Went racing on saturday and went a best of 11.38 at 118 or 119 (no paper slip) and i reviewed the direct scan run i was at 94% inj pw. they are the 65/60# inj. car weighs 3553 w/ out me im 165lb. it was 55 degrees out and i was running 26-27 # boost w/ 25 timing and either 6 or 8 % rich on translator. My 02's were in the 720's-730's during the run. My buddies watching said they didnt see much black smoke coming from the exhaust. Im using a stock dut neck intercooler and 125k mile stock bottom end. Thanks Rich.
Why would i be using so much injector%
- Thread starter jetmech
- Start date
BlackBandit
God loves Buicks!
- Joined
- Mar 29, 2003
I would think that if your buddies are seeing any black smoke you're rich. Maybe disregard your O2 readings and pull some fuel and see what happens. Perhaps you have an exhaust leak that is causing you to show lean. Are you running alky or race gas?
get a WB sensor. im sure the car is still rich. we started tunning my bothers car inj duty cycle was at 91 now its at 79 and its still rich.
johnplogii
Senior citizen
- Joined
- Aug 13, 2005
I don't know how reliable the direct scan readings are but those injectors are capable of a lot more than that & should not be at 94% duty cycle. I run the same injectors without alky. Sorry, no duty cycle #'s. Not much black smoke sounds like there was some.
Sorry, let me rephrase , they said they didn't see any black smoke. The exhaust leak is possible. My pass side sounds like an exhaust leak but i can't find it. I will pull the header and look for cracks. So i shouldnt put much trust in the direct scan inj. numbers?
also i will pull a plug and see what it looks like
sorry, race gas 110
also i will pull a plug and see what it looks like
sorry, race gas 110
johnplogii
Senior citizen
- Joined
- Aug 13, 2005
The direct scan should be more accurate than the narrow band o2 like others said. Exhaust leaks are a good thing to look for.
i just check the left front plug and its a light shade of brown, to me it looks good. I see your going 10.20's on these same inj. thanks
sorry, I was wrong, I take back what I said, with a caveat - how high are you revving it? If you are up to 6000+ rpm, then I can see the duty cycle getting that high. Direct Scan duty cycle should be good, the inj pw comes straight from the computer, and then duty cycle is just a formula using that and rpm. So, what rpm is that 94% duty cycle at?
Are you using an Extender chip? If so, what kind of gm/sec does it say at that 94% point? Just wondering since you are running a Translator, it's worth a shot.
As for how far a set of injectors will take you, it is a little variable. If you are moving a bunch of air, you have to give it the fuel to achieve a desirable a/f ratio. Whether the engine turns that air and fuel into 100 hp or 500 hp is immaterial; you still have to match the fuel to the air. An engine in poor tune or poor health, or a car with drivetrain issues, could need 10 sec type fueling and yet still be stuck in the 14's...
John
Are you using an Extender chip? If so, what kind of gm/sec does it say at that 94% point? Just wondering since you are running a Translator, it's worth a shot.
As for how far a set of injectors will take you, it is a little variable. If you are moving a bunch of air, you have to give it the fuel to achieve a desirable a/f ratio. Whether the engine turns that air and fuel into 100 hp or 500 hp is immaterial; you still have to match the fuel to the air. An engine in poor tune or poor health, or a car with drivetrain issues, could need 10 sec type fueling and yet still be stuck in the 14's...
John
It is shifting between 6000 and 6175. and the maf reading gets as high as 252gm/sec. I see the point on the worn engine theory. My buddy is running 11.05 and 50# inj. w/ gn1 heads pte front mount and a fresh motor and is not pushing his inj as hard as i am. Makes sense. thanks and he is only shifting around 5500
I have checked it a month ago but i could check again. Thanks
turbobose13
New Member
- Joined
- Nov 18, 2004
my 60# pounder's are go to Height 10's, with my sig below.
GNVYUS 1
Well-Known Member
- Joined
- Dec 15, 2002
Good times, but 6100rpm on a 125k stock bottom end, 
I am sure you have a hot wired 340 so look into that WOT pressure like 750 mentioned and also check when you replaced your fuel filter last or maybe a collapsed fuel sock.
