Fuel System Primer

[andreleroy]

I can approach this from a fuel system management perspective, but if you were to ask me exactly what whp level requires what, I can only make suggestions. We have written a few tech articles on the subject found here: http://www.wolfkatz.com/articles.php

But another good place to look is our MR2 FAQ found here: http://www.wolfkatz.com/MR2FuelFAQ.php

The basics work like this:
--- When you demand more fuel than the stock injectors can put out (you can raise your base fuel pressure with an adjustable FPR to get a bit more out of them), then you will need to start changing things around. This seems to happen at about 250 ish whp for most folks...some earlier.

---The most common first step is to go up to a 550 cc/min Supra Mk IV injector which can get you over the 300 whp mark, but not too much farther. (Generally speaking this is the way to go for turbos sized similarly to the CT27 from ATS racing or maybe a T3/T4 or TD06 with stock cams and relative mild boost (IE these turbos on a completely stock engine). This will require a few additional things to be completely safe.
- Some sort of tuning device will be needed. I.E. a piggy back system (AFC or Emanage), Rom Tune (ATS is your best bet), or a stand alone (Nemisis, AEM, Motec...). Without this, your car will not run properly.
- Also of extreme importance is going to be replacing the Fuel Pump. The Stock 3S-GTE Turbo pump runs out of steam around 15 psi of boost with a stock base pressure and the 550s held wide open. If you are going to safely use these injectors, you need to go up to a pump like the Supra MkIV pump ($230 from the dealer) or a Walbro GS 341 with an MR2 specific install Kit (~$130). Both work well, the Supra pump is a bit quieter.
- However, as shown in the tech articles above, the stock fuel rail cannot support the increased flow of larger pump. A large pressure drop across the rail is now present thus you engine is not receiving even fueling from cylinder to cylinder (bad). Thus, an upgraded side feed rail is needed. We offer a Billet side feed rail (WolfKatz Side Feed Fuel Rail), ATS offers a bored out stock rail, and there are other options as well (If you have a Gen III rail, it is already improved and will work fine with the largest side feed injectors available (it WILL NOT fit a Gen II can cannot be made to fit so don't waste your time!).
- A Supra or Walbro pump can be run with your stock regulator or the various aftermarket or modified regulators available. If you choose to run the stock regulator, it is recommend that you leave the stock fuel pump resistor pack in place as this will slow the pump down at lower fuel loads.
- The stock supply and return lines can safely support a Supra or Walbro pump.

--- When your power goals go up above the 300 whp mark. For example, a T3/T4 or TD06 sized turbo with cams or any of the various strokers around. Engines that will run higher boost levels with cams and or other head are most definitely in this group. Now, larger injectors are needed. The largest injectors that either of the above mentioned pumps can safely support are those around the 850-880 cc/min range. Thus, there is really no reason to buy smaller ones. These injectors will get you to around 450 whp on our cars give or take a bit.
- There are two options from a packaging point of view to make this work, both with similar costs but different advantages. If you already have a modified side feed fuel rail you can buy the SARD 800 cc/min injectors. These are drop in injectors similar to the Supra 550's, but they can be very difficult to get your hands on (8 week lead times are the norm).
- The second option (preferable option in my mind if you have larger power goals or have not bought a modified rail is to buy a Top Feed Rail, standard domestic top feed injectors (we like the Delphi's as they are easy to get, but there are many others like RC, Bosch, Siemens Deka...) and new electrical clips for the injectors. These rails can support injectors up to 1600 cc/min (good luck getting these to idle or run below 2k rpm) and thus power levels up to around 800 whp. Top Feed Rails are available from various sources (us, Hux, and others). Be sure you get a complete system as many of the rails are not compatible with the stock supply line, return line, and FPR (for example, the WolfKatz TFFR's (Gen II and Gen III) are adaptable to work with the stock supply, return, FPR, and include -10 fittings for those who want to run larger lines).
- A nice setup for folks with the T3/T4, TD06, or similar sized turbo and the quickly becoming coming standard stroker with cams, head work, and improved intake manifold is a Top Feed Rail, 84 lb/hr (~870 cc/min) low impedance top feed injectors, and the clips. Some folks opt to add an aftermarket FPR like the Aeromotive 13109 or others to complete the package (I run a personal car this way). With this setup you can run the stock supply line and a good stock fuel filter with your Supra or Walbro pump.
- Be sure to get your hands on a stand alone EMS for this level system.

