From: "Lanham, Wade A."
To: "'rx7@world.std.com'"
Subject: (rx7) [3] Fuel Pump technical info
Date: Mon, 23 Oct 2000 10:38:57 -0400
I've done a little research on the Bosch pumps. If I keep this up, none
of the tuners will sell me parts any more. :)
The information for the Bosch pump that Carlos Iglesias describes on
Cirian's site is incorrect (the numbers he lists as LPH are actually LBPR
- *big difference!*) It is also the same one that Wael got from M2.
The bottom line is the Bosch flows almost exactly the same as the GSS-341
Walbro pump in the "useful" pressure ranges. The difference is the Bosch
has a much more linear fuel flow curve, while the Walbro flows more at
lower pressure and barely flows at very high pressures (100+ psi).
BUT, the Bosch costs twice as much, and my opinion is that the Bosch
appears to be a higher quality pump. I don't think that anyone who has
seen both pumps would argue with that. So, go cheaper (Walbro) or more
expensive (Bosch), either one will flow more than you'll ever need. I'd
probably buy the Bosch if I knew then what I know now. However, the
Walbro is working fine for me, so I'll use it until it fails, if it ever
fails.
** Published flow rates (provided by manufacturers):
** 13.2v for the Bosch and 13.5v for the Walbro (so the Bosch numbers are
slightly higher than this)
BOSCH WALBRO
PN 10208 PN GSS-341
PN 10209 at 13.5v
PN 10210
at 13.2v
Pressure GPH Amps GPH Amps
0 66 5.5 86 5.0
20 62 6.9 79 6.1
50 54 8.7 65 8.5
70 50 10.0 57 10.2
100 43 11.7 34 13.2
120 33 13.0 12 15.5
The performance of both of these pumps is excellent, and according to
David Henry's tests, they destroy the Cosmo pump. The only question in
many of your minds is probably quality. If you are one of these people,
just buy the Bosch and forget about it.
Also, the flows I quoted from David Henry (also, I have his testing method
if anyone wants to know more):
PSI Walbro Cosmo MKIV MKIII
---------------------------------------------
26 60.0 gph 61.6 gph 60.4 gph 40.1 gph
30 58.1 gph 57.5 gph 55.4 gph 35.6 gph
40 51.0 gph 48.4 gph 47.2 gph 26.3 gph
50 43.9 gph 38.0 gph 37.3 gph 16.7 gph
60 37.3 gph 28.0 gph 28.7 gph 8.0 gph
70 32.1 gph 16.6 gph 16.5 gph no test
80 20.9 gph dribbling dripping no test
85 dribbling no test no test no test
The flow shown for the Walbro pump is the GSS-315. The GSS-315 is the
same as the GSS-341, except the 341 flows more at high pressure. So, the
numbers shown above for the Walbro are actually on the LOW side. It should
be obvious that the Cosmo should only be used as a very mild upgrade. It
is also noteworthy that the MKIV Supra pump could be used in place of the
Cosmo pump, for those wanting to take that option. Chris Davis found a
dealer selling the Supra pump for $190 IIRC.
Many of you are probably wondering why the measured flow for the Walbro
pump is so much lower than the published numbers. The pressures measured for
these tests were at the pressure regulator, not at the pump outlet. This
suggests that the 3rd gen Supra fuel system has approximately a 20psi
pressure drop through the lines, fuel filter, etc. at working pressure.
If the pressure had been measured at the pump outlet, the fuel pressure might
have been 10psi or 20psi higher. My point is that measuring the flow of a
pump working against a fuel system will always give lower flow numbers
than the published numbers.
In reality, it is the flow at the injector rails that matters (which is
usually just before the pressure regulator), so the numbers measured by
David Henry would actually be better numbers to use when planning your
fuel system. If a pump will supply just enough pressure for your application
based on its published flow rates, then it probably won't be up to the
task in reality.
Wade
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