# 62 heads compression



## 71Goatwannabe (Jan 17, 2020)

Ok so I have a 69 model 400 out of a Grand Prix in my 71 Lemans. It has the high compression 62 heads and as far as I know the engine is completely stock. The engine has pinging/ detonation issues and diesels on shutdown (ie tries to continue to run after turning the key off) . Will do so very badly if run on anything lower than 93 octane. I realize the gas of yesterday was much better and therefore this was not a problem. But with today’s gas quality could a cam with larger duration help my case? Based on other websites I believe if my cam is the oe then I have 269 degrees of duration ( I assume advertised not at .050) and I was thinking going up some degrees would lower cylinder pressure to a point within reason but I thought I would ask to see if I’m totally wrong or what( which I very well could be). I realize I could either change heads or change from flat tops to dished but I’m 17 and broke and it is out of the price range to rebuild the old girl.


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## Gremlin66 (Oct 11, 2009)

Did you try retarding the timing ?


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## 71Goatwannabe (Jan 17, 2020)

Yes I believe the last time I checked I set it to 6 degrees


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## PontiacJim (Dec 29, 2012)

First, the gas in the "old days" was not necessarily better. What it was was higher available octane at the pump. True, the lead was indeed used as an anti-knock agent, to raise octane, and as a lubricant for the valves/valve seats. Put some unleaded Sunoco 260 100 octane in the tank and you won't have any problems. So it's the octane you select that is the problem.

Detonation and dieseling after shut down will damage the engine real fast. To stop the dieseling, keep the car in gear and then shut it off. That was what a lot of us did back in the "old days" to stop that. Pontiac, as well as many other makes, used an electric solenoid that when keyed "on" would raise the idle as needed for the car to run, and when the key was shut "off," the solenoid retracted dropping the carb below idle speeds and effectively closing off the carb's throttle plates so no air could enter the engine and keep the engine running/dieseling on the gas that was left in the carb through the idle circuits. This solenoid is also found on AC cars so when you had the AC running, it bumped up the idle speed so when you came to a stop, the additional power robbed from the engine at idle would not pull the idle below its needed RPM and stall out the engine. But, this solenoid was set at the car's normal idle setting and bumped it up, as opposed to setting the car's idle in the "bumped up" position and then dropping below idle speed when the key was shut off - so same solenoid, different purpose.

So first, check your idle speed and adjust the idle mixture screws accordingly. You may want to even lean them out a little to help with the dieseling.

Pulling back the timing can work to better things, but may not pull out enough. Then you sacrifice horsepower, and too much will retard timing and the engine runs hot.

Yes, a bigger cam can help, but a bigger cam also puts the engine into a higher useable RPM range and you can wind up giving up bottom end torque/horsepower and possibly driveability. It'll require a matching set of valve springs which means some disassembly of the heads and the needed tools to do this on the engine. The bigger cam generally needs a 4-speed or higher stall converter as a bigger cam typically will have a higher idle speed which is needed due to more valve overlap. You'll want to have factory Ram Air cast iron exhaust manifolds and 2 1/2" pipes or headers to get the spent gases out. You also want rear-end gearing closer to 3.55 and up to match the cam.

So, are you willing to do more than just install a cam? 

What you can try is to adjust your distributor's advance curve - slow it down. I would run the timing at 9-12 degrees (vacuum to distributor unhooked and vacuum source plugged). Then using one of the advance spring kits available (assuming points distributor?) you want to use a medium or heavy spring, or combination of the two, and get your total mechanical advance (9 degrees initial + 20-21 degrees from the distributor weights) to be full in at 4,000 RPM's. Presently, it is probably all in by 2,800-3,000 RPM's - if it is working and nothing stuck/sticking which can be your problem.

So check your distributor to make sure it is functioning correctly. You will need a "dial back" timing light to do this. Then if it checks out, play with the springs found on the weights to get the above 4,000 RPM's with the total timing advance at this RPM to be around 30-32 degrees. The vacuum advance will be disconnected to do this. 

The vacuum advance is used to help cool the engine and provide better gas mileage when the car is running light throttle or coasting. However, a "sluggish" vacuum advance can keep the total mechanical advance too far advanced when you mash the gas and the vacuum does not drop fast enough to bring the vacuum advance cannister to its non operational use when no vacuum is present and the engine is utilizing its mechanical advance coming from the distributor. You can run a car with no vacuum advance and can even test this by driving without it hooked up, and mash the gas to see if anything improves. If detonation lessens, then you may need a different vacuum advance cannister found on the side of the distributor.

