*UPDate*So...lets talk about precision 96# injectors...

[fastblackracing]

So after we went to the track 2 weeks ago and had a successful day we did the normal after race maintenance on the car and then the next good night we had we started to turn up the boost and re tune for the higher boost and the car goes from seemingly all good at 30 to all bad at 32....... Plugs, coil pack,module,wires, fuel pumps etc... are all good and verified to make sure......turns out my son has a friend who has an injector flow bench-machine. So we take the injectors up to have them flowed, and we find out that between 80 and 84 pounds fuel pressure 3 of the injectors basically just shut off...now these are the precision 96 # injectors that alot of you guys run. These were bought new by me and have maybe 500 miles on them and only fed c16 fuel from a sealed drum that we bought. Are they just a bad set or do they not work at higher pressures? Any one have issues with there 96's? Im very glad we caught this before we lost the engine.​

 

[Chuck Leeper]

The injector machine does not take boost into consideration. Therefore, the nozzle end of the inj does not see 32psi.
43 base, + 32 on the reg = 75# fp. Boost working on the nozzle end "counters" the pressure rise, {32}, created by boost on the reg. Therefore: 43+32-32 = 43. Now the injector is working in a 43psi environment.
BTW, I've seen this frequently on the Delphi inj designs....

 

[pacecarta]

id agree with you chuck but id be wrong
on his test at 80 psi rail pressure in atmosphere the injector was unable to lift and flow
i agree in boosted condition when open the injector is seeing 80psi FP less the boost pressure trying to come in so flow stays constant at base 43psi fuel pressure
when the injector is closed the pressure in the rail is what it is, the boost pressure cant help unseat the needle
if the injector wont open with 80 psi on the bench it wont open in a boosted enviornment

does the bench cleaner test at 13.5volts

 

[turbobitt]

The differential pressure is all that matters.
AG.

 

[Chuck Leeper]

id agree with you chuck but id be wrong
on his test at 80 psi rail pressure in atmosphere the injector was unable to lift and flow
i agree in boosted condition when open the injector is seeing 80psi FP less the boost pressure trying to come in so flow stays constant at base 43psi fuel pressure
when the injector is closed the pressure in the rail is what it is, the boost pressure cant help unseat the needle
if the injector wont open with 80 psi on the bench it wont open in a boosted enviornment

does the bench cleaner test at 13.5volts

The inj does not rely on boost to open it. The application of voltage to the coil does. This coil power, coupled w/ the boost opens the inj.
My bench operates at 13.5 VDC on a dedicated, regulated, power supply. We've done tests on smaller injs, and found that @10vdc, or less, most would not open. We also scoped the injs, and at 11+ vdc, found little to no loss in opening times.
I had those same injs in my stage car. They did exactly what's being discussed. Strangely enuf, they worked perfectly at 28psi boost.

What Alan said is what I attempted to convey...

 

[fastblackracing]

id agree with you chuck but id be wrong

The differential pressure is all that matters.
AG.

The inj does not rely on boost to open it. The application of voltage to the coil does. This coil poer, coupled w/ the boost opens the inj.
My bench operates at 13.5 VDC on a dedicated, regulated, power supply. We've done tests on smaller injs, and found that @10vdc, or less, most would not open.
I had those same injs in my stage car. They did exactly what's being discussed. Strangely enuf, they worked perfectly at 28psi boost.

What Alan said is what I attempted to convey...

on his test at 80 psi rail pressure in atmosphere the injector was unable to lift and flow
i agree in boosted condition when open the injector is seeing 80psi FP less the boost pressure trying to come in so flow stays constant at base 43psi fuel pressure
when the injector is closed the pressure in the rail is what it is, the boost pressure cant help unseat the needle
if the injector wont open with 80 psi on the bench it wont open in a boosted enviornment

does the bench cleaner test at 13.5volts

Heres what I do know.....at 30-30 1/2 pounds boost every thing was good. Later on At 31-32 pounds every thing went bad real fast, Im talking 1 second runs after the boost came up in third gear from a 70 roll. ,,,,,, When I cut the plugs that I raced on there are 3 that look leaner than the other three....... And they match up with the injectors...... Im thinking now that we were very borderline at the track and the fuel we added was being put in to cover up the marginally lean cylinders and making the good ones slightly rich....... since the o2 sensor reads an average of all six holes we dont know what is going on until you examine the plugs....... Not sure what direction I want to go at this point......we do have a set of 120#'s left over from the mustang blower engine.....maybe set them up with 32 or 34 pound base pressure and start over.....

