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I’m rebuilding the motor for my 94 Z28 and I’m going with a 383, a cam, then freshening up the heads. Hoping to be good for around 500 hp (probably gonna get disappointed on that number lol) but I was wondering what fuel pump and what # injectors I should run for it. I was also planning on 100-150 shot somewhere down the road. I was looking at the Walbro 255iph fuel pump and some 42# injectors. Will this be enough? If it isn’t, maybe with a Hotwire kit it would be?
Thanks in advance!
You can make 500 HP at the flywheel with a 36 #/HR injector. That's based on a build/tune that can achieve a brake specific fuel consumption (BSFC) of 0.46 #/HR/HP, at a duty cycle of no more than 80%. A well built/tuned engine should be able to achieve that BSFC. My 490 HP build achieved an 0.42 BSFC. I ran that on a 208 LPH Bosch high pressure in-tank pump, running 58 PSI (4 bar) at the injectors. The 80% max duty cycle used to be a "standard", but based on the design of modern injectors, that's fairly conservative.
You will be fine going with a 42 #/HR injector. Leaves you room for some additional tweaks, a sub-sea level density altitude track day, etc.. The stock LT1 PCM is OK with the 36 #/HR injectors in regard to it's ability to turn the short pulse widths required for the engine to idle. Not sure if it gets a little skittish on the 42 #/HR variety. Probably varies with the type of injector,
A real (not counterfeit) Walbro 255 should be OK for 500 flywheel HP. I would use the Hotwire kit no matter how much HP you are looking for. You could also consider the higher pressure version of the Walbro if you want to run the injectors at a higher pressure.
With nitrous BSFC goes up, and can exceed 0.50 #/HR/HP. What you need in the way of a fuel pump depends on what type of nitrous system you are running (wet or dry) and how you are adding the extra fuel. For my setup with a 275 HP dry shot, I added an outboard 208 LPH high pressure Bosch pump, pulling off a sump at the rear/bottom of the stock fuel tank. That pump only ran when the nitrous system was armed. Flow from both pumps was combined before the fuel filter. Injectors were high impedance Bosch 74 #/HR, and I was using MoTeC engine management system, not the stock LT1 PCM. But it got awkward because if you need to run high octane racing fuel it means you have to change the fuel in the tank,
For a wet system (more common) some people like to run a separate small fuel tank with its own pump, feeding the N2O system spray bar or nozzle(s). You put the high octane fuel through that system.
You can make 500 HP at the flywheel with a 36 #/HR injector. That's based on a build/tune that can achieve a brake specific fuel consumption (BSFC) of 0.46 #/HR/HP, at a duty cycle of no more than 80%. A well built/tuned engine should be able to achieve that BSFC. My 490 HP build achieved an 0.42 BSFC. I ran that on a 208 LPH Bosch high pressure in-tank pump, running 58 PSI (4 bar) at the injectors. The 80% max duty cycle used to be a "standard", but based on the design of modern injectors, that's fairly conservative.
You will be fine going with a 42 #/HR injector. Leaves you room for some additional tweaks, a sub-sea level density altitude track day, etc.. The stock LT1 PCM is OK with the 36 #/HR injectors in regard to it's ability to turn the short pulse widths required for the engine to idle. Not sure if it gets a little skittish on the 42 #/HR variety. Probably varies with the type of injector,
A real (not counterfeit) Walbro 255 should be OK for 500 flywheel HP. I would use the Hotwire kit no matter how much HP you are looking for. You could also consider the higher pressure version of the Walbro if you want to run the injectors at a higher pressure.
With nitrous BSFC goes up, and can exceed 0.50 #/HR/HP. What you need in the way of a fuel pump depends on what type of nitrous system you are running (wet or dry) and how you are adding the extra fuel. For my setup with a 275 HP dry shot, I added an outboard 208 LPH high pressure Bosch pump, pulling off a sump at the rear/bottom of the stock fuel tank. That pump only ran when the nitrous system was armed. Flow from both pumps was combined before the fuel filter. Injectors were high impedance Bosch 74 #/HR, and I was using MoTeC engine management system, not the stock LT1 PCM. But it got awkward because if you need to run high octane racing fuel it means you have to change the fuel in the tank,
For a wet system (more common) some people like to run a separate small fuel tank with its own pump, feeding the N2O system spray bar or nozzle(s). You put the high octane fuel through that system.
So by stock PCM I assume you mean without a tune, I assumed this even before I thought about the injectors I thought about the cam, so I went ahead and bought the Tunercat so I assume I should be fine running 42# injectors as long as I account for that in the tune.
The motor is gonna be running at about 11.5 compression ratio so I was going to run 94 octane (highest near me) and then throw octane booster in there to hopefully account for the rest.
