I have run a Supra TT pump for a while now with no problems, but the last time I was on the dyno and made the power in my sig (421 rwhp), Steve mentioned that my fuel pump seemed to be on the edge and was running out of steam. My peak fuel pressure has been hovering around 4 bar, or 58 psi.

I used max's fuel calculator page, found here:

http://www.maxcooper.com/rx7/how-to/...tem/calcs.html

to determine that my fuel injectors (850s/1300s) with a 0.60 BFSC (I chose this based on the ported motor and unpgraded turbos) will support 473 rwhp at 85% injector duty cycle. No problem there, these turbos won't get me that high.

Now to the fuel pump. According to the chart at the bottom of that page, I need a pump that will flow 56 g/hr at 70 psi fuel px (15 psi boost pressure) and at 75 psi fuel px (20 psi boost px). Max gets the fuel px by adding baseline fuel px (40 psi) plus the pressure drop through the filter and lines (15 psi) plus your boost pressure.

By looking at this page:

http://www.stealth316.com/images/flo...ensowalbro.gif

[note that 1 gallon equals 3.785 liters]

I know that the Supra TT pump flows about 220 L/hr (58 g/hr) at 70 psi and 13.5V, and 200 L/hr (50 g/hr) at 75 psi and 13.5V.

I'll also include the Walbro GSS341 at 13.5V: 224 L/hr (59 h/hr) at 70 psi and 218 L/hr (58 g/hr) at 75 psi.

Keep in mind the above flows are at 13.5Vs, not the 12V peak that the pump sees with the stock wiring.

Looking at this it would appear that the Supra pump is adequate for my setup up to 15 psi boost pressure but it's efficiency falls off sharply between 15 psi and 20 psi. Not what I am looking for, as I want to push my BNRs as high as 20 psi.

The Walbro appears it might get the job done, but those figures are listed at 13.5Vs, which would be correct when the fuel pump is hotwired to the battery.

I am not 100% sure that I want to overly complicate my fuel system wiring by doing this, plus I want a safety margin with my fuel system, not one that is barely adequate. I looked for a pump that will support my fuel flow requirements with the stock wiring, and came upon this:

http://www.maxcooper.com/rx7/parts_i...exi_bnr32.html

This Apexi BNR32 pump flows over 72 g/hr at 70 psi and 67 g/hr at 75 psi, at 13.2 volts. This is more than enough flow for my setup, and factoring in a loss for the drop from 13.2 to 12 volts still leaves me more than enough room.

I ended up getting a deal on this pump through Fritz Flynn (who by the way shipped promptly and packed very well) and installed it. It came on the stock tree and ready to drop in, but it doesnt look much more difficult to install than the stock or supra pump. As I understand it, this pump is used in Japan as an upgrade for the Skyline GTR, and is one of the highest flowing intank (read:quiet) pumps you will find. I have read that SR Motorsports performs a slight modification to the pump so that it can use the stock sock filter.

The best prices I have seen on this pump brand new are at my shop Gotham Racing and also at rx7store, both at $399. Quite a bit more expensive than a Walbro (or two walbros for that matter) but the piece of mind and ease of install made the choice easy for me.

I'm pretty happy with my current fuel system---it is nice and simple (uses the stock rails, lines, regulator, and pulsation dampener) yet safely flows enough to allow me to basically double stock power output.

I hope all of this proves useful to some of you, I am sure many of us are running similar boost/power levels because I have just about reached (in my opinion) the 'safe' upper limit for street car/pump gas FD setups.

Edit: After making some 2nd and 3rd gear pulls, as I predicted I will need to take out some fuel. After 6500 rpms the AFRs dropped towards 10.0:1 and the car started to stumble. I guess that's what happens when you switch to a pump that flows 25% more

 

Good stuff!

Really, upping the voltage to the stock fuel pump shouldn't be that terribly bad, and you can use the stock fuel pump resistor to keep the 9v/12v operation. I've done it on MANY FC's with great results. Even just running a fused wire straight from the battery to the input for the fuel pump resistor relay would likely net much better voltage.

On my old FC with a very healthy starting/charging system, I would see as low as 11v to the fuel pump with a full load on the car - AC, headlights, stereo, etc. That's way not cool, and also means you get inconsistent voltage to the pump depending on electrical load. I haven't tested the FD's system myself, but I've heard reports that the result was similar.

Anyhow, good stuff! Be interesting to see if your numbers change when you tune in for the new fuel pump!

