Ok, I have a stock motor with all the bolt ons, and a large wet shot, upwards of a 200 at the crank. When speaking to NOS, they asked if I was still running stock programming. When I said yes, they said I am probably losing 50 hp or more from not having the timing retarded. However, I just got off the phone with a tuner who said NOS is full of ****, and if it's rich enough (.930's) and there is no KR (there isn't), there is no need to mess with the timing. So can anyone explain to me exactly what pulling the timing does, and do I need to do it. <img border="0" title="" alt="[Confused]" src="images/icons/confused.gif" /> Thanks!

- Matt

 

This is just a guess... but if you lower the timing you probably don't have to run as rich (don't quote me on this just a guess). If you're not running as rich and still have 0kr then you should make more power

 

Sure i'm not an expert, but i can explain some stuff. Retarding timing LOOSES horsepower. However, if your engine advances too much it will begin to ping (or knock). This is very bad and literally burns holes into the pistons. LS1 engines have knock sensor that if detecting knock will automatically retard timing. As far as using nitrous, as soon as you hit the button, the computer retards engine timing because of the increased volumetric compression in the cylinders. If it didn't retard it would start knocking. Pulling more timing pretty much is just a safeguard so that your engine will not explode. Knowing this, the second guy you talked to (not NOS) would be correct. As long as you are not running lean you will be good. When using the nitrous, your knock sensors will pull timing on their own. I know for sure that as long as you aren't lean your engine can handle a 200 shot. Hope this helped at least a little. <img border="0" title="" alt="[Wink]" src="gr_images/icons/wink.gif" />

 

See, thats what I thought. But the mechanic that usually does my nitrous work thought that perhaps if the timing was retarded, it would position the combustion at a better point in the piston cycle... At least, I think thats what he said. <img border="0" title="" alt="[Razz]" src="gr_tounge.gif" />

- Matt

 

That's exactly right, I have it triggered so when I arm the N20, it retards my timing VIA a resistor hooked to the MAF (The right resistor tells the computer that it's 125 degrees out thus retarding timing 2 or 3 degrees)

Since Nitrous burns faster then gas/air you have to retard the timing so the piston is a little closer to TDC to ignite. Otherwise you might get detonation.

<small>[ April 23, 2002, 03:45 PM: Message edited by: 69Muscle ]</small>

 

</font><blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr /><font size="2" face="Verdana, Helvetica, sans-serif">Originally posted by 69Muscle:
<strong>That's exactly right, I have it triggered so when I arm the N20, it retards my timing VIA a resistor hooked to the MAF (The right resistor tells the computer that it's 125 degrees out thus retarding timing 2 or 3 degrees)

Since Nitrous burns faster then gas/air you have to retard the timing so the piston is a little closer to TDC to ignite. Otherwise you might get detonation.</strong></font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">So Air/Fuel aside, you CAN gain power from retarding the timing? Hmmmm.... go F'n figure....

 

</font><blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr /><font size="2" face="Verdana, Helvetica, sans-serif">Originally posted by Trans Am WS6 420:
<strong>Ok, I have a stock motor with all the bolt ons, and a large wet shot, upwards of a 200 at the crank. When speaking to NOS, they asked if I was still running stock programming. When I said yes, they said I am probably losing 50 hp or more from not having the timing retarded. However, I just got off the phone with a tuner who said NOS is full of ****, and if it's rich enough (.930's) and there is no KR (there isn't), there is no need to mess with the timing. So can anyone explain to me exactly what pulling the timing does, and do I need to do it. <img border="0" title="" alt="[Confused]" src="images/icons/confused.gif" /> Thanks!

- Matt</strong></font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">I think the tuner must not be very experienced with N2O. He's right though, if it's rich enough (helps control the heat) and there's no KR, there is no need to mess with the timing, but you can make more power by retarding it. The reason is that regular air has only 24% O2 or something like that, while N2O has 36% O2. So when you use N2O, it might come out to be about 30% O2 mix inside the cylinder. O2 burns faster, so with this higher mix of O2, the burn rate increases. Therefore, with the higher burn rate, you want to spark sooner for maximum power. It's not necessary, but it's a good power increase. I wouldn't say 50 hp on a 200 shot, possibly 15-20 though, hard to say.

 

Actually I'm looking to do something similar to a 275-300 shot. <img border="0" title="" alt="[Smile]" src="gr_stretch.gif" />

 

</font><blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr /><font size="2" face="Verdana, Helvetica, sans-serif">Originally posted by Trans Am WS6 420:
<strong>Actually I'm looking to do something similar to a 275-300 shot. <img border="0" title="" alt="[Smile]" src="gr_stretch.gif" /> </strong></font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">When running something that large, you definately need to retard timing, and you probably need some type of fuel suitable for N2O.

I would recommend getting a book or reading about it on the internet before going to that large a shot.

 

</font><blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr /><font size="2" face="Verdana, Helvetica, sans-serif">Originally posted by akw408:
<strong> </font><blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr /><font size="2" face="Verdana, Helvetica, sans-serif">Originally posted by Trans Am WS6 420:
<strong>Actually I'm looking to do something similar to a 275-300 shot. <img border="0" title="" alt="[Smile]" src="gr_stretch.gif" /> </strong></font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">When running something that large, you definately need to retard timing, and you probably need some type of fuel suitable for N2O.

