998 turbo mod

[Doc Harley]

TD runs 1050 injectors with their modstock turbo.

Well, read this, then maybe you could shed some light on it. To me it reads, race fuel would need injectors & pump gas would not need bigger injectors?!?! Im guessing you've already deciphered this...

 

[DMCTurbo]

Well, read this, then maybe you could shed some light on it. To me it reads, race fuel would need injectors & pump gas would not need bigger injectors?!?! Im guessing you've already deciphered this...View attachment 178903

I'm going off of conversations I've had with them.

 

[Doc Harley]

I'm going off of conversations I've had with them.

Understand, Derek. I'll call them Monday. I'd rather have room to play then to be sitting on the edge.

 

[earthling]

It depends on what the tune was "written" with. 3-bar tunes use base 43 psi fuel pressure. Injector pulse width is calibrated to that to meter the correct amount of fuel.
4-bar tunes use 58 psi as base. Again, injector pulse is controlled by ecu to that base pressure. It is not determined by how much boost there will be, directly.
You can't just change a 3-bar tune to 4-bar, or vice versa, on same tune map. Fuel control will be way off. I doubt the engine would start, and even it did, it wouldn't run well at all.
Theoretically, within a range, you can get to the same place with 3-bar or 4-bar with same injector. With 3 bar, the injector pulse width ("on" time) will be longer because fp is lower. With 4-bar, pulse width will be shorter because fp is higher.
PEFI decided to create their Stage 4 tune as a 4-bar, I assume to ensure adequate fuel flow, and not push injectors to maximum duty cycle (amount of on time compared to off time). If an injector is undersized, it will have to on too much and that will overheat it and cause failure.

It occurs to me, thinking about your original post that fuel pressure needs to be raised as you increase boost pressure (and therefore dynamic cylinder/manifold pressure) because the injector gets less efficient at fuel delivery, this in turn creates demand for greater relative fuel pressure to keep up the flow. At idle the system is in a vacuum, at full throttle it is fighting the pressure in the system. Its like pumping air into a tire, the higher the tire pressure, the less volume you can put into it.

 

[Doc Harley]

I just remembered....There's a formula for BSFC or Brake Specific Fuel Consumption. The only way it could be off, is if the horsepower level is incorrect/ inaccurate. Has nothing to do with Any particular tune, just uses raw facts.
hp, fuel pressure, injector delivery capacity & duty cycle for any given injector. I'm sure more info is required?!?!
And yes, a boosted motor requires a higher BSFC rating at any given hp # then it's N/A counterpart.

 

[DMCTurbo]

Understand, Derek. I'll call them Monday. I'd rather have room to play then to be sitting on the edge.

Just buy the big turbo.

 

[Turboflash]

I just remembered....There's a formula for BSFC or Brake Specific Fuel Consumption. The only way it could be off, is if the horsepower level is incorrect/ inaccurate. Has nothing to do with Any particular tune, just uses raw facts.
hp, fuel pressure, injector delivery capacity & duty cycle for any given injector. I'm sure more info is required?!?!
And yes, a boosted motor requires a higher BSFC rating at any given hp # then it's N/A counterpart.

These 998 fuel systems have no feedback to ecu as to what fp is. Ecu does not know what fp is. The pump runs, fpr controls how much pressure there is. They are boost reference regulators. For each 1 pound of boost increase, the fp increases 1 lb. The ecu adjusts injector pulse width according to all inputs it has (inlet air temp, throttle position, rpm, coolant temp, barometric pressure, timing). Ecu looks up desired injector pulse width (and timing) from the tune table and sends it to injectors. If that pulse of fuel is not enough for the amount of air, then the mixture could be lean. With closed loop, ecu gets input from O2 sensor and adjusts pulse width to achieve desired afr.
So if one alters air volume (or temperature) into engine (pm, turbo mods, head porting, larger turbo, cold-air, etc) it's risky to not know what afr is. Many guys have found out the hard way what happens when they put a pm on a stock tune (not knowing what PM did to afr).

 

[Doc Harley]

These 998 fuel systems have no feedback to ecu as to what fp is. Ecu does not know what fp is. The pump runs, fpr controls how much pressure there is. They are boost reference regulators. For each 1 pound of boost increase, the fp increases 1 lb. The ecu adjusts injector pulse width according to all inputs it has (inlet air temp, throttle position, rpm, coolant temp, barometric pressure, timing). Ecu looks up desired injector pulse width (and timing) from the tune table and sends it to injectors. If that pulse of fuel is not enough for the amount of air, then the mixture could be lean. With closed loop, ecu gets input from O2 sensor and adjusts pulse width to achieve desired afr.
So if one alters air volume (or temperature) into engine (pm, turbo mods, head porting, larger turbo, cold-air, etc) it's risky to not know what afr is. Many guys have found out the hard way what happens when they put a pm on a stock tune (not knowing what PM did to afr).

