Overheating, need help

[cob427sc]

Looking for some true hot rod and/or engineering help. My 33 runs great around town but as soon as I hit highway speeds the engine overheats within a mile. Here's the particulars:

33 hot rod with a 1958 Buick Nailhead engine, 364 c.i. basically stock except for headers and 3 - 2 barrel carbs. Starts and runs great after complete rebuild.
1964 Turbo 300 transmission
FFR 32 grill shell and radiator. FFR supplied radiator fan
Engine has 160 t-stat. Electric fan comes on at 180. Cycles up to 200 then back down around town. On the highway just keeps climbing and won't cool back down unless shut down for 30 minutes.

I have tried replacing t-stat, running without t-stat, replaced water pump, removed trans cooler from in front of radiator with no success. With raditor cap off water flow is visible through the hoses.

I have been told that these engines normally ran in the 170 - 190 range.

Curious if someone knows a way of calculating the required size of a radiator based on the engine displacement? The stock radiator cooling area of the FFR radiator is about 16" wide by 17.5" tall and 3" thick.

Another possibility is going to a higher cfm fan. There are several that will fit and nearly double the cfm.

Any suggestions or help would be appreciated. I have driven about 300 miles so far, just around town, etc. since I don't dare go on any highways. Thanks.

[mike223]

The best way to evaluate radiator / fan / shroud efficiency is to look at water temperature leaving the radiator.

You should be running 50-60 degrees cooler leaving the radiator unless you've been running it really hard.

If it's hot leaving the radiator you need more airflow or a bigger radiator or both.



If it's not hot leaving the radiator something is probably not right with water circulation through the block.


Hope that helps narrow it down.

[jwhit]

highway driving should provide all air needed.i would be looking at water pump to make sure its not cavitating at higher rpm or maybe pulley size not correct water is either 1 moving to fast or 2 moving to slow or stalling out

[cob427sc]

I have the stock original size wp pulley and a brand new water pump. I found an article on sizing radiators with a lot of variables. Based on there info I need approximately 3 cubic inches of radiator for each cubic inch of engine displacement. That figures to 1092 cubic inches of cooling capacity. The stock FFR radiator measures 840 cubic inches. This might be my problem. I don't believe its cavitation in the pump as the engine is only turning about 2000 rpms at 55 mph.

[NAZ]

You asked how to calculate the size of a radiator required for a specific engine application. There are calculators online and you can also find a rule of thumb size per cubic inch displacement but here’s a way to get a closer size needed for a particular application:



1 HP is = 2544.43 BTU/hr or 42.407 BTU/min

Approximately 50% of the heat produced by the engine is wasted out the exhaust and ~30% of the heat is sent to the cooling system.


Calculating BTU/min heat load a radiator transfers: Q=MxFxT

Q: Heat load in BTU/min
M: Mass flow (weight of water per gal)
Note: Weight of water changes with temperature (actually density changes with temp) but water is most dense and weighs the most at 4-deg C (39.2-deg F) = 8.3452 lb/gal. Water weighs 7.9978 lbs/gal at 100-deg C (212-deg F).
F: Flow rate in GPM
T: Temperature change through the radiator (inlet temp – outlet temp)
EX: 8.3 x 35 GPM x 10-deg = 2905 BTU/min
Now find HP by: 2905 / 42.4 = 68.5 HP

But before you start thinking about procuring another radiator for a car with limited choices, consider increasing the flow rate with a larger GPM pump. Typically, the more flow the cooler running the car but there are limits with a down flow radiator as higher flowing pumps may generate more system pressure at the upper tank (that’s where the pop-off valve is located – AKA radiator cap).

Coolant absorbs heat at a progressively slower rate as it gets closer to its vapor point (boiling point).

Laminar flow creates a boundary layer of coolant against the tube walls. This boundary layer of slow-moving coolant acts as an insulator inhibiting heat transfer. Creating enough flow through the tubes to create turbulence but not too much that will aerate coolant (also inhibits heat transfer) will prevent laminar flow. The optimum coolant flow rate through the radiator tubes is ~ 6-8 FPS (enginebasics.com).

Learn more here: https://www.stewartcomponents.com/index.php?route=information/information&information_id=14

[RoadRacer]

Have you made sure it's bled 100%, I've never had the problem but I heard that an air pocket can stop water flowing?

