Impco 425 on Ford FE 428 engine

[gerrit11]

hi,
i recently swapped my 390 for a 428 engine in my 66 Galaxie.
i run a Impco Model E evaporator and 425 mixer on a 4 Barrel holley throttle plate on an Edelbrock intake
i got the impression when accelerating, that there is a difference in acceleration with 3/4 throttle and throttle all open.
i think i feel better acceleration with 3/4 throttle.
is it possible that either mixer or evaporator is not capable for this engine at w.o.t.?
i run shortest possible dry gas hose
cold air intake with no air cleaner
40 degrees total advance ignition at 2500 rpm
any advice please.
thanks!

[C3H8]

The main question is have you adjusted your power valve? It is possible to feel better acceleration at 3/4 if your power valve is not adjusted correctly. The power valve should only be adjusted for best WOT operation. Some users try to use it to maximize fuel economy by turning it in which leaves the engine lean during WOT. On a 428 I would suggest you turn the power valve screw all the way out until it stops and try it there. If you are still having a lean condition take the brass restrictor plate out of the vapour inlet in the mixer and try it again. Once removed you may have to turn the power screw in as you may be too rich at full throttle.

[gerrit11]

thanks for your reply.
i'll check what you suggested.

[gerrit11]

i took the restrictor plate out, and turned the screw all the way out , which was 1.5 turns.
now it feels like an improvement, but still got the feeling that i'm missing something
hard to say if it still runs lean.
how can i measure that?

[C3H8]

Many of our Australian members have used a fuel ratio monitor called Innovator. It is fairly expensive but well known. Other similar monitors can be found on Amazon under the search function called Fuel ratio monitors. There are many available but the most important consideration is the monitor must come with a wide band Oxygen sensor. Really inexpensive monitors are available with narrow band oxygen sensors but narrow band only gives two readings, lean (don't know how lean, or rich, don't know how rich!

A wide band can tell you exact fuel air ratios so spend the extra and get one with a wide band if you really want to know how rich your getting.

An additional solution for additional fuel at WOT is the use of an IMPCO VPV (vacuum power valve). This serves two purposes. It provides automatic enrichment while cranking for faster starts with big blocks. Secondly it provides additional fuel at WOT throttle when vacuum is below three inches. It is also adjustable to change the enrichment at different vacuum ranges.

The monitor is the key to sending you in the right direction though.

[gerrit11]

thanks for your advice!
i'll try to get this innovate air-fuel ratio gauge.

[gerrit11]

found this device:

what O2 sensor should i get for it?

[C3H8]

It appears to check fuel air ratio but it doesn't appear to have a wide band O2. To explain, a narrow band O2 only shows rich or lean, not how rich or lean. A narrow band sensor considers anything over 450 MV to be rich. Anything under 450 mv is lean. The reaction time from 450 to 0 is very quick and the same for 450 up to 900 or a 1000 MV. The narrow band is usually not very accurate at in-between voltages. A wide band O2 has the ability to accurately show voltages from 100 MV up to 4.5 or even 5 volts. The rich lean readings are quite accurate. The disadvantage is the kit with a wide band is significantly higher due to the wide band O2 sensor. I would lean towards the wide band as a better choice depending on how detailed you want to be.

The Halmeter will give you basic information at the very least but don't expect much detail from it. It's better than nothing.

[gerrit11]

thanks, but is it sufficient to determine if my engine runs lean or rich at WOT?
and what 02 sensor do i need with it?

[C3H8]

Sure. It will show if you are on the rich side with a standard O2 sensor. Normally these units come with an O2 sensor but if it doesn't have one you can use any 3 wire or 4 wire sensor heated O2 sensor from most vehicles from the 1995 to early 2000 model years. Go with the least expensive as they all work the same. Both GM and fords were similar. The main issue will be identifying the proper wires. Usually the sensors came prewired to match a specific vehicle but from the connector to the O2 sensor the wire colours were all white or all black. The wires only changed colour from the plug in connector upstream. You may have to do a pin out ohm check to determine which wire is which.

[gerrit11]

ok, so the wiring can be a bit tricky.
i go find a used o2 sensor, thanks again!