# '65 GTO 389 Timing Specs w/modified engine



## Roqetman (Aug 31, 2015)

I'm wanting to get the best tune possible for my 65 GTO. I know the factory spec for initial timing is 6*BTDC but since my engine has been modified, I wanted to see what expert advice or resources were recommended.

The mods are as follows: '65-389 bored 30 over = 395 cu in, Wolverine Blue Racer cam #WG 1169K for excellent mid-range power 2000-4600 rpm, '69 #48 heads, Edelbrock Performer intake with soon to be installed '68 428HO Q-Jet, GM HEI - vacuum advance distributor, Hooker Headers, and TH400 Tranny.

Any advice on timing specs would be greatly appreciated.

Thanks, Roqetman!


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## BearGFR (Aug 25, 2008)

I've posted on here several times about how to find the correct timing settings for your Pontiac engine. You should be able to find the information about the procedure using the search tool. Short version: Initial timing setting is mostly unimportant. What matters most is the total mechanical timing (vacuum advance disconnected, since when the motor is pulling hard at wide open throttle, it's not making vacuum to activate the vacuum advance). Set your total timing to the value that produces the best engine performance - then use a light to READ (not change) that value at idle so that in the future you'll know how to return to the same setting. (Reaching in to adjust the distributor on the engine with it running at 3000 rpm or so can be a little daunting.) If your distributor is "weird" (i.e. damaged or has been trifled with by someone in the past such that the advance curve is way out of whack) and causes your engine to be very hard to start (i.e. advanced so far that it trys to run backwards during startup) or overheats (because it's extremely retarded) - then you'll want to repair/replace the whole distributor. Otherwise, the 'total' setting is the way to go. A good starting point for most Pontiacs with open chamber iron heads is usually around 34-36 degrees total. Closed chamber (1967 670 and others) and aluminum heads tend to "like" a little more, depending on combustion chamber design.

Example: My 69 with ported aluminum heads seems to like (i.e. make the most power) with 36 degrees total. My distributor (Davis Unified ignition HEI) has 20 degrees of mechanical advance baked into it. That leaves me with an initial timing setting of 16 degrees, which the engine is fine and happy with.


Bear


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## Roqetman (Aug 31, 2015)

Bear, thanks for the Information! Very helpful!


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## geeteeohguy (Feb 2, 2008)

In '69, Pontiac made two different #48 heads: a pressed-in -rocker-stud 64cc version for the 350, and a screw- in rocker stud 72cc version for the 400. The 64cc version will limit the amount of timing you can run on pump gas. If you have the 72cc version, you will be better off. I am running the 64cc #77 heads on my .030" 389 and a rather large Sig Erson single profile cam with a 4 speed, headers, and 3.36 gears, and run my initial at 10 degrees for a total of 38 degrees all-in. Due to my compression, I need to run about 98 octane fuel. What timing you can run will vary with your compression ratio, camshaft, transmission, and rear end ratio. You can get by with more compression and more timing if you have a stickshift and a stiffer rear ratio, like a 3.55 or 3.90. My 9.3:1 TH400 068 cammed 'stocker' '67 GTO ragtop never pinged on hot days with the 3.36 rear end. Now that I'm running a 2.56 gear out back, it will ping a bit on 100 degree days pulling a long grade at cruise. There are a lot of variables that will determine the 'best' timing curve to run. As a down-and-dirty rule of thumb, though, if you have a bigger cam and exhaust, you can run a little more initial timing due to loss of cylinder pressure at low speeds.


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## Lemans guy (Oct 14, 2014)

The guys are spot on, and like Bear said find out the mechanical and then dial in the base for no more than 36 total....

Put in a 16 degree (crankshaft) B28 Vacumn can in the distributor....from autozone....they are all from the same makers....

And you will have 52 degrees for light throttle cruise, which is perfect....

Or you can use an adjustable Vacumn can...like crane etc....base & Mechanical is total advance....Vacumn advance is not included because like Bear said when throttle wide open, not much Vacumn....

But you don't want to much vac advance ...cause that can ping at cruise if you have too much.....


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## john23 (Mar 6, 2016)

what everybody said plus as you go up in altitude the engine will want more advance


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## Roqetman (Aug 31, 2015)

BearGFR said:


