns. Ethanol laced gas runs a little leaner, so I might back them out 3 turns, then 3 1/2, then 4 just to see if any differences. On the other end of the spectrum, not having experience with the Edelbrock, it could be set-up too rich. There are a number of things to adjust on them. You could have a step up piston spring that is too stiff and not allowing the metering rod to drop as it should.

No vacuum leaks?

Other causes could even be a valve being held open - bad lifter pumping up and not bleeding down fast enough or a valve out of adjustment ie, heads/block have been milled and the stock lock nuts when torqued down are holding a valve just slightly open. Does it happen at 1500 RPM's, 2000 RPM's, 2500 RPM's, etc..?

Have you looked at the plugs lately to see if they give you any indications of rich or lean burning?

These are just my guesses and a few things I might check/test for. :thumbsup:


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## rob40999 (May 18, 2018)

Hello Jim: I'll check everything on the wish List. I think I'll back out the Idle Mixture screws. Check timing again. Adjust Idle at 650RPMs in gear. Just put in a new fill tank of gas, and this started. Maybe I need more Octaine Booster??? I'll get back to you. It's not a loud back fire. It's like if the engine had a cam in it. Mine doesn't. Just a soft pop, pop.
on decell... I'll get it straten out. Have a great weekend. 

Bobby


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