Doesn't 252 grams seem low for a 61 turbo at 27psi??
Sounds like a stock remanned Maf reading to me.
BTW, those 9 second 60lb times are with twin nozzle alky, it didn't sound like Jetmech was on Meth.
I am sure you have a hot wired 340 so look into that WOT pressure like 750 mentioned and also check when you replaced your fuel filter last or maybe a collapsed fuel sock.
Doesn't 252 grams seem low for a 61 turbo at 27psi??
Sounds like a stock remanned Maf reading to me.
BTW, those 9 second 60lb times are with twin nozzle alky, it didn't sound like Jetmech was on Meth.
OK, it all sounds explainable:
Method 1: 252 x 2 = 504 gm/s of air. Target an a/f ratio of 11:1. So you need 45.8 gm/s of fuel. 45.8 gm/s = 363.5 lb/hr, or, with 6 injectors, 60.6 lb/hr per injector. With 65 lb/hr injectors, 60.6/65 = 93.2%, which matches the duty cycle that Direct Scan is saying. Now, the question is, is that 504 gm/s right? You said you had the translator set at 6-8% rich. I think the way the translator does that is by increasing it's air flow output signal to the ecm by 8%. So maybe your are overfueling by 8%, *if* the MAF reads correctly at the 0 setting. Of course it may not, it might need that 8% to make the MAF signal match real life. Hard to say. What is Direct Scan saying for A/F ratio commanded? Whatever the case, sounds like we can explain the ecm's thinking when it commands such a high duty cycle. Anyway, here's another check:
Method 2:
231 cid, 6 cylinders, 27# boost, 6175 rpm, assume 125F manifold air temperature, what volumetric efficiency is required to get 504 gm/s of air (which we've already shown to require the duty cycle you are seeing)? Answer = 84%. That sounds very reasonable to me, esp. with the cam and other mods you have.
Based on that kind of air flow and fuel flow, I would expect you to be making anywhere from 475 hp to 625 hp (crankshaft), depending on how efficiently your engine is using that air and fuel. How does that flange up with your mph?
John
Method 1: 252 x 2 = 504 gm/s of air. Target an a/f ratio of 11:1. So you need 45.8 gm/s of fuel. 45.8 gm/s = 363.5 lb/hr, or, with 6 injectors, 60.6 lb/hr per injector. With 65 lb/hr injectors, 60.6/65 = 93.2%, which matches the duty cycle that Direct Scan is saying. Now, the question is, is that 504 gm/s right? You said you had the translator set at 6-8% rich. I think the way the translator does that is by increasing it's air flow output signal to the ecm by 8%. So maybe your are overfueling by 8%, *if* the MAF reads correctly at the 0 setting. Of course it may not, it might need that 8% to make the MAF signal match real life. Hard to say. What is Direct Scan saying for A/F ratio commanded? Whatever the case, sounds like we can explain the ecm's thinking when it commands such a high duty cycle. Anyway, here's another check:
Method 2:
231 cid, 6 cylinders, 27# boost, 6175 rpm, assume 125F manifold air temperature, what volumetric efficiency is required to get 504 gm/s of air (which we've already shown to require the duty cycle you are seeing)? Answer = 84%. That sounds very reasonable to me, esp. with the cam and other mods you have.
Based on that kind of air flow and fuel flow, I would expect you to be making anywhere from 475 hp to 625 hp (crankshaft), depending on how efficiently your engine is using that air and fuel. How does that flange up with your mph?
John
Grumpy's also spraying a crap load of alky too more than one would think. Think about it he only has a single in tank walbro 340. you think it's flowing that much fuel to support that kinda horsepower. not happening.
Like someone stated up above i think it's time for a better fuel pump or a set of dual intank pumps.
when flowing liquids when pressure goes up the volume goes down. what's the base fuel pressure? If you have a extender chip it should be set @ 45 line off. so 45psi plus the 28 psi it makes when under boost for the 1-1 rate of rise. so thats 73 psi of flowing pressure. Unless the walbro 340 has been modified the pressure relief valve in the pump is set at 80 psi per walbro specs. So that tells me that your almost over running your fuel pump.
HTH