When will 42lb injectors be maxed out?
Thread Starter
Teching In
Joined: Apr 2003
Posts: 26
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From: St. Louis
When will 42lb injectors be maxed out? I am running a 372ci engine with the A&A ATI P1 setup. I should be pushing between 8-10psi. I am curious, when will my 42lb injectors max out? We are getting ready to start tuning and I just want to see what you guys think. . .should I be running 60lb injectors?
TECH Regular
Joined: Oct 2005
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The general rule of thumb is "1/2 lb. of fuel per HP per hour" and to avoid overheating the injector coils it is recommended to use a maximum of ~85% duty cycle, so 42 lb./hr. would give (42 x 8)/.5 x .85 or 571 CHP, maybe 460 -490 WHP, depending on the dyno and if auto or manual. That said, a few other considerations:
o Turbos and SCs typically run richer than normally aspirated engines.
o Smaller injectors give better fuel control at idle/low speed.
o To truly be "sequential", injectors should be running at <65% DC, otherwise they're flowing almost all the time at high RPM and might as well be batch fire.
o To count as "42 lb." as installed, obviously fuel pressure has to be the same psi above boost as when flowed.
O I'm not an SC expert, but depending on your other mods, I would guess 10 psi would be good for closer to 700 CHP, suggesting injectors of at least 55 lb./hr.
Hopefully someone with actual experience will now jump in to 'fine-tune' my S.W.A.G...
o Turbos and SCs typically run richer than normally aspirated engines.
o Smaller injectors give better fuel control at idle/low speed.
o To truly be "sequential", injectors should be running at <65% DC, otherwise they're flowing almost all the time at high RPM and might as well be batch fire.
o To count as "42 lb." as installed, obviously fuel pressure has to be the same psi above boost as when flowed.
O I'm not an SC expert, but depending on your other mods, I would guess 10 psi would be good for closer to 700 CHP, suggesting injectors of at least 55 lb./hr.
Hopefully someone with actual experience will now jump in to 'fine-tune' my S.W.A.G...
Thread Starter
Teching In
Joined: Apr 2003
Posts: 26
Likes: 0
From: St. Louis
I have been figuring 42's should be good for about 550rwhp.
Hopefully this weekend I will get a chance to run it on the ease program and I will take a look at the duty cycle.
I am also concerned that perhaps my O2 sensors need to be replaced. I was seeing a good A/F ratio. I went to the dyno Friday and saw it was running a bit lean.
Keep it coming, just curious what you guys have seen. . .
Hopefully this weekend I will get a chance to run it on the ease program and I will take a look at the duty cycle.
I am also concerned that perhaps my O2 sensors need to be replaced. I was seeing a good A/F ratio. I went to the dyno Friday and saw it was running a bit lean.
Keep it coming, just curious what you guys have seen. . .
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Are you running the stock fuel pump? The amount of fuel delivered by the injectors will also depend on pump pressure. You can calculate a safe hp limit for the 42#ers, but it will be based on maintaining 58 psi (or close to it) at wot. If your fuel pump drops pressure, it will effectively lower that hp limit. It might be a good idea to put a pressure gauge on the fuel rail to make sure your pump is healthy.
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Originally Posted by bshell
Are you running the stock fuel pump? The amount of fuel delivered by the injectors will also depend on pump pressure. You can calculate a safe hp limit for the 42#ers, but it will be based on maintaining 58 psi (or close to it) at wot. If your fuel pump drops pressure, it will effectively lower that hp limit. It might be a good idea to put a pressure gauge on the fuel rail to make sure your pump is healthy.
Svo 42's have been used for almost 5 years on boosted LS1's for ~600 plus or minus. Remember most folks run them at higher Ls1 fuel pressure, so they flow allot more.
Rule of thumb has been if if plan to go around 600 the 42's are perfect but if are going much above to upgrade. I think 60's (motrons?) were the next logical step as they tune easily like the 42's.
Rule of thumb has been if if plan to go around 600 the 42's are perfect but if are going much above to upgrade. I think 60's (motrons?) were the next logical step as they tune easily like the 42's.
Duty cycle is also highly dependent on your tune. If you are using a rich tune (ie, FI), you will run higher IDCs than an NA car with a leaner tune. I have seen 20% IDC swings through tuning alone.
Things to check to ensure you are getting the correct injectors:
Fuel pump - pressure idle through wot (steady pressure, no dips and minimal trailing off).
Injectors - if using used injectors, send them to a shop for cleaning / flow matching.
Tune - make sure your fuel trims are all slightly negative, verify wot fuel with a wideband.
Remember that the injector sizing calculators do not take into account a rich tune, clogged injectors, a tired fuel pump, or rich / lean tune.
Things to check to ensure you are getting the correct injectors:
Fuel pump - pressure idle through wot (steady pressure, no dips and minimal trailing off).
Injectors - if using used injectors, send them to a shop for cleaning / flow matching.
Tune - make sure your fuel trims are all slightly negative, verify wot fuel with a wideband.
Remember that the injector sizing calculators do not take into account a rich tune, clogged injectors, a tired fuel pump, or rich / lean tune.
