adjusting fuel pressure on TBI - Various Options
Walter Sherwin
wsherwin at home.com
Sat Oct 21 15:55:19 GMT 2000
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Assuming you are using the common GM 2bbl TBI's, you have the following =
options for playing with fuel pressure (NOTE: most garden variety 2bbl =
TBI regulators were factory set for a range of 9-13psig, but be aware =
that there were also some identical looking ones that were set for =
"other" ranges. So, it's best to check where you're at before =
swapping). Options are as follows......
1) Bolt on an aftermarket adjustable TBI regulator from Turbo City, =
Hypertech, JET, etc. All of these will adjust up to about almost =
15psig, depending upon your setup and pump voltage. This would be a =
logical replacement for a factory 9-13psig unit, for an engine that has =
been warmed over with a few mods.
2) A step beyond......GM TBI regulator P/N 17113186 is a direct bolt-on =
jobbie, and will give you about 18-20psig fuel pressure. Additionally, =
this regulator has vacuum compensation capability. If you hook the =
included vac port to manifold vacuum, then you'll get a part throttle =
fuel pressure decay of roughly 1psig per every 2"Hg manifold vacuum. =
This comes from certain marine and HT502 applications.
3) A little bigger step beyond.......GM TBI regulator P/N 17113079 is a =
direct bolt-on jobbie, and will give you about 26-32psig. It does not =
have vac compensation. This comes from some of the late 90's BBC =
applications.
4) You can add vac compensation to any TBI regulator, if you have the =
time and patience to get creative. Basically, you just need to make =
the can assembly that surrounds the backside of the diaphragm "sealed", =
and then plumb it to manifold vacuum. You can either do this thru =
sealing/welding shut the existing can, or machining a new can. The shop =
manual tells you not to disassemble these regulators, but in truth they =
are quite easy to dis/re assemble if you are careful. =20
5) You can change the setpoint of your stock regulator by roughly +/- =
2psig, quite easily. Sometimes without even having to disassemble it. =
Remove the whole fuel meter cover and regulator assembly from your TBI =
and flip it upside down in your left hand. You should note a =
rectangular window cut in the side of the regulator can, with the end of =
a tang visibly located somewhere between the extreme ends of that =
window. The tang is attached to the spring perch within, and it's =
relative up/down position is roughly proportional to the setpoint of the =
regulator. Move tang up, more pressure, move tang down, less pressure. =
Now, look at the bottom of the can and you will probably see a beefy =
collar with what appears to be a screw tack welded in the middle. You =
can either dremel away the tack weld and manipulate the screw, or, you =
can try this next approach. Firmly grasp the collar with a good set of =
vice grips or channel-lock pliers, and gently attempt to force the =
collar counter clockwise. Chances are pretty good that the tack welds =
between the can and the collar will snap, and you can then proceed to =
turn the whole collar assembly counter clockwise to raise the pressure =
slightly. If this does not work for you, or if your regulator does not =
have a collar (as some don't), then you'll have to disassemble the =
regulator to modify it. Again, spin the perch counter clockwise on the =
screw shaft to compress the spring and raise the pressure.
6) The external regulator approach.........You can also leave your stock =
TBI regulator in place (no need to gut it unless planning to get really =
wild with pressures, and fear a burst diaphragm), and then graft-in any =
flavour of external regulator, into the TBI return fuel line, remote =
from the TBI assembly. The external regulator can either be a "fixed" =
pressure jobbie without vac compensation (intended to continually =
override the setpoint of the stock TBI regulator), or, it can be a =
"variable" vac compensated jobbie (intended to provide more fuel when =
needed and then cut back and allow the stock TBI regulator to take =
control during cruise). =20
7) Whether to run a fixed pressure, or a variable pressure, at the TBI =
injectors all comes down to your personal level of comfort with the TBI =
software at hand. The most elegant approach is to select a fixed =
pressure operating point, then modify the software injector BPC's to =
suit, and then cal the VE's to suit your engine mods (this carries with =
it the assumption that you will either measure or calculate your new =
injector flow rates at your new pressure setpoint). But, if software =
modifications are troublesome, then variable pressures can be used to at =
least get things pretty durn close, and then rely upon the INT/BLM =
features to reign things into control.
