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Discussion Starter #1
Hi Folks,

Yes, another Pontiac 400 overheating post. I know. Sorry. But, before i begin, a few facts:

I am old. I bought leaded gas.
Grew up in a Pontiac family (Star Chief- grandfather, Catalina wagon - dad, 68 GTO convert, brothers, and several Grand Prix's and Firebirds). Been a car guy pretty much since the beginning. i have managed to rebuild Porsche and Mercedes engines, so I am probably not a total handicap. That said...

So i am pretty sure i have addressed all of the known and possible gremlins...(water pump plate spacing, cast iron impeller, radiator, air flow, radiator fan, shroud spacing, timing cranked to max advance possible, thermostat working right, good top to bottom radiator temp delta T's, flow is excellent) and on and on. The only thing i can think of on this is that the vehicle might be running a bit lean, so i installed an AEM wide band sensor and ran the car across a broad range of conditions (freeway, hard acceleration, part throttle, up hills, over hill, over dale, you name it) and it's running at what appears to be excellent AFR's at all demand levels but perhaps just approaching 14.7 at cruise at highway speeds. One thing i have observed is that the car heats up amazingly fast. Like crazy fast. It can jump to 180 in just a minute or so. Might be exaggerating a but here but i will time it. The car will idle all day in the hottest weather at 180. Get it out on the highway and she gets hot. Question is, how lead does she need to be before she get hot because of a lean cruise mix? I am certainly not above 14.7 at cruise. Probably closer to 14.

Also, probably important to note that it's .40 over and the PO put a cam in it (i will check to see if it's possibly too rowdy when i yank it) but do these blocks start to run hot when they get bored out this far?

My car has a 73 400
.40 over
4X heads with small valves
Stage 1 Quadrajet
HEI from mid 70's Yak but it was set curved by Majhor Murray in PDX (seem competent)
Pretty sure I am getting 32+ degrees of advance but it jumps around a lot
Runs beautifully
TH350
3:23 Rear end

Again, i am yanking the engine to address this mystery leak (car only has 2k on it since rebuild) but i can't deal with leaks. Any advice is welcome at this point. And no, i refuse to put a modern engine in it. Who would give up the sound of a 400 with a quadrajet for that ?

Ideas?

Thanks!

Allen
 

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Put a Chevy LS3 in it and you will never have problems again........not. :smilielol:

Since you stated that it heats up rather fast, first guess is the timing is retarded. If you have a dial-back timing light, you may want to write down the RPM and your timing numbers beginning at 1,000 RPM's up to your maximum advance RPM's in 250 RPM increments to see what is actually happening within the HEI.
 

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There are a lot of threads on this forum and The PY site. Two things that come to mind immediately are related. Bottom hose collapses on high rpm. The next is related to flow throughout radiator and engine as you get to higher RPM ( possible clogs) good luck and keep us informed. Doug
 

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Discussion Starter #5
Will do. Flow is good. Lower hose has the coil in it, so it shouldn't be collapsing.

Any thoughts on the .040 over topic? Do these blocks begin to run hot when bored over?
 

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Will do. Flow is good. Lower hose has the coil in it, so it shouldn't be collapsing.

Any thoughts on the .040 over topic? Do these blocks begin to run hot when bored over?
I questioned my machinist about that same thing because I was concerned too. He said "no". The amount of overbore is like the thickness of a human air and not enough to have any effect on cooling. He said if you have cooling issues its not because of the overbore.

You did not provide what "hot" temps mean. What are your actual readings? Perhaps the gauge is incorrect or sending unit is not matched to the gauge. Where are you reading your temps? Higher temps will be read if using the gauge plugged into the side of the head versus the water crossover at the thermostat.

Have you used a hand held digital laser temp gun to shoot the various areas of the radiator & cooling system as well as head/exhaust temps? These will be more accurate than your gauge reading OR can confirm your gauge reading. My '73 Fury gauge reads "hot" and climbs to a level nearing boiling in hot summer heat in stop/go traffic. I did all the checks and replaced a few things hoping to help(which did not) and then got a laser temp gun. The gauge is way off as my radiator temps were near 170 degrees when my gauge reads into the "hot" range.

