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VAFPR and dialing in high pressure spring

Old 01-06-2019, 02:04 PM
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VAFPR and dialing in high pressure spring

I read lots of mixed opinions on whether or not a VAFPR is a worthwhile setup on a TBI using a 7427 PCM. I currently have a 27 PSI spring in my regulator, hoping to fuel a SBC that I estimate should make about 400 FWHP.

So, should I be using a VAFPR to lower pressure at idle? Or can this be tuned around without using a VAFPR?
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Old 01-06-2019, 03:04 PM
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Re: VAFPR and dialing in high pressure spring

After about 18 psi you want to go to a VAFPR. The problem with high pressure @ idle is overfueling.
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Old 01-06-2019, 04:38 PM
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Re: VAFPR and dialing in high pressure spring

Originally Posted by morgsie View Post
After about 18 psi you want to go to a VAFPR. The problem with high pressure @ idle is overfueling.
I did not overfuel at idle at 30 psi running 61# high pressure marine injectors. I was at 1.1-1.2 msec at idle. I have also taken a lesson from 2.8s and 4.3s and 454s and run completely asynch calibrations to stretch the injectors further at both idle and WOT.
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Old 01-06-2019, 05:02 PM
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Re: VAFPR and dialing in high pressure spring

Fast, so you were running 30 psi WITHOUT a VAFPR??

Will you please elaborate on what parameters you had to tweak to get idle not to be crazy rich?
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Old 01-06-2019, 06:30 PM
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Re: VAFPR and dialing in high pressure spring

Originally Posted by Fast355 View Post
I have also taken a lesson from 2.8s and 4.3s and 454s and run completely asynch calibrations to stretch the injectors further at both idle and WOT.
And can you explain this as well?

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Old 01-09-2019, 11:28 AM
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Re: VAFPR and dialing in high pressure spring

Originally Posted by Cdeez View Post
Fast, so you were running 30 psi WITHOUT a VAFPR??

Will you please elaborate on what parameters you had to tweak to get idle not to be crazy rich?
I ran 30 psi without a VAFPR. Pulse width was about 1.1-1.2 msec at idle on my setup. Biggest change I made was use the injector correction data from a 1995 454 that used the high pressure fuel system to start with. Even though those 454s used the smaller high pressure 4.3 injectors it is still a closer starting point than the low pressure stuff.
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Old 01-09-2019, 11:35 AM
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Re: VAFPR and dialing in high pressure spring

Originally Posted by DynoDave43 View Post
And can you explain this as well?
The 2.8/4.3 and later 454s often have asynchronous injection only. Asynch fires the injectors at a fixed rate rather than in synch with the distributor reference pulses. This gives you more control over them at both low pulsewidths and allows you to run a longer pulsewidth at higher PRM. Asynch fires at a fixed 80 hz or once every 12.5 msec.
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Old 01-10-2019, 09:25 PM
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Re: VAFPR and dialing in high pressure spring

Originally Posted by Fast355 View Post
I ran 30 psi without a VAFPR. Pulse width was about 1.1-1.2 msec at idle on my setup. Biggest change I made was use the injector correction data from a 1995 454 that used the high pressure fuel system to start with. Even though those 454s used the smaller high pressure 4.3 injectors it is still a closer starting point than the low pressure stuff.
Would that be either of these two binaries? BMHK BHDF are both 7427 454 $0E codemask... Would these be the later model TBI 454 binaries you speak of that used high pressure injectors? The injector data you're talking about is "Injector Offset VS Battery Voltage" and "BPW Multiplier VS Fuel Pump Voltage" ???

Originally Posted by Fast355 View Post
The 2.8/4.3 and later 454s often have asynchronous injection only. Asynch fires the injectors at a fixed rate rather than in synch with the distributor reference pulses. This gives you more control over them at both low pulsewidths and allows you to run a longer pulsewidth at higher PRM. Asynch fires at a fixed 80 hz or once every 12.5 msec.
Makes me wonder why did they not set them all up to run asynch to begin with if it gives more control over the injectors??

Last edited by Cdeez; 01-10-2019 at 09:29 PM.
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