So ive begun to notice what i could describe as a flat spot in the end of each gear, its only really noticeable in 3rd and 4th gear just because the car is in those gears longer( The car doesn't seem to pop or make any odd noises during the flat spot). The part I find odd is I really haven't touched the tune or the timing at all and it started doing this everyonce inawhile. The car will be pulling hard then you can feel it nose down or lose a bit of power for a split second then pick back up again and sometimes it will nose over like that a couple times unless i decide to shift or stop flooring it. I stared at the AFR gauge last night and it seemed to be steady while this was happening, which leads me to what one of the speed shop guys was thinking he was saying you may be blowing the spark out and to tighten the gap on the plugs. So i wanted to check with you fellas about the whole blowing the spark out thing. Things i've done so far for the flat spot was change the plugs, ajdust the valves, clean the air filter, which seemed to make it go away that night but the flat spot is obviously still hiding somewhere lol. I thought maybe a weak ignition coil but i didn't want to go switching parts until I got some sort of direction.

Thanks, Kev

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Spark blowout sounds like a real possibility - what's it using for ignition?

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"Mad Scientist" Matt Cramer
'66 Dart - turbocharged 225
My blog - Mad Scientist Matt's Lair

I'm using the msd digital 6 box with a msd ignition coil msd wires stock electronic distributor with new cap and rotor and welded slots couple years ago. Ya it's the first time I ever heard of the spark blowing so I wanted to ask about it

Kev

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What gap are you guys running on the turbo motors?

Kev

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I have mine gapped at .024"

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11.02 @ 120.56
http://www.youtube.com/watch?v=EAxRmoDgsdY
Chassis dyno
http://www.youtube.com/watch?v=wd6hFGzLJMc

I'm at 0.030". I sometimes get a little surging or flat spot if my AFR drops down a bit with weather change or whatever (below 10.5 or so). I would think you would see an AFR change if the spark was blowing out, OR if fuel was changing. Hmmm.

Lou

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Home of Slant6-powered fun machines since 1988

What plugs are you guys running in your turbo setups? I gapped the plugs to .025 they were all like 35 to 39 when i took them out to check them, seemed to run better but still had the flat spot up top. Seems kind of irratic floored it in 2nd gear yesterday no flat spot left the gym flat spot was back. Checked the ign coil seems good ohmed all the spark plug wires all were 50ohms except one was reading 90ohms is that enough to warrant changing that plug wire? Oh i also retarded the timing per charlies advice just made the car slower and seemed to get a flat spot earlier maybe? advanced the timing got into some valvetrain rattle then backed the timing back to where i had it for the past year. I still feel a bit fishy about the spark plugs I put it in a couple weeks ago seems the car is missing slightly during normal driving after changing them could it be a bad plug new out of the box? Going to compression test the cylinders tonight just to check that out. Not sure if these means anything but my meth kit is mixed 50/50 with water and meth, think that may contribute to anything with all that water in the mix? Speedshop guys are telling me to run straight meth regardless

Kev

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How old are your valve springs? If the springs are old or stock, it maybe something to think about. Boost on the surface of the intake valve and back pressure on the exhaust valve plays hell on springs.

Close the plug gap to .22 and see if it changes. My wagon would blow spark out at .24

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1967 Dodge A100 Van

Weak valve springs as mentioned above will cause some funky stuff to happen. Especially on the exhaust side because the pressure can be and most likey 2-3 times what the intake side sees. Consider 15psi on the intake. This can translate to 45psi on the exhaust valave and if it is weak it may not fully close.


I have NGK plugs. I don't remember the number but do remember it was quite colder then an RN9YC.

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11.02 @ 120.56
http://www.youtube.com/watch?v=EAxRmoDgsdY
Chassis dyno
http://www.youtube.com/watch?v=wd6hFGzLJMc

Valvesprings were new erson cam kit deal when I built this setup 2 years ago I think. I'm pretty sure i'm out of the woods the cars runs good again after changing the plugs. I'm pretty sure i was to rough with the champion plug when i closed the cap down seemed like the electrode got pushed down lower into the ceramic portion of the plug. Put new ngk plugs in purs like a kitten again haven't floored it yet though so we'll see about the up top issue it was having. Compression test gave me 150psi for every cylinder.

Kev

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Sounds like the plug were it. Always try to remember the last related thing(s) you worked on, and that will usually be the culprit.

Lou

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Home of Slant6-powered fun machines since 1988

I called the NGK tech line yesterday and asked for a recommendation for out turbocharged slant six.

The tech guy recommended a B9ES (NGK part # 7148) and a B10ES (NGK part # 7928.)

NGK plugs get colder as the numbers increase (a 10 is colder than a 9.)

Hope this helps...

Bill

Thanks, Bill. I have seen B9ES before, and will try those at some point. I am still using the 20 yr old new-in-box autolite 63s I got from Seymour. I have put about 12k on them and maybe 100 drag passes and lots of hwy thrashes.

Lou

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Home of Slant6-powered fun machines since 1988

Sometimes the old ways are the best... LOL!

Bill

Well the flat spot went away a bit ago just to let you guys know think i fixed it when i was hunting down a boost leak. So heres the update finally did the brpv and changed my baseplate because the bg one had enough slop in the front it wouldnt like returning all the way to idle.

New tuning issues have arose
Upon start up with brpv and new baseplate everything was the same except i dropped the main jet 5 sizes down and did not put my rubber hoses for the vent tube extensions back on. Drove it ran beautiful cruising around felt like a efi car driving around but when i stomped it goes way lean at wot and bucks like a bronco. Next step after checking some things I put my vent tube extensions back on (8 inch rubber hoses). Stomped it afr literally went from 16.0 to 12.0 and scooted along under wot BUT, after driving around notice extremely rich off traffic light accleration that begins to cough and shows 10.0 afr or ---- and if i rev it nuetral 1/4 throtle revs fine but if you give it a 1/2 pedal wack hesitates when secondaries crack which is wierd never had a nuetral rev bog with this carb before.

I would like some guidance here because i'm unsure if I want to keep the vent tube extensions on and just try to lean out the system until it cruises fine and figure out the stab bog. Yet i'm also thinking the other route may work too I lose the vent tube extension so it cruises nice and try to richen it up for the wot pulls?

I never noticed my vent tubes extensions making a difference back in the day when i first put them on but i did back to back pulls and saw the huge afr change just from putting them back on.

Oh I almost forgot to mention I have not tightened up the main air bleeds yet anyone think this may help should i tighten up the secondary air bleed also? just curious what route to pursue first

Kev

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