Ignition interference and spark plug choices

Discussion in 'Race 400/430/455' started by Bens99gtp, Oct 3, 2017.

  1. Bens99gtp

    Bens99gtp Well-Known Member

    On our new top end( te2 heads, sp2, sv1 carb ) we upgraded our ignition to the msd grid, matching coil, msd pro billet dist, went with the larger mag cap. I have been fighting interference and when i get it the car won't rev above 4000 rpn and when I look at the data from the grid everything is smooth till that point and the my rpm look more like seismograph, just very rapid up and down till the rpm demand drops then all is smooth. It's not a setting issue in the grid, been through all that with msd. Every once in awhile it will rpm mostly smooth

    I'm going to add more grounds between the frame, motor, firewall, have a shield 6ft pickup wire to reroute that out and away as far as possible and hopefully that takes care or it. But I'm laying in bed, can't sleep wheels turning and I'm wondering if my non resistor plugs could be part of this too.

    I'm running ngk 7173/R5672A-8 I wanted the smaller 5/8 he nut for better clearance on my headers. Called ngk and they said the closest plug in a resistor was the 4644/BKR7E. TA recommend the bp6-9es plugs which are also non resistor but the larger 13/16 hex. They make bpr6-9es with a resistor.

    I haven't made enough passes to know what heat range I need, motor is about 11.75:1 compression. I opted to start on the cooler side to be safe. Just wondering 1st off what others are running for their plugs.

    2nd I can't find what all the letters mean to make a comparison. I found it for 4644 but cant find any chart for 7173 seeing it starts with a r then all numbers. I know the 6,7,8,9 is the heat range and the larger the number the colder the plug.

    3rd has anyone else gone rounds with emi/rfi and what did you have to do to correct it, just incase what I have done and am doing doesn't fix it.
    Last edited: Oct 3, 2017
  2. hugger

    hugger Well-Known Member

    Autolite racing plugs are nice and use a 5/8
  3. LARRY70GS

    LARRY70GS a.k.a. "THE WIZARD"

    Sounds like the rev limiter is kicking in?

    BQUICK Well-Known Member

    That shielded pickup wire should help as well as resistor plugs but you can run non-resistor if you have fairly high resistance mag supression wires.

    Also, set the rev limiter 500 higher....they sometimes come in early.

    I like the R42XLS AC plugs....have run them for years.....
    Last edited: Oct 4, 2017
  5. Bens99gtp

    Bens99gtp Well-Known Member

    This was my first thought too, but it's not. If you look at 2 step, which is set at 3500 just start with. It's very smooth, even and hardly a ripple on the rpm line. But when the interference start rpm will rapidly jump from 400 to as low as 500. I will try to screen shot the trace so the difference can be seen.

    I even applied voltage to the burn out activation wite for the 3 step and that bypasses all but top end limit and it still does it. Msd agrees by setting and what it looks like it's not a rev limiter. The rev limiter sounds very smooth, this sounds very awful, pops in headers, in the intake, shakes the motor hard
  6. Bens99gtp

    Bens99gtp Well-Known Member

    The r42lts is a tapered seat plug, the AL heads need a gasket seat.

    I don't have any rev limiter set around 4000,. 2 step us 3500, top end 6850, safety limit is also 3500, but that won't kick in till 12.5 seconds after I let go of the transaction brake

    BQUICK Well-Known Member

    No, I meant R42XLS....sorry
  8. Jim Weise

    Jim Weise 1000+HP

    Your using my plug of choice for that application, I can assure you that I have built many race and street cars with it, and MSD 6 and 7 systems, never had any issues.

    So no the plug is not the problem.

    In My experience the MSD unit is what usually causes issues with other electronic devices on race car.. interesting that you seem to be having the problem in reverse.

    What is on the car that can be omitting that much interference?

    I assume you don't have the mag pickup wires wrapped around the ignition coil.. LOL..

    I would find some RFI shielding and cover the mag pickup wires, from the distrib to the MSD unit. And while your at it, insure that your connections are solid and clean, both at the box, and at the distrib.

    I also assume you have spiral core plug wires.. if not, you should. Some of the "race" wire sets can be really noisy.

    I also assume that you have not lengthened the heavy Red or Black wires on the MSD, and ran them straight to the battery. I certainly have not done this in the past, building new race cars, but if I had an issue like yours, it's the first thing I would do.

    After that.. alternator... make a run with it disconnected, and the belt off it. Your fully charged battery is enough power for the MSD system. I have often found that changing the source voltage, affects ignition issues in some way, and that way can often lead you to the issues.. i.e. If it misses sooner/worse on just the battery, I suspect a voltage issue.. so either a bad connection, or your coil is failing..