Check your spark plugs. Make sure you have the correct heat range. Too hot a heat range can be a problem. You can try 1 heat range colder, but no more. The gap should be .032-.035".

Engine heat will contribute to detonation. You want as cool as possible an engine temperature. Make sure your cooling system is in good order, like the radiator, good fan & fan shroud. I prefer a 160 degree thermostat over a factory195 - which will make the engine run hotter.

Have a good air cleaner to let air flow in. A restrictive air cleaner can cause an engine to run lean and detonate.

The carb could be in need of a rebuild. It could have something plugged up and not delivering the needed fuel which will make it run lean. The wrong jets, too small, will cause a lean condition and run hot. The ethanol gas runs leaner than non-ethanol just by nature. I would increase my jet sizes to get the carb a little richer. A richer carb (within reason) will help the engine to run cooler because it is not running leaner.

Pull the valve covers to make sure all the valves/rocker arms are working correctly. If you have one not working - ie sticking, cam lobe worn down, or out of adjustment due to the factory rocker arm nut backed off, it will affect valve opening/timing which could contribute to detonation.

Your timing could be off - timing gear/chain is sloppy. This will effect timing events and can cause your problems. Factory cam gears were aluminum and the teeth were nylon coated for less noise. The nylon on the gears does deteriorate and beak off. Factory set-up were only good to about 60,000 miles and then generally needed to be changed out. The chains also stretched. 

So you wanted a quick fix? You can see that may not happen. There are many things that can contribute to detonation and dieseling and they all have to be checked. Lower compression can be the best answer, but you may have other issues that can correct your problem and I would look into these first.

Just a cam change will not do it unless you are willing to do the corresponding and matching changes and then this will not guarantee that you won't have any detonation as you will still have an engine with high compression.

But, know that detontion and dieseling can break pistons and damage your bearings real fast. So avoid this at all costs.


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## LATECH (Jul 18, 2018)

static compression ratio is too high. It will be tough to tune that out into a safe range to avoid detonation.It will likely run hot no matter what you do to "band aid" it.
A simple head change to a larger chambered head can be an easy fix. Something around 85 CC (or a tad larger for some wiggle room) would get you down just under 9 to 1 .That and a good curve set upon your distributor should be an easy/workable fix.


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## 71Goatwannabe (Jan 17, 2020)

First, thank you Mr. Jim for your detailed response. I realize the octane difference of the different times. And I already do the shutdown in gear trick as you said. I don’t believe there is an electric solenoid for the carb. I haven’t had to mess with carb much other than adjust the floats because it ran so well. I will adjust the mixture screws to see if running a little leaner or richer helps. And I know what is needed to do the cam swap. I will keep the distributer advance curve adjustment in mind. I have a 160 degree thermostat in the engine. It tends to sit at 180. It has a new air cleaner. I just installed a lightly used quick fuel slayer 650cfm that I do not believe needs a rebuild. I will check the rocker arms. I believe the engine has been rebuilt semi- recently but timing could possibly be off. I really appreciate your input.


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## 71Goatwannabe (Jan 17, 2020)

And yes LATECH I believe that is the culprit I was just trying to find a compromise other than a piston or head change.


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## LATECH (Jul 18, 2018)

A throttle "kicker" solenoid may help alleviate the dieseling.Use the kicker to open the throttle when the key is on , and set your idle with that. Then when you shut of the key, the kicker de energizes closing the throtte plates and cuts off fuel and air to the engine.

This will ot however alleviate detonation. Pulling out timing , initial and advance, will just cause it to heat up in the combustion chamber. Runnng a cooler thermostat will not warm up the engine correctly and can cause carbon build up in the cyliders and sludge buildup as the oil wont be warm enough for detergents to clean it up


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## Lemans guy (Oct 14, 2014)

Well said by the gang. Have seen 9 to 1 compression and the car still diesels like PJ and LA said. Sometimes there is just too much throttle opening. The solenoid described shuts that.

but you have a quick carb, I run one too and you can close that throttle plate just a bit and and also adjust your idle air bleeds on top of the carb to get a bit leaner or richer. They are just screw in jets.

