Hey guys,well i'm just buttoning up my dualstage dry/wet.
Now my question is this,Dry out of the hole and the 2nd stage which is Wet rolls in 2nd gear.Now what should i do about timing.Should i throw a resistor in the IAT to pull timing when spraying or just have the timing pulled in my tune?
Any input would be much appricated
BTLFEDSS

 

I am curious too.........

 

I would just pull the timing with your tune on your first stage out of the hole using the maf.

 

You have to be very careful doing that. The "blocks" you tune for a dry stage retard are NOT a very fine resolution. Meaning if you want full timing NA...and then pull say 6 degrees out for the 150 shot dry..the cells that you have to make the adjusments in are just barely above what is NA.

What I have seen when doing a dual stage dry/wet with dry tuning to pull the timing is....timing is pulled on the first stage when the dry hits, just as it was intended, that part works like a charm. But when the wet hits it actually causes the MAF to report less airflow due to dsiplacement of air behind the MAF. This can kick the tune back out of the area that would be retarded from the dry shot. Its a very tight margin.

If the car is going to be used strictly for 1/4 mile runs and you arent concerned about the best NA performance...I would put a dedicated nitrous tune in it. That way you can base your timing on the TQ peaks that each stage hits thru the rpm.

If you where doing a single stage large shot you would need to pull a ton of timing at low rpm where cylinder pressure is greatest and gradually feed a bit back in with rpm as that Tq/cylinder pressure falls off rapidly. You can do the same thing for a dual stage...except your peak Tq may now be at the activation of the second stage.

When I do a dual stage I try to get the 2 tq peaks of each stage equal to each other (like 700 rwtq at 3000 rpm and then 700 rwtq at 4800 rpm) and then give a nearly flat timing across the rpm range. You could add a bit back in the very upper rpms...maybe a degree or two depending on shot sizes and how many rpm away from the second stage activation you are...because tq will fall off rapidly (much less rapidly than a single stage though).

This is how I have always approached it. I do not do thet actual tuning. Jeremy Formato does all the actuall changes. I just tell him what timing I want and were. Then he figures out how to get it there by various means.

 

You can pull timing through your maf in the tune. when i ran a wet kit i was tricking the IAT through a relay and saying the intake air was like 130 degrees. then i went ahead and pulled timing through one of the tables. So when my nitrous system was armed...i would see timing pulled.

 

in your tune, go to your IAT tables and change the numbers to take out the amount of timing you want to retard it when the dry nitrous activates, should be like all the sections below 0 degrees IAT. Make sure you have the spray hitting the IAT sensor though.

This way you can tune for NA and have your timing NA, then when the IAT sensor reads the spray it will retard the timing....making two tunes in one

 

Ahh...yes. The IAT is much better. But I dont think all years have that IAT table. I know we tried that in my 99 and we ended up having to use the MAF tables. It may be 2000 and up. If thats an option thats what I would do. Much easier than trying to split hairs with the MAF tables.

Can anyone confirm what year PCMs can do this. because I will certainly be sure to use this next time. Definately simplifies things.

 

My car is a 2000,I'll have to run this thread and see what my tuner has to say.Thanks for the input,and keep it coming
BTLFEDSS

 

Same here, good info.

 

Have you logged your spray temps, sometimes you won't see close to 0 degrees.

Here's the method that I have been using and many, many others with no reports of it not working. Now what Al was talking about (we have talked about it before), maybe this is an F-bod thing, as the vettes MAF is a long ways away from your wet nozzles. However, I have had no reports of this not working on any car, at least not yet...

This write-up will explain how to tune your PCM to pull timing when you use a dry shot of nitrous. It is fairly simple, if you have the proper tools. All you need is a tuner program ie: HP Tuner. To perform this, you should have a good working knowledge of Excel, how to log parameters and know how to use tuner program. I would like to note up front that this tuning method WILL ONLY WORK WITH A DRY SHOT OF NITROUS!

HOW AND WHY IT WORKS: The timing value that your PCM selects from the high-octane timing table is based mainly on the calculated load (measured in Gms/Cyl) that is being placed on your engine at any given time and RPM. For example, if you are at 4000 RPM and the PCM is calculating 0.56 Gms/Cyl of load, it reads the portion of the table that corresponds with those figures and selects that timing figure. Now remember, I said that it is "mainly" based on load and RPM, but there other factors involved such as intake air temp and coolant temp that may pull a few more degrees away from the base value in the table, depending on conditions. Alright.....because the load being calculated is based on the amount of air that the Mass Airflow Sensor (MAF) is detecting (measured in Gm/Sec), a dry N2O shot will cause a higher load to be measured and calculated, and cause the PCM to access a different section of the timing table; a part that is NOT used during NA operation. Because of this, you can modify the part of the table that is used when you spray and leave the portion of the table that is used during NA operation unaffected. That is why this method won't work for a wet kit; because the N2O isn't being measured by the MAF with at wet kit, so no additional load is calculated for the nitrous and timing is based on the amount of air that the MAF sees. (Sorry wet guys).

1. The first step is to determine the highest amount of load that your PCM calculates under NA conditions. This needs to be done so that you only modify the values in the timing table that are "above" the point that is accessed during NA ops. This will allow your timing to remain unchanged when you aren't spraying.

2. To determine this, you need to do some wide open throttle (WOT) logging. At a minimum, you need to log Throttle Position Angle (TPA), Engine RPM, Ignition Timing Advance, and Mass Airflow Rate (in Gm/Sec, not Lbs per minute). Beyond that, log whatever you would like. I personally log both O2s and/or WB and Knock Retard (KR) as well for monitoring purposes, but they will not effect what we are doing. Make sure you get plenty of data with lots of time at WOT. Make sure that your WOT time is spent throughout a wide RPM range. I recommend doing this at the local drag strip to remain safe and legal.

