512 mopar getting hot quick.

[rebelrouser]

I was reading the thread on the 454 chevy with interest. 1977 Dodge truck 4x4 factory 400 big block automatic. Guy just wanted it to be more fun. Stroked the 400 to 512, flat to pistons 10-1 compression, hydraulic roller .520 lift 220 duration @ .050 , 110 centerline. FiTech fuel injection. just ported the 452 heads and put some stainless valves in them. 440 source stroker kit. .045 quench on the flat top pistons, can hear no spark knock, has 165 lbs cranking compression.
Engine ran good on the dyno 508HP @ 5,400 rpm and 541 ft. lbs 4,200 rpm.

Engine really runs smooth on the highway. O2 sensor says it is running right on the air fuel ratio. Issue is it gets to 240 degrees in just a few miles. Would get hotter no doubt, but I shut it down. I installed a new 4 core aluminum radiator, new thermostatic 7 blade clutch fan, twin electric cooling fans, and a FlowKooler high flow water pump. Ran with several thermostats, even completely removed the thermostat. FiTech temp and dash temp readings agree so it is getting warm, plus when it gets to 240 degrees will not start, kicks on the starter. I took some timing out of it and no difference. New starter and cranking 1000amp battery.
So I am down to pulling the engine and looking for something I screwed up or missed. I don't recall any issues with mopar head gaskets that I could have messed up with. No water in the oil, leak test is good on all cylinders. Advice on what to look for?

[Tuner]

What is the A/F when it is "right on the air fuel ratio" ??

Single plane or dual plane intake?

How is the ignition advance configured? Is the FiTech managing the timing or is it a mechanical distributor? What is the WOT advance curve and is there a vacuum advance timing increase in light load?

[BillK]

Did it overheat on the dyno ? It almost sounds more like an airflow problem to me. I would start by taking the electric fans off and then make sure the clutch fan is correctly positioned in the shroud. Use an ir temp gun and see what the temperature is at the inlet and the outlet of the radiator when running.

Just running down the highway shouldn't be using any more hp than the 400. Did it run cool prior to the swap ?

Personally doubt that it has much to do with timing.

Just thinking out loud

[Tuner]

Did it overheat on the dyno ? It almost sounds more like an airflow problem to me. I would start by taking the electric fans off and then make sure the clutch fan is correctly positioned in the shroud. Use an ir temp gun and see what the temperature is at the inlet and the outlet of the radiator when running.

Just running down the highway shouldn't be using any more hp than the 400. Did it run cool prior to the swap ?

Personally doubt that it has much to do with timing.

Just thinking out loud

Do you really think engine temperature doesn't have "much to do with timing"?

[PRH]

Doesn’t look like the best scenario for air flow past those electric fans.

[BillK]

Do you really think engine temperature doesn't have "much to do with timing"?

Yup. The engine will detonate itself to death before the timing is high enough to cause severe overheating. If his timing was the issue it would have overheated on the dyno.

Timing absolutely affects combustion chamber temperatures and exhaust gas temperature which might affect cooling system temperature some but not to the extent he is seeing.

Thats just been my experience,

[Tuner]

Do you really think engine temperature doesn't have "much to do with timing"?

Yup. The engine will detonate itself to death before the timing is high enough to cause severe overheating. If his timing was the issue it would have overheated on the dyno.

Timing absolutely affects combustion chamber temperatures and exhaust gas temperature which might affect cooling system temperature some but not to the extent he is seeing.

Thats just been my experience,

Did you miss this in the OP?

Engine really runs smooth on the highway. O2 sensor says it is running right on the air fuel ratio. Issue is it gets to 240 degrees in just a few miles.

The overheating is in highway driving so the possibility is much more likely not enough advance than too much.

