My brother has a 1973 dodge Challenger with a fresh 340 putting out around 400hp. He has a 180* thermostat, aluminum radiator, and clutch fan.

Well the car wants to overheat really fast at an idling or or under 30mph.

We know the clutch fan is working.

Now the initial timing for some reason bounces from 8-10* with an total advance of 34* at 2500 rpms. Car is idling at 1100rpms since its where the engine idles best. The 340 has a Voodoo 512 lift cam.



We're using an Accel vacuum advance distributor although the vacuum ports are plugged. Reason being the car will not run with the vacuum advance hooked up. The rpms are all over the place ranging from 800-2500rpms with the vacuum advance hooked up. We do have a vacuum canister also.

The car idles ok as is and runs like a wild indian on the road.

I'm thinking the initial timing isn't enough ?

Thanks guys !

I assume the engine has headers. The initial hould be up in the 12-15 area total may need to stay had 34-38 degree's. What is cranking compression? Also what carb? You may have too much transfer slot open on the carb and hence the increase fuel threw tubes. Keep in mind try to get the balance right on carb and get the dist set up to run full cent advance

What adv springs? as the bouncing is from either too light of springs or the dist tang fitting too loose in the top of the inter gear/shaft/. Twist the rotor by hand back & forth being carefull not to get into the spring tension & see how much play there is. It's also classic sloppy tchain but assuming you replaced them w this being a rebuild. Sumpin ain't right as it shouldn't need to idle that high & yes I'd stabilize the initial & get the idle sp lowered. I'm doing alot of speculating here but holler back & we'll continue on.

What kind of temperature are you seeing?

.Shroud
.180 Napa super stat
.Laser temp gauge for accurate reading
.1100 seems high for idle

Engine has headers.

Cranking compression 10:1

Carb 750 Holley with vacuum secondaries

Thanks

Its just a factory Accel distributor with no modifications

What kind of temperature are you seeing ?
190* while cruising at 65mph
210 and climbing when idling or under 30mph

He has aftermarket autometer gauges in it.

Thanks

Give it 18 degrees of timing at idle and then turn the idle down to 800 and it will cool down. I'd give it some more jet also.

Your not even using the idle curcuit as it is.

How far is the fan away from the radiator?

From the back edge of the radiator to the front edge of the fan blade 2 inches

If the timing is not retarded at the offending speed I'll say not enough air flow thru the rad

Is it somewhat normal for the initial timing to bounce 2-4 degrees ?

Thanks guys !

Sorry I didn't explain it well.

When you have the timing light on the harmonic balancer you can see when idling at 1100rpms the timing bounces from 8*-10* and sometimes up to 8*-12*

Also the radiator is a Jegs 2 row 1" core aluminum radiator.

Thanks guys

Actually you exp it well & it was my chart/post not being specific about what I was saying (or trying to say ). Bouncing marks are from sloppy tchain or dist tang or dist weights bouncing from light springs or bad connection in the light (had one like that). I would get the idle sp lowered/timing in the ballpark & see that the rad has good airflow (no excessive obstructions either sheetmetal ductwork or condensor/aux cooler). EDIT assuming the shroud/fan location in the shroud are right & you said the fan is tight

I saw a couple of questions on a shroud - not sure if you have one. The shroud is really important to get enough air pulled through the radiator at a stop and slow speeds. Since it runs cool on a roll, the radiator is probably sufficient.

Agree more initial timing, reduced idle speed and correct mixture will help a lot. Some tuning opportunities with the carb and distributor.

Radiator:

26" Copper 3 or 4 row. Ma Mopar knew what she was doing.