Originally Posted by DLSJ5
With the VT3, I've used twin Walbro's, Bosch 044's, etc. I had 2 Walbro 255's fail on me. The problem with using those pumps is you can have pickup issues, starvation issues, unless you use a serge tank, and you can't run your car below 1/4 of a tank or you will starve for fuel.
The OEM M3 pump coupled with a 335I pump is good for 850+WHP, plenty of fuel for his application. It's not as easy as dropping in a pump, or two pumps into the stock M3 tank, it's about proper pick up, transfer of fuel from the saddle type tank, and working transfer / siphon jets. The OEM M3 and 335I pumps, have mini surge tanks, "buckets", that keep the pumps submerged in fuel at all times, even when the fuel is almost on empty. Besides the pump differences and few other things at the top mounting points for lines, etc., the buckets are identical in size, and share the exact same shell and the sending units on the drivers side share identical parts, siphon jet, etc.
Both pumps have a venturi valve at the bottom of the bucket that constantly keeps it full of fuel, to make that work with an aftermarket pump is a lot of work and more apt for failure, leaks or issues. The M3 pump has an additional siphon jet on the side to keep the bucket full, then the return line goes to both pumps to keep the buckets over flowing with even more fuel.
The "transfer" siphon jet on the other side of the tank is now operated by the return fuel so you don't lose volume by using the feed pumps to activate it, the stock FPR, filter and smaller lines are bypassed as well and the stock feed line is used now as a return. All of this prevents starvation, overheating the pumps, and they both operate at 5bar which is what you need for the S65. Along with larger lines, modified fuel rails, 1:1 fpr it works quite well.
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