Smc Test Resultz

Chuck Leeper

Toxic old bastard
Staff member
May 28, 2001
Here's the numbers I've come with on the tests for PSI vs flow rates on the latest design
The setup:
13.5VDC stabilized voltage control
New SMC controller and pump.
Certified ga.
Denatured alky @ .809 SP R.
#15 nozzle.
10 sec timing.
3 repeats at each setting to get an average.

Motor speed PSI
5 - 35
6 - 38
7 - 42
8 - 47
9 - 57
9.5 - 60 [Knob would not go to a setting of 10]

I then ran the flow tests at the following settings

Motor Ml/10 sec oz/10sec [.0338 conversion]

5 96 3.24 35 psi
7.5 106 3.58 46 psi
10 [9.5] 120 4.06 60 psi

The pressure rise was taking approx 2+seconds before the PSI stabilized.
The time for flow to stop when the power was terminated was about the same, 2+ sec.
The nozzle has a good, conical pattern.

I think the time to stabilize the flow on startup is important when considering whatboost level the switch is set to. This will allow for max flow at each pump speed setting prior to getting into a boost level that could cause knok. [IE: turn it on sooner]
Now that the lower pump speed pressures are known, it would be easy to add a "NO FLOW" warning lite using a pressure switch in the feed line.

Good info, Chuck! In vehicle, we need to think about the effects of 20-25 (or more?!) psi boost working against those pressures, too, don't we? Remember our fuel pressure regs are "backed" by boost for a reason!
effects of boost

Jay, you are correct!! I had no way to put the boost to the nozzle.
The boost could further delay the press. rise. I'd think that the effect would be the same as on an injector.. Delta P is the total PSI in the fuel system minus the boost.. I'd guess it would be the same here too.
SOOOO... The PSI numbers I found would be reduced to the "Delta P" as above. IE: 60psi @ a setting of 10 would net a nozzle psi of 35. Thus looking at the flow at 35psi would tell us what the actual flow is @ that setting and boost level.
An interesting point. Could we"boost reference" the bottle? The first system Steve made had the bottle pressurized.
I could try that and put "boost" to the bottle w/ a regulated air source and see what the system would do.

Any engineering types have any input??
Not trying to reinvent the wheel.. Just better understand the variables in the system...:cool: :cool: :cool:
Do you know if the single nozzle kits Steve is selling now are still boost supplied like the first ones and the one I have or has he done away with that? Seems like you would loose a lot of output if the tank wasn't boost referenced.
I bought a plastic flow switch to add to my kit someday. Less than 1 psi. drop when working. Uses 1/4" NPT fittings and hopefully will withstand alky. and underhood temps.

I think it was about $40.

You could always get a professional stainless one for a couple hundred bucks that would work.

I have other pump issues to fix before I can test the flow switch with BSTC scaling out.

Mark, the boost referenced tank design was done away with some time back. ALL the current tanks should have a small vent hole in the cap. If anyone has a tank w/out the boost line to it, and there is not a vent hole in the cap, you should drill one. I drilled mine to about an 1/8th inch.

Is a #15 nozzle stock in the kit now? I have a #10 nozzle and the #15 is just too much for my Stealth (couldn't get the pump speed over halfway). With the pump speed maxed and a #10 nozzle it's MUCH quicker. I wonder what the line pressure would be with a #10 nozzle.