N/F RATIO'S

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supernova
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N/F RATIO'S

#1 Post by supernova » Mon Nov 07, 2011 11:37 am

I got a chance to optimize my nitrous tune up this last weeked. I was wondering if a n/f ratio of 5.2 to 1 was normal or does it seem low? It seems low to me but the plug readings and mph was the best it could be at the setting it's set at. .091n, .082f, 6 lbs pressure.
What does everyone else have as a n/f ratio?
Blackhoodmafia!!!! :mrgreen: :mrgreen:

1972 Nova SS
572 C.I. BBC

Best to date: 1/8
et: 5.28
mph: 134
new wt. 3340 lbs

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John_Heard
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Re: N/F RATIO'S

#2 Post by John_Heard » Thu Nov 10, 2011 12:02 pm

One thing to keep in mind, on a plate especially on the bigger jets you won't get what you think you're getting. The N/F numbers you're looking at are theoretical, only by flowing the plate to see how many lbs per hr you're actually getting will you know what the true N/F ratio actually is. As you start getting into the 90's range, each jet you go up will have less and less additional flow as you're approaching the flow limits of the spray bar. Not to mention, you may be reaching, or have already reached the flow potential of the solenoid you're using also. Big tune up's on a plate, like a big shot or double cross tend to have stupid sounding jet staggers.

That said, you're probably still quite fat with that tune up at the jet level. There's a LOT left in it I'd bet. How do you "know" you've got it optimized?

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Re: N/F RATIO'S

#3 Post by supernova » Thu Nov 10, 2011 3:54 pm

I made 6 passes last Saturday night on the .091 pill set up and read plugs while tweaking the set up. We alsu went up and down in fuel jets and pressure looking for the best mph.
Blackhoodmafia!!!! :mrgreen: :mrgreen:

1972 Nova SS
572 C.I. BBC

Best to date: 1/8
et: 5.28
mph: 134
new wt. 3340 lbs

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John_Heard
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Re: N/F RATIO'S

#4 Post by John_Heard » Thu Nov 10, 2011 4:02 pm

Was just curious, MPH tells no lies. If I had to guess, that jetting I would expect to be a bit fat on a single bar plate though.

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supernova
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Re: N/F RATIO'S

#5 Post by supernova » Thu Nov 10, 2011 8:12 pm

This is what we have learned about my engine. My heads are large. Now that i'v gotten to run it with all the issues fix it showed us more of the characteristics of what it is doing and it's needs to be happy. It is rich but only at the lower rpm's. I looked at the rpm graph after each run to get a idea of where it really wanted to come alive. I was amazed at the rpm in which it really started to accelerate..... The line is starting to go vertical at about 6400 rpm's and stay on that path well past 7500. It looks like 6400 is where the heads are starting to flow good. I even shifted at 7800 one time to see what the rpm line would do, it stayed on the same path even to that rpm. Shutting it off at the end of the track and looking at the plugs was confusing at first until we figured out the rpm line. Yes I think it's rich but not at the higher rpm the heads like......
I know I'm probibly missing something but the mph shows this is what it likes. The 60' sucks, the new converter is too tight ( better than the "too loose" one's that's been in the car ) and I think the 3.70 gear is killing it off the starting line.
Mike at CFM did the heads and talking to him about it, he said to put more in it and it should help the heads to flow better sooner so I've pilled it to the top of what my plate kit will go to and back to the track this weekend to see what it's got. The converter needs to be looser on the launch and the gear change which should help the all around performance.
Blackhoodmafia!!!! :mrgreen: :mrgreen:

1972 Nova SS
572 C.I. BBC

Best to date: 1/8
et: 5.28
mph: 134
new wt. 3340 lbs

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John_Heard
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Re: N/F RATIO'S

#6 Post by John_Heard » Fri Nov 11, 2011 8:57 am

Good luck this weekend!

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Re: N/F RATIO'S

#7 Post by supernova » Fri Nov 11, 2011 9:30 am

I'm trying to bring the car up to the Ardmore race on the 19th to run with the "B" feature class with whats in the car now. Just need a good base tune to be competitive. Over the off season we'll make some changes that should help the performance for next year. :D

Are you coming down for the race?
Blackhoodmafia!!!! :mrgreen: :mrgreen:

1972 Nova SS
572 C.I. BBC

Best to date: 1/8
et: 5.28
mph: 134
new wt. 3340 lbs

User avatar
John_Heard
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Re: N/F RATIO'S

#8 Post by John_Heard » Fri Nov 11, 2011 9:36 am

Probably, I'm not real thrilled about the 6 hour drive, which is gonna require hotels, $ fuel, etc. But, last race of the season so we'll probably go. Jeff is saying the weather is supposed to be good.

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Re: N/F RATIO'S

#9 Post by 71 chevy » Sun Nov 13, 2011 2:16 pm

your converter may not be too tight.

If you are pulling a lot of timing at the hit, that could be costing power, which is slowing your 60' down,

and it is also causing the converter to flash at a lower rpm because it is being hit with less torque.

I would try putting timing back in at the hit

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Re: N/F RATIO'S

#10 Post by 572 BBC » Sat Jan 07, 2012 5:13 am

been told dont listen to any air fuel reading! just read plugs...i have similar combo(572 355 darts 286/296 @.050 10:1 compression)have been 8.60s on a 73 nitrous pill.8.40s sofar best on a 93n jet 82 fuel @ 6.5 lbs(i think my gage is a lil off) and shows a tick rich. 3000 lb racing down road-chassis car

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