8) As a general rule of thumb, I've found that most GM Rochester TBI =
injectors will comfortably tolerate up to 30'ish psig without issue, =
assuming that they are connected to individual 4/1 amp drivers. There =
are some TBI injectors that can be driven has high as 70psig, but they =
are an exception rather than the norm.
Sorry for the long missive, but I thought I'd dump as many related ideas =
as I could in one place, while I had the chance, in case someone was =
surfing the archives in a couple of years.
Walt.=20
----- Original Message -----=20
From: thom358=20
To: diy_efi at diy-efi.org=20
Sent: Friday, October 20, 2000 11:14 PM
Subject: adjusting fuel pressure on TBI
Is there an adjustable fuel pressure regulator for a TBI setup? is =
there a way to bypass the origional, or gut it and run an aftermarket =
regulator? I am would like to run more fuel pressure, but I want to be =
able to adjust it. Any thoughts are appreciated.
THOM
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<META content=3D"text/html; charset=3Diso-8859-1" =
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<BODY bgColor=3D#ffffff>
<DIV><FONT size=3D2>Assuming you are using the common GM 2bbl =
TBI's, you=20
have the following options for playing with fuel pressure (NOTE: =
most=20
garden variety 2bbl TBI regulators were factory set for a range of =
9-13psig, but=20
be aware that there were also some identical looking ones that were set =
for=20
"other" ranges. So, it's best to check where you're at before=20
swapping). Options are as follows......</FONT></DIV>
<DIV> </DIV>
<DIV><FONT size=3D2>1) Bolt on an aftermarket adjustable TBI regulator =
from Turbo=20
City, Hypertech, JET, etc. All of these will adjust up to about =
almost=20
15psig, depending upon your setup and pump voltage. This would be =
a=20
logical replacement for a factory 9-13psig unit, for an engine that has =
been=20
warmed over with a few mods.</FONT></DIV>
<DIV> </DIV>
<DIV><FONT size=3D2>2) A step beyond......GM TBI regulator P/N 17113186 =
is a=20
direct bolt-on jobbie, and will give you about 18-20psig fuel =
pressure. =20
Additionally, this regulator has vacuum compensation =
capability. If=20
you hook the included vac port to manifold vacuum, then you'll get a =
part=20
throttle fuel pressure decay of roughly 1psig per every 2"Hg manifold=20
vacuum. This comes from certain marine and HT502=20
applications.</FONT></DIV>
<DIV> </DIV>
<DIV><FONT size=3D2>3) A little bigger step beyond.......GM TBI =
regulator P/N=20
17113079 is a direct bolt-on jobbie, and will give you about =
26-32psig. It=20
does not have vac compensation. This comes from some of the late =
90's BBC=20
applications.</FONT></DIV>
<DIV> </DIV>
<DIV><FONT size=3D2>4) You can add vac compensation to any TBI =
regulator, if you=20
have the time and patience to get creative. Basically, you =
just need=20
to make the can assembly that surrounds the backside of the diaphragm =
"sealed",=20
and then plumb it to manifold vacuum. You can either do this thru=20
sealing/welding shut the existing can, or machining a new can. The =
shop=20
manual tells you not to disassemble these regulators, but in truth they =
are=20
quite easy to dis/re assemble if you are careful. </FONT></DIV>
<DIV> </DIV>
<DIV><FONT size=3D2>5) You can change the setpoint of your stock =
regulator by=20
roughly +/- 2psig, quite easily. Sometimes without even =
having to=20
disassemble it. Remove the whole fuel meter cover and regulator =
assembly=20
from your TBI and flip it upside down in your left hand. You =
should note a=20
rectangular window cut in the side of the regulator can, with the end of =
a tang=20
visibly located somewhere between the extreme ends of that window. =
The=20
tang is attached to the spring perch within, and it's relative up/down =
position=20
is roughly proportional to the setpoint of the regulator. Move =
tang up,=20
more pressure, move tang down, less pressure. Now, look at the =
bottom of=20
the can and you will probably see a beefy collar with what appears to be =
a screw=20
tack welded in the middle. You can either dremel away the tack =
