Breaking up in the higher rpms?

AgFormula02 · 11-02-2009, 09:50 PM

I am going over the logs and it seems the car is acting funny above 6700 rpms.
Couple of things happen here:
- I added extra fuel for safety
- We pulled some timming (3 degrees, plus we got another 2 from IAT) so we went from 18 to 13 degrees in the higher rpms.

I was going over the log and I can see were the car stuttered 3 or so times. (Even before we reached the rev limiter at 7200)
The log shows the rpm and suddenly there is a drop. Nothing huge, maybe 30rpms, then it climbs back up. hundred rpms later, it did it again. And then once more.

Could this be spark repated? AFR seemed ok at 11.5 or so.
Maybe the coils can't keep up? My voltage does drop steadily during the run from 13.5 to 12.5 volts, but we are back up as soon as we lift. (Car has an alternator still.)

Anyone else experienced this?

Tiago · 11-02-2009, 09:52 PM

I wouldn't pull timing in the higher rpms for no reason...

1BAD_LS1 · 11-02-2009, 10:02 PM

check coils, plugs, wires..... aslo if you have hptuners bump up your spark dwell and see if it helps....

aslo check all your spark plug wire are ALL the way seated....

AgFormula02 · 11-02-2009, 10:21 PM

Quote:

Originally Posted by Tiago

I wouldn't pull timing in the higher rpms for no reason...

I wanted to be as conservative as possible. This was our first quarter mile pass and we had never logged that high. I figured adding fuel and pulling some timming was a way to add a bit extra safety.
I want to go back out with the rev limiter at 7500 instead of 7200 and see what it does.
But I want to figure out this break up issue we are having.

DeltaT · 11-02-2009, 10:30 PM

What do you have for valvesprings?

Jim

1BAD_LS1 · 11-02-2009, 11:21 PM

atleast you arent trying to figure out a problem like this! I have good springs so no valve float, good coils, new plug wires, new plugs, no spark blowout, no boost leak, tune is good, ect....

Im down to the tranny slipping its driving me nuts! I know it has 600hp+ in it, i just cant figure this out!

I hope you can figure yours out a little easier! GOOD LUCK! you might check some of the other stuff i listed that i checked!

Louis · 11-02-2009, 11:48 PM

Whats the dyno curve look like at 7k? What plugs/gap? How old/reliable is the wide band?

onfire · 11-03-2009, 09:20 AM

I'd look hard at the plugs.

AgFormula02 · 11-03-2009, 10:24 AM

Springs are whichever came with the AFR 225 heads. (The ones good to 650 lift) ANyone know the specs?
No dyno runs past 6700 rpms. Wideband is pretty accurate at the gauge, but .5 off in HP Tuners. (Hp tuners shows .5 leaner than it really is)

For this run, we put new NGK BR7EFs before the run. Shut of and coasted after the run. Got towed to the trailer so we could check plugs. Plugs looked good. A little lean, but nothing horrible. They were straight out of the box.
Timming mark looked good.

'Trust' · 11-03-2009, 10:32 AM

May be blowing the spark out, mine did at .035 gap, but at .028 it's fine, might want to try fresh plugs at that gap. Also, the springs in the AFR's suck.

If HP Tuners is getting A/F from a wideband upstream of the tail pipe (assuming it is) it should be substantially richer than what the dyno is reading. Get a new wideband in it and recalibrate it.

98Z28CobraKiller · 11-03-2009, 10:40 AM

Quote:

Originally Posted by 'Trust'

May be blowing the spark out, mine did at .035 gap, but at .028 it's fine, might want to try fresh plugs at that gap. Also, the springs in the AFR's suck.

If HP Tuners is getting A/F from a wideband upstream of the tail pipe (assuming it is) it should be substantially richer than what the dyno is reading. Get a new wideband in it and recalibrate it.

If I understand him correctly, what he is saying is that the wideband display or the gauge attached to it is reading correctly but the output to HPTuners is off by 1/2 a point on the scanner. I ended up tweaking the formula for the custom PID that I created to get the WBO2 reading in my logs.

AgFormula02 · 11-03-2009, 10:49 AM

Quote:

Originally Posted by 98Z28CobraKiller

If I understand him correctly, what he is saying is that the wideband display or the gauge attached to it is reading correctly but the output to HPTuners is off by 1/2 a point on the scanner. I ended up tweaking the formula for the custom PID that I created to get the WBO2 reading in my logs.

Correct. I wish I could change the PID I am using. (Hptuners has one for the AEM wideband)
How did you set yours up?

Thanks

Tiago · 11-03-2009, 11:00 AM

plug gap + dwell time would be first things I would look at

98Z28CobraKiller · 11-03-2009, 11:10 AM

Quote:

Originally Posted by AgFormula02

Correct. I wish I could change the PID I am using. (Hptuners has one for the AEM wideband)
How did you set yours up?

Thanks

You are likely using the I/O version of the HPTuners box and are wired right in. I'm not sure how that one works. I have the non-I/O box and I get my AFR reading thru the EGR sensor. I use this formula.

([PID.2811]/.625)+10

PID.2811 is EGR Position.

onfire · 11-03-2009, 11:42 AM

Quote:

Originally Posted by AgFormula02

Springs are whichever came with the AFR 225 heads. (The ones good to 650 lift) ANyone know the specs?
No dyno runs past 6700 rpms. Wideband is pretty accurate at the gauge, but .5 off in HP Tuners. (Hp tuners shows .5 leaner than it really is)

For this run, we put new NGK BR7EFs before the run. Shut of and coasted after the run. Got towed to the trailer so we could check plugs. Plugs looked good. A little lean, but nothing horrible. They were straight out of the box.
Timming mark looked good.

I ran that plug for a year. Good plug. At your power level it's time to step up to the NGK R5724-8 at 0.030.

I ran that plug also for a year....then got lazy and tried the NGK TRix 8...killer plug , but expensive.

98Z28CobraKiller · 11-03-2009, 04:37 PM

Quote:

Originally Posted by onfire

I ran that plug for a year. Good plug. At your power level it's time to step up to the NGK R5724-8 at 0.030.

I ran that plug also for a year....then got lazy and tried the NGK TRix 8...killer plug , but expensive.

I also run the 7317 #8 plug that onfire mentioned above. I gap it at .023.

cablebandit · 11-03-2009, 06:54 PM

i might need to close my gap...they are at 30 i think
r5672a-8

Boo"SS"t · 11-03-2009, 07:53 PM

[quote=AgFormula02;12455840]Springs are whichever came with the AFR 225 heads. (The ones good to 650 lift) ANyone know the specs?........

I'm sure you have the spring part#8019 (155lbs @ seat/rated @428lbs per square inch), which are now standard on those heads. Are you still on hydraulic lifters?? and what kind of power are you making on a dyno right now???