View Full Version : Bosch fuel pump plubing ???'s
06-30-2005, 02:30 PM
Ok Charley and Kurt I have my two new Bosch fuel pumps. They have a check valve on them to restrict backfeed after the car is turned off. It seems like that might be very restrictive. Should I ditch it or run them. I am still rounding up my wastegates etc for the turbo setup so i just want to install one pump to prove to myself i'ver cured the problem. Plus if it evers quits raining here I might drive my car while I'm waiting on parts for the turbos. Anyhow It has -8an hose feeding the pump and into the regulator which I plan to mount low on the firewall. And it has -6an return. Some guys are telling me to run -10an & -8an return for the turbos. Should I change it for the turbo setup then? I am setting up up to run a mild low boost setup 850hp goal but dont want to choke the fuel system. I am using the new fast controller since Rob @ Force could not get much response from Big Stuff. I like the idea of the new 02 sensor on the fast and Rod seemed to think that was a good system for me needs. I'll let you know how it works out.
06-30-2005, 03:36 PM
Restriction on the inlet side of the pump is a bad thing.
Personally, I'd run -10 from the tank to coarser pre-filters and -10 from the pre-filters to the pumps, then -8 out of the pumps to the regulator, then -6 or -8 from the regulator back to the tank. Run the return line the same size as the feed if you want to play it totally safe. I'd also put a fine fuel filter just before the fuel rails to keep junk out of the injectors (or carb.)
Are you going to run the 2nd pump off a Hobbs switch? If so, I would "tee" two Hobbs switches together for redundancy, so if one fails the other one will still turn the 2nd pump on.
06-30-2005, 08:29 PM
yes Troy I plan to activate second pump with hobbs switch. I never thought of running two hobbs switches though but better safe than sorry. I wasnt sure about the hose sizes since the pump inlet is about -8 and outlet is -6 size not sure what type threads these pumps use they shop i bought them from said the threads were metric but he had no fittings. I left the pump on my desk at the shop but i have loads of fitting in the garage so i'll check with an fittings first if they are metric i dont know where to look for fittings.
Ya the check valve makes me nervous looks very restrictive. I was hoping Charley or Kurt would be able to tell me what they did on the mule. Id feel better not running the check valve though.
06-30-2005, 09:19 PM
If you're worried about the check valves causing a problem, you should flow check the fuel system after you install it (ALWAYS a good idea, you may have a weak pump out of the box.) Here's how: turn the pump on and adjust the regulator to the highest pressure you'll see under boost, or even a little more to be safe since volume will decrease with increased pressure. Then disconnect the return line from the regulator and have it dump into a bucket. Run the pump for a given amount of time then shut it off, and weigh the fuel that's been collected in the bucket. Based on the time the pump ran and the weight, convert to lbs/hr and see if you are moving enough volume to feed your engine. In your case, figure 850 hp at .65 lb/hp/hr BSFC, and you'll need about 553 lbs/hr of fuel flow to support it minimum. I like safety margins, so I'd want at least 600 lbs/hr of fuel flow, which will support 923 hp @ a .65 BSFC.
On my car I was getting close to the limits of my single SX pump (only had about 20 lbs/hr margin at WOT after flow checking it) so I got a Kenne Bell volt booster and rigged it to two Hobbs switches set to 5psi. When the engine sees 5psi of boost the volt booster kicks on and bumps the fuel pump to 16.5 volts which gives the pump over 100 lbs/hr extra flow than at 14.2 volts (normal voltage with the engine running.) Plenty of safety net for me, and easier than adding a second pump in my case.
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