Author Topic: Advise on Nitro tune  (Read 600 times)

Offline Cparten

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Advise on Nitro tune
« on: May 16, 2017, 06:27:39 AM »
Spud,
   I need so advise on which direction to go on our tune. Our set up is, SBC with 415 cubic inch, AFR heads, Hillborn Stack Injection, Our normal tune on methanol is timing at 38*, 85 pill. We can run a very consistent 8.00 with this tune. In order to try to break into the 7's decided to run some nitro this year. I started out with 20% to get a feel for it. I put the timing back to 32* and put a 80 pill in.It  ran a 8.30 out of the gate (kinda what I expected). On the next pass I set the timing to 36* and put the 85 pill back in. On the next pass it was running like a scalded dog on the first half of the track (best numbers so far) but second half of the track it was slow but still ran a 8.00. After we got back to the pits I knew something was wrong and I was right. It burned both head gaskets (copper) between the two center cylinders, also burned the electrode off 1 spark plug. I mixed the nitro by volume then checked it with a hydrometer then added 1 qt of toluene for 5 gallons. I have since repaired the damage but this leaves me with a choice and I don't want to get this wrong again.
 Do I
    1, Run the same 85 pill with less timing
    2, Run the 80 pill with more timing
    3, Run 25% with the 80 pill and 36* -38* timing
I'm just trying to be carefull on what I put in to it. We need to get into the 7's in order to run with the group but at the same time I don't want to burn it up.
  Oh sorry, It also is running 14.3 compression (I know its high)
 

Offline dreracecar

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Re: Advise on Nitro tune
« Reply #1 on: May 16, 2017, 07:55:37 AM »
What type of Magneto??
Increasing the timing AND the jet change to an 85---went lean
Beside the electrode, how many threads on the plug were dis-colored 3-4 max never over 4 = danger

Offline Supercat

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Re: Advise on Nitro tune
« Reply #2 on: May 16, 2017, 08:33:39 AM »
Always run on the wet/rich side of things when trying something new. Try a 70-75 pill and if using a high-speed bypass turn it around.
Sounds like you went lean with the higher rpm. Stay about 38 on the timing for now I would say.
We run 40-42 with a 13.6to1 injected 20-30% tune.
I'm sure you will get plenty of info for your next time out.
Also what fuel pump are you using?

Offline Cparten

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Re: Advise on Nitro tune
« Reply #3 on: May 16, 2017, 09:15:37 AM »
We run a MSD Promag set up by spud. It is showing 2-3 threads. High speed bypass is turned around and has been. Hillborn pump (also set up by spud).
I feel that a 80 pill is plenty rich going off of prior runs on methanol.
 

Offline dreracecar

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Re: Advise on Nitro tune
« Reply #4 on: May 16, 2017, 12:51:57 PM »
Broke rule #1 by changing more than 1 thing at a time, Change timing or change jet--not both unless you have hard data to back it up

Offline Cparten

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Re: Advise on Nitro tune
« Reply #5 on: May 16, 2017, 02:17:13 PM »
dreracecar, Ya I know. Only one change at a time. We only had time for 1 more run that day and I pushed it........Lesson learned!!!

Offline Spud Miller

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Re: Advise on Nitro tune
« Reply #6 on: May 17, 2017, 06:54:57 AM »

 Is the toluene something that was on board when you damaged the head gaskets? Or is that something you're adding for your next outing? Definitely a MUST with that much compression ratio.

 As high as your compression ratio is, I don't think you're going to be able to run nitro very well with any combination of timing/main pill.

 My advice would be to keep the toluene in the act, back the nitro down to 15%, timing at 36 and main pill at 80 and make a pass. If that proves safe and happy, then I'd leave everything else alone and put the 85 pill in it and see what you get. I think that's probably your limit. Hopefully, that gets you in the 7's and doesn't damage anything.

 Are you leaving the starting line from an idle? Richen your metering valve a flat or two and try that. You might shed some ET just from doing that alone.

 Spud

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Offline Cparten

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Re: Advise on Nitro tune
« Reply #7 on: May 18, 2017, 06:00:01 AM »
Spud,
    Yes the toluene was there from the start. When I tore the motor down I did take note that there was no indication of detonation, it just simply ran lean. We leave the line on the trans break at 4000 rpm. I will try leaving off idle which is something I wanted to try anyway. I am going to start over with the tune and be cautious while making 1 change at a time.
  Thanks for the replies and good advise. We are heading to the track tomorrow for some test and tune to try to reach the 7's

Offline dreracecar

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Re: Advise on Nitro tune
« Reply #8 on: May 18, 2017, 08:19:59 AM »
My car has always left at idle, but I do it in two phases.

  on your idle adj knob , scribe a line from the center out to the edge and paint white (or whatever).
 set a good running idle and remember the clock (1-2-3-12) possision.
 after the burnout and behind the line, crack the jam-nut and raise the idle, roll into the beams.
 I did it this way so the driver wouldnt have to back up with the rpms up too high
 Did not run a tach, driver gave me a nod when he felt a good pull on the hand brake.
 if the run was good and no changes were to be made, looked at the knob for where the line pointed.
 So from then on, would set the line at say 1 oclock for idle burn out, and behind the line adj it to 7oclock for stageing and the run, back in the pits would set it back to 1 oclock-- your reference numbers may vary

Offline JrFuel Hayden

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Re: Advise on Nitro tune
« Reply #9 on: May 20, 2017, 01:33:01 AM »
On the more extreme side of things, when we ran an all iron 301ci SBC on 95% nitro in my high gear car, in the mid 60's. We ran a some what odd ball combo; 10.75 to 11.25 compression, a 110 Enderle fuel pump, that Kent Enderle said it's too big, it's a pump the top fuel guys were using, not a unblown 300" SBC. But how we got it to work is our Vertex mag had 20 of advance on top of the 55 static timing we set it with, which Kent said 55 was about the JF cars were runing at Lyons. Yes, we had to push start it faster, but we ran 191mph in 1964, running 75, with a "Too Big " pump.
On the west coast a number of FED are running under 20% with 12-1 compression racing in the 7.60 class. With 14+ pistons I agree with Spud, you will have detonation, and blow head gaskets, running 20%.
Jon
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Offline Cparten

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Re: Advise on Nitro tune
« Reply #10 on: May 22, 2017, 06:34:05 AM »
Update,
   Went to the track on Friday for some test and tune. I went with 15% mix, A 80 pill and set timing to 38*. First pass was 8.25@163. Plugs showed really wet. On the next pass I left everything as is and put 20% in the tank. That pass it went 8.00 @ 164. Plugs now showed good heat with 2 threads. On the next pass I bumped the timing to 40 (on the advise of a trusted racer) It ran a 7.98 @ 167. On the last pass of the day I didn't change anything because I wanted to back up. At launch when the front end came up it went left and I had to drive it back into the groove, That pass was a 8.00 @ 165. Leaving off Idle as Dreracecar suggested made a big difference and is how we will leave from now on. With this round of testing I have noticed another problem. ALL our runs are ending with a top speed of around 165 with different et's. we are only gaining 30mph in the 2nd half of the track. I did some calculations and it seems we have 12% slippage in the converter which is too high. I believe our power band is too low. Finish line rpm is 8500. We are going to head to the dyno to get some actual numbers and get this thing set up properly. I know....what a concept.
 Again I want to thank everybody for their knowledge and advise!!