> as the engine is only turning about 2000 rpms at 55 mph

Totally irrelevant to the topic but that's quite surprising.. I'm doing ~75mph at 2000rpm.

[Bob Cowan]

Don't forget that there are other things that can cause the engine to overheat: Incorrect timing, lean mixture.

[cob427sc]

Timing is set dead on and the carbs are actually set on the rich side. Thanks Naz, I was hoping you would jump in with some suggestions. All of this helps and also reminds me of the time I wasn't paying attention during Thermodynamics and Fluid Mechanics. I think I'm going to start with a couple of easy items first: relocate the transmission cooler, install a smaller water pump pulley and maybe construct a shroud around the fan. If this makes no headway I'll look further into the radiator sizing which based on the calc's may be on the small size.

[NAZ]

Sounds like a good plan.

[J R Jones]

cob, you did not mention cap pressure or recovery tank. Are you blowing off coolant when it gets hot? Is the cap at the system's highest point? Besides the gauge, what is the O/H indication? Are you measuring coolant temperature at the OEM location?
Your Buick power is ~250hp plus mods, but unless you are spinning it up you are not creating much power. I assume the FFR radiator is spec'd for power greater than you are making.
It is basic but unmentioned so far, your pump creates flow and sucks on the engine. Is your lower radiator hose collapse proof? Corrugated or coil spring?

As jwhit mentioned, the fan is not intended for highway, ram air on the core should be enough. The fan is for low/no forward speed. What kind of mesh/trim is ahead of the radiator core?
Does your water pump require a heater core, or in it's absence, a by-pass?

Exhaust obstruction?
jim

[David Hodgkins]

Too much oil in the pan?

:)

[GoDadGo]

Stupid Questions From Steve:

1. Is the fan wired correctly?
2. Is it possible that you've got the wires reversed?
3. Could you be pushing air forward and not notice this issue?

If this were the case, then at low speeds the air could flow forward through the radiator and cool the car, but at higher speeds, the airflow would basically stop.

Why would I ask these stupid questions?

I did it during my first start so I figured I'd throw the suggestion out there just in case you did the same thing.

[cob427sc]

Fan is wired correctly and draws air through the radiator.
The coolant temperature is measured where the takeoff point for the heater would be located on the water pump.
I do have an overflow tank and it will blow out the overflow just before it really starts to boil.
Stock FFR radiator cap and housing. located at the highest point.
Bottom hose is SS corrugated.
One thing I read last night was the possibilty of old loose deposits in the block that did not come out during the rebuild process. The machine shop baked the block to remove residues but other builders have found stuff floating out once the engine is filled with antifreeze. They actually suggested installing a temporary filter between the engine and the radiator to catch these deposits before they plugged the radiator. I did not do this and could be a contributing factor.

[GoDadGo]

Darn; I was really hoping you had made the same mistake that I did.
I was hoping you'd have a super easy fix for your issue.
Good luck and please keep us posted.

[33fromSD]

Is it actually over heating (boiling / steaming) or is the temp sensor or gauge possibly giving a false reading?

[J R Jones]

cob, I misspoke, your water pump sucks on the radiator through the lower radiator hose, thus the potential for collapsing the hose.
Googling photos of similar engines suggests to me that the pump also sucks on the heater core, and it looks like heater flow returns to the thermostat housing.
By blocking the heater port with the temperature sender you are restricting flow which can cause low pressure and pump cavitation.
Moreover you are measuring the temperature of return flow from the radiator, not engine temperature.
For what it is worth, the water pump circulates coolant into the block, up into the heads, and back through the thermostat to the upper radiator hose for cooling.
That does not mean that you are not overheating or that this will fix it, but the basics need to be right.

[J R Jones]

cob, A clogged radiator is possible, do you see flow with the radiator cap off? A flow evaluation is easy, disconnect the lower radiator hose and run water into the top of the radiator. Obviously water should flow through unrestricted. If flow is restricted a good flush is required, the passages are small.

[j33ptj]

Curious to know if the overheating occurs if the car is stationary with engine running at 2000rpm? Does it start overheating than too??

[mike223]

By blocking the heater port with the temperature sender you are restricting flow which can cause low pressure and pump cavitation.
Moreover you are measuring the temperature of return flow from the radiator, not engine temperature.
For what it is worth, the water pump circulates coolant into the block, up into the heads, and back through the thermostat to the upper radiator hose for cooling.



