383, D1SC, 12lb, 60lb injectors, stock rail mount regulator
has ~ 35psi fuel now, pumps up to ~ 40psi at WOT - car is a monster!
but -
running single Walbro 255 w/hotwire now - can't keep pressure at WOT 12lb boost. will drop to 20psi and burp. Otherwise car runs mint - even pulling part throttle up to ~ 5lb boost.

adding a 2nd Walbro - if I run it together full time will volume/presssure be too much?

If I power the 2nd pump only during boost - will that work OK?

don't want to get into more money - just enough fuel on the top end

 

Most have the second pump come on with a hobbs switch at a set psi of boost rather than running both pumps all the time. As for the stock regulator, it will react appropriately with vacuum/boost but I would just pick up a nice aeromotive adjustable FPR to dial everything in since you have a solid boost setup.

 

Ditto..... I run dual pumps, but the second pump only comes on when the nitrous system is armed.

I personally have seen multiple failures of the Aeromotive LT1 AFPR. For some reason, as good as the Aeromotive products are, their LT1 unit has problems. There are numerous posts on this site complaining of failures.

I have a Weldon AFPR, and its been faultless, but it's not mounted on the rails like the stocker.

 

OK, pretty much as expected for answers - thank you.
I have to ask - because the set up is ready to swap in except a switch - what will happen if both pumps are on together?? I understand wear and potential heat build up that could be spared by using the 2nd pump only part time, but will both pumps actually change or hurt the cars ability to drive under no boost, cruising conditions?

I will have a switch and second hotwire installed - but would like to drop the twins in the tank powered by my already 10AGW wire, 40amp relay, fused alternator power wire - just to see if the added fuel corrects my stumble / pressure drop under WOT / boost.

Can I do that and add the Hobbs switch, second power wire after a couple of weeks - maybe 100 miles?

I also was considering using a toggle switch for me to power the 2nd pump when the hammer is gonna go down - way before boost comes on.
Anything adverse with that idea?

 

You can do that, but be aware that is too large a current draw for a single 10 gauge wire. Although I do not have the figures in front of me, I have done the math. Due to the length of the wire (unless you have a trunk mounted battery) you will have greater than the accepted 2% voltage drop over the length of the wire. Over time this will cause the pumps to overheat and eventually fail. But for a short, proof of concept run, you should be O.K.
You really want the capability of turning the second pump off. The extra fuel is pumped back into the tank, and those that claim to know the facts state this will cause the fuel to heat up, which would be a bad thing. IMHO a Hobbs switch is the best method for a FI system, as it automatically switches the second pump on and off. A toggle switch would be adequate, but you need to remember to turn it on and off as the situation requires.

 

this set up is how I am running so far with greatly improved engine pull at boost with the added pump / Hobbs switch - thanks for letting me know stock regulator would do it

 

update after full day driving - too much fuel now?
see thread: https://www.camaroz28.com/forums/sho...=815495&page=2

 

second pump will net you about a 7psi bump in rail pressure in my exp as it changes the ratio of supply vs return volume.
*this is on a twin feed line setup expect less bump on a single feed line system.

If you run both pumps all the time you can tune for the majority of that change in pressure via fuel injector constant.
Then fine tune from there.

If your on a pressure switch to engauge the second pump you will get an intuitive effect of enrichement as you enter boost in just the fuel pressure bump.

On a 2bar program a slight dent will exist in the VE table values were the second pump hits.

Hobbs 2nd pump + 2bar SD OL is the shizzle for boosted applications.

 

that all sounds reasonable - but Greek to me - I am no tuner

I know the tune was spot on but fell short of fuel volume up top once I got the car. Adding the 2nd pump via Hobbs did net a ~5-7psi increase at my gauge - but steady supply, no drop like on single pump.
Just that fuel 'hit' snuffed my top end response and ability to rpm as high as before = bogged the WOT

I have no tuners near me, no idea what type tune is in my PCM

I'm tempted to back off on the 2nd pump capacty until it just stabalizes volume from the primary pump. Ths might keep me in 'tune'.

Just thinking of ways to reduce the 2nd pump - 12v to 6v power reducer??

 

get a nice Wideband AFR gauge
get an adjustable fuel pressure regulator
professional assistance and a dyno may be needed...
adjust Fuel pressure referencing WOT AFR

 

found a tuner - yeah!! I'll see what he finds in my current tune before I throw parts at it.

Any chance the boost activated pump fuel increase can be tuned in without adding an aftermarket fuel pressure regulator?

 

yes, yes it can!

 

ok, just as more info for me: a turbo Buick guy told me my problem is not new, the 2nd pump is too much for my return line to handle thus confuses my tune by jolting up the pressure.
He said first and maybe only thing needed is open up the return line fitting at the regulator - a typical GM restriction point. Possibly need improve the entire return lines ability to flow the added fuel at max set psi.
Anyone vouch for / disclaim this theory?
Thinks if I allow the 2nd pump to add volume without such a spike in pressure, my 'sweet tune' with the single pump will still be sweet. I'll just have the volume I needed.
He was confident enough to bet the money I save by not needing tuning!!
Should I pay a mechanic to work on my return line or just pay for the tuning?

 

The return line will be a problem if you are running both pumps all the time and you will see higher fuel pressure because of this.

You should or do have a hobbs switch for the second pump to come on at WOT only so you should be OK.

It isn't a good idea to run both pumps all the time.

 

I do have Hobbs activated 2nd pump, but not OK
when activated, fuel pressure jumps about 7psi and flattens my tune.

I'm thinking my stock regulator is just not able to allow the return anymore - this car was dynoed, tuned and running before I got it - but has sat for a long time..