Injector sizing Q&A
#1
Injector sizing Q&A
I got an 1987 GXL with 4 little 460cc injectors in an FC S4 NA 6-port with stock ECU and original motor.
Well, old reliable finally needs a rebuild after 25 years. So I'm gonna tear it down and build it to last another 25 solid years. You know, do it once and do it right.
I want to keep the low idle and low end torque, so I don't want to port the primary intake at all. Therefore a pair of stock 460cc primary injectors should be fine, right?
But let's say, when I get to 4000RPM, my auxilary ports open up and I want them to suck more air. Would a large street port on just the secondary ports do that for me? Would the stock ECU and stock injectors be able to keep up without running lean or detonating?
If I could port the secondary intakes to flow 20% more air, then I would need 20% more fuel. And if I throw in a pair of 550cc injectors as my secondary injectors, that would mathematically give the proper air/fuel balance, while retaining the stock ECU.
But realistically, if I could only port the secondary intake by 10% and it would actually only flow 5% more air, should I choose to run super rich with the 550cc injectors dumping more than enough gas for the short time I spend above 4000RPM?
Or is the stock ECU generous enough to cover the fuel requirements of a street ported secondary intake, provided the primary intake is still stock size.
And I got stock exhaust ports...if that matters.
Remember, I want it reliable and built to last another 25 years. I don't want it to run lean and detonate (BANG) or backfire (POP) from running too rich.
Well, old reliable finally needs a rebuild after 25 years. So I'm gonna tear it down and build it to last another 25 solid years. You know, do it once and do it right.
I want to keep the low idle and low end torque, so I don't want to port the primary intake at all. Therefore a pair of stock 460cc primary injectors should be fine, right?
But let's say, when I get to 4000RPM, my auxilary ports open up and I want them to suck more air. Would a large street port on just the secondary ports do that for me? Would the stock ECU and stock injectors be able to keep up without running lean or detonating?
If I could port the secondary intakes to flow 20% more air, then I would need 20% more fuel. And if I throw in a pair of 550cc injectors as my secondary injectors, that would mathematically give the proper air/fuel balance, while retaining the stock ECU.
But realistically, if I could only port the secondary intake by 10% and it would actually only flow 5% more air, should I choose to run super rich with the 550cc injectors dumping more than enough gas for the short time I spend above 4000RPM?
Or is the stock ECU generous enough to cover the fuel requirements of a street ported secondary intake, provided the primary intake is still stock size.
And I got stock exhaust ports...if that matters.
Remember, I want it reliable and built to last another 25 years. I don't want it to run lean and detonate (BANG) or backfire (POP) from running too rich.
#4
So stock injectors with stock ECU and stock ports are very rich. (I knew that)
And stock injectors with stock ECU and a large street port won't be too lean, then.
I know the stock injectors with a standalone can be tuned to compensate for the porting/air flow.
But I wasn't sure if the stock tune from a stock ECU could keep up.
I'm trying to avoid the exta cost of buying a standalone and the complexityand time required to tune properly.
And stock injectors with stock ECU and a large street port won't be too lean, then.
I know the stock injectors with a standalone can be tuned to compensate for the porting/air flow.
But I wasn't sure if the stock tune from a stock ECU could keep up.
I'm trying to avoid the exta cost of buying a standalone and the complexityand time required to tune properly.
#5
Rotors still spinning
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You are going to get a bit of a power bump from porting on a stock ecu but it is my opinion that you can get more power out of a stock motor with a properly tuned aftermarket ecu than you can a stock ecu on a ported motor. Porting should always be the very last thing you do since it's the least important.
#6
I need to rebuild now, so I have an opportunity to port the intake a little.
(I'm also upgrading to a light steel flywheel.)
Once it is all put back together it should be solid and reliable with a little power gain.
After I pay for this rebuild, I can start saving for a standalone, which will maximize the porting that I'm doing now.
Over time, I get the benefit of both.
Than a header...and re-tune
(I'm also upgrading to a light steel flywheel.)
Once it is all put back together it should be solid and reliable with a little power gain.
After I pay for this rebuild, I can start saving for a standalone, which will maximize the porting that I'm doing now.
Over time, I get the benefit of both.
Than a header...and re-tune
#7
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however any small porting done isn't going to make any significant difference in air flow or power, especially without an exhaust. so it should still be totally fine.
from a tuning standpoint the injectors are sized really well, and you could arguably have a better combo with a larger fuel pump, and running higher fuel pressure, but stock injectors
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