Tuning in hot weather, and converter slip at cruise

[travis]

Yesterday was the first drive of any real distance in my '83 F-150, almost 250 miles in some absolutely brutal heat (104* when we left Texas). The combo is a .030" over 351w, 10:1 compression, Promaxx 9175 heads, Jones 218/222@.050 hydraulic roller, Weiand Stealth, 1407 Edelbrock, 1 5/8" JBA long tube headers, etc. The truck has a C-6 trans, 3.55 gears, and a fresh Hughes 2500 converter.

I had put the 750 Edelbrock on along with 2 new fuel filters (before and after the fuel pump) recently due to fuel tank rust issues that I didn't have time to resolve correctly before we moved out of state. I had tuned it when the outside temps was in the mid 70's and it ran really well...14 initial, 32 total mechanical plus 8* vacuum, although it was a bit fat at cruise (12.8-13.2 range) and I couldn't find my metering rods to lean it out a bit because everything was packed up. The tune it liked in cooler weather it clearly hated in the heat...it was running hot (nearly 220) and was super lazy. A/F's was still a little fat. By backing the timing up to 8 initial, 32 total mechanical (removed my advance limiters) with a slower curve plus 8* with vacuum advance it was able to maintain around 195-205 degrees coolant temps at 65-70mph which I felt was ok considering the ambient temperatures. It pulled 12.72 mpg average with lots of rolling hills and 3100-3200 rpm cruise speeds...it typically averaged 13.3 mpg with 100-150 less hp.

The torque converter is a refreshed Hughes 2500 stall "heavy duty" unit. I'm calculating 12% slippage at steady cruise which seems pretty excessive to me. It still flashes to 3200 easily even though Hughes supposedly fixed an issue with it. What should you see slippage wise with a mild street converter at steady speed?

[amc fan]

Well, not for your application exactly but food for thought. I saw a neat convertor deal on a John Cope racing trans video. He built a high horsepower 904 trans and used a pump and input shaft from a lock up 904 for an 800 hp Pro street/race car. Very high stall and you lock it up with a switch for no slip. I know GM has a lock up for the TH350 also. Maybe they have something like that for a Ford C6. I bought a lock up 904 out of Gremlin and I am going to do the swap for my 68 Pro street AMX.

[Walter R. Malik]

If cruising speed is anywhere below stall RPM the torque convertor will slip a lot, unless it has a lock-up feature.

AND, that also means it will create a lot of fluid heat while slipping which transfers to the radiator; unless you have a completely separate trans cooler.

Engine cooling probably needs the water pump turned faster or a different water pump which will be most efficient in the lower RPM range you want.

[F-BIRD'88]

If cruise efficientcy matter then a high stall converter may not be your best overall choice.
You are going to notice the slippy mussy driving impression more if its a heavy truck with higher wind drag and any type of knobby agressive tire tread.
Especially when going up hills.
There may be a factory oem Ford C6 converter that will create say a 2000-2200 max stall behind your 351w.
It will by nature have better coupleing efficientcy in the highway driving range for that truck.
Its always a trade off with any modified "high stall" converter.
I like the Eddy 750 carbs for what they are but if fuel mileage is a priority a different carb may work better.
A dialed in Qjet can work very well.
The eddy 750's are calibrated more for performance than being fuel sippy. Yup custom dialing in the primary metering rods can help. So can trying various carb spacers for effect. Controling the carb body and manifold plenum runnint temp +/- effects things too.
If you don't mind GM parts on your Ford truck the QJet carb has a lot to offer for fuel efficient cruising.

[F-BIRD'88]

Would you be willing to try ducting cooler denser ambient air to the carb with an enclosed air cleaner with ducting either to the front end (headlight area or just below the front bumper) or to the trucks cowl area?
Ducted outside air is better than underhood air especially on the hiway in summer.
The apparent different carb jetting setup for cool winter VS hot summer driving should be closer.
Then with cooler denser ducted inlet air some method of controlling added carb/plenum heat +/- as required can improve things. Better overall control of fuel vapourization at steady cruise.

A sealed forward facing hood scoop and carb box would be great.

[travis]

I normally run a Edelbrock 650 AVS2 carb that is well dialed in, but due to fuel tank rust it yet again needs gone through...I just didn't have time. It's definitely snappier than the OOTB 1407. I also have a big factory style 4bbl air cleaner and ducting that pulls from in between the core support and grill area...it just doesn't clear the HEI (yet). And... I'll be putting the stock or a lower stall aftermarket converter back in it. Just another thing I haven't had time to deal with.

But now we are completely moved, and I've got a big awesome shop to work in now as well. It's just going to take a while to get everything set up and organized again lol

[Roadknee]

I think the cruise slip with the converter is normal. My experience was similar with a Hughes 2000 stall in a 79 GMC C35. Big heavy trucks aren’t nearly as forgiving as hot rods at low speeds. Unless your goal is upper RPM HP I’d go back to the smaller carb. It should provide better response and fuel efficiency.