I would recommend getting a book or reading about it on the internet before going to that large a shot.</strong></font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">I have been... Hence my posting here <img border="0" title="" alt="[Wink]" src="gr_images/icons/wink.gif" />

I''ve been running a 200 shot for a while now. I'm just curious to push the limits... <img border="0" title="" alt="[Smile]" src="gr_stretch.gif" />

 

I am not sure why it is believed that timing should be reduced when running N20, but I suspect it may be a holdover from the days before knock sensors and OBDII, when the last thing you wanted to do when on the squeeze was to run lean and/or have pinging/detonation.

However, one thing I am sure of is that N20 does not burn faster than air/fuel. N20 doesn't burn, its inert. N20 going into the intake tract cools the mixture, making it denser and less prone to ping/detonate. Of course, during the compression/combustion process, the 02 is liberated from the N20 and the extra fuel, introduced via the injectors (dry) or by separate nozzles (wet) is needed to keep the a/f ratio in proper balance.

 

There have been a few discussions about this recently. I still havent seen hard technical evidence one way or the other. Just what a few people have stated with there experiance. Even some of the well known nitrous gurus and manufacturers disagree on this point.

One thing is for sure...I wouldnt rely on the knock sensors for timing retard. They only come into play AFTER detonation has occured. Nice safety feature..but IMO not a sound practice to rely on that.

As for wether or not a nitrous charge burns at a different rate than an NA charge? Hmmm. I always thought it did burn faster. Not due to the fact that nitrous is introduced, but that it was due to a more dense mixture. The more densely packed the AF mix is the faster the flame front will travel due to the closer proximity of the fuel/air molecules in the charge. Kinda like how sound travels much faster through a solid than through air. Now again...I am just stating thoughts...still learning a great deal here everyday.

So if the above is true in one way or another....at some point in HP gains...it seems it would be benificial to start retarding timing or a great deal of the burn will not occur at the most ideal portion of the power stroke. Even if detonation is not present.

Does any of this sound reasonable? Or way off? Lets keep this rolling since I am at the point where I may need to do more to retard timing. This stuff is right on time for me. <img border="0" title="" alt="[Smile]" src="gr_stretch.gif" />

<small>[ April 23, 2002, 11:46 PM: Message edited by: 383LQ4SS ]</small>

 

Gees, this actually turned out to be a pretty big posting subject. I run nitrous in my truck (5.3L LS1 derived engine) I'm pretty sure on the NOS bottle that i have it says something about "vigorously increasing the rate of combustion" I think that means it does burn at a faster rate than NA air intakes. As far as relying on the knock sensors to retard timing, 383LQ4SS is correct. Knock sensors only retard timing after they detect detonation. However, I think the computer is able to read this event and change timing so quickly that it is not worth buying something expensive to retard when nitrous is hit. I have never had any bad experiences with detonation in my truck by relying on just the knock sensors.

Maybe I'll talk to some engine builders and nitrous junkies that know about this more than my fairly mediocre engine theories. But I still dont see how retarding timing can build horsepower when using N2O. You have a constant volume and percentage of N2O and air (simply based on a constant valve lift and duration). So now all that we are worried about is timing... Detonation happens when combustion does not occur all at once evenly. Rather, little pockets of fuel begin to burn on one side of the cylinder while other pockets burn on the opposite side. When these "little" burns hit eachother it rattles(knocks). Sort of like trying to combust with a buch of little firecrackers instead of one solid Cherry bomb <img border="0" title="" alt="[Wink]" src="gr_images/icons/wink.gif" />

Anyway, engines are more prone to detonation when the fuel is compressed more. Retarding timing= less compression at the time of ignition= less a chance of knock. But!! (at least this is what i always have thought) less compression= less power. Maybe I just took a long time to get nowhere, but I want to find this question out myself also.

<small>[ April 24, 2002, 04:05 AM: Message edited by: Ryan23silverado ]</small>

 

Is there something out there for us Ls1 drivers that will automatically decrease timing when the nitrous is armed? I feel that on a head/cam car that only sprays maybe 30-40% of the time shouldn't have its PCM tuned for nitrous. If you tune the PCM for nitrous usage(decrease timing tables) then essentially you are de-tuning the car's NA performance. We need a plug and play module that will reduce timing by 2-4 degrees or so only when the nitrous switch has been armed.

 

[/QUOTE]So Air/Fuel aside, you CAN gain power from retarding the timing? Hmmmm.... go F'n figure....[/QB][/QUOTE]

On spray, yes!!!