 

[Chuck Leeper]

Pump at it's max??
680 wheel, is about what my stage put out on the 95's. {142+ mph}. @ 28#, the plugs looked hot. {AC42}. I turned it back to 26, all was well. I drove it on the street, and 26 was plenty.
I'd try the 120's, and see what the plugs look like, then.

 

[Nick Micale]

A while back I was not pleased with my 120 injectors after Chuck flowed them and ordered a set from Precision and was pissed when they arrived without a flow sheet as I paid a premium price and expected that info?

I was not happy with how these 120's acted after a few runs and replaced them with with 140's from a quality source and received lots of documentation with them.

Even before a retune, the 140's idled and ran better!

 

[Eticket]

Had same thing happen at lower boost with msd 50s which are similar in style...

 

[fastblackracing]

A while back I was not pleased with my 120 injectors after Chuck flowed them and ordered a set from Precision and was pissed when they arrived without a flow sheet as I paid a premium price and expected that info?

I was not happy with how these 120's acted after a few runs and replaced them with with 140's from a quality source and received lots of documentation with them.

Even before a retune, the 140's idled and ran better!

Pump at it's max??
680 wheel, is about what my stage put out on the 95's. {142+ mph}. @ 28#, the plugs looked hot. {AC42}. I turned it back to 26, all was well. I drove it on the street, and 26 was plenty.
I'd try the 120's, and see what the plugs look like, then.

Chuck the pumps are good and the pressure is there...the injector duty cycle looks good as well it will usually start to climb if your out of pump. I am going to run the 120's and see how it goes, kinda sucks cause we had the tune-up nailed down pretty good on those 96's.......... Wish I would have known they were not a good hi boost injector. Nick do you know who made the 120's you had issues with and the 140's you liked also? Thanks guys, Mannie

 

[fastblackracing]

Had same thing happen at lower boost with msd 50s which are similar in style...

I had issues with a guys car 15+ years back with msd 50's.....surely they dont still make injectors?

 

[bison]

The same problem occurs with a lot of injectors when the inlet side is subjected to higher pressures. Some as low as 70psi. Pintle style genuine Bosch injectors or Siemens Deka 3105 or the 3145 have been fine in my car up to 85psi. I've seen pintle style injectors work with 100psi of pressure.


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[fastblackracing]

The same problem occurs with a lot of injectors when the inlet side is subjected to higher pressures. Some as low as 70psi. Pintle style genuine Bosch injectors or Siemens Deka 3105 or the 3145 have been fine in my car up to 85psi. I've seen pintle style injectors work with 100psi of pressure.


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Thanks for the info bison I appreciate it.

 

[Chuck Leeper]

A while back I was not pleased with my 120 injectors after Chuck flowed them and ordered a set from Precision and was pissed when they arrived without a flow sheet as I paid a premium price and expected that info?

Nick, my 95's came w/o a sheet. I called, and was told, "we don't usually send the flow sheets"....

 

[ttypewhite]

I've taken my Dad's full weight GN to 9.40 @146mph with lots of room to spare (3,700+ with me in it). This 95lb injector would easily take us into the 8's without a problem.

 

[Jerryl]

Excuse my relative ignorance on the subject.

I see three seperate issues.
Size, pressure, and impedance.

Size:
If the injector works at the required pressure, and supplies the required fuel, there are no issues.

Pressure:
If the injector locks up below the required pressure, the injector size is less relevant.

Impedance:
Lower impedance injectors may be less suseptable to lockup to some extend because the supplied amperage for initial opening is higher. (???)