the idle transfer slots are often way too far open, and on shutoff the car diesels, by closing the throttle plate more and adjusting the mixture screws and idle air bleeds you may help it a bit.

also heat range of the plugs, NGK with a heat range of 6 runs good for me. Gap like PJ said, check all the things that the guys said, start small and see what improvements you might get.

if you have to change head or cam later youalways can......

put some 93 and some octane boost......as well


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## LATECH (Jul 18, 2018)

71Goatwannabe said:


> But with today’s gas quality could a cam with larger duration help my case? Based on other websites I believe if my cam is the oe then I have 269 degrees of duration ( I assume advertised not at .050) and I was thinking going up some degrees would lower cylinder pressure to a point within reason but I thought I would ask to see if I’m totally wrong or what( which I very well could be). I realize I could either change heads or change from flat tops to dished but I’m 17 and broke and it is out of the price range to rebuild the old girl.


 Since the budget is tight , I would put on a different set of heads and re curve the distributor. 
A different cam would just be a patch job .You could lower the DCR with a longer duration, but it would lose low end torque, and the stretch between Static and dynamic CR is too wide to get a happy medium with just a cam change. The 72 CC heads are the trouble spot

A different cam and heads would be Ideal, along with a recurve on the distributor , but heads and a recurve would work satisfactorily IMHO.


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## 71Goatwannabe (Jan 17, 2020)

Thanks for all the suggestions. As this is my project car and extreme budget build I was going to try to find a fix other than a head swap but I see now that the 62s even with the good flow may not be for me with the high compression. Probably will have to bite the bullet and look for some different heads.


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## PontiacJim (Dec 29, 2012)

Using the Wallace Dynamic Compression Calculator, and the closing point of the "066" cam used in your engine (63 degrees), the dynamic compression is 8.25. Anything above 8.0 will be a problem for pump gas from what I have read. So this means blending in some racing gas or octane booster. 

Using the same calculator and inserting the factory "067" cam (intake closes @ 70 degrees) and the "068" HO cam (intake closes @ 77 degrees), the dynamic ratio drops to 7.78, and 7.29 respectively.

So the "068" HO cam may be an option, but as LATECH has pointed out, you may loose a little bottom end HP/TQ, but I don't think enough to be concerned about.

The Lobe Separation Angle (LSA) on the "066" cam is 111.3, the "067" is 113.5, and the "068" is 116. The wider LSA decreases cylinder pressure while the tighter LSA build cylinder pressure which is demonstrated by the range in the Dynamic Compression ratio's from the "066" to "068" cams. So the "066" cam is only compounding the problems associated with the high compression engine.

That said, a head swap while still keeping your cam, would need to drop the compression to 9.0 or under - in my opinion. So you are looking at a head with a range of 83 cc's for 9.0 compression and 87 cc's for 8.72 compression which is going to really limit your choices. The more readily available 6X heads are the 6X-4 with 96 cc's giving you a 7.53 compression and the 6X-8 100 cc's would be 7.32. Then you will have to rebuild them as it would be highly unlikely you can just bolt them up as is, nor would I want to without having them checked out by a machine shop. The lower compression looks ugly on paper, but that's where you would want to go with a different cam to build cylinder/dynamic pressure - But, more money.

You best bet is to consider using your present heads and going for dished pistons. Of course this will mean engine tear down and probably out of your budget.

So try the few basic changes already listed and see what that gets you. Next best inexpensive route might be a cam swap. Read this posting on the "068" cam which may give you a little more info: 068 cam in 68 WS 400 - PY Online Forums - Bringing the Pontiac Hobby Together


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## LATECH (Jul 18, 2018)

My 64 has a 9.49 to 1 static and an 8.29 to one DCR.

I run 93 octane, but I can run 91 if need be without issue. I have a 389 bored to 4.12, 82 CC head chambers, Block is decked to .005, .039 compressed head gasket.Forged rods and pistons. Balanced. Crane cam . Crower springs.
That being said , My cooling system is excellent, 2 core aluminum with a shroud, 7 blade and thermal clutch.
Plus I have the divider plate cleranced properly t the water pump for postive flow of coolant. I also have a cast impeller on the water pump
Distributor is also worked a Tad. 12 degrees initial, 36 all in. by 3000rpm,Vac can set with ported source, light spring tension and limited to 10 dgrees all in when active.