    Good luck with it

    Harlockssx likes this.
  9. Bens99gtp

    Bens99gtp Well-Known Member

    Power wires do go right to the battery, I did have to add length to get there and did go up in size for the extension. No the pickup wire is not wrapped around the coil, tried taking the wire and belt off alt, no change. Have the wires msd recommend, they are spiral core wires. Box, dist, coil and everything is new, so I didn't see any corrosion on the connectors but will recheck.

    My previous system was 6520 dig 6 plus and mallow dist and promaster coil. That setup was a hall effect not mag like msd.

    I feel confident the issue is going to lay in how close the connector was in proximity to the actual dist itself. The new msd coil coil is huge and am assuming just the raw power output is causing the issue itself. The new shielded extension wire will allow me to route it out and away from the motor ( not across it ), under the core support, up the drivers side of the motor from the bottom. Was going to try to get some copper wrap to coverify the wires from dist down and the connector. Both the new shielded wire and the wire from grid have the additional ground wire, but leave the connector exposed.

    The plugs were my last thought as I was laying in bed, if no one else has had an issue with them before I'm sure then it's not my issue. Just thinking.

    Jim thanks for the idea of other things to check, sometimes it's the simple thing that are easily over looked
  10. Bens99gtp

    Bens99gtp Well-Known Member

    Jim on a side, the 7173/R5672A-8 is a heatest range 8, if needing in the end I feel I need a 7 heat what would you recommend? I can't find a R5672A-7, just the 4644/BKR7E. I can find a colder 9.

    Do you normally run them as gapped at thev.031 or open the up. We opened our up but only to .035
    joegsx likes this.
  11. Bens99gtp

    Bens99gtp Well-Known Member

    On the pic below the 2 step is at 3500 very smooth even trace. .25 seconds in I get to 4000 and the trace goes crazy. I stayed in longer than I should have to see it by chance it would drive through it.

    Attached Files:

  12. Jim Weise

    Jim Weise 1000+HP


    I run all V power plugs at .045, never had an issue with multiple different types of ignition systems. Certainly not an issue with what you have there.

    If you need a hotter plug, you can use the stock number 5913 ones.. that's a ZFR7F plug.

    But we have found over the years that the 7173 is a virtually universal application for over 11-1 compression in both street and race BBB motors. A good ignition system like you have insures that.

    Were I faced with this issue, I would trigger the msd outside of the mag trigger circuitry, with another distributor.. use your old Mallory, or even points for that matter, via the white wire on the 6 and 7 series units, just to rule out everything but the distributor and wiring in the mag trigger circuit.

  13. Bens99gtp

    Bens99gtp Well-Known Member

    I sold the mallory with the old motor, but I think I know someone who has one. Have to find d a way to temporarily lock it out......mine I drill through both shafts and pinned it.

    I might have an old points setup somewhere. I always liked that mallor used the hall effect not mag pickup.

    So far this week I added an extra 6 ft of shielded group wire to the distance pick up, rerouted against the passenger fender, behind and under the battery, down under the core support, back up above the steering box, and make the connection to distribute below it down by the fuel pump block off. I twisted the wire from the dist, much like new car crank sensor wires, and wrapped them in a copper sleeve.

    Added new ground straps from both heads to frame, from frame to battery, from firewall to head, and increased the wire size for the strap that runs head to head. I really don't know what else I can do.

    I read somewhere that drilling holes in the dist cap or cap adapt helps disaster the build up of electrons inside the cap. But I though with mag style mad cap and rotor they did that by all the vans and stuff in there to move the air around. Hate the though of drilling holes in a good cap.
  14. Bens99gtp

    Bens99gtp Well-Known Member

    Got out on the road last night, was pushing my luck, the roads were not fully dry. Dropped the 2 step to 2500 just to start the recording, was not flat on the floor against it, just basically foot braked up to it. There was a bog while against the 2 step, I rolled more throttle in and came but up, let go of brake and 2 step rpms went up to just under 3, rold though the throttle, never got wide open, lots of on and off due to road conditions. But I had rpms...........just wondering why my trace is so thick and fuzzy looking. If I zoom in it showing about a 20 rpm ripple all the time. I wonder if this could be because I'm using the pick up in the msd dist. Not a crank trigger?

    I did also drill a 1/2 hole in the cap and verify rotor phasing. I'm using the pro cap setup, so it's the 5 inch cap that is adjustable at the base.

    Still has a nasty bog especially in gear on the brake as I roll up towards 2500, it will loose rpm, break apart. Out of gear at those rpm it doesn't sound happy at all either. It's not the 2sted that was at 3500 till right b4 road test and huge that bog all day. The sv1 has a port that is ment to tune the 1000 to 2500 rpm. The port came open and is about .140. Takes an 8-32 Allen key set screw as its jet, tried on with a .086 hole in it no better, have a .050, they say don't go smaller than that, but also have one that is closed. Will try those tomorrow to see if that bog goes away or gets better

    Attached Files:

    Last edited: Oct 7, 2017
  15. Bens99gtp

    Bens99gtp Well-Known Member

    Played around today, could only make the bog worse, put it back loaded up to go to the track. Warmed everything up, still sounded like crap driving g around the pits, but I was ready to see if it ran wide open. After talking to patrick at prosystems this morning sound like I need to add a 3rd circuit to my carb to clean that area up.

