Instrumentation... a wise investment
11-07-21, 12:36 PM
#1
Racing Rotary Since 1983
Thread Starter
iTrader: (6)
Instrumentation... a wise investment
my best sell job on instrumentation always starts with making sure we appreciate just how much combustion chamber pressure and heat exist even with our non modified engines.
i generally list all the current Supercars and list their hp per cubic inch... yes i am old school.
instead of the list, which averages 1.91 hp per cubic inch and is somwhat dated (2018) how about the 2023 Corvette C8 R. you wouldn't believe what's in that motor. if you want the details:
https://www.caranddriver.com/news/a3...-z06-revealed/
670 flywheel, call it 570 rwhp from 336 cu inches/5.5 L.
looks like 1.99 rwhp per cubic inch
O K, so it is N A.
turbo'd Supercars peak around 2.2.
sure they could make more but the factory decided to call it at that number for obvious reasons.
compare to our FD using 160 cu inches
unmodified 217 rwhp 1.36 rwhp per cu inch
350 rwhp 2.19
400 rwhp 2.5
450 rwhp 2.81
500 rwhp 3.13
550 rwhp 3.44
600 rwhp 3.75
i will bet many consider a 350 rwhp FD to be in a very low state of tune. not so. by a mile.
fortunately, most of the solutions are here on our wonderful forum.
instrumentation is the required tool to sidestep broken motors. instrumentation can provide the best return on the invested dollar.
for instance:
i have always advised that a digital fuel pressure sensor should be one of the first instruments onboard. i have run one since 2003.
yesterday it paid another dividend. i had been doing a bunch of research on intercoolers this year and after finishing it started prepping for the Texas Mile. i had been running at 20 psi testing the intercoolers.
i turned up the boost to 30 psi and did a run yesterday. 30 psi with an EFR9180 is quite a ride.. 'just was tuning my fuel map. lots of nice numbers until i looked at my Differential Fuel Pressure. (Diff F P, for those that don't know is simply the difference between actual fuel pressure and boost. it should always be your static pressure).
take a look at my log and notice the dip.
notice how it drops significantly as boost pressure heads north from the low 20s. Diff FP should ideally be a flat plot. clearly something is amiss. it is probably a leak in the signal hose from the manifold. a leak within the FP reg or the fittings. maybe a partially occluded fuel filter. it probably isn't a pump issue as i recently switched to a Hellcat pump and i run it with my Kenne Bell Boost A Pump at 15 V in boost. the point here is not my specific fix but that my digital fuel pressure sensor let me know of an issue. looking back at other logs i found a bit of give up even around the 20 psi range but it was only about a pound or two.
accurate logged fuel pressure readings can help in a less esoteric situation. our FDs have a fuel filter in a non user friendly location. if you have a FP sensor you can just look at the log and conclude you don't have to change it because at 10 pounds of boost and 43.5 static your sensor reads 53.5. should it read less it might be time to swap in a new filter.
if Diff FP rises under boost there would be a problem with the return lines.
all our FDs are closer to the razor's edge than we often think. instrumentation is the solution.
what's your fav instrument?
i generally list all the current Supercars and list their hp per cubic inch... yes i am old school.
instead of the list, which averages 1.91 hp per cubic inch and is somwhat dated (2018) how about the 2023 Corvette C8 R. you wouldn't believe what's in that motor. if you want the details:
https://www.caranddriver.com/news/a3...-z06-revealed/
670 flywheel, call it 570 rwhp from 336 cu inches/5.5 L.
looks like 1.99 rwhp per cubic inch
O K, so it is N A.
turbo'd Supercars peak around 2.2.
sure they could make more but the factory decided to call it at that number for obvious reasons.
compare to our FD using 160 cu inches
unmodified 217 rwhp 1.36 rwhp per cu inch
350 rwhp 2.19
400 rwhp 2.5
450 rwhp 2.81
500 rwhp 3.13
550 rwhp 3.44
600 rwhp 3.75
i will bet many consider a 350 rwhp FD to be in a very low state of tune. not so. by a mile.