You also stated the timing jumps around a lot -it shouldn't. Again, check the HEI for issues like sticking weights, worn parts, or bad module. What is your initial timing setting at the crank? How much mechanical advance does the HEI provide? How much advance does the vacuum advance provide? Is the vacuum advance connected to the manifold or ported at the carb?
 

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Discussion Starter #7
All good clues to the puzzle and i will document them all in one place as soon as i get back out to the shop. What kind of exhaust temps would i be looking for at idle? It's pretty cool here in OR this time of year so no amount of gymnastics will heat it up. One interesting symptom is that it's pressurizing quickly...

I will be back...
 

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Discussion Starter #8
Ok,

Here are the stats. Again, thanks in advance for any tips.

The initial timing is about 18 BTDC

Total timing is about 32 BTDC

Vacuum advance appears to give about 12 degrees of advance

Vacuum advance looks to be on a ported nipple

Exhaust temps vary from center to ends but it's running 480 on the R, 460 on the L

The heads above the exhaust are at 380

Radiator appears to be pulling about 18F from top to bottom at idle

The timing is not jumping as previously reported...think that's my timing light

Plugs look perfect, if they can be read these days...

Compression is 140, 130, 130, 125, 135, 130, 128, 130

Seems low but I never checked it after it was rebuilt 3000 miles ago

It has low vacuum readings at idle and I don't have a record of what cam is in it, but I will check that when it comes out.

Temp gauge reads accurately

Good lower radiator hose spring

Correct fan blade sits 1/2 way in

Radiator is an original Harrison but was worked on (tanks off) by a reputable radiator guy

Radiator is properly sealed and shrouded

No one has commented yet as to whether or not a close to lean setting will have an effect on running hot at part throttle (highway speeds)...again, it's not real lean but it's close to 14.5 at highway speeds.

So I will report back once I yank the engine and look inside.

Seems like other folks engines don't burn the paint off the heads like mine?
 

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You did not say if your initial advance taken was with the vacuum advance plugged? 18 degrees initial and with 12 degrees of vacuum advance would indicate that you have 6 degrees initial and 12 degrees vacuum for 18 initial which would mean your vacuum advance is not hooked up to a ported nipple.

If you have 18 degrees advance with the vacuum advance plugged and disconnected, I'd say you have too much initial advance. 10-12 degrees would be better.

Compression can be a function of cam timing - when the intake valve closes. So you could have a lower reading with a bigger cam, but if your vacuum reading is low then you may have a big cam. So what is your vacuum reading?

Air/fuel ratio. You gave us cruising A/F ratio, but what is your idle A/F ratio and wide open throttle A/F ratio?

Have never used an A/F ratio meter, but have on going on my present build. From my research into the best A/F ratio's, I personally feel 14.5 is too lean. I think 13.8-14.0 would be better. Keep in mind that ethanol laced & oxygenated fuels do run leaner by nature and an older type carbed engine should run a little richer using bigger jets, and a bigger cam can increase the need for even more fuel. A lean engine will heat up quick and run hotter. Fatten up the carb and you may see the problem go away.

I found this on the internet: A starting point for A/F mixtures for most mild performance engines is:• Idle: 13.4-14.1; • Cruise rpm: 14.1:1 with a mild performance engine, or 13.4-14.1 with a high performance cam; • Power and acceleration: 12.5:1 for a “normal” engine or high performance engine

You still have not shared what your temperature is that you consider "Hot". But in any case, looks like you have your cooling system well built, so I'd be looking at timing and carb issues to see if any changes can be had.

Could not find a definite exhaust gas temperature as they varied widely depending on cast iron, headers ( coated or not), and RPM's. Your temps may be a little high at 480/460 at idle, but fall into some of the numbers I read off other sites on the internet. So at least the temps are fairly close one side to the other.
 

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Discussion Starter #10
Hi Folks,

Ok, sorry, i will fill in a few of the blanks.

The initial timing was taken with the vacuum line disconnected and plugged.

Vacuum reading is about 14 at idle.

WO throttle AF is running in the 12's, so that feels pretty good. The car pulls well.

My part throttle ratio is closer to 14.5.

As far as my definition of hot, it will run up to 200 quickly on the freeway, sometimes hotter. It never really gets hot here, so 90F ambient is probably all it sees.

