I got a dp 750 and wanted to tell you guys about the mileage i am getting. my 86 z28 with a vortec 383 without an overdrive with a 3.42 rear.

combo is as follows:

3500 weight no driver.
383 eagle shortblock assembly.
224-230 @.050 duration comp cams 276hr with 1.6 roller tipped rockers. Beehive 26918 springs.
9.4.1 compression on stock non ported cylinder heads.
Rpm air gap intake with 3" open element, sealed to carb tray and to 3" cowl hood for full function.
holley 4779 carb with lots of mods.
turbo 350 transmission.
moser crate axle with a 3.42 gearset.
Autolite 104 spark plugs.

Ok what i did was remove the 3.73 gears. Installed a 3.42 ring and pinion. recalibrated the idle circuits, p.v.r.c size, and main jets on primary side. I set it up with .008" wire in the idle feeds all 4 corners. .067" idle bleeds primary. .078" idle bleeds secondary. 69 primary jets. Redrilled primary p.v.r.c size to .067" to retain proper enrichment. Set mixture screws to the leanest slow speed cruise it would run with without any stumbles. 1/1/4 turns out. due to the fact low speed cruise is on the idle circuit.
Choke tower is milled off.

the carb was with the stock idle air bleeds and the stock ifr's about a half turn out on the mixture setting. Obviously not calibrated correctly for my engine way too rich. What i had done along time ago was drilled the idle air bleeds significantly larger and left the ifr's alone. I think this had messed with the carbs circuit timing and there was always a little lean spot on very light throttle movements. Due to the delay from the bleeds being way to large. I had corrected this with larger than normal squirters and moved on.

My mileage prior to this without the o.d trans and the 3.73 gearset was 14mpg when babying it at 2800rpm or less. My last tank was 19mpg. Amazing I must say do to the fact that i was cruising 65mph at around 3000rpm. All the while drinking 87 octane.(it wont knock unless driven very aggressively then i use 91 for safety sake)

I recomend everyone to take that holley and work with it because you can have your cake and eat it too!

 

Similar stuff to a magazine article a year or so ago.

Get back to us after 3 or 4 more tankfuls. I wouldn't trust one tank's data only.

 

I'm getting 23-24 mpg highway and about 19-20 around town with a 383 the same cam but on a 112 lsa, 75/80 jets Quick Fuel 750dp. Only difference is I have a 2:73 rear and a t-5, 10.8:1 compression and aluminum heads. The best thing I did after I got my carb right was to setup my vacuum advance I picked up like 2-3 mpg highway getting it setup right. $.02

Seth

 

yeah i almost wish i had gone with a 3.08 rear. The engine would have been just fine with it. I bet i would be in the 20 -21 mpg range. Its also nice to see the spark plugs clean after some run time on the engine (1000 miles). Im thrilled with the throttle response too. I mean its great to have a performance carbed car get acceptable mileage with the current price of fuel.

The only difference now with the leaner idle circuits is the lack of a choke when its 50 degrees or so the leaner idle circuit makes for a cold blooded car. before even without the choke is was not nearly as fussy. oh well.

 

did you notice a difference when you drilled out the pvrc's?

 

yeah defenetly. with the pvrc left at .054-.056" the car would stumble and break up do to being too lean under high load . That was with the temps at or around 50 degrees. when you drop jet size you need to compensate for enrichment.