--- If the power goals push north of 450 whp, drastic measures are now needed. Lets talk about injectors first. 1000 cc/min (96lb/hr) injectors will get you to around 550 whp, maybe a bit more and are the same price as the 84 lb/hr (~870 cc/min) discussed above. However, if you have a really modified car that has say a GT35R, head work, stroker, big manifolds...the works, you will possibly need more than the 1000's. Until recently, we had not found a good answer to this problem as the 1600's really run poorly. However, now we can offer for a bit more money an 1150 cc/min injector that seems to work out very nice. This will get to a bit higher number, and still manage to idle.
- However, a single Walbro or Supra pump will not keep up. Various things have been tried including Dual Walbro pumps or a larger Aeromotive or Weldon pump. I prefer the larger single pump to running two pumps in parallel. That way if you have a problem, you will know about it and not just run out of fuel leading to a blown engine.
- When you go to this kind of pump, you now have to upgrade all supply lines (-10 is a good size), return lines, and run an even larger FPR (the aeromotive 13101 is the smallest I would try). You will also need some sort of improved tank pickup or a custom fuel cell in the front trunk. We make a custom tank pickup that re-uses the stock tank (well, we make a full system with a larger Aeromotive pump, filters, reg and so on ...), but I can see the weight distribution advantages of having a cell in the front trunk. For track driven cars, I feel using the stock tank an its baffle with a modified pickup is sufficient, for a pure drag car, moving the weight forward is helpful but could upset your balance as a track session wore on.
- In any case, a Top Feed Rail is now a requirement. In extreme cases, I have seen folks go to twin top feed rails an a now very custom intake manifold, staged injection control in the EMS, even more custom plumbing, and careful tuning. This requires a lot more work and with the new availability of the 1150's, is not as necessary as it once may have been. Later today I will post up a few plots.

[andreleroy]

Here is the chart showing the various fuel pump curves and the injector curves. The way to use it is as follows. Travel along from left to right on a fuel pump curve. Find the point where the pump curve crossed a given injector size curve. This is the point of maximum output and thus the x axis of the graph gives the maximum fuel pressure for that point. For example, if you follow the MR2 3S-GTE pump along till it hits the 550 cc/min injector line, you look down and find yourself at ~60 psi, or about 15-18 psi above the normal base fuel pressure of 42-45 psi. Thus, because the regulators raise fuel pressure at a 1 to 1 ratio with boost pressure, you can not safely run much more than 15 psi in a perfect world. Remember, these are lab tests, your pump could be a bit weaker or you may have a bit of pressure drop in your supply line so these numbers are not leaving any margin.

[andreleroy]

Here is the plot showing our pressure drop test data from various rails, pressures, and injectors. The areas in red are definitely a problem IMHO.




Garrett and Julie

[5FistsoftheNorthStar]

Wow this is awesome. I only understand so much, but it definitely helps alot. Thanks for finally coming up with this.

[Weasy2k]

There is more in the EFI corner too Thanks for the input!

[Sang]

Originally Posted by MR. 2Lanes

Wow this is awesome. I only understand so much, but it definitely helps alot. Thanks for finally coming up with this.

All testing and verification was done by Garret and Julie from Wolfkatz.com

their most recent test (thanks to justin scremin) was with a intank walbro/supra in conjunction with a inline pump.

[Weasy2k]

you can download the PDF file with graphs on the wolfkatz website thats where i learned alot on the 3s fuel system