jetting

Discussion in 'PSI Superchargers Tech Questions' started by IGO1320, Nov 5, 2005.

  1. IGO1320

    IGO1320 T/D 2268

    Joined:
    Oct 14, 2005
    Messages:
    87
    Likes Received:
    0
    Hi I have a SBC I am running in TD 393" 3.75x4.080 filled bowtie block, 867 pontiac 23' heads, 8-71 littlefield stripped, bird catcher, 5.5% overdrive (57/54 pulleys). I am a novice at this blower stuff used to run nitrous till this year then switched, I have been trying to sneak up on it without killing parts, my question for anyone who might have an opinion is with the jetting. I am running a hilborn 150-1 pump flowed 6.55 @ 100psi @ 4k, I am only running hat nozzels started out with 52 nozzels and a blank main car ran 6.91 @ 197.75 could not get any heat in the plugs worked my way to 56 nozzels and 60 main car @ 4300 feet oxygen altitude (same altitude as earlier this has all been during the summer) runs 6.82 @ 201.19 plugs now show slight color on ground strap just shy of the bend and the ring at the base of plugs whitens about three quarters to four fifths the way around the base no color in threads, egt's (red alert unit) are 1350 - 1400 which to me does not agree with the plugs. I have taken to believing the plugs, now the million dollar question, the air is getting much better do I have enough left in the pump to raise the nozzells to say 58-60 so that I have more adjustment on the main? any suggestions appreciated.
     
    #1
    IGO1320, Nov 5, 2005
  2. Leon

    Leon New Member

    Joined:
    Feb 4, 2005
    Messages:
    69
    Likes Received:
    0
    Well, im getting an a/f of 4.059 with .056 nozzles and using 87.5% of the pump flow with 78 lbs system pressure. Do you track pressure? It sounds real lean especially with not much plug color..060 nozzles with .050 main is 3.858 a/f and 66 lbs and using 92% pump flow. Hello,it needs a bigger pump and get some port nozzles in their,it will make life easier. RBS and Koehler can get your system flowed and give you somewhere to start frm with a bigger pump. With a pump flowing 11 gpm, its using 55% flow with a .154 main.Even tho i bet it will be smaller than that jet.Then you can get the nozzle area down to get some system pressure and get the main back in line.OOPs didnt realize RBS didnt do flowing,sry.Trying to get our sponsors some business.LOL
     
    #2
    Last edited: Nov 6, 2005
    Leon, Nov 6, 2005
  3. IGO1320

    IGO1320 T/D 2268

    Joined:
    Oct 14, 2005
    Messages:
    87
    Likes Received:
    0
    reply

    where can I find the formulas to do that math, and how are you figuring the A/F ratio? Do I have enough fuel for the air to get 2000' better? Starting line rpm is 7000 and finish is 8400 with a shift at 7950. Thanks.
     
    #3
    IGO1320, Nov 6, 2005
  4. IGO1320

    IGO1320 T/D 2268

    Joined:
    Oct 14, 2005
    Messages:
    87
    Likes Received:
    0
    Info

    Anybody else got any info, suggestions, useful formulas????
     
    #4
    IGO1320, Nov 10, 2005
  5. Mike Canter

    Mike Canter Top Dragster
    Staff Member

    Joined:
    Mar 10, 2004
    Messages:
    4,630
    Likes Received:
    189
    Heat is moved in and out of the combustion chamber by the ignition timing. You can be right on on the jetting but if you have the ignition too retarded the flame (heat) moves out of the chamber into the exhaust where the EGT is and up goes the temps. If you advance the ignition the EGTs will drop down.

    To observe ignition timing in the chamber you can read the "blue line" on the plug's groundstrap. This is not just color where the cadium burned off and shows a greenish color this is medium to dark gray with a definite line that is blue in color that needs to be just above the bend in the strap if you are usinga plug with a 90* bend in the strap. All your indicators that you have listed in your post point to not enough ignition advance but that is hard to tell without actually seeing the plugs groundstrap.

    Read this article especially about the groundstrap color:
    http://www.draglist.com/artman/publish/guest_shoe/article_001172.shtml

    What is your ignition system and where are you running the ignition timing?
     
    #5
    Mike Canter, Nov 10, 2005
  6. IGO1320

    IGO1320 T/D 2268

    Joined:
    Oct 14, 2005
    Messages:
    87
    Likes Received:
    0
    plugs

    Thanks for responding Mike, this is were I am getting lost on the tuneup....with the plugs in front of me right now the ground strap turns from a gray to a very light purple right about where the bend is in the ground strap but it is not a real defined line it kind of blends. I am running 28' of advance right now I had 30' and I pulled the heads to change the head gaskets at 35 runs and saw some light detonation on the pistons and heads so I took 2' out of it, I did not see any noticible change in the egt's...the egt's go up as I take fuel out and down when I put it back.....the plugs to me do not agree with the egt's. When I had the .052 nozzels in it with the blank main the plugs were dark gray you could clean them with brake parts cleaner and all the cadium would be there nice and shiny, egt's read around 1250. I am not trying to run on the ragged edge but I would like to get most of the performance, be consistant, and learn about tuning this thing correctly...so far I am just kind of trying things with crossed fingers. I have 12.3 to 1 compression, I set the cam at 114' intake centerline with 112 lobe separation, duration is 281' intake and 290' exhaust @ .050. I am real low budget and try to attend a few IHRA races a year and then the quick 16's that are local. Thanks again any advice or thoughts are appreciated. ignition is msd7al2 with pro power coil, plugs are gapped at .020.
     
    #6
    Last edited: Nov 11, 2005
    IGO1320, Nov 11, 2005
  7. Mike Canter

    Mike Canter Top Dragster
    Staff Member

    Joined:
    Mar 10, 2004
    Messages:
    4,630
    Likes Received:
    189
    Here is my guess and that is all I can really do. Your EGTs indicate to little advance because it is pushing the flame into the exhausts which should make the chambers cool but you have leaned it out enough so the plugs are showing the correct mixture indication. With that type of ignition I would have thought your advance should be up in the 34-35* area and I think that if you move the timing up there the EGTs will come down but the only way you can do that is to add more fuel to cool the chambers and stop detonation. Both the additional fuel and ignition advance should make that car increase its MPH because you will get more horsepower. I think you would have to do this step by step in enriching the mixture and advancing the ignition one degree at a time. It would be safer to add enough extra fuel to make it run rich first than play with the advance. I think that once you get the advance up to 34* and work the fuel until the plugs look right I think the perfoprmance will really pick up. Watch the finish line MPH because that is directly effected by horsepower and will show you if you are going the right way. My biggest concern is giving you my thoughts and having something go wrong with the motor so it is entirely up to you. You may find that you need to close the plugs up to .018 when you start getting more fuel in it. At some point a 7AL2 maybe will not be enough to fire it and the performance may roll off. I would be very interested as to what happens if you do change anything.
     
    #7
    Mike Canter, Nov 12, 2005

Share This Page





XenPorta 2 PRO © Jason Axelrod from 8WAYRUN.COM