As for the nitrous I was planning on a dry system then maybe wiring either a button somewhere on the steering wheel or a switch on at full throttle then do something with the tune, I don’t really know how tuning works a whole lot so I might be wrong on that.
I probably missed something responding to that so if I did, sorry
Thank you
Octane requirement is not determined solely by the static compression ratio. It is determined by the dynamic compression ratio, which is a function of the static compression ratio and the cam event timing. Roughly, the more aggressive the cam, the lower the dynamic compression ratio.
By mentioning the stock PCM with regard to dry nitrous, I was pointing out there are limits to how you can properly tune for normally aspirated operation, and also for nitrous, particularly with a dry system. That's why I chose to use an aftermarket ECU that could be tuned to perfection normally aspirated, plus independent tunes for a single stage (125 HP) of nitrous, plus a second stage (150 HP). Can't do that with a (tuned) stock PCM. Ignition timing can be addressed somewhat with an external retard box. A window switch (can be set to limit the RPM and/or throttle % at which the N2O can be activated, and when to shut the N2O off. You can’t spray a lot of nitrous at low RPM. It will build cylinder pressures that damage pistons, ring, and heads.
After that, when I had the stroker built, and went with a 275 shot of nitrous, I left the tuning to a highly skilled professional, who had built a 1,125 HP S/C LT1 for a friend's 1997 30th SS. They went with a relatively mild cam to insure the engine would pass NJ tailpipe emissions, and set up the 2-stage nitrous system that was activated at the push of a button (or two). I think the tuner was a bit conservative, because I had to run VP Fuel C16 heavily leaded racing fuel (116 motor octane) for the full 275 shot. Spent a lot of time on the engine dyno, then more on the chassis dyno, wrapping up with testing and tweaking 1/8th-mile pulls during a track rental.
But fuel control is difficult with a dry system. It's easier with a wet system, where you can add the correct amount of fuel required for the N2O by adjusting the fuel flow from the auxiliary fuel system. My first venture with nitrous was in 1995 when I installed (brand new at the time) an NOS 125 HP dry nitrous kit, designed specifically for the LT1. It added the extra fuel by increasing the fuel pressure to 85-90 PSI, using a slipstream of nitrous through a CO2 pressure regulatior, applying the high pressure to the vacuum side of the fuel pressure regulator. Was really a hit-or-miss control system, so they ran the system on the rich side to avoid running lean and getting detonation severe enough to break piston ring lands.
Octane requirement is not determined solely by the static compression ratio. It is determined by the dynamic compression ratio, which is a function of the static compression ratio and the cam event timing. Roughly, the more aggressive the cam, the lower the dynamic compression ratio.
By mentioning the stock PCM with regard to dry nitrous, I was pointing out there are limits to how you can properly tune for normally aspirated operation, and also for nitrous, particularly with a dry system. That's why I chose to use an aftermarket ECU that could be tuned to perfection normally aspirated, plus independent tunes for a single stage (125 HP) of nitrous, plus a second stage (150 HP). Can't do that with a (tuned) stock PCM. Ignition timing can be addressed somewhat with an external retard box. A window switch (can be set to limit the RPM and/or throttle % at which the N2O can be activated, and when to shut the N2O off. You can’t spray a lot of nitrous at low RPM. It will build cylinder pressures that damage pistons, ring, and heads.
After that, when I had the stroker built, and went with a 275 shot of nitrous, I left the tuning to a highly skilled professional, who had built a 1,125 HP S/C LT1 for a friend's 1997 30th SS. They went with a relatively mild cam to insure the engine would pass NJ tailpipe emissions, and set up the 2-stage nitrous system that was activated at the push of a button (or two). I think the tuner was a bit conservative, because I had to run VP Fuel C16 heavily leaded racing fuel (116 motor octane) for the full 275 shot. Spent a lot of time on the engine dyno, then more on the chassis dyno, wrapping up with testing and tweaking 1/8th-mile pulls during a track rental.
But fuel control is difficult with a dry system. It's easier with a wet system, where you can add the correct amount of fuel required for the N2O by adjusting the fuel flow from the auxiliary fuel system. My first venture with nitrous was in 1995 when I installed (brand new at the time) an NOS 125 HP dry nitrous kit, designed specifically for the LT1. It added the extra fuel by increasing the fuel pressure to 85-90 PSI, using a slipstream of nitrous through a CO2 pressure regulatior, applying the high pressure to the vacuum side of the fuel pressure regulator. Was really a hit-or-miss control system, so they ran the system on the rich side to avoid running lean and getting detonation severe enough to break piston ring lands.
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Hmm, I didn’t even think of an aftermarket ECU, I’ll have to look into one once I start thinking about putting nitrous on the car, thanks a lot for your insight!
