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Discussion Starter · #1 ·
Question for all you nitrous saavy guys....

What is the correct amount of timing to run for large shots of nitrous?

I've read through previous posts on the subject and have seen the following-

"rule of thumb is to pull 2 degrees timing for each 50 HP of nitrous."

-and-

"run a total of 34 degrees timing" (talking about a 75 HP shot)


But what should I run for a 200, 230, or 250 HP shot on my combo for most power?

Some background-
I am running 11.6:1 compression ratio and 35 degrees BTDC timing at WOT. Generally I do pull about 1.5 to 2 degrees timing for each 50 shot, and in fact my best run was with a 175 shot pulling 6.8 degrees timing, so that's really close to the 2 degrees per 50 HP rule, however that means I was only running 28.2 degrees of timing. Is this right? Should I pull less timing? What about bigger shots?

Let's discuss this and help me learn some more on the subject.
 
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Discussion Starter · #2 ·
Here's the general rules of thumb:
What are some of the general rules for even higher H.P. gains?

A: Generally, forged aluminum pistons are one of the best modifications you can make. Retard ignition timing by 4-8 degrees (1 to 1½ degrees timing retard per 50 H.P. gain). In many cases a higher flowing fuel pump may be necessary. Higher octane (100+) racing type fuel may be required as well as spark plugs 1 to 2 heat ranges colder than normal with gaps closed to .025"-.030". For gains over 250 H.P., other important modifications could be necessary in addition to those mentioned above. These special modifications may include a forged crankshaft, a high quality race type connecting rod, a high output fuel pump dedicated to feeding the additional fuel demands of the nitrous system, and a racing fuel with high specific gravity and an octane rating of 110 or more.
 
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Discussion Starter · #3 ·
Chris,

I pull only 1 degree per 50 shot. Also, with a 350ci motor, I think you will find little to no gain in spraying anything over a 200 shot.
Also I would recommend disabling the knock retard function in the pcm.
 
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Discussion Starter · #4 ·
Chris,

I agree with Nab - leave the knock retard functioning.

What I did when I installed my kit was put in 8 degrees of retard then backed off on the retard until I started getting some knock retard on the Autotap.

I've recently noticed that I'm getting some retard whenever I run with the cutouts open. This happens in cold weather and not hot weather, so I'm thinking that the exhaust is just loud enough when the weather's cold to set of the knock sensors. If that's true, then there may still be a few tenths hiding in the motor. In any case, I think backing way off on the timing and then adding in 2 or 3 degrees at a time until you get a little knock is probably the safest way to go.
 
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Discussion Starter · #5 ·
Thanks for all the responses guys.

Mike, there are only forged parts in my future if something goes really wrong this year - otherwise that will be next winter's project.

Nab and Stone.
So what I am hearing is run less retard (via the 685) on the timing and "tune" this by adding timing until I just hear detonation (eek!) and then retard this a degree or two from that point.

I still have the knock sensors enabled but have to figure out how to log that function on the new AutoXray I am now using for a data logger. I will consider disabling them if the sensors are pulling more than a few degrees of timing. I can't help but think that they probably have saved my engine in the past though because I have had a run or two where for whatever reason (lower FP or more N2O pressure maybe) I have heard some detonation. :eek:

Also I just got some cat delete pipes last week with cutouts. I am hoping this will be worth a tenth or two - especially on the 200+ shots :cool: - Stay tuned!
 
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Discussion Starter · #6 ·
The best way to tune is by reading the plugs. Pull 4deg per 100hp, make a pass, and have a look. The ground strap should be heated to the point where it meets the plug body, and a clean grayish color. If it turns a little blue, you are at the edge; back off a degree or two. If instead you add more timing, the next step is a rainbow coloring, and then you'll nip (burn off) the strap. You can also tune fuel by looking at the insulator deep down in the plug. There will be a ring where the pocelain turns darker. The ring should be most of the way down inside without disappearing. When it disappears, you're too lean. If it's way up top you're too fat. Too much timing or too lean will start to burn off flecks of piston dome, and leave peppering on the insulator. Learn what the plugs are telling you and you'll be a much better tuner. I've become pretty profficient by necessity at dialing in n2o tune-ups by plug reading; the big motors we run are'nt very forgiving when spraying 800-1000hp.
 
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Discussion Starter · #7 ·
Originally posted by SSONIC:
Thanks for all the responses guys.

Nab and Stone.
So what I am hearing is run less retard (via the 685) on the timing and "tune" this by adding timing until I just hear detonation (eek!) and then retard this a degree or two from that point.
Not exactly - if you leave your knock sensors enabled, you'll never hear any pinging - you'll just see a little knock retard dialed in on the log.

On the cutouts, what I was trying to say was that I think I'm getting some false knock when using them during cold weather, which would logically dictate that I'm also getting some false knock during the nitrous runs. I think I may try to put some turndowns on the cutouts to possibly eliminate or at least reduce the false knock.
 
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Discussion Starter · #8 ·
And damn chris is still running on the stock transmission... Lets hope that the one that i just went through myself holds up to the 383 and the edelbrock 175 shot in the next few weeks!!
 
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Discussion Starter · #9 ·
Originally posted by stonebreaker:
</font><blockquote>quote:</font><hr />Originally posted by SSONIC:
Thanks for all the responses guys.

Nab and Stone.
So what I am hearing is run less retard (via the 685) on the timing and "tune" this by adding timing until I just hear detonation (eek!) and then retard this a degree or two from that point.
Not exactly - if you leave your knock sensors enabled, you'll never hear any pinging - you'll just see a little knock retard dialed in on the log.</font>[/QUOTE]The PCM can only pull as much timing as it's allowed to. In a really horrible extreme case, it could pull all it's allowed and not stop pinging, in which case you would hear it.
 
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