Honda Injector Guide

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Honda Injector Guide​

Choosing the correct size injector for you build is a vital part of the process. There's a lot to consider, including, size and type. There are two basic types of injectors that work on Honda and Acura cars and every size for every power need. Let's dive in.

Peak / Hold VS Saturated Injectors​

Peak and Hold:

Peak/hold injectors are low impedance, usually in the 1-4 ohm range. When the ecu calls for fuel to be injected, it sends out voltage via the wire clips until a certain current level is reached (the peak part) (varies by injector size, company). For the duration of 1 pulse width, that current is slightly reduced and held (the hold part).

Advantages of this design:
  • minimizes the injectors "on" time, resulting in faster response
Disadvantages of this design:
  • increases coil heat, which can lead to failure over time
  • On most obd1+ Honda's, this type requires a resistor box, which can mean wiring changes.


Saturated injectors are generally higher impedance than peak and hold, running in about the 10-15 ohms range. Unlike peak/hold, a saturated injector remains "on" for the entire pulse width.

Advantages of this design:
  • reduces heat
Disadvantages of this design:
  • slower response time
  • can't handle large CC or lb/hr styles due to limitations in its speed.

Injector Type Decision

There are a ton of factors involved in this.
  • First, power level. If you're going big, there simply won't be a saturated injector that will support your power level. The largest common saturated injectors on the market are 550cc, with 440cc being a common "cap" in saturated size. Most boosted people run peak/hold setups for not only their availability, but also their ease of upgrading later on if so desired. simply swap the injectors. no need to re-wire again.
  • How is your car wired? most obd0 civics and some preludes are wired for peak/hold and have a resistor box already. No point in changing to a saturated. Obd1+2 civics, and most other Honda/Acura cars after 1992 are all saturated and are not wired with resistor boxes. Again, if there is an injector available in your power range for flow of your car's design type, there's little sense to change.
  • Price. DSM eclipse/talon 450cc peak and hold injectors fit Honda rails and, with just a minor modification, plug right in. Best of all, these can be had for about $50-75 a set of 4 instead of $350+ for a set of aftermarket injectors. Add a $25 resistor box from an obd0 civic/crx, wire it up, and you're good to go in you're saturated car.
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What size injectors do I need for my build?​

Picking the correct size injector is a critical part of your build. Too small and you'll not have enough fuel to make the desired power or run lean. Too big and you'll have streetability issues such as requiring a high idle and poor part throttle smoothness.. Larger injectors will pour in more fuel for any duty cycle length and it may simply be too much leading to cylinder wash out.

Luckily, there's a formula to help you choose!

injector size in lbs./hr. = (Max. HP x BSFC) / (number of injectors x duty cycle)
  • Max Horsepower. Understand your realistic horsepower goals. If you just put a header on, no, your goal is not 300whp. Be Real. This figure will help determine the proper size.
  • Target your BSFC, Brake Specific Fuel Consumption factor. Generally, turbo/super charged cars target richer a/f mix. Some tuners will target a 10:1 ratio while all motor builds may use a leaner 11.5:1 ratio. This multiplier helps account for this difference.
    • All motor BFSC: .45 - .55
    • Turbocharged BFSC: .55 - .65 (lower for lower hp, higher for higher hp)
  • Safe Duty Cycle. As a general guide, you want to target no more than 80% duty cycle at peak RPM. Some race cars break this but the streetability factor is greatly reduced.
So, if you have a 300whp turbo b18c build, your math might look something like:

lbs/hr = (300 * .60) / (4 * .80)
lbs/hr = (180) / (3.2)
lbs/hr = 56.25

I used .60 as the BFSC factor as 300 whp is a 'medium', if not small, build factor that won't need the extra fuel multiplier.

At this point, due to most import injectors using cc/min instead of lbs/hr, we need to do one final conversion.

There's a simple formula for converting lbs/hr to cc/min:

cc/min = lb/hr * 10.5

If you ever need to go back, the reverse is also true:
lb/hr = cc/min ÷ 10.5

Back to our example and we have 56.25 lbs to convert to cc.

cc/min = 56.25 x 10.5
cc/min = 590

So, we should be targeting at least a 590cc injector (but that's an odd size), and even going to a 650cc is a good idea.

