KillerRons - James Monroe
KillerRons - James Monroe







We believe this myth has its roots in the 1960's when racers attempted to utilize poorly metered gasoline injected fuel systems on smaller displacement, lower powered engines with limited success.  This myth is perpetuated today as racers attempt to utilize alcohol systems with oversized fuel pumps.  These racers often experience tuning issues on or around the rev limiter at the lower RPM's and ultimately struggle to get consistently "clean" runs in varying weather conditions.  Hence, someone somewhere took a leap and declared that "you cannot use a rev limiter with alcohol" and unfortunately someone believed him along the way.  The fact of the matter is that this is simply not the case and we will do our best to explain this situation as it sometimes presents itself to us at KillerRONS.

Comparing a mechanically injected gasoline engine of yesteryear to today's mechanically injected alcohol engine is not a fair comparison.  We're not going to say that mechanically injecting gasoline is impossible as it is still done even today.  What we will say is that due to gasoline's narrow tuning window it would require frequent recalibration when even small atmospheric (temperature) changes are presented.  In our opinion, the best way to successfully run gasoline in an injected application is with an expensive electronic fuel injection system that can manipulate the fuel curve at many points throughout a run.  To try and run gasoline in a mechanically injected engine would almost guarantee tuning issues at or around the rev limiter at lower RPM's.  It could be as simple as this being the root of this myth.  That being said, alcohol has an extremely wide tuning window and will tolerate richer air/fuel mixtures at lower RPM's.  The bottom line is that starting line rev limiter issues are rarely evident with mechanical alcohol injection. 

In the event of these rare occurrence of tuning issues at lower RPM's (on or around the rev limiter) in an alcohol injected engine one can usually look to only a few places for the reason.  As mentioned previously, this is primarily due to the use of an oversized fuel pump for the application.  Larger displacement pumps are especially strong at low RPM's.  Combine that with an oversized pump for the application and tuning the engine at low rpm's becomes more difficult.  The keystone of our business at KillerRONS.COM is supplying properly sized fuel pumps that create a flatter and more correct fuel curve which greatly increases the ease of tuning in all conditions and all but eliminates low RPM issues.  We would estimate that 95% of our customers using nothing more than their main bypass pill and nozzle jets for tuning. 

The second item that could cause a low RPM tuning issue in an injected alcohol engine is an incorrect idle mixture or "barrel valve adjustment" (as it is sometimes referred to).  The idle mixture plays a role in low RPM tuning on or around the starting line rev limiter.  Since injection doesn't have an accelerator pump the idle mixture must be set on the slightly rich side so that the engine doesn't hesitate due to a lack of fuel when the throttle is opened quickly and the large amount of air rushes into the engine.  If you go too far with richening the idle mixture you increase the possibilities of being overly "fat" when initially coming onto a starting line rev limiter.  This is easily avoided as we recommend that the idle mixture should only be as rich as need be to avoid a possible stumble.  Please note that this idle mixture tuning window is very large and only a complete disregard for this adjustment will create such an issue.

All that said, there are a few engine combinations that will act rich when revving up to the starting line limiter even with the correct pump and idle mixture. Usually these occurrences are reserved for small displacement engines with relatively large duration camshafts for the amount of compression present.  These engines have narrow and peaky power bands and are usually "finicky" at low RPM's no matter what induction system is utilized.  Converter selection is paramount with these engines (usually on the looser side is better) and even then some will need the assistance of an electronic bypass to bleed off a small amount of extra fuel while on the rev limiter.

In summary, of the popular fuels, alcohol is the most forgiving for tuning and with the right combination of fuel pump and idle mixture setting literally everyone should expect their engine to operate flawlessly on a starting line rev limiter.   We will take it one step further and say that due to its ultra-quick throttle response with no concern for a "carb stumble" along with its ability to operate in an overly rich condition alcohol injection should be the primary choice in rev limiter applications.


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KillerRons - James Monroe