higher rpm problems

[1320quick]

Back again looking for ideas. Still having problems with engine running at higher rpm's after the changes to the ignition system and wiring this winter. The car seems almost like it's on the rev limiter at the top of each gear. Seems to start having problems about 6800rpm. It can't be as the max rpm limit is set to 8500 and I shift at 6900rpm. It doesn't seem to matter if I'm running the bottle or just on the motor. On the bottle, it pops between shifts and on the motor, it just feels lazy like the rev limiter is on. What I've done so far to troubleshoot/fix this issue:

-replaced valve springs - old springs tested good but replaced them anyway
-verified air/fuel mixture running on the motor was right - plugs look great
-re-routed crank trigger wires further away from other wires
-began charging the battery between rounds
-double and triple checked the setting in the digital 7 programmable box
-verified the timing is correct and the rotor is properly phased

The car... All steel 3600lb stock suspension 71 Nova, 14.1:1 540bbc, T400, 8" 5500 converter, 3:90's. Also, I race at Bandimere where the elevation is over 5800ft. Over the winter, changed the ingition from a MSD 6al, pro billit dist and blaster2 coil to a MSD 7530T prog digital 7, pro power hvc coil and crank trigger. Also went from a adj Nitrous Works plate to a Cold Fusion fogger with Edelbrock progressive controller.

[Rick M]

Have you tried ohming your plug wires? What kind of cam are you using hydraulic or mechanical?

[John_Heard]

Just throwing a few more thoughts up... Did you use the MSD grounded crank trigger wire - the one with the shield and ground connection on one end? Ditto what Rick said plug wires maybe.

[1320quick]

I've not checked the plugs wires but I'll add that to the list. The motor has a Comp Cams custom grind solid roller cam. I did use the gray sheilded pickup wire with ground on it for the crank trigger. The ground on that cable isn't very long so I didn't route it to my common buss bar ground. It's just to a bolt under the dash that I use to use for the nitrous grounds. Any chance this could be a voltage/amps issue? I did notice last night that the car seemed to run a bit better when I "screwed up" and forgot to turn on the electric water pump. I'm only running a single red top Optima.

As a side note, the car did run a best ever of 9.39 @ 149 in the finals last night for my first ever USP limited street heads up series win! Weird to complain about how bad it's running when it's making it's fastest passes ever but it's true. If I can figure this out, the rest of the class better look out! LOL

[John_Heard]

Yes it very well could be a low voltage situation, I think that's something worth pursing more. The grounding on the crank trigger wire ought to work.

Congrat's on your win!

[Rick M]

Are you running an altenator if so how big?

[1320quick]

I am running an altenator. It's still the stock type ext regulated type. I believe it's a 60amp. It certainly is nothing special, it's whatever the local discount auto parts store had that was the cheapest at the time.....

If this is a lack of voltage issue, any thoughts on how to resolve it. Do I need to go to two batteries? Maybe a new battery and a higher output one wire alternator???

[John_Heard]

First it would help to be able to tell for sure what voltage you have at the ignition box (not at the battery) during a run. Maybe you can strap a digital voltmeter into the car for testing and see what you have when all the load is on like when you're making a pass (including nitrous solenoids). My guess is it's lower than you want.

Improving it might be a matter of increasing alternator cable wire sizes, higher amp alternator, more or better batteries or reducing load in some way (like turning your fan off during a pass). You might even consider switching to a 16 volt system. Anything you can do to make the voltage more stable is going to help your nitrous tuning also because when the voltage fluctuates it affects your fuel pump output. Higher voltage also creates better spark for your ignition.

[demented]

I have seen some of msd's stuff, mainly anything that has some form of digital retard (digital 7 or ditgital multi step retard) has problems with a top end miss or popping. I personally had a problem with a multi step digital retard that missed and popped on or off nitrous. Started immediately after I put it in the car. A couple friends have had similar problems with there digital 7 or retard box. I disconnected mine and the problem went away.Sent the box to msd they said "nothing wrong" but as soon as I put back in the car the problem returned. I would check your box. When it does act up it seems like a rich fuel popping only on the top end over 6500rpm. Just my 2 cents.

[jones_performance]

lots of guys are having issues with the digiatl 7 stuff.

we went back to a old school 7al2 -7al3 box

[Troy Patterson]

How about an update - did you fix it or would you like more ideas??

Troy Patterson TMPCarbs.net TMP Carbs

[1320quick]

Funny that you ask! I actually figured it out yesterday. The car had still not made a single clean pass all year long so last week we added a ProLogger wideband O2 setup on the car. It records the A/F ratio and RPM for the whole pass. When looking at the log, you can see that everytime the RPM got to 7000, the A/F shows super lean and the rpm drop to 6200 for a split second. Take a wild guess where my burnout RPM limit was set to? Yep, 6200 rpm. The problem all along was the seat to steering wheel interface! I was touching the line-lock button when I was shifting and activating the burnout RPM limit. With the gloves on, I just don't have much feel and didn't know I was touching the button. STUPID STUPID STUPID!!! We set the burnout RPM to 8000 and the car made two flawless 9.40 @ 148mph passes in a row. I don't know whether to be happy that we figured it out or frustrated that it took almost a whole season to figure out the driver is an idiot!

[TubbedTruck67]

Well atleast you figured it out!