Holley base plate

[Marco]

Hi everybody,

I've got a question about a holley 4 barrel base plate underneath a impco 425 (LPG mixer) on a 400ci mild street car.

I've been thinking about this for a while now, the impco 425 flows about 460cfm max, now the holley base plate underneath it is a 850cfm (1-3/4 throttle bore) the car runs alright, idles perfect at 600 rpm (i've got a real small cam).

Would replacing the 850 cfm with a 600cfm base plate increase mileage& low end torque? The impco is the resticting factor so in not sure if replacing the base plate makes a difference?

Hope some of you could help me out.

Thanks in advance!

 

[oldkimmer]

It may help. But h would probably have to try it. Kim

 

[Marco]

I just ordered a 600cfm one, it'll take about two weeks to get here (send to the Netherlands). Hope it will help because im only getting about 8 mpg.

If anybody is able to explain why it would or wouldn't have any effect please do.
Gr marco

 

[RJRENTON]

IMO....
Its not do much of a CFM a issue but one of the heating value (energy content/standard cubic foot) of of the fuel being used, to approximate the fuel-air rstio. IMCO devices are typically used on gaseous fuel systems and provide the liquid to gas vaporization function plus fuel metering function. You did not mention what type of fuel you are using. Is is LNG (Liquified Naural Gas), LPG (Liquified Petroleum Gas) or Propane ? Each has a specific heating value. Typically, the fuel is extracted ftom the pressurized holding tank as a liquid, then vaporized, then metered to the application with a demand controlled vacuum operated metering system. It is possible that the IMCO device will need to be adjusted to supply more fuel at the new flow rate. Gasseous fuels tend to burn slower than gasoline requiring more ignition advance characteristics. Just thinking out loud...
BOB RENTON
.

 

[Marco]

Hi Bob,
Thank you for your response!

Im running LPG and I actually forgot to mention im running an AFR meter and at idle its about 16-1, cruise speed 15-1 and WOT 15,5-1 so this is about perfect (The stoichiometric ratio for burning LPG is about 15.7) only the cruise ratio is a bit to rich.

The ignition timing curve has been properly adjusted.

Gr Marco

 

[RJRENTON]

Hi Bob,
Thank you for your response!

Im running LPG and I actually forgot to mention im running an AFR meter and at idle its about 16-1, cruise speed 15-1 and WOT 15,5-1 so this is about perfect (The stoichiometric ratio for burning LPG is about 15.7) only the cruise ratio is a bit to rich.

The ignition timing curve has been properly adjusted.

Gr Marco

Marco,
Thanks for the update.....was not sure as in the States, LPG is called propane. Propane has, typically, ~ 2400 Btu/std cubic ft. Heating value. With an air/fuel measuring device, you should be able to adjust the fuel ratio electronically with great accuracy. If also measuring air flow, you could program the fuel metering system to provide pin point accuracy trimmed by the down stream oxygen sensor.
When in industry, I was involved in burning refinery off gas, as a fuel source for a thermal decomposition process. But, because of the varying Btu content of the fuel gas, in order to provide the correct fuel to the decomp process to maintain the correct decomp temperature, we used a gas calorimeter to determine heating value of the fuel to adjust the burner's fuel flow based on instantaneous heating value of the fuel.
Best of luck with your endeavours....
BOB RENTON