Safest compression ratio for the bottle
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Safest compression ratio for the bottle

  1. #1
    Senior Member holorinhal's Avatar
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    Default Safest compression ratio for the bottle

    Is there a range of compression ratio that is safe to run with a Nitrous system.
    I plan on running a plate system with about a 150 shot to start but would like to step it up at some point.The pistons I have now with the afr 325 head's I have,with a chamber of 119, I should be around 10:1-10.2:1, I would like to be at 11:1-12:1,which would require me to purchase new pistons,which is not a problem,I just want to know if it matters of the compression ratio when running nitrous?
    I am building a dual carbed ,tunnelramed ,aluminum headed,489 w/splayed main caps .Thank's.....Hal

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    Senior Member vee-driven's Avatar
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    it does not matter.


    It's not that i don't care, I just dont give a sh!t!

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    Resident Ford Nut Sleeper CP's Avatar
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    You could run 14:1 if you wanted to, you just have to back out more timing and use better (higher octane) enrichment fuel with a higher compression ratio.

    Sleeper CP

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    Distinguished Member David 519's Avatar
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    Default Safe is a subjective term.....

    I ran NOS in our old flat combo for about 5 seasons with a lot of success. It was a 13.5:1 850 HP 509 with less than a 75 HP shot. Worked really well in that combo. But I made a timing mistake in testing once and that small shot broke a nice steel crank into 3 pieces (ripped the rod journal out of the crank). NOS is a perfect power enhancer in almost any N/A combo, but you have to pay attention to the details. A mistake will punish you with seriously blown up parts.
    That said, we'll likely be using it later this season in our new combo. Best of luck to you.

  7. #5
    415 M3
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    Quote Originally Posted by holorinhal View Post
    Is there a range of compretion ratio that is safe to run with a Nitros system.
    I plan on running a plate system with about a 150 shot to start but would like to step it up at some point.The pistons I have now with the afr 325 head's I have,with a chamber of 119, I should be around 10:1-10.2:1, I would like to be at 11:1-12:1,which would require me to purchase new pistons,which is not a problem,I just want to know if it matters of the compretion ratio when running nitros?
    I am building a dual carbed ,tunnelramed ,aluminum headed,489 w/splayed main caps .Thank's.....Hal
    Hal, check out yellowbullet.com. There is alot of guys w/ good info on nitrous engines on that forum. A dedicated nitrous engine usually requires a combo that a naturally asperated motor does not. If you are not planning on a dedicated nitrous motor, try to make all the HP you can without the bottle. You will still be able to spray plenty of gas for a river racer when you need it, and haul ass off the juice as well. What are your goals? IMO if you are going to run race fuel you might as well bump the compression up a bit and run a little less bottle. On a well built combo a 150 hit will be a substancial increase in performance on the river and you can go from there. The guys building dedicated nitrous motors are using custom pistons that set deeper in the cylinder, spend alot of $$ on cylinder heads with nitrous friendly combustion chambers, camshafts that will support a large spray, the list goes on and on. If you do decide to go balls out on a spray motor you should work with an engine builder that knows nitrous combos. The spray motors require you to be right on with the tune-up to prevent expensive melt downs. At the end of the day you have to determine how much power you can throw at your hull before you're pissin up a rope. Take care, Jerry.

  8. #6
    mo balls than $cents$ IMPATIENT 1's Avatar
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    i'm runnin a 13.5 to 1 505bbc and spray what you guys would consider alot of nitrous. i either race with a 2 stage 300,350,400,450,500hp shot depending on how froggy i feel i need to be to beat the guy in the other lane i keep the 1st stage of nitrous getting the cam to peak at 6500, the 2nd stage is just there if i need it or wanna put some serious distance between us on the holeshot.

  9. #7
    CarbGuy RumRunner's Avatar
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    There is not a Safest copression ratio for Nitrous...


    It's a matter of building the engine properly for nitrous.

    Meaning: Proper Ring location, type, and tension... Proper cylinder wall finish... Type of piston, & PTW clearance... Proper fuel system... And finally having the proper ignition system and timing retards.

    I've run nitrous on engines from 9:1 up to 15:1....

  10. #8
    B1 Racing cs19's Avatar
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    Rum runner said it best. There are guys running heavy nitrous with all different combinations. for what its worth, the guys at CP pistons said 14-14.5:1 is about as high as they like to see it for heavy nitrous.

    You mentioned you might be at 12:1 later when you get new pistons, that will work fine.

    If your going to be spraying over 250 you need to start changing up your combination with nitrous in mind. Some of the things CP looked at for my nitrous piston were intake pocket design, ring groove depth, piston thickness, wrist pin material and pin clearances, ring locations and piston to wall clearances. Also ran a heavy duty top ring and STD tension oil ring which I may not do next time.
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