New NOS jet chart for Cheater Plate

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New NOS jet chart for Cheater Plate

Post  4604X4 on March 9th 2017, 7:33 am

I have the NOS Cheater Plate. I'd like to set it up for a 150Hp shot.

I was reading on various forums that the old "jetting chart" is way fat (i.e. recommends 63n and 71f for 150hp).

I read that there is a "new" jetting chart but I have been unable to find it. It seems from the forums that the "best" starting point is to have the fuel about "8 points" lower than nitrous (opposite the old NOS chart). So a 150HP spray would be more like 63n and 55f. Or does the new chart say 150hp is 71n and 63f?

I know it is a matter of engine/tune/etc. to get the right combination (right tune) but I would like to have a reasonable starting point.

This is on a street driven 4x4. I have flowed the fuel through a 73 jet into a bucket and adjusted pressure to 6 psi. I have a separate fuel pressure regulator feeding NOS solenoid and one for carb. But I can't be sure that when carb is WOT that is not dropping fuel pressure some across the board as the feed line to both regulators is shared. When I flowed the NOS and adjusted fuel pressure that was with engine off (electric fuel pump).

I have MSD spark retard and set it for 6 degrees retard.

I made a couple of runs and pulled a couple of plugs, but honestly I don't see any change (over running truck without spraying).

Any advice would be much appreciated.
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Re: New NOS jet chart for Cheater Plate

Post  4604X4 on March 10th 2017, 1:45 pm

I did find this - which now lists a "smaller fuel jet" than the original installation manual (which was 63n/71f for 150HP)

Nitrous/Fuel Jetting --- Approximate PowerGain --- Approximate N2OConsumption Rate
47/47                        100HP                              1.0 lbs./10 sec.
55/55                        125HP                              1.25 lbs./10 sec.
63/63                        150 HP*                           1.5 lbs./10 sec.
73/73                        180 HP*                           2.0 lbs./10 sec.
82/82                        210 HP*                           2.5 lbs./10 sec.
93/93                        250 HP*                           3.0 lbs./10 sec

from here http://documents.holley.com/a5051-1-snosrev1.pdf
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Re: New NOS jet chart for Cheater Plate

Post  tbirdmike on March 10th 2017, 5:20 pm

yeh the old jet chart was fat.
The one posted above is the newest and is a good place to start.
You might look at instructions for some other brand kits. Some of them give a better baseline for timing retard. NOS doesnt consider the type of engine/head/chamber for timing retard. Some of the others give
recommedations for specific motors.
For street use you might consider 8 deg.

You will want to flow for fuel pressure using the fuel jet for your tuneup.

If this is an older kit it may not flow on the nitrous side as well as stated. Make sure you have the proper nitrous feed line. If its not the size that comes with the kit it will be seriously restricted.

If you have a real loose converter it might be harder to feel. But on a good 150 hit it should be a big wake call on engine performance.

You really need to verify that your WOT switch is working and that both solenoids are coming on. Do this safely with bottle off , engine off.
If you question fuel pressure you can unhook the feed line to one bowl on the carb and feed it to the bucket you are flowing into while set the fuel pressure the the nos kit.
This will show if the fuel system can keep up or not.

FYI, if you are using a msd retard box and you change a retard module, you must reset your timing.

Hope that helps

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Re: New NOS jet chart for Cheater Plate

Post  4604X4 on March 10th 2017, 5:36 pm

Mike,
Why do you say I need to reset my base timing when using the MSD retard module. Or did I misunderstand you?

If I set initial timing to 12 BTDC (total at 34) and the retard is set for 6 or 8 degrees, won't the timing revert back to base (initial) once the N02 spray ends (retard module "ends the retard")? Doesn't the retard module just subtract timing from whatever is the actual timing at the time the "retard is applied"?

The new jet timing is square (63n/63f) but all of the forums I've visited and read up on , say the fuel should be at least 8 steps lower (like 63n/55f) to get close to a correct tune. Do you find this ti be true?

And thanks for the info.
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Re: New NOS jet chart for Cheater Plate

Post  nuclearcobra on March 13th 2017, 5:25 pm

Those even jet spreads are the 2nd (new jetting) but still rich , the 3rd they came out with finally is pretty much reversed from the original settings. Last time i tried nitrous i ran a 72N and 64F jet and it ran good but still a little rich.
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Re: New NOS jet chart for Cheater Plate

Post  4604X4 on March 14th 2017, 6:02 am

I've got a 63n and 57f in there now (for 150HP shot). I haven't had a chance to test yet but that should be a good starting pint from what I've read.
I also bought a purge solenoid which I am in the process of installing now.
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Re: New NOS jet chart for Cheater Plate

Post  tbirdmike on March 21st 2017, 3:14 pm

4604X4 wrote:Mike,
Why do you say I need to reset my base timing when using the MSD retard module. Or did I misunderstand you?

If I set initial timing to 12 BTDC (total at 34) and the retard is set for 6 or 8 degrees, won't the timing revert back to base (initial) once the N02 spray ends (retard module "ends the retard")? Doesn't the retard module just subtract timing from whatever is the actual timing at the time the "retard is applied"?

The new jet timing is square (63n/63f) but all of the forums I've visited and read up on , say the fuel should be at least 8 steps lower (like 63n/55f) to get close to a correct tune. Do you find this ti be true?

And thanks for the info.

yeh, when you change the chip it changes your base timing.
Dont take my word for it. Check your timing with your current chip. Then swap it for a different one and check it again.

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