14point7 Spartan 2 install, Holley 4150 tuning, & exhaustcapades

Bustedknuckle

Member
Jun 5, 2020
18
10
13
60
Kingman AZ
I confirmed the power valve size. 5.5 should be correct, but I think as insurance I may pick up another 5.5 PV when I pick up the sensor bung from the parts store.

Edit: The more I think about it I think I'll pick up a 4.5. I think I should err to the lower side with this, and since it was somewhere in the 10-11 inch range for vacuum, I'm going to go with 10 which would require a 4.5 power valve. Since they don't carry a 4.5 PV, I guess I'm at a standstill with actually going farther with the carb once I get the gauge installed. So this escapade will continue for at least a few days.....

IMG_20200422_114551__01.jpg
I like going a bit smaller, just a tad lean at full tilt, on the power valve; Tune the accelerator cam and squirter size to cover a hole in the fuel curve, if there is one. Then tune the secondaries
 
  • Sponsors(?)


LILCBRA

I wish I didn't have all of these balls in the air
15 Year Member
Dec 6, 2005
2,719
1,733
164
49
Marietta, Ga
My personal choice was to go a tad rich, especially under load. As I understood the effects of AF ratios before and over the course of going through this, lean conditions can lead to detonation which in turn can lead to engine damage. Then I found this video on the YouTube which helped to reinforce everything. It sounds like it's a common misconception that the AF ratio being a little lean produces the maximum amount of horsepower, but these guys dynoed an engine and produced the curves to prove that that is false and also explain the reasoning behind it. It logically made sense to me and reinforced what I had felt for a long time.

View: https://youtu.be/JzbLrn-2jyw
 

extra_stout

Advanced Member
Aug 27, 2018
401
422
73
Germany
I didn't know about that myth... but interesting to know that such BS goes around. With carb instead EFI it is a little more complicated because the amount of fuel is controlled by the volume flow. But the mass flow changes with temperature even if the volume flow is the same. This means if the car is tuned in warm weather near lambda 1. It can happen that if its cold outside you get lean condition. For partial load and idle that is not a problem IMO. But for WOT you should always be a little bit rich.
And exhaust popping can also come from lean condition...
 
  • Like
Reactions: LILCBRA

LILCBRA

I wish I didn't have all of these balls in the air
15 Year Member
Dec 6, 2005
2,719
1,733
164
49
Marietta, Ga
I've had it out a couple times, but nothing of interest to post about. It's running great now though! A/F stays in the low 12s to mid 13s most of the time. There was a couple times where it popped into the high 14s/low 15s upon acceleration, but only for a split second and dropped back into the 12s/13s. I attribute that to shifting. It would be awesome if I could record the gauge for longer than a couple minutes to show instead of explaining it through text. :shrug:
 
  • Like
Reactions: Enzio and 2Blue2