Pump sizer loop

Can anyone explain the pump sizer loop circuit for me? I understand it will allow me to get rid of a little fuel but trying to wrap my head around how the jet size works in conjunction with the main pill size.
Is the sizer loop the same thing as a hi speed mechanical lean out with just a lower PSI setting on the poppet?

We just upgraded the blower and Injector and added a riser on our setup with Hammer, the additional boost from where we were at looks like we will run out of pump as it would stick us around a .065 pill on are average day of 1500"DA. The old pump is a 990 @15.5 and now Rage suggested going to a pump at 18gpm but he says we will need to add the sizer loop to get rid of a little fuel.

 

If you are running out of pump with 15 and going to a 18 It would seem all you need is proper jetting. If you need the pump sizer it would seem you should stay where you are at. I
If my deal I would just lean it in the main and/or main and hi spd. combined.

 

If you want to call it something other than a pump sizer call it a low speed. Pressure to be set above your idle pressure so it comes on quick.
Rage will probably have a good guess as to the jet size to knock it down from 18 to say 17 and so on.

 

Basically a pump sizer is a secondary main jet looping (bypassing) fuel back at the pump itself. It allows you to run a pump that is larger than what you need. It will allow you to add improvements that will require more fuel without having to go to a new pump. It also helps by allowing you to keep your pump the same as it wears over time without having to change your tuneup main jet which you use for a given weather condition. On the big show car, we have 2 fuel pumps, one is slightly larger than the other. we use a main jet (pump loop) to balance the higher down to the flow of the lower gpm pump. Thus if we need to change pumps for any reason, the backup pump will perform exactly as the main pump. It sounds as though Rage has recommended a pump that is slightly larger than what you need with the improvements you are making. If you make more improvements requiring more fuel, there will be no need to get a larger pump.

 

Yes, Mike at Rage said he would probably make the pump for 18 gpm and loop 1 gpm out of it i believe he said after going through my original setup and where we will be now with upgrades.. Then, when we have one of our great air days of negative -500DA (which does happen at are local track) will still have extra fuel if we need. This is a 540 billet solid block and head BBC deal in a promod car. I am just confused on how to figure the jet size for the loop that gets me back to that .075 - .100 pill size for the main, but as mentioned above I am sure Rage will get me squared away close once he gets the new pump finished.

 

The pump sizer and the main operate in parallel. So basically you would have to take your total area and split it up. So basically, let’s say you have .100 in the main and your software calls for a negative jet. Let’s say it’s a negative .020 you’d take the area of that and subtract it from the area of the jet in the loop. This would be your new jet for the sizer with a blank in the main. Some people like to keep a certain size in the main, in that case you would do basically the same thing but remove it from the loop and keep .xxx in the main. All a matter of personal preference. Just make sure you calculate off of jet AREA when making changes, this includes if you do any “nozzling” in the ports.

 

I get what RB is saying but that’s sort of confusing to read.

pi*r^2 of the main plus pi*r^2 of the sizer = total area

equivalent main size = sqrt(total area/pi)

setup a spreadsheet and you’ll see all your options for pump sizer vs main size to get the same total area.

I have found 2 reasons to possibly not open the pump sizer check right off idle:

1. you don’t want to hit the sizer while opening the Lean out to warm the car up. Makes it too hard to control the lean out lever.

2. if the sizer jet is very large you want the sizer check to be higher to prevent a lean spot while going on the converter. Not an issue when only sizing out 1 gpm like you are planning.

 

There is jet diameter to area charts available online. If you have to crank your shutoff to lean the engine to get some heat in it, you likely milk the oil and in my opinion you don’t have your barrel valve set correctly.

 

Thanks for all the help with this, I think i am starting to understand the math. Let me know if this sounds correct or not.
Lets say the tune required a .090 jet (without a pump sizer) which equals .0063617 area then if we added the loop with a .050 jet which is .0019635 I would need to change the main jet to a .075 which is .0044179. If I add the area .050 and .075 area together gets me back real close to the same area as the .090 jet with .0063814.

Am i on the right track?

 

I didn’t check your math, but ya, that looks right

 

Very helpful thread... I just switched to a larger pump and sizer at the end of the season. My advisor gave me the initial set up and suggested jet changes but not the theory. Now I know. Did a test tonight on my Alkypro as Mike C. mentioned previously and the numbers worked. Thanks again!

 

All my blower combos lean out as they warm up. I don’t want to get hung out sitting behind the stage beam overheating if I have the bv set just perfect. I do have a click adjust so will have the crew chief add a couple clicks of the guy is really screwing around.

ive never heard of a serious blower combo that didn’t milk the oil? The only way around it is a cooling system and Ive never had one of those on a blower car