So . . The fact that some can run xxx injector to support higher mass flow could imply that they are doing it at a lower boost level . . Or lower fuel pressure. So a bigger injector may not be the aswer as the injector inlet pressure will be the same. The only difference will be a lower DC for a bigger injector . . . Unless of course, the base pressure is lowered as indicated by fastblackracing.

Increased voltage can also assist "stuck injectors" in some situations.

I am here to learn but believe that the variables need to be reviewed somewhat independently.

 

[murphster]

This is very interesting and made me take a look at whats going on. While I agree once the injector is opened up then the pressure differential makes an impact with the fuel flow, the thing that needs to be looked at is differential pressures on the valve that opens the injector.

The 95lb Precision injectors are ball and seat design. The MSD 50s are too. Easy to find multiple references on the web where these designs don't like very high inlet pressures, like the 80psi limit the OP found. The pintle design doesn't seem to be affected as much. Looking at the designs I don't think the boost pressure on the outlet side has much to do with it and its probably a function of the valve design and the inlet pressure.

Why? Take a look at the two injector designs:

On the outlet sides of both injectors you only have a very small surface area seeing the boost coming from the manifold side. The size of the pintle nozzle is very small, and the holes on the director plate of the ball and seat injector are also very small. I don't think its going to add much force to the valve even if the boost was 50psi. Now on the inlet side coming from the fuel pump you not only have a larger surface area, its fluid. 80psi of fluid pressure on the inlet side of the injector on a larger surface area vs 30psi of air pressure on the outlet side over a very small area. I think the boost pressure has a minimal affect on the valve action.

Now when you look at the different designs, for the ball and seat style you got all this fluid surrounding the surface area of the ball working against it while the pintle nozzle being a cylinder the pressure is mainly coming from the sides and not working against it opening. At high inlet pressures it makes sense that the ball would be harder to unseat compared to the pintle nozzle.

Also coming into play would be the coil strength to lift the valve up. High Z injectors usually are weaker due to the lower current. So running high impedence ball and seat injectors at high boost would seem to be of more concern, for example the MSD 50s. Other high z injectors with bad designs or weak coils at high boost would be of concern too. The 96lb injectors are low z and should be better but as the OP found out they can fail too.

Obviously I'm just trying to figure out whats going on and there may be more to it, but its something I never looked at before but definitely has me thinking now. Just put a set of MSD 50s in my truck too darn it.

 

[fastblackracing]

I've taken my Dad's full weight GN to 9.40 @146mph with lots of room to spare (3,700+ with me in it). This 95lb injector would easily take us into the 8's without a problem.

Mike what was the boost and fuel pressures you were running in your dads car? and are they the same 96 pound injectors I have.

Excuse my relative ignorance on the subject.

I see three seperate issues.
Size, pressure, and impedance.

Size:
If the injector works at the required pressure, and supplies the required fuel, there are no issues.

Pressure:
If the injector locks up below the required pressure, the injector size is less relevant.

Impedance:
Lower impedance injectors may be less suseptable to lockup to some extend because the supplied amperage for initial opening is higher. (???)

So . . The fact that some can run xxx injector to support higher mass flow could imply that they are doing it at a lower boost level . . Or lower fuel pressure. So a bigger injector may not be the aswer as the injector inlet pressure will be the same. The only difference will be a lower DC for a bigger injector . . . Unless of course, the base pressure is lowered Increased voltage can also assist "stuck injectors" in some situations as indicated by fastblackracing.
am here to learn but believe that the variables need to be reviewed somewhat independently.

. . jerryl you are understanding it very well my DC is in the low to mid 60% range but this particular engine combo is not the most efficient, for me to run fast I have to run big boost 30+.... and that is beyond what these injectors want to do.

I

 

[ttypewhite]

Mike what was the boost and fuel pressures you were running in your dads car? and are they the same 96 pound injectors I have.

Base fuel pressure is 45psi, not sure which version he has, but we got them from Racetronix.

 

[SCOOBY DOO]

What's the verdict on Siemens injectors? I put a set of 80 high Z's in last spring.