Bigger is not better with carbs. Too much carb, as DanLee has pointed out, can cause driveability issues. Without forced induction, you cannot exceed ~115% volumetric efficiency on an engine. The CFM rating of a carb = airflow. If the A/F ratio is too lean, that is not an airflow issue - it is a fuel (jetting) issue - as long as the CFM is adequate for the displacement of the engine. My calculation is from 602-779 CFM at 6,000 RPM. 779 is all-out race with 115% VE, which I do not have. I don't have headers. My "detailed" calculations come in at 635 CFM...thus my decision to sell my 600 CFM carb and go to a 650. I have an Innovate Motorsports Wideband I'll install and check my AF ratios...or I'll get a dyno pull done and report back.

 

Engine is running pretty darn good.

IN the hot ATL weather, temp will hit 220 when running the A/C full blast. I do have dual electric fans on the stock radiator.

Also, after I turn the key off, it will sputter for a second or so.

Two questions:

1) Has anyone installed an aftermarket (aluminum) radiator, and did it help with peak coolant temps?

2) Does anyone think cooler spark plugs will help with the after shut down sputtering? Obviously there is an ignition source inside the hot cylinder (besides spark at the plugs) that is allowing the after shut down sputter. On a side-note, the current tank is 89 Octane (vs. the 93 I usually run) I wanted to see how well it tolerates the lower octane. It sputter more on the lower octane vs. the 93 (which is normal - higher octane is more resistant to combustion).

Lastly, occasionally the car will die at idle (with A/C on, especially)- especially when the battery has not been on the trickle charger. I am thinking it might be an ignition issue (I am running an MSD pro billet dizzy). I wonder if the MSD #6425 (Digital 6AL ignition)box has a voltage regulator that makes for a very strong spark even when vehicle voltage is low (like a Jacob's regulator type box). I'll call MSD this week and ask about advantages of their ignition. I can of course avoid the dying by raising the idle RPM, but I think it is more of a spark / voltage issue than anything else.

What plugs are you guys normally running when you choose one-step cooler?

I've got 302C Aussie Heads.

 

I use Autolite AP24 or AP 25s, which ever is colder. I use an 8 coil ignition in a wasted spark mode, instead of a conventional coil/distributor. I have a 4 row copper radiator with a 16" electric fan. I also have a conventional fan on the waterpump pulley. I drive the truck in parades. The engine temperature will climb until the electric fan turns on.
I always use 93 Octane. I won't even use the 92 available at some stations.

If it dies at idle, it might be too lean. Instead of raising the idle speed, try to increase the idle mixture a little.

 

What kind of shape is the stock radiator in? Is it a 2-row or 3? What thermostat? Do you have an AC idle solenoid on the carb? Colder plugs won't help with dieseling after shut-down, that's usually to high of an idle, too rich at idle or a lot of carbon build-up on the pistons.

If you're hitting 220* at idle with the A/C on but fine when moving 30mph+ you probably don't have enough fan. If it's a problem even on the highway then it's not enough radiator or a plugged radiator.

 

Well... it may not be pertinent to your application, but i have had a couple of issues with later model cars (of same maker) with multiple coils (approx 50K volts) that did all sorts of horrible things when the battery went flat.
Would stall when put into drive, which was a royal PITA as it took ages to recharge and about 6 attempts to get it going and a big 3k wheelie drop to get it on the road.

 

A couple of suggestions. The MSD boxes don't work if the voltage across it goes below 9 Volts. A bad ground on one of those boxes can knock a volt or two off the total. What ignition are you running with now?

Having converted to EFI, I have an Innovate Wideband setup. If I ever get another carb'ed vehicle, I'd get a wideband for that as well.

 

. Ever figure out the ignition/stalling problem? Do you have direct power to the electronic ignition or is it going through some older style of ignition resistor? Do you have a drain on the battery while sitting for days, such as a radio memory? A sensitive VOM/amp meter from one battery post to the car's battery cable can spot such a drain.

 

MSD says I need a diode. I bought one at Radio Shack, but I have yet to install it. I'll report back when it is done.

 

Man I'm slow.

I finally put the diode in...and the run-on after shut-down problem is solved.

I used a Radio Shack 1N4002 diode from a 1 amp assortment pack. It is a 100V 1A diode. I placed it in-line in the first wire (terminal 1) coming off the voltage regulator box with the diode stripe closest to the voltage regulator, although my terminals are actually labelled differently instead of 1,2,3,4.

Info in case anyone else experiences this:

http://www.msdignition.com/page.aspx?id=3296

I'll have to wait until summer to find out if my idling in traffic with A/C on temp climbing issue remains.

I think I am just going to invest in a big thick modern aluminum radiator.

Stalling is never an issue if I keep the car trickle charged and keep the idle up a bit higher than normal.

The idle is indeed lopey..the Pantera grind cam from T Meyer is great, but it is lopey. I might have had the idle too low for such a cam.

I do NOT have an idle boost solenoid on the carb for when A/C is on. I still have the old one somewhere from the OEM carb, I could maybe find a way to add it...but if Edelbrock makes one that is plug-and-play on my Thunder AVS carb that would be even easier.

 

Forgot to answer this...My ignition is in the MSD distributor itself. It is a #8350 Pro-Billet Ready-To-Run distributor with an MSD blaster coil.

 

I use an electric fan as a pusher fan. I don't have enough room for a normal puller fan. I still have the belt driven fan. The electric fan is thermost controlled.

I don't have A/C, but drive the truck in parades. It will stay cool in all but the hottest weather.

My idle is a little higher than normal, but EFI corrects for all those little problems that carbs don't handle.

 

Well, I called the run-on after key turned off solved too soon. Despite the diode, it is still running-on after shut-down.

Any other ideas? Ugh.

 

Idle is too high.

 

Too advanced initial timing plus a week vacuum on the dizzy? try running it without the vacuum advance hooked????

 

. Shut off engine while still in gear... add an ounce or two of kerosene to a tank of gas to bump up octane...