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WOT MAP and 02 sensor readings showed it made a big improvement in airflow when I still ran small block TBI units. I had to add 1-2 psi fuel pressure to get the 02 reading back to where they were at WOT. I later compared a stock TBI unit to a 454 TBI unit on the same 3704 Edelbrock manifold that had been bored to 2" with a 2" oval open center spacer under the TBI units. The difference was 10 hp peak to peak and closer to 15 at higher rpm. 2-3 in/hg manifold vacuum went to less than 0.25 in/hg. The moded small block TBI dropped to less than 1 in/hg vacuum. That was a stock head, stock cam L05 with headers. Stock 305 air intake does pull a considerable vacuum at WOT, but a 14 x 3" open element with a flat base that eliminates the choke collar eliminates most of the restriction by itself. Removing the TBI ridges and adding a 1/4" spacer helps a bit more.
I ran 350 injectors in a 305 that had airflow improvements back in the day as well to feed the 305 enough fuel on the stock chip to keep it happy.
You can do all the stuff to the intake you want, but it is really the whole exhaust system from the head ports out that choke the power in stock form. The G-van L03s starting in about 1992 recieved the L05s 2.25" outlet manifolds, 3" Y-pipe and 3" single exhaust. They were net rated at 185 hp and that was with GM still using the restrictive pellet box cat. GM made 15 hp more than the F-cars using the flat tappet cams. The LG4 gained 5 hp when it recieved the roller cam with the same cam profile.
This was before and after a 1/4" pod spacer and a stock bore TBI unit that had the rings trimmed off and radiused. Both runs had a 1" open center spacer and Edelbrock 3704 manifold bored to 2". 6 kpa increase in MAP. Stock heads and stock cam at the time. 454 TBI unit increased the MAP to 99 KPA which was almost barometric pressure. All 3 tests were also done with a 454 air cleaner assembly, K&N filter and a 454 air inlet duct. Stock TBI, no spacer and 350 air cleaner pulled down to 82 kpa. I had to increase the pressure and decrease the BPW and even later had to add more preasure because the injectors were static. Notice the injector pulse width is higher with the increased MAP. More airflow and thus more fuel demand. I also played around with maximum IAC opening for throttle follower as well. 255 counts at WOT vs 160 counts increased the MAP about 2 kpa by having the IAC wide open.
10-07-2023, 08:24 PM