I was just trying to understand duty cycle and/or a specific injector needed to do a specific job.
Example: a 325hp 3cyl. Motor needs an injector that can deliver 65lbs of fuel per hour @ 100% duty cycle.
The factory injector is appx 73.5lbs.
So the factory injector is running at appx 88% duty cycle at wot to keep afr in order.
That should be close...someone else correct me if I'm mistaken.
TurboFlash, like dmc explained, injectors can be over taxed for a given horsepower and not be able to maintain the correct afr.
And the tune I purchased (TD) claims my stock injectors could become suspect for failure when moving more air then a stock turbo can. That's all.
I was attempting to do my due diligence to verify TD's claims...

 

[earthling]

I just remembered....There's a formula for BSFC or Brake Specific Fuel Consumption. The only way it could be off, is if the horsepower level is incorrect/ inaccurate. Has nothing to do with Any particular tune, just uses raw facts.
hp, fuel pressure, injector delivery capacity & duty cycle for any given injector. I'm sure more info is required?!?!
And yes, a boosted motor requires a higher BSFC rating at any given hp # then it's N/A counterpart.

BSFC is a dyno measurement (=g/j), not an input or influence on anything in the motor in the same way that horsepower (Torque x RPM / 5,252) is a byproduct of torque and RPM. BSFC is just a way of expressing an efficiency ratio. It is a useful tool when designing a commercial engine (e.g. for a commuter car), and a reference when making changes to an engine but most tuners could really care less as the goal isn't efficiency, its power. Even if you are designing for some form of lap racing, BSFC is interesting but the far bigger influences on economy will come from aerodynamics and chassis dynamics not engine tuning.

 

[Doc Harley]

BSFC is a dyno measurement (=g/j), not an input or influence on anything in the motor in the same way that horsepower (Torque x RPM / 5,252) is a byproduct of torque and RPM. BSFC is just a way of expressing an efficiency ratio. It is a useful tool when designing a commercial engine (e.g. for a commuter car), and a reference when making changes to an engine but most tuners could really care less as the goal isn't efficiency, its power. Even if you are designing for some form of lap racing, BSFC is interesting but the far bigger influences on economy will come from aerodynamics and chassis dynamics not engine tuning.

Understand, earthing.
But if you were to build a turbo charged motor today, it would give you a reference point on how much fuel would be needed for that particular build and take some of the guess work out of which injector do I choose. Or carburetor for that matter.
It's all coming back to me from my Buick Grand National days when guys were telling me I needed upgrade injectors and the formula says otherwise. BTW, never hurt that motor.
You can verify my findings by simply plugging in the appropriate numbers and get an understanding on why & when you need to upgrade injectors.
my initial findings are inline with Turbo Dynamics in that on the low side, stock injectors will continue to do their job perfectly. But once we get into that 350hp+ range, they will be over taxed. And yes an injector can achieve 110% of capacity...but i wouldn't take that risk.

 

[earthling]

Understand, earthing.
But if you were to build a turbo charged motor today, it would give you a reference point on how much fuel would be needed for that particular build and take some of the guess work out of which injector do I choose. Or carburetor for that matter.
It's all coming back to me from my Buick Grand National days when guys were telling me I needed upgrade injectors and the formula says otherwise. BTW, never hurt that motor.
You can verify my findings by simply plugging in the appropriate numbers and get an understanding on why & when you need to upgrade injectors.
my initial findings are inline with Turbo Dynamics in that on the low side, stock injectors will continue to do their job perfectly. But once we get into that 350hp+ range, they will be over taxed. And yes an injector can achieve 110% of capacity...but i wouldn't take that risk.

BSFC as I said is a measurement, yes you can use averages from different engine types as a rule of thumb if you were trying to pick injector sizing, but unless you are the guy building the fuel maps, you aren't going to change away from what is already there in a 'purchased' tune. If you just wanted to know where the limits are then good on you for doing the homework but TD is doing this emperically and they know where the cutoff point is. You cannot push an injector passed 100% duty cycle, its physically impossible as 100% means it is wide open constantly. When someone says that they are hitting 110% they are being lied to by the ECU which is doing a cacluation on relative fuel delivery because air mass is lower than expected, skewing the calculation. This happens because the ECU can calculate 'effective duty cycle' as opposed to actual. It is likely aslo just a blip in an otherwise correct data stream.