The 452 head is an advance hungry smog open chamber head with the quench pad recessed about .100" above the gasket deck. If it actually has .045" squish clearance it has special pistons like the KB units that have the quench pad .095" above the deck which require the heads to be machined to qualify the depth of the quench area in the head. Getting the deck clearance right in the Mopars is a real bisch compared to "brand C".

If, on the other hand, the piston deck is .045" down and the head is .100" deep or so, the combination has about .145" quench clearance, which is nearly the absolute worst it can be and will likely result in extremely high exhaust temperature. Been there, done that, only way to fix it is change pistons and qualify the piston quench dome height and the quench depth in the heads, like the Mopar people are familiar with doing when they want it right.

Bottom line, if it is overheating in a level road cruising situation, the odds are greater it has too little timing than too much.

Plus, the OP hasn't replied with what the A/F actually is in the overheating condition. He says, "O2 sensor says it is running right on the air fuel ratio." If that is the 14.7/1 default table in the FiTech that is the worst possible A/F to cause overheating if it does not have vacuum advance to compensate for the slow lean burn.

That's just been my experience,

[Geoff2]

Make sure your coolant jackets in the engine are not full of debris & clogging the rad tubes. I had this happen on a 440.

[mag2555]

Part of your issue might be the heads and the pistons you are running .

The chamber shape on those heads collect a lot of fuel that burns too late to contribute much to the power stroke and when this takes place the bulk of that late burning fuel just contributes to engine temp.

In terms of the piston design, if the top ring land is more then .150” down then the fuel charge in that crevice once dumped out has the same effect as the poor chamber design, so both detract from power and only serve to make heat, or worse yet ping or detonation.

Getting this right contributes to 2% added power.


It may not sound like much, but 2% greater power on a 550 Hp motor is 27 Hp and likely just as much torque.

Also note that the dish shape used on many pistons cause the same inefficiency as I posted above about the chamber shape.

And to a much lesser degree valve notches can do the same thing, but it’s all additive.

[71vette]

On a few different engine types I’ve seen similar eng temp issues w/ aftermarket TBI units and dual plane intakes. Some I was able to fix leaving the dual plane, a few I had to install a single plane and of course retune. One 496 bbc I left the performer rpm airgap properly installed a carb, dialed in the carb, and it quit overheating in (tucson, az. no less). Maybe someone smarter than me can confirm this, but I think some orig 4bbl big block mopars came w/ stagger jetting in their factory carbs?

[rebelrouser]

So I did the following I installed a new 4 core aluminum radiator, high flow water pump and water pump housing, tried a 160 thermostat and then just took out the thermostat. twin 1,200cfm cooling fans, and a new clutch for the stock fan. I even took the engine out took it all apart and could not find anything wrong. I re-flushed the water jackets, and drilled extra cooling holes in the head gaskets. Honed a little more clearance in the cylinder walls, took some ignition and camshaft timing out of it. It did make it some better, but still in about 6 miles the temp slowly just keeps creeping up to 250 degrees. I have never in mylife had an engine ack like this.

With a heat gun it shows a 20 degree drop in temp across the radiator, is there a rule of thumb for how much temp a radiator should drop?

Any other ideas? And in one of the comments, it mentioned intake manifolds, it has a single plane 'Edelbrock intake. I have the timing down to 6 degrees at idle and 32 degrees total. It does have a vacuum advance and it does work replaced it and rebuilt the distributor. It does not spark knock that I can hear until it gets really warm and then just a little . Just looking at the FiTech controller the O2 says 14 to 14.5 air fuel ratio on cruise.

[PRH]

This isn’t likely to cure the problem, but may slow down how long it takes to heat up.
A lot of the aftermarket w/p housings have the bypass hole sized way bigger than necessary.
Any coolant that flows thru the bypass hole is coolant that’s not going thru the radiator.

I usually tap the hole for a pipe plug, and put a drilled plug in there as a restrictor.
I also drill a few holes in the stat, which allows it to effectively become the “bypass”, although now most all the coolant is forced thru the radiator.

