I have been using successfully now for a month the Aeromotive VAFPR. My FP is set with vac line disconnected and vac plugged at TBI to 19lbs FP. Upon attaching the vac line the pressure drops to 14 lbs. I expected more of a drop but that is what it is. Looking at the "calculator" given to me by a fellow member(thank you) I see it starts at 0 VAC which is 100 MAP. There I placed my calc BPC at say 92(80lbs injs/350CID). I idle at 40 MAP or 60 VAC. so in the 60 VAC field I have BPC of 144. That calculator given to me assumes a FP of 10.3 at 60VAC? Mine again is 14.0. That does not seem to be right as the calculator assumes less FP? Maybe it is not all that important as my VE tables are looking good on BLM. On hard deaccelration I may see 80VAC. There I have 169 in table. I believe Dominic did do an accurate calculation on what the values should be based upon observed VAC with gauge attached. Not quite sure how that is done(under load, etc). I dont see how a computer based calculator could ever work as each modded motor is different on observed VAC and corresponding FP as regulated with VAFPR. VAFPR manufacturerers may vary as well in design and result-output. Is a sliding scale(92-94-96-98-100, etc.) OK as long as you are correct on 0 VAC or 100 MAP-WOT? And just tune with that for VE? Please correct me if I am confusing VAC with MAP. I thought I had it right.

Ron,

I started out by measuring FP at "key on" so determining what 0kpa or 100VAC was.
Fuel pump runs and I measure Fuel pressure with motor off. I had fuel pump wired so it would run continuously even tho motor was off. I teed in my Mighty Vac with Vacuum gauge to vacuum port on VAFPR. Could also do this with scantool hooked up.
I applied an amount of vacuum having already converted " of Hg into kPa.(See attachment) Read Fuel Pressure at that point. Knowing the pressure and beginning Injector flow, I could calc new BPC at that VAC and FP. The spring I used, the larger one, gave me 10psi at about 40kPa/60VAC(idle), and went to 20psi at 98-100kPa/0VAC.
Not completely linear especially at lower kPa.
Hope that helps.

Thanks for the response. I kinda figuered you would comment soon. That appears to be the scientific approach !

I assume you are using the Aeromotive FPR as I am. Did you find that when you attached the vac line the FP dropped from 20 to 14-15? I expected it to drop a bit further. I idle at 39 MAP and key on is 98 MAP. PW is 1.6msec idle. WOT I see about 95 MAP so that is a good thing. Cold air kit is going in as soon waiting on UPS. I believe I am getting way too much engine heat with the traditional round AC.

Ron,

I had the Aeromotive 13301 which I think is the one most used on the Xfire.
I had the larger spring in it and my idle was at ~ 11.5 or so depending. It would idle at ~ 45kPa. My cam had a 108LSA. WOT MAP came in at about 98kPa dropping to 96 by 5500rpm. Overall I thought that indicated minimal restriction in the air inlet. Just for grins and comparison, I've attached a dyno run of the ZR. Significantly elevated power peak.