Dale

 

I have never seen you write so much at once. You're really getting into this project! The only way the pump could make the car run rich is by increasing the fuel pressure. You have a pressure gauge installed, what is it telling you? What is your pressure under boost after factoring in MAP (which I believe your gauge does)?

 

Or, if the car was tuned with diminishing top end fuel pressure and the duty cycle was richened up to compensate.

Dale

 

You have too much free time in your hands. If you're as enthusiastic with your car as you were with your job, I bet you'll be a millionaire by now.

To answer Chris's comment, if your fuel pressure drops at higher rpm, you can compensated it by adding more duty cycle/inj time to offset the pressure drop (eventhough, it is not ideal but it is predictable since the flow rate is a linear function). Once the fuel pressure drop problem is fix, the a/f ratio will go richer because the duty cycle was setup to include the pressure drop.

It is very common for this to happen in the FD and I always tell customers when I was tuning their car that there's a fuel pressure issue. Every car is different and fuel pressure drops at different rate. The only two cars I know that never had fuel pressure issue were max cooper's car and Lupe's car. All of the others have issues one way or another initially.

 

Just to clarify, I think he should make sure he is seeing different fuel pressure with the new pump before attributing the change to the pump as his car was previously running pig rich under certain conditions due to the temp correction.

 

Interesting, and nicely summarized. Thanks for the info Rich. If I ever get into upgrading my fuel system, I'll probably start here for an example.

Dave

 

Pretty sure this is the case. My peak fuel pressure is the same, right around 4 bar.

 

In your first post you said your car was running rich after installing the pump. You just said the fuel pressure is the same. So why do you think the pump is causing it to run rich?

 

he sasid it peaked at 4 bar, not that it held steady at 4 bar till redline

 

No problem Dave, glad you found it useful. I enjoy posting up my findings in order to help out future forum users

One other thing that makes this pump a great upgrade for me---Now my peak fuel injector duty cycles (once properly tuned) will be below 85%, which will allow me/my tuner to control the fuel injectors. As per Max's site, after 85% you are beyond the controllable limit and basically wide-open.

Rich

 

^ how many lbs of boost thave you run and still stayed under 85% duty? It says you want to push 15 - 20lbs but have you done 20lbs yet? I also have 850/1300's (w/Sard FPR) and a Nismo Skyline R34 pump whic is most likely the same thing as Apexi's Skyline pump.

 

If I remember correctly, on a recent third gear pull at 16 psi my peak injector duty was around 84%, AFRs in the low 11s. It seems like Max's calculator isn't working too well for my setup in it's current state of tune, lol.

 

D'oh!

 

Wow, that sucks. I originally hoped for 15 & 25lb tunes but after my calculations I figured i'd max (85%) at 20lbs. Max's calculator must be using P' Bush Jr.'s fuzzy math "lol".

 

how does the Cosmo pump stack up? is that the same as the Supra pump?

 

i run 850/1600 injectors to 87% duty cycle w a cosmo-supra pump w no problem.

instead of getting a huge noisy pump that constantly recycles/warms my gas i opted for a Kenne Bell Boost A Pump (BAP). $200.00

as i go into boost the BAP sends a user adjustable zero to 50% increase of voltage to my pump. i am currently running plus 20%. i have had it for 2 years. no problems.

i digitally log my fuel pressure thru my datalogit so i KNOW i have no pressure issues.

the module and adj dial sit near my battery in the pass side compartment. the solenoid is under the hood and sends an electronic signal to the module.

they have an excellent tech-rich site and have been making the unit for 30 plus years.

howard coleman

 

If anything, I think it might flow less.

Howard, that boost-a-pump looks pretty damn cool. Seems like a good solution for those whose nippondenso/cosmo/supra pumps aren't performing properly. Also, just to clear things up, my apexi bnr fuel pump is as quiet as a stock pump

 

This thread is GREAT! thanks for all the info guys.

 

Lol, your avatar pic with you giving the 2 thumbs up goes perfectly with your comment

 

that was an hour after i got the car... i was and somwhat still am in heaven... ive spent a lot of time and energy in life just to have it all fall apart in my face and this represent my revenge. short version regarding the car is that i owned an FD for a day before i realized that my now ex had sent all the money out of the account and i had to give it up cause i didnt want the payments at the time.

also the very first 3rd gen i ever saw was a SSM r2 and i was immediately in love and it was next to a 69 camaro SS. they took off from a light and i was mexmerized at the two cars, one my ex fav and one my new fav. im a car nut! actually i think i my just be plain nutz!! lol.

 

what would this forum do without howard?

(except for the hood louvers)

 

I'd like to see this thread in the archives. Dave, Tyler, what do you think?