fortunately, most of the solutions are here on our wonderful forum.
instrumentation is the required tool to sidestep broken motors. instrumentation can provide the best return on the invested dollar.
for instance:
i have always advised that a digital fuel pressure sensor should be one of the first instruments onboard. i have run one since 2003.
yesterday it paid another dividend. i had been doing a bunch of research on intercoolers this year and after finishing it started prepping for the Texas Mile. i had been running at 20 psi testing the intercoolers.
i turned up the boost to 30 psi and did a run yesterday. 30 psi with an EFR9180 is quite a ride.. 'just was tuning my fuel map. lots of nice numbers until i looked at my Differential Fuel Pressure. (Diff F P, for those that don't know is simply the difference between actual fuel pressure and boost. it should always be your static pressure).
take a look at my log and notice the dip.
notice how it drops significantly as boost pressure heads north from the low 20s. Diff FP should ideally be a flat plot. clearly something is amiss. it is probably a leak in the signal hose from the manifold. a leak within the FP reg or the fittings. maybe a partially occluded fuel filter. it probably isn't a pump issue as i recently switched to a Hellcat pump and i run it with my Kenne Bell Boost A Pump at 15 V in boost. the point here is not my specific fix but that my digital fuel pressure sensor let me know of an issue. looking back at other logs i found a bit of give up even around the 20 psi range but it was only about a pound or two.
accurate logged fuel pressure readings can help in a less esoteric situation. our FDs have a fuel filter in a non user friendly location. if you have a FP sensor you can just look at the log and conclude you don't have to change it because at 10 pounds of boost and 43.5 static your sensor reads 53.5. should it read less it might be time to swap in a new filter.
if Diff FP rises under boost there would be a problem with the return lines.
all our FDs are closer to the razor's edge than we often think. instrumentation is the solution.
what's your fav instrument?
Last edited by Howard Coleman; 11-12-21 at 07:21 AM.
11-07-21, 03:28 PM
#2
Nice save. There's so much static in the power/displacement conversation. I prefer when you start your thesis in combustion chamber pressure and volumetric efficiency.
Regardless, we're making a lot more power than the block was engineered for. Making that power reliably requires precision information and accountable components.
Regardless, we're making a lot more power than the block was engineered for. Making that power reliably requires precision information and accountable components.
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Howard Coleman (11-08-21)
11-08-21, 12:05 AM
#3
I agree a fuel pressure sensor is probably the second or third sensor to add to a modified car, after a wideband O2 sensor and possibly an oil pressure sensor if you don't trust the factory system. My car's order of operations was wideband (2007), then ECU (2007), then fuel pressure sensor (2009), then oil temperature and oil pressures sensors (2020) and I haven't got an EGT sensor yet but I could see arguments for doing an EGT sensor before oil sensors. I'm surprised it's not common to see two wideband O2's (one per rotor) on big power rotaries since O2 sensors respond more quickly than EGT sensors.
Mostly unrelated, is your car really making 30 psi of boost at 40% throttle opening? It should be much easier to drive if you configure the boost control settings for lower boost at part throttle and then ramp up to full boost at full throttle.
Mostly unrelated, is your car really making 30 psi of boost at 40% throttle opening? It should be much easier to drive if you configure the boost control settings for lower boost at part throttle and then ramp up to full boost at full throttle.
11-08-21, 01:56 AM
#4
Two things:
- Are those measured or theoretical pressure numbers?
- Can they be directly compared to a rotary from a piston engine? Given that the combustion chamber volume per crankshaft rotation does not align with the normal "designation" used in pistons? (if we treat it as a 2.6l based on combustion volume/crank rotation)
(im just curious
)
- Are those measured or theoretical pressure numbers?