Just offering some known 393W (SBF) data - I think it should be similar for a 1958 Nailhead Buick since they appear to plumb similarly.

I pulled the heater return nipple from my (SBF) water pump and added a temp sensor there in an attempt to monitor radiator return temp (no heater - no heater flow).

It has caused no problems with water flow.


When running a thermostat, this will not measure radiator return water temp.

It heats up at the water pump first, several minutes before water temp comes up in the intake at the water outlet (I was surprised to discover this).

After that, both temps run about the same - water temp in the water pump *maybe* averages 10 degrees (F) lower than water temp at the water outlet (thermostat).


I suspect you would probably get a more accurate return temp reading if you weren't running a thermostat - but that probably comes with it's own set of problems (typically cold weather problems) - I haven't tried it.



Just offering what I have observed having two water temp sensors (one in the water pump).

I wired them up through a microswitch mounted next to the water temp gauge so I can swap between the two instantly.

[NAZ]

In my experience it takes quite a bit of large debris particles to do any significant impact to a modern radiator as they usually have much larger tubes than the ones we had back in the nifty fifties. A consideration? Yes, but I believe there is other low hanging fruit to look at.

I haven't calculated the BTU exchange on the 32 style radiator but the 33 style has more than enough exchange capacity to handle a moderately powered engine (moderate power to me is 500-600 HP). The 32 style radiator is likely sufficient for a garden variety medium sized Nailhead. The Nailhead came with a 3-vane impeller as standard and a 5-vane for the A/C cars as they needed more flow to keep from overheating. As I stated above, coolant flow is extremely important for cooling and more often than not, OEM coolant flow is no where close to ideal. More is better! And as you might imagine, air flow across the the radiator is also of paramount importance. You just can't get too much airflow across a radiator (at least not below Mach-1).

I would also like to see a temp gauge mounted on the return from the engine, typically mounted on or near the t-stat housing. But when diagnosing a heating issue I use an IR gun on several spots around the engine and measure the delta between the coolant return and supply to aid in troubleshooting an issue. I only rely on a temp gauge for a relative indication of "normal", above normal, and TOO DAMN HOT.

I also run at least a 20lb cap, especially on a down-flow radiator. If an engine runs so hot it is boiling over (venting steam past the cap) that's way too hot no matter the temp as steam has very poor heat transfer properties.

[J R Jones]

NAZ I'm with you, I prefer the sending unit be in engine outflow, in the flow path. Not knowing how cob's sending unit is plumbed, could it be in the heater nipple tube? That would make it somewhat remote in an appendage. That may not represent operating conditions or inlet flow.
As you say, current technology is bigger tubes in radiators.
I did see the three blade Buick impeller in a photo, hard to believe that works. Could be the issue here.
I did troubleshoot a cooling issue on a 1928 Studebaker and found one brass blade missing from the pump. Yeah, you have to fix stuff that old.

[cob427sc]

Let me fill in some details, then I can share what I found so far. The water pump is a 5 blade impeller, usually on an a/c car. The water flow in a nailhead is from the lower radiator hose, through the block to the back, then up through the heads to the front mounted water pump, then the t-stat and on into the top of the radiator. The water pump came with a plug in the heater outlet as some cars back then did not have heat as a standard. I installed the fan switch here. The tem sending unit is mounted in the PS cylinder head just before the water exits to the water pump. Bottom and top hoses are SS corugated so no collapsing.

I removed the top hose and looked into the radiator and saw all kinds of black residue. Removed the radiator and back flushed out all kinds of black particles and black water. Back flushed the engine (actually both ways) with over 50 gallons of water before water ran clear and without sediment, Water pressure of 60 psi. Appears clean as I'm going to get it.
While apart I'm going to see if I can get a radiator shop to back flush and test the radiator properly before reinstall. Then relocate trans cooler.

The engine as it was after a short highway burst would pin the temp gauge and boil over. If i stopped and shut down the engine the fan kepps running and in about 15-20 minutes cools down to where you can start to drive again.

Thanks for all the input for everyone. I've run some quick calc's on the radiator size and seems like if everything is correct it should be of sufficient size for this engine.

