a FEW questions

jimberg · 06-15-2001, 09:56 PM

WOT's been covered.

Fuel Injectors
When we say 24 lb injector, it means that if it were just a nozzle, you'd be able to inject 24 lbs of fuel through it in an hour if the pressure of the fuel is at 39 psi. By raising the fuel pressure to something like 47 psi, you can increase the output of the fuel injector. The formula is Sqrt( Target fuel pressure / 39psi ) * Injector Rating. e.g. Sqrt( 47 / 39 ) * 24 = 26.35 lbs/hour.

This is important since an engine uses a certain amount of fuel per horsepower per hour. This is called the BSFC (Brake Specific Fuel Consumption). We generally use .5 (.55 is probably more accurate for a naturally aspirated engine) for a rough estimate since it makes calculating easy. The formula is basically ( injector rating * BSFC * No. of Injectors * 0.85 ) Injectors aren't just nozzles that can operate at 100% duty cycle. They open and close which takes time. 85% duty cycle is about all they should be expected to produce. That's why the 0.85 is in the formula. So, for example, 24lb injectors should be able to support 24 * .5 * 8 * 0.85 = 326 HP safely.

Don't confuse this to mean that if you slap 24 lb injectors on your car that you will have 326 hp. You need air to go with that. About 13 lbs of air for every lb of fuel for optimal power.

Blower vs. Supercharger
Blower and supercharger are synonymous. A supercharger is a device that is driven by the engine to force air into the intake. It's usually belt driven.

ET
Simply the elapsed time it takes to cover the length of a drag strip whether 1/8 or 1/4 mile.

Timing @18 degrees
Read the My head choice dilema.. thread for more info. For here, I'll just say it's the number of degrees left for the crank to rotate before the piston hits top dead center. This is the base point at which the computer will send a spark to ignite the air/fuel mixture. I say base point because timing gets advanced as RPMs increase. The 18 degrees is the point at which the computer will start advancing the timing. Total timing is the total number of degrees of advance + the base timing. The computer usually advances about 20 degrees at max rpm under max load so total timing would be 38 in the example you used.

I guess that should about cover it.

------------------
351W 89 Mustang GT Convertible

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06-15-2001, 09:56 PM	#4
jimberg Registered Member Join Date: Oct 1998 Location: Rogers, MN Posts: 2,089	WOT's been covered. Fuel Injectors When we say 24 lb injector, it means that if it were just a nozzle, you'd be able to inject 24 lbs of fuel through it in an hour if the pressure of the fuel is at 39 psi. By raising the fuel pressure to something like 47 psi, you can increase the output of the fuel injector. The formula is Sqrt( Target fuel pressure / 39psi ) * Injector Rating. e.g. Sqrt( 47 / 39 ) * 24 = 26.35 lbs/hour. This is important since an engine uses a certain amount of fuel per horsepower per hour. This is called the BSFC (Brake Specific Fuel Consumption). We generally use .5 (.55 is probably more accurate for a naturally aspirated engine) for a rough estimate since it makes calculating easy. The formula is basically ( injector rating * BSFC * No. of Injectors * 0.85 ) Injectors aren't just nozzles that can operate at 100% duty cycle. They open and close which takes time. 85% duty cycle is about all they should be expected to produce. That's why the 0.85 is in the formula. So, for example, 24lb injectors should be able to support 24 * .5 * 8 * 0.85 = 326 HP safely. Don't confuse this to mean that if you slap 24 lb injectors on your car that you will have 326 hp. You need air to go with that. About 13 lbs of air for every lb of fuel for optimal power. Blower vs. Supercharger Blower and supercharger are synonymous. A supercharger is a device that is driven by the engine to force air into the intake. It's usually belt driven. ET Simply the elapsed time it takes to cover the length of a drag strip whether 1/8 or 1/4 mile. Timing @18 degrees Read the My head choice dilema.. thread for more info. For here, I'll just say it's the number of degrees left for the crank to rotate before the piston hits top dead center. This is the base point at which the computer will send a spark to ignite the air/fuel mixture. I say base point because timing gets advanced as RPMs increase. The 18 degrees is the point at which the computer will start advancing the timing. Total timing is the total number of degrees of advance + the base timing. The computer usually advances about 20 degrees at max rpm under max load so total timing would be 38 in the example you used. I guess that should about cover it. ------------------ 351W 89 Mustang GT Convertible