This is what I arrive at, using a standard fuel calculator (e.g. https://deatschwerks.com/pages/fuel-pump-calculator but they're all the same)

450 crank hp with 55 psi requires 143 LPH, which is 39.72 grams per second. 143 LPH is 0.0397 liters per second. For 20 seconds of run time, with a fuel pump delivering exactly the amount of fuel that the injectors need, you would want a 0.8L surge tank. But, that 20 seconds runs the tank dry, IF you're only pulling out of the tank the fuel that you need for the injectors and no more.

However, keep in mind that unless you have the fuel return feeding back into the surge tank, what matters is the LPH that the high pressure pump will move at the regulator's pressure.

Since you're talking "low" power levels, a single high pressure pump would work. So, consider the following, with the pump mounted inside the surge tank:

http://www.radiumauto.com/FST-Fuel-S...dard-P515.aspx

With a single submerged Walbro GSS342, it will pump approximately 50 GPH (208 LPH) with the stock 928 fuel pressure regulator. 208 / 60 / 60 = 0.0578 Liters per Second. If you want 20 seconds, you need 1.156 Liters before it runs the tank dry.

The above single pump surge tank is 1.5L, which gives you 26 seconds before it runs dry. That's best case scenario, assuming you can get that last drop. Really, I wouldn't want the tank to drop below 50%. So, 13 seconds to be safe. The nice thing about this particular tank is they have a version for the Bosch 044, in case you prefer that pump. But, the 044 pumps more fuel, giving you even less time.

If you want more time at WOT with the fuel tank pickup uncovered, then this would work well. You would start with one pump inside the tank, and move up to two pumps if you drastically increase your horsepower in the future:

http://www.radiumauto.com/MPFST-Mult...ank-P1565.aspx

In the single pump configuration and a Walbro 342, you get 2.09L. Which is 36 seconds until dry, or 18 seconds until 50%. The larger tank also has an option for a fuel level switch. You could have it trigger a count down in the aftermarket ECU that will cut the fuel/ignition if time runs out. Or, just a light on the dash.


My point is, there are some really nice surge tanks that would be very easy to plumb, wire and mount. And give you a lot of time at WOT with the fuel pickup uncovered.

The stock high pressure fuel pump is positioned where you would normally place a lift pump. So, you can either treat the stock high pressure pump like a lift pump (not my preference), or replace it with another inline pump designed for low pressure. Mounted in the exactly same place where the stock high pressure pump was. Typically, lift pumps only need to deliver 50% of the fuel needed at WOT. Since you are not at WOT the majority of the time, the lower capacity lift pump is always more than enough to feed the high pressure pump. For those periods when you are at WOT, the surge tank provides the rest.

Feeding the engine bay fuel return back into the surge tank would definitely buy you more time at WOT, but I would worry about the fuel temperature in the surge tank. Not worth the risk in my personal opinion.

Anyway, interesting thought exercise. I'm wondering if the edge cases where the fuel pick up would be uncovered the way that I use my car would be worth it. Even if not, it sure would be cool

 

Although technically interesting as you correctly surmise the problem is not a practical concern for the most part. To expose the suction line you have to be pulling over 1G in a right hand bend and have the fuel tank with less than 20 litrees in it - possibly going uphill as well or so I found out the hard way in one of our autocross events- lesson quickly learned.

If there was ever a case that requires the in-tank pump I would have said it would be when using the 044 pump and felt that Jim was correct to deploy the stock unit in his build. However, given your exeprience if one does not need such for the 044 pump that can pump 250 litres per hour or whatever then for sure it is not needed for the 01 and 03 pumps. All these pumps are from the same type of design family best i can make out and all will be low NPSH pumps with a NPSHR of circa 3 ft. Howver that is more or less irrelevant and what matters is the vapour pressure of the fuel. In the States you really do not have an issue as Federal law demands that the RVP not be higher than 9 psia [as I last recall] and may be even lower these days. What this means is that the fuel has a considerable margin compared to atmospheric pressure and with 6 psi in the bag that amounts to the equivalent of 17 ft of head to play with. The suction line will only lose a foot or two of losses at most so even with the in-tank pump ommitted the NPSHA is going to be circa 15 ft when the NPSHR needed for secure operation is about 5 ft.

That your Federal specs are what they are is what makes all the difference but in other parts of the world the situation is way more difficult as the gap between RVP and atmospheric pressure is much tighter with as little as 2 psi or 6 feet in some countries and then it going to be marginal. You should see what happens in summer over here- open the fuel tank and the fumes can be over powering when filling the gas tank. On examples with the in tank pump the system gains an NPSHA improvement of about 2 ft. In the States that will make no difference but in places where the fuel is marginal it can make all the difference in the world. Therein [I suspect] is why Porsche re-introduced it.

So, regarding the original proposition about whether the in tank pump can be safely removed- in the States the answer most certainly is yes. Put another way, many owners have already deleted such years ago- if there was an issue their main fuel pumps would have been trashed by cavitational damage long since- never ever read about any list owner posting about such- not one!

On the other hand, the problem with the in-tank pump [besides cost] is that when they do go wrong once they stop working they become a "blockage" in the pipe to the main pump and that could easily induce cavitation. So, when working it is an enhancement of sorts but when not working it is probably a liability. Where these in-tank pumps get really interesting is when one strips them down- the impeller is a pissy little piece of plastic that looks as though it would not last 10 minutes- that they last as long as they seem to do do is quite amazing.

When it comes to the 02 and 03 pumps the only difference i have been able to determine is that the earlier one [02] has a design capacity of 140 litres per hour and the later one [03] about 150 litres per hour. Unfortunately it seems Bosch hide their data sheets for some weird reason but they appear to be from the same design series and thus will have similar characteristics unless they did something remarkably dumb and made a fuel pump with other than a low NPSH requirement and Porsche engineers were somehow dumb enough to deploy such because they had an in-tank pump- possible but not probable.

 

Thanks guys! you guys are amazing!