WHP limits of Walbro 255
Here's a good page on in-tank pumps:
http://www.stealth316.com/2-fuelpumpguide.htm
What's interesting here is that bench testing by RC Engineering and others show the Walbro GSS341 HP (255lph high pressure) to be able to flow enough fuel to support well over 600bhp at a boost pressure of 30psi.
Obviously, people here have reported lesser figures. This makes me wonder if the factory pump circuit is undersized for the power demand. Has anyone checked into this?
http://www.stealth316.com/2-fuelpumpguide.htm
What's interesting here is that bench testing by RC Engineering and others show the Walbro GSS341 HP (255lph high pressure) to be able to flow enough fuel to support well over 600bhp at a boost pressure of 30psi.
Obviously, people here have reported lesser figures. This makes me wonder if the factory pump circuit is undersized for the power demand. Has anyone checked into this?
Good link Ted. I also use this helpful link for info: http://www.roadraceengineering.com/f...pflowrates.htm and this one: http://www.roadraceengineering.com/e...elpumpinfo.htm and finally, this one: http://www.roadraceengineering.com/fuelpumptechtip.htm
I'm up to my elbows in this at the moment. The Walbro seemed on its last legs with my 539whp/492wtq. I hate to give up the cool dual voltage of our stock wiring to the fuel pump, but I've already run a 10gauge wire from my battery to my fuel pump. I haven't hooked it up yet, but I'm hoping to be able to run my pump with nearly one more volt. On low voltage output (at idle for example) it measured 10.6 volts. Under load, our cars' measure 13.4 volts at the pump. With my new wiring I should be able to get around 14.2 volts. I have an Aeromotive FPR, so I'm hoping this change won't enrichen my car at idle or during low load driving.
I'm planning on using a Supra TT denso pump with this system which should allow me to make the little bit more power I want (~575whp dynojet) safely. If I was going for broke, I would shell out for the big Aeromotive pump and all the related lines, fittings, and modifications.
I'm up to my elbows in this at the moment. The Walbro seemed on its last legs with my 539whp/492wtq. I hate to give up the cool dual voltage of our stock wiring to the fuel pump, but I've already run a 10gauge wire from my battery to my fuel pump. I haven't hooked it up yet, but I'm hoping to be able to run my pump with nearly one more volt. On low voltage output (at idle for example) it measured 10.6 volts. Under load, our cars' measure 13.4 volts at the pump. With my new wiring I should be able to get around 14.2 volts. I have an Aeromotive FPR, so I'm hoping this change won't enrichen my car at idle or during low load driving.
I'm planning on using a Supra TT denso pump with this system which should allow me to make the little bit more power I want (~575whp dynojet) safely. If I was going for broke, I would shell out for the big Aeromotive pump and all the related lines, fittings, and modifications.
Last edited by Smogrunner; May 16, 2006 at 07:13 AM.
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Thanks for the input guys. I ended up putting an in line external Walbro 255 in front of the fuel filter just before the entry to the fuel rail...works like a gem...car made 612 WHP with no drop in fuel pressure...
I really don't like describing the capacity of a fuel pump in terms of WHP and Track times. The former depends entirely on setup and tuning (how much power you extract from your air/fuel flow rate) and the latter depends on all that plus weight, suspension, track, driver, etc. Waaay too many variables. I prefer to describe a pumps capacity in terms of how much airflow it will support. If you are not on speed density, it's a no brainer, since we can measure mass flow, which compares directly to mass fuel flow according to AFR. What you are able to do with this air and fuel flow is up to you, as far as WHP or track times.
Assuming fuel specific gravity of .724 (sunoco 117), target AFR of 12:1, and boost of 30 psi and base of 43 psi, the 255 LP supports 57 lbs/min, and the 255HP supports 68 lbs/min. The 35r will do ~65 lbs/min for most poeple. The HP version should do much better. With a stroker the HP will work. With a 2 liter it will require more boost to reach that 65 lbs/min, and that will effectively make the pump smaller. It is risky, and I would only attempt a 255 with a 35r on a 2 liter while watching AFR closely, and if possible comparing it to target AFR. Or datalogging fuel pressure, or differential pressure. This is a quick page I tossed up a couple years back when this happened. But again this is on a 2.3, a 2.0 will be in worse shape with the 255. In my case the math and measured data lined up to within tenths of a lb/min.
