What size jets to try?

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stroker1
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What size jets to try?

#1 Post by stroker1 » Thu Jul 10, 2008 2:53 pm

I have been checking out some jet calculators. They ask how many nitrous jets and I put 1, so I guess it works the same with either a fogger nozzle or a spray bar. Reason for asking is if I use cheater kit solenoids I'm thinking I should be OK with using a jet calculator for any thing less than a 250 shot either a plate or fogger shot. Is that correct?
Last edited by stroker1 on Fri Jul 11, 2008 12:54 pm, edited 1 time in total.
'87 S10 stock suspension, Caltracs, 9" rearend, 1.82 Glide, 383 SBC,
Brodix Track1 Heads, 14:1 compression, 180 shot plate,
2" tube Hussler Headers, 1.38 60ft., 6.20 ET 1/8th, 109 MPH,
Still Tuning, more to come.

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stroker1
Posts: 333
Joined: Tue Apr 03, 2007 1:14 pm
Location: Dunn, NC

Re: What size jets to try?

#2 Post by stroker1 » Fri Jul 11, 2008 11:46 am

Never mind, I think I asked a stupid question.
'87 S10 stock suspension, Caltracs, 9" rearend, 1.82 Glide, 383 SBC,
Brodix Track1 Heads, 14:1 compression, 180 shot plate,
2" tube Hussler Headers, 1.38 60ft., 6.20 ET 1/8th, 109 MPH,
Still Tuning, more to come.

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John_Heard
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Re: What size jets to try?

#3 Post by John_Heard » Sat Jul 12, 2008 7:35 am

No it's not a stupid question, the number of jets on the calculator is for figuring the HP level based on the size of the jet. If you want a really good calculator for your jetting get Dave Koehlers
http://www.koehlerinjection.com/Koehler ... master.htm

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stroker1
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Joined: Tue Apr 03, 2007 1:14 pm
Location: Dunn, NC

Re: What size jets to try?

#4 Post by stroker1 » Sun Jul 13, 2008 11:26 pm

I know my Cheater kit is really rich on fuel. All the jet calculators I've used say around a .060" fuel jet with a .063" nitrous jet, 1000 psi bottle pressure and 5.5 to 6 psi fuel pressure. My NOS paper says use a .071" fuel jet, but all my buddies say NOS is very conservative and they are really fuel rich. A few have recommended me to square jet it, go a little lower on timing than I would normally and read the plugs from there. They say after all, look at the jetting for Cold Fussion and Speedtech. (I'm not going to get into Edelbrock jetting, they are way different even on the nitrous jet than all the others I've seen and different from the jet calculators too. According to some jet calculators an Edelbrock 150 plate shot should be about 200 to the wheels if the fuel jet was smaller!)I need to get by as cheap as possible, I cant afford to buy a pile of jets to swap in and out. But I can't afford a melt down either. What ya'll think? What about it John? :scratch: BTW, it's a 150 plate shot I'm trying to tune. The more I dig into this shit the more I see that different companies have way different settings for getting the same results. And some nitrous brands instructions are real close to what the the jet calculators say and some are way off from the calculators. And I'm not talking RWHP V/S FWHP either. Somebody 'splain some shit to me!
'87 S10 stock suspension, Caltracs, 9" rearend, 1.82 Glide, 383 SBC,
Brodix Track1 Heads, 14:1 compression, 180 shot plate,
2" tube Hussler Headers, 1.38 60ft., 6.20 ET 1/8th, 109 MPH,
Still Tuning, more to come.

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John_Heard
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Posts: 5691
Joined: Thu May 12, 2005 11:20 am
Location: Resume Speed, Kansas
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Re: What size jets to try?

#5 Post by John_Heard » Mon Jul 14, 2008 6:04 am

The .063 N / .060 F jets @ 5.5/1000 psi should yield about a 5.76 N/F Ratio, which is a pretty good tune up, it shouldn't be too far off. .063/.063 (square) is a 5.23 N/F Ratio which should be just a bit fat at 5.5psi. Depending on manufacturer they may have some real fat jetting to cover their asses should someone have low fuel pressure (like T'ing it into the stock pump kind of thing) - at least that's what I've been told. In other cases the tune up from the mfg. looks real lean, in that case it could be due to a restriction in the nitrous flow path that they have to make up for with larger jetting.

A cheater shouldn't have those issues with the weird jet patterns at that HP level - it will have issues when you start turning it up to the flow capacity of the solenoids and/or plate. If you want to avoid buying extra jets that .063N/.060F is a pretty good place to start at, and you can bump the pressure up to 6.5 psi or so (5.31 N/F) ratio if you want to start out fatter with the tune up, then start taking fuel out. Remember to take about 4-5 degrees out to start with until you are able to take a look at the plugs to see how it likes it.

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