rpm issue

[EAMShater]

The issue I am having is when I was running my crate motor my rpm's were always spot on what they should be at every track for the gear ratio I have in the car. I put my nlms motor in and suddenly I have to run 30 points more gear than anyone else to make the motor turn the proper 7800. And I know the info I am getting from my fellow racers is correct. The ones I am very close to and ones I am not so close to all gave me very comparable gear ratios to what each of them run then I have to go another 30 points higher than that. I dropped my crate back in during the rebuild period on my steel motor and the rpm's were correct again so I know it isn't a binding issue in the driveline and I rebuilt the motor with better flowing bowtie vortec heads for this season and updated some other things that should help it turn more rpm's a bit easier. Still same problem. Now I've gotten rid of my crate for another all steel motor. This one is a roller not nlms and same problem on it. I'm looking for some info on what the problem could be. I've ran it without the chip and installed another tach that gave the exact same reading and I'm not sure where to go from there. I called msd and they said they doubt it would be the box with it running fine with one motor but not the other. They oretty much said either it will work or it wont. Thanks in advance for any info.

[ep33510]

rpm issue

EAMShater

First question what MSD box are you running? HEI with 8728 or MSD 6al/aln? When you run without the chip does it feel like someone has hung an Anchor on the tail of the car?

[EAMShater]

The 6 al is what I am running now. When there is no chip in it, it seems to run like normal.

[ep33510]

rpm issue

EAMShater

Couple additional questions, what coil are you running with the MSD 6al? If its a BlasterII is the coil mounted straight up & down or laying on its side? Have you tried a different chip? They do go stupid once in a while. The other thing I want you to look at is the power going to the small Red wire. It should be connected to a ignition on switch. The voltage being supplied to the small red wire Needs to be steady no drifting or dropping down. If this voltage is moving around or is current limiting the box. A box will act flat and not rev as it should. Let me know what you find....

[EAMShater]

Ok thanks I will check that. I am currently out right now due to having one motor freshened and the other I just broke but as soon as I get a motor back in I will check all that. Thanks guys!

[EAMShater]

I will check on the model coil also. I know it's an msd but I'm not positive on the model. But it is mounted straight up and down.

[drtrkr244]

Question for ep33510. If the voltage is changing, what are the issues?...Thanks

[ep33510]

rpm issue

drtrkr244

The power being used by the small Red wire is 12,14,16 volts and around 135 ma of current draw. If the voltage is drifting around usually the box is being current limited. Depending on how severe a change is being made will typically determine how the box reacts to it. You can end up with a engine pulling softer or run into rpm missing at different rpm ranges. The game with the boxes when their happiest is to make it think its sitting at the shop with its power source sitting right next to it. Each racing season we see at least 20 to 30 issues with a Bad ignition On switch acting up and causing the power being fed to the MSD box to move around. Another common one would be a power pickup stud that is no longer staying tight providing drifting power to the box. This is no different than getting your fuel pressure & fuel volume correct to get best effort out of the engine. I hope this helps........

[drtrkr244]

Thanks for the info!