- Can they be directly compared to a rotary from a piston engine? Given that the combustion chamber volume per crankshaft rotation does not align with the normal "designation" used in pistons? (if we treat it as a 2.6l based on combustion volume/crank rotation)
(im just curious
)
11-08-21, 04:29 AM
#5
Corn-to-Noise Converter
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Howard, 'we're in violent agreement. Generous' instrumenting is a cornerstone principle of why I bought the best ECU I could afford. While it won't complete preclude catastrophic mechanical failures, it certainly can help sense and (with sufficient warnings and fail-safe tables) mitigate the effects. Figured that the extra few thousand dollars invested in the control systems favorably offset the prevention and potential replacement of trashed housings, rotors, e-shaft bearings and turbo... and more importantly, the resulting porting, balancing, machining, and 'blueprinting' time. Not that I've been there before...
Regarding your particular data capture (1:27-1:28), have you reconciled why the AFR actual trends slightly richer given the 10% decrease in fuel flow from the pressure drop (i.e. 88-72 abs. psi). Do you think that's the overarching influence of the decreasing TPS or perhaps previous injector map compensation or even some other failsafe table?
Regarding your particular data capture (1:27-1:28), have you reconciled why the AFR actual trends slightly richer given the 10% decrease in fuel flow from the pressure drop (i.e. 88-72 abs. psi). Do you think that's the overarching influence of the decreasing TPS or perhaps previous injector map compensation or even some other failsafe table?
Last edited by Carlos Iglesias; 11-08-21 at 04:32 AM. Reason: ADD
11-08-21, 01:38 PM
#6
Racing Rotary Since 1983
Thread Starter
iTrader: (6)
here's a better look as to my fuel pressure dip. thanks to my fuel pressure sensor it is Obvious a problem exists.
prior to boost my fuel pressure shows 57.6. i had recently switched from 3 BAR (43.5) to 4 BAR (58)
note it is reported at 57.6 with the engine showing minus .2 psi
later in the run i am at 29.7 psi boost, my actual fuel pressure is 72.2 making my Differential fuel pressure 42.5.
why might the addition of a digital fuel pressure sensor keep you from calling an engine re-builder?
consider:
the engine is at, say, 7000 rpm, 20 psi boost. timing might be around 11 and maybe 80 on the fuel table.
the fuel pressure signal line blows off... while the engine remains at 7000 and boost remains at 20 the engine now receives fuel for zero boost pressure, about 45 on the fuel table... fuel flow rises and falls with the square root of the pressure change a drop from 80 to 45 on the fuel table is 43.75%. this decreases fuel flow 21% at 20 psi boost. not a good thing.
in my instance my pressure drop was from 57.6 too 42.1 or 27%. fuel flow down 5.2%. most probable would be a leak past my double tie wraps at the regulator or a slightly ruptured silicone hose.
the progression of this would be a total disconnection or larger tear resulting in a possible internal engine problem. thanks to my instrumentation the cost will be some new silicone hose and tie wraps.
Digital loggable pressure sensor, Plan A.
this is Plan B
great for setting static fuel pressure. not so great when you close the hood and need to know you have proper fuel pressure when it counts.
if you log fuel pressure you look at the log. if you are set at 43.5 static your fuel pressure better show 63.5 at 20 psi boost.
if it shows less, it is easy to sort through the variables and find the problem. fuel pump, filter, voltage etc. easy stuff.
you won't get the message with the stone age gauge.
what's your favorite instrumentation and what's your favorite save the motor story?
prior to boost my fuel pressure shows 57.6. i had recently switched from 3 BAR (43.5) to 4 BAR (58)
note it is reported at 57.6 with the engine showing minus .2 psi
later in the run i am at 29.7 psi boost, my actual fuel pressure is 72.2 making my Differential fuel pressure 42.5.
why might the addition of a digital fuel pressure sensor keep you from calling an engine re-builder?
consider:
the engine is at, say, 7000 rpm, 20 psi boost. timing might be around 11 and maybe 80 on the fuel table.
the fuel pressure signal line blows off... while the engine remains at 7000 and boost remains at 20 the engine now receives fuel for zero boost pressure, about 45 on the fuel table... fuel flow rises and falls with the square root of the pressure change a drop from 80 to 45 on the fuel table is 43.75%. this decreases fuel flow 21% at 20 psi boost. not a good thing.
in my instance my pressure drop was from 57.6 too 42.1 or 27%. fuel flow down 5.2%. most probable would be a leak past my double tie wraps at the regulator or a slightly ruptured silicone hose.
the progression of this would be a total disconnection or larger tear resulting in a possible internal engine problem. thanks to my instrumentation the cost will be some new silicone hose and tie wraps.
