One, single, hot-wired WALBRO will almost supply enough volume on E85 for a Green. You shouldn't need the second pump kicking in below 10-12# of boost. You don't want the second pump activating in the middle of a corner.

Depending on your driving style, you probably won't be seeing over 12# in the corners. At least not until corner exit. Me I would want the secondary pump activating when I see the straightaway at the earliest.

A double pumper is almost overkill for a Green even on E85. I did a search and a lot of guys get away with a single hot-wired Wally on E85 with a Green at least they don't start to run out of fuel until about 30#. So, my guess is that you won't need the second pump till well up over 15#.

I wouldn't want the second pump kicking in at low boost, low rev situations, especially in the middle of a corner. If you try to get it to come on at low boost situations when you are feathering the throttle and boost levels are oscillating. This would cause the second pump to oscillate on and off in the middle of the corner. You want the second pump to activate only under WOT conditions.

So, 10-12# is the earliest IMO. 10-12# won't usually happen in the middle of a corner, it'll happen when you are exiting the corner and have already gone WOT.

 

As a practical matter how do you plan to monitor the secondary pumps activation point? The Hobbes switch is adjustable but you are going to need a way to determine at what boost level it is activating when you start to adjust it. So, you need some sort of telltale light, etc.

Nowadays with zeitronix and similar devices you could monitor the activation point that way. In the old days, and all you really need is a little LED wired off the output wire of the hobbes switch. You can drill a tiny hole next to the boost gauge in the pod. That way the telltale light goes on when the Hobbes switch makes a circuit. You place the LED right next to the bezel of your boost gauge.

 

Thats what I was going to do with the LED light, or I was going to have it activated via dsmlink and base it off of RPM, load, tps, etc. but I think Ill just do it off of a hobbs switch, switch it close to the psi I need it, and see what my logs/tune looks like. Easy enough to see when it kicks in off of that.

 

FYI Im on an FP black, Ill probably run it at wategate pressure at the road race track (25psi) but I need something that will work well at the drag strip also when Im running high boost (34-36psi)

Thank you