Car is a beast.

So 8.3 Dynamic would be max IMHO . That to can also depend on alltitude and humidity levels.(coolant temp too)


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## LATECH (Jul 18, 2018)

Here is a little chart I found


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## MarkS57 (Feb 8, 2014)

PJ is on to something with the 068. I ran my 400 w/ the 62 heads first with a CC 280M cam and it rattled like crazy at operating temperature. I switched over to the 068 and bingo, much better. Not the beast it was with the 280M but still plenty quick and ran well on 93.


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## 71Goatwannabe (Jan 17, 2020)

Thanks for your input guys. I probably will end up doing the 068 cam swap at some point. But it seems I have my answer. I’ve not been on this site for long but I’ve already learned a lot, coming from a Chevrolet background. I still have lots of questions about pontiacs but that’ll have to wait until I can get the detonation under control.


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## Lemans guy (Oct 14, 2014)

And 71.....make sure that your carb throttle return springs are new and strong...

they get old and weak and will not pull the throttle closed enough when the pedal is off.....

this can cause diesel in hand run on, you need that throttle to shut firmly....

good luck let us know how you do......


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## Lemans guy (Oct 14, 2014)

My auto correct..sorry......”dieseling and run on”


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## PontiacJim (Dec 29, 2012)

LATECH said:


> My 64 has a 9.49 to 1 static and an 8.29 to one DCR.
> 
> I run 93 octane, but I can run 91 if need be without issue. I have a 389 bored to 4.12, 82 CC head chambers, Block is decked to .005, .039 compressed head gasket.Forged rods and pistons. Balanced. Crane cam . Crower springs.
> That being said , My cooling system is excellent, 2 core aluminum with a shroud, 7 blade and thermal clutch.
> ...


Closed chamber heads can go a little higher on compression and distributor advance. Your combo of .005" deck clearance and the .039" head gaskets provide an optimum quench area which also promotes better flame travel and can be an asset in reducing/eliminating the detonation. So the 8.3 Dynamic works.


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## greg69gto (May 28, 2019)

Jim, I read your take on dieseling. I followed through on your suggestions, but still have intermittent dieseling which has become a problem in just past 2 months after years of running well. What am I missing? What’s still causing this dieseling?

The car is a 69 GTO that had a rebuild by previous owner back in 2005 on the YS 400 ci with 0.030 overbore, 3 2bbl Carburetors (formerly 4 bbl), mild Comp Cams and Roller-Tip Rockers, 5 speed Tremec. Car has been running great for years.

Several months ago (approximately 190 miles) had mild engine refresh including new Petronix Ignition, new heavy duty 4 core radiator with 2 electric fans (engine temp runs about 200 – 220 oF in Houston driving), installed Vintage AC, rebuilt the carbs, had the heads off for block-deck surfacing, fitted new gaskets/seals and pistons looked good – nominally little carbon build up. . 

Run high octane (95+) gasoline

Had mechanic adjust the idle. Idles at around 800 – 850 RPM. No air leakage on out board carbs. The throttle doesn’t seem to be sticking. New spark plugs.

Don’t want to put car in gear when shutting off and dubious about putting water or Seafoam in carbs to “clean out” the engine. Any other ideas you could help me with?


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## PontiacJim (Dec 29, 2012)

greg69gto said:


> Jim, I read your take on dieseling. I followed through on your suggestions, but still have intermittent dieseling which has become a problem in just past 2 months after years of running well. What am I missing? What’s still causing this dieseling?
> 
> The car is a 69 GTO that had a rebuild by previous owner back in 2005 on the YS 400 ci with 0.030 overbore, 3 2bbl Carburetors (formerly 4 bbl), mild Comp Cams and Roller-Tip Rockers, 5 speed Tremec. Car has been running great for years.
> 
> ...


OK, I see what could be a couple problems.

First, give us you timing specs. Initial timing at the balancer, 6,9,12 ? degrees with vacuum to distributor unhooked. Total timing at "X" RPM's - with vacuum advance unhooked. Could have some timing issues that can be adjusted that may help.

Spark plug brand and heat range? Some of the foreign makes use a thinner wire verses the old fatory style AC/Champion/Autolite and can be a heat conductor that causes run-on. I also like to run a tighter .032"-.035" gap even if you have a bigger coil/hotter ignition.

