90 degree injector line fitting causing restriction?

I wouldn't think a fuel line under pressure with the restriction {jet} at the end could get bubbles.

 

I'm thinking a couple hard 90's on every line, and my junk could get to 8000HP! LOL!

 

Can you explain how air bubbles can be "produced" inside this captured enviroment?

I would like to learn.

Or how could one test this or calculate it?

Is it believeable that 275 psi in this 90° fitting with a .072" nozzle jet would create air bubbles?

 

Mike, do you think the same air bubbles could form with a #3 line being fed by a larger line, under pressure with a restriction at the end?

 

I agree with mike that a straight fitting will in some cases flow more than a drilled 90 deg fitting. But that will not cha he the fact that there are good reasons to use a 90 deg fitting ( looks, more room to adjust valves, and more built in slack if you pop the blower. Another plus is hat they are more durable and less prone to breaking when you tire shake. Top fuel cars run a close or drilled 90 on the back of the heads for their down nozzles. The 60 ton crane that I'm running right now has drilled fittings of at least an 20 feeding the winches. This is with a system pressure of over 2000 psi and it should be noted that ANY cavitation or air bubbles going to a 25000 dollar winch motor would be a very bad and potentially deadly thing. They , Terex/Demag , could have used any type of fittings they wanted ( there is a mix of fitting types all over the crane) but they chose a big drilled 90 to feed the winch motor. The bottom line is if you like the look of the drilled 90 deg fittings better than a straight fitting just put them on and run the car. If in doubt then send the system to a reputable shop and have it flowed with the fittings you chose.

 

I understand Kármán vortex street effect to be around a blunt object in the stream with flow on both sides. If it happen on a drilled hole then it would be on any jet also. Cavitation is caused by low pressure area that is lower than the fluids vapor pressure. You are not introducing air into the system but actually causing the alcohol to turn from liquid to vapor (boil). I see it like the pump is pulling a vacuum in one very small area because it can't feed the gears enough fuel fast enough. I believe in returning fuel to the inlet to help this also. Alway feed the pump with the biggest hose possible.

 

You will find some good answers on here....... But there is no shortage of shithouse scientists on here with differing points of view, me included, so read them all and pick the average. LOL Like picking which quote on some work you want done to use. Throw away the cheapest and the highest and choose from what's left. Canter is almost always correct , he will not post up some bullshit that will bust your motor, but there are a hundred diff ways to tune an alcohol car and still get it to run well.

 

Pump mod changes the inlet to feed fuel to both sides of the gear. On the flow bench it will still cavitate, just at a higher rpm that hopefully you don't see. Returning fuel to the inlet lowers the amount that has to be drawn from the tank inlet. If tank is higher than pump and close, there is less chance of cavitation. Problems when tank is lower than pump with long inlet hose. Just my shithouse observations if anyone cares. LOL

 

I think this horse is about dead, but will add a little. The pump stand that we had was originally build for a manufactuer of fuel injection parts, pumps etc. It had 3 flow meters in ranges from very big, 50 gal, down to less than one. We tested a lot of things like flow loss through barrel valves, jet holders, etc. We tested the exact question about flow through fittings. The setup was a .070" Enderle port jet flowing 150 psi. The flow was just over 1 gpm and with straight fittings, or 1 and 2 90 dgree there was absolutely no measureable difference. We also tested another question that comes up here often, the size of tank vents. At 14 gpm, we could find no change in flow until going from a #8 to a #6. Also never saw any reason not to return fuel to inlet side of pump.

All of these things would change if any of the parts were maxxed out, such as pump barely big enough, really high pressures, flowing really large jets, etc. The "happy spot" always seems to be a pump looping back 2-4 gals, pressures 100-150, jets in mid range. Most important, if you get the car in a good tuning range, never change fittings, etc. Jet to maintain the fuel pressure.

 

Very good info 481. Thanks

 

Cavitation occurs when local pressure drops below the vapor pressure of the fluid.
It causes a vapour bubble that then collapses almost immediately.
It can occur in our fuel pumps at high RPM, also boat props, etc.

As others have said, if the restrictor after the 90 degree fitting (the nozzle) is smaller than the ID of the fitting, then the pressure before the nozzle should be maintained and I really doubt that cavitation is occurring there. The fact that the fuel is already under pressure makes cavitation a lot less likely
I can't remember the ID of the 90s but will check.

We changed from straight to Enderle 90 degree fittings after Enderle assured us they flow as good or better than the straights.

No change in tune up or performance for us.

This, and what aj481x has said, makes me happy with the setup.. although if I'd known that radiused fittings are available I would have gone with them.

IMO, a 90 back into the pump inlet is a similar situation.. if the flow has been restricted through a jet (main jet or pump loop), then the velocity of fluid through the fitting is going to be pretty low and it won't really care about a 90 degree turn.

 

Concerning the back to the pump thing.
It's kind of hit and miss and depends on the combo. I run into it occasionally and it flat vibrates the flow bench. For my sportsman racers we just go back to the tank via a return collection block. It's easier than trying to diagnose it later.

It's been a decade or 2 and I have forgotten the results. I need to do another back to back to see the difference in the back pressure to the check valves between back to the pump versus to the tank. The question would be does the incoming fuel back up the returning fuel and/or does the returning fuel interrupt the flow to the pump or both.

The big thing for me in returning to the pump is that the fuel heats up quicker.
You wouldn't think that in the short time span these engines run that returning to the pump would be a problem but factor in the burnout and other run time it can change. This has to be considered when one is being fussy about their tune up. It's one of those "pick your battle" things. On a side note, I sat in the stands at Indy 1 year and timed the alcohol cars run time from start to finish. 3-4 minutes on average when there were no delays or burn down wars.

Even returning a foot before the pump seems to work fine.
When I have fabbed up something for the 1 foot or more scenario the fitting is angled back toward the pump as opposed to being 90 degrees to the fluid flow.

Dave Koehler
http://www.koehlerinjection.com

 

Here is some food for thought...Hat and port blocks are drilled 90* fittings, should they all be reengineered ?
If the volume and flow rate going through the system is greater than the the requirements at the orfice there is no issue.
Just my opinion

 

What They Want To Hear

Well said, Will. A lot of different opinions out there.