Adjustable rev chip

Who uses these and why? I've always used the fixed ones, but Mo only sells the adjustable.

You set it with an ohm meter, right? One post I saw in a drag racing forum showed a chart with resistance for each 100 of RPM. For 6800 RPMs, set to 5449 ohms. How expensive does that ohmmeter have to be to be accurate enough?

I don't want to wonder if the chip or ohm meter is accurate enough for a particular day and I'm not going to be re-setting it because ambient temp, age or something else makes the thing vary which might get my rental hotshoe DQ'd.

So why should I buy an adjustable one when I can go down to the local performance shop and buy the fixed one. (although last I checked I have to buy a range of 10, so maybe there's no savings.)

As one who was on the CRB at the time - the fixed chips were not accurate enough for the Runoffs front runners when the box was hot so it was allowed to run the adjustable chip and there was a setting procedure. Does it make a difference - I think that a couple of DQs or times disallowed started Star Mazda down this path and the SCCA followed their rules changes.

so it's the fixed chip that is less accurate at temps. Does that mean the materials in the adjustable are less susceptible to heat or just that the point teams calibrate them every day or once a month. Who sets it once and forgets it? And is an ACE hardware general purpose meter good enough?

Thanks.

adjustable was the way to go. The rev limiter is greatly affected by heat. IIRC the legal limit is 6850 w/o looking it up. anything set much higher then 6800 cold and you were asking for a DQ on rev limit when teched in impound. MSD sells a nice tool, same one tech uses, or used when I prepped cars in 04/05. The rev limit and choke size led to more DQ's in big events then any other item. Even the stupid super trapp plates which we had to run at the time by rule and couldnt move didnt catch as many people out.

what phil said.. we would use the adjustable one and set it 50 rpm lower than the limit just to be safe

Testing the rev chip is similar to weigh ins. Always use the tester that the techs are using to determine rev limit. Testing equipment is like scales, even if your scales are dead balls accurate and the tech scales are 15 lbs off...you still have weigh proper on the tech scales.

Words of experience were given...:( you are welcome

How do they tech the chip? measuring with an ohm meter or a specialty tool only from MSD?

But whatever it is that they use, what you're saying is that their equipment may be different than mine and I should always calibrate the chip with their equipment each day or at least each weekend to be safe ?

Thanks.

Ted

The rev chip is checked with a MSD Single Channel Digital Ignition Tester p/n 8998

No need to check the adjustable or fixed chip every weekend, it doesn't really fluctuate all that much unless there is something wrong with the Msd Box, the Msd tester and maybe the Tech Official. I've also heard that heat and moisture can mess things up.

In 2010, I crossed the line first in FM at the Runoffs, the best race of my life was taken away from me because of the damn chip/faulty box. I will never trust an older MSD box or chip. I will never forget that day or that weekend.

I feel that the new MSD 6AL Digital should be allowed in FM soon . The new box has built-in rotary dials with numbers to set the rpm soft cut/limiter. Since my disqualification, I have personally seen two older MSD 6AL boxes where the rev chip was not working consistently (adjustable or fixed). I swapped to the new style MSD6A boxes for those customers since they are not in SCCA...

regards

I don't know that an Ohm meter is going to work because the individual MSD boxes are a bit off from each other. FYI if you've put a new box in you should double check the rev limiter. Every once in a while you get a brand new box that the Rev limiter doesn't work in. I've also seen people get DQ'd because the socket the rev chip fits into wallows out or fails internally and the chip isn't connected to the system.

Then there was the time I had 2 out of four boxes with tach feeds that didn't work....

I've always run the adjustable chips. I tried some of the fixed chips but they always seemed off: a little to high or way too low.

I purchased an MSD testing unit a years ago and I do check them pretty frequently, but that's because I run pretty close to the limit (ideally about 25 RPM below maximum).

Quote:

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Originally Posted by JRMarchand

I feel that the new MSD 6AL Digital should be allowed in FM soon . The new box has built-in rotary dials with numbers to set the rpm soft cut/limiter. Since my disqualification, I have personally seen two older MSD 6AL boxes where the rev chip was not working consistently (adjustable or fixed). I swapped to the new style MSD6A boxes for those customers since they are not in SCCA...

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I second this idea for the reasons stated. And the fact I can get them wholesale for WAAAAY cheaper than the old-style ones.

Especially since the 6AL 6420 box has been discontinued

Quote:

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Originally Posted by Darryl Wills

Especially since the 6AL 6420 box has been discontinued

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Moses gets them custom made, at least as of last year when I needed a new one.

I ahve been following this discussion and wanted to check the chip in my car. Set up the MSD tester and have been trying to figure out exactly how to use it. I have set the box to both 4 and 8 cylinder to figuring that there may be one that has half of the RPM readout. I am gettign to about 12000 RPM before the spark device cuts out.

I know that the rev chip was working because I hit it at several points on the track and seems to be in the 6000-7000 range. I just got off the phone with the guys at MSD and they say that the 8998 test box will not be accurate as the rotary is closer to a 6 cylinder.

Can somebody help me figure out how this is supposed to work. The instructions for the tester are very brief and don't offer much info. Here is how I have it connected

violet and green wires out of the MSD box two pin connector to the violet and green out of the tester.

Red and black hooked to the power and ground

wire from the coil connected to the spark device and clipped to chassis/ground


Appreciate any direction you guys can give a newbie.

Steve

The selector goes on 4. Sounds like you have the tester connected properly. Maybe the tester is bad. Can you try it on another MSD box installed on another vehicle?

I second the question. i have the tester but no idea how to use. Installed a new box last summer and want to know that I am in spec. Can some supply a step by step process to help us use this?
Thanks

Make sure you are connecting the sparking device to the end of the coil wire that you pulled from the distributor cap.

I do have the spark on the coil wire. Also don't have another vehicle with MSD in it. Will see if I can find a person in the area that does. In talking with the MSD techline they did say the 6000 rpm would be 4777.5 ohms of resistance, but could not tell me what 6850 was. I presume this is supposed to be a direct read out in RPM.

Darryl is your test unit the 8998? I understand that an earlier unit is no longer made and that may be the issue.

Yep, I do have the older unit. I am surprised that the new unit works different. I guess you guys on your own to figure out how to get the 8998 to work on a rotary.

Good luck

When I was talking to the guys at MSD the tech was saying something about taking a cap off the side of the 6AL box and cutting either the red or blue wire. He totally lost me on this one, as he was talking with me like I knew what he was talking about. This may be something that comes with the installation instructions for the MSD box and from looking on line seems to be a setting for 4/6/8 cyl setup. The MSD guys said our rotaries are closer to a 5 cylinder which really got me confused. I will keep trying to figure out the MSD 8998 and post what I come up with. Will give you a resistance value of my existing chip, which seems to be close to rev-limit.

Steve