BUILD THREAD 86 GP 2+2~Blown 6.0

64nailhead

Goat Herder
Dec 1, 2014
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Overkill
For.
The.
Win.
Yeah buddy on this! X2^3

I just made two hits to 21 psi with FP at 77psi and duty cycle hovering between 40-41. Mr. Holley said 735lb/hr.

I'm pulling for Bruce to be correct - never run out of fuel!! I do need to add some oil though 😜
 
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motorheadmike

Geezer
Nov 18, 2009
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Hey I said a few weeks back that 'Mike is right', I gotta crawl back to sanity a little :)

To clarify - not only is my feed line a -10AN but it uses "full flow" elbows to the Y block at the rails. That wasn't by accident.

Mike is right far more often than you or my wife want to acknowledge. ;)

d generation x wrestling GIF by WWE


(It's Mike Tyson and a midget!)
 
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81cutlass

Comic Book Super Hero
Feb 16, 2009
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I'm fully open to putting a second pump in, I just want to see what the results are after I swap to -8 hose.

I am (slightly) opposed to running 2 pumps for the same reason I am concerned running 2 sets of injectors, If one set of injectors or one pump dies and you only have one, the car just shuts down. If you have 2 and one dies, it goes lean and kaboom. I'd prefer to put a HC 525 pump in for simplicity, but I am not firm any direction.

It's my inner engineer and management telling me to make it as cheap as possible but still meet requirements :)

My -8 hose should be here Saturday. I'll get that put in and collect more data. The math says the 450 should be more than enough, but math doesn't always match reality.


In other news, I got my clutch delay valve switch installed and wired. The switch is a 80 G body cruise equipped brake light switch. Built a bracket to mount to the console and it closes the ground of the relay. Closes the circuit when it's in 1st gear and I used one of the switches on the dash to trigger it off if I want.

I need to build a bracket for the solenoid, put it in the clutch line and bleed the system.
1620912293115.png


1620912368520.png
 
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81cutlass

Comic Book Super Hero
Feb 16, 2009
4,639
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Just for fun, what's 1200lb/hr with a 12 feet of -8 line through the calculator? 43psi base pressure.

Survey says 86.2 PSI of pressure drop on 1/2" (-8) line.

28.1 PSI of drop on 5/8" (-10) line

11.3 PSI of drop on 3/4" (-12) line

Make sure to look at rated pump flow at base pressure plus whatever boost raise you get. AKA your real base pressure is 43+boost, so 20psi of boost is 63psi base pressure.
 

64nailhead

Goat Herder
Dec 1, 2014
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Upstate NY
You present a good question if the pump really is large enough.



80lb/hr injectors at 58psi base pressure flow 92lb/hr which is 14gal/hr per cylinder or 428lph for the entire engine. I need 428lph of fuel flow (at the pump) to max out 80lb/hr injectors.

Not sure about ^^^. I have to do some more checking. But I believe that is not correct, but I can't find/figure out how to prove it - yet.

But, that's assuming the injector would be firing all the time, which it can't. If the engine is running at 6000 rpm its making 3000 combustions per minute, and you only have half the cycle to use because one half is intake and the other is exhaust, which means essentially the injectors run at a max duty cycle of 50%, even if they are at 100%. Can't inject fuel on the exhaust stroke. Really I need 214lph to max the injectors out on a 4 stroke engine. That's 56 GPH which according to this chart is achieved below 105psi on 12v or 115psi on 13.5v.

Gotta keep the pressure AT THE PUMP below ~100 psi on a 450 lph pump with 94lb injectors.

See bold - I'm not clear about how GM did this, but I'm not aware of an aftermarket ECU that does this. I'm quite sure that your ECU is operating with sequential injection. If it operates like a Megasquirt, Holley or Haltech, then your statement is erroneous (please correct me if you know I'm wrong about GM). Batch fire, doesn't really care much about valves events, other than it is setup to have at least one of the events occur with the valve open if it's designed for 2 squirts per 720 degree crank cycle. Many systems will allow for 4 squirts per 720 degrees of crank cycle, which implies that there is definitely fuel being injected against a closed intake valve. The reason the OEM's run sequentially is to allow for a cleaner burn in high vacuum/low KPA conditions - which implies emissions standards.

