ideal and safe air to fuel ratio??? nitrous gurus please come in....
05-08-2007, 05:40 PM
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ideal and safe air to fuel ratio??? nitrous gurus please come in.... Im running about 11.2 to 1 motor with heads, cam, etc. Last time I went to the dyno my a/f was between 12.9 and 13.1. A guy I talked to at NX said that was way too rich and I should be closer to 14.7 to 1??? The boggling part is Im running a dp kit, and The jets that they gave me were for a low pressure system, which I have and he said that those jet settings were for 1050 psi on the bottle and 9psi on the dedicated pump. Im only running about 4.5 psi and Im way too rich, generally around 11.0 and 10.5 especially above 6000. The crazy thing is Im running a 250 shot and only picking up about 150 to the wheels. Im pulling about 2-4 degrees out, running 112 sunuco fuel, and runnonh ngk iridiums which are 4 steps colder than stock. The pump im running is the holley blue. What should I do???
05-08-2007, 05:56 PM
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First off..don't listen to the KID at NX....
Here's some recommended SAFE AFR numbers...
12 to 1 for 100-150shot
11.5 to 12 for 175-225shot
11 to 1 at 250
Like I said these are just reference numbers but you in NO FRIGGIN way want to run 14.7 to 1 WOT. Talk about killing an engine....Infact are you sure he said that?
Here's some recommended SAFE AFR numbers...
12 to 1 for 100-150shot
11.5 to 12 for 175-225shot
11 to 1 at 250
Like I said these are just reference numbers but you in NO FRIGGIN way want to run 14.7 to 1 WOT. Talk about killing an engine....Infact are you sure he said that?
05-09-2007, 06:42 PM
#7
I think you are asking for trouble with those tiny iridium electrodes and that big a shot reguardless of how much colder than stock they are.
Thes guys are right about AFR and this is why you should not necessarily trust the "tech" advise from big companies. You have some goober who this is just a job to, non-enthusiasts do not put forth the effort to truely understand.
Now tech advise you get from small shops founded and still run by an enthusiast can often be good advise.
Thes guys are right about AFR and this is why you should not necessarily trust the "tech" advise from big companies. You have some goober who this is just a job to, non-enthusiasts do not put forth the effort to truely understand.
Now tech advise you get from small shops founded and still run by an enthusiast can often be good advise.
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05-09-2007, 08:25 PM
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Keep your NGK's and do some more tunning if you are running at 11.0 A/F you will pick up some good #'s if you get it to a 12.3-12.8 Your HP will come up and you TQ will come down.
05-09-2007, 11:15 PM
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Do not run 12.8 AFR on a 250 SHOT...Period....
Infact, at the drags I find that anything more than 12.5 AFR "NA" on a cammed LT1 slows them down past the 1/8 mile (and that's "NA"). Now factor in burn rates, cylinder pressure and the actual AFR (remember the more Nitrous the more your AFR should drop) and you can see just that alone will change an engines fueling characteristics. Little know fact, that if a engine was run just on Nitrous alone the AFR will be 6-7 AFR range (if I remember the number right). So, the more Nitrous you shoot in the richer the combo will be...
You timing will need to be further reduced if your already seeing 2-3* Knock retard. We use 20* total timing on Ellis's 200RWHP shot and 11-11.5 AFR. His engine is SCR 12.1 to 1 though. And we can only run 31-32 total on his engine "NA." So, your timing may be more or less. We also use Autolite copper race plugs so, that the electrode and backstrap will give up first rather than the piston...We have already seen melted tips even at our AFR. A little engine fubar during a run, with the fuel, timing or load, that you have not noticed, and you can have a real bad day....quick.... The recommended plug from AFR at heat range 9 ''Autolite 3910'' is a real good plug for a 250 flywheel shot.
Infact, at the drags I find that anything more than 12.5 AFR "NA" on a cammed LT1 slows them down past the 1/8 mile (and that's "NA"). Now factor in burn rates, cylinder pressure and the actual AFR (remember the more Nitrous the more your AFR should drop) and you can see just that alone will change an engines fueling characteristics. Little know fact, that if a engine was run just on Nitrous alone the AFR will be 6-7 AFR range (if I remember the number right). So, the more Nitrous you shoot in the richer the combo will be...
You timing will need to be further reduced if your already seeing 2-3* Knock retard. We use 20* total timing on Ellis's 200RWHP shot and 11-11.5 AFR. His engine is SCR 12.1 to 1 though. And we can only run 31-32 total on his engine "NA." So, your timing may be more or less. We also use Autolite copper race plugs so, that the electrode and backstrap will give up first rather than the piston...We have already seen melted tips even at our AFR. A little engine fubar during a run, with the fuel, timing or load, that you have not noticed, and you can have a real bad day....quick.... The recommended plug from AFR at heat range 9 ''Autolite 3910'' is a real good plug for a 250 flywheel shot.
