Hilborn Injection: From Strip to Street and Back

By Andy Starr, Hilborn EFI Specialist


True Individual Runner Manifolds for the Serious Enthusiast!



As racers, our inner hot rodder will always look for ways to transition racing components to street use. Some products will have an easy transition, others such as the Hilborn Injector, not so much. This was primarily due to the rudimentary fuel control of the barrel valve and its inability to control fuel during the common part throttle no-load dynamic experienced during street driving. This lack of fuel control over fueled the engine creating numerous drivability issues rendering the mechanical Hilborn Fuel Injector lacking for street use.

The institution of EFI dramatically changed the ability to run a Hilborn Injector on the street. But what we didn’t know was that a Hilborn Injector would also dramatically improve drivability especially with engine combinations sporting large camshafts. How is it possible that a performance part that provides a tremendous increase in throttle response, low speed torque, top end power and engine acceleration rate can also claim drivability as one of its key attributes?

First, precise butterfly adjustments are a key component to achieving excellent part throttle with a Hilborn Injector. Racers will routinely rotate the hex link, which controls the side to side to have an even idle. This type of adjustment is typically all that is needed since we will transition from idle to WOT with very little time at part throttle. But with street applications we spend a majority of time at part throttle so now the hex link must resume its original intent of controlling the geometry of the two butterfly shafts. This will ensure that both butterfly shafts lift evenly from the closed position all the way to wide open throttle. Once the angle or the arc of the butterflies is the same side to side, the idle positions can then be set with the use of a synchrometer, but we will no longer rotate the hex link as it will change the geometry we just set, rather loosening a hex link arm that will allow one of the shafts to be rotated to match the other.

Call any of the cam companies today for a cam recommendation and then mention you are using EFI and they will promptly reduce duration and widen the lobe centers in an attempt to increase vacuum signal at the idle and part throttle positions. They know that it is this difference in vacuum signal that sets the resolution for the fuel map, the greater this difference the better the fuel control between idle and wide open will be. Problem is, being racers at heart, we don’t want a compromise in performance whether we use that last horsepower or not.

We all know larger cams have more overlap which in turn hurts low speed drivability. This is due to the introduction of reversion pulses which knock the air and fuel out of separation at opposing cylinders; the larger the cam the worse the low speed performance becomes. A Hilborn IR with its segregated runners, eliminates the effect of these reversion pulse allowing a clean shot into the cylinder even at low speeds. Engines with big cams now have excellent idle characteristics with plenty of low speed vacuum for excellent resolution for the MAP sensor. Also, the excellent throttle response and the dramatic increase in low speed torque of a Hilborn IR manifold proves how effective the elimination of these reversion pulses can be.

We routinely see larger cid engines with camshafts in the 270-280 @.050 range that exhibit stellar low speed drivability even with a stick shift. Also, since torque is generated by cylinder fill, most applications will see an increase in mid-range torque with a larger cam that historically hurt mid-range due to the reversion pulse.

It is a common request for us to build EFI injectors with rubber or metal lines but we have found that this is not the best option when it comes to fuel control. We never encountered issues using hoses or lines in constant flow mechanical system due to the fact that the flow of fuel never stops but with EFI we stop the fuel flow numerous times a second. Since fuel has mass, the stored energy in fuel flow causes the fuel to bounce back after the injector closes creating a pulse which is amplified especially in metal lines. EFI is all about fuel control and it is imperative that we have consistent fuel pressure and volume and fuel line pulsing upsets this precise arrangement making for a tough time tuning at lower pulse widths. Due to this fuel pulse there are times when an injector opens where the pressure or volume of fuel is not consistent forcing us to use a richer target air fuel to cover up this inconsistency. This condition is amplified when we open more than one injector at a time such as in bank to bank or batch fired system. The use of a fuel rail on the other hand along with firing one injector at a time can dramatically reduce these pulses allowing us to tune the system more efficiently.

Finally, the Hilborn injector has successfully transitioned from a dedicated hardcore racing component to a completely drivable performance component any hot rodder would love to have while exceeding the racers performance demands on the street.

Race car power with street car manners, a Hilborn EFI injector has both with plenty to spare.

Andrew Starr
Hilborn EFI-R Specialist



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