I will report back when she comes out. I am going to be happily embarrassed if there's a mechanical issue with the flow. But given the low vacuum readings I am guessing the previous owner put a big cam in it. I am going to swap out the 4x heads with small intake valves for a set of 6x heads with a smaller chamber volume and larger intake valves. Not sure i am going to see a huge improvement but since i have them....

When i get on the other side, i will contemplate bigger primary jets!

Thanks for the tips.

Allen
 

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Just a quick comment on your cam that you mention. When I bought my '71 GTO, someone before me, put a bigger cam in the original, stock 400 engine. You could hear and feel it. It just sounded over cammed if there is such a thing. I had 10-11 inches of vacuum on a good day, not even close enough to operate my power brakes which are of the upmost importance to me, and the engine ran hot; 210 and higher at times. I pulled the cam and found it to be a Voodoo "pro touring" cam with a high lift. I replaced it with a Voodoo 268 cam. The motor sounds and feels so much better. Doesn't seem to struggle like it once did. Have 17-18" of vacuum at idle. Once I got the cam broken in, timing and cooling straightened out, I noticed at idle, the temp. only reached 175 degrees. Quite an improvement. Haven't driven it yet on the highway, because of the snow. I blame the previous cam for at least part of my running hot issues. Just wanted to share this experience with everyone.
 

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Discussion Starter #12
Update.

I tore it down tonight. Before doing so I tested the flow of the pump. Not sure i can load the video but I will try. Seems to have excellent flow, so I am going to rule that out.

Update on the cam though...it has a Comp cam in it and it might be too much. Eager to hear thoughts on this.

COMP Cams 51-224-4
Xtreme Energy 274H Hydraulic Flat Tappet Camshaft Only Lift: .488" /.491" Duration: 274°/286° RPM Range: 1800-6000

Is this more than i should have in this car? Again, it's a plain 73 400 40 over. It will now have 6X heads with the larger valves. I was lead to believe the heads had smaller chambers than my 4x heads but my unscientific exam suggests they are the same volume.

So i am once again steering back to the lean part throttle settings.

Also, interesting to note, my oil leak was not the rope seal. I think it's "pan fit". I had one of those nice BOP one piece seals but i think the pan fit at the rear was bad. It was installed on the car and I probably didn't notice the pan fit like crap.

Anyway, any thoughts on the cam are welcome. This is new territory for me. Just want it to run strong. It's not a 1/4 mile car.
 

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Discussion Starter #13
Ok, had to put the water pump flow video on youtube. Again, I think the flow here is fine. The car idles very low, and the coolant was at 180.

On a side note, I had to run a vacuum pump to supply enough vacuum for my disk brake set up.


 

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Hmmm. The Comp Cam is the same as I used in my low compression '72 400. .040" over, with 7K3 heads. Did an inexpensive rebuild and used a rebuild kit that included the cast pistons, bearings, oil, pump, etc.. I went with the Comp Cams just because CC seems to be the more advertised company for Pontiac cams. Don't think it was too big at all.

The 110 LSA helps to build cylinder pressure with the lower compression engines. I liked the specs on lift/duration as it wasn't too extreme and I did my own gasket port matching and cleaned up the intake runners a bit. Used stainless steel valves and CC matched valve springs & lifters, ie the CC Kit. My '68 Lemans had the manual 3-speed on the floor & 3.23 non-posi rear end. I went with a taller tire out back, 28", so it made the rear gear more like a 3.08. Little more slipping of the clutch to get it rolling, but not excessive.

I really liked the cam for what it was. Sounded good at idle. Good power - really pulled hard. What I did not like is that once the power range was peaked, power fell off like a stone. I think it was about 5,500 - 5,700 RPM's (which is really high enough if using cast rods). I could run it up to 6,000 RPM, but it struggled and I was wasting engine as there was no real power to be gained so my full throttle shifts were kept about 5,700 RPM's. Curious enough, the engine ran hot when I first installed it. Stop & go traffic was difficult as I would watch the temps really climb and sometimes have to pull over and sit or get off an exit just to keep airflow moving to get it cool again - and that was after throwing the heater on full blast. The original 350CI had no cooling issues prior to the 400CI I installed.

