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Author Topic: Flat under low end Load  (Read 12409 times)

Offline tdietz

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  • Your Best Time: 7.88 - 1/4
  • Your Engine: SBC, 410 ci, Alcohol Injected
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  • Your Vehicle: Shack Engineering Front Engine Dragster
Flat under low end Load
« on: May 11, 2015, 04:49:50 AM »
Ok guys, 175" WB FED, 410 SBC timing around 36 degrees, MSD Pro-Billet Dist, MSD Blaster 2 coil, MSD 6 ignition box, MSD starter saver, and MSD 2 step rev control.  Engine is fuel injected on Alcohol (down nozzles), Kinsler 450 mechanical pump.

The car on launch runs flat and breaks up.  Our first pass of the day our 60' times were 1.415ish and our normal 60' times are roughly 1.16ish.  It is flat then all of a sudden will pick up and our MPH on top end is normal 166MPH.

We tried leaning the barrel valve, then we tried richening the barrel valve, nothing made a difference.  And by the end of the day the engine would clean out until I hit high gear (powerglide) and then it would break up again. 

I'm pretty certain this is ignition, but where or what part of the ignition should I be looking at?  Our tach is the digital shift light with the tach built in, and it seems very erratic as well....
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dreracecar

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Re: Flat under low end Load
« Reply #1 on: May 11, 2015, 08:39:21 AM »
Dump the ignition system and put a Magneto in it.
It takes a lot of battery to run a MSD ign and unless you have an alt on the car, the battery cant keep up with it.
  Mags do take HP to turn(very little) verses a standard ign system, but it also takes HP to turn an alt and push the extra weight of a battery, so its a wash, but the Mag gets the nod for its simplicity and reliability.
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Offline tdietz

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Re: Flat under low end Load
« Reply #2 on: May 11, 2015, 09:31:33 AM »
That's all great and I understand you are probably correct.  BUT, I didn't have issue last year and I don't have 600-800 for a Mag.  I'm sorta stuck at this point with what I got.  I can't afford to just dump all of it and go to a MAG. 

For the previous 2 years we've had no issues.  It developed late last year and we attributed it to weather.  But, now I'm almost certain it is ignition related.
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Offline H.G. Wells

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Re: Flat under low end Load
« Reply #3 on: May 11, 2015, 09:44:21 AM »
Can you bypass the two step? take it out of the equation, borrow a coil if you do not have a spare.
If neither of those helps, I think the box itself may be suspect.

Assuming you have looked inside the distributor? No tracking in the cap or anything noticeable?

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Racecar spelled backwards is racecaR

Offline ricardo1967

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Re: Flat under low end Load
« Reply #4 on: May 11, 2015, 09:49:49 AM »
Tim,
In in lieu of temporarily replacing ignition components individually to aid troubleshooting, sometimes tightening the plugs' gaps is suffice to flag a weak ignition system. Another thought is checking rotor phasing.

No argument that magneto has its advantages, but there are tons of drag cars running CDI ignition systems, w/o alternator.
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Offline tdietz

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Re: Flat under low end Load
« Reply #5 on: May 11, 2015, 10:56:08 AM »
I can take the 2-step out of the equation.  I also thought the same thing about checking the rotor phasing.  I'll see what I can come up with.  Really want this thing right before Memorial Day.....
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Offline masracingtd1167

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Re: Flat under low end Load
« Reply #6 on: May 11, 2015, 12:00:11 PM »
I have a couple of idea's for you to try . First is Battery voltage you need at least 12 volts at the box at all times durring a run . I have seen a battery with a bad cell that would start the car but not hold 12 volts . Next would be rotor phasing . Next thing I would check are the pickup wires . If they are backwards the car will run like you explained . Do you charge your battery between rounds ? If you don't you should . Another thing to check are your grounds also very important . I use a separate ground for my box to the chassis and I also ground the motor to the chassis .Plug gaps .025 or so I am not a big fan of large gaps . Double check that starter saver to make sure it is not staying activated . Hope this helps . Bill     
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Offline tdietz

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Re: Flat under low end Load
« Reply #7 on: May 11, 2015, 12:25:52 PM »
Bill we are getting 12 volts at least while it's running.  I've checked this before.  We charge the battery after every run.  I'm going to check rotor phasing later this week and pick-up wires.  I'm almost positive the wires are right but will make sure.  I was thinking of eliminating the starter saver just to get that out of the system all together.  We run a high torque starter and I feel it would start the same without it.
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dreracecar

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Re: Flat under low end Load
« Reply #8 on: May 11, 2015, 01:01:28 PM »
Borrow a mag for the weekend
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Offline Paul New

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Re: Flat under low end Load
« Reply #9 on: May 11, 2015, 01:44:28 PM »
Remove any RPM chips from the system they do go bad.... I was stuck at 186 mph for a long time removed the chip and went 205
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Offline masracingtd1167

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Re: Flat under low end Load
« Reply #10 on: May 11, 2015, 03:39:43 PM »
I re read your original post and you said that your tack is erratic . If you could borrow an MSD tester from someone it would help you a lot . You would be able to test your chips and see if your coil is working . A clogged fuel vent could also cause a similar problem . I had a problem one time with a nitrous bottle a spider decided to climb into the end of the bottle ! the little sucker made it all the way up to my nitrous solenoid and clogged it right up it wasn't very good for the spider either ! 
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Offline BK

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Re: Flat under low end Load
« Reply #11 on: May 11, 2015, 06:04:06 PM »
Did you try the basics? New cap, rotor, plugs and wires. Especially the cap and rotor.
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Offline George

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Re: Flat under low end Load
« Reply #12 on: May 12, 2015, 02:55:56 AM »
Try a fresh battery. The mag is the best fix.
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Offline tdietz

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  • Your Engine: SBC, 410 ci, Alcohol Injected
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Re: Flat under low end Load
« Reply #13 on: May 12, 2015, 03:42:43 AM »
All thanks for giving me some stuff to check.  Going to begin looking through everything tonight.  Hopefully it's something really noticeable that we just missed at the track!  (but it never is!  LOL)
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Offline Spud Miller

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Re: Flat under low end Load
« Reply #14 on: May 12, 2015, 06:22:29 AM »

 Sorry being late to the party...Mondays are brutal for me this time of year.

 Lots of great ideas to try here! It does sound like ignition and you should find improvement pretty easily by trying some of them.

 Let us know how it goes...

 Spud

 
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