[NAZ]

I'm keeping my fingers crossed that fouling is the issue and you'll be up and running in no time. Not sure there's any good chemical flush anymore but if you can find some, I bet the block & heads need a bath as well.

Good luck my friend.

[J R Jones]

cob, I was wondering where your fan switch is, I thought the temp gauge sensor was in the water pump heater port. That location is not good for the fan switch either as it is sensing (relatively) cool water.
See this Hot Rod article: https://www.hotrod.com/articles/tech-qa-correct-fan-switch-location/
jim

[mburger]

I had a plow truck that ran fine in stop and go traffic. As soon as I got on the highway, I watched the water temp climb and would have always overheated had I not pulled over or took a detour onto a slow route. My issue was that at highway speed the plow caused a vacuum in front of the radiator. I had to keep the plow angle and at a specific height and I was fine. I was surprised because the plow seems pretty far from the radiator on the truck. So I am just wondering because it runs OK at lower speeds and gets hot at highway speed‘s is there anything different you’ve done at the front of your car that might cause an air disturbance. I’m gonna go out on a limb and say you’re not running a plow. ;)

[NAZ]

I’m gonna go out on a limb and say you’re not running a plow.

Mark, that almost made me spill my beer...

I'm guessing that plow truck didn't have Florida plates.

[wrp]

I had a lot of trouble with heat with my first two motors. So much so I went to louvered side panels to get relief and I ran without side cover panels in the hotter months. When I went to my current engine, I added a computer timing controlled Holley Sniper. I had briefly run a vacuum advanced MSD ignition. The vacuum advanced had helped over the initial mechanical advance in the car. The computer controlled timing solved all my issues with heating up. I have conclude that a preponderance of my overheating issues were due to poorly setup timing. Initially I had the mechanical advanced system. Great system for redline shifting and high performance driving. Terrible for idle speed around town driving. Further when I did get out on the highway my Holley car was feeding fuel as if the car were accelerating. Long story short the timing was never right for anything though would have been perfect for street/drag racing. With the computer controlled timing I have had to put a higher temp thermostat in to get the car to run at or above 180 degrees. I also use Wetter Water which I have found is good for about 15 degrees. One interesting exercise was double checking the actual temperature at the sensor input with a digital thermometer and comparing that to what was on the gauge. I did add a 3000 cam fan when I put the last motor in. That probably had a big impact as well.

Just a few more thoughts.

[mburger]

I’m gonna go out on a limb and say you’re not running a plow.

Mark, that almost made me spill my beer...

I'm guessing that plow truck didn't have Florida plates.

Ha! Yeah, that was when I was living in the upper Hudson Valley NY. Lived there 52 years.

[J R Jones]

wrp your comment on timing is very significant. That should be evaluated. The old Buick should have a vacuum advance at least, and it better work, could have a leaky diaphragm.

I have a street rod running a Lexus 2JZ that came from an IS300 donor. The Lexus ran the fan switch in the radiator tank, and so did I when I built the new radiator. That makes sense to me. Hot Rod suggested that in a 2020 article that is an update to the previous article I posted:
https://www.hotrod.com/articles/stop-hot-day-overheating-on-500hp-ls-engine/
jim

[wrp]

Thanks Jim, the variables affecting this are not that overwhelmingly common. I wrestled with it and cursed FFR for several years. My solution was an accident. Over 50 years ago we’d plug the vacuum advance at the track, advance the timing and run all night. We set everything back before we started the drive home. I’ve been running computer controlled engines so long I had forgotten. My SBC had a Holley Carburator which I cursed continuously. Went to an old timer and he told me the problem wasn’t the carburetor, it was the timing. The Holley had an idle circuit and a cruise circuit as well as a wide open circuit. It the timing was not adjusting to the different transitions, the the motor would run lean or rich. The lean was creating the heat. Not sure I am knowledgeable enough to explain it, but you have to decide how you are going to drive em when you set em up.

[i.e.427]

Two things. Running a cooler temp thermostat doesn't necessarily mean the engine runs cooler, it just means the thermostat opens earlier. And in some cases, may increase flow depending on the manufacturer. More flow isn't always a good thing. You need to keep the coolant in the radiator long enough so the the heat transfer occurs. If you're flowing more fluid through the rad than it can cool efficiently the engine will run hot. Same thing that happens when you run no thermostat. I'd go back and install the proper temp thermostat. A 1958 364 calls for the stock temp thermostat as a 180*.