> I've posted on here several times about how to find the correct timing settings for your Pontiac engine. You should be able to find the information about the procedure using the search tool. Short version: Initial timing setting is mostly unimportant. What matters most is the total mechanical timing (vacuum advance disconnected, since when the motor is pulling hard at wide open throttle, it's not making vacuum to activate the vacuum advance). Set your total timing to the value that produces the best engine performance - then use a light to READ (not change) that value at idle so that in the future you'll know how to return to the same setting. (Reaching in to adjust the distributor on the engine with it running at 3000 rpm or so can be a little daunting.) If your distributor is "weird" (i.e. damaged or has been trifled with by someone in the past such that the advance curve is way out of whack) and causes your engine to be very hard to start (i.e. advanced so far that it trys to run backwards during startup) or overheats (because it's extremely retarded) - then you'll want to repair/replace the whole distributor. Otherwise, the 'total' setting is the way to go. A good starting point for most Pontiacs with open chamber iron heads is usually around 34-36 degrees total. Closed chamber (1967 670 and others) and aluminum heads tend to "like" a little more, depending on combustion chamber design.
> 
> Example: My 69 with ported aluminum heads seems to like (i.e. make the most power) with 36 degrees total. My distributor (Davis Unified ignition HEI) has 20 degrees of mechanical advance baked into it. That leaves me with an initial timing setting of 16 degrees, which the engine is fine and happy with.
> 
> ...


I did as you recommended and set total timing at 36 degrees BTDC at 2500 rpm. this gave me 18 degrees at 650 rpm idle. The engine seems to like it here. Good idle with 14-15” of vacuum. Good highway performance. But I’m still having two other problems. The 389 + .030 over with 10.75:1 compression, ‘69 400 #48 heads , which I understand are ping monsters, GM HEI. The only solution I have found for that is adding a couple gallons of 112 octane per tank full and no more Pinging. I was hoping to adjust this out with timing but if i back off the timing it seems to struggle at idle. The other problem is when i try to do a burn out it starts out ok but then seems to stall like a fuel starvation problem. Top end is great and the secondaries come on strong when I hit passing gear. It’s a ‘70 Olds Q-Jet 750 freshly rebuilt with new jets, rods, power piston, needle and seat. Can you recommend what I should check of this Low end hole shot? Thanks!


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## Old Man Taylor (May 9, 2011)

Your compression is way too high for modern day gas. You'll have to mix race gas with it. Start at 50-50, but you might be able to get by with 2 parts pump gas to 1 part race gas. This assumes you're using 110 race gas.


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## BearGFR (Aug 25, 2008)

Sounds like you've found the timing the engine likes. "Playing" with timing to try to avoid detonation can work to a degree, but that will always be accompanied by a decrease in performance/drivability. It's a band-aid at best. If it's right on the edge you MIGHT get some releif by slowing down the advance curve (stronger springs and/or lighter weights) and also adding more travel to the mechanical side so that you can still get 35 total with less "initial". The latter is going to involve cutting on/modifying the advance mechanism itself. All that's a lot of tinkering and may do nothing at all to help - so keep that in mind. 

On your 'starvation problem': does it bog as soon as you hit the throttle or does it "go" for maybe a half second or so and then fall over? If it's an initial bog, then there are ways to work on that. Be very careful because there's a lot of "trick of the month club" QJet recommendations for that out here on the net that are just plain wrong and can make things worse. Be very suspicious of anyone/anything that tells you to disconnect or disable any of the carb's systems or make radical changes to the air valve spring tension. If you don't have one already, grab a copy of Cliff Ruggles's book on QJets. It's very good.

If it "goes" and then falls over after a very short time and the car also launches pretty hard, what could be happening is fuel may be sloshing to the back of the bowl, up out of the holes where the secondary metering rods pass through, and over into the secondaries causing a momentary over-rich condition. A temporary/test fix for that is to put a strip of electrical tape over those holes in the air-horn to body gasket, carefully poke the secondary rods through the tape when you reassemble it, and "work" them a little so that they can move freely through the tape. The tape makes a seal to keep the fuel from sloshing over. The tape will wear out eventually and you'll have to replace it every so often, or you can use a very thin piece of aluminum, cut/drill holes in it to make a permanent baffle. It'll probably take several tries to get the holes the right size and spaced correctly. I fought a "bog" problem like that on my '69 for a long time and even made a several different sized restrictors that let me tune how quickly the pull-off diaphragm on the front of the carb allowed the air-valves to open. I used short pieces of brass tubing, plugged them with epoxy, then drilled different sized holes in the epoxy using a pin vise and various sized wire drills. I cut the vacuum line to the diaphragm so I could insert one of those in the line to control the air-valve opening rate. I used one of those hand-held vacuum pumps that you use to bleed brakes to pull a vacuum through a restrictor installed into the line to the diaphragm, then release it to time low long it took to allow the diaphragm to release. That's how I made a set of restrictors with various different timings for testing. You do have to make sure everything else (accelerator pump shot, air-valve spring, diaphragm opening rate, linkage adjustment) is right before you try sealing the rods though, that's where Cliff's book comes in handy.

Nothing I tried worked --- until I used the tape trick to seal the secondary rods. One of the clues I got that my problem was somewhere else was that no matter how fast or slow I tuned the air-valve opening rate to, the car still reacted exactly the same.

Trying to tune air-vavle rate by futzing with air valve spring tension is the wrong way to do it, especially if you need to slow it down. It's easy to get the spring tight enough that the engine can't pull the valves completely open.

Good luck!
Bear


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