Digital loggable pressure sensor, Plan A.
this is Plan B
great for setting static fuel pressure. not so great when you close the hood and need to know you have proper fuel pressure when it counts.
if you log fuel pressure you look at the log. if you are set at 43.5 static your fuel pressure better show 63.5 at 20 psi boost.
if it shows less, it is easy to sort through the variables and find the problem. fuel pump, filter, voltage etc. easy stuff.
you won't get the message with the stone age gauge.
what's your favorite instrumentation and what's your favorite save the motor story?
Last edited by Howard Coleman; 11-08-21 at 01:56 PM.
11-08-21, 01:54 PM
#7
Racing Rotary Since 1983
Thread Starter
iTrader: (6)
"I'm surprised it's not common to see two wideband O2's (one per rotor) on big power rotaries since O2 sensors respond more quickly than EGT sensors."
i think many would be shocked if they were able to generate AFRs from each rotor. so many single turbo manifolds place the turbine housing which can get to 1850 F very close to the front LIM runners. a turbo blanket, while very helpful for lowering engine bay temps, does almost nothing to lower heat transfer. (Mica)... i bet for many setups there is more than a full AFR point diff front to rear. the problem is that the rotary generates approx 300 F more heat than a piston and it is hard to maintain wideband sensors on a piston engine. (of course ethanol drops egts V gas a bunch) as to your point re EGT sensors/thermocouples... they read at 4 per second which works for me.
"making 30 psi of boost at 40% throttle opening" you are correct. i had just changed boost solenoid and some other setiings and will ramp things down a bit.
i think many would be shocked if they were able to generate AFRs from each rotor. so many single turbo manifolds place the turbine housing which can get to 1850 F very close to the front LIM runners. a turbo blanket, while very helpful for lowering engine bay temps, does almost nothing to lower heat transfer. (Mica)... i bet for many setups there is more than a full AFR point diff front to rear. the problem is that the rotary generates approx 300 F more heat than a piston and it is hard to maintain wideband sensors on a piston engine. (of course ethanol drops egts V gas a bunch) as to your point re EGT sensors/thermocouples... they read at 4 per second which works for me.
"making 30 psi of boost at 40% throttle opening" you are correct. i had just changed boost solenoid and some other setiings and will ramp things down a bit.
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scotty305 (11-08-21)
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11-12-21, 07:18 AM
#8
Racing Rotary Since 1983
Thread Starter
iTrader: (6)
i will continue posting until my Diff fuel pressure is flatline.
while my pressure signal hose to the regulator had two tie wraps on both ends i found i could rotate it a bit at the regulator so i removed it and replaced it with a hose that had one mm less I D. after a run at 29.5 psi my diff FP now has a 3 psi dip. prior to hose replacement it was 16 so major progress. since i still have a small slippage the next item will be the Aeromotive fuel filter element...
stay tuned.
while my pressure signal hose to the regulator had two tie wraps on both ends i found i could rotate it a bit at the regulator so i removed it and replaced it with a hose that had one mm less I D. after a run at 29.5 psi my diff FP now has a 3 psi dip. prior to hose replacement it was 16 so major progress. since i still have a small slippage the next item will be the Aeromotive fuel filter element...
stay tuned.
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DaleClark (11-12-21)
11-12-21, 08:42 AM
#9
RX-7 Bad Ass
iTrader: (55)
Amazing what a loose vacuum line can do!
I've found for vacuum lines a good tight fit is the only way to go. Loose fit and zip ties doesn't work long term.
Dale
I've found for vacuum lines a good tight fit is the only way to go. Loose fit and zip ties doesn't work long term.
Dale
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