Next (and it happens all the time so I'm not pointing any fingers), are you sure the thermostat is installed properly? If installed backwards, it will cause the engine to run hot.

[NAZ]

Two things. Running a cooler temp thermostat doesn't necessarily mean the engine runs cooler, it just means the thermostat opens earlier. And in some cases, may increase flow depending on the manufacturer. More flow isn't always a good thing. You need to keep the coolant in the radiator long enough so the the heat transfer occurs. If you're flowing more fluid through the rad than it can cool efficiently the engine will run hot. Same thing that happens when you run no thermostat. I'd go back and install the proper temp thermostat. A 1958 364 calls for the stock temp thermostat as a 180*.

Next (and it happens all the time so I'm not pointing any fingers), are you sure the thermostat is installed properly? If installed backwards, it will cause the engine to run hot.

I've been hearing that "slow the coolant flow" myth since the fifties and as with all good myths, there is some truth to it. Yes, contact time in the heat exchanger will reduce the temp just as contact time with the heat source will increase the coolant temp but that does not improve steady state cooling in a closed loop system. It's the wrong way to look at it.


Improve cooling system performance by increase coolant flow rate to 6-8 feet a second through the radiator. Anything you do to reduce flow rate below 6-8 FPS will reduce cooling performance.


You might find this explanation interesting: https://www.enginebasics.com/Engine%20Basics%20Root%20Folder/Engine%20Cooling.html

[J R Jones]

Who needs Google when we have NAZ doing the research? You caused more work than my Saturday AM, coffee fueled brain usually gets. That was a paradigm busting article.
"Even a blind pig occasionally finds an ear of corn". Maybe I found 6-8FPS with a 5/8 inch diameter washer.
Back in the seventies we raced 289, 302, Boss 302 and Boss 351 engines in SCCA Nationals and Trans Am. 375 to 450HP That duty cycle was 2cd - 4th gear at 4000 to 7000RPM WOT for 45 to 60 minutes, typical 18 gear/accelerations per 2.5 minute lap. Top speeds to 164MPH. Large radiators and oil coolers were SOP. Simplification was a mantra. If I ran a flex fan, the blades flew off, no fan. We needed no thermostat but we put a 5/8 diameter baffle plate in place of the thermostat to "slow down the coolant at high RPM". The gauges indicated we were OK. It would be interesting to see how our (undocumented) numbers compare.

wrp, Simplification was a mantra. We ran Ford dual point distributors with mechanical advance only. We timed for no more than 36-37 degrees from 3500RPM-up, the rest took care of itself. I think we started the engine with about 10 degrees.
jim

[NAZ]

Yup, conventional wisdom said if you pull the t-stat you had to install a washer to restrict the flow. For several years I followed that advice I got from folks I respected. We all have ideas of what we believe to be true and can go for years not having them challenged.

My street legal race car (400 SBC) has no choke and no t-stat, a high-rise air-gap manifold with a 1050 CFM double-pumper setting on it. Starts right up and runs great. But conventional wisdom says that shouldn't happen. Sometimes we just need to challenge conventional wisdom just to make sure it holds true.

[J R Jones]

Naz, I have done development in and for OEMs and that is where the kind of data you linked comes from. It is likely that even in the sixties/seventies, the 6-8 FPS was a velocity target. How much slower could it be?
Our theory was whatever their target, with a thermostat, we had to respect the (open) restriction and acknowledge that we were running at 2.5 normal operating RPM. I do not know what our coolant flow velocity was, but it was not slow and it met our needs. OTOH I had a Ford 460 that had water pump impeller cavitation so bad that it eroded a hole in the back plate. They did not know everything.

[Desert Cobra]

Now this is just a guess, but some of the other responses are guesses as well. Water pump rotational direction? Ford does make both clockwise and counter-clockwise pumps for small blocks.Not sure what Buick does.