I had the HD 4-core copper radiator, but used a 4-blade metal fan thinking it would pull more air all the time. I did not have a shroud. Used a 160 T-stat that I drilled 1/8" holes in the top ring to ensure no trapped air pocket. New water pump, divider plate and sleeves, but did not clearance it as I never heard of such a thing at the time. 50/50 anti-freeze. Eventually went to an aftermarket flex fan which pulled a hole lot more air and improved things in stop & go traffic, but it would still run hot, and I could raise the RPM's to help cool it down. Added a product called "Water Wetter." I am a skeptic, but was willing to try anything at that point. Sure enough, my water temps did drop about 10 degrees. But still it ran 180 & up to 210 in stop & go summer heat, but did not boil over. Then one day - the engine temps were down, running 160 and never got past 180 in stop & go heat on the hottest of days, other wise it ran near 160 all the time. What changed? Unknown. Something unplugged in the water system, the heads, the block? Blockage in the radiator?

What I did experience was an internal carb leak on the Q-jet. I could see the tell tale signs of the gas stains on the aluminum intake where it would run out the throttle shaft. At times I could see it drip just after shutting down. Never fixed it. Is it possible the leak caused a richer running of the engine versus when I first rebuilt the carb and ran it for several years without the leak? Quite possible. Maybe the carb ran lean due to lower than required fuel pressure - never checked this but when I took the gas tank sending unit out of the tank, the sock on the end was some what plugged & very brittle. Maybe it had a lot more crap on it and my WOT blasts all the time cleared up some of the plugged up sock. Fuel float may have been too low causing the carb to run a little lean, never checked it, just ran it after my rebuild.

Back to the CC cam. Installed one in my brother's 360 SixPack engine, .030" over, hypereutectic pistons, that I built up for him. 110 LSA cam with a similar spec as the Pontiac cam. Car ran hot right out the gate. It mirrored my experience. I installed the HD water pump used on AC cars which I think was an 8-blade impeller to move more water. Temps would climb fairly fast and then slowly towards overheat. Timing was right, so not a timing issue. SixPack was a brand new piece, so it wasn't a carb issue. Did the 160 T-stat & flex fan (no radiator shroud). The flex fan improved things, but still ran hot. His new 2 core radiator that was used on the 318 was replaced with an aftermarket 2 core aluminum radiator to see if that would help. Cooling problems went away. It has been a couple years now, and his cooling temps are still nice and low. I drove the car last summer and temps stay below the median line, almost on the first mark on his gauge, and he says in stop & go traffic on the hottest of summer days that the needle will reach the middle mark and drop right down once he is rolling.

So what is the root cause, is it the 110LSA cam with its tighter overlap that causes the engine to run hot? Is it a carb problem wherein the bigger than stock cam requires more fuel so the engine does not run lean? A fuel supply problem? Is it a cooling problem of some sort that might be aggravated by the cam and/or carb? Is it a combo of all of the above?

So simply check things when you reassemble. I still feel maybe jumping up 2 jet sizes might be worth experimenting with if you keep the CC cam. With regards to the oil pan, you will need the Oil Pan Reinforcement Plates or leaks can develop at the rear of the pan: https://www.bopengineering.com/pontiac_replacement_parts.shtml
 

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some great discussion here from the gang. let me add a bit. I do think that is too lean to cruise. I use an AFR gauge and wide band in each exhaust. I like about 14.3 at idle, 13's for cruise, 12's for power.

lean running will burn a little hotter. Also your timing at 14 base and you say 12 from the vac can,...Is that one of those adjustable vac cans? First thing I do is toss those out, I know some guys like em, but I curve em on my Sun machine and just don't prefer them.

those cans are not limited to 12, they pull much more, over 20 usually and the adjustment is for the rate and not total. To control the total vac advance you must put in a stop. Also if your vac is low is the can even pulling in the 12?

Here is what I do get a HEI Vac can Standard Motor Parts SMP VC 302, rock auto has them; Napa has it as VC 1703; and O'Reilly calls it a BWD V482. They are all made by Standard and stamped 626 10. The spec is 3-6hg 5* @ 7-9, so it will start pulling in the advance early and below your vac at idle, it will pull in 5* dist advance which is 10 at the crank.

