Fuel Requirement for Head/Cam Mod

[Robert Dyck]

Another question about my heads/cam mod on my 02 RT: Expecting in the upper 500 whp.

Are the stock injectors and fuel pump adequate with the proper tuning?

Thanks.

 

[banton]

The stock fuel system should support your N/A set-up. The stock system seems to top out near the 600 rwhp mark. My N/A set-up ran out of steam at 592 rwhp.

 

[Robert Dyck]

Thanks...what year is the car?

 

[chopperpilot]

When I did my heads/cam build this spring, I talked with Chuck Tator about the injectors and he recommended sending them to Tony Armour at Armour Racing for cleaning and bench testing. Now the injectors look like new, work like new, are marked for specific cylinders, and the turnaround time was incredible!

 

[DrumrBoy]

What Banton said. If the pump is good and the injectors are clean, stock should be good to around 600.

 

[banton]

Thanks...what year is the car?

It is a '97 GTS.

 

[ViperTony]

Stock pump and injectors are fine with GG mods in my signature. I had to cut back on fuel during my tuning. I didn't record fuel injector duty but the fuel pressure was fine. Next time I tune I'll record injector duty and post. I think the stock GenII fuel system is good for 550-600rwhp based on what I've seen for similar NA builds. Greg advised me as such and this has been the case for me.

 

[345s-bspinnin]

The stock fuel system should support your N/A set-up. The stock system seems to top out near the 600 rwhp mark. My N/A set-up ran out of steam at 592 rwhp.

Do you know your duty cycle when you ran out of fuel? Do you know if the injectors were static at that point, or could the tune have been further modified for a higher injector duty cycle at those operating conditions (MAP pressure, rpm, % throttle, etc.)



Has anyone ever actually recorded injector duty cycle? I am curious to see if we are approaching the recommended max duty cycle (80%). Most injectors go static (full open) after about 90%.

While I know that the inquiry from the OP is for a Gen II, my Gen III has seen seen over 660whp (actual uncorrected) on the OEM fuel system.

 

[KNG SNKE]

I run 560+ whp on a 2001 and I am running out of fuel in the upper rpms. This is a Roe car but I would think the fuel requirements would be the same no?

 

[Tagoo]

I believe that it takes more fuel to get to a given whp (let's say 500 whp) with a supercharger that it takes to get to the same whp with a NA motor. My reasoning is based on the idea that a twin screw supercharger requires a bunch of hp just to turn the screws (I've heard up to 100 hp). A normally aspirated (or even a turbo) motor doesn't have that same "parasitic hp drain". Therefore, more fuel is required to get to 500 whp with a supercharger than with NA or turbo engines.

Note, the supercharger will more than make up for the hp it consumes by making an extra 200 whp. However, to make that extra 200 whp, it actually is making an additional 100 hp that you do not see because it is being consumed in the process of spinning the supercharger. So, if a supercharger has to make more hp in the motor, than NA motors or turbo motors,to get to a given whp level, then it seems supercharged motors would take more fuel to get to that whp level as well. I welcome any thoughts on this theory.

I run 560+ whp on a 2001 and I am running out of fuel in the upper rpms. This is a Roe car but I would think the fuel requirements would be the same no?

 

[KNG SNKE]

You are probably right. I know I run out of fuel but that makes sense.

 

[Green Viper]

I agree with what the others stated, we have looked at mine carefully in different temps on the dyno and also while driving to make sure the air fuel ratio is fine. The stock pump and injectors have had no problem supporting 570 rw-hp on race gas or 545 rw-hp on 91 octane and I am running a touch on the rich side to keep it cooler and less likely to have a problem. Good luck with your build!

 

[banton]

Do you know your duty cycle when you ran out of fuel? Do you know if the injectors were static at that point, or could the tune have been further modified for a higher injector duty cycle at those operating conditions (MAP pressure, rpm, % throttle, etc.)



Has anyone ever actually recorded injector duty cycle? I am curious to see if we are approaching the recommended max duty cycle (80%). Most injectors go static (full open) after about 90%.

While I know that the inquiry from the OP is for a Gen II, my Gen III has seen seen over 660whp (actual uncorrected) on the OEM fuel system.

When they were dyno tuning my car they were monitoring injector duty cycle, but I don't recall the peak percentage they went to trying to hit 600 rwhp on the stock fuel. I know it was above the 80% you reference and am guessing my car is set-up to be over 80% on the top end. I have had the same tune for serval years without issue. Being a street car I don't forsee any issues I will never be running on the top end for long periods of time on the street.