weld and=20
manipulate the screw, or, you can try this next approach. Firmly =
grasp the=20
collar with a good set of vice grips or channel-lock pliers, and gently =
attempt=20
to force the collar counter clockwise. Chances are pretty good =
that the=20
tack welds between the can and the collar will snap, and you can then =
proceed to=20
turn the whole collar assembly counter clockwise to raise the pressure=20
slightly. If this does not work for you, or if your regulator does =
not=20
have a collar (as some don't), then you'll have to disassemble the =
regulator to=20
modify it. Again, spin the perch counter clockwise on the screw =
shaft to=20
compress the spring and raise the pressure.</FONT></DIV>
<DIV> </DIV>
<DIV><FONT size=3D2>6) The external regulator approach.........You can =
also leave=20
your stock TBI regulator in place (no need to gut it unless planning to =
get=20
really wild with pressures, and fear a burst diaphragm), and then =
graft-in any=20
flavour of external regulator, into the TBI return fuel line, remote =
from the=20
TBI assembly. The external regulator can either be a "fixed" =
pressure=20
jobbie without vac compensation (intended to continually override =
the=20
setpoint of the stock TBI regulator), or, it can be a "variable" vac =
compensated=20
jobbie (intended to provide more fuel when needed and then cut back =
and=20
allow the stock TBI regulator to take control during cruise). =20
</FONT></DIV>
<DIV> </DIV>
<DIV><FONT size=3D2>7) Whether to run a fixed pressure, or a =
variable=20
pressure, at the TBI injectors all comes down to =
your personal level=20
of comfort with the TBI software at hand. The most elegant =
approach is to=20
select a fixed pressure operating point, then modify the =
software=20
injector BPC's to suit, and then cal the VE's to suit your engine mods =
(this=20
carries with it the assumption that you will either measure or calculate =
your=20
new injector flow rates at your new pressure setpoint). But, =
if=20
software modifications are troublesome, then variable =
pressures can be=20
used to at least get things pretty durn close, and then rely upon the =
INT/BLM=20
features to reign things into control.</FONT></DIV>
<DIV><FONT size=3D2></FONT> </DIV>
<DIV><FONT size=3D2>8) As a general rule of thumb, I've found that =
most GM=20
Rochester TBI injectors will comfortably tolerate up to 30'ish psig =
without=20
issue, assuming that they are connected to individual 4/1 amp =
drivers. =20
There are some TBI injectors that can be driven has high =
as 70psig,=20
but they are an exception rather than the norm.</FONT></DIV>
<DIV> </DIV>
<DIV> </DIV>
<DIV><FONT size=3D2>Sorry for the long missive, but I thought I'd dump =
as many=20
related ideas as I could in one place, while I had the chance, in case =
someone=20
was surfing the archives in a couple of years.</FONT></DIV>
<DIV> </DIV>
<DIV> </DIV>
<DIV><FONT size=3D2>Walt.</FONT> </DIV>
<DIV> </DIV>
<DIV> </DIV>
<DIV> </DIV>
<BLOCKQUOTE=20
style=3D"BORDER-LEFT: #000000 2px solid; MARGIN-LEFT: 5px; MARGIN-RIGHT: =
0px; PADDING-LEFT: 5px; PADDING-RIGHT: 0px">
<DIV style=3D"FONT: 10pt arial">----- Original Message ----- </DIV>
<DIV=20
style=3D"BACKGROUND: #e4e4e4; FONT: 10pt arial; font-color: =
black"><B>From:</B>=20
<A href=3D"mailto:thom358 at netzero.net" =
title=3Dthom358 at netzero.net>thom358</A>=20
</DIV>
<DIV style=3D"FONT: 10pt arial"><B>To:</B> <A =
href=3D"mailto:diy_efi at diy-efi.org"=20
title=3Ddiy_efi at diy-efi.org>diy_efi at diy-efi.org</A> </DIV>
<DIV style=3D"FONT: 10pt arial"><B>Sent:</B> Friday, October 20, 2000 =
11:14=20
PM</DIV>
<DIV style=3D"FONT: 10pt arial"><B>Subject:</B> adjusting fuel =
pressure on=20
TBI</DIV>
<DIV><BR></DIV>
<DIV>Is there an adjustable fuel pressure regulator for a TBI =
setup? is=20
there a way to bypass the origional, or gut it and run an aftermarket=20
regulator? I am would like to run more fuel pressure, but I want =
to be=20
able to adjust it. Any thoughts are appreciated.</DIV>
<DIV> </DIV>
<DIV>THOM</DIV></BLOCKQUOTE></BODY></HTML>
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