I thought long and hard about what to do to improve the fuel system. I don't like the idea of inline/series pumps. It will hold a little better at high pressure, and flow doesn't improve dramatically as poeple expect it to. Some guys running in the 600 whp range have also expressed thier dissatisfaction with this setup. Parellel pumps make the most sense mathematically, but in reality they don't seem to work well. There is a lot of speculation why, but I haven't seen any hard evidence. Some poeple have been able to make this work well enough though at ~70 lbs/min airflow levels. Twin pumps with two feed lines on both ends of the rail with a center exit might do better with more fuel volume available to dampen the pulses, but I never tried it. The supra pump is a little bigger, but is not a true bolt in in most cases, and I've never heard of it used in an EVO. You can use a 255 as a lift pump to feed a Aeromotive A1000 or similar, but there are some funny things that go on. Fine for a WOT race car, but idle and cruise will cause some starvation of the A1000 and shorten it's life (people already have trouble getting that pump to last in street cars). One or two 255s feeding a low pressure swirl pot might keep a A1000 fed, but no one I know has tried this either. But enough of my rambling, just thinking out loud...
I never rebuilt the 2g, so I never got to try another fuel system. But I had decided on doing a fuel cell and race type external pump if the time came. This should be an easier choice in an EVO since it has a trunk, making the rules a little easier to follow. I think the ideal setup would be both the stock setup with a 255 in tank for pump gas use, and a fuel cell/race setup for the race gas, with 3 way valves to plumb in the one you want to use and a switch on the pumps. The only real drawback is that you have the weight of two full fuel systems. Not sure what that adds up to though, and I'm sure it beats a blown moder
But again, I'm just tossing ideas around. I ran a completely custom fuel system from the pump outlet back to the tank, but never went beyond the stock tank and drop in pumps, so take all of this for whatever it's worth. 
Assuming fuel specific gravity of .724 (sunoco 117), target AFR of 12:1, and boost of 30 psi and base of 43 psi, the 255 LP supports 57 lbs/min, and the 255HP supports 68 lbs/min. The 35r will do ~65 lbs/min for most poeple. The HP version should do much better. With a stroker the HP will work. With a 2 liter it will require more boost to reach that 65 lbs/min, and that will effectively make the pump smaller. It is risky, and I would only attempt a 255 with a 35r on a 2 liter while watching AFR closely, and if possible comparing it to target AFR. Or datalogging fuel pressure, or differential pressure. This is a quick page I tossed up a couple years back when this happened. But again this is on a 2.3, a 2.0 will be in worse shape with the 255. In my case the math and measured data lined up to within tenths of a lb/min.
I thought long and hard about what to do to improve the fuel system. I don't like the idea of inline/series pumps. It will hold a little better at high pressure, and flow doesn't improve dramatically as poeple expect it to. Some guys running in the 600 whp range have also expressed thier dissatisfaction with this setup. Parellel pumps make the most sense mathematically, but in reality they don't seem to work well. There is a lot of speculation why, but I haven't seen any hard evidence. Some poeple have been able to make this work well enough though at ~70 lbs/min airflow levels. Twin pumps with two feed lines on both ends of the rail with a center exit might do better with more fuel volume available to dampen the pulses, but I never tried it. The supra pump is a little bigger, but is not a true bolt in in most cases, and I've never heard of it used in an EVO. You can use a 255 as a lift pump to feed a Aeromotive A1000 or similar, but there are some funny things that go on. Fine for a WOT race car, but idle and cruise will cause some starvation of the A1000 and shorten it's life (people already have trouble getting that pump to last in street cars). One or two 255s feeding a low pressure swirl pot might keep a A1000 fed, but no one I know has tried this either. But enough of my rambling, just thinking out loud...
I never rebuilt the 2g, so I never got to try another fuel system. But I had decided on doing a fuel cell and race type external pump if the time came. This should be an easier choice in an EVO since it has a trunk, making the rules a little easier to follow. I think the ideal setup would be both the stock setup with a 255 in tank for pump gas use, and a fuel cell/race setup for the race gas, with 3 way valves to plumb in the one you want to use and a switch on the pumps. The only real drawback is that you have the weight of two full fuel systems. Not sure what that adds up to though, and I'm sure it beats a blown moder
But again, I'm just tossing ideas around. I ran a completely custom fuel system from the pump outlet back to the tank, but never went beyond the stock tank and drop in pumps, so take all of this for whatever it's worth.