<small>[ April 24, 2002, 08:18 AM: Message edited by: Big Mike ]</small>

 

99 mongoose Ram Charger is coming out with a device that you are looking for.As far as i can tell when you retard the timing it don't really loose hp but looses low end torque but you will gain high end hp. That iis why prostocks use a high speed retard even on na engines thier timing is locked it don't adjust like ours does.The cylinder pressure will increase a great deal with nitrous that will cause detonation and kr so if you use a high octane race fuel 100 octane to 114octane that will help and if you can lean it down and remove timing to loose the kr from leaning it out it should be faster and last longer because it isn't hammering the bearings as hard. If your car can't take all the torque out of the hole(spinning the tires) then by removing a couple degress of timing it will tone it down alittle and not abuse your engine or drive tran as much.I am still learning on the ls1 but on a 800hp bbc with 500 hp of n2o in 2 stages 225 1st 275 2nd in a 2400# car(promod) we would have 36 degrees of base timing locked the first stage would remove 12 degrees of timing putting it at 24 degrees and then the second stage would come on in 4 tenths of a second and it would take out 8 more degrees that would put it at 16 degrees. the car ran 7.55 @ 175 on 1 stage and 7.37 @185 on both the car would 60ft 103

 

</font><blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr /><font size="2" face="Verdana, Helvetica, sans-serif">Originally posted by 99MONGOOSE:
<strong>Is there something out there for us Ls1 drivers that will automatically decrease timing when the nitrous is armed? I feel that on a head/cam car that only sprays maybe 30-40% of the time shouldn't have its PCM tuned for nitrous. If you tune the PCM for nitrous usage(decrease timing tables) then essentially you are de-tuning the car's NA performance. We need a plug and play module that will reduce timing by 2-4 degrees or so only when the nitrous switch has been armed.</strong></font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">I use a resistor switched in for the IAT. I get about 4 to 5 degrees of retard with it.

 

What size resistor.Just making the computer think it is real cold intake temp.?Is that how it works ? Real curious.

 

Right now I have a potentiometer 6k ohm hooked inline with the IAT plug. It also has a 300ohm resistor wired in so when the potentiometer is at 0 the comupter will not see 0 ohms (possibly shorting the computer). Doing that gives a controllable range of 300 ohms to 6300 ohms (6.3k). The potentiometer is mounted in the cockpit right next to my scanmaster. So on the scanmaster I look at the air temp sensor display and then dial up the IAT i want to advance or retard timing. Turn the dial to the left (300 ohms) and IAT reads 40 degrees. All the way right (6.3k) and it reads 154 degrees. I just put this in and have been testing it back to back last night. Seems to give me about a 2.5-3 degree swing on timing from 25.5 to 27.5 degrees at WOT. I am going to change it around and get a 9k pot and a 100 ohm resistor inline. That should give a temperature range of 0 degrees F to around 200 degrees F. Hopefully get a little more of a swing in timing each way. I would like to see 24-28 degrees. Total cost at Radio Shack is about $8 and about an hour of time.

I am trying to tune in the second stage for around 700rwhp. After these discussions I am fairly certain I want to take out a little timimg and run some higher octane. <img border="0" alt="[Burnout]" title="" src="graemlins/burnout.gif" /> <img border="0" title="" alt="[Eek!]" src="gr_eek2.gif" /> <img border="0" alt="[Burnout]" title="" src="graemlins/burnout.gif" />

<small>[ April 26, 2002, 11:53 AM: Message edited by: 383LQ4SS ]</small>

 

</font><blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr /><font size="2" face="Verdana, Helvetica, sans-serif">Originally posted by 383LQ4SS:
<strong>Right now I have a potentiometer 6k ohm hooked inline with the IAT plug. It also has a 300ohm resistor wired in so when the potentiometer is at 0 the comupter will not see 0 ohms (possibly shorting the computer). Doing that gives a controllable range of 300 ohms to 6300 ohms (6.3k). The potentiometer is mounted in the cockpit right next to my scanmaster. So on the scanmaster I look at the air temp sensor display and then dial up the IAT i want to advance or retard timing. Turn the dial to the left (300 ohms) and IAT reads 40 degrees. All the way right (6.3k) and it reads 154 degrees. I just put this in and have been testing it back to back last night. Seems to give me about a 2.5-3 degree swing on timing from 25.5 to 27.5 degrees at WOT. I am going to change it around and get a 9k pot and a 100 ohm resistor inline. That should give a temperature range of 0 degrees F to around 200 degrees F. Hopefully get a little more of a swing in timing each way. I would like to see 24-28 degrees. Total cost at Radio Shack is about $8 and about an hour of time.

I am trying to tune in the second stage for around 700rwhp. After these discussions I am fairly certain I want to take out a little timimg and run some higher octane. <img border="0" alt="[Burnout]" title="" src="graemlins/burnout.gif" /> <img border="0" title="" alt="[Eek!]" src="gr_eek2.gif" /> <img border="0" alt="[Burnout]" title="" src="graemlins/burnout.gif" /> </strong></font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">383, actually, you have it backwards. So using the larger potentiometer will not help you. The lower the resistance, the higher the temperature. I have probably 500ohms, it makes the PCM think it's 140 degrees out, and I get my timing retarded to about 24 degrees. Normally it's 28 or 29 degrees.

Give it a try again on your car, make sure it's the same for your car, but I'm pretty sure it is. Lower resistance, higher temp, retarded timing. Higher resitance, lower temp, advanced timing.