Check engine temp with a hand held laser gun to verify your gauge temps. Too high in my opinion. I'd like to see lower, no higher than 200, but below 200 would be better. Do you know what temp T-stat you are using?

Electric fans may not be the best. They must pull air through, not push as that is the worst case scenario. The fans/motors/structure blocks air flow. I assume the AC condensor is in front of the radiator and the electric fans may not pull enough CFM's as compared to a factory set-up. The fans also need to have a shroud that fits around the radiator. Maybe a couple pics?

Not a fan of the Comp Cams with 110 LSA in any high compression engine - they build more compression/pressure at your lower RPM's. Not what you need. It is possible that the timing chain/gears have worn a little and have changed cam timing which again affects combustion pressure. Easy to check. Distributor cap off, watch rotor movement. Put chalk mark on the crank balancer that lines up with the "0". You do not have to bring the crank timing line to "0" to do this, just make the mark. Now rotate the crank by hand to the right and watch for the rotor to move - stop when it does. Look at the mark and see how many degrees/far it has moved. Now do the same thing but go left and watch the rotor. It should wind up at "0" again just as the rotor moves. The chalk mark should not move any more than 3-5 degrees. Any more and the chain/gears are loose.

A compression check on all cylinders will let you know how much cranking compression you have. High readings are not what you want. This is done with all plugs removed so the engine can spin fast to get you best reading. If this is known, it is another clue that can be used.

800-850 RPM at idle is too high, but my guess is it is because with AC the engine will die if anything less? Should be 650RPM. 800-850 may be allowing the center carb throttle blades to be open enough to still draw fuel from the carb through the idle circuits which causes the run-on. Can you get the carb to idle lower? Sometimes the idle air bleeds have to be enlarged to get the carb on a tri-power to idle lower as we have had a couple instances where this was the fix.

Set the idle to 650 and see if that helps - with AC off.

Cars having factory AC used an electric solenoid to raise engine speed when the AC was activated. If you do not have this, then you will want to add it. The engine will idle at 650 and when the AC is turned on, the electric solenoid gets energized and raises the idle to the higher 800-850RPM to prevent the engine from stalling when coming to a stop as 650 will be too low with the extra drag put on the engine by the AC. These can be purchased aftermarket and installed.

Check these things and report back with the results and we'll go from there.


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## greg69gto (May 28, 2019)

Jim – Thank you so much for the reply. I value your suggestions.

In response to your suggestions:

When engine went through a refresh short time ago (3 months ago, approx. 190+ miles) in addition to the things I mentioned, a new timing chain was installed and new harmonic balancer. They said timing was set at 9 degrees. But that was what they said – I’ll have to check.

The spark plugs are New ACDelco Conventional Resistor Spark Plugs R45S. Have to check what the gap is, but assume it set at 0.035. Plugs are somewhat dirty but no excessive carbon build.

When engine went through a refresh short time ago a new Temp Gauge installed and the sensor was re-calibrated in recent engine refresh. Assume temp reading is close but will check when can get hold of a laser temp gun. Yet the new heavy duty radiator and dual electric fans should have addressed any heat issue.

Electrics fans are installed so as to pull air through the radiator. Shroud fully fits around fans – see pictures. Fans turn on at 160 oF.

The cam was installed by previous owner. I’ll use your technique as described to check the cam timing. But note that there is that new timing chain (double roller) and the gears look good shape.

Compression check showed about 6 psi difference between the lowest and highest cylinder. Leak check showed about 6% leakage.

Have idle setting set such that will hold idle when AC is off and then checked with AC on. Anything below 800 rpm when AC is on causes the engine to bog a bit. 800 – 850 rpm seems to be the best setting for a stable idle.

No idle solenoid seems to be installed. See pictures.

I’ll be working on rechecking engine temp, and the cam timing.

Sorry, but curiosity still abides – engine has been running well and only last couple weeks have seen the dieseling – and intermittent at that. No change in carb setting, no cam timing change, same high octane gas (no additives other than what is in the pump gas) and without having the AC on. Hope the pics came out OK - still trying to get handle on the new forum format. Included pic of the car.


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## PontiacJim (Dec 29, 2012)

OK, great pics, nice car, and good info. All looks well. Yep, the new format sucks and takes some time to get used to.

