[slowmover]

The latest 1960s-early 1970s emissions controls were predicated on an intake manifold floor temp of 115F.

Though no real effort beyond minimal was incorporated, I chased the second half of the equation to get cool fuel. This was with a big block Chrysler where I changed the coolant thermostat from 185F (stock) to 195F.

I installed an electric fuel pump and vacuum-regulated fuel pressure regulator.

The spreadbore carburetor was mounted atop an insulated 4-hole spacer. Etc.

The genuine advantage of EFI is only in two areas; initial warm-up and altitude calibration. The other problems remain.

You may not have “failed” so much as chosen to stop prior to success.

I drew hot air per the OEM exhaust manifold shield (re-designed). Your hot air source may simply be TOO hot.

My hot air intake was controlled by a thermostat. It mixed hot & cold air after warmup. Under full throttle, the low vacuum closed off the hot air portion.

FE was about the transitions the carburetor saw. As they work off of pressure differentials, all sorts of temptations about internal air cleaner airflow presented themselves.

One must resist temptation to remain pure (ha!)

Under cruise conditions where terrain varies (not even hills) the need for warm air decreases as a function of distance. During de-cel, it rises. So, THE TRANSITIONS in terms of engine vacuum were what I used as a gauge against rpm (engine load). Messing with the APT (adjustable part throttle) mixture was how I found smoothness (for a given load & road).

The “hot air” was more of a backdrop. Not the constant once moving. Come to a stoplight, or maybe extended idling, it was predominant.

I could see where NO LOAD and high heat would be counterproductive while moving down the road. And could be overwhelming while idling. Total engine vacuum was how these emission-devices worked to regulate engine intake air temperatures.

It was the introduction of EGR that made those cars balky. The air temp regulation plus hotter coolant really was an improvement (generally speaking).

The exhaust manifold shield drew cold air over a very long cast iron surface. After expansion the only time those manifolds were radiating TOO MUCH heat was in an extended mountain ascent with trailer in tow. Flipping the air cleaner lid @solved@ that problem.

So my thought is that your intake may be restricted to too much hot air at all times versus engine draw. A heat exchanger is practically PUMPING hot air.

And how to measure effectiveness is still against a constant: use of cruise control, and a speed setting which allows one to avoid lane-change while en-route. The WAI is always going to show better results in city driving. It’s no real trick to get good MPG highway. Steady-State.

Load your car to GVWR by using a CAT SCALE and then re-test after fighting how to get closest to 105-115F intake temp.

Testing an otherwise empty car is a conceit around here. Means nothing, as Interstates ARE DESIGNED to reduce engine load. Until you EMPHASIZE transitions (vacuum) against the terrain, winds, etc, highway mpg improvements are going to be slight.

As before, cruise control-only. A constant constant
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