[cob427sc]

Great info from everyone, although I must admit almost overwhelming. I have pulled everything apart, back flushed the block, cleaned as best as I can the radiator which is going to a radiator shop this week to be inspected and flow tested. Removed the snow plow - just kidding - and have ordered a bunch of new silicone elbows and aluminum tube to simplify the plumbing. I did realize that I had the fan switch in the water pump and the temp switch in the cylinder head. I have reversed these as the flow for the Buick brings the water back from the radiator to the water pump. This way the temp gauge should give me the temperature as it exits the radiator in its "cooled" state. The water pump is made to rotate in a counterclockwise direction and is installed properly. I spoke with a known Buick expert who filled me in on a couple of items. First this engine normally ran in the 170-190 range and had very few problems with overheating although they also had large copper radiators. He had me check the distance from the back of the WP impeller to the face of the timing cover which should be about 1/16" which it is. He suggested the washer trick if nothing else works, the assumption being that the radiator being smaller than a stock Buick and also being aluminum, that the pump is pushing the water through too fast to cool. He also brought up another issue he has seen in that I used FelPro head gaskets which are made of multiple layers instaed of the single steel sheet gasket that was original. He mentioned that these gaskets cause potentially 2 problems: that they will weep oil through the gasket near the rear of the head (and I do have that problem) and also twice he has seen the gaskets with improper alignment of the water jacket holes in the gasket and the block/head. If nothing else works I will pull the heads and research the gasket issue.

[cob427sc]

After reading the article Naz suggested above, and from my engineering background returning through the fog, it makes sense not to restrict the flow of water through the radiator by any means. It does raise another question which I will explore. The engine doesn't overheat in slow drives around town. The fan comes on and off as needed and temperature stays around 200 or less. Only on the highway at speed does cooling become a problem. I have the electric fan mounted directly against the radiator. I'm wondering if the fan and its mounting cage are restricting air flow at speed? I may try moving the fan away from the radiator even if I need to fabricate a shroud for low speed cooling. Learning alot here.

[JimLev]

A shroud would help as that would allow the fan to pull air thru the whole radiator core, not just the area the fan covers.
I have my fan running at about 1/3 speed (adjustable PWM controller) all the time. When the engine wants more cooling the fan relay energizes and the fan goes to 100%. My logic is a fan that is always running is removing some heat from under the hood and it’s easier to keep an engine cool than it is to cool a hot one down.

[mike223]

Interesting - stumbled across Old Yeller II in Jay Leno's Garage.

Nailhead Buick - mentioned that Max had put the biggest radiator he could find in it because the Nailheads were notorious for running hot.

Fascinating stories of Carroll Shelby, Dan Gurney, Viva Las Vegas, etc.

Possibly "Carroll Shelby's inspiration for the Cobra".

Enjoy:

https://www.youtube.com/watch?v=zBs6O_D1D3k

[mburger]

I’m sticking with the plow theory. The entire system works as designed and expected until the car is moving at speed. For some reason, air flow through the radiator is being restricted at highway speeds whether by vacuum or other means.

[Brastic]

We had a car do this once. It would be fine at start up and below 25 MPH. Anything above that and it would over heat. After months, we found out that the plastic impeller water pump was the issue. We installed a metal impeller water pump and the issue went away. The next month a friend came over with the same issue. We did the same cure. That was in the 90s, so maybe the plastic they use now days is better. I will never know.

[cob427sc]

Thought I'd just follow up now that the overheating problem is solved (I believe). As I mentioned I back flushed the block as best as possible along with the radiator and had all kinds of black debris come out. I had the radiator back flushed and flow checked by a radiator shop and checked out fine. I built an aluminum fan shroud and reinstalled everything. Currently with a 160 t-stat, the temp gauge reads 190 when it opens and the fan comes on at 200. On the highway where I had my problems, the gauge rises to 210 and never goes higher tested today in almost 90 degree weather. The overflow never received any water, not even a burp. All in all it seems to have cured the issue although I suspect that the temp gauge ( FFR cluster ) is not accurate and I may do some more research. Now all I have to do is stop the slow leak on the rear main seal that I've been told is normal for these engines. They even put a drip hole in the bell housing cover to allow the oil out! Thanks everyone for the help and insight.

[NAZ]

Just thought I'd mention that t-stats start to open at the rated temp and may not be fully open until they reach 15-20 above the rated temp. https://www.stant.com/index.php/english/products/consumer-products/thermostats/abcs-thermostats/

[Fixit]

A buddy of mine is running practically the same setup in his steel '31. Next time I see him I'll take a closer look at his setup - he lives in the boonies and has to drive highway to get anywhere... never has an overheat problem.
149167

[FFinisher]

Sounds like you may have it, But you also want to check the cap. FFR supplies a 20LB cap, Do you have a significantly lower cap pressure? lower cap pressure = lower release pressure.