 

[Turboflash]

I was just trying to understand duty cycle and/or a specific injector needed to do a specific job.
Example: a 325hp 3cyl. Motor needs an injector that can deliver 65lbs of fuel per hour @ 100% duty cycle.
The factory injector is appx 73.5lbs.
So the factory injector is running at appx 88% duty cycle at wot to keep afr in order.
That should be close...someone else correct me if I'm mistaken.
TurboFlash, like dmc explained, injectors can be over taxed for a given horsepower and not be able to maintain the correct afr.
And the tune I purchased (TD) claims my stock injectors could become suspect for failure when moving more air then a stock turbo can. That's all.
I was attempting to do my due diligence to verify TD's claims...

Yes, I agree (thought I said that?) injectors can (and will be) overtaxed at some point.
But also, the fuel delivery in your example is at a given fp. 88% on a 3-bar system might be 65% on a 4-bar system (didn't do the exact math) because fp is 33% higher (43 psi base vs. 58 psi base). Each injector pulse will deliver maybe 30% more fuel.
I'm not sure what stock injectors can handle pressure-wise. What is too much?
So far so good is all I can say. I like my chances better on a 4-bar tune at the max end (for example waste gate lock installed - max boost - C16) with stock injectors.

 

[Doc Harley]

BSFC as I said is a measurement, yes you can use averages from different engine types as a rule of thumb if you were trying to pick injector sizing, but unless you are the guy building the fuel maps, you aren't going to change away from what is already there in a 'purchased' tune. If you just wanted to know where the limits are then good on you for doing the homework but TD is doing this emperically and they know where the cutoff point is. You cannot push an injector passed 100% duty cycle, its physically impossible as 100% means it is wide open constantly. When someone says that they are hitting 110% they are being lied to by the ECU which is doing a cacluation on relative fuel delivery because air mass is lower than expected, skewing the calculation. This happens because the ECU can calculate 'effective duty cycle' as opposed to actual. It is likely aslo just a blip in an otherwise correct data stream.

You can push an injector further then its ability by adding more fuel pressure then its intended use. I use the words "duty cycle" but perhaps I should use the word like capacity. It's when the pindle can't overcome the fuel pressure and the pindle can actually lock up, possibly opened or closed

Yes, I agree (thought I said that?) injectors can (and will be) overtaxed at some point.
But also, the fuel delivery in your example is at a given fp. 88% on a 3-bar system might be 65% on a 4-bar system (didn't do the exact math) because fp is 33% higher (43 psi base vs. 58 psi base). Each injector pulse will deliver maybe 30% more fuel.
I'm not sure what stock injectors can handle pressure-wise. What is too much?
So far so good is all I can say. I like my chances better on a 4-bar tune at the max end (for example waste gate lock installed - max boost - C16) with stock injectors.

I think and agree. But 10 short pulls on a dyno run is nothing like pushing the flipper wot for 1/4 mile, gulping in large amounts of 0°F. No harm meant, just my thought.

 

[Turboflash]

You can push an injector further then its ability by adding more fuel pressure then its intended use. I use the words "duty cycle" but perhaps I should use the word like capacity. It's when the pindle can't overcome the fuel pressure and the pindle can actually lock up, possibly opened or closed

I think and agree. But 10 short pulls on a dyno run is nothing like pushing the flipper wot for 1/4 mile, gulping in large amounts of 0°F. No harm meant, just my thought.

Agree, winter air will be more taxing for sure. Let's hope we get enough winter so we can find out.
BTW- the dyno pulls (both pump gas and C16) totalled close to 100, groups of 4, meaning about 25 groups of 4 runs that were back-to-back-to-back. Cool down period in between each group that took about 20 minutes. Runs began at about 160 degrees coolant temp and ended close to180+.

 

[Doc Harley]

Agree, winter air will be more taxing for sure. Let's hope we get enough winter so we can find out.
BTW- the dyno pulls (both pump gas and C16) totalled close to 100, groups of 4, meaning about 25 groups of 4 runs that were back-to-back-to-back. Cool down period in between each group that took about 20 minutes. Runs began at about 160 degrees coolant temp and ended close to180+.

Oh, my...100 pulls Lol!! I get it. I wish I didn't go on TD's webpage. It's like opening up doors that I'm not exactly wanting to.
I believe what you believe in that, 325hp+/-, on stock injectors would not be at all risky.
And the BSFC factor was basically a reinforcement/education to verify to myself.
However I'll need to upgrade my map sensor/tune along with a few other items to prepare for winter.

Just buy the big turbo.

I'm just not ready to make that commitment.