Aloha! Everyone!
I am in the process of swapping a TBI 350 into my 91' RS and have a question about "BPW" settings for larger displacement engines.... I have seen a few different posts about where to adjust BPW higher for larger engines and another for setting the BPW lower for larger engines, can anyone set the record straight?
I am going to (Haven't done this yet) run a ZZ4 cam with an otherwise stock bottom end 350, the cam, lifters, and roller timing chain from a ZZ4 crate engine along with a set of Comp Cams roller rockers, that's it, stock Cast Iron heads (Valve job done) and stock TBI and Injectors. I have my bin file ready to go, but now I am getting conflicting reports on where I should be in setting my BPW. Anyone know where I should set this?

should BPW be increased to 154 (134 x 350 / 305) or decreased
(134 x 305 / 350). ( my car had a 305 originally)
Hopefully you guys who have been doing this for a while can set me on the straight and narrow path here.
Thanks in Advance!
Ben Smith

 

From the $42 1227747 ECM hack:

; TBI:
; Val = 1461.5 * (VOL/RATE)
; VOL = Vol of 1 Cylinder in liters, (0.7125l)
; RATE = Injector flow in gms/sec
: 5.7l = 7.71 gms/sec (61.2#/HR)
; (VOL/RATE) = 0.0924 l/gm/sec
; LD2B4: BPW = 135


Now, what you really ought to be doing is removing those 305 injectors and installing a set of 454 BB injectors and then figuring out what your bpw should be...

 

MonteCarSlow,
after I figure out the final details of smoothing out the idle and other issues, I will do just what you suggested, go for the BB injectors. but for now, I needed to figure where to go with my stock Injector BPW. Sounds great, I'll try that and see where it gets me!
By the way, where do you get the cylinder volume info from? Just curious.....
Thanks again!
Ben Smith

 

5.7L / 8 = Volume in L for 1 cyl.

Or...

((350 * 16.387) / 1000) / 8 = .7169 L

Would be the more technical answer.

 

Thanks! that does make sense, the answer was right in front of me
Ben

 

assuming a FP of 12 lbs. if you run 15 lbs you need to adjust BPW for that change.

 

Really sounds alot harder than it is. The BPW is important because it gives you the most tuneability in your other fuel tables.

 

BPW = 11600*Displacement/# of cylinders/injector size at rated pressure/square root of (new pressure/rated pressure)

Displacement is in Liters ex) 5.7
# of cylinders ex) 8
Injector size in lb/hr ex) 65
Rated pressure in psi ex) 12
New pressure in psi ex) 28

BPW = 11600*5.7/8/65/sqrt(28/12) = 83