Hook it to full manifold vac, you said you had 18 and 32 total and then you said 14 base, so if 14 base is right and 32 total is right, you have 18 centrifigal.

You need to get that set in right, base at 14 and 10 degrees from vac at idle is fine will idle smooth and cool, if you have 18 centrifigal, then you are 32 total and 36 is more ideal. I think you are running a little lean and a little retarded on the spark, to fire a lean cruise mixture you need more advance not less.

Maybe put a curve kit in that distributor and get yuor centrifigal advance to 24 or 26, then add 10 or 12 at base to get 36,...with that vac can I described to you you will get 10 more degrees at idle and light throttle cruise, which should be

46 to 48 on today's gas for a good burn. with your setup the vac can may be way too high at cruise or not coming in, way too high will misfire, Most I see are like that on those adjustable cans, but with way too retarded timing say vac can not even coming in at your low vac, even lower vac at cruise than idle you the have 32 degrees advance trying to fire an overly lean mixture......won't work good.

rather have a hair richer cruise AFR, 13's ......and a 46 to 48 BTDC timing as well .....at light throttle cruise

both may be working against you, too lean and too retarded.......you need amore advance to fire leaner, that is why you want the vac can at full manifold vac, and pick up that extra 10 degrees to fire that lean...14.3 or 14.4 idle mixture..


just something to consider, those vac cans are $13 and the curve kits are $15 so you can make it happen. One last note if your Centrifigal springs are real stiff, most are your timing can be very retarded at light throttle......

:nerd: Hang in there you will get it!!:nerd::nerd::nerd:
 

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Discussion Starter #17
So would i be best off taking the distributor to someone who can curve it and adjust it off the car? It's torn down now so i have a week or so of gaskets on order, degreasing, trying to make that oil pan fit, etc. I opened the carb and it has 77 jets and a 46 primary needles. Are you thinking i should stay with that and go for the timing first? That seems like an amazing amount of timing advance.



I was also doing some research on aluminum radiators. Seems to be broad disagreement on the physics behind aluminum vs. brass cooling efficiency. I am tempted to keep everything else the same before i go at the radiator.
 

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Sorry for not weighing in sooner, but I also have been playing with my tuning and wideband and think you may be going down the wrong path.

14.x while cruising or idle is NOT TOO LEAN and actually it really depends on your throttle and load, but you could go much leaner with a true cruise (<15% throttle).

Have you verified your thermostat is not only working, but working properly ? Do you have a 180* Tstat ?

Have you tested your coolant to see if it has exhaust gas present (head leak?) ? If not an easy test (WHEN ENGINE IS COLD) is open radiator cap, start the car and then look inside the radiator at the fluid. If you see bubbles you most likely have a head gasket issue.

Also, your timing values don't really add up. Base is 18* and total is 32* then you have 14* centrifugal. I'd triple check these values and also record at what RPM full advance comes in (Lars has a great paper on timing). PM me (or him) your email and I'll send you what he sent me. (Lars' email is [email protected])
 

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Yes I would get your Distributor curved. If you have someone local then do it first, Lars also does them and CJ gave you his email. I go by everything Lars says on timing, he knows more than anyone. I curved a distributor yesterday on my Sun machine and I always use his recomendations.

I use Lars recomendations of 46 to 48 at light throttle cruise, it will make your car run smooth. As for lean and rich AFR's their is some range there and you can do it as you see fit. If your cruise is set too lean, and try a fast downhill run and release the throttle quickly and see if it backfires, a lean backfire. In my view that is too lean, your throttle should be able to handle a fast decell without backfire and cruise easy with no stumbling.

there are lots of articles on AFR;s out there, too rich is bad washes cylinders, too lean can cause detonation and hot running so you have to apply it to the car and see where it runs best.

Good Luck you will get!
 

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Two things that come to mind for me. First you said that it builds pressure fast. And it heats up fast. To me that sounds like it could be a head gasket . It could be getting combustion gasses in the coolant. I had a Pontiac 350 years ago that had the same symptoms, turns out it was a head gasket.

Get the test kit and see. Hopefully you get it figured out.
 
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