Racing Fuel Systems

Gentlemen, I modified my DaVinci 1050 Dom from a 3 circuit to a 2 circuit using the old forum as a guide.
The car: 1978 Camaro 3600lbs w/driver, ladder bar coil over, 10 x 29.5 slick, 4.88 gear, 6400 converter, TH 400 trans
The engine: 468 Chevy 4.320 bore 4.00 stroke 14.25:1 comp, GM 781 iron head mild ported, 37,45,60 radius valve job, Edlebrock Victor 454-o intake w 4500 flange, 278/282 dur @ 0.050" 0.832/0.756 lift on 111 centerline, intake timed at 109, 1.8/1.8 rockers.
The carb is set up with the Motorsport Village baseline parameters:
IJ=0.039 in low position
TSJ=0.055
Pump shot: Holley 44
IAB=0.065
MAB=0.032
EB=0.28,0.028,0
Last october after I did the mod the car ran much better. 60 foot was best ever @1.33 Best et/mph 10.02/134.49 with a pretty flat afr curve. I have a Innovate log of that run here:
The Green line is G METER, Black is Engine RPM, Blue is Driveshaft RPM, Magenta is AFR

I changed the exhaust side rockers from 1.73 to 1.8s and changed the push rods from 3/8" to 7/16" 0.165 wall. I took it out on Thursday and got a good log. the afr curve is very different now. I figured changing the exhaust would influence the fuel curve, I need some guidance where I should look to change the curve. I launch the car at 4000 off the two step, shift 7400 and trap 7600. The log is posted here:

Green is G Meter, Black Engine RPM, Blue Driveshaft RPM, Magenta AFR
Thank you,
Paul

One more important detail, started with 95/96 Holley jets last year. Looked at data this last outing and started dropping Main jets. Went down to 89/89. The second log posted is with 89/89 jets.

Does it run better with more lift? Logs are hard to read.

Car lost some et and mph. Went 10.27/130.8/1.37 60. The weather wasn’t great 87f/ 30% humidity/ 28.49 barometer. Time out before weather was 57/ 68 humidity/ 29.3 baro, car went 10.02/134.49/1.33 60. My biggest concern is the leaning out in top of 1st and 2nd gears. 1st leaned out to 14.9 and 2nd 13.5 shifting at 7500. Went through traps at 12.66. Off the trans brake the engine went to 10.6 AFR but it was dead hooking. Car 60 foots better when it rotates a full turn before weight transfer. The AFR curve looked better when the car went faster, 12.0 to 13.0 with a small lean spike top of 1st gear. This last time out the AFR curve didn’t look happy at all, just trying to learn what engine is telling me it wants.

I just took the valve covers off and looked at the valve train after 4 passes. Going to switch back to the 1.73 rockers on the exhaust and keep the 7/16” push rods in and see if it goes faster again. Measured lift at the valve with the 1.73 is 0.670” , with the 1.8 it is 0.700”. Running 300lbs on the seat/ 800 open. I am also going to shorten installed height from 1.875 to 1.825 to get the spring within 0.080” of coil bind with the shorter lift of the 1.73 rocker.

I did just purchase 0.023” dia air bleeds so if I need to adjust the high bleed I have some room(I have pin gages and drills). Current high bleeds are 0.032”.

While going through process of swapping back to the 1.73 rockers I found loose lash on 4 cylinders. Also found 2 exhaust rocker trunnion bearings that were tight up to the snap ring. The loose lash is from not having the cam fully on the base circle when going through the lash. Also found a broken guide plate on number 5 exhaust. Sheared right off at the stud bend. Looks like push rod may have been pushing on the throat too much. Overall the 1.8 switch has not been a happy experience for the valve train.

I did a net valve lift check with both the 1.73 and 1.8 rockers. With the 1.73s and 0.022” lash I have a net lift of 0.670”. With the 1.875” install height there is too much clearance to coil bind. I am replacing the plus 0.050” locks with std locks which brings install height to 1.825” and puts me at 0.080” to coil bind.

I am adding two channels to the data logger. Adding fuel pressure at the regulator and manifold vac under carb. The fuel pressure regulator has always acted erratic so I want to keep an eye on it.I am using a Product Engineering 460 gph pump and PE regulator. The bypass is at the rear and discharges into the fuel cell. I checked the head pressure, it was 32lbs with 12.5 volts. I backed it down to 28lbs at 12.5 volts.

Going to replace guide plates, swap the locks, set lash to 0.20” on intake and 0.018” on the exhaust and see how it runs. Hoping fuel curve returns to where it was on my 10.04/10.04 runs.

Figured it was likely valve train related. Let us know after you get it fixed

exhaust opening, adjust intake. intake closing, adjust exhaust. This will put you adjusting the valves with lifter close to the center of the base circle. still the best after all these years.