The idle in my opinion is suspect. It is too high, and I get it's for smooth running with the AC. So an electric idle solenoid would be my first investment. Get the idle down to 600-650 RPM's with no power applied to the solenoid. The when energized, set it to the 800-850 for AC operation. You can tie the 12Volts needed to the power wire on the AC, which means you will need to shut down the AC before shutting off the engine so as to drop idle speed back to slow idle, or a 12V key source that will shut down when key is turned off and power is cut to the solenoid.

New chain/gears should be fine as a double roller doesn't get sloppy any time soon, so I would skip that check.

Plugs are the factory range and type. If dirty, ie blackened, they are running rich which could be indicative of a problem contributing to the run-on. Clean them up and check the gap. Back in "the day", it was not uncommon for the plugs/cylinders to load up with carbon and make the engine run poor. The mechanic would recommend you to "blow out" the carbon by stomping on the gas to the floor when entering an onramp to the highway, or on a long straight stretch. I had a car that did run rich and learned to recognize when it began running less than ideal and I would open it up a couple times to clean out the cylinders and it would wake right back up again. So with a high compression engine, you gotta use it once in a while and not drive it like grandma.

Check your PCV valve. Make sure it is operating correctly, tight in the grommet.

What is your setting on the idle mixture screws? I typically turn them in gently until they stop, then back out 2 1/2 turns for my initial setting. Then adjust by sound, but some will use the vacuum gauge to get the best vacuum reading. If they are too far out and the idle running too rich, this is another area that could be causing a problem.

It looks like points? Very important to have the point gap/dwell set correctly. You can actually change the advance/retard of the plug firing by making small adjustments to the dwell, ie when the points fire off and send the signal to the plugs to fire. So check this and watch the dwell meter (at a steady RPM) to make sure the needle is steady and not bouncing around.

I see the vacuum advance. Where is the line connected? Is it manifold or ported on the carb? I am thinking tri-power is manifold. With the initial set at 9 degrees with vacuum line disconnected, as soon as you reconnect the vacuum advance, the initial may advance a few degrees or so due in part to the higher idle RPM's or even the direct port vacuum. So leave the vacuum advance disconnected/plugged so the initial does not advance past 9 degrees. 

Again, keep the AC off and get the engine idled down to 600-650 RPM's. Now with no vacuum advance going to the distributor, shut the engine off and see if that works. I am thinking the vacuum advance is increasing your initial at the balancer (you can check exactly how much by setting it to 9 degrees, vacuum line unhooked, and then connecting it. The amount it increases will give you an idea of how much). It might jump right up to 19-21 degrees which might not work for your engine.

The .030" over bore will raise compression slightly if using the stock type pistons. More compression always means more heat.

I still don't care for the electric fans, but if they had been working all along, then they should be OK. With the aluminum radiator, it should cool better in my opinion. With the fans kicked in, can you place a sheet of paper on the front of the radiator and the suction from the fans hold it in place? This is a simple test you can do that'll let you know you have good air flow/suction through the radiator.

If the temp sensor turns on at 160, then the fans must be on most of the time? Maybe you meant 180? I personally like the 160 T-stat, but that does not mean the engine runs at 160 - it mean the T-stat opens at 160 and the engine will find the temp it likes to run. I also like to drill two 1/8" holes in the brass ring of the T-stat to allow any trapped air in the sytem out. It is possible that an air bubble can get trapped in the system and not have a means to escape. This can cause a hot spot and higher engine temps.

Another thing that can happen is the bottom hose can collapse shut at higher engine RPM's. It is recommended to use a hose having an expander spring inside the hose to keep it from collapsing. You can also buy the spring and add it.

And lastly, could be the gas. I know there is a "winter blend" and "summer blend." With the high compression my guess is you need closer to 100 octane, but if you are not getting any spark knock, you are OK.

AND.... are those valve cover breathers functional? Looking at the drivers side valve cover below the breather, looks like the gasket is blowing out? You need to have breathers on both valve covers to allow internal engine pressures out, otherwise you will blow out gaskets, to include rear main seal leaks. If those are oil fill caps which twist down onto the covers and are sealed, then replace them with a breather style cap which will be raised up off the cover and have holes/mesh to let the engine breath and the PCV valve to operate correctly.

So I am leaning towards the high idle as an issue, and then do the other checks to see what the results provide.


