News & Analysis

Why isn’t Dan Olson using the rev limiter to slow ‘em down?

By Jeff Burk

Top Fuel guru Dan Olson, at the behest of his bosses at the NHRA, is hell bent on slowing down the current Top Fuel and Funny Cars so that they won’t or can’t run over 320 mph. Or is he?  

NHRA management has been trying to accomplish this more or less since Darrell Russell’s tragic death at St. Louis more than five years ago. So far they have failed to do so, and only shortening the length of the track succeeded in lowering the speeds numbers. Currently the NHRA and their nitro guru Olson are in the middle of expensive and tedious testing of smaller fuel pumps, smaller clutches, smaller engines, and flow restricted superchargers. That research so far has supplied little or no results.

And now the issue is getting urgent again with Top Fuel cars going nearly 325 mph on the 1000-foot tracks.

So, here is my question. Why doesn’t the NHRA or Olson simply adjust the rev-limiter that is mandatory on every NHRA Top Fuel or Funny Car and control the speeds using engine rpm and nothing else?

Back when former nitro racer/tuner Ray Alley had Olson’s position he went to the MSD folks immediately after Russell’s death and had them design a rev-limiter that was incorporated into MSD’s ignition system.

The MSD engineers had the device ready to use in less than 90 days as I recall. After some testing Alley mandated that the device activate 3.8 seconds into the pass and at that point it would pull a maximum of 25 degrees of timing out of the engine starting at 8200 or 8300 rpm. The system works brutally efficiently. If the engine exceeds the maximum rpm limit, timing is taken out immediately and if the driver isn’t off of the throttle, the engine tends to blow the rods out the side of the block!

Fast forward to 2010. The speeds recorded by Top Fuel cars are reaching the 325 mph mark and the ETs are rapidly dropping below four seconds. So, on a good run the MSD rev-limiter may actually be working for less than a tenth of a second. The Funny Cars aren’t at that point yet but, if history is any indicator, they soon will be.

In checking with the MSD folks before writing this I found out another interesting fact. The MSD device -- which isn’t actually a rev-limiter but an ignition timing limiter -- as it currently functions won’t instantly take 25 degrees of timing out of the motor when the max rpm is reached unless the engine hits the limit hard and fast.

As it was explained to me by an MSD spokesman, if the engine just “tickles” the rpm limit then the device may just take 5 or 10 degrees of timing initially. Evidently some crew chiefs have found this characteristic of the device allows them to partially circumvent the rev-limiter and go faster.

So here is the $64,000 question. Why are Dan Olson and the NHRA trying to re-invent the wheel by trying to come up with a brand new set of engine specs for Top Fuel/Funny Car engines. It would appear to me that any or all of the changes NHRA and Olson are proposing are going to cost the car owners a lot of money in one way or another.

According to MSD, they could easily change the settings on the “rev limiter” so that it came on line at 2.8 or 3.0 seconds into the run and set the rpm limit at, say, 7800-8000 -- and it wouldn’t be expensive.  

As I understand it, the crew chiefs would be able to keep their engine and drive train exactly as they are. Their data would still apply, right?  So there wouldn’t be a need to buy new heads, superchargers, fuel pumps, ignition systems, etc. They could keep and use all of the parts they now have in stock and wouldn’t have to design, build and test a new engine combo!

So, what is the holdup? Car speed is directly related to engine rpm so lower maximum rpm means less Top Speed for the car. Am I missing something obvious here? 

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