The hole in the new “restrictor” is really only there to help with filling the system.

https://www.enginebasics.com/Engine%20B ... ant%20flow.

[71vette]

You have done an incredible amount of work on this. I salute your work ethic. Like mentioned earlier I have seen this w/ fi tech, sniper, and atomic tbi systems. On sbc’s, bbc’s, a stroker 409, a pontiac 400, and a 385 series bbf. One of the sbc was a nicely rebuilt 283 in a beautifully restored 63 impala that always ran below 200* w/ the orig 2bbl carb. Started to heat up to 240* in 10mins after the owner installed a 2bbl fitech on the orig intake. Then the owner went to an expensive bigger capacity rad, installed a high cfm pusher fan in front of the radiator, 90* blade nylon fan, a new hi flow water pump, no t-stat etc. It would then take about 30 mins but again it just kept getting hotter until he would shut it off at 240. I found a sizeable vac leak being masked by the iac and after fixing that, the car would run at 210* while cruising in summer temps of a 100+. The owner stopped driving the car during the summer if he thought he might get stuck in any traffic. The owner accepted this but after the 2nd time the fitech left the car stranded he allowed me to install an edel eps dual plane and a 600dp carb utilizing his fi fuel tank w/ a stock gm tbi pump and a return regulator. The car now creeps to 200* but only when stuck in traffic w/ the a/c on and during 100+ hot summer days. Once he gets moving again the car cools back down to 180-185 after a short while. He drives the car a whole lot more and doesnt fear getting stuck in traffic. I’m sorry I never got to investigate why exactly this car cooled off so much going back to carb. The same mech / vac distributor was used the entire time w/ the same curve, same timing settings, and the same timing light. I hope you get this fixed and let us know how you did it.

[Tuner]

Just looking at the FiTech controller the O2 says 14 to 14.5 air fuel ratio on cruise.

14.5 is the ideal A/F to make it overheat. Should be 16/1, or leaner if it will run leaner without misfiring, with 50 degrees of advance on a level road load.

6 degrees initial is causing high exhaust temperature. Initial should be 18 degrees or nearly so.

If you can program the advance, do this:

RPM advance
18 deg at 1000
30 deg at 2000
35 deg at 3500

Vacuum advance
0 deg at 6"
1 deg at 7"
10 deg at 10"
15 deg at 13"

Like the post above, the throttle body "self learning" EFI may not work out on this engine. I am accumulating a growing core pile (of all brands) that have been replaced with the EFI Delete Carb and Distributor Package.

[Tom68]

So I did the following I installed a new 4 core aluminum radiator, high flow water pump and water pump housing, tried a 160 thermostat and then just took out the thermostat. twin 1,200cfm cooling fans, and a new clutch for the stock fan. I even took the engine out took it all apart and could not find anything wrong. I re-flushed the water jackets, and drilled extra cooling holes in the head gaskets. Honed a little more clearance in the cylinder walls, took some ignition and camshaft timing out of it. It did make it some better, but still in about 6 miles the temp slowly just keeps creeping up to 250 degrees. I have never in mylife had an engine ack like this.

With a heat gun it shows a 20 degree drop in temp across the radiator, is there a rule of thumb for how much temp a radiator should drop?

Any other ideas? And in one of the comments, it mentioned intake manifolds, it has a single plane 'Edelbrock intake. I have the timing down to 6 degrees at idle and 32 degrees total. It does have a vacuum advance and it does work replaced it and rebuilt the distributor. It does not spark knock that I can hear until it gets really warm and then just a little . Just looking at the FiTech controller the O2 says 14 to 14.5 air fuel ratio on cruise.

240 and you shut it off in the first post, does it then heat soak and spew it's guts out ?

If not the 240 reading might be erroneous.

6 degrees at idle isn't anywhere near enough. is the vac adv manifold or ported ?

You want more than 40 degrees advance at cruise, you need to confirm what the cruise ign adv is.