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## greg69gto (May 28, 2019)

OK, I’ve run through your items like a checklist:

[] Timing = 9 degrees > OK
[] Spark Plugs = New ACDelco Conventional Resistor Spark Plugs R45S correct gap, dirty, but not too much carbon build> Running Rich
[] Engine Temp = 180 oF to 210 oF > TOO HIGH
[] Timing Chain/Gears = newly installed, double roller > OK
[] Cam Timing = rotor between “0” mark , approx. 6 degrees difference > OK
[] Compression Check = 6 psi difference between the lowest and highest cylinder. Leak check showed about 6% leakage. > OK
[] Valve Cover Breathers = functioning > OK
[] Radiator Hoses = bottom hose does not collapse > OK
[] Gas = 95 – 98 Octane > OK
[] Idle Speed = 800 – 850 RPM > High
[] Idle Solenoid = None > Need to Check

So, it seems I need to address Engine Temp and check having an Idle Solenoid on the Carb

Your many ideas and suggested issues set me up well to methodically check each potential causes and by working through them hope I have narrowed down what I need to do.

Thank you Pontiac Jim, I am grateful. Stay safe and healthy during this pandemic.


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## PontiacJim (Dec 29, 2012)

OK, great. You did what is needed, step by step checks and a process of elimination.

Get the idle down using an electric idle solenoid stop - which you will have to do some fabricating to adapt to your tri-power.

Pic #1 - I posted a pic of a 1966 tri-power. If me, looking at the pic, I would fashion a bracket to come off the front carb at the rear intake stud. Looking at the way the center carb linkage sets, making a bracket to come off the center carb appears that it would be too close, or not fit at all, on the throttle linkage. Fabricating a bracket to come out from the front carb looks more feasible.

Pic #2 is simply an idea of how the "L" bracket could be fabricated. The small hole at the end of the leg slips over the stud/nut, or bolt, that holds the front carb to the manifold. You will need a longer stud or bolt to compensate for the extra thickness of the bracket. I would use a piece of manila file to shape/cut-out a template (something like the bracket shown) and adjust as needed until you get a template that looks like it will work. Then lay the template over a piece of 1/16"/16 gauge steel plate (I am kinda guessing at the bracket thickness, but it has to be rigid enough so as not to flex/bend) and follow the shape of your template. Cut out the flat steel bracket and bend it to shape. Drill the bracket hole so the solenoid will slip through and tighten up with the large nut so as to hold the solenoid in place.

Now the bracket may not be perfect in its alignment to your carb's throttle bracket. My fix would be to fabricate and other small "L" bracket that will have a hole drilled in it so I could bolt it on the throttle linkage - maybe replace what looks like the washer under the nut holding the extension that opens up the outboard carbs. If not, then I would be drilling a new hole in the throttle bracket and installing a short bolt/nut. Look at Pic #3 and you will see how the Q-jet uses a bent "ear" that the idle solenoid contacts. This is what I am talking about in making an "L" bracket that could be bolted on to the carb throttle linkage so as to create the "ear" that solenoid would strike when energized. Again, once you have the solenoid/bracket secured to the front carb stud, make a template that will get you close to where it needs to be. Then fabricate one out of steel.

There are a number of electric solenoids available, but I am not sure which ones will be best as I see the same ones being sold by different companies for reasonable & crazy prices. Summit has them, but in reading the reviews, some of these don't seem to have enough power to work unless you give a little throttle to help the solenoid out. If you had a Pull-A-Part nearby, I would walk through looking for something I might be able to adapt. Ebay seems to have reasonable prices on some: Nos 1976 1979 Pontiac 5.7 350 400 455 Carburetor Idle Stop Solenoid 4 bbl | eBay

So this is just my idea as to what I might do, but you may have another idea or some other set-up made to bolt on.

You have shown that you have 9 degrees initial advance, but have not yet mentioned if you have a vacuum advance distributor, how it is connected, and your total mechanical advance (initial plus the advance provided by the distributor weights). The vacuum advance, when set-up correctly, WILL affect engine temps when driving and helps to cool it down under part/no throttle conditions. This is one of the purposes of this feature as well as deliver better gas mileage.


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## integrity6987 (May 10, 2017)

Greg - in the picture of the distributor showing the vacuum advance PJ had asked about the source being ported or manifold. This was not answered in your checklist and will impact the timing if not plugged when the timing was checked - so confirming the 9 degrees is with the vacuum line plugged. The picture looks to me like the vacuum diaphragm is capped off but it might just be the angle of the shot.