Adding Fuel Rail Pressure​

If you already bought 550cc injectors for your 590cc need, there may be hope! If you come up a little short due to making more power than expected, you can add a little rail pressure to help push a little more fuel in. This should be used only as a 'fine tuning' objective and the proper size injector should be used wherever possible.

Most Honda's run 42 psi rail pressure from the factory. You can increase this with a pressure regulator. Say you go to a 50psi rail pressure setting, you can add on some flow.

Once again, we have a formula for that!

[Square root of (new pressure/old pressure)] * old flow rating in lbs/hr = adjusted flow rating at pressure (AFR@p)

[Sqrt(50/42)] * 56.25 = AFR@p
[Sqrt(1.19)] * 56.25 = AFR@p
1.09 * 56.25 = AFR@p
61.36 = AFR@p

By adding 8 psi of rail pressure, we bumped our flow rate over 9lbs/hr or, almost 100cc!

That puts our 550s at 50psi of rail pressure comfortably in range to run the 300whp goal. Again, caution on going too high on pressure - 10-20% gain is as high as you want to go in most cases.

Of course, remember to adjust your tuning software to match the injector size. It is critical to a successful tune.

Related content:

Get help in our tuning forum ECU's, Electronics, and Tuning
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RC now makes Saturated injectors in 650cc and 750cc and 850cc varieties. More may be available in the future as well, thus taking the saturated injector market up to support larger power numbers.
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Just ran into this site... lots of great info about injectors:

Fuel Injector information & Specifications specs

VehicleInjector TypesFactory Flow RatingNotes
1990-'93 Geo Storm GSiPeak and Hold 222cc
1990-'93 Geo Storm 2+2 & Stylus SSaturated222cc
1990-'93 Isuzu Impulse & Stylus XSPeak and Hold 222cc
1991-'92 Isuzu Impulse RS AWDPeak and Hold 322cc
1988-'91 Civic Si/CRX SiPeak and Hold 240cc
1992-'95 CivicSaturated240cc
1996-'00 Civic dx cx and lxSaturated190cc
1996-'00 Civic ex/siSaturated240cc
1990-'91 Integra RS/LS/GSPeak and Hold240cc
1992-'00 Integra LS/GSSaturated240cc
1992-'96 Prelude Non-VTECPeak and Hold240cc
1992-'96 Prelude VTEC Peak and Hold345cc
1997-up Prelude VTEC H22Saturated280cc
1991-up Sentra SE-R/200SX SE-RSaturated265cc
1991-up MR2 Turbo Peak and Hold440cc
1987-'92 Supra Turbo Peak and Hold440cc
1993-up Supra non-Turbo Saturated315cc
1993-up Supra Twin-Turbo Peak and Hold550cc
2000-up Celica GT-S Saturated310cc
1990-up Miata 1.6-liter Saturated215cc
1993-up Miata 1.8-liter Saturated240cc
1984-85 RX-7 195500-0900Peak and Hold680ccOrange Top
1986-87 RX-7 195500-1350Peak and Hold460cc Red Top
1986-87 RX-7 195500-1370Peak and Hold550ccTan Top
1988 RX-7 195500-1350Saturated460ccPurple Top
1988 RX-7 195500-1370Saturated550ccPurple Top
1989-91 RX-7 195500-2010Saturated460ccRed Top
1989-91 RX-7 195500-2020Saturated550ccPurple Top
1993-up RX-7 Twin-Turbo SaturatedPrimary 550ccSecondary 850cc
1990-'96 300ZX Twin-Turbo Saturated370cc
1991-up 3000GT/Dodge Stealth non-turboSaturated210cc
1991-up 3000GT VR-4/ Dodge Stealth R/T TTPeak and Hold360cc
1989-up Eclipse/Laser/Talon Turbo/non-turboPeak and Hold450cc Blue Top(95+ Black top) 390cc Tan top 240cc Orange/pink Top 210cc Light Tan Top
Mitsubishi EVOPeak and Hold510cc Yellow Top (1-3) 560cc Red top (4+)
1986-89 Ford turboCoupePeak and Hold35lb/hr Brown Top 30lb/hr Green Top

There's a ton more pics and info available at the link.
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