[cob427sc]

My cap, which came form FFR says 14# release. Might try a 20# see what happens. Thanks.

[NAZ]

Ditch the 14lb and install a 20lb. It will not keep the coolant cooler but will add a margin of safety against boil-over.

[JimLev]

A lower pressure cap will allow it to boil over sooner at a lower temp.
Mine came with a 16 Lb cap.

[wrp]

wrp, Simplification was a mantra. We ran Ford dual point distributors with mechanical advance only. We timed for no more than 36-37 degrees from 3500RPM-up, the rest took care of itself. I think we started the engine with about 10 degrees.
jim[/B]

Thanks, I guess this is where I was going, I will admit I spend a lot of time at 3500+ RPM, probably a good deal more than I need to on the street. If I drive like an average person is supposed to, I rarely get over 2000 RPM. That is especially true when I am cruising on a four lane highway. My SBC likes 12-14 degrees on starting. With the mechanical advance MSD setup I only had about 18 degrees of advance to play with. With the vacuum advance, I could back the timing down with a wider range of advance available but I still had issues because of the cam size and resulting weak vacuum. Without the computer controlled timing I had to set it around 18-20 degrees to get it to advance to 34 degrees at WOT. So when going through the gears from light to light I am likely to get over 3,000 rpm, cough cough, depending on the model 5.0 Mustang beside me. My Holley carburetor is trying to use the already weak vacuum to decide whether to be in the idle circuit, transition circuit, or the cruise circuit. With only the mechanical advance, the low speed performance resulted in a wide range of over fueling and under fueling (rich/lean). 2000 RPM seemed to keep me in the lean side of operations, read from my plugs. Some people are good enough to tune the carb and time the motor to meet specific driving conditions. I am not. Hence I noticed the operating temperature drop when going to the computer controlled timing EFI system. One thing I forgot to mention about is that I took the whole radiator down and had it pressure tested with the cap on and found I had a weak spring in the cap that came with the original kit. Changing that seemed to help too.

[NAZ]

Most folks know that we set the timing advance BTC because it takes time to burn the mixture and the AFR (lean or rich) will affect how far advanced we need to go. But not everyone knows what we're trying to achieve by starting the fuel burning before top dead center. So here's a couple of articles that help to explain what the goal is and how too much advance too soon can be a bad thing. If you search you'll find more out there but these two will get you started.

https://www.hotrod.com/articles/set-ignition-curves-create-optimal-performance/
https://innovatemotorsports.com/resources/myths.php

[J R Jones]

NAZ, I was at Mercury Marine when emission laws were applied to the marine industry. Merc was experimenting with four-stroke and clean two-stroke they called Optimax. It was licensed from Orbital in Australia. High pressure fuel and high pressure air. Anyway, to evaluate the combustion event we made clear acrylic plastic head/combustion chamber and took high speed film. We revved the engine to speed with a motor, introduced fuel, lights, camera, ignition. It was similar to a slow-mo movie explosion.

[NAZ]

NAZ, I was at Mercury Marine when emission laws were applied to the marine industry. Merc was experimenting with four-stroke and clean two-stroke they called Optimax. It was licensed from Orbital in Australia. High pressure fuel and high pressure air. Anyway, to evaluate the combustion event we made clear acrylic plastic head/combustion chamber and took high speed film. We revved the engine to speed with a motor, introduced fuel, lights, camera, ignition. It was similar to a slow-mo movie explosion.

That had to be interesting. You had the kind of jobs I should have had.

I've seen ones like these before: https://www.youtube.com/watch?v=jdW1t8r8qYc

[J R Jones]

NAZ,
Jezus, I managed a similar Briggs 12 engine development too. Took it from 5.5 to 7.5hp. It was an old cart/snowblower engine they made 3.3 million/yr.
GD spark plug and exhaust valve were so close I couldn't keep one of the head bolts tight. I put a heat sink under the bolt head and cooled her down. Too Expensive.
I had to go external with the oil drain-down with the enlarged bore. Not my favorite job.