The reason to run sequential in a performance situation is to make your injector bigger. Every injector has a dead time - more accurately referred to as off time. I'm sure you know about this, but .... it's the minimum amount of time that an injector takes to turn off fuel flow and turn it back on. A Deka 80 is somewhere in the .8 of a millisecond, or .0008. At 6000 rpm's it takes 20ms, or.020 seconds for a 720 degree cam cycle (if my math is correct). So this means that the injector can only be open .0192 seconds for a sequential setup. If you run batch fire with 2 squirts, then you're down to .0184 seconds and if you run 4 squirts per cycle your only have .0168 seconds of available time to inject fuel. The difference between from sequential to 4 squirts is .0024 seconds of additional time injecting fuel. So this mean that an injector with .8ms dead time is 10% larger running sequentially - that's freaking HUGE if you're on the edge of your injector. The trade off is idle quality - it's very easy to make a 4 squirts per cycle batch fire run super smooth at idle as opposed to sequential with one squirt per 720 of crank cycle. It can be done, but it has to be at a precise interval related to intake valve opening. The OEMs have the testing ability to do this - the hotrodder (or me - not so much lol.

I messed around with this with my sons 421 and set of 80lb Dekas alot, and I mean alot. I did manage to get it run pretty well sequentially, but I could never get it to idle as well as with 2 or 4 squirts per cycle. On 93 octane at 18 psi of S480 boost with sequential injection and 20 gallons per hour of 50/50 meth injection fluid his duty cycle is at 85% which is an 18-18.4 ms injection cycle. Those same injectors run in batch fire with 4 squirts per cycle are maxed out at 14 psi of boost.

My point to these several paragraphs is to point out that the injector cycle doesn't give a crap if the intake valve is open when the rpm's are up. And boost keeps the mixture atomized without effort. which also makes the timing of the injection less important.

I believe, repeat believe, GM did the same.

p.s. - great discussion, hopefully you appreciate it. Let me know if you don't so that I'll stop it.
 
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64nailhead

Goat Herder
Dec 1, 2014
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Upstate NY
And I'm interested in pressure drop to a degree. The equalizer to pressure drop from the rear pump to the engine is larger line. If I ever max out a -10 line then I'll worry about it then lol. Perhaps Duke will be maxing out -10 on E, but wow, will that be making some steam. I know guys running methanol can't get by on -10 line, but that's an entirely different league - not many of them are running a 10+ gallon fuel cell to be cruising around town at a sub 5:1 AFR.
 

81cutlass

Comic Book Super Hero
Feb 16, 2009
4,639
13,542
113
Western MN
Not sure about ^^^. I have to do some more checking. But I believe that is not correct, but I can't find/figure out how to prove it - yet.



See bold - I'm not clear about how GM did this, but I'm not aware of an aftermarket ECU that does this. I'm quite sure that your ECU is operating with sequential injection. If it operates like a Megasquirt, Holley or Haltech, then your statement is erroneous (please correct me if you know I'm wrong about GM). Batch fire, doesn't really care much about valves events, other than it is setup to have at least one of the events occur with the valve open if it's designed for 2 squirts per 720 degree crank cycle. Many systems will allow for 4 squirts per 720 degrees of crank cycle, which implies that there is definitely fuel being injected against a closed intake valve. The reason the OEM's run sequentially is to allow for a cleaner burn in high vacuum/low KPA conditions - which implies emissions standards.

The reason to run sequential in a performance situation is to make your injector bigger. Every injector has a dead time - more accurately referred to as off time. I'm sure you know about this, but .... it's the minimum amount of time that an injector takes to turn off fuel flow and turn it back on. A Deka 80 is somewhere in the .8 of a millisecond, or .0008. At 6000 rpm's it takes 20ms, or.020 seconds for a 720 degree cam cycle (if my math is correct). So this means that the injector can only be open .0192 seconds for a sequential setup. If you run batch fire with 2 squirts, then you're down to .0184 seconds and if you run 4 squirts per cycle your only have .0168 seconds of available time to inject fuel. The difference between from sequential to 4 squirts is .0024 seconds of additional time injecting fuel. So this mean that an injector with .8ms dead time is 10% larger running sequentially - that's freaking HUGE if you're on the edge of your injector. The trade off is idle quality - it's very easy to make a 4 squirts per cycle batch fire run super smooth at idle as opposed to sequential with one squirt per 720 of crank cycle. It can be done, but it has to be at a precise interval related to intake valve opening. The OEMs have the testing ability to do this - the hotrodder (or me - not so much lol.

I messed around with this with my sons 421 and set of 80lb Dekas alot, and I mean alot. I did manage to get it run pretty well sequentially, but I could never get it to idle as well as with 2 or 4 squirts per cycle. On 93 octane at 18 psi of S480 boost with sequential injection and 20 gallons per hour of 50/50 meth injection fluid his duty cycle is at 85% which is an 18-18.4 ms injection cycle. Those same injectors run in batch fire with 4 squirts per cycle are maxed out at 14 psi of boost.