 

[Jack B]

The fuel pump is no issue. The problem can be the injectors. If you run the numbers they go static at approx 525-550 rwhp, however, several cars on this site have gone further. I have dozens of detailed logs that show good fuel pressure, but, also show trying to increase injector pulse width has little effect on a/f - that is a sign of the injector going static. This is with an engine in the 525 hp range, again, there are people on this site that have gone further.

 

[Camfab]

I believe that it takes more fuel to get to a given whp (let's say 500 whp) with a supercharger that it takes to get to the same whp with a NA motor. My reasoning is based on the idea that a twin screw supercharger requires a bunch of hp just to turn the screws (I've heard up to 100 hp). A normally aspirated (or even a turbo) motor doesn't have that same "parasitic hp drain". Therefore, more fuel is required to get to 500 whp with a supercharger than with NA or turbo engines.

Note, the supercharger will more than make up for the hp it consumes by making an extra 200 whp. However, to make that extra 200 whp, it actually is making an additional 100 hp that you do not see because it is being consumed in the process of spinning the supercharger. So, if a supercharger has to make more hp in the motor, than NA motors or turbo motors,to get to a given whp level, then it seems supercharged motors would take more fuel to get to that whp level as well. I welcome any thoughts on this theory.

Right on the money

 

[Jack B]

Here is the math for a NA engine, the math shows the car going static at 500 hp rw (580 flywheel), keep in mind this is the math, not the real world.

Fuel @ 500 RWHp (lbs/hr)	BSFC	Required Injector (Lbs/hr)		Gen 2 Injector lbs/hr	Adjusted for 50 PSI (lbs/hr)	Static Point (lbs/hr)
265	0.45	26		29	33	27
294	0.5	29
Fuel @ 600 RWHp (lbs/hr)	BSFC	Required Injector (Lbs/hr)
318	0.45	32
353	0.5	35

 

[Robert Dyck]

Excellent discussions....big thanks to all that responded!

 

[345s-bspinnin]

Good post Jack B.

I did similar math for my Gen III setup and found some surprising data:

Power: ~750 bhp (650whp*1.15= 747bhp)
BSFC: 0.5
Fuel Press: 55 psi (OEM)
Max Duty cycle: 0.8
Required Inj: 41.7 lbs/hr @ 43.5 psi

The adjusted injectors size is 46.8 lbs/hr @ 55 psi. For all 10 injectors, the math works outto 252 L/hr at 40psi

This shows me approaching exceeding a single 255 L/hr walbro flow limit. Does anyone know the Gen III OEM injector size? How about the Gen III OEM fuel pump flow rate?

 

[SEASNAKE]

My car put down 530RWHP after heads/cam. And I have had no issues (and I've put close to 70,000 miles on my car after the mods).

 

[Jack B]

Good post Jack B.

I did similar math for my Gen III setup and found some surprising data:

Power: ~750 bhp (650whp*1.15= 747bhp)
BSFC: 0.5
Fuel Press: 55 psi (OEM)
Max Duty cycle: 0.8
Required Inj: 41.7 lbs/hr @ 43.5 psi

The adjusted injectors size is 46.8 lbs/hr @ 55 psi. For all 10 injectors, the math works outto 252 L/hr at 40psi

This shows me approaching exceeding a single 255 L/hr walbro flow limit. Does anyone know the Gen III OEM injector size? How about the Gen III OEM fuel pump flow rate?

The general theory is that the Gen II is 190 LPH and the Gen III is 255 LPH. I have a Gen III pump on my shelf and it is a Walboro. Take a look at he Kenne Belle or MSD voltage booster, I have run one on my car and have no issues with it. The flow increase is dramatic at increased voltage.

 

[Camfab]

I've got 585 RWHP on a stock GEN II fuel system...................Naturally Aspirated, go figure.

 

[345s-bspinnin]

The assumed value for BSFC can alter the equation quite a bit. I found Kai SRT10's Exotic Engine Dyno thread from a few years back. EE's engine dyno shows it at 0.459 at redline. That engine made 710hp, 710 lbft of torque on the engine dyno, and 609whp and 609 whp (14.8% loss).

The 0.45 BSFC explains why a couple of folks have cleared 585whp on the stock Gen II system, and why some of us Gen III naturally aspirated builds have have exceeded 650whp on the stock system.