3. Once you are done logging (I would make a few logs), export the data to an excel spreadsheet for analysis. Arrange your data so that your Mass Airflow Rate is in the column next to RPM. The timing and TPA columns can be wherever you prefer them to be. I would delete all of the other rows of data so you don't get confused. Now sort the data (using the data-> sort function in excel). I usually sort based on TPA and have it sorted as descending. That way all of the WOT data will be at the top and you can delete any "non-WOT" data. We won't be using it. Make sure to "expand the selection" when you sort, so that all of the data stays in the proper order. You should now have a spreadsheet that looks something like this.

TPA Ignition Timing Advance(°) MAF Air Flow Rate(gm/s) Engine Speed(RPM)
99.6 28.0 248.55 5782.3
99.6 27.5 44.42 5538
99.6 26 251.25 5221.8
99.6 27.5 247.75 5870.5
99.6 23.5 208.83 4890.5
99.6 25.5 239.21 5238.3
99.6 27 235.07 5578
99.6 30.5 13.13 5260.3
99.6 24 212.82 4602.5
99.6 23.5 18.8 4543.8
99.6 25 200.72 4844
99.6 30.5 38.89 5329.3
99.6 25.5 247.43 5465.3
99.6 28 199.49 5670.8
99.6 27.5 265.33 5437.5
99.6 27.5 270.14 5744.8
99.6 24 202.89 4698.3
99.6 24.5 231.66 5048.5
99.6 27.5 173.25 3765
99.6 25 174.12 3995.5
99.6 25 194.35 4224.5
99.6 24.5 204 4464.3
99.6 24.5 177.34 4316.8
99.6 27.5 244 6215
99.6 27.5 247.75 5832
99.6 27.5 260.66 5396.3
99.6 37.5 10.49 5201.8
99.6 24 213.62 4636.5
99.6 24 231.92 4966.8
99.6 26 251.25 5321.8
99.6 27.5 271.51 6066.5
99.6 33.5 12.59 5058.8
99.6 27.5 251.73 5592.8
99.6 26.5 252.25 5308.8
99.6 27.5 271.51 5914.5
99.6 23.5 224.98 4913
99.6 25.5 251.73 5284.3
99.6 24.5 188.27 4325.8
99.6 24 215.87 4692.5
99.6 24.5 239.21 5058.8
99.6 26.5 255.48 5412
99.6 27.5 243.62 5749
99.6 27.5 14.38 4646
99.6 28 162 3645
99.6 26.5 175.71 3855.3
99.6 25 190.89 4040.8
99.6 24.5 196.78 4233
99.6 25.5 247.43 5641
99.6 27.5 55.72 5758
99.6 27.5 243.43 5798
99.6 27.5 260.66 5517.5
99.6 27.5 252.85 5989
99.6 23.5 211.96 4874
99.6 25.5 227.99 5225.3
99.6 30.5 18.1 4000.8


4. Ok, now its time to calculate your load, the same way your PCM does. Remember, I said before that timing is base off of load in Gms/Cyl and RPM. What we have logged is airflow in Gm/Sec. We must now convert our figures into Gms/Cyl. This is done with a simple math equation that can be performed in your spread sheet. Gms/Cyl = Gm/Sec * 15/RPM. Lets take my very first row of data for example. The formula would be would be 248.55 * 15 / 5783.2 = 0.64 Gms/Cyl. I now have a figure that I can use to reference on my timing table in Edit. I simply find 0.64 on the left of the table and 5600 RPM (round down to the closest value for both RPM and Gms/Cyl) on the top of the table and I see that the come together at 28 degrees advance. I can now verify this by looking at my log and seeing that I, infact, logged 28 degrees at that data point. Pretty simple, right?

5. Now perform the same function on all of your data sets. You can easily enter the formula into excel and have them all calculated in no time. The point of all of this is to find the highest (numerically highest) amount of load that your PCM ever calculates while driving at WOT. I would do this with a few data logs, just for maximum confidence. This may vary from car to car, depending on different MAF calibrations and a whole slew of other variables, so I recommend that you log YOUR OWN data and see what YOUR highest amount of load is. Don't use your buddies data for reference. My car happens to see a mximum of 0.69 Gms/Cyl at any given RPM (remember that RPM is a factor).

6. Now that you know your maximum NA load value, it is very easy to determine the "highest" point of the timing table that you use NA. Now, simply change the timing values in all of the cells above (physically below on the table) that point. These are the values that will be accessed when you spray. It is advisable to leave yourself a gap between your uppermost NA access point and your lower most N2) access point. That way you will be SURE to never access the retarded portion of the table while running NA. I don't recommend changing the values below the RPM at which you start spraying. For example, I spray starting at 3000 RPM, so I changed all of the values from 2800 RPM (I rounded down) and up, which correspond with values of 0.72 Gms/Cyl and numerically higher. (Basically the bottom right quadrant of the table. What you change the values to is up to you. I personally changed all of mine to 24 degrees, and have had pretty good luck there. How much you retard is really dependant on how large of a shot you are using.

7. Once you have modded your timing table, upload you new tuning, fill your bottle and head back to the track. Do some more logging and you should be pleasantly surprise. Your timing will remain normal during NA runs and will jump right back when you spray. As I said before, you may see some variances in timing, depending on ambient air temperature and coolant temperature. Also, you may occasionally get some odd MAF readings that will cause your load to be calculated incorrectly, and your timing may temporarily jump to a different value. This happens to me both NA and while spraying and has nothing to do with the changes you made to your timing table.

Well, that's. All in all, a pretty simple mod that will allow you to run a healthy amount of timing NA and a very healthy amount of N2O without detonation. HAPPY SPRAYING!

Robert