My point to these several paragraphs is to point out that the injector cycle doesn't give a crap if the intake valve is open when the rpm's are up. And boost keeps the mixture atomized without effort. which also makes the timing of the injection less important.

I believe, repeat believe, GM did the same.

p.s. - great discussion, hopefully you appreciate it. Let me know if you don't so that I'll stop it.

No, certainly I appreciate the discussion. I'm open to expanding my understanding. The more we understand things the better stuff works! I very well could be wrong!

I was under the impression sequential injection means the injectors fire in sequence equal to the firing order. It's not flooding the intake manifold with fuel like a carburetor or TBI. Batch fire is just like 8 little carbs at each intake runner and it just PWM's the injectors and floods the intake with a haze of fuel mist and whatever is available in the intake manifold when the valve opens is what the cylinder sees. It delivers a 'batch' of fuel for all injectors disregarding valve timing. Obviously a TBI just dumps it at the top of the manifold and batch port injection just dumps it closer to the valve but it has the same controls philosophy.

I assumed sequential pops the injector once for each intake stroke only when the valve is open, or at least when the valve is starting to open or close . I always thought this is good because you aren't just puddling raw fuel behind the valve when there is no airflow.

If the engine is running at 6000 rpm or 100rps a single up and down cycle takes 1/100 or 0.01s, or an entire 720 degrees or rotation takes 0.02s. That would mean (if I'm right and it only injects during the valve being open) that you have 0.005s to get all the fuel in the engine.

But the math agrees with you and I'm wrong. I know for a fact that I have 0.02s of possible injector open time as my duty cycle is 88% and the injector open time is .0185 ish seconds.

A direct injection or diesel only has 25% of the cycle to inject because it never 'stores' fuel in the runner. The stock lt4 injectors are 214lb/hr but since they can only be open 25% of the time they are really like 55lb/hr, and since an lsa is rated at 52lb/hr and they are both boosted 6.2 that totally makes sense.

When the duty cycle is 25% or less in can inject all the fuel during the intake valve opening which greatly helps emissions at low flow, but I agree at high flow it doesn't matter.

I know I've heard you can run DI LT stuff like a point leaner even in boost, I wonder if that's because the atomization is better and it's not pooling under the injector when the valve is closed which makes the fuel lazy to burn.

So yeah I agree, I can't cut my flow rate in half. My assumption was wrong, it was actually inconsistent too, I did it by 50% but really I'd need to reduce it by half again.

I need 430lph to supply my injectors. I am on board now. 100% duty times 8 injectors is 430lph.

Even a hellcat 525 pump only can flow that at 50psi but I calculated 80 at the pump to overcome boost and loss.

A pair of 450's will supply 430lph up to 95psi.

I could turn my base pressure down to 42psi and have enough overhead with a hellcat 525 pump, but I don't think my 80's have the capacity to flow the flow I need on e85. They might.

I'll put the #8 feed line in and see what my duty cycle and pressure looks like.

The calcs are saying a 450 absolutely won't supply these 80's on 58psi base. I'm on board there. I have seen the light.

A 525 is about as small as I can go on 43psi base and still supply these 80's. I'm not sure if the 80's will be large enough for the HP demand however. The online calculators say mostly yes.
 
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64nailhead

Goat Herder
Dec 1, 2014
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You could go down to 35 base pressure and Deka's will run. The 1st year or two of TPI ran at a base pressure of 35 - little known fact by me until my son bought a TPI setup off from an '85 Vette and the stock regulator only ran at 35 psi - we put an adjustable on their but didn't really need to.

Another often overlooked, hard to test and misunderstood piece of information, when injectors and pumps are rated at varying pressures they are most commonly tested with the pump and injector discharge in atmospheric pressure. That's a great test that offers very legitimate results for you if your motor is NA. On a boosted application if you're running 15psi of boost in the cylinder and you have 15 psi of of fuel pressure, then exactly zero fuel will be discharged from the injector when it opens. Implying if you test your injectors at 73 psi of fuel pressure (58+15psi of boost pressure raising the fuel pressure), then they will flow the exact same amount as at 58 psi of fuel pressure if the test apparatus could put the injector tip in an environment that's pressurized to 15 psi.

Not all tests are performed at atmospheric pressure, but try finding information on the testing apparatus when you see test results - not easy to find or just not available.

I'm sure you can do the math part of it more accurately than I can as I'm 30+ years removed from physics and chemistry class lol, and at times it was struggle for me back then.


Food for thought. IMO the best thing that we can do is to watch injector DC and fuel pressure. When the DC approaches 85% or you see the fuel pressure start to fall off, then you know you need to add more of .............something. At the end of the day, Bruce's last post, #971, is the winner.
 
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