Recalibrating For Horsepower Gain

[Brian B.]

After a mild camshaft change, my engine produces 22% more horsepower based on track testing.  Carburetor is 7044270 with stock dimension air bleeds.  Should primary jets/rods be changed to reflect 22% larger effective area now?   I'm using .147 needle/seat, 5psi pump, small float, 11/32" float level.  Car runs strong with no issues but trying to fine tune.  I feel like I am missing something basic here but don't know what is.  Thank you!

[Brian B.]

After re-reading my post, I realize this makes no sense.  I'd remove if I could. I apologize.

[Cliff Ruggles]

Test in all areas and tune if/as needed.

Not sure why only 5psi fuel pressure, that carb will take nearly twice that W/O issues even with the larger inlet seat and small float in it.

More power requires improved fuel delivery more than metering changes.  Most of these engines operate in about the same A/F ratio across the load/speed range.

Matter of fact, things done to improve VE often require less fuel and timing, not more.  The typical exception is that larger cams often require more idle fuel to the mixture screws if/when the vacuum or signal to the carb at idle is lower.......Cliff

[Brian B.]

Sorry  Cliff....... I meant 6psi pump.  194 gph free flow/91 gph @ 4.5 psi. Thanks for the insight on delivery versus metering.  I'll focus in that area. 

[Cliff Ruggles]

Electric pump? 

I've had next to zero success here with high output mechanical pumps.  They really don't "free-flow" as valves open and close with each cycle of the pump. 

I've had perfect success with electric pumps, but only when they have a return system to the tank.  Some are dubbed as being able to run "dead-head", but I've never had any luck doing that either.

In any case the 7044270 is excellent, they are actually 850 cfm not 800.  One of the very few early units that had the larger primary bores and shorter secondary stop to allow the flaps to open to the optimum angle.

They also have an excellent airhorn design with no open holes (venting) to allow fuel to exit the carb out the top on hard launches.  Combined with the front located large vent they work very well for drag racing. 

I ran one for many years before upgrading to a 1977 unit with the APT system.  The 1977 unit is equal everyplace once correctly set-up plus you get APT for fine tuning the primary side without pulling the top and changing parts.  It also uses the later type choke pull-offs which are much easily to modify than the early type the Super Duty carb uses.......Cliff

[Brian B.]

Cliff I'm using a mechanical pump with a vapor return line which is operational.  6psi with the return line working and 7psi without.  Thanks for the background details on the carb. 

[Cliff Ruggles]

I tried a high output mechanical pump about 20 years ago.  It was not able to keep up with the mild 428 engine I was running at the time.  Did fine on the street, but with DOT's or slicks at the track it couldn't keep up on hard launches. 

I tried a "pusher" pump to it and it still didn't make the grade.  Ended up sumping the tank and installing a 140gph electric pump behind the tank with 8an lines/fittings everyplace.  That was flawless but I fried the brushes in the pump quickly.

I kept that system but installed a return and nearly 20 years later it finally required a brush replacement last Fall. 

Since modifying the fuel delivery system I've upped the power level and vehicle performance significantly and it's never even hiccupped once no matter how hard the car leaves or runs at the track........Cliff

[PonchoVia]

I    don't suppose there is a need to use such a high volume pump? I'm looking at the Phantom 340 liters which is about 75gph in a return system.

Should be safe for that horsepower range.