    Went through tech at Norwalk, drove back to pits, went up a few mind later to make pass, back to not review over 4000 and when it does this you can actually watch the tach go backwards. Clearly it's not inteference.......some is wrong with grid, either the 7720 or 7730 or the coil, or pick up coil.

    Went home pulled it all off the car going to summit tomorrow to either exchange or return and go back to the 6520 box. Also going to buy a new puck up coil just for good measures. I don't think that's it.....it measures 630 ohm which is in the 500-700 specs.....but that's after towing home not right when it was messing up. But for 30 bucks it's a cheap thing to swap out.....I just wasted more money than that towing to the track and back.

    If this won't work I will put my stand alone heI on just to totally bypass everything ignition related
  16. Bens99gtp

    Bens99gtp Well-Known Member

    Update, after pulling the entire msd grid system off swapping the pick up and installing a new msd 6520 box, all seemed well. Loaded up the car and to a race in ky. We got luck they were going to have a test and tune thrusday night and I was going to need it. I dropped the jetting on the sv1 10 jets front and rear cause I know it wa's crazy rich, went up for a pass. Burn out went as should, staged, launched.....not surprisingly the car spun pretty hard.....I was only like the 10th car down that night and I'm sure the prep wasn't stellar. Car ran well through the rpms with no breaking up. Clicked off a personal best 6.92. After getting g ticket 60 ft was off by .05 from normal, and gets were 300 cold from previous normal with the stg1 heads. So given all that I wasn't feeling too bad till I look over and saw the oil.pressure was down to 15 at idle.....not the 25 it has been.....oil temp was only 160.

    Once back to pits and cooled a little......I cracked the oil filter loose to take a sample.....oil looked to have a lot gold color. Called it quits till I check out more....in the morning I cut the filter apart to find this......race over

    Attached Files:

  17. Bens99gtp

    Bens99gtp Well-Known Member

    Finally got the motor out and apart found mains 2,3,4 all down to copper but only the bottom half of 3.....all the rods look very similar to this....pic 1

    Now I'm ting to figure out what could eat the main out and not the rods.....crank appear to only have .001 bend after all this......it's going to go and be wet magged for crack.......it has a fresh 10/10 grind and magged crank we we put it together.

    All the main bore check out exactly at 3.439 so the aline hone seems straight.

    I'm also going to have the block main wet magged too

    But if all that checks out any other ideas as to what could eat the main........during the pass I had 70psi....I would assume if it was lack of oil the rods should also be burnt up.

    Is it possible that all the crazy ignition stuff caused this......I would assume though that to rod bearing would had been damaged too or first if this was the case

    Attached Files:

    nitrousfish likes this.
  18. Bluzilla

    Bluzilla a.k.a. "THE DOCTOR"

    Ben, Today was the first day I read this thread. From the very first post I was wondering in the back of my mind, .... what kind of living hell the rods and bearings must be going through? Now I know, ...... Hope you get this sorted out.

    Last edited: Dec 9, 2017
  19. Bens99gtp

    Bens99gtp Well-Known Member

    The rods and their bearing all seem ok. I will have the big end checked out to verify no damage........and I figured it would had beat them out well before the mains........

    It's looking very much so like my brand new 1000 dollar msd grid with matching coil destroyed this motor.

    I wish I would of had the time and money to test it part by part, but once I pulled all that off and put my 6520, all the pickup wires and everything running in the exact same areas, my ignition issues went away
  20. Bens99gtp

    Bens99gtp Well-Known Member

    Update....upon close inspection on everything we found the center 3 main caps to not have any press to fit into the block, front and rear had minimal press, and timing chain has a lot of slack. Now I had installed my 308s a's close to 104 when assembled and normal ran it close to 108, so switching it back in the middle of all this was done and I don't remember the chain being this loose.

    What I can't determine and never will know is where the caps and chain that far off on assembly and I just missed them, or were they damaged because of what was going on. It is possible I guess that if there was a lot of slop in the chain it cause false triggers to the msd unit?? And maybe the new grid unit is more sensitive than the 6520?

    But motor has been put back together with billet main caps, new molar rods, new crank, new pistons, custom ground cam. A HUGE thanks to Finishline Motorsports for going above and beyond in helping get this back together.

    Motor got set into the car over the weekend, so we will see how she runs shortly.

    I want to thank the board as well many of you I called and talked to about this, thanks for lending me an ear and your time for ideas and thoughts
    Last edited: Jun 11, 2018
    Harlockssx likes this.

Share This Page