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## greg69gto (May 28, 2019)

PontiacJim said:


> OK, great. You did what is needed, step by step checks and a process of elimination.
> 
> Get the idle down using an electric idle solenoid stop - which you will have to do some fabricating to adapt to your tri-power.
> 
> ...


Took time off for Easter. Hope yours was good.

You know how you can walk by something everyday and not notice it? Or something is out of place, but your eyes/mind doesn't register it? I guess I missed not seeing that the vacuum advance on the Distributor is not connect to anything. I even had a Mechanic I trust working on the engine and didn't say anything to me. 

But maybe it was set up so. This is a Pertronix electrical ignition system. Pictures attached 1 and 2 show more close up of the Distributor.

And Picture 3 shows the Tri-Carb set up - note the vacuum part on the center carb choke/throttle plate (white).


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## greg69gto (May 28, 2019)

integrity6987 said:


> Greg - in the picture of the distributor showing the vacuum advance PJ had asked about the source being ported or manifold. This was not answered in your checklist and will impact the timing if not plugged when the timing was checked - so confirming the 9 degrees is with the vacuum line plugged. The picture looks to me like the vacuum diaphragm is capped off but it might just be the angle of the shot.


Took time off for Easter. Hope yours was good.

You know how you can walk by something everyday and not notice it? Or something is out of place, but your eyes/mind doesn't register it? I guess I missed not seeing that the vacuum advance on the Distributor is not connect to anything. I even had a Mechanic I trust working on the engine and didn't say anything to me. 

But maybe it was set up so. This is a Pertronix electrical ignition system. Pictures attached 1 and 2 show more close up of the Distributor.

And Picture 3 shows the Tri-Carb set up - note the vacuum part on the center carb choke/throttle plate (white).


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## PontiacJim (Dec 29, 2012)

Get that vacuum advance connected. It will help with the higher engine temps at cruise.

The plastic white "thing" is a vacuum can, ie choke pull-off. It is correct for 1966. I suggest you get a diagram, or search the forum, for a diagram that shows your vacuum line/PCV hook-ups. On some set-ups, there is a hollow carb stud with a hose nipple that can be used. It goes on the passenger side, I believe center carb, and provides direct manifold vacuum. You can get these reproduction. I have read it is used for the automatic trans vacuum, but I am not a tri-power expert.

Still get the RPM down, so hooking up the vacuum advance won't drop the high idle. You may have to readjust the idle speed. Typically when you hook up the vacuum to manifold vacuum, it will bump up the intial timing and idle speed, so you may have to drop it back down a bit if it speeds up.


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## greg69gto (May 28, 2019)

PontiacJim said:


> Get that vacuum advance connected. It will help with the higher engine temps at cruise.
> 
> The plastic white "thing" is a vacuum can, ie choke pull-off. It is correct for 1966. I suggest you get a diagram, or search the forum, for a diagram that shows your vacuum line/PCV hook-ups. On some set-ups, there is a hollow carb stud with a hose nipple that can be used. It goes on the passenger side, I believe center carb, and provides direct manifold vacuum. You can get these reproduction. I have read it is used for the automatic trans vacuum, but I am not a tri-power expert.
> 
> Still get the RPM down, so hooking up the vacuum advance won't drop the high idle. You may have to readjust the idle speed. Typically when you hook up the vacuum to manifold vacuum, it will bump up the intial timing and idle speed, so you may have to drop it back down a bit if it speeds up.


Thank you, Jim. Very good direction. I appreciate it. Now I've got to work on it and get it all sorted out..


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## PontiacJim (Dec 29, 2012)

Sounds like a plan, keep us posted of the progress.


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## Old Man Taylor (May 9, 2011)

The dieseling problem has an easy solution with a stick shift. Leave it in gear and let the clutch out as you turn off the key. I'm in the habit of automatically doing that on my car.


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## greg69gto (May 28, 2019)

Old Man Taylor said:


> The dieseling problem has an easy solution with a stick shift. Leave it in gear and let the clutch out as you turn off the key. I'm in the habit of automatically doing that on my car.


I appreciate that this is a "hack" back in the day. I remember my Dad doing it. But, that doesn't seem to be good for the engine. It seems to me, should fix the root of the problem.


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