I posted this in my thread Good 3,000 RPM Launch Photo in the 10 sec thread section of Drag Racing but thought I should also post my question here to get the opinions of folks that use Nitrous all the time, since I have not used nitrous for two years now.

We are working on a new tune and I have a question. If you have your NA tune in the car with timing at 30 degrees and are using 104 unleaded race gas and will be using a dry shot with 75 HP jets max does the timing need to be retarded at all? Also running TR55's at .048 gap. Should I reduce the gap to .044?

AFR is 12.8 WOT NA run and 11.2 +/- WOT on Nitrous with bottle pressure at 900 PSI. I think with it at 950 to 1000 PSI the AFR should be at 11.6 +/-.

346CI at 11to1 compression ratio. I have more details of my setup in the thread mentioned above if you need to know any more details.

Thanks for your input!

N2

 

I would first pull those plugs out of there. TR55 is way too hot of a plug for that compression and nitrous. 75 shot isn't much but factor in your compression ratio and the current timing...I would definitely pull some timing out of it.

Rick

 

I agree with Rick.

TR6 and 4* out to start, check plugs from there.

 

I agree. Mines not an LS1, but I run 11:1 compression as well. For my car (s2k) and nitrous for just a 125shot people are pulling 6-8degrees timing from their NA tunes for spraying.

 

The car put 400 NA HP to the wheels on a Mustang dyno through a TH400 and 9 inch with ET Drags!

I agree with changing to TR6's and already have them purchased. Suggestions on gap? I will pull 4 degrees timing and see what happens.

Any other input?

Thanks,

N2

 

Try to keep as much gap as possible. If you feel its blowing out pull the gap tighter. What's the duty of the vehicle? I have a part number for a non-projected tip TR6 if it really only sees track use.

Nick

 

Thanks Nick the car is used at the drag strip most of the time now so I would appreciate the part number for the plug you are suggesting for me to try!

Thanks again for the help!

N2

 

Not a problem. I'm home today babysitting my dog that had surgery but once I get to the office tomorrow I will shoot you over the part number.

Nick

 

r u spraying ur dry before or after ur maf? if before it will pull the timing for you.

 

I agree on running a better plug like an autolite AR-472 that's made for racing. As long as you're not spraying with the engine hot you shouldn't HAVE to pull your timing while running race gas, but in the interest of tuning for the best power it's better to reduce the timing a little and pull out some of the fuel enrichment. With the race gas you don't need to be running that rich.

I like to keep plugs gapped around 0.030" when spraying.
The AR-472 plug is a very cold non-projected tip with large ground straps to shed the heat quickly.

The correct timing is a matter of juggling factors that influence the burn rate of the fuel.
30* advance may be just fine with the engine temp at 170*F and the AFR in the mid 11's range. 27* advance may be better if your engine temp is 200*F and your AFR is in the mid 12's range.

The less the octane of the fuel, the less spark advance is needed.

 

Does anyone have an ideal how much timing will be pullled if this is true. I am spraying before the MAF.

N2

 

This is some very good information. I do run the car with the temp as low as it can go. I will look at leaning out the tune some as well as taking out some timing if the MAF does not pull timing when spraying before it.

N2

 

It's gonna pull what's in your program, ask a tuner, I assuming your running an Ls1 Computer? My bet is 6-10 degrees with cold air hittin it (N20). I've put a lot of dry shots on cars with out retuning it, including V6's.

 

It will NOT pull timing on it's own unless you change the tune for it to do so. Robert56 has a guide on how to do this with HPtuners.

I have been running my TR6s gapped at .038 with my heads/cam setup, and have occasionally sprayed a 100 shot with them with no ill effects.

 

This is not right.


If you spray before the MAF, the fueling required for the dry shot is adjusted. MAF does not adjust timing. Usually people manipulate the IAT sensor as a cheap/easy way to adjust timing.

 

It all depends on the tune. Spraying before the maf will show a colder/denser airmass and be running in a different timing cell as opposed to the n/a run.Since most timing tables are set up to remove advance as airmass increases there will be a natural drop in timing(or this can be factored into the tune). When sprayed after the maf or in speed density mode (mafless) this does not occur & you will need to find another way to remove the timing.

 

This is true.
Every factory timing table I've looked at pulls a few degrees of timing at the higher load ranges that you see when spraying through a MAF.
How much it pulls depends entirely on how much higher the load range reads when you spray it. I think an average is 3